3.1.1. Temporal Properties
It was found that the land use/cover changed significantly after statistical analysis of the land-use area over the study period in Zhenlai County (
Table 2 and
Figure 3). In 1954–2005, arable land, grassland, and wetland were the dominant land use types, with over 70% of total area percentage. Arable land, forest, and settlement expanded continuously from 1954 to 2005 (
Figure 4). It is especially important to note that arable land had the largest increase, from 31.48% in 1954 to 39.07% in 2005, while both grassland and wetland had significant loss during the past 60 years. In 1954, grassland and wetland occupied 30.54% and 32.26% of the total study area; however, these areas had declined to 12.27% and 18.81%, respectively, by 2005. The proportional area of water bodies changed slightly, fluctuating from 4.89% in 1954 to 5.50% in 2005. Water bodies were mainly influenced by natural factors, especially affected by climate change in the absence of irrigation facilities such as reservoirs. Other unused land surged from 1954 to 1976 and continued to increase until 2000, and then it began to decline slightly as people started to emphasize controlling desertification and salinization.
Figure 3.
Percentage of area of each land category, 1954–2005.
Figure 3.
Percentage of area of each land category, 1954–2005.
Table 2.
Area and percentage changes during the time intervals.
Table 2.
Area and percentage changes during the time intervals.
Categories | Area (in ha) and percentages (%) | Changes (in ha) |
---|
1954 | 1976 | 2000 | 2005 | 1954–1976 | 1976–2000 | 2000–2005 |
---|
Area | % | Area | % | Area | % | Area | % |
---|
Arable land | 16,7355.69 | 31.48 | 19,2533.35 | 36.22 | 198,950.45 | 37.42 | 207,717.83 | 39.07 | 25,177.66 | 6417.10 | 8767.38 |
Forest land | 488.65 | 0.09 | 12,117.17 | 2.28 | 19,065.53 | 3.59 | 18,900.88 | 3.56 | 11,628.51 | 6948.36 | –164.65 |
Grassland | 16,2371.84 | 30.54 | 88,892.09 | 16.72 | 60,215.14 | 11.33 | 65,223.77 | 12.27 | −73,479.75 | −28,676.94 | 5008.63 |
Water | 26,000.01 | 4.89 | 29,352.35 | 5.52 | 30,024.12 | 5.65 | 29,259.09 | 5.50 | 3352.34 | 671.78 | –765.03 |
Settlement | 2944.58 | 0.55 | 11,109.70 | 2.09 | 12,503.21 | 2.35 | 12,547.33 | 2.36 | 8165.12 | 1393.51 | 44.12 |
Wetland | 17,1500.15 | 32.26 | 111,101.27 | 20.90 | 107,753.65 | 20.27 | 99,975.96 | 18.81 | −60,398.88 | –3347.62 | −7777.69 |
Other unused land | 945.22 | 0.18 | 86,500.22 | 16.27 | 103,094.04 | 19.39 | 97,981.28 | 18.43 | 85,555.01 | 16,593.82 | −5112.76 |
Figure 4.
Land use/cover maps for the years (a) 1954; (b) 1976; (c) 2000 and (d) 2005.
Figure 4.
Land use/cover maps for the years (a) 1954; (b) 1976; (c) 2000 and (d) 2005.
3.1.2. Bitemporal Change Detection
A transition matrix was used to summarize the state of each land use in each time interval and the transitions through time with respect to each land category. From
Table 3,
Table 4, and
Figure 5, the results indicated that arable land expanded at the expense of grassland and wetland. Grassland had the largest cumulative transition probability (34.37%) during the period from 1954 to 2005, and 15.41% of grassland was changed into arable land while 15.02% of grassland was converted to wetland and other unused land. However, from 1954 to 1976, 38.90% of grassland was turned into arable land due to the fast growth of the population (from 145,328 persons in 1954 to 277,146 persons in 1976). Furthermore, 24.20% of grassland was converted to other unused land during 1976–2000, indicating serious environmental degradation. Wetland had the second largest cumulative transition probability (32.90%) during the study period. Wetland was mainly changed into arable land and other unused land, reflecting both human activities and natural processes affected by the climate. Wetland was changed to arable land with similar transition probabilities during the three time intervals from 1954 to 1976 (11.79%), 1976 to 2000 (16.75%), and 2000 to 2005 (15.45%). Also, 33.35% of wetland was changed to other unused land between 1954 and 1976. In addition, abandoned land could not be ignored during the study area. The cumulative transition probability of arable land is 26.20%, ranking third.
Table 3.
Transition probability matrices of land changes in each period (%).
Table 3.
Transition probability matrices of land changes in each period (%).
Categories | Period | Arable land | Forest land | Grassland | Water | Settlement | Wetland | Other unused land |
---|
Arable land | 1954–1976 | 56.19 | 3.74 | 15.58 | 2.01 | 5.55 | 8.51 | 8.42 |
1976–2000 | 81.27 | 1.80 | 2.91 | 0.10 | 2.84 | 11.05 | 0.04 |
2000–2005 | 84.97 | 5.87 | 0.00 | 0.00 | 9.16 | 0.00 | 0.00 |
Forest land | 1954–1976 | 12.99 | 21.04 | 57.91 | 0.00 | 5.26 | 2.81 | 0.00 |
1976–2000 | 19.93 | 79.80 | 0.00 | 0.00 | 0.26 | 0.00 | 0.00 |
2000–2005 | 15.86 | 84.14 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Grassland | 1954–1976 | 38.90 | 3.96 | 18.28 | 2.25 | 1.15 | 24.55 | 10.90 |
1976–2000 | 10.11 | 9.83 | 54.66 | 0.23 | 0.13 | 0.84 | 24.20 |
2000–2005 | 16.19 | 0.00 | 83.81 | 0.00 | 0.00 | 0.00 | 0.00 |
Water | 1954–1976 | 5.89 | 0.19 | 4.78 | 41.97 | 0.14 | 25.16 | 21.87 |
1976–2000 | 2.50 | 2.50 | 2.50 | 85.00 | 2.50 | 2.50 | 2.50 |
2000–2005 | 1.39 | 0.00 | 3.15 | 70.41 | 0.00 | 23.33 | 1.72 |
Settlement | 1954–1976 | 36.31 | 0.79 | 5.91 | 0.82 | 42.04 | 3.76 | 10.37 |
1976–2000 | 2.50 | 2.50 | 2.50 | 2.50 | 85.00 | 2.50 | 2.50 |
2000–2005 | 2.50 | 2.50 | 2.50 | 2.50 | 85.00 | 2.50 | 2.50 |
Wetland | 1954–1976 | 11.79 | 0.58 | 20.15 | 6.02 | 0.41 | 27.70 | 33.35 |
1976–2000 | 16.75 | 0.00 | 4.05 | 0.83 | 0.00 | 77.86 | 0.52 |
2000–2005 | 15.45 | 0.00 | 0.25 | 8.68 | 0.00 | 75.62 | 0.00 |
Other unused land | 1954–1976 | 0.44 | 0.00 | 1.14 | 85.29 | 0.00 | 7.53 | 5.60 |
1976–2000 | 0.69 | 0.00 | 0.00 | 3.20 | 0.33 | 11.33 | 84.44 |
2000–2005 | 0.09 | 0.00 | 18.64 | 0.55 | 0.00 | 0.19 | 80.53 |
Table 4.
Cumulative transition probabilities (%).
Table 4.
Cumulative transition probabilities (%).
1954–2005 | Arable land | Forest land | Grassland | Water | Settlement | Wetland | Other unused land | Total |
---|
Arable land | 0.00 | 4.03 | 5.96 | 0.67 | 6.20 | 6.68 | 2.67 | 26.20 |
Forest land | 1.04 | 0.00 | 0.05 | 0.00 | 0.01 | 0.00 | 0.00 | 1.10 |
Grassland | 15.41 | 2.85 | 0.00 | 0.73 | 0.37 | 7.64 | 7.38 | 34.37 |
Water | 0.50 | 0.15 | 0.55 | 0.00 | 0.14 | 2.69 | 1.30 | 5.34 |
Settlement | 0.31 | 0.12 | 0.14 | 0.12 | 0.00 | 0.13 | 0.17 | 0.99 |
Wetland | 10.44 | 0.19 | 7.40 | 3.87 | 0.13 | 0.00 | 10.87 | 32.90 |
Other unused land | 0.13 | 0.00 | 3.62 | 0.78 | 0.05 | 1.89 | 0.00 | 6.47 |
Figure 5.
Cumulative transition areas from 1954 to 2005 (×10,000 ha).
Figure 5.
Cumulative transition areas from 1954 to 2005 (×10,000 ha).
3.1.3. Spatial Distributions and Trajectories of Land Cover Change
During the study period, unchanged land occupied 35.83% of the total area, and one-step, two-step, and three-step changed land occupied 55.54%, 8.07%, and 0.56%, respectively. Taking land use data in 1954 as a baseline, 64.80% of arable land, 49.33% of settlement, and 44.91% of water bodies remained the same during the study period (
Table 5), indicating that these land categories had relatively strong stability and certainty in the spatial distributions.
Table 5.
Percentages of unchanged land areas to the corresponding land areas in 1954 by types (%): A = Arable land; F = Forest land; G = Grassland; W = Water; S = Settlement; M = Wetland; O = Other unused land.
Table 5.
Percentages of unchanged land areas to the corresponding land areas in 1954 by types (%): A = Arable land; F = Forest land; G = Grassland; W = Water; S = Settlement; M = Wetland; O = Other unused land.
Unchanged land use | % | Unchanged land use | % | Unchanged land use | % | Unchanged land use | % |
---|
A | 64.80 | F | 24.97 | G | 13.53 | W | 44.91 |
S | 49.33 | M | 27.26 | O | 6.88 | | |
There were 34 types of one-step land changes (
Table 6), mainly including grassland→arable land (18.33%), wetland→other unused land (14.95%), grassland→wetland (8.71%), wetland→grassland (6.80%), grassland→other unused land (6.22%), and wetland→arable land (6.17%). The rest of the one-step changes were less than 4%. Moreover, among these one-step changed trajectories, “G→A→A→A” contributed the largest percentage (16.80% of the total changed land area from 1954 to 2005), while “G→G→A→A” and “G→G→G→A” contributed the percentages of 1.50% and 0.03%, respectively. The percentages of “M→A→A→A”, “M→M→A→A” and “M→M→M→A” contributed 4.74%, 0.89%, and 0.54%, respectively. The above analyses illustrated that people reclaimed and cultivated land intensely during 1954–1976, creating the dominant effect on land use. This could be driven by the national macro-policy actively encouraging people to reclaim and farm to develop local agriculture. The adjustment of production relations mobilized people’s enthusiasm to reclaim land since the 1950s [
49,
50]. One-step changes showed that once one land type was changed to another, it would then reach a steady state. For example, two-step changed land use would not occur if a quantity of grassland was changed into arable land. This might illustrate that people would not easily give up their reclaimed land unless an irresistible force exists. “Wetland→Other unused land” indicated that land degradation has difficult reversibility. Moreover, there were many conversions between grassland and wetland for the following two reasons: (1) wetland had a clear relationship with precipitation and would be changed into grassland in the years with less precipitation; (2) there were plenty of lakes and ponds inside and surrounding the Nenjiang River and the Tao’er River to the east and south of the study area, respectively, which made the nearby wetland, grassland, and other unused land convert frequently.
There were 60 types of two-step changes, mainly including wetland→grassland→other unused land (2.08%), grassland→wetland→arable land (1.93%), and arable land→grassland→forest land (1.43%). However, there were only 13 types of three-step changes, all with small percentages of the areas. Altogether, the analysis of two-step and three-step changes showed that arable land, grassland, wetland, water bodies, and other unused land were converted frequently; this may be due to the influence of rainfall.
Figure 6c shows that the trajectory analysis of land cover can display the histories of land use change and their features related to different driving forces over the study period. During the 60-year study period, unchanged land occupied 35.83% of the total area, human-induced changes occupied 26.89%, and natural evolution land area occupied 37.28%, respectively. In the study area, human-induced changes were mainly distributed in two areas, namely, cultivation in the northwest and east along the Nenjiang River. Unchanged, natural, and human-induced land use appeared stepwise from east (along the Nenjiang River) to west. Natural change along the Nenjiang River was likely to be caused by the fluctuation between flooding and drying. The fertile flood plain on the river’s banks allowed the land to be cultivated easily and produce a high grain yield.
From 1954 to 2005, once unchanged land and the land influenced by natural type were subject to human-induced changes, they tended to reach stability and were less likely to change in the following time nodes. In contrast, areas where changes were once influenced by natural evolution were more likely to change further. A plausible explanation for this is that land cover tends to be changed into a certain type that could increase its value or improve quality due to human activities. If it is converted into another type, the land value tends to decline or the switching cost tends to increase. Thus, it sometimes may drastically reduce the possibility that the land is used for other purposes. Analysis found that grassland, which decreased—the opposite of the continuously increasing artificial ecological environment construction—was changed into arable land and settlement. Moreover, water bodies, settlement, and arable land, which were closely related to human activities, were the most stable types. The second was other unused land related to land degradation, including sand, saline-alkali land, and bare land, whereas forest land, grassland, and wetland had the weakest stability. It is plausible to suggest that these illustrate the following three phenomena: (1) people do not easily give up their reclaimed land; (2) water bodies were difficult to replace by other land-use types; and (3) land degradation was often irreversible, at least on the observed time scales. Grassland and wetland with greater plasticity tended to be reclaimed into cultivated land and were affected by human impact on land development. In addition, land-use conversions often occur between grassland and wetland, or among wetland, water bodies, saline, and alkaline land influenced by precipitation.
Table 6.
Percentages of changed land areas by types, 1954–2005 (%). A = Arable land; F = Forest land; G = Grassland; W = Water; S = Settlement; M = Wetland; O = Other unused land.
Table 6.
Percentages of changed land areas by types, 1954–2005 (%). A = Arable land; F = Forest land; G = Grassland; W = Water; S = Settlement; M = Wetland; O = Other unused land.
| Changed types | % | Changed types | % | Changed types | % | Changed types | % |
---|
One-step changes | A→G | 3.28 | A→S | 2.33 | A→F | 1.55 | A→O | 3.13 |
A→W | 0.53 | A→M | 3.11 | G→A | 18.33 | G→S | 0.53 |
G→F | 2.05 | G→O | 6.22 | G→W | 0.84 | G→M | 8.71 |
F→G | 0.02 | F→A | 0.02 | F→S | 0.01 | W→G | 0.28 |
W→A | 0.38 | W→S | 0.01 | W→F | 0.01 | W→O | 1.44 |
W→M | 1.56 | S→G | 0.03 | S→A | 0.25 | S→O | 0.08 |
S→W | 0.01 | S→M | 0.03 | M→G | 6.80 | M→A | 6.17 |
M→S | 0.19 | M→F | 0.26 | M→O | 14.95 | M→W | 3.25 |
O→W | 0.20 | O→M | 0.02 | | | | |
Two-step changes | A→G→A | 0.40 | A→G→S | 0.01 | A→G→F | 1.43 | A→G→O | 0.62 |
A→G→M | 0.03 | A→F→A | 0.06 | A→O→G | 0.06 | A→O→A | 0.01 |
A→O→M | 0.01 | A→W→G | 0.02 | A→W→M | 0.21 | A→M→A | 0.25 |
A→M→W | 0.02 | G→A→G | 0.23 | G→A→S | 0.08 | G→A→F | 0.04 |
G→A→M | 0.48 | G→F→A | 0.19 | G→O→G | 0.52 | G→O→A | 0.01 |
G→O→W | 0.06 | G→W→G | 0.01 | G→W→M | 0.18 | G→M→G | 0.37 |
G→M→A | 1.93 | G→M→O | 0.03 | G→M→W | 0.16 | S→G→O | 0.01 |
S→A→S | 0.02 | S→A→F | 0.01 | F→G→F | 0.05 | O→W→G | 0.03 |
W→G→O | 0.11 | W→G→W | 0.01 | W→G→M | 0.01 | W→O→G | 0.02 |
W→O→W | 0.01 | W→O→M | 0.02 | W→M→G | 0.01 | W→M→A | 0.21 |
W→M→O | 0.01 | W→M→W | 0.05 | M→G→A | 0.37 | M→G→S | 0.01 |
M→G→F | 0.10 | M→G→O | 2.08 | M→G→W | 0.01 | M→G→M | 0.12 |
M→A→G | 0.14 | M→A→S | 0.07 | M→A→W | 0.01 | M→A→M | 0.37 |
M→F→A | 0.02 | M→O→G | 0.60 | M→O→W | 0.01 | M→O→M | 0.10 |
M→W→G | 0.01 | M→W→A | 0.03 | M→W→O | 0.04 | M→W→M | 0.55 |
Three-step changes | A→G→O→G | 0.20 | A→G→W→M | 0.01 | A→M→W→M | 0.01 | F→G→O→G | 0.01 |
G→A→G→A | 0.01 | G→A→M→A | 0.21 | G→M→W→M | 0.04 | W→A→M→A | 0.04 |
W→G→O→G | 0.01 | W→M→W→M | 0.01 | M→A→M→A | 0.20 | M→G→O→G | 0.10 |
M→G→W→M | 0.03 | | | | | | |
Figure 6.
Trajectories of unchanged land use (a) and land use changes (b,c), 1954–2005.
Figure 6.
Trajectories of unchanged land use (a) and land use changes (b,c), 1954–2005.