Topographical Gradient Characteristics of Land-Use Changes in the Agro-Pastoral Ecotone of Northern China
Round 1
Reviewer 1 Report (Previous Reviewer 2)
This is a resubmission. The authors made a careful revision and gave satisfying responses to the questions and suggestions of referees. The main text and the figures and tables have been improved.
They also added new analyses, multiple linear regressions (MLR) and a new conceptual figure. The main results seem to be robust and they support the conclusions. The Introduction and Discussion properly revised and well elaborated. However, still I found missing details in data processing, analyses and interpretations, and I have some questions about the new MLR analyses.
Major Comments
1, Missing details of data used in the study.
Please, define explicitly the scale (extent, resolution=pixes size) of each dependent and explanatory variables and the related sample sizes. Was LUCC defined at the very fine resolution, at 30x30m scale completely for the whole AENC area? How many pixels? Please, add the scale and sample sizes to Table3. I guess explanatory variables x1…x7 were all defined at fine 30x30m resolution and they cover completely the total area of AENC. However, the other explanatory variables: x8…x12 are meaningless at 30x30m scale and they should represent some coarser scales. Please, clarify these scales and the related sample sizes. How MLR analyses could be calculated with explanatory variables of different scales and varying sample sizes?
2, New results of MLR are missing from the Result section.
Table 9 presents results from the MLR. However, it appears only in Discussion. Please refer Table 9 in the Result section in details (focusing on detailed results represented by numbers) and refer only the general patterns, trends in Discussion focusing on interpretations and comparing them to results of other studies.
3, Format of Table 9 is not appropriate.
This is a very important part of results. However, it is hard to read and it is confusing in the present form. Please avoid using x1,x2…y1,y2…etc abbreviations. Write the full name of these key variables and mark (in bold or with colors) the most important regression coefficients. In case the table is too big, it can be divided to several tables. Please, note also how much variance were explained by these models.
4, Figure 5 and the related terminology.
I like this new figure with the conceptual frame of this study. However, the figure needs improvements. Please, fit better the structure and terms of Fig 5 to the types and scales of variables used in the paper (cf Table 3 and 9). The paper addresses spatial and temporal patterns of LUCC (dependent variables) and different types of explanatory variables working at different scales. Figure 5 should summarize these relationships in accordance with existing data and analyses. The terms “driving” “regulate” “condition”, and the direction of arrows and the different box types are confusing now. Land use happens by humans and it changes also due to human decisions. The direct drivers of LUCC are human actions and not climate or soil etc. variables (which might drive productivity of a land type but not its transformations to other types). It is confusing also why some variables were called “inherent” or “external” they rather differ in scales. All these details need explanations and clarifications. Method section describing data types, scales, and the analyses for exploring their relationships could guide clearly the proper structure of Figure 5.
5, Limitations of the study.
I have concerns about using linear regression (a relatively simple analysis with assumptions about the independence of data points, independence of explanatory variables and assumptions of homogeneity and linearity of relationships). There are alternative methods e.g. regression trees, multi-scale geographically weighted regressions that could offer more articulated results from this very heterogeneous data set. MLR gave reasonable results and demonstrated that different land use changes could be explained by different explanatory variables. Still, these pilot results can only be accepted as first approximations and more detailed analyses should be necessary in the future. The limited temporal extent and resolution are other weaknesses that should have been discussed.
6, “ecotone” ”barrier to curb desertification”
Both referee asked for more explanations on this key issue. Authors improved the related text: The agro-pastoral ecotone of northern China (AENC) is an important ecological barrier, where the topographical features play basic roles in land-use change”(L11, L91) AENC “an important ecological barrier to curb desertification”(L94,136,L489). However, there are important details that need further clarification. AENC is an excellent study area for studying the effects of various gradients of natural, socioeconomic and political factors on LUCC due to the large variations, broad gradients, broad range of these factors. However, when LUCC responds to these gradients (cf. results) it is not necessary reflect some ecotones (gradient is not synonym of ecotone). When authors used multiple linear regression, they assumed linear responses along these gradients. In contrast, ecotones represent non-linear responses. I missed the demonstration that the frequency of certain land use changes, e.g. farmland-grassland-farmland is more frequent in the ecotone zone and I also missed the discussion how and why “topographical features play” more important role within the ecotone, i.e. what is the mechanism “to curb desertification” here.
7, Other important problem related to the application of MLR is the difference between topological versus topographical gradients. MLR assumes topological gradients without autocorrelations (it assumes independent sample points). In contrast, neighboring points are more similar along topographical gradients where the local (fine-scale) variability (represented by slope, terrain relief etc..) might play important role in local human decisions on LUCC. Please, explain the related issues.
8, Figure 6 in the previous manuscript (in the first submission)
This figure showed the impact of terrain niche gradient effects on land-use structure changes and summarized the most important and most robust results in a nice way. I suggest keeping this figure. Table 8 in the new manuscript is less clear about these basic trends. Why slope effects were added when terrain niche index already represent both elevation and slope.
Minor Comments
1, Figure 1 “sample point” were these 281 (random?) points used in all analyses or were they used only for verifying the image classifications?
2, L86 “agricultural production” (i.e. both animal husbandry and crop production) or only “crop production”?
3, L160 “unused land” please clarify because it could be confusing. Unused rocky area on the top of a mountain differs substantially from an unused abandoned agricultural field or from an abandoned construction area.
4, Table 6 shows two types of proportion%, please define better the second one (cf L330)
5, Table 9 shows 10 types but Table 6 shows only 8 types, please use the same types in both tables.
6, L348 “persistent” should be “continuous” (I guess).
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report (New Reviewer)
The study of the agro-pastoral ecotone of northern China is interesting to reveal the influence of topographical factors on land use changes from 2000 to 2020, for optimal development and protection of territorial space. To better understand the territory considered, it is essential to provide more information on agricultural land. Above all, to allow a more complete understanding of the data, it is necessary to consider the possible change of the active population in agriculture between 2000 and 2022 and of agricultural production based on the most innovative forms of irrigation. It is also necessary to offer more information on the issue of breeding with reference animals reared and the evolution between 2000 and 2022, a fundamental element in the changes in land use. Furthermore, it is important to specify China's lines of political action on this issue from 2000 to today and for the future.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report (New Reviewer)
If the following points are improved, the manuscript will be considered acceptable for publication.
L.238-244 On what basis were these indicators selected? It seems that the reasons for the selection are succinctly stated.
L.366 “terrain niche index exceeded 1.17.”
This number seems to be 0.97, am I correct?
L.369-373 The numbers in the text don't seem to match those in the table, is that correct?
Table 9 is a new result, which should not be included in “Discussion” but the “Results.” It should be noted that there is a difference between results and discussion. If it is difficult to describe, the results and discussion may be combined into one chapter.
L.378-509 The correspondence between the explanations in the text and the tables is confusing and difficult to read. Please make it easier to understand by writing clearly which part of the table is being explained, or by writing the names of the driving factors in the notes in the table, etc.
L.451 economic density bad (had?) a better explanation
L.547-548 The key goal is to reasonably guide the urbanization process and precent (prevent?) the loss of farmland.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report (New Reviewer)
The integrations relating to agriculture have improved the article that can be published.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
I leave the review of the remote sensing analytics to those with a more expert background. I have focused on the output content and logic.
Foremost, this paper provides a 30 m assessment of categories of land change and their sequencing from 2000 to 2010 to 2020 for the AENC. The rationale for assessment is that the AENC is a critical ecotone and sensitive to land uses. No theory, hypothesis, or concept is proposed and nothing is said about the changes in the AENC ecotone performance or changes in its sensitivity. As such, the paper stands largely as a descriptive assessment of the land change sequencing.
In addition, the paper claims (perhaps this is an English phrasing issue only) that topographic factors are “the basic natural factor” and elsewhere, “the determinant” of land changes. Convincing evidence that topographic factors are the most basic natural factor is not presented, as opposed to atmospheric, ecosystemic, or soil factors. Also, Section 4.2 tells us that socioeconomic factors are the most important for land change, but no evidence is presented for this (otherwise obvious) claim. I would at least expect a table linking population changes, policy changes, and so forth by dates coinciding with or previous to the three dates of the evidence.
Note as well that an explicit rationale for the use of AENC is not provided. We are told that area constitutes an ecotone but not what ecosystems it transitions from and to. We are told that the area is sensitive to land uses but not what set of factors are common throughout that create the sensitivity.
In short, the paper is strong on descriptions of the land sequences but weak on a problem rationale and weak on area rationale, basic natural factor, and causes. I recognize that some of the problems noted may be the English phrasing. I suspect, however, that the land sequencing was the study objective with less attention given to rationale and various claims noted.
Specific items:
Abstract needs work in its phrasing, as well as throughout. Example from text.
Line 40-41: “As the most basic natural geographic” should be “As a basic natural geographic”; throughout topographic is spoke of as “the basic” as opposed to an important factor. Others would claim atmospheric factors or soil factors are as or more basic.
The authors may wish to check various articles in the Journal of Land Use Science and Global Environmental Change over the last several years that address the causes of land change conceptually and theoretically in order to weigh their claims about topography against the literature at large.
Line 75: what is AENC a barrier to?
Line 82: what is this “law” of land use change?
Line 118: what are the “two barriers and three belts”
Note as well that it is not clear why the AENC constitutes an area—what is common? It appears that it is an “ecotone” but it is not clear what resides on either side of it.
Line 140: construction land means “constructed” land? Also what is unused land? Would this be native-wild or secondary growth, and would it be both forest and grassland?
Table 1: some folks will not understand the measure of “terrain relief”---is it the same as TNI?
Table 2 and text. Prophase and Anaphase are not common terms in land system science; text needs to define beyond the examples in Table.
Figs. 3-4 are impossible to read/see with any clarity…make them larger
Line 402- what does “human production and life” mean.
Lines 401-4. This sentence is not clear. “Agricultural farming [redundant]…were subject to topographic factors, which determined the distribution the land use…..” This sentence can be interpreted to say [1] that farming, influenced by topography, determines land use. But this is saying land use determined land use. So I take it to really say [2] topography determines land use, a claim consistent with “the basic” phrase applied to the topographic variables throughout the paper. This claim, however, is follow immediately below in 4.2 by that which states socioeconomic factors are the base cause???
Note that nowhere are there any tests or empirical evidence to demonstrate that the claims about socioeconomic causes and land changes. While clearly tests cannot be derived from the data presented, one might expect a table showing dates of policy change, population levels, and so on relative to the dates of the land changes observed.
Author Response
Dear Editors and Reviewers,
Thank you for your letter as well as the reviewers’ comments concerning our manuscript entitled “Terrain gradient characteristics of land-use change in the agro-pastoral ecotone of northern China” (ID: land-1548540). Those comments are all valuable and very helpful for revising and improving our manuscript, which are the important guiding significance to our researches. We have made revisions according the comments and suggestions from reviewers. Revised portions are marked in red in the manuscript. The main revisions in the manuscript and the responds to reviewers’ comments are as following.
Responds to the reviewers' comments
Response: According to the suggestion proposed by the reviewer, we have revised the abstract. The result is as following:
Abstract: The agro-pastoral ecotone of northern China (AENC) is an important ecological barrier, where the topographical features play basic roles in land-use change. In order to reveal the influence of topographical factors on land-use changes the in the AENC, we used land-use transfer matrix, geo-information graphics, terrain niche, and distribution index to explore the topographic gradient effect of land-use changes during 2000–2020 in the AENC based on remote-sensing image data from 2000, 2010, and 2020. The results show the following: (1) From 2000 to 2020, the total areas of land-use changes were 121 744 km2, accounting for 17.41%. It was characterized by increasing amount of land-use changes in the AENC. The changes of land-use were dominated by the conversions among farmland, forestland, and grassland, which were distributed widely in the mountainous areas of northern, western, and eastern margins. The expansion of construction land was derived mainly from farmland and grassland occurred in river valleys. (2) The pattern of land-use changes was divided into five types including stable type, prophase change, anaphase change, continuous change, and repeated change type.Stable type accounted for 559 868.86 km2 and 80.09% of the total area. It was dominant in high altitude and complex terrain areas with elevations exceeding 1000 m, slopes exceeding 6°, terrain reliefs of more than 100m, and terrain niches of more than 1.61. Prophase and anaphase changes accounted for 3.95% and 13.03%, respectively, which occupied to dominant positions in the topographic gradient, respectively. Continuous and repeated changes occupied dominant positions in low altitude and flat complex areas with elevations of less than 1000m, slopes of 0-6°, terrain reliefs of 0-100m, and terrain niches of 0.04-1.17. (3) The topographic gradient effect of land-use changes in the AENC was influenced comprehensively by natural, socioeconomic, and policy factors. Natural factors played a basic role in the formation of topographic gradient effect. Socioeconomic factors and policy factors were important push-drivers, such as human migration, construction of infrastructure facilities, and the project of "Grain for Green". (Seen in P1 the section of 'Abstract')
Response: According to the suggestion proposed by the reviewer, we have changed "As the most basic Natural Geographic" to "As a basic Natural Geographic". (Seen in P1 Line 48-49)
Response: According to the suggestion proposed by the reviewer, we have made revisions. The result is as following:
Given that human production and economic activities often occur in low terrain areas, the ecological policies mainly focuses on ecological fragile areas with complex terrain [6-8]. Socioeconomic activities and policies have topographic gradient effect on land-use changes.(Seen in P1 Line 45-48)
Add three references (Seen in P17 Line 583-589),
[6] Matasov, V.; Prishchepov, A. V.; Jepsen, M. R.; Müller, D. Spatial determinants and underlying drivers of land-use transitions in European Russia from 1770 to 2010. J. Land Use Sci. 2019, 14, 362-377. https://doi.org/10.1080/1747423X.2019. 1709224
[7] Zaehringer, J. G.; Atumane, A.; Berger, S.; Eckert, S. Large-scale agricultural investments trigger direct and indirect land use change: New evidence from the Nacala corridor, Mozambique. J. Land Use Sci. 2018, 13, 325-343. https: //doi. org/10. 1080/1747423X. 2018. 1519605
[8] Swette, B.; Lambin, E. F. Institutional changes drive land use transitions on rangelands: The case of grazing on public lands in the American West. Global Environ Chang. 2021, 66, 102220. https://doi.org/10.1016/j.gloenvcha.2020.102220
Response: According to the questions proposed by the reviewer, we have added the description of the barrier. The result is as following:
the AENC is an important ecological barrier to curb desertification, desertification eastward and southward, which is a typical ecological fragile area in China. (Seen in P2 Line 88-89)
Response: According to the questions proposed by the reviewer, we have made an explanation. The “law” in this sentence represents the characteristics of spatiotemporal pattern of land-use change. (Seen in P2 Line 96)
Response: According to the questions proposed by the reviewer, we have made an explanation. The “two barriers and three belts” refer to the ecological barrier of the Qinghai-Tibet Plateau, the Loess Plateau-Sichuan-Yunnan ecological barrier, the northeast forest belt, the northern sand prevention belt and the southern hilly and mountain belt. The AENC is an important ecological barrier to curb desertification, desertification eastward and southward, is also an important element of the “two barriers and three belts” strategic pattern of ecological security in China. (Seen in P3 Line 130-134)
Response: According to the questions proposed by the reviewer, we have made an explanation about the AENC. The AENC is located in the transition zone of traditional agriculture and animal husbandry in northern China. The southeast side of the AENC is traditional farming area, and the northwest side is the natural pastoral area.
Response: According to the questions proposed by the reviewer, we have made an explanation about construction land and unused land.
(1) Construction land means the land for construction, which refers to the land for building buildings and structures, includes land for urban and rural housing and public facilities, industrial and mining land, transportation and water conservancy facilities land, tourism land, military facilities land, etc.
(2) Unused land refers to the land beyond agricultural land and construction land, including the land that is difficult to use, such as barren grass land, saline-alkali land, marsh land, sandy land, bare land, bare rock and stone land, and other types.
Response: According to the questions proposed by the reviewer, we have made an explanation about terrain relief and TNI. Terrain relief, also known as topographical fluctuation, relative terrain or relative height, refers to the difference between the highest point elevation and the lowest point elevation within a certain region, which reflects the surface fluctuation characteristics in the macro region. TNI (terrain niche index) is a composite terrain factor, which can reflect the combined impact of elevation and slope.(Seen in P5 Table 1)
Response: According to the suggestions proposed by the reviewer, we have added definition of five types of land-use change pattern. The result are as following:
Prophase change referred to changes of land-use structure occurring in 2000-2010 and remaining unchanged in 2010-2020. Anaphase change meant that land-use structure remained unchanged in 2000-2010 and changed during 2010-2020. Continuous change indicated that land-use changes occurred in 2000-2010 and 2010-2020, and land use types were different in 2000 and 2020. Repeated change indicated that land-use changes occurred in 2000–2010 and then returned to 2000 use in 2020. Stable type meant that land-use remained unchanged during 2000-2020. (Seen in P6 Line 198-204)
Response: According to the questions proposed by the reviewer, we have revised figure2-4. The results are as following:
Figure 2. Land-use maps within the agro-pastoral ecotone of northern China (AENC) in 2000, 2010, and 2020.
Figure 3. Main conversion types of land-use change in the AENC during 2000–2020.
Figure 4. Geo-information of land-use structure change in the AENC during 2000–2020.
Response: According to the questions proposed by the reviewer, we have made an explanation about the ”human production and life”. In this study, “human production and life” refers to the activities of Human agricultural production, industrial production, and mining production, as well as urban and rural residents living activities.
Response: According to the questions proposed by the reviewer, we have made revisions in the section of “4.1. Effects of natural factors on topographic gradient characteristics of land-use changes”. The result are as following:
4.1. Effects of natural factors on topographic gradient characteristics of land-use changes
Natural factors were the basis of the evolution of the land-use pattern in the AENC, generally either boosting or restraining the evolution of the topographic gradient pattern of land-use changes. The AENC was an important ecological security barrier and water conservation area of Beijing-Tianjin-Hebei with sensitive ecological environment. Those natural environmental factors represented the regional natural conditions, which reflected the macro-geographic background of the AENC to a certain extent. Therefore, the effects of those natural environmental factors on the spatial pattern of land-use changes was synthetic in the AENC. According to the results of this study, topographic factors including altitude elevation, slope, terrain relief, and terrain niche were the basic influence factors for the spatial pattern of land-use changes, which were consistent with the existing researches. Many scholars found that topographic factors played important roles in the redistribution of surface water and thermal conditions, blocking mode, and soil erosion strength [13,26,31,46]. Similar results were reported from Sun et al and Li et al, who found that topographic gradient effect of land-use changes was resulted from terrain relief, change rate of slope, aspect and terrain niche [10,28]. Area with elevations of less than 2000 m and slopes of 0–15° accounted for 90.93% and 78.62% in the AENC, respectively, which mainly determined the basic spatial pattern of land-use changes. Farmland, forestland, and grassland occupied the dominant position and were distributed widely in many topographic gradients during 2000–2020. The change types of “farmland–farmland–farmland” and “grassland–grassland–grassland” had the widest distribution in the AENC. Since the 21st century, ecological policies and ecological projects were carried out in the AENC, which resulted in the land-use changes of “farmland-grassland-grassland” and “farmland-forestland-grassland” in high altitude and complex terrain areas with elevations exceeding 1000 m, slopes of more than 15°, and terrain relief of more than 150 m. By the end of 2020, construction land and farmland were mainly distributed in low altitude and flat terrain areas. Similar result was confirmed by Saha et al and Liu et al [11,36]. (Seen in P14-15 Line 436-463)
Response: According to the questions proposed by the reviewer, we have made some revisions in the section of “4.2. Effects of socioeconomic factors on topographic gradient characteristics of land-use changes” and “4.3. Effects of policy factors on topographic gradient characteristics of land-use changes”. The result are as following:
4.2. Effects of socioeconomic factors on topographic gradient characteristics of land-use changes
Socioeconomic factors played important roles in the spatial pattern evolution of land-use structure in the AENC. Qu et al found that economic development, population, and urbanization level had significant impacts on the spatiotemporal evolution of land-use pattern [22]. During the last 20 years, rapid development of economic and urbanization level, structure of industry upgrade, and urban population growth usually led to land-use changes occurred mainly in low altitude and flat terrain areas located in Xining, Lanzhou, Datong, Shuozhou, the southeastern area of Jining, and the southern area of Tongliao City. By the end of 2019, the total population had exceeded 70 million, of whom 83.08% were distributed in low-altitude and flat terrain areas with elevations of 0–1500 m, slopes of 0–25°, and terrain reliefs of 0–200 m. During the same time, the urbanization rate increased by nearly 15% in the AENC. With the acceleration of urbanization, many of rural population migrated to urban, which led indirectly to the abandonment of farmland [34,45]. From 2000 to 2020, the total areas of farmland converted to forestland, grassland, and water areas were 3240.69 km2, 23 751.22 km2, and 625.99 km2, respectively. Considering the topographical conditions, economic activities were concentrated in low-altitude and flat terrain areas, where construction land constantly occupied farmland in terrain niche of less than 1.17. It was characterized by change type of“farmland/grassland–farmland–construction land”. Meanwhile, farmland spread to areas with higher topographic gradients to meet food demand in the AENC. The change types of “grassland–grassland–farmland” and “unused land–unused land–farmland” happened mainly in complex terrain areas with terrain niche of 1.17-1.61. The present results were basically consistent with those from previous studies in the AENC [25,33,45,47].(Seen in P15 Line 464-487)
4.3. Effects of policy factors on topographic gradient characteristics of land-use changes
Policy factors reflect the government’s basic guidance on economic development and land resource allocation, which are important driving forces for the spatiotemporal evolution of topographic gradient pattern of land-use changes [33,45,48-50]. Related studies have shown that policies of urbanization and industrialization played important roles in the evolution of topographic gradient pattern of land-use in the AENC [10,45]. Ecological policies had significant impacts on the topographic gradient effect of land-use changes in the AENC [33]. This was mainly due to the complexity of natural environment and socioeconomic development and the particularity of human-land relationship in the AENC as well as the function of national ecological barrier to curb desertification and conserve water [10,42]. Since the 21st century, with the implementation of new-type urbanization construction and the coordinated development strategy of Beijing-Tianjin-Hebei, the impact of socioeconomic factors on the land-use changes has gradually increased. This is mutually consistent with the results of research by Liu et al and Du et al [34,34]. Implemented in 1999 and restarted in 2014, policy of “Grain for Green” has resulted in dramatic changes in sloping farmland. The conversion of farmland into grassland and forestland occurred mainly in complex terrain areas with slopes exceeding 15° in the AENC during 2000–2020. Since the sand prevention and control project in Beijing and its surrounding areas was launched in 2000, Zhangjiakou and Chengde City have been listed as sandstorm source project areas around Beijing. Moreover, with the implementation of ecological civilization strategy, ecological projects such as Three-North Shelter Forest Phase IV Project, Beijing–Tianjin Sandstorm Source Control Project, and Taihang Mountain Greening Project have had significant impacts on the evolution of topographic gradient pattern of land use in the AENC. Forestland and grassland have been restored in the areas with high terrain gradient and complex terrain, which expanded toward lower terrain gradients during 2000–2020. The conversion of farmland to grassland and forestland was distributed mainly in the mountainous areas of the northern, western, and eastern margins as well as low mountainous and hilly areas of Loess Plateau [25,38,49-50]. Given the 2022 Winter Olympics held in Beijing and Zhangjiakou, the topographic gradient pattern of land use has changed dramatically. (Seen in P15 Line 488-518)
We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we don’t list all the changes in this report but marked in red in revised manuscript.
We appreciate for Editors and Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Piling Sun
E-mail: [email protected]
Tel: 18763321108
January 16, 2022
Author Response File: Author Response.pdf
Reviewer 2 Report
This is a valuable and interesting case study exploring relationships between topographical attributes (altitude, slope, relief complexity) and types and rates of specific land-use changes. The paper is well documented, clearly written with good data and relevant methods. Results are interesting, clearly presented and relevant. I suggest some improvements mainly in Introduction and Discussion. Quality of some key figures should be improved.
Introduction
It is well written with good logic. However, the conceptual background needs some clarification. Please, clarify how the terms of “topographic factors”, “terrain factors”, “terrain characteristics”, “topographic gradient effects”, “topographic gradient patterns” and “topographic gradient effects” are related. These terms are not synonyms. Please, clarify if you defined the related characteristics at the level of the individual pixels or at landscape level including neighborhood effects and scaling issues. Exploring relationships between altitude, slope, relief complexity and LUCC along topological or topographical gradients might need different approach and confounding factors should have also been considered.
I understand that such relationships are unexplored within the study area (AENC). However, I miss a summary of the existing knowledge in general sense and in global context. Providing specific research background with previously found relationships (more specific than saying that these papers emphasized the importance of the topic) could help to develop explicit hypotheses instead of descriptive/explorative aims.
L 49-62. I like the perspective delineated in this section. Please, return to these aims in Discussion and evaluate how results from the present study could contribute to this program.
L 75 “AENC is an important ecological barrier” not clear what barriers you mean. Please, discuss.
Why the last 20 years were concerned? What was the reason for distinguishing two periods within the 20 years? AENC is a large and heterogeneous area (from forest steppe to desert grasslands). How topographic patterns might interact with broad-scale environmental (climatic, soil) gradients? Was the land-use history homogeneous over AENC?
L 95-97. I strongly agree with the last sentence of Introduction about the importance of providing data rich scientific reference (by monitoring spatiotemporal temporal characteristics of land-use transitions) for sustainable development, resource management and environmental protection.
Material and Methods
Study area
For general readers who are not familiar with the study area, please, explain the concept of agro-pastoral ecotone. Is AENC a specific landscape where farmlands and grasslands are mixed? Is it distinct from the surrounding landscape (from pure pastoral areas in one side and from dominant agricultural areas at the other side)? Why an ecotone area was selected? Can we expect specific relationships between topographic factors and LUCC if we investigate these relationships within an ecotone?
Figure 1. Please improve the quality of the upper-left subfigure. I suggest using stronger colors and you might show the ecotone together with the neighboring (pure pastural versus pure agricultural) areas. AENC is very large area with climatic and soil gradients. I suggest adding two subfigures showing the related patterns.
Climatic data. What does the range of data refer? (for example, mean annual precipitation 300-450 mm) Do these data represent spatial or temporal variability? Please, give reference for the source of these data and for the temporal period that data represent.
L 117-120 Not clear. Please explain. How study on LUCC are related to the sensitivity and vulnerability of this landscape?
L 134-138. Please, add references to these methods.
Table 1. What is the spatial scale represented by these data? (individual 30x30m pixel or some larger area?)
Methods
Methods are clearly described. I have problems only with notations. You use the same letters in different indices with different meanings. For example the meaning of “i” is different in Tij and Yi
“A” used in equation (4) and also in equation (6) but with different meaning. These formulas are correct and understandable, still a more consistent notation would be helpful.
L 164. The range of Ni in formula (2) is not [0,1] but [0,100%]. Please, correct.
Geo-topographical graphics
Formula (4) and the types (stable, prophase, anaphase, continuous change, repeated change) (Table 2) have been developed to a specific situation for evaluating three subsequent images, i.e. the related methodology is very specific. Are some extensions of these models available for longer time series with multiple imageries? I am sure that many readers will be unfamiliar with this model and the related specific terms. Please, use more general terms in Abstract or these terms (stable, prophase, anaphase, continuous change, repeated change) should have been defined already in Abstract.
Terrain niche
Please, give the detailed background of this concept. The concept of “niche” has important (and different) meaning in ecology. Why relief attributes were not considered in this index?
Results
Figure 3 and Figure 4. These are important figures. However, they are too small and low quality and it is not possible to read the patterns that they should deliver. Please, try to improve.
- 269-270. The related sentence is unclear. “obviously different” what from what?
L 281-288 Interesting local variability of results. Please, explain in Discussion. You state that there is an intensification of human impact in the area, i.e. some would expect smaller prophase type changes and larger changes with the anaphase type. What is the explanation for the opposite trends?
L 339-340. this reasoning should be moved to Discussion.
Points 3.2.1, 3.2.2., 3.2.3, 3.2.4, the patterns found with these specific topographical characteristics were very similar. Please, quantify and explore the correlations of these variables.
Fig.5 and Fig.6. Please use the same colors for the same change types.
Discussion
I miss here the summary of main results in the first paragraph.
L 379-387. Very general, a bit superficial text. Please, specify it and move it to Conclusions. Contrary, please, remove the specific data (numbers) from Conclusions and try to formulate there only the most important general trends, patterns and implications of the study.
Numbers (specific results) are important and I suggest to highlight them in Abstract and in Discusssion. I think the found increasing amount of land-use changes (more LUCC changes in the 2010-2020 period than in the previous one) is a basic and important result that should appear in Abstract.)
The general logic and structure of Discussion is good. However, I miss the discussion of some relevant points that are presently missing. I suggest discussing the following points:
1, Please, discuss the results in general context (comparing with similar relationships described from other regions, out of AENC).
2, Please, highlight the novelty of this study and discuss the (specific, concrete) practical implications related to the perspective mentioned in Introduction (L 49-62).
3, Please, discuss the role particular topographic attributes and their correlations.
4, Please, discuss the potential confounding factors (e.g. spatial climatic gradients, temporal changes of climate, climatic extremes).
5, Relative importance of natural versus anthropogenic factors inducing land-use changes. I am not sure that natural factors can be considered here as primary “drivers”. In LUCC context, humans (due to socioeconomic, political factors) make direct operations (changing the land-use) while environmental conditions works as constraints, modulating what human operations are reasonable.
6, Exploring mechanisms behind LUCC (aim iii,). Please, revise and improve these parts. Citing statistics, experiments or other mechanistic proofs would be welcome. Try to disentangle speculations, hypotheses from known facts and published scientific results.
7, Were the found LUCC patterns already consequences of some environmental management programs? Are there any specific results from the present study that can be used to further modify/improve the present environmental policy?
8, Give some information about the process of particular changes. For example how farmlands change to grasslands (using active restoration with specific measures or by spontaneous succession)?
In Discussion you have cited several studies that were consistent with the results of the present study. However, you also stated in Introduction that this is the first study addressing these relationships. What does consistency mean in this context?
References are relevant. However, they emphasize the local context of the study. Please, search for some similar (comparable) studies from other areas to increase the generality of the study.
Author Response
Dear Editors and Reviewers,
Thank you for your letter as well as the reviewers’ comments concerning our manuscript entitled “Terrain gradient characteristics of land-use change in the agro-pastoral ecotone of northern China” (ID: land-1548540). Those comments are all valuable and very helpful for revising and improving our manuscript, which are the important guiding significance to our researches. We have made revisions according the comments and suggestions from reviewers. Revised portions are marked in red in the manuscript. The main revisions in the manuscript and the responds to reviewers’ comments are as following.
Responds to the reviewers' comments
Response: According to the suggestions proposed by the reviewer, we have made some revisions in the manuscript. The results are as following:
(a) The ”terrain factors” was changed into “topographic factors”, ”terrain characteristics” was changed into “topographic characteristics”, ”terrain gradient effects” was changed into “topographic gradient effects”, and ”terrain gradient pattern” was changed into “topographic gradient pattern”.
(b) Topographic factor refers to the indicators of topographic information, such as elevation, slope, terrain relief, terrain niche, terrain types, and so on. Topographic characteristics can be summarized from altitude elevation, terrain relief, main terrain types, topographic distribution pattern and so on. Topographic gradient effect refers to the vertical differentiation characteristics of geographic phenomena or processes. In this study, topographic gradient effect indicates the impact of topographic factors on land-use changes. Topographic gradient pattern indicates the spatial distribution characteristics of land-use information maps in the vertical direction.
(c) We used spatial superposition method to explore the relationships between altitude, slope, relief complexity and land-use changes. We used Geo-information graphics and spatial superposition method to analyze the topographic effect of land-use changes.
Response: According to the suggestions proposed by the reviewer, we have made some revisions in the manuscript. The results are as following:
We have added a summary of the existing knowledge in general sense and in global context in the section of “Introduction”. With the intensification of contradiction between human and land, three-dimensional use mode of land resources has become the hot issue in the research of global environmental change and sustainable development. Many scholars focused on the influence of topographic factors on the selection of agricultural regions, and regional LUCC and its ecological effects under the constraints of elevation conditions. (Seen in P2 Line 51-56)
[12] Xue, L.; Zhu, B.; Wu, Y.; Wei, G.; Liao, S.; Yang, C.; Wang, J.; Zhang, H.; Ren, L.; Han, Q. Dynamic projection of ecological risk in the Manas River basin based on terrain gradients. Sci. Total Environ. 2019, 653, 283-293. https://doi.org/ 10.1016/ j. scitotenv.2018.10.382
[13] Zhang, L.; Hu, N. Spatial Variation and Terrain Gradient Effect of Ecosystem Services in Heihe River Basin over the Past 20 Years. Sustain. 2021, 20, 11271. https:// doi.org/10.3390./ SU132011271.
Response: According to the questions proposed by the reviewer, we have made revision in the section of “Discuss”. (Seen in P14-16 Line 436-518)
Response: According to the questions proposed by the reviewer, we have added the description of the barrier. The result is as following:
The AENC is an important ecological barrier to curb desertification, desertification eastward and southward, which is a typical ecological fragile area in China. (Seen in P2 Line 133-134)
Response: According to the questions proposed by the reviewer, we have made some description about the study phase. The result are as following:
(a) Ecological policies, especially Grain for Green project had significant effects on the spatiotemporal variation of land-use changes in the AENC. Since 1999, the AENC has begun to pilot ecological farmland. Since the 21st century, with the implementation of the ecological civilization strategy, ecological projects such as the Three-North Shelter Forest Phase IV Project, the Beijing-Tianjin Sandstorm Source Control Project, and the Taihang Mountain Greening Project had significant impacts on the pattern of land use changes in the AENC. With the evolution of ecological policy, the research period was divided into stages 2000-2010 and 2010-2020 to explore the topographic gradient effects of land-use changes in the AENC.
(b) Topographic factors including elevation, slope, terrain relief, and terrain niche determine the basic pattern of land-use spatial distribution in the AENC. Human agricultural farming, economic construction and other activities are subject to topographic condition, which determines that the types of land-use (i.e., farmland, water area and construction land, etc.) closely related to human production and living activities are all distributed in areas with low altitude, slope, and terrain relief. Forestland and grassland are more concentrated in the areas with high altitude, large slope and terrain relief. The topographic gradient effects of land-use pattern in the AENC is the response of topographic factors on the redistribution of precipitation and temperature conditions.
Response: According to the questions proposed by the reviewer, we have made revision in the section of “Conclusion”. The result is as following:
In this study, the methods of gro-information graphics and distribution index were used to realize the effective integration of land-use pattern and evolution process, and reveal the trend and direction of land use structure changes in different topographic gradients. The topographic gradient effect and hierarchical distribution law of land-use changes can be used to guide the adjustment of land use structure according to local conditions. The low topographic gradient is the dominant distribution area of farmland and construction land, and it is also key area for comprehensive development, where attentions should be paid to the relationship of economic development and ecological environment protection. The key goal is to reasonably guide the urbanization process and precent the loss of farmland. Forestland, grassland, and unused land are dominant in high topographic gradient areas, where agricultural production should be restricted, natural vegetation should be protected, and ecological protection policies should be strictly implemented. (Seen in P16 Line 545-557)
- The section of “Material and Methods”
Response: According to the questions proposed by the reviewer, we have made revisions in the manuscript. The result are as following:
(a) The AENC located at the junction of the western part of the Northeast Plain and the eastern part of the Inner Mongolia Plateau and extends northwest to the northern part of the Loess Plateau, is located in the transition zone of traditional agriculture and animal husbandry in northern China. The southeast side of the AENC is traditional farming area, and the northwest side is the natural pastoral area. The location is 34°43′31"–46°57′46"N, 100°57′11"–125°34′11"E, which includes 226 counties (banners, cities, districts) in Inner Mongolia, Jilin, Liaoning, Hebei, Shanxi, Shaanxi, Gansu, Ningxia, and Qinghai provinces (autonomous regions).
(b) The elevation of the AENC ranges from −160 m to 4973 m above sea level. Plateau, mountains, and hills are dominant in this area. The ecological environment of the AENC is typically sensitive and fragile, but it is also an important element of the ”two barriers and three belts” strategic pattern of ecological security in China, which is an important ecological barrier to curb desertification, desertification eastward and southward.
(c) The topographic condition is complex in the AENC, where the three-dimensional development and use of land resource is obvious. Topographic factors including elevation, slope, terrain relief, and terrain niche determine the basic pattern of land-use spatial distribution in the AENC. Human agricultural farming, economic construction and other activities are subject to topographic condition, which determines that the types of land-use (i.e., farmland, water area and construction land, etc.) closely related to human production and living activities are all distributed in areas with low altitude, slope, and terrain relief. Forestland and grassland are more concentrated in the areas with high altitude, large slope and terrain relief. The topographic gradient effects of land-use pattern in the AENC is the response of topographic factors on the redistribution of precipitation and temperature conditions.
Response: According to the questions proposed by the reviewer, we have improved Figure1. Given that this study aims to reveal the influence of topographical factors on land-use changes the in the AENC, we show the altitude elevation feature in Figure 1.
Figure 1. Location of study area.
Response: According to the questions proposed by the reviewer, we have made revisions in the section of “Data sources and processing”. The result are as following:
(a) We have added reference [41] to the climate data (Line 127-129). In addition, we added the sources of climate data in the section of “Data sources and processing”.
Reference: [41] Fang, Z.; He, C.; Liu, Z.; Zhao, Y.; Yang, Y. Climate change and future trends in the Agro-Pastoral Transitional Zone in Northern China: The comprehensive analysis with the historical observation and the model simulation. J. Nat. Resour. 2020, 35: 358-370. https://doi.org/10.31497/zrzyxb.20200209
(b) Climate data, including multi-year average temperature and precipitation (from 1981 to 2019) were obtained from China Meteorological Science Data Sharing Service Network (http://data.cma.cn/), which were interpolated onto raster-formatted surfaces with a resolution of 30 m×30 m using the tension spline method [41]. (Seen in P4 Line 157-160)
Reference: [42] Huang, A.; Xu, Y.; Sun, P.; Zhou, G.; Liu, C.; Lu, L.; Xiang, Y.; Wang, H. Land use/land cover changes and its impact on ecosystem services in ecologically fragile zone: A case study of Zhangjiakou City, Hebei Province, China. Ecol. Indic. 2019, 104, 604-614. https://doi.org/10.1016/j. ecolind.2019.05.027
Response: According to the questions proposed by the reviewer, we have revised the abstract, the result is as following:
The AENC is located in the transition zone of traditional agriculture and animal husbandry in northern China with an arid and semi-arid climate, which is an important ecological barrier to curb desertification, desertification eastward and southward. The ecological environment of the AENC is typically sensitive and fragile, where the land ecosystem is vulnerable to interference from human activities. Excessive agricultural farming and economic construction led to ecosystem degradation, such as soil erosion, desert encroachment, grassland degradation, and so on. It is characterized by the conversion of forestland, grassland to farmland and construction land. However, with the implementation of the ecological civilization strategy, ecological projects such as the Three-North Shelter Forest Phase IV Project, the Beijing–Tianjin Sandstorm Source Control Project, and the Taihang Mountain Greening Project have had significant impacts on the pattern of land use changes in the AENC. It is characterized by the conversion of farmland to forestland and grassland. Therefore, the study of land-use changes is closely related to the sensitivity and vulnerability of ecosystems in the AENC.
Response: According to the suggestions proposed by the reviewer, we have added references [10] and [18]. the results are as following:
[10] Sun, P.; Xu, Y.; Wang, S. Terrain gradient effect analysis of land use change in poverty area around Beijing and Tianjin. Transactions of the CSAE 2014, 30, 277-288.
[18] Liu, C.; Xu, Y.; Lu, X. Spatiotemporal evolution and optimization of trade-off and synergy of land use functions in cologically fragile and poverty areas: a case study of Zhangjiakou City. Econ. Geogr. 2021, 41, 181-190. https://doi.org/10. 15957/j.cnki.jjdl. 2021.01.021
Response: According to the suggestions proposed by the reviewer, we have made some revisions in the manuscript. The results are as following:
The topographic data in table 1 was derived form a digital elevation model (DEM) with a resolution of 30 m×30 m. The slope and terrain relief were extracted from the DEM with a resolution of 30 m×30 m. Therefore, the spatial scale of elevation, slope and terrain relief represented individual 30 m×30 m pixel. (Seen in P5 Line 166-167)
Response: According to the questions proposed by the reviewer, we have used different letters to show different meanings. The result are as following:
|
|
(2) |
|
|
(3) |
where Np (range: [0, 100%]) is the importance index of land-use change type p, Yp (km2) is the area of change type p, and Y is the sum area of land-use change in the AENC. The larger the value of Np, the more dominant the land-use change. The main types of land-use changes were then selected according to the rank of Np. (seen in P6 Line 183-187)
Response: According to the questions proposed by the reviewer, we have used different letters to show different meanings. The result are as following:
|
(6) |
where SAkq (km2) is the area of land-use change pattern k on terrain niche q, SAk (km2) is the area of land-use change pattern k, SAq (km2) is the area of terrain niche q, and TA (km2) is the total area of the study area. When DI > 1, terrain niche q is dominant in land-use change pattern k, and the larger the value of DI, the greater the dominance.(seen in P7 Line 217-221)
Response: According to the questions proposed by the reviewer, we have corrected the range of Np in formula (2). (seen in P5 Line 184)
Response: According to the suggestions proposed by the reviewer, we have added definition of five types of land-use change pattern. The result are as following:
Prophase change referred to changes of land-use structure occurring in 2000-2010 and remaining unchanged in 2010-2020. Anaphase change meant that land-use structure remained unchanged in 2000-2010 and changed during 2010-2020. Continuous change indicated that land-use changes occurred in 2000-2010 and 2010-2020, and land use types were different in 2000 and 2020. Repeated change indicated that land-use changes occurred in 2000–2010 and then returned to 2000 use in 2020. Stable type meant that land-use remained unchanged during 2000-2020. (Seen in P5 Line 197-203)
Response: According to the questions proposed by the reviewer, we have defined the “Terrain niche” in this manuscript.
Terrain niche is a composite terrain factor, which can reflect the combined impact of elevation and slope. Terrain relief, also known as topographical fluctuation, relative terrain or relative height, refers to the difference between the highest point elevation and the lowest point elevation within a certain region, which reflects the surface fluctuation characteristics in the macro region. We have considered altitude elevation attributes in the formula (6) of TNI (terrain niche), where E (m) is the elevation of the pixel, E0 (m) is the average elevation. (Seen in P7 Line 206-213)
- The section of “Results”
Response: According to the suggestions proposed by the reviewer, we have revised figure2-4. The results are seen in P4 Line 147 Figure 2, P8-9 Line 267-268 Figure 3, and P9 Line 273 Figure 4.
Response: According to the questions proposed by the reviewer, we have made an explanation for “obviously different” in Line 269. The “obviously different” refers to differences of spatial pattern among stable type, prophase change type, anaphase change type, continuous change type and repeated change. That is, the spatial pattern of one type of land-use changes is obviously different from the spatial pattern of other types of land-use changes.
Response: According to the questions proposed by the reviewer, we have given the explanation for the trend of larger prophase type changes and smaller changes with anaphase type. It was characterized by the changes of “farmland-forestland- forestland” and “farmland-grassland-grassland”, which were mainly occurred in the junction among Inner Mongolia, Hebei, and Shanxi including Taiservant Temple Banner, Kangbao, Zhangbei, Guyuan, Duolun, Wuchan, and Shanyin County. It was mainly due to the intensity of ecological policies. Since the 21st century, with the implementation of the ecological civilization strategy, ecological projects such as the Three-North Shelter Forest Phase IV Project, the Beijing–Tianjin Sandstorm Source Control Project, and the Taihang Mountain Greening Project had significant impacts on the pattern of land use changes in the AENC. The intensity of these projects during 2000-2010 was much stronger than that in 2010-2020.
Response: According to the suggestion proposed by the reviewer, we have moved the reason for the main change types of “farmland-grassland-grassland” and “farmland- forestland-grassland” to the section of “Discussion”.
Response: According to the suggestions proposed by the reviewer, we have given the explanations for the topographic gradient characteristics. The distribution index and geo-information graphics were used to reveal the topographic gradient pattern of land-use changes types. There is some correlation among topographic factors including altitude elevation, slope, terrain relief, and terrain niche. Moreover, there was approximately 78.26% of population distributed in low topographic gradient, while the population distributed in the high-terrain gradient was less than 5%. Therefore, land-use changes including anaphase change type, continuous change type, and repeated change type were mainly distributed in the topographic gradient areas with elevations of less than 500m, slope of 0-6°, and terrain relief of less than 50m. However, land-use changes including stable type occupied the dominant position in the topographic gradient areas with elevation exceeding 1000m, slope of more than 15°, and terrain relief of more than 100m.
Response: According to the suggestion proposed by the reviewer, we have revised figure5-6. The results are as following:
Figure 5. DI of terrain relief gradient for land-use structure changes.
Figure 6. DI of terrain niche gradient for land-use structure changes.
- The section of “Discussion”
Response: According to the questions proposed by the reviewer, we have revised the “Discussion”. The result is as following:
This study explores the spatiotemporal pattern and topograhic gradient effect of land-use changes during 2000-2020 in the AENC. The results show that the total areas of land-use changes were 121 744 km2, accounting for 17.41% during 2000-2020 in the AENC. From 2000 to 2020, it is characterized by increasing amount of land-use changes in the AENC, which indicates that more land-use changes has occurred in 2010-2020 than in 2000-2010. This was mainly due to the acceleration of China’s new-type industrialization and urbanization process during 2010-2020. Meanwhile, the expansion of construction land was derived mainly from farmland and grassland, which was concentrated mainly in urban districts and their surrounding areas located in river valleys and intermountain basins. The pattern of land-use changes was divided into five types including stable type, prophase change type, anaphase change type, continuous change type, and repeated change type. Stable type accounted for 559 868.86 km2 and 80.09% of the total area during 2000-2020. It was dominant in high-altitude and complex terrain areas with elevations exceeded 1000 m, slopes exceeding 6°, terrain reliefs of more than 100 m, and terrain niches exceeding 1.61. The distribution index of prophase and anaphase change types fluctuated obviously with the change of topographic gradient. Prophase and anaphase changes occupied two dominant positions in the topographic gradient. Continuous and repeated change types occupied dominant positions in low topographic gradients with elevations of less than 1000 m, slopes of 0-6°, terrain reliefs of 0-100 m, and terrain niches of less than 1.17. The types of prophase change and continuous change were characterized mainly by “farmland-grassland- grassland” and “farmland-forestland-grassland”, which were mainly due to the strategy implementation of ecological policies during 2000-2010 and the construction of new-type urbanization.
The AENC is located in the transition zone from traditional agriculture to animal husbandry in northern China with an arid and semi-arid climate, which is an important ecological barrier to curb desertification, desertification eastward and southward. The ecological environment of the AENC is typically sensitive and fragile, where the land ecosystem is vulnerable to interference from natural factors, human activities and regional policies. (Seen in P14 Line 405-434)
Response: According to the suggestions proposed by the reviewer, we have revised the abstract. The result is as following:
The results show the following: (1) From 2000 to 2020, the total areas of land-use changes were 121 744 km2, accounting for 17.41%. It was characterized by increasing amount of land-use changes in the AENC. The changes of land-use were dominated by the conversions among farmland, forestland, and grassland, which were distributed widely in the mountainous areas of northern, western, and eastern margins. The expansion of construction land was derived mainly from farmland and grassland occurred in river valleys. (Seen in P1 Line 16-21)
Response: According to the questions proposed by the reviewer, we have revised the “Discussion”. We have revised and improved the section of “4.1. Effects of natural factors on topographic gradient characteristics of land-use changes”, “4.2. Effects of socioeconomic factors on topographic gradient characteristics of land-use changes” and “4.3. Effects of policy factors on topographic gradient characteristics of land-use changes”. (Seen in P15-16 Line 435-517)
Response: According to the questions proposed by the reviewer, we have revised the question in the last of “Conclusion”. The result is as following:
In this study, the methods of gro-information graphics and distribution index were used to realize the effective integration of land-use pattern and evolution process, and reveal the trend and direction of land use structure changes in different topographic gradients. The topographic gradient effect and hierarchical distribution law of land-use changes can be used to guide the adjustment of land use structure according to local conditions. The low topographic gradient is the dominant distribution area of farmland and construction land, and it is also key area for comprehensive development, where attentions should be paid to the relationship of economic development and ecological environment protection. The key goal is to reasonably guide the urbanization process and precent the loss of farmland. Forestland, grassland, and unused land are dominant in high topographic gradient areas, where agricultural production should be restricted, natural vegetation should be protected, and ecological protection policies should be strictly implemented. (Seen in P16 Line 545-556 )
Response: According to the sugestions proposed by the reviewer, we have discuss the impact of the topographic factors including altitude elevation, slope, terrain relief, and terrain niche on land use changes in the section of “Discuss”. The result is as following:
This study explores the spatiotemporal pattern and topograhic gradient effect of land-use changes during 2000-2020 in the AENC. The results show that the total areas of land-use changes were 121 744 km2, accounting for 17.41% during 2000-2020 in the AENC. From 2000 to 2020, it is characterized by increasing amount of land-use changes in the AENC, which indicates that more land-use changes has occurred in 2010-2020 than in 2000-2010. This was mainly due to the acceleration of China’s new-type industrialization and urbanization process during 2010-2020. Meanwhile, the expansion of construction land was derived mainly from farmland and grassland, which was concentrated mainly in urban districts and their surrounding areas located in river valleys and intermountain basins. The pattern of land-use changes was divided into five types including stable type, prophase change type, anaphase change type, continuous change type, and repeated change type. Stable type accounted for 559 868.86 km2 and 80.09% of the total area during 2000-2020. It was dominant in high-altitude and complex terrain areas with elevations exceeded 1000 m, slopes exceeding 6°, terrain reliefs of more than 100 m, and terrain niches exceeding 1.61. The distribution index of prophase and anaphase change types fluctuated obviously with the change of topographic gradient. Prophase and anaphase changes occupied two dominant positions in the topographic gradient. Continuous and repeated change types occupied dominant positions in low topographic gradients with elevations of less than 1000 m, slopes of 0-6°, terrain reliefs of 0-100 m, and terrain niches of less than 1.17. (Seen in P14 Line 405-424)
According to the results of this study, topographic factors including altitude elevation, slope, terrain relief, and terrain niche were the basic influence factors for the spatial pattern of land-use changes, which were consistent with the existing researches. Many scholars found that topographic factors played important roles in the redistribution of surface water and thermal conditions, blocking mode, and soil erosion strength [13,26,31,46]. Similar results were reported from Sun et al and Li et al, who found that topographic gradient effect of land-use changes was resulted from terrain relief, change rate of slope, aspect and terrain niche [10,28]. Area with elevations of less than 2000 m and slopes of 0–15° accounted for 90.93% and 78.62% in the AENC, respectively, which mainly determined the basic spatial pattern of land-use changes. Farmland, forestland, and grassland occupied the dominant position and were distributed widely in many topographic gradients during 2000–2020. (Seen in P14 Line 443-454)
Response: According to the sugestions proposed by the reviewer, we have discuss the potential confounding factors in the section of “4.1. Effects of natural factors on topographic gradient characteristics of land-use changes”. The result is as following:
Natural factors were the basis of the evolution of the land-use pattern in the AENC, generally either boosting or restraining the evolution of the topographic gradient pattern of land-use changes. The AENC was an important ecological security barrier and water conservation area of Beijing-Tianjin-Hebei with sensitive ecological environment. Those natural environmental factors represented the regional natural conditions, which reflected the macro-geographic background of the AENC to a certain extent. Therefore, the effects of those natural environmental factors on the spatial pattern of land-use changes was synthetic in the AENC. According to the results of this study, topographic factors including altitude elevation, slope, terrain relief, and terrain niche were the basic influence factors for the spatial pattern of land-use changes, which were consistent with the existing researches. Many scholars found that topographic factors played important roles in the redistribution of surface water and thermal conditions, blocking mode, and soil erosion strength [13,26,31,46]. (Seen in P15 Line 435-448)
Response: According to the questions proposed by the reviewer, we have revised the section of “4.1. Effects of natural factors on topographic gradient characteristics of land-use changes”. The result is as following:
4.1. Effects of natural factors on topographic gradient characteristics of land-use changes
Natural factors were the basis of the evolution of the land-use pattern in the AENC, generally either boosting or restraining the evolution of the topographic gradient pattern of land-use changes. The AENC was an important ecological security barrier and water conservation area of Beijing-Tianjin-Hebei with sensitive ecological environment. Those natural environmental factors represented the regional natural conditions, which reflected the macro-geographic background of the AENC to a certain extent. Therefore, the effects of those natural environmental factors on the spatial pattern of land-use changes was synthetic in the AENC. According to the results of this study, topographic factors including altitude elevation, slope, terrain relief, and terrain niche were the basic influence factors for the spatial pattern of land-use changes, which were consistent with the existing researches. Many scholars found that topographic factors played important roles in the redistribution of surface water and thermal conditions, blocking mode, and soil erosion strength [13,26,31,46]. Similar results were reported from Sun et al and Li et al, who found that topographic gradient effect of land-use changes was resulted from terrain relief, change rate of slope, aspect and terrain niche [10,28]. Area with elevations of less than 2000 m and slopes of 0–15° accounted for 90.93% and 78.62% in the AENC, respectively, which mainly determined the basic spatial pattern of land-use changes. Farmland, forestland, and grassland occupied the dominant position and were distributed widely in many topographic gradients during 2000–2020. The change types of “farmland–farmland–farmland” and “grassland–grassland–grassland” had the widest distribution in the AENC. Since the 21st century, ecological policies and ecological projects were carried out in the AENC, which resulted in the land-use changes of “farmland-grassland-grassland” and “farmland-forestland-grassland” in high altitude and complex terrain areas with elevations exceeding 1000 m, slopes of more than 15°, and terrain relief of more than 150 m. By the end of 2020, construction land and farmland were mainly distributed in low altitude and flat terrain areas. Similar result was confirmed by Saha et al and Liu et al [11,36]. (Seen in P15-16 Line 435-462)
Response: According to the questions proposed by the reviewer, we have revised the “Discussion”. We have revised and improved the section of “4.1. Effects of natural factors on topographic gradient characteristics of land-use changes”, “4.2. Effects of socioeconomic factors on topographic gradient characteristics of land-use changes” and “4.3. Effects of policy factors on topographic gradient characteristics of land-use changes”. (Seen in P15-16 Line 435-517)
Response: According to the questions proposed by the reviewer, we have revised in the last of “Conclusion”. The result is as following:
In this study, the methods of gro-information graphics and distribution index were used to realize the effective integration of land-use pattern and evolution process, and reveal the trend and direction of land use structure changes in different topographic gradients. The topographic gradient effect and hierarchical distribution law of land-use changes can be used to guide the adjustment of land use structure according to local conditions. The low topographic gradient is the dominant distribution area of farmland and construction land, and it is also key area for comprehensive development, where attentions should be paid to the relationship of economic development and ecological environment protection. The key goal is to reasonably guide the urbanization process and precent the loss of farmland. Forestland, grassland, and unused land are dominant in high topographic gradient areas, where agricultural production should be restricted, natural vegetation should be protected, and ecological protection policies should be strictly implemented. (Seen in P16 Line 545-556 )
Response: According to the questions proposed by the reviewer, we have added the process of particular land-use changes in the section of “Discussion”. The result is as following:
(a) Farmland, forestland, and grassland occupied the dominant position and were distributed widely in many topographic gradients during 2000–2020. The change types of “farmland–farmland–farmland” and “grassland–grassland–grassland” had the widest distribution in the AENC. Since the 21st century, ecological policies and ecological projects were carried out in the AENC, which resulted in the land-use changes of “farmland-grassland-grassland” and “farmland-forestland-grassland” in high altitude and complex terrain areas with elevations exceeding 1000 m, slopes of more than 15°, and terrain relief of more than 150 m. By the end of 2020, construction land and farmland were mainly distributed in low altitude and flat terrain areas. Similar result was confirmed by Saha et al and Liu et al [11,36]. (Seen in P15-16 Line 453-462 )
(b) During the same time, the urbanization rate increased by nearly 15% in the AENC. With the acceleration of urbanization, many of rural population migrated to urban, which led indirectly to the abandonment of farmland [34,45]. From 2000 to 2020, the total areas of farmland converted to forestland, grassland, and water areas were 3240.69 km2, 23 751.22 km2, and 625.99 km2, respectively. Considering the topographical conditions, economic activities were concentrated in low-altitude and flat terrain areas, where construction land constantly occupied farmland in terrain niche of less than 1.17. It was characterized by change type of“farmland/grassland–farmland–construction land”. Meanwhile, farmland spread to areas with higher topographic gradients to meet food demand in the AENC. (Seen in P15 Line 473-482 )
(c) Forestland and grassland have been restored in the areas with high terrain gradient and complex terrain, which expanded toward lower terrain gradients during 2000–2020. The conversion of farmland to grassland and forestland was distributed mainly in the mountainous areas of the northern, western, and eastern margins as well as low mountainous and hilly areas of Loess Plateau [25,38,49-50]. (Seen in P16 Line 511-515 )
Response: According to the questions proposed by the reviewer, we have made some expansions. In this study, we chose the entire AENC as study area. Most of the relevant studies focus on part of the AENC.
Response: According to the questions proposed by the reviewer, we have added four references. In addition, there are some research focused on other areas.
[6] Matasov, V.; Prishchepov, A. V.; Jepsen, M. R.; Müller, D. Spatial determinants and underlying drivers of land-use transitions in European Russia from 1770 to 2010. J. Land Use Sci. 2019, 14, 362-377. https://doi.org/10.1080/1747423X.2019.1709224
[7] Zaehringer, J. G.; Atumane, A.; Berger, S.; Eckert, S. Large-scale agricultural investments trigger direct and indirect land use change: New evidence from the Nacala corridor, Mozambique. J. Land Use Sci. 2018, 13, 325-343. https://doi.org/10. 1080/ 1747423X.2018. 1519605
[8] Swette, B.; Lambin, E. F. Institutional changes drive land use transitions on rangelands: The case of grazing on public lands in the American West. Global Environ Chang. 2021, 66, 102220. https://doi.org/10.1016/j.gloenvcha.2020.102220
[41] Fang, Z.; He, C.; Liu, Z.; Zhao, Y.; Yang, Y. Climate change and future trends in the Agro-Pastoral Transitional Zone in Northern China: The comprehensive analysis with the historical observation and the model simulation. J. Nat. Resour. 2020, 35: 358-370. https://doi.org/10.31497/zrzyxb.20200209
We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we don’t list all the changes in this report but marked in red in revised manuscript.
We appreciate for Editors and Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.
Yours sincerely,
Piling Sun
E-mail: [email protected]
Tel: 18763321108
January 16, 2022
Author Response File: 
Author Response.docx
Round 2
Reviewer 1 Report
The authors clearly attempted to respond to the reviews of this paper. As it stands, however, the paper is not ready for publication. Let me be clear. The positives are its strong analytics of the land changes across time for an area of China. This “meat” of the paper is not in question. What remains less appealing are its problem set up, discussion, and English phrasing. (It may be that this phrasing interferes with the problem set up and discussion).
Problem set up. Why do we want to know the land changes in question? Knowing them informs us of what problems. Indeed, what is the AENC (see below)? These queries remain less than well answered. Has land change been large, not so much according to the data. Has the change taken place on topographic gradients with significant impacts on ecological functioning or downstream impacts? The latter seems to be the case—barrier to desertification, reduce Beijing dust storms—but details about why we should a care are weak. Also note that all of the land changes noted are precisely those that we would expect given Chinese plans and policies.
The discussion section is relatively weak because the claims made are broad stroke with less than strong details to support the claims made (see below)
As noted, the phrasing throughout is somewhat problematic as I noted below through examples. I suspect that some of my comments about detail and clarity follow from the terms and phrases used.
Specific comments
Given that human production and economic activities often occur in 50 low terrain areas, the ecological policies mainly focuses on ecological fragile areas with 51 complex terrain [6-8]. Socioeconomic activities and policies have topographic gradient ef-52 fect on land-use changes.
In appropriate use of “the” and “an” throughout parts of the text as in “the ecological policies”; or “policies have [a] topographic gradient”; verb agreement in various parts of the text “policies mainly focuses”
With the 55 “intensification of contradiction” between human and land—odd construction
Line 57: if this is a hot issue, provide references that indicate it is so..two are provide, both Chinese in origin. Perhaps the statement should say “significant issue, especially in China”..note that Lambin et al. is cited as part of the attention to topographic interest but this work really does not emphasize topography..almost all of citations to topographic importance are to Chinese researchers and topics…Without references that topographic gradients are replete in the land system community, then the text should tell us that it is of major concern in China and not imply that it is elsewhere
to curb desertification, desertification 92 eastward and southward, which
Odd to have desertification back to back as in the phrasing above—and this phrasing is used subsequently in the text
Line 100… the response letter does not adequately clarify the use of the term “law” or the use of that term in line 100. A law is an explanation, in this case, of land-use changes. The top paragraph on page 3 and the response letter imply that the law has something to do with the spatiotemporal characteristics …. But overall it is not clear what the law is; characteristics per se are not laws.
The AENC remains inadequately introduced. Lines 90+ give us a location and its function as an ecological barrier to impeded arid land degradation. However, here and in 2.1 we are never told what the AENC functions as and hence constitutes an area of concern. Is it an administrative unit? An ecosystem? We are told that it is proposed to be an ecotone but we are not told that the authors accept and use the AENC as an ecotone, apparently an area of rolling hills between the Mongolian-Loess Plateaus and the plains that serve to impeded arid land degradation to the east and south.
Land uses/covers: water area is usually called water; construction land is simply not a term used in land system science, at least not outside China. Perhaps the more common term is “built” land, in this case, non-agricultural built land. The authors might note that construction land is their terms for built land.
Prophase and anaphase are defined (ok) but their use here is not what is meant in biology (the origin of the word) and the terms are not used in land change studies. On the other hand, I am not sure land studies have complementary terms.
Figures 5-6. what is the measure of distribution index
Line 400 land-use changes were 121 744 km2, accounting for 17.41% during 2000-2020 in the AENC. 399 From 2000 to 2020, “it is” characterized
“they are”
Line 402. This was mainly due to the acceleration of China’s new-type industrialization 402 and urbanization process during 2010-2020.
What is/was “new-type”
4.1… this study is about land/use-cover change; there is no evolution per see.
Therefore, the 432 effects of those natural environmental factors on the spatial pattern of land-use changes 433 was synthetic in the AENC.
What does this mean?
4.2 Qu et al found that economic development, population, and 455 urbanization level had significant impacts on the spatiotemporal evolution of land-use 456 pattern [22].
Where? Not in AENC although the sentence infers the AENC.
4.3 While many words have been added here, I am not sure they are needed. What was previously confusing was the claim that policy had impacts on the topo-gradient effect, as if topo-gradient is a cause (See belowO.
- In the context of ecological civilization construction
What does this mean?
We are told that the study examines the topographic gradient effect on land use. (1), however, is a listing of land changes with no reference to topography per se, although mountainous and river valleys are labels used. Would be better to refer to metrics of high and low gradients.
Natural factors played a 528 basic role in the formation of topographic gradient effect. Socioeconomic factors and pol-529 icy factors were important push-drivers, such as human migration, construction of infra-530 structure facilities, and the project of “Grain for Green”.
The above is clear in its meaning but expressed in a way that is inconsistent with land system science. Biophysical conditions are generally considered the backdrop or template of land systems, and the drivers are socioeconomic ones, including policy. Biophysical conditions become drivers only IF they change independent of the immediate land uses. Hence, climate change might be a driver or tectonic forces might be. Throughout this work the authors tend to conflate the “basic natural condition” as a driver.
Comments for author File: Comments.pdf
