Next Article in Journal
Diversity or Redundancy in Leaf Physiological and Anatomical Parameters in a Species Diverse, Bottomland Hardwood Forest?
Previous Article in Journal
Study on Evaluation of Timber Security in China Based on the PSR Conceptual Model
Previous Article in Special Issue
Soil and Nutrient Cycling Responses in Riparian Forests to the Loss of Ash (Fraxinus spp. L) from Emerald Ash Borer (Agrilus planipennis, Fairmaire)
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Forests
Volume 11
Issue 5
10.3390/f11050518
forests-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Shifts in Riparian Plant Life Forms Following Flow Regulation

by
María D. Bejarano
1,*,
Judith Sarneel
2,
Xiaolei Su
3 and
Alvaro Sordo-Ward
4
1
Departamento de Sistemas y Recursos Naturales, Universidad Politécnica de Madrid, 28040 Madrid, Spain
2
Department of Ecology and Environmental Sciences, Umeå University, SE-901 87 Umeå, Sweden
3
Key Laboratory of Eco-Environments in Three Gorges Reservoir Region (Ministry of Education), Chongqing Key Laboratory of Plant Ecology and Resources in Three Gorges Reservoir Region, State Cultivation Base of Eco-agriculture for Southwest Mountainous Land, School of Life Sciences, Southwest University, Chongqing 400700, China
4
Departamento de Ingeniería Civil: Hidráulica, Energía y Medio Ambiente, Universidad Politécnica de Madrid, 28040 Madrid, Spain
*
Author to whom correspondence should be addressed.
Forests 2020, 11(5), 518; https://doi.org/10.3390/f11050518
Submission received: 10 March 2020 / Revised: 28 April 2020 / Accepted: 30 April 2020 / Published: 5 May 2020
(This article belongs to the Special Issue Spatial and Temporal Patterns and Ecosystem Services of Riparian Forests)
Browse Figures
Versions Notes

Abstract

:
Flow regulation affects bordering riparian plant communities worldwide, but how different plant life forms are affected by river regulation still needs further research. In northern Sweden, we selected 10 rivers ranging from free-flowing to low, moderately, and highly regulated ones. In 94 reaches across those rivers, we evaluated the relative abundance of woody and herbaceous (i.e., graminoids and forbs) life forms, their species richness, and their relative presence. We also explored which, and to what extent, hydrological variables drove species assembly within each life form. The relative abundance and species richness of each life form decreased across river categories with increasing levels of regulation. This was particularly apparent in herbaceous life forms, and the most drastic decreases were observed in all life forms in moderately or highly regulated reaches. Additionally, when river regulation increased, the relative presence of many species from all life forms decreased. Unlike woody species, only a few new herbaceous species appeared in regulated reaches. A canonical correspondence analyses (CCA) revealed that a wide range of hydrological variables explained the occurrence of woody species, while fewer variables explained variation in the graminoid and forb life forms. We conclude that flow regulation and its intensity result into clear shifts in the relative abundance of different life forms, as well as in changes of within-group species richness and composition. Consequently, the modification of certain flow attributes in flow regulation schemes, as well as the intensity of these modifications, may alter the ratio between herbaceous and woody species, ultimately impacting the functions and benefits derived from each life form.

1. Introduction

It is obvious that changed flow regimes affect plant growth, performance, and distributions [1,2]. However, since studies on many species at once are relatively scarce or restricted to smaller spatial scales, many questions about community responses are still unanswered. This is unfortunate, as general frameworks (as opposed to species-specific or site-specific frameworks) are essential to develop flow management guidelines for regional or national water management plans. To overcome the difficulties of working at a species level, classification into functional groups has been advocated and used in other ecological theories [3]. Functional groups include species sharing certain traits, resulting in common habitat requirements and responses to environmental changes. Despite the growing number of studies using functional groups, they remain somewhat controversial because they depend on which traits have been considered, especially when classification is limited by the information that is available in trait databases [4].
Plant life form schemes are widely accepted functional groups (first conceived by the authors of [5]). A plant life form is defined as the structural form of a plant in its typical or preferred habitat. The simplest life form classification separates woody and herbaceous species. Other more complex classifications have developed within these two categories and are well known [6,7,8]. Despite these being very broad groups, species within each life form bear enough similarities when dealing with broad or general questions on community structure. For instance, life span separates long-lived woody species from more frequently annual herbaceous species, and it allows for the generalization of, for instance, community turnover. Additionally, stature and associated plant height separate tall woody species from shorter graminoid and forb species, resulting in clear differences in resource acquisition between life forms. Propagation, seasonal growth habits, and protective structures are other characteristics that separate those life forms that allow for the generalization of the community processes based on them. To balance between generalization and detail, sub categories are distinguished (e.g., trees, shrubs, sedges, grasses, legumes, clonal and non-clonal forbs).
Because plant life forms reflects a plant’s adaptation to its environment, it also has consequences for the response to disturbance [9]. A large body of literature has documented life form-specific responses to changed climatic factors [10], increased anthropogenic pressure [11], fire [12], and water shortage [13], among others. Flow regulation serves different purposes (e.g., irrigation, water supply, and hydropower generation) and has been shown to promote or disfavor certain species and, ultimately, whole functional groups depending on what species traits are favored by the new conditions [14,15,16]. However, flow regulation includes many specific changes in the flow regime (e.g., flooding frequency, flooding duration, and flooding timing), each of them with differing ecological implications [17].
Shifts in the relative abundance of different life forms may or may not result in shifts in species and functional diversities. The maintenance of functional diversity can guarantee the continuation of important ecosystem processes and functions despite decreased species numbers [18]. Therefore, changes in flow regime are expected to induce larger changes in riparian communities when the functional diversity, rather than the absolute species diversity, is affected. A simple classification of riparian plants into few different life forms could enable a straightforward visual evaluation of riparian plant communities and their susceptibility to flow regulation and associated ecological consequences.
In this study, we used flow attributes to characterize a wide range of flow regulation regimes and tested the effects of flow regulation on the relative abundance of woody and herbaceous (i.e., graminoids and forbs) life forms, their species richness, and their relative presence across large spatial scales. We hypothesized that (i) certain life forms contain more plant species that are sensitive to flow regulation. Because of that, flow regulation (ii) will affect that particular life form more strongly than other life forms, eventually removing such life form from the riparian community, along with an associated loss of functional diversity. Finally, because species within woody and herbaceous life forms exhibit specific traits that interact differently with hydrological regimes, we hypothesized that (iii) different hydrological variables drive species within that functional group.

2. Material and Methods

2.1. Study Area and Data Collection

The study area in northern Sweden comprises 205,764 km2 and is dominated by boreal coniferous forest (Figure 1). The study reaches were selected along 10 rivers within nine basins: Torne, Kalix, Sävarån, Vindel, Öre, Pite, Lule, Skellefte, Ume, and Ångerman (Figure 1). The rivers run from the Norwegian border and end at the Gulf of Bothnia, except for the Vindel River that joins the Ume River 35 km from the coast. Most rivers are large (i.e., a channel length between 360 and 510 km, a catchment area between 11,285 and 40,157 km2, and a mean monthly discharge between 131 and 501 m3/s), except for the Sävarån and Öre rivers, which are smaller (128–185 km, 3029–1160 km2, and 34–15 m3/s, respectively). Some rivers have no major dams and may be considered free-flowing (Torne, Kalix, Sävarån, Vindel, and Öre), whereas others are regulated by one to several dams and are considered moderately-to-strongly regulated rivers (Pite, Lule, Skellefte, Ume, and Ångerman). Despite river specific differences, the upland vegetation (furthest away from the channel) is generally characterized by birch (Betula pubescens Ehrh.) and coniferous forests (Pinus sylvestris L. and Picea abies (L.) H. Karst.). The riparian vegetation closer to the river channel frequently includes woody species like Alnus incana (L.) Moench, Betula pubescens, and Salix spp.; graminoids like Carex sp. and Poa sp.; and forbs like Ranunculus reptans L. and Filipendula ulmaria (L.) Maxim.
We obtained hydrological and floristic data from 94 reaches across 10 rivers from [16], as available in the Dryad repository [19]. The hydrological data consisted of 16 variables that characterize ecologically relevant facets of the annual hydrograph at a reach scale (e.g., the magnitude, timing, duration, frequency, and rates of change of the flows; Table 1 and Annex 1). As an overall measure of the degree of regulation, we calculated the percentage of the natural mean annual discharge potentially stored in reservoirs upstream from the reach. Based on the degree of regulation, we categorized reaches into free-flowing (<0%; n = 63) and with a low (>0% and <15%; n = 14), moderate (>15% and <60%; n = 8), and high (>60%; n = 9) degree of regulation. The floristic data of each reach consisted of plant species’ presence–absence, as recorded along a 200 m long section by the Landscape Ecology research group (Umeå University, Sweden) (Annex 2). Species were classified into the simplest life form groups: woody, graminoid, and forb species. The few number of woody species compared to the herbaceous ones prevented us from subdividing this group into trees and shrubs. Conversely, the large number of herbaceous species led us to subdivide them into graminoids and forbs. For the sake of simplicity, we discarded other more complex groupings (e.g., [6]). Hydrological series were either recorded (the longest from 1909 and the shortest from 1988) or modeled (when no recorded data were available; from 1999 to 2011). Floristic data were collected during the nineties by the Landscape Ecology Group at Umeå University. The reader is referred to the [16] for more details on the dataset.

2.2. Data Analysis

Differences between flow regulation groups (i.e., free-flowing, low regulated, moderately regulated, and highly regulated) for each hydrological variable were tested with a Kruskal–Wallis test followed by a multiple comparison BH (Benjamini–Hochberg) test. This was appropriate because the data were not distributed normally. We used the R package “dplyr” [20] in R 3.6.1.
Three vegetation metrics were computed. First, we computed the ‘species richness’(#) within the woody, graminoid, and forb functional groups for each regulation group as the number of species from each life form present in free-flowing, low-, moderately-, and highly-regulated reaches. Second, we computed the ‘relative abundance‘ (%) of each life form for each regulation group (i.e., mix of plant life forms) as the ratio between the species richness within each life form (see above) and the total number of species (including woody species, graminoids and forbs) present at each regulation group. Third, we computed the ‘relative presence‘(%) of the species within each life form in each flow regulation group as the number of reaches from a regulation group where a species was present in relation to the total number of reaches of that regulation group.
Afterwards, we fitted linear regressions for each individual species with ‘relative presence’ as dependent and the ‘percentage of regulation’ as independent variables, and we extracted the regression coefficients using the lme4 package in R [21]. A positive regression coefficient indicates that the species benefits from regulation (i.e., the presence of the species is more likely when regulation intensifies), whereas a negative coefficient indicates that the species is disfavored by regulation (i.e., the presence of the species is less likely when regulation intensifies). From the pool of all species, we also noted whether each species from each life form were (i.e., appeared) or were not (i.e., disappeared) in reaches beyond 15% regulation (i.e., moderately and highly regulated). For the interpretation of the results, we clustered the individual species in the following response groups: positive response (i.e., species with regression coefficients >2), negative response (i.e., regression coefficient <−2), impassive response (i.e., regression coefficient <2 and >−2), present only when regulation is beyond moderate (>15%), present only when regulation is high (>60%), absent when regulation is beyond moderate (>15%), and absent when regulation is high (>60%). By ‘regulation beyond moderate’ we mean in moderately regulated reaches, in highly regulated reaches, or in both, whereas by ‘high regulation,’ we mean only in highly regulated reaches. Subsequently, we calculated the percentage of species in each response group for each life form group.
Finally, we ran three canonical correspondence analyses (CCA), explored to what extent the hydrological variables drive species assembly within each life form, and identified which hydrological variables play key roles. We used the presence–absence-species-by-reaches dataset and the hydrological data per reach as the input and tested the significance of the CCA models and axes using the R package “vegan” [22]. The relative importance of each hydrological variable was evaluated using the loadings on the first three axes that were extracted. Higher loadings indicate a higher importance of that variable for that axis and thus for the spread of species along that axis. We considered 0.45 as the threshold of significance [23]. For the interpretation of the results, we indicated species by their response groups to flow regulation. Statistical analyses that were performed in R used the 3.6.1 version [24].

3. Results

3.1. Hydrological Variables

All hydrological variables differed significantly (p < 0.05) among flow regulation groups except for the duration of the minimum monthly flows (Table 1). Multiple comparisons tests showed that differences between regulation groups reflected decreased long-time scale (i.e., intra-annual) flow variation but increased short-time scale (i.e., daily) flow variations. That is, when comparing groups with increasing levels of flow regulation, we observed an increased magnitude of the minimum monthly flows, an increased duration of the maximum monthly flows, an increased frequency of the daily reversals and extreme low flows, and increased rates of change in the daily discharge, as well as delayed maximum monthly flows and two-year floods. Furthermore, we observed a decreased magnitude of the maximum monthly flows and two-year floods, a decreased duration of the extreme low flows and two-year floods, and a decreased frequency of monthly reversals and early minimum monthly and extreme low flows (Table 1). In summary, these changes indicated that regulation stabilizes intra-annual flows but results in highly fluctuating and faster daily flows, earlier minimum and later maximum flows, and shorter extreme high and low flow events

3.2. Riparian Plant Species and Life Forms

Across the 94 study reaches, 372 plant species consisting of 44 woody species, 107 graminoids, and 221 forbs were found. In each life form, species richness decreased across categories with increasing flow regulation (Figure 2a). When comparing free-flowing conditions to high flow regulation, species richness decreased, on average, by 20% for woody species, 40% for graminoids, and 45% for forbs (Figure 2a). While the decrease was rather gradual for woody species, there was a more sudden decrease in species richness between free-flowing and ‘low regulation’ for the graminoid and forb species (Figure 2a). The diversity of the forb species substantially contributed to the diversity in natural riparian zones, with the ratio of relative abundance between woody, graminoid, and forb species being 13/29/58 (Figure 2b). Due to a slight increase in relative abundance of woody species and a decrease in the relative abundance of herbaceous species (graminoids and forbs), the herbaceous:woody ratio decreased from 6.7 in the free flowing category to 4.4, 5.7, and 5.1 in the low, moderate, and high flow regulation categories, respectively (Figure 2b).
Across all functional groups, the relative presence of most species correlated negatively with the degree of flow regulation (Figure 3a and Figure 4; Annexes 3 and 4). A relatively higher percentage of woody species had a strong negative correlation compared to graminoids and forbs, among which, many showed an impassive response. That is, negative responses were observed for 61%, 44%, and 36% of woody, graminoid, and forb species, respectively (Figure 3a). Additionally, the mean response within those groups differed, with the average regression coefficient being −8 (±6.6 standard deviation) for woody species, −6 (±6.1 SD) for graminoids, and −4 (±4.4 SD) for forbs. The relative presence of fewer species correlated positively with the degree of flow regulation, and the same fraction of species in each life form group showed a positive response to increased regulation (i.e., 11% woody species, 16% graminoids, and 13% forbs) (Figure 3a). The strength of the relationship did not differ much between life forms (on average +3.0 (±3.0 SD)). While almost half of the graminoid and forb species were impassive to regulation, only a quarter of the woody species were impassive (Figure 3a).
A high number of species was solely found in free-flowing reaches, irrespective of life form. Furthermore, 70% of all woody, 46% of all graminoid, and 53% of all forb species found in the entire study grew along reaches with a free-flowing and/or low-regulated flow regime. A lower fraction of species was sensitive to high regulation, as 9% of all woody, 20% of all graminoid, and 6% of all forb species were absent in reaches with highly regulated flow regime (Figure 3b and Annex 3). In contrast, only a few graminoid and forb species were restricted from free-flowing and/or low-regulated reaches, as 4% of all graminoid and 5% of all forb species only occurred in reaches with an above moderate flow regulation, with, respectively, 1% and 2% of the species occurring exclusively in reaches with high flow regulation regimes (Figure 3b and Annex 3). No woody species were restricted to reaches with a higher flow regimes.
The three CCA models (i.e., for woody species, graminoids, and forbs) were statistically significant (Table 2). The first two CCA components were significant in each CCA model, whereas the third and fourth components were significant for the woody and forb species but not for the graminoid species (Table 2). The highest cumulative variance was observed in woody species, for which the selected hydrological variables explained up to 52% of the variance in the first three axes, whereas 49% and 40% variance was explained by the first three axes for graminoids and forbs, respectively (Table 2). Woody species showing positive, negative, and impassive trends in response to increased degrees of flow regulation were well segregated in CCA space. Negative trends were found for willow Salix glauca L., mosses (Lycopodium selago (L.) Bernh. ex Schrank & Mart. and L., annotinum L.), heaths (Vaccinium microcarpum Aiton, Vaccinium oxycoccos L., Andromeda polifolia L., and Ledum palustre L.), Betula nana L., Linnaea borealis L., and Rosa majalis Herrm., whereas most willows (Salix herbacea L., Salix lapponum L. and Salix pentandra L., Salix lanata L., Salix triandra L., Salix hastata L., and Salix cinerea L.) along with other shrubs such as the black and red currants (Ribes ningrum L. and Ribes rubrum L.), raspberry (Rubus idaeus L.), and trees such as birches (Betula pendula Roth and Betula pubescens Ehrh.) showed marked positive or impassive trends with regulation (Figure 4 and Figure 5; Annex 5). Hydrological variables that were strongly correlated to woody species arrangement in CCA space were related to the percentage of regulation, extreme low flow conditions (duration, frequency, and timing), monthly flows (magnitude of maximum and minimum), and daily flows (frequency of reversals and fall rates) (Figure 5 and Table 2). In general, woody species with positive and impassive trends were separated along the second axis that aligned with a higher percentages of regulation and related hydrological characteristics such as shorter, more frequent, and earlier extreme low flow periods; lower maximum but higher minimum monthly flows; and more frequent and faster daily flow reversals. These latter two had highest loading on the second axis (Figure 5 and Table 2). The opposite was true for species characterized by negative trends.
Graminoid species with different responses to flow regulation were not as well segregated in the CCA space as woody species. However, species with positive trends were located more to the left of the first axis (Figure 5). Among graminoids that showed negative trends to increased flow regulation, we found several Carex species (Carex acuta L., Carex Lasiocarpa Ehrh., Carex rostrata Stokes, and Carex vesicaria L.), as well as Alopecurus aequalis Sobol, Eleocharis palustris (L.) Roem. & Schult., Phragmites australis (Cav.) Trin. ex Steud., Schoenoplectus lacustris (L.) Palla, Juncus bulbosus L., and Equisetum fluviatile L. (Figure 4 and Figure 5, Annex 5). Positive and impassive trends were frequently observed in the genus Poa sp., Carex sp, and Festuca sp. For instance, Poa glauca Vahl and Poa alpina L. showed strong positive trends, while Poa annua L. and Poa pratensis L. were impassive to regulation. Within Carex sp., positive responses were found for Carex panacea L., Carex brunnescens, (Pers.) Poir. and Carex canescens L., but many Carex species were impassive to regulation (e.g., Carex elongata L., Carex bigelowii Torr. ex Schwein., Carex ornithopoda Willd., Carex capitata L., Carex saxatilis L., Carex digitata L., Carex livida (Wahlenb.) Willd., and Carex loliacea L.). Species from the genus Festuca sp. (e.g., Festuca vivipara (L.) Sm., Festuca rubra L., and Festuca ovina L.) also responded positively to regulation. Other graminoids with positive trends to increased flow regulation were: Eriophorum scheuchzeri Hoppe, Calamagrostis chalybaea (Laest.) Fr. and Calamagrostis stricta (Timm.) Koeler, Juncus trifidus L., Alopecurus aequalis Sobol., Juncus trifidus L., and Agrostis mertensii (Trin.) Kuntze (Figure 4 and Figure 5; Annex 5). From the CCA, it became clear that a considerably smaller number of hydrological variables explained this arrangement for graminoids on the first two axes compared to woody species. Positive and impassive trends of graminoids aligned with higher percentages of regulation and, subsequently, more frequent extreme low flows and delayed floods (Figure 5). The opposite was true for species with negative trends to increased flow regulation.
Finally, forb species with positive, negative, and impassive trends in response to increased flow regulation were mixed in the CCA space (Figure 5). For example, Sedum rosea L., Erigeron borealis L., Cerastium alpinum L., Persicaria foliosa (H.Lindb.) Kitag. Cicuta virosa L., and Arabis arenosa L. showed positive trends, whereas Euphrasia frígida Pugsley, Euphrasia stricta Kunth, Melampyrum pretense L., Persicaria lapathifolia (L.) Delarbre, and Spergula arvensis L. showed negative trends (Figure 4), but all were scattered throughout the biplot (Figure 5 and Annex 5). A couple of hydrological variables correlated to forb species arrangement, with variation along the first axis being related to decreased intra-annual flow fluctuation (i.e., frequency of monthly reversals) and variation along the second axis being related to an increased duration of the extreme low flows (Figure 5 and Table 2). Unlike the CCA of the other life forms, the variable ‘percentage of regulation’ had a minimal effect on species distribution, as indicated by much lower axes loadings for this variable in the forb CCA compared to the CCA’s of the other life forms (Table 2).

4. Discussion and Conclusions

The high spatial and temporal heterogeneity of environmental conditions such as hydrology, geomorphology, light, and temperature determine the richness and distribution of plants along riparian zones of free-flowing rivers. Hydrological factors, however, are seen as the most important ones [25]. In boreal streams, hydrological heterogeneity results from a flow pattern with a strong seasonality and ice disturbance. During fall and winter, flows are low, while during spring, large and snowmelt-driven floods shape rich riparian plant communities. Characteristic riparian forbs, graminoids, shrubs, and trees are arranged as clear belts at different elevations, parallel along the channel because each life form is thought to have a different resistance to the hydrological forces of the spring flood [26]. Naturally recurrent ice disturbance usually restrains the development of woody plants at lower elevations, while it favors annual and biennial species (i.e., mostly forbs) or perennial hemicryptophytes that die back to ground level during winter. The natural flow conditions imposed by the spring flood can explain the typically high ratio between herbaceous and woody species in the riparian areas of boreal free-flowing rivers [27].
In our study area, river regulation is mostly due to hydropower production, and the selected hydrological variables showed that it drastically alters flow regimes at long and short times scales. At long time scales, it evens out differences in monthly flows, induces shorter, more frequent, and earlier extreme low flows, and it also delays floods. At short time scales, regulation enhances daily flow fluctuations, with hydropeaking in some extreme cases [28]. Our results reinforce other studies demonstrating that flow alterations that are associated with regulation translate into declined riparian diversity and modified riparian community composition [29,30,31]. Our study showed how flow regulation through changes in various flow attributes exerts differing effects over specific riparian life forms and breaks the balance between them that exists in riparian communities along free flowing rivers.
The substantial decrease in the herbaceous:woody species ratio, as observed in regulated reaches in our study, suggests stronger impacts of regulation on the richness of graminoids and forbs compared to woody species. Unlike the authors of [32], who described the almost complete disappearance of shrubs and trees over the herbaceous species following dam-induced changes in the winter flooding in the Yangtze River, in our study, the richness of herbaceous species (the sum of graminoids and forbs) declined more strongly with increased regulation compared to woody species (both in absolute numbers as well as a net reduction, i.e., the species that appear minus the ones that disappear). Herbs, characterized by short generation times and ruderal life strategies, seem to be especially affected by long-term flow stabilization, as such species benefit from natural formation of disturbance patches [33]. Such bare patches allow for germination, and other studies on the effect of river regulation on species diversity have frequently associated reduced species richness with difficulties in germination and establishment [32,33,34,35]. In addition to recruitment, those bare patches may change the competition among woody, graminoid, and forb species. In riparian systems, frequent occurrence of disturbances could relax competition for resources, especially light [12,36]. The observed shift towards less short-lived species in our regulated rivers is therefore consistent with life-history theories regarding adaptations to disturbance [33,37]. Empirical studies in riparian zones further confirm that annuals increase following increased flooding and/or give way to perennials with increased time since major flood disturbance [30,32,38,39,40]. A field experiment in riparian zones in the semiarid savanna showed a comparable recruitment of grasses and forbs in treatments with and without water addition and disturbance [12]. In our study however, graminoids were more responsive to regulation than forbs.
The results of our CCA suggested that graminoid community composition seems to be particularly affected by regulation through delayed floods and more extreme low flow events, whereas forb community composition was less clearly affected by most hydrological variables, as only intra-annual flow stabilization was able to explain some of the variance. This somewhat contrasts results by the authors of [41,42] who found that herbaceous species are very responsive to changes in flow regime. The variability in the woody, graminoid, and forb community compositions that was unexplained by hydrological variables suggests that other environmental variables may co-determine community composition. Our results point that such other variables gain importance in herbaceous communities. In addition to hydrology, the variables of land-use, nutrient availability, soil moisture, air temperature, and light availability have been shown to be particularly critical for riparian community composition [43,44,45]. In addition to intra-annual flow stabilization, the alteration of many other hydrological variables was found to determine the community composition of woody species in our study. The community composition of woody species appeared to be sensitive to both long term (intra-annual) and short-term fluctuations in flows. On the one hand, the desynchronization of a species’ life story stages with intra-annual flow regime patterns may strongly affect woody species, which highly depend on recruitment from seeds rather than clonal dispersal—as is common among herbaceous species [46,47]. Seed dispersal and establishment are highly dependent on flood schedules, and other studies in the same area [16] have described important impacts of regulation on woody species as being linked to, among other phenological traits, their particular dispersal and germination periods. On the other extreme, very frequent and rapid variations of daily flows related to intense hydropower production schemes may hamper woody species germination and survival [48,49]. Such short-term changes in flows cause repeated wetting and, ultimately, nearly permanent moist or inundated soils. In general, woody, graminoid, and forb species have intrinsically different water requirements and tolerances during most life stages, with graminoids and forbs being better adapted to waterlogged environments than woody plants [50,51].
In addition the described negative effects of regulation, the fact that few species from all life forms increased their presence along regulated reaches and that some graminoids and forbs only occurred at higher levels of flow regulation, demonstrated that meager positive effects may be also expected following regulation. According to the deletion/addition/replacement theory (i.e., assembly rules by the authors of [52]), species-specific differences in the ability to tolerate hydrological alterations may underlay the observed wide range of species responses. Eventually, this results in a non-random sorting of species along hydrological gradients [2,53] and across reaches with different degrees of regulation. Numerous examples from scientific literature have shown that woody species (both native and non-native) frequently take advantage of the new hydrological conditions and invade regulated reaches (e.g., [54,55]). Though we found positive responses to increased flow regulation among woody species, there were no woody species that uniquely occurred in reaches with some degree of regulation. This may indicate dispersal limitations [56] or that requirements for establishment were not met under regulated conditions. Conversely, although of a relatively small number, the fact that new graminoids and forbs appeared in regulated reaches suggested that there is a source of new species from the upstream and upland herbaceous flora that can find success under the new hydrological conditions. However, no exotic species were found among new species appearing only in regulated reaches, which, on the other hand, is not surprising at this high latitude [57].
Woody, graminoid, and forb species coexist in the riparian areas, and flow regulation may affect those life forms differently, thus leading to unbalances in community composition. Our results showed that riparian diversity in boreal rivers is driven by graminoid and forb life forms, as well as that regulation, due to a reduction of graminoid and forb diversity, results in overall poorer communities. This agrees with trends in other plant communities suffering from pressures such as heavy logging and overgrazing [9]. When population and community structure are altered, an array of ecosystem functions can be affected too, in particular when shifts in community structure includes (major) shifts in plant functional types [58,59]. For example, impoverished riparian woodlands may ultimately stimulate bank collapse through reduced rooting structures, decreased nitrogen assimilation, and changed stream hydrology, temperature, and primary production [60]. Similarly, the impoverishment of the herbaceous riparian community may affect erosion-related processes like trapping and the storing processes of suspended sediment, or provisions of habitat and refuge for biota. This impoverishment may also induce changes in phosphorous assimilation [61]. Since riparian community composition also affects macroinvertebrate and fish assemblages, changes in the ratio between herbaceous and woody species following flow regulation may have cascading effects. For instance, salmonid fishes could be particularly negatively affected by changes in herbaceous community composition [62]. Moreover, unbalances between life forms may also influence the success of the restoration of degraded systems [63]. In conclusion, the modification of certain flow attributes in flow regulation schemes, as well as the intensity of these modifications, result in shifts in the relative abundance of woody, graminoid, and forb life forms, as well as changes of the within-group species richness and community composition. Consequently, flow regulation may alter the characteristic herbaceous:woody species balance of riparian plant communities, ultimately impacting the functions and benefits derived from riparian zones.

Supplementary Materials

https://www.mdpi.com/1999-4907/11/5/518/s1. Annex 1. List of hydrological variables. Annex 2. List of species. Annex 3. Species from each life form group which appeared or disappeared compared as the intensity of flow regulation increases, compared to the free-flowing species pool. Annex 4. Code for each forb species according to the slope of the fitted line from the regression between the mean percentage of regulation and the relative presence of each species (see Figure 4). Code 1 corresponds to the lowest slope and code 221 to the highest slope. Annex 5. Species scores for the three first CCA components, the slope of the fitted line from a linear simple regression between the mean percentage of regulation and the relative presence at the study reaches of each species from each life form group, and the assigned response according to the slope (i.e., negative, positive or impassive). The list of species names is in the Annex 2.

Author Contributions

All authors conceived the ideas; M.D.B. designed the methodology; M.D.B. and A.S.-W. prepared and analyzed the data; M.D.B. and J.S. discussed and interpreted results; M.D.B. led the writing of the manuscript and J.S. and X.S. contributed critically to the manuscript´s drafts and revised it for important intellectual content. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministerio de Economía, Industria y Competitividad (IJCI-2016-29157); Proyectos de I + D para jóvenes investigadores de la Universidad Politécnica de Madrid, en el marco del Convenio Plurianual entre la Comunidad de Madrid y la Universidad Politécnica de Madrid (2019/REGING-1563); and the Swedish research council Vetenskapsrådet (2014-04270).

Acknowledgments

We thank the Landscape Ecology Group for providing vegetation data, and Roland Jansson and Christer Nilsson for their valuable comments.

Conflicts of Interest

The authors declare that they have no conflict of interest.

References

  1. Garssen, A.G.; Baattrup-Pedersen, A.; Voesenek, L.A.; Verhoeven, J.T.; Soons, M.B. Riparian plant community responses to increased flooding: A meta-analysis. Glob. Chang. Biol. 2015, 21, 2881–2890. [Google Scholar] [CrossRef] [PubMed]
  2. Sarneel, J.M.; Bejarano, M.D.; van Oosterhout, M.; Nilsson, C. Local flooding history affects plant recruitment in riparian zones. J. Veg. Sci. 2019, 30, 224–234. [Google Scholar] [CrossRef] [Green Version]
  3. Merritt, D.M.; Scott, M.L.; Poff, N.L.; Auble, G.T.; Lytle, D.A. Theory, methods and tools for determining environmental flows for riparian vegetation: Riparian vegetation-flow response guilds. Freshw. Biol. 2010, 55, 206–225. [Google Scholar] [CrossRef]
  4. Bejarano, M.D.; Maroto, J.; Nilsson, C.; Aguiar, F.C. Traits of riparian woody plants responding to hydrological and hydraulic conditions: A northern Swedish database. Ecology 2016, 97, 2892. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Warming, E. Oecology of Plants; Clarendon Press: Oxford, UK, 1909. [Google Scholar]
  6. Raunkiær, C. Types biologiques pour la géographie botanique. Overs. Det K. Dan. Vidensk. Selsk. Forh. 1905, 347–438. [Google Scholar]
  7. Du Rietz, G.E. Life-forms of terrestrial flowering plants. I. Acta Phytogeogr. Suec. 1931, 3, 95. [Google Scholar]
  8. Clements, F. Plant Indicators, the Relations of Plant Communities to Process and Practice; Carnegie Institution of Washington Publisher: Washington, DC, USA, 1920; p. 388. [Google Scholar]
  9. Arnold, J.F. Plant life-form classification and its use in evaluating range conditions and trend. Rangel. Ecol. Manag./J. Range Manag. Arch. 1955, 8, 176–181. [Google Scholar] [CrossRef]
  10. Bhattarai, K.R.; Vetaas, O.R. Variation in plant species richness of different life forms along a subtropical elevation gradient in the Himalayas, east Nepal. Glob. Ecol. Biogeogr. 2003, 12, 327–340. [Google Scholar] [CrossRef]
  11. Marini, L.; Battisti, A.; Bona, E.; Federici, G.; Martini, F.; Pautasso, M.; Hulme, P.E. Alien and native plant life-forms respond differently to human and climate pressures. Glob. Ecol. Biogeogr. 2012, 21, 534–544. [Google Scholar] [CrossRef]
  12. Casillo, J.; Kunst, C.; Semmartin, M. Effects of fire and water availability on the emergence and recruitment of grasses, forbs and woody species in a semiarid Chaco savanna. Austral Ecol. 2012, 37, 452–459. [Google Scholar] [CrossRef]
  13. Dodd, M.B.; Lauenroth, W.K.; Welker, J.M. Differential water resource use by herbaceous and woody plant life-forms in a shortgrass steppe community. Oecologia 1998, 117, 504–512. [Google Scholar] [CrossRef] [PubMed]
  14. Palmquist, E.C.; Ralston, B.E.; Sarr, D.; Merritt, D.M.; Shafroth, P.B.; Scott, J.A. Functional traits and ecological affinities of riparian plants along the Colorado River in Grand Canyon. West. N. Am. Nat. 2017, 77, 22–30. [Google Scholar] [CrossRef]
  15. Aguiar, F.C.; Segurado, P.; Martins, M.J.; Bejarano, M.D.; Nilsson, C.; Portela, M.M.; Merritt, D.M. The abundance and distribution of guilds of riparian woody plants change in response to land use and flow regulation. J. Appl. Ecol. 2018, 55, 2227–2240. [Google Scholar] [CrossRef]
  16. Bejarano, M.D.; Nilsson, C.; Aguiar, F.C. Riparian plant guilds become simpler and most likely fewer following flow regulation. J. Appl. Ecol. 2018, 55, 365–376. [Google Scholar] [CrossRef] [Green Version]
  17. Poff, N.L.; Allan, J.D.; Bain, M.B.; Karr, J.R.; Prestegaard, K.L.; Richter, B.D.; Stromberg, J.C. The natural flow regime. BioScience 1997, 47, 769–784. [Google Scholar] [CrossRef]
  18. Dĺaz, S.; Cabido, M. Vive la différence: Plant functional diversity matters to ecosystem processes. Trends Ecol. Evol. 2001, 16, 646–655. [Google Scholar] [CrossRef]
  19. Bejarano, M.D.; Nilsson, C.; Aguiar, F.C. Data from: Riparian plant guilds become simpler and most likely fewer following flow regulation. Dryad 2017. [Google Scholar] [CrossRef]
  20. Wickham, H.; Francois, R.; Henry, L.; Müller, K. dplyr: A Grammar of Data Manipulation, 0.4-3 ed.; R Package; CRAN: Wien, Austria, 2015; Available online: https://CRAN.R-project.org/package=dplyr (accessed on January 2020).
  21. Bates, D.M.; Maechler, M.; Bolker, B.M.; Walker, S. lme4: Linear Mixed-Effects Models Using Eigen and S4, 1.1-7 ed.; R Package; CRAN: Wien, Austria, 2014; Available online: https://cran.r-project.org/web/packages/lme4/ (accessed on January 2020).
  22. Oksanen, J.; Blanchet, F.G.; Kindt, R.; Legendre, P.; O’Hara, R.B.; Simpson, G.L.; Solymos, P.; Stevens, M.H.H.; Wagner, H. vegan: Community Ecology Package, 1.17-4 ed.; R Package; CRAN: Wien, Austria, 2010; Available online: https://cran.r-project.org/web/packages/vegan/index.html (accessed on January 2020).
  23. Dattalo, P.V. A Demonstration of Canonical Correlation Analysis with Orthogonal Rotation to Facilitate Interpretation. School of Social Work; Virginia Commonwealth University: Richmond, Virginia, Unpublished work; 2014. [Google Scholar]
  24. R Core Team. R: A Language and Environment for Statistical Computing Computer Program, 3.6-1 ed.; Foundation for Statistical Computing: Vienna, Austria, 2019. [Google Scholar]
  25. Naiman, R.J.; Decamps, H. The ecology of interfaces: Riparian zones. Annu. Rev. Ecol. Syst. 1997, 28, 621–658. [Google Scholar] [CrossRef] [Green Version]
  26. Ström, L.; Jansson, R.; Nilsson, C. Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate-driven hydrological change along the Vindel River in Sweden. Freshw. Biol. 2012, 57, 49–60. [Google Scholar] [CrossRef]
  27. Arnqvist, G.; Dynesius, M. Ranealven. Naturin- Ventering och bed6mning av Vetenskapliga Naturvarden; Lansstyrelsen i Norrbottens Lan: Lulea, Sweden, 1987. (In Swedish) [Google Scholar]
  28. Bejarano, M.D.; Sordo-Ward, Á.; Alonso, C.; Nilsson, C. Characterizing effects of hydropower plants on sub-daily flow regimes. J. Hydrol. 2017, 550, 186–200. [Google Scholar] [CrossRef] [Green Version]
  29. Nilsson, C.; Jansson, R. Floristic differences between riparian corridors of regulated and free-flowing boreal rivers. Regul. Rivers Res. Manag. 1995, 11, 55–66. [Google Scholar] [CrossRef]
  30. Jansson, R.; Nilsson, C.; Dynesius, M.; Andersson, E. Effects of river regulation on river-margin vegetation: A comparison of eight boreal rivers. Ecol. Appl. 2000, 10, 203–224. [Google Scholar] [CrossRef]
  31. Bejarano, M.D.; Nilsson, C.; Del Tanago, M.G.; Marchamalo, M. Responses of riparian trees and shrubs to flow regulation along a boreal stream in northern Sweden. Freshw. Biol. 2011, 56, 853–866. [Google Scholar] [CrossRef]
  32. Wang, Q.; Yuan, X.; Liu, H.; Zhang, Y.; Cheng, Z.; Li, B. Effect of long-term winter flooding on the vascular flora in the drawdown area of the Three Georges Reservoir, China. Pol. J. Ecol. 2012, 60, 95–106. [Google Scholar]
  33. Grime, J.P. Plant Strategies and Vegetation Processes; John Wiley & Sons: Chichester, UK, 1979. [Google Scholar]
  34. Polzin, M.; Rood, S.B. Effects of damming and flow stabilization on riparian processes and black cottonwoods along the Kootenay River. Rivers 2000, 7, 221–232. [Google Scholar]
  35. Dixon, M.D.; Turner, M.G. Simulated recruitment of riparian trees and shrubs under natural and regulated flow regimes on the Wisconsin River, USA. River Res. Appl. 2006, 22, 1057–1083. [Google Scholar] [CrossRef]
  36. Aguilera, M.O.; Laurenroth, W.K. Neighborhood interactions in a natural population of the perennial bunchgrass Bouteloa gracilis. Oecologia 1993, 94, 595–602. [Google Scholar] [CrossRef]
  37. Walker, L.R.; Zasada, J.C.; Chapin, F.S. The role of life-history processes in primary succession on an Alaskan floodplain. Ecology 1986, 67, 1243–1253. [Google Scholar] [CrossRef]
  38. Friedman, J.M.; Osterkamp, W.R.; Lewis, W.M., Jr. Channel narrowing and vegetation development following a Great Plains flood. Ecology 1996, 77, 2467–2481. [Google Scholar] [CrossRef]
  39. Cosgriff, R.J.; Nelson, J.C.; Yin, Y. Floodplain forest response to large-scale flood disturbance. Trans. Ill. State Acad. Sci. 2007, 100, 47–70. [Google Scholar]
  40. Stromberg, J.C.; Lite, S.J.; Dixon, M.D. Effects of stream flow patterns on riparian vegetation of a semiarid river: Implications for a changing climate. River Res. Appl. 2010, 26, 712–729. [Google Scholar] [CrossRef]
  41. Viers, J.H.; Fremier, A.K.; Hutchinson, R.A.; Quinn, J.F.; Thorne, J.H.; Vaghti, M.G. Multiscale patterns of riparian plant diversity and implications for restoration. Restor. Ecol. 2012, 20, 160–169. [Google Scholar] [CrossRef]
  42. Stromberg, J.C.; Boudell, J.A. Floods, drought, and seed mass of riparian plant species. J. Arid Environ. 2013, 97, 99–107. [Google Scholar] [CrossRef]
  43. Walker, M.D.; Ingersoll, R.C.; Webber, P.J. Effects of interannual climate variation on phenology and growth of two alpine forbs. Ecology 1995, 76, 1067–1083. [Google Scholar] [CrossRef]
  44. Angiolini, C.; Nucci, A.; Frignani, F.; Landi, M. Using multivariate analyses to assess effects of fluvial type on plant species distribution in a Mediterranean river. Wetlands 2011, 31, 167–177. [Google Scholar] [CrossRef]
  45. Angiolini, C.; Nucci, A.; Landi, M.; Bacchetta, G. What drives riparian plant taxa and assemblages in Mediterranean rivers? Aquat. Sci. 2017, 79, 371–384. [Google Scholar] [CrossRef]
  46. Greet, J.; Cousens, R.D.; Webb, J.A. Seasonal timing of inundation affects riparian plant growth and flowering: Implications for riparian vegetation composition. Plant Ecol. 2013, 214, 87–101. [Google Scholar] [CrossRef]
  47. Lytle, D.A.; Poff, N.L. Adaptation to natural flow regimes. Trends Ecol. Evol. 2004, 19, 94–100. [Google Scholar] [CrossRef]
  48. Stella, J.C.; Battles, J.J.; McBride, J.R.; Orr, B.K. Riparian seedling mortality from simulated water table recession, and the design of sustainable flow regimes on regulated rivers. Restor. Ecol. 2010, 18, 284–294. [Google Scholar] [CrossRef]
  49. Bejarano, M.D.; Sordo-Ward, Á; Alonso, C.; Jansson, R.; Nilsson, C. Hydropeaking affects germination and establishment of riverbank vegetation. Ecol. Appl. 2020. [Google Scholar] [CrossRef]
  50. Wilson, T.B.; Witkowski, E.T.F. Water requirements for germination and early seedling establishment in four African savanna woody plant species. J. Arid Environ. 1998, 38, 541–550. [Google Scholar] [CrossRef]
  51. Schwinning, S.; Sala, O.E. Hierarchy of responses to resource pulses in arid and semi-arid ecosystems. Oecologia 2004, 141, 211–220. [Google Scholar] [CrossRef] [PubMed]
  52. Weiher, E.; Keddy, P. Ecological Assembly Rules: Perspectives, Advances, Retreats; Cambridge University Press: Cambridge, UK, 2001. [Google Scholar]
  53. Mouillot, D.; Graham, N.A.J.; Villeger, S.; Mason, N.W.H.; Bellwood, D.R. A functional approach reveals community responses to disturbances. Trends Ecol. Evol. 2013, 28, 167–177. [Google Scholar] [CrossRef] [PubMed]
  54. Décamps, H.; Planty-Tabacchi, A.M.; Tabacchi, E. Changes in the hydrological regime and invasions by plant species along riparian systems of the Adour River, France. Regul. Rivers Res. Manag. 1995, 11, 23–33. [Google Scholar] [CrossRef]
  55. Zelnik, I.; Haler, M.; Gaberščik, A. Vulnerability of a riparian zone towards invasion by alien plants depends on its structure. Biologia 2015, 70, 869–878. [Google Scholar] [CrossRef]
  56. Nilsson, C.; Brown, R.L.; Jansson, R.; Merritt, D.M. The role of hydrochory in structuring riparian and wetland vegetation. Biol. Rev. 2010, 85, 837–858. [Google Scholar] [CrossRef] [PubMed]
  57. Nilsson, C.; Jansson, R.; Kuglerová, L.; Lind, L.; Ström, L. Boreal riparian vegetation under climate change. Ecosystems 2013, 16, 401–410. [Google Scholar] [CrossRef]
  58. Chapin, F.S.; Walker, B.H.; Hobbs, R.J.; Hooper, D.U.; Lawton, J.H.; Sala, O.E.; Tilman, D. Biotic control over the functioning of ecosystems. Science 1997, 277, 500–504. [Google Scholar] [CrossRef] [Green Version]
  59. Lyons, J.; Thimble, S.W.; Paine, L.K. Grass versus trees: Managing riparian areas to benefit streams of central North America. J. Am. Water Res. Assoc. 2000, 36, 919–930. [Google Scholar] [CrossRef]
  60. Watson, C.C.; Abt, S.R.; Derrick, D. Willow posts bank stabilization. J. Am. Water Res. Assoc. 1997, 33, 293–300. [Google Scholar] [CrossRef]
  61. Parsons, J.E.; Gilliam, J.W.; Munoz-Carpena, R.; Daniels, R.B.; Dillaha, T.A. Nutrient and sediment removal by grass and riparian buffers. Trans. Am. Soc. Agric. Eng. 1994, 37, 147–154. [Google Scholar]
  62. Peterson, A.M. Effects of electric transmission rights-of-way on trout in forested headwater streams in New York. N. Am. J. Fish. Manag. 1993, 13, 581–585. [Google Scholar] [CrossRef]
  63. Gómez-Aparicio, L. The role of plant interactions in the restoration of degraded ecosystems: A meta-analysis across life-forms and ecosystems. J. Ecol. 2009, 97, 1202–1214. [Google Scholar] [CrossRef] [Green Version]
Forests 11 00518 g001 550
Figure 1. Selected reaches along the 10 river basins in northern Sweden. Black lines are free-flowing rivers, and grey lines are regulated rivers. Dots represent the 94 study reaches, and lines represent the course of the main channels of the rivers.
Figure 1. Selected reaches along the 10 river basins in northern Sweden. Black lines are free-flowing rivers, and grey lines are regulated rivers. Dots represent the 94 study reaches, and lines represent the course of the main channels of the rivers.
Forests 11 00518 g001
Forests 11 00518 g002 550
Figure 2. (a) Species richness within each life form group for each flow regulation group and (b) relative abundance of each life form group for each flow regulation group. Regulation groups involve the following levels of regulation: free-flowing (<0%), low (>0% and <15%), moderate (>15% and <60%), and high (>60%).
Figure 2. (a) Species richness within each life form group for each flow regulation group and (b) relative abundance of each life form group for each flow regulation group. Regulation groups involve the following levels of regulation: free-flowing (<0%), low (>0% and <15%), moderate (>15% and <60%), and high (>60%).
Forests 11 00518 g002
Forests 11 00518 g003a 550Forests 11 00518 g003b 550
Figure 3. Fraction of species separated by their response to flow regulation for each life form group. (a) Fraction of the total species pool which showed negative, positive, or impassive responses to increasing degrees of regulation. (b) A specification of the above showing the fraction of total species that disappeared or appeared at reaches with beyond moderate flow regulation (>15%) or in the high flow regulation category (>60%).
Figure 3. Fraction of species separated by their response to flow regulation for each life form group. (a) Fraction of the total species pool which showed negative, positive, or impassive responses to increasing degrees of regulation. (b) A specification of the above showing the fraction of total species that disappeared or appeared at reaches with beyond moderate flow regulation (>15%) or in the high flow regulation category (>60%).
Forests 11 00518 g003aForests 11 00518 g003b
Forests 11 00518 g004 550
Figure 4. Regression coefficients of the species-specific linear regressions between the relative presence of a species and the mean percentage of regulation separated for each life form group (Woody species (a), graminoids (b) and forbs (c)). Different regression coefficients are indicated with a line below and with arrows at the top of each. The full names of the species are in Annex 1.
Figure 4. Regression coefficients of the species-specific linear regressions between the relative presence of a species and the mean percentage of regulation separated for each life form group (Woody species (a), graminoids (b) and forbs (c)). Different regression coefficients are indicated with a line below and with arrows at the top of each. The full names of the species are in Annex 1.
Forests 11 00518 g004
Forests 11 00518 g005 550
Figure 5. Biplots of the canonical correspondence analyses (CCA) on woody (a,d), graminoid (b,e), and forb (c,f) presence–absence species data. (a–c) represent the canonical loadings for the hydrological variables, and (d–f) show species scores. For a better visualization, only hydrological variables with loadings of >0.5 are labeled. Each point is one species, with the fill color representing species response to increased flow regulation being: negative (white dots), positive (black dots), and impassive (grey dots) trends. The two dots at the top left corner in (e) represent two species outside the range of the x- and y-axes; their coordinates are indicated between parentheses. An explanation of the codes of the hydrological variables are in Table 1 and Annex 1.
Figure 5. Biplots of the canonical correspondence analyses (CCA) on woody (a,d), graminoid (b,e), and forb (c,f) presence–absence species data. (a–c) represent the canonical loadings for the hydrological variables, and (d–f) show species scores. For a better visualization, only hydrological variables with loadings of >0.5 are labeled. Each point is one species, with the fill color representing species response to increased flow regulation being: negative (white dots), positive (black dots), and impassive (grey dots) trends. The two dots at the top left corner in (e) represent two species outside the range of the x- and y-axes; their coordinates are indicated between parentheses. An explanation of the codes of the hydrological variables are in Table 1 and Annex 1.
Forests 11 00518 g005
Table
Table 1. Mean and standard deviation of the hydrological variables characterizing each flow regulation group. “n” indicates the number of sites included within each flow regulation group. Letters “a,” “b,” “c,” and “d” identify significant differences between groups (p < 0.05), while the trend across groups is indicated with an arrow.
Table 1. Mean and standard deviation of the hydrological variables characterizing each flow regulation group. “n” indicates the number of sites included within each flow regulation group. Letters “a,” “b,” “c,” and “d” identify significant differences between groups (p < 0.05), while the trend across groups is indicated with an arrow.
Hydrological VariableFree-flowing (n = 63)Low (n = 14)Medium (n = 8)High (n = 9)Trend
MeanStd. DeviationMeanStd. DeviationMeanStd. DeviationMeanStd. Deviation
Reg0.00 a0.006.71 b2.2039.99 c7.3484.48 d18.07 Forests 11 00518 i001
MMaxMst3.07 a0.462.48 b0.321.39 c0.351.37 c0.18 Forests 11 00518 i002
MMinMst0.21 a0.080.30 b0.070.68 c0.210.51c 0.23 Forests 11 00518 i003
MT2st5.47 a1.523.33b0.582.62 c0.571.95 d0.26 Forests 11 00518 i004
TMaxM1.52 a0.622.00 b0.003.29 b3.248.39 c2.47 Forests 11 00518 i005
TMinM10.86 a0.6611.86 b0.538.25 a5.204.56 c4.61 Forests 11 00518 i006
TXLow293.69 a112.21298.93 a103.72106.89 b94.6289.13 b83.61 Forests 11 00518 i007
TT232.37 a15.2661.67 b17.47100.12 c27.30152.77 d78.36 Forests 11 00518 i008
DMaxM1.32 a0.521.71 b0.475.31 c4.256.83 c3.14 Forests 11 00518 i009
DMinM1.86 a0.501.86 a0.363.38 a2.922.78 a2.82 Forests 11 00518 i010
DXLow37.65 a13.4313.30 b,c16.383.21 c2.496.65 c5.99 Forests 11 00518 i011
DT264.32 a17.9597.55 b30.5546.60 c11.5238.42 c23.17 Forests 11 00518 i012
FMRev4.24 a0.983.21 b0.585.29 c1.164.33 a,c2.06 Forests 11 00518 i013
FDRev43.69 a17.1340.86 a37.14138.61 b44.08106.49 b42.09 Forests 11 00518 i014
FXLow1.10 a0.541.02 b2.406.94 c5.713.87 a,b,c6.21 Forests 11 00518 i015
Rrisest0.13 a0.080.07 b0.060.15 a0.070.10 a,b0.09 Forests 11 00518 i016
Rfallst0.05 a0.030.04 b0.060.14 c0.060.10 a,c0.09 Forests 11 00518 i017
Reg: percentage of regulation (%); MMaxMst, MMinMst, and MT2st: magnitude of maximum monthly flow, minimum monthly flow, and 2-year recurrence flow (standardized to the mean annual flow; unitless), respectively; TMaxM and TMinM: timing of the maximum and minimum monthly flows, respectively (being 1 May and 12 April). TXLow and TT2: timing of the extreme low flows and of 2-year recurrence flow (Julian days); DMaxM and DMinM: duration of the maximum and minimum monthly flows, respectively (#months). DXLow and DT2: duration of extreme low flow conditions and of 2-year recurrence flow events (#days); FMRev, FDRev, and FXLow: frequency of the monthly flow reversals, daily flow reversals, and extreme low flows (# per year), respectively; Rrisest and Rfallst: daily rate of flow rise and fall, respectively (standardized to the mean annual flow; unitless). Further details on hydrological variables are available in Annex 1.
Table
Table 2. Summary table of the variable loadings and cumulative variance explained of the first three axes of the CCA, separated for woody, graminoid, and forb species distribution data. In addition, the significance of each axes in each CCA is provided (bottom row), as is that of the CCA as a whole (top row). For an explanation of the hydrological variable names see Table 1 and Annex 1. We highlight the cells (bold) with loadings beyond 0.45.
Table 2. Summary table of the variable loadings and cumulative variance explained of the first three axes of the CCA, separated for woody, graminoid, and forb species distribution data. In addition, the significance of each axes in each CCA is provided (bottom row), as is that of the CCA as a whole (top row). For an explanation of the hydrological variable names see Table 1 and Annex 1. We highlight the cells (bold) with loadings beyond 0.45.
Woody Species (F = 2.08, p = 0.001)Graminoids (F = 1.76, p = 0.001)Forbs (F = 1.99, p = 0.001)
CCA1CCA2CCA3CCA1CCA2CCA3CCA1CCA2CCA3
Reg0.290.560.17−0.460.090.000.14−0.08−0.47
MMaxM_std−0.07−0.46−0.110.22−0.070.060.110.190.27
MMinM_std−0.170.55−0.03−0.110.180.13−0.170.04−0.40
MT2_std−0.08−0.28−0.100.280.040.14−0.030.250.07
TMaxM0.290.130.30−0.370.01−0.220.21−0.06−0.24
TMinM−0.01−0.220.030.04−0.39−0.050.22−0.210.53
TXLow−0.01−0.460.290.04−0.18−0.200.10−0.220.32
TT20.300.390.50−0.720.26−0.110.30−0.22−0.56
DMaxM0.000.350.33−0.14−0.01−0.25−0.09−0.07−0.07
DMinM−0.410.350.34−0.040.11−0.32−0.29−0.24−0.04
DXLow−0.46−0.140.040.400.14−0.67−0.54−0.290.41
DT20.10−0.280.21−0.27−0.32−0.320.20−0.380.36
FMRev−0.150.17−0.590.310.130.47−0.120.64−0.05
FDRev0.030.630.01−0.210.300.27−0.010.17−0.64
FXLow0.430.66−0.15−0.450.180.340.18−0.09−0.53
RRise_std0.170.15−0.130.020.170.330.080.26−0.34
RFall_std0.340.60−0.04−0.410.140.260.24−0.07−0.53
Eigenvalue0.100.070.050.140.120.080.180.130.09
Proportion Explained0.230.170.120.200.170.120.180.130.09
Significance of axisp = 0.001p = 0.001p = 0.027p = 0.049p = 0.072p = 0.113p = 0.001p = 0.001p = 0.003

Share and Cite

MDPI and ACS Style

Bejarano, M.D.; Sarneel, J.; Su, X.; Sordo-Ward, A. Shifts in Riparian Plant Life Forms Following Flow Regulation. Forests 2020, 11, 518. https://doi.org/10.3390/f11050518

AMA Style

Bejarano MD, Sarneel J, Su X, Sordo-Ward A. Shifts in Riparian Plant Life Forms Following Flow Regulation. Forests. 2020; 11(5):518. https://doi.org/10.3390/f11050518

Chicago/Turabian Style

Bejarano, María D., Judith Sarneel, Xiaolei Su, and Alvaro Sordo-Ward. 2020. "Shifts in Riparian Plant Life Forms Following Flow Regulation" Forests 11, no. 5: 518. https://doi.org/10.3390/f11050518

APA Style

Bejarano, M. D., Sarneel, J., Su, X., & Sordo-Ward, A. (2020). Shifts in Riparian Plant Life Forms Following Flow Regulation. Forests, 11(5), 518. https://doi.org/10.3390/f11050518

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop