Article Shifts in Riparian Life Forms Following Flow Regulation

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, ; [email protected] 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; [email protected] 4 Departamento de Ingeniería Civil: Hidráulica, Energía y Medio Ambiente, Universidad Politécnica de Madrid, 28040 Madrid, Spain; [email protected] * Correspondence: [email protected]

 Received: 10 March 2020; Accepted: 30 April 2020; Published: 5 May 2020 

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 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.

Keywords: forb; functional group; graminoid; hydrological variable; vegetation; woody

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

Forests 2020, 11, 518; doi:10.3390/f11050518 www.mdpi.com/journal/forests Forests 2020, 11, 518 2 of 18 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 [6–8]. 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, , 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 [14–16]. 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 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 (Figure1). The study reaches were selected along 10 rivers within nine basins: , Kalix, Sävarån, Vindel, Öre, Pite, Lule, Skellefte, Ume, and Ångerman (Figure1). The rivers run from the Norwegian border and end at the , except for the Vindel River that joins the Ume River 35 km from the coast. Most rivers are large (i.e., a channel length Forests 2020, 11, 518 3 of 18 Forests 2020, 11, x FOR PEER REVIEW 3 of 18 betweenRiver 35 360 km and from 510 the km, coast. a catchment Most rivers area are betweenlarge (i.e., 11,285 a channel and 40,157length kmbetween2, and 360 a mean and 510 monthly km, a dischargecatchment between area between 131 and 11,285 501 and m3/ s),40,157 except km2, for and the a mean Sävarån monthly and Öredischarge rivers, between which are131 and smaller 501 (128–185m3/s), except km, 3029–1160for the Sävarån km2 ,and and Öre 34–15 rivers, m which3/s, respectively). are smaller (128–185 Some rivers km, 3029–1160 have no km major2, and dams 34– and15 maym3/s, berespectively). considered Some free-flowing rivers have (Torne, no major Kalix, da Sävarån,ms and may Vindel, be considered and Öre), free-flowing whereas others (Torne, are regulatedKalix, Sävarån, by one toVindel, several and dams Öre), and whereas are considered others are moderately-to-strongly regulated by one to several regulated dams rivers and (Pite, are Lule,considered Skellefte, moderately-to-strongly Ume, and Ångerman). regulated Despite rivers river (Pite, specific Lule, di ffSkellefte,erences, theUme, upland and Ångerman). vegetation (furthestDespite awayriver specific from the differences, channel) the is generally upland vegeta characterizedtion (furthest by birchaway from (Betula the pubescens channel) isEhrh.) generally and coniferouscharacterized forests by (birchPinus ( sylvestrisBetula pubescensL. and PiceaEhrh.) abies and(L.) coniferous H. Karst.). forestsThe riparian(Pinus sylvestris vegetation L. and closer Picea to theabies river (L.) channel H. Karst.). frequently The riparian includes vegetation woody speciescloser to like theAlnus river incana channel(L.) frequentlyMoench, Betulaincludes pubescens woody, andspeciesSalix likespp.; Alnus graminoids incana (L.) like Moench, Betulasp. and pubescensPoa sp.;, and and Salix forbs spp.; like graminoidsRanunculus like reptans Carex sp.L. andand Poa sp.; and forbs like Ranunculus reptans L. and Filipendula ulmaria (L.) Maxim. Filipendula ulmaria (L.) Maxim.

FigureFigure 1. 1.Selected Selected reaches reaches along along the the 10 10 river river basins basins in in northern northern Sweden. Sweden. BlackBlack lineslines areare free-flowingfree-flowing rivers,rivers, and and grey grey lines lines are are regulated regulated rivers. rivers. Dots Dots represent represent the the 94 94 study study reaches,reaches, andand lineslines representrepresent the coursecourse of of the the main main channels channels of of the the rivers. rivers. Forests 2020, 11, 518 4 of 18

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; Table1 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. Forests 2020ForestsForests, 11, 2020 5182020,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 5 of 18 55 ofof 1818

TableTable 1.1. MeanMean andand standardstandard deviationdeviation ofof thethe hydrologicalhydrological variablesvariables characterizingcharacterizing eacheach flowflow regulationregulation group.group. ““nn”” indicatesindicates thethe numbernumber ofof sitessites includedincluded withinwithin TableForestsForests 1. 2020Mean2020,, 1111 and,, xx FORFOR standard PEERPEER REVIEWdeviationREVIEW of the hydrological variables characterizing each flow regulation group. “n” indicates the number of sites included within each 55 ofof 1818 eacheach flowflow regulationregulation group.group. LettersLetters “a,”“a,” “b,”“b,” “c,”“c,” andand “d”“d” identifyidentify significantsignificant differencesdifferences betweenbetween groupsgroups ((pp << 0.05),0.05), whilewhile thethe trendtrend acrossacross groupsgroups isis indicatedindicated withwith 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. anan arrow.arrow. TableTable 1.1. MeanMean andand standardstandard deviationdeviation ofof thethe hydrologicalhydrological variablesvariables characterizingcharacterizing eacheach flowflow regulationregulation group.group. ““nn”” indicatesindicates thethe numbernumber ofof sitessites includedincluded withinwithin ForestsForests 20202020,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 1818 each flow regulation group.Free-flowing Letters “a,” (Free-FlowingnFree-Flowing= “b,”63) “c,” and ((nn == “d”63)63) identify Low (n significant= 14)LowLow ((nn = =differences 14)14) between MediumMediumMedium groups (n = 8) ((nnp = =< 8) 8)0.05), while the High trendHighHigh (n =across ((nn9) == 9)9) groups is indicated with Hydrologicaleach flow Variable regulation group. Letters “a,” “b,” “c,” and “d” identify significant differences between groups (p < 0.05), while the trend across groups isTrend indicated with Forests 2020, 11, xHydrologicalHydrological FOR PEER REVIEW VariableVariable TrendTrend 5 of 18 anan arrow.arrow. Mean Std.MeanMean Deviation Std.Std. DeviationDeviation Mean MeanMean Std. DeviationStd.Std. DeviationDeviation Mean MeanMean Std. DeviationStd.Std. DeviationDeviation MeanMeanMean Std.Std.Std. Deviation DeviationDeviation TableTable 1.1. MeanMean andand standardstandard deviationdeviation ofof thethe hydrologicalhydrological variablesvariables characterizingcharacterizing eacheach flowflow regulationregulation group.group. ““nn”” indicatesindicates thethe numbernumber ofof sitessites includedincluded withinwithin a b c d Reg a 0.00 a 0.00 b 6.71 b 2.20 c 39.99 c 7.34 84.48d d 18.07 eachReg flow regulationReg 0.00group. Letters “a,”0.00Free-Flowing0.00Free-Flowing “b,” “c,” and ((n0.00n ==6.71 “d”63)63) identify6.71 significant LowLow2.20 ((nn = =differences 14)14)2.20 39.99 between39.99Medium Medium groups7.34 ((nnp = 7.34=< 8) 8)0.05), while84.4884.48 the trend HighHigh across ((nn18.07 == 18.07 9)9) groups is indicated with eachTable flow 1. Mean regulation and standard group. Letters deviation “a,” of “b,” the “c,” hydrological and “d” identify variables significant characterizing differences each betweenflow regulation groups group.(p < 0.05), “n” while indicates the trend the number across groupsof sites isincluded indicated within with Forests 2020, 11, xHydrologicalHydrological FOR PEER REVIEW VariableVariable a b c c TrendTrend 5 of 18 an arrow. MMaxMst a Mean3.07 a Std. Deviation0.46 b Mean2.48 b Std. Deviation0.32 c Mean1.39 c Std. Deviation0.35 Mean1.37c c Std. Deviation0.18 MMaxMsteachan arrow. flow regulationMMaxMst 3.07group. Letters Mean3.07“a,”0.46 “b,” “c,”Std. andDeviation0.462.48 “d” identify Mean2.48 significant 0.32Std. differences Deviation0.32 1.39 betweenMean1.39 groups0.35Std. ( pDeviation0.35 < 0.05), while 1.37Mean1.37 the trend Std. across0.18 Deviation0.18 groups is indicated with a b c c Forests 2020, 11, x FOR PEERMMinMst REVIEW 0.21 aa 0.08 0.30 bb 0.07 0.68 cc 0.21 0.51 cd 0.23 5 of 18 ForestsMMinMstan 2020 arrow., 11, x FOR PEERMMinMstRegReg REVIEW 0.21 a 0.000.210.00Free-Flowing0.08 a (0.00n0.000.08 = 63) b 6.716.710.30 b Low0.07 (n = 14)2.202.200.07 0.68 c 39.9939.990.68 Medium c 0.21 (n 7.34=0.217.34 8) 0.5184.4884.48c0.51 d High (n0.23 =18.07 18.079)0.23 5 of 18 Table 1. Mean and standard deviationFree-Flowing of the hydrological (n =0.30 63) variables characterizingLow (n = 14) each flow regulationMedium group.(n = 8) “n” indicates theHigh number (n = 9) of sites included within Hydrological Variable a b c dc Trend Forests 2020, 11, xHydrological FOR MMaxMstPEERMT2st REVIEW Variable a 5.473.07 a 0.461.52 2.483.33b b 0.320.58 c 1.392.62 c 0.350.57 1.951.37 dc 0.260.18 Trend 5 of 18 eachMT2st flow regulationMMaxMstMT2st 5.47group. Letters MeanMean“a,”5.473.071.52Free-Flowing “b,” “c,”Std.Std. and Deviation Deviation(0.461.52n = 3.33b “d”63) identify MeanMean2.483.33b significant Low 0.58Std. Std.(n =differences DeviationDeviation14)0.320.58 2.62 betweenMeanMean1.392.62 Medium groups0.57Std.Std. ( np DeviationDeviation 0.350.57=< 8)0.05), while 1.95MeanMean 1.951.37dthe trend HighStd. Std.across (n0.26 = DeviationDeviation 0.260.189) groups is indicated with TableTable 1.1. MeanMean andand standardstandard deviationdeviation ofaof thethe hydrologicalhydrological variablesvariablesb characterizingcharacterizing eacheach flowflow regulationregulationb group.group. ““nn”” indicatesindicatesc thethe numbernumber ofof sitessites includedincluded withinwithin Forests 2020, 11, xHydrological FOR PEERTMaxM REVIEW Variable 1.52 aa 0.62 2.00 bb 0.00 3.29 cbc 3.24 8.39 c cd 2.47 Trend 5 of 18 an arrow. MMinMstMMinMstTMaxMReg a 0.210.00Mean1.520.21 a Std. Deviation0.000.080.080.62 b 6.710.30Mean0.302.00 b Std. Deviation2.200.070.070.00 b 39.990.68Mean3.290.68 c c Std. Deviation0.217.343.240.21 84.48Mean0.518.39c0.51 c d Std. 18.07Deviation0.230.232.47 eacheachTMaxM flowflow regulationregulationReg 1.52group.group. LettersLetters “a,”0.00“a,”0.62 “b,” “b,” “c,”“c,” andand0.002.00 “d”“d” identifyidentify6.71 significantsignificant 0.00 differencesdifferences2.20 3.29 betweenbetween39.99 groupsgroups3.24 ((pp 7.34 << 0.05),0.05), whilewhile 8.3984.48 thethe trendtrend acrossacross2.4718.07 groupsgroups isis indicatedindicated withwith Table 1. Mean and standard deviation aofa the hydrological variablesb characterizing each flow regulationac group. “n” indicatesdc the number of sites included within Forests 2020, 11, x FOR PEERTMinMTMinMMT2st REVIEW 10.8610.865.47 a a a 1.520.660.66 11.8611.863.33bb b 0.530.580.53 8.252.62 8.25 cac 0.575.205.20 1.954.564.56 cdc 0.264.614.61 5 of 18 ananTMinM arrow.arrow. MMaxMstMMaxMstMT2stReg 10.86 a 3.075.470.003.07Free-Flowing0.66 a (0.46n0.000.461.52 =11.86 63) b 2.486.712.483.33b b Low0.53 (n = 14)0.322.200.320.58 8.25 a 39.991.391.392.62 Mediumc c 5.20 (n 0.35=0.350.577.34 8) 4.5684.481.371.951.37c c d High (n4.61 = 18.070.189)0.260.18 eachTable flow 1. Mean regulation and standard group. Letters deviation “a,” of a“b,” the “c,” hydrological and “d” identify variables significant acharacterizing differences each betweenflow regulationb groups group.(p < 0.05), “n” while indicates the btrend the number across groupsof sites isincluded indicated within with HydrologicalTXLow Variable 293.69a a 112.21 298.93b a 103.72 106.89bc b 94.62 89.13c c b 83.61 Trend MMinMstTMaxMTMaxMTXLow a 293.69Mean1.520.211.52 a Std. Deviation112.210.080.620.62 a 298.93Mean0.302.002.00 b Std. Deviation103.720.070.000.00 b106.89Mean3.290.683.29 bc Std. Deviation94.623.240.213.24 Mean 89.138.390.518.39b c c Std. Deviation83.610.232.472.47 eachanTXLow arrow. flow regulationMMaxMstMMinMst 293.69 group. Letters 0.213.07“a,”112.21Free-FlowingFree-Flowing “b,” “c,” and ((n0.080.46n 298.93 == 63)“d”63) identify0.302.48 significant 103.72LowLow ((nn == differences 14)14)0.070.32 106.89 between0.681.39 MediumMedium groups94.62 ( (n(np =0.210.35= < 8)8) 0.05), while89.131.370.51 the trend HighHigh across ((nn83.61 == 9)0.230.189) groups is indicated with Table 1. Mean and standard deviation ofa the hydrological variablesb characterizing each flow regulationa c group. “n” indicatesc d the number of sites included within Forests 2020, 11, xHydrological FOR PEERTMinMTT2 REVIEW Variable 32.3710.86a a 15.260.66 61.6711.86 b 17.470.53 100.12 8.25 ca c 27.305.20 152.774.56 dc d 78.364.61 Trend 5 of 18 HydrologicalTMinMMT2stRegTT2 Variable a 32.3710.865.470.00 aa 15.260.001.520.66 b 61.6711.866.713.33b bb 17.472.200.580.53 c 100.1239.992.62 8.25 cc 27.300.577.345.20 152.7784.481.954.56d cd 18.0778.360.264.61 Trend eachan TT2arrow. flow regulationMMinMstMT2st 32.37 group. LettersMean Mean5.470.21“a,”15.26Free-Flowing “b,” “c,”Std.Std. Deviationand Deviation(1.520.08n 61.67= “d”63) identify MeanMean0.303.33b significant 17.47LowStd. Std.(n = differences DeviationDeviation14)0.070.58 100.12 betweenMeanMean0.682.62 Medium groups27.30Std.Std. ( (n DeviationpDeviation 0.570.21= < 8) 0.05), 152.77while MeanMean1.950.51 the trend HighStd.Std. across (n78.36 = DeviationDeviation 0.260.239) groups is indicated with a a b a c b cb Forests 2020, 11, x FOR PEERDMaxMDMaxMTXLow REVIEW 293.691.321.32 aa a 112.210.520.52 298.931.711.71 bb a 103.720.470.47 106.895.315.31 bc b 94.624.254.25 89.136.836.83 cc b 83.613.143.14 5 of 18 HydrologicalMMaxMstTMaxMTXLow Variable 293.691.523.07 aa 112.210.460.62 298.932.482.00 bb 103.720.320.00 106.893.291.39 cbcc 94.623.240.35 89.138.391.37 cd c 83.610.182.47 Trend anDMaxM arrow. TMaxMMT2stRegReg 1.32 a 0.00Mean5.471.520.000.52Free-Flowing a Std. Deviation0.00(0.001.520.62n =1.71 63) b 6.71Mean6.712.003.33b b Low0.47 Std.(n = Deviation14)2.202.200.000.58 5.31 c 39.9939.99Mean3.292.62 Mediumc 4.25Std. (n Deviation7.34 3.240.577.34= 8) 6.8384.4884.48Mean1.958.39c d HighStd. (n3.14 = 18.07Deviation18.07 0.262.479) Table 1. Mean and standard deviation ofaa the hydrological variablesa bcharacterizing each flow regulationa c group. “n” indicatesa dthe number of sites included within DMinMDMinMTT2 32.371.861.86 a a 15.260.500.50 61.671.861.86 ab b 17.470.360.36 100.123.383.38 aa c 27.302.922.92 152.772.782.78 ca d 78.362.822.82 Forests 2020, 11, xHydrological FOR PEERMMinMstTMinMTT2 REVIEW Variable 10.8632.370.21 a a a 15.260.080.66 11.8661.670.30 b b b 17.470.070.53 100.12 8.250.68 cba 27.300.215.20 152.774.560.51 cc c 78.360.234.61 Trend 5 of 18 eachDMinM flow regulationMMaxMstMMaxMstTMaxMTMinMReg 1.86group. a Letters 10.863.07Mean“a,”1.520.003.070.50Free-Flowing a “b,” “c,”Std. and Deviation0.46(0.000.460.620.66n = 1.86 “d” 63) aidentify 11.862.48Mean6.712.482.00 significant b Low0.36 Std.(n =differences Deviation14)0.322.200.320.000.53 3.38 betweena 39.991.39Mean3.29 8.251.39 c Mediumc groups2.92Std. (np Deviation0.35 3.240.357.345.20=< 8)0.05), while 2.7884.481.37Mean 8.391.374.56athe ctrend d High Std.across (n2.82 = Deviation18.07 0.180.182.474.619) groups is indicated with Table 1. Mean and standard deviation ofaa the hydrological variablesbb,c characterizing each flow regulationc group. “n” indicatesc the number of sites included within DMaxMDXLowDXLow 37.6537.651.32 a a 13.4313.430.52 13.3013.301.71 bb,c a 16.3816.380.47 3.215.31 3.21 c b 4.252.492.49 6.836.656.65 cb 3.145.995.99 Forests 2020, 11, xHydrological FOR PEERDMaxMTXLowTMinMTXLowMT2st REVIEW Variable 293.69293.6910.865.471.32 a a a 112.21112.211.520.520.66 298.93298.9311.863.33b1.71 b b a 103.72103.720.580.470.53 106.89106.892.62 8.255.31 ca b 94.6294.620.574.255.20 89.13 89.131.956.834.56 c d c b 83.6183.610.264.613.14 Trend 5 of 18 anDXLow arrow. MMinMstMMaxMstMMinMstReg 37.65 a 0.21Mean0.210.003.0713.43 a Std. Deviation0.080.080.000.4613.30 b,c 0.30Mean0.306.712.48 b 16.38Std. Deviation0.070.072.200.32 3.21 c 39.990.68Mean0.681.39 c c 2.49Std. Deviation0.210.210.357.34 6.6584.48Mean0.511.37c0.51 c c d Std.5.99 Deviation18.070.230.230.18 each flow regulation group. Letters “a,”a a“b,” “c,” and “d” identify significantab differences betweenac groups (p < 0.05), while the actrend across groups is indicated with Table 1. Mean andDMinMDT2DT2 standard deviation64.3264.321.86 of a a the hydrological17.9517.950.50 variables97.5597.551.86 ab bcharacterizing 30.5530.550.36 each flow46.6046.603.38 regulation a cc group.11.5211.522.92 “n” indicates38.4238.422.78 a cd the number23.1723.172.82 of sites included within TMaxMDMinMTT2TT2 32.3732.371.521.86 a a a 15.2615.260.620.50 61.6761.672.001.86 b b a 17.4717.470.000.36 100.12100.123.293.38 bc bc 27.3027.303.242.92 152.77152.778.392.78 dc b d 78.3678.362.472.82 an arrow. MMaxMstTXLowMT2st a 293.695.473.07Free-Flowing a 112.21(1.52n0.46 = 63) b 298.933.33b2.48 b Low (n = 14)103.720.580.32 c 106.892.621.39 Mediumc c (n 94.620.57=0.35 8) 89.131.951.37c cd c d High (n = 83.610.269)0.18 DT2MMinMstMT2stReg 64.32 5.470.210.0017.95 a 1.520.080.0097.55 0.306.713.33b b 30.550.072.200.58 46.60 39.990.682.62 c 11.520.570.217.34 38.4284.481.950.51a,c 23.1718.070.260.23 each flow regulationFMRev group. Letters 4.24“a,” a “b,” “c,” and0.98 “d” identify3.21 significant b,cb differences0.58 between5.29 cc groups (p1.16 < 0.05), while4.33 the a,c ctrend across2.06 groups is indicated with Table 1. MeanHydrological andDXLowFMRev standard Variable deviation 37.654.24 of a a the hydrological13.430.98 variables13.303.21 b b,ccharacterizing 16.380.58 each flow 3.215.29 regulation cc group.2.491.16 “n” indicates4.336.65 cc the number5.992.06 of sites includedTrend within DMaxMTMinMDMaxMDXLowTT2 10.8632.3737.651.321.32 aa a 15.2613.430.520.660.52 13.3011.8661.671.711.71 b b b 16.3817.470.470.530.47 100.12 8.255.31 3.215.31 bac c 27.304.255.204.252.49 152.776.834.566.836.65 cc d 78.364.613.143.145.99 anFMRev arrow. MMaxMstMMinMstTMaxMTMaxMMT2st 4.24 a Mean1.525.471.520.213.07Free-Flowing0.98 a Std. Deviation(0.62n1.520.620.080.46 =3.21 63) b Mean2.002.000.302.483.33b b Low0.58 Std.(n = Deviation14)0.000.000.070.320.58 5.29 c Mean3.293.290.681.392.62 Mediumbc 1.16Std. (n Deviation 3.24=3.240.570.210.35 8) 4.33 Meana,c8.391.958.391.370.51 cdc HighStd. (n2.06 = Deviation 2.479)0.260.232.470.18 a ba cb cb each flow regulationFDRevFDRevDT2 group. Letters64.3243.69 43.69“a,”a “b,”a “c,” and17.9517.1317.13 “d” identify97.5540.8640.86 significant a ba differences37.1430.5537.14 between138.61138.6146.60a c bgroups (p11.5244.0844.08 < 0.05), while106.49106.4938.42 the a trend c b across23.1742.0942.09 groups is indicated with HydrologicalDMinMDMaxMTXLowDMinMDT2 Variable 293.6964.321.861.321.86 a a 112.2117.950.500.520.50 298.9397.551.861.711.86 b a a 103.7230.550.360.470.36 106.8946.603.383.385.31 aac b 94.6211.522.924.252.92 89.1338.422.782.786.83 cac b 83.6123.172.822.823.14 Trend MMinMstTMinMTMaxMTMinMMT2stReg a 10.86Mean10.860.005.471.520.21 aa a Std. Deviation0.000.661.520.620.080.66 a 11.86Mean11.866.712.000.303.33b b b b Std. Deviation2.200.530.000.070.530.58 b 39.99Mean 8.253.29 8.250.682.62 bacc Std. Deviation7.345.203.240.570.215.20 84.48Mean4.561.958.394.560.51b cdc Std. Deviation18.074.610.260.232.474.61 anFDRev arrow. 43.69 17.13Free-Flowinga (n = 40.86 63) b 37.14Low (n = 14) 138.61 cMedium44.08 (n = 8) 106.49 a,b,ca,c High (n42.09 = 9) FMRevFXLowFXLow 1.104.241.10 a 0.980.540.54 3.211.021.02 b,cb 0.582.402.40 5.296.946.94 cc 1.165.715.71 3.873.874.33 a,b,ca,cc 6.212.066.21 HydrologicalDXLowDMinMDXLowFMRevTT2 Variable 32.3737.6537.651.864.24 a a 15.2613.4313.430.500.98 13.3013.3061.673.211.86 ab,cb a 16.3817.4716.380.580.36 100.12 3.213.38 3.215.29 ac bc 27.302.492.491.162.92 152.774.336.652.786.65 ac b d 78.365.992.822.065.99 Trend MMaxMstTXLowTMaxMTMinMTXLowMT2stReg a 293.69293.6910.860.003.075.471.52 aa a a 112.21112.210.000.461.520.620.66 b 298.93298.9311.866.712.482.003.33b bb b a 103.72103.722.200.320.000.530.58 c 106.89106.8939.991.393.29 8.252.62 c bac c b 94.6294.620.357.343.240.575.20 a,b,c84.48 89.13 89.131.371.958.394.56 cd c b 83.6118.0783.610.180.262.474.61 FXLow 1.10 Mean0.54aa Std. Deviation1.02 Meanba 2.40Std. Deviation 6.94 Meana b 5.71Std. Deviation3.87 Meana,b b Std.6.21 Deviation FDRevRrisestRrisest 43.690.130.13Free-Flowing a a 17.13(0.08n0.08 = 63) 40.860.070.07 b a Low (n = 14)37.140.060.06 138.610.150.15 Mediuma c b (n44.08 0.07=0.07 8) 106.490.100.10 a,b c b High (n =42.09 0.099)0.09 FDRevDT2 64.3243.69a aa 17.9517.13 97.5540.86b b,cbb 30.5537.14 138.6146.60c c cc 11.5244.08 106.4938.42c c cd 23.1742.09 HydrologicalDMaxMDXLowTT2DT2 Variable 32.3737.6564.321.32 a a a a 15.2613.4317.950.52 13.3061.6797.551.71 bb b a 17.4716.3830.550.47 100.1246.605.31 3.21 cba bc 27.3011.524.252.49 152.7738.426.836.65 c c b d 78.3623.173.145.99 Trend MMaxMstMMinMstTMaxMTMinMTXLowTT2 293.6932.3710.860.213.071.52 a 112.2115.260.460.080.620.66 298.9361.6711.862.480.302.00 b 103.7217.470.320.070.000.53 106.89100.121.390.683.29 8.25 cc 94.6227.300.350.213.245.20 152.77 89.131.370.518.394.56 c d 78.3683.610.230.182.474.61 Reg a Mean0.00 a Std. Deviation0.00 b Mean6.71 b Std. Deviation2.20 a 39.99Meanc Std. Deviation7.34 84.48Meana,b a,b,ca,c Std. Deviation18.07 RrisestFXLowRfallstRfallst 0.13 0.051.100.050.08 aa 0.540.030.030.07 1.020.040.04 bb 0.062.400.060.06 0.15 6.940.140.14 cc 0.07 5.710.060.06 0.103.870.100.10 a,b,c a,ca,c 0.096.210.090.09 FMRevFXLow 4.241.10 aa a 0.980.54 3.211.02 bab b 0.582.40 5.296.94 acc c 1.165.71 3.874.33 a,cac c 2.066.21 DMaxMDMinMFMRevDT2 64.321.321.864.24 aa a a 17.950.520.500.98 97.551.711.863.21 b b a 30.550.470.360.58 46.603.385.315.29 cac bc 11.524.252.921.16 38.424.332.786.83 dc bd 23.172.823.142.06 MMinMstDMaxMTMinMTXLowMT2stTT2 293.6932.3710.865.470.211.32 a 112.2115.260.081.520.520.66 298.9361.6711.860.303.33b1.71 b 103.7217.470.070.580.470.53 106.89100.120.682.62 8.255.31 c 94.6227.300.210.574.255.20 152.77 89.131.950.516.834.56 c c 78.3683.610.260.234.613.14 MMaxMst a 3.07 a 0.46 2.48 b 0.32 c 1.39 ac 0.35 a,c1.37a,b d 0.18 Table 1 footer:RrisestReg Reg: percentage 0.130.00of regulation a (%);0.080.00 MMaxMst,b 0.076.71 MMi ba nMst, and0.062.20 MT2st: magnitude39.990.15 a b of maximum7.340.07 monthly84.480.10 a,b flow,b minimum18.070.09 monthly flow, and 2-year RfallstTable 1 footer:FDRevRrisest Reg: 0.05 percentage43.69 0.13of0.03 regulation aaa 17.13(%);0.080.04 MMaxMst,40.860.07 MMi a b,cba 0.06nMst, 37.14and0.06 MT2st: 0.14 magnitude138.610.15 acc b 0.06 of maximum44.080.07 monthly 0.10106.490.10 a,cac flow,b minimum0.0942.090.09 monthly flow, and 2-year DMinMDXLowFMRevFDRev 37.6543.691.864.24 aa a a 13.4317.130.500.98 13.3040.861.863.21 bba b a 16.3837.140.360.58 138.613.38 3.215.29 bac bc 44.082.492.921.16 106.494.332.786.65 cac b d 42.092.825.992.06 TMaxMDMaxMDMinMTXLowMT2stTT2 293.6932.375.471.521.321.86 a 112.2115.261.520.620.520.50 298.9361.672.003.33b1.711.86 b 103.7217.470.000.580.470.36 106.89100.123.292.623.385.31 c 94.6227.303.240.574.252.92 152.77 89.131.958.392.786.83 c d 78.3683.610.262.472.823.14 MMaxMstMMinMst 0.213.07 a 0.460.08 2.480.30 b 0.320.07 1.390.68 c 0.350.21 1.370.51 a,cc 0.230.18 recurrence flow (standardizedRfallst to the mean0.05 annual aa flow; unitless),0.03 respectively;0.04 bb TMaxM0.06 and TMinM:0.14 timing cc of the0.06 maximum and0.10 minia,b,c a,c mum monthly0.09 flows, respectively (being Reg:recurrence percentage flow of regulation (standardizedFXLowFXLowFDRevRfallstDT2 (%); MMaxMst, to the mean MMinMst,64.3243.691.100.051.10 annual a a and flow; MT2st:17.95 17.130.54unitless),0.540.03 magnitude respectively; of97.5540.861.021.020.04 maximum b,cb a TMaxM monthly30.5537.142.402.400.06 andflow, TMinM: minimum138.6146.606.946.940.14 timing monthly c cc b of flow,the11.5244.085.715.710.06 maximum and 2-year recurrence and3.87106.493.8738.420.10 mini a,b,c c c b flowmum (standardized monthly23.1742.096.216.210.09 flows, to the respectively mean (being DXLowTMinMDMaxMDMinMDXLowTT2 37.6510.8632.3737.651.321.86 aa a 13.4315.2613.430.660.520.50 13.3013.3011.8661.671.711.86 b b ab,cb 16.3816.3817.470.530.470.36 100.12 8.253.213.38 3.215.31 baac c 27.302.495.204.252.492.92 152.776.654.562.786.836.65 cac d 78.364.615.992.823.145.99 annual flow; unitless), respectively;TMaxM TMaxM and TMinM:1.52 a timing of0.62 the maximum2.00 and b minimum monthly0.00 flows, respectively3.29 c (being3.24 1 May and 128.39 April). cd TXLow and2.47 TT2: timing of the MMinMstMT2st 5.470.21 a 0.081.52 0.303.33b b 0.070.58 0.682.62 a 0.210.57 1.950.51 a,b 0.260.23 Table 1 footer:Rrisest Reg: percentage 0.13of regulation aa (%);0.08 MMaxMst,0.07 MMi bb nMst, and0.06 MT2st: magnitude0.15 cac of maximum0.07 monthly0.10 a,b,c a,ca,bflow, minimum0.09 monthly flow, and 2-year extreme1 May low andTable flows 12 April). and1 footer: of 2-yearFMRevTXLowFXLowRrisest Reg: recurrence percentageand TT2: flow timing4.24 0.131.10of (Julian regulation a of days); the extreme DMaxM0.98(%);0.540.08 MMaxMst, andlow DMinM:flows3.211.020.07 MMi band durationnMst, of 2-year ofand0.582.400.06 the recurrenceMT2st: maximum magnitude5.290.156.94 andflow c minimum (Julian of maximum days);1.16 monthly5.710.07 DMaxM flows,monthly3.874.330.10 respectively and cflow, DMin minimum (#months).M:2.06 6.210.09duration mont DXLow ofhly the andflow, maximum and 2-year and 1 May and 12 April).DMaxMTXLow DMinMDXLowTXLowDT2DT2 and TT2: 293.6964.32timing37.6564.321.321.86 a a of the extreme112.2117.9513.4317.950.520.50 low fl298.9313.3097.5597.55ows1.711.86 b ab,c band a of 2-year103.7230.5516.3830.550.470.36 recurrence 106.8946.6046.603.38 3.215.31 flow a ac c b (Julian 11.5294.6211.52days);4.252.492.92 DMaxM 89.1338.4238.422.786.836.65 and c ac bc DMinM:83.6123.1723.172.823.145.99 duration of the maximum and TMaxMTMinM 10.861.52 a 0.620.66 11.862.00 b 0.000.53 3.29 8.25 bc 3.245.20 8.394.56 dc 2.474.61 DT2: duration of extreme lowMT2st flow conditions and5.47 of a2-year recurrence1.52 flow events3.33b (#days);b FMRev,0.58 FDRev, and2.62 FXLow: c frequency0.57 of the monthly1.95 flow a,c reversals,0.26 daily flow reversals, recurrence flow (standardizedRfallst to the mean0.05 annual aa flow; unitless),0.03 respectively;0.04 bba TMaxM0.06 and TMinM:0.14 timing cac b of the0.06 maximum and0.10 mini a,ca,ba,cb mum monthly0.09 flows, respectively (being minimumrecurrence monthly flow (standardized flows,FMRevFDRevRrisestRfallst respectively to the mean (#months).43.694.240.050.13 annual a a flow;DXLow17.13 0.98unitless),0.030.08 and DT2: respectively; 40.86du3.210.040.07ration bab,c b ofTMaxM extreme37.140.580.06 and low TMinM: flow138.615.290.150.14 cond timing ac c c itions of the and44.081.160.060.07 maximum of 2-year and recurrence106.494.330.10 mini a,cac cd mum flow monthly42.09 2.060.09events flows,(#days); respectively FMRev, FDRev, (being andminimum extreme low monthly flows (# flows, perDMinMDXLowFMRevTT2DT2 year), respectively respectively; (#months).32.3737.6564.321.864.24 Rrisest a a and DXLow Rfallst:15.2613.4317.950.500.98 and daily DT2: rate13.3061.67 of97.55du3.211.86 flowration b a rise of and extreme17.47 fall,16.3830.550.580.36 respectively low flow100.1246.603.38 3.215.29 (standardized cond a b itions and27.30 to11.522.491.162.92 the of mean2-year annual 152.77recurrence38.424.332.786.65 flow; c b unitless). flow78.3623.17 2.822.065.99events Further (#days); details FMRev, on FDRev, TMaxMTMinMTXLow 293.6910.861.52 a 112.210.620.66 298.9311.862.00 b 103.720.000.53 106.893.29 8.25 b 94.623.245.20 89.138.394.56 c 83.612.474.61 hydrologicalTable variables 1 footer: are available Reg: inpercentage Annex 1. of regulationaa (%); MMaxMst, MMibba nMst, and MT2st: magnitudeccb of maximum monthlya,b,c a,cflow,b minimum monthly flow, and 2-year 1 May andTable 12 April). 1 footer: FXLowFDRevTXLowRfallst Reg: percentageand TT2: timing43.691.10 0.05of regulation aa a of the extreme 17.130.54(%);0.03 MMaxMst, low fl40.86ows1.020.04 MMi b bb,cand ba nMst, of 2-year 37.14and2.400.06 recurrenceMT2st: magnitude138.616.940.14 flow cc c b (Julian of maximum 44.08days);5.710.06 DMaxM monthly106.493.870.10 and a,ccc flow,cb DMin minimumM:42.096.21 0.09duration mont ofhly the flow, maximum and 2-year and and1 May FXLow: and 12 frequency April).DMaxM DXLowFMRevFDRevTXLow ofDT2 the monthly and TT2: flow timing37.6564.3243.691.324.24 reversals, a a of the dailyextreme13.4317.9517.130.520.98 flow low reversals, fl13.3097.5540.861.71ows3.21 b anda and ofextreme 2-year16.3837.1430.550.470.58 low recurrence flows138.61 46.605.31(# 3.215.29 flowper bc year), (Julian respectively; 11.5244.084.25days);2.491.16 DMaxM Rri106.4938.424.336.836.65sest and b d and DMin Rfallst:M:23.1742.093.142.065.99 duration daily rate of of the flow maximum rise and fall,and and FXLow: frequencyTMinMTXLow TT2of the monthly flow293.6932.3710.86 reversals, a daily112.2115.260.66 flow reversals,298.9361.6711.86 b and extreme103.7217.470.53 low flows106.89100.12 8.25 (# per a year), respectively;94.6227.305.20 Rri152.77 89.134.56sest c and Rfallst:78.3683.614.61 daily rate of flow rise and fall, a b ac a,b,ca,b recurrenceTable flow 1(standardized footer:FXLowRrisest Reg: percentageto the mean0.131.10 of annual regulationaa a flow; unitless),0.540.08(%); MMaxMst, respectively;1.020.07 MMi ab ba nMst, TMaxM and2.400.06 and MT2st: TMinM: magnitude0.156.94 timing ac cb ofof the maximum5.710.07 maximum monthly and3.870.10 mini a,b,c a,caflow,c b mum minimum monthly6.210.09 montflows,hly respectively flow, and (being2-year minimumrecurrenceminimum monthly monthlyflow (standardized flows,flows,DMinMFMRevFXLowFDRevDT2 respectivelyrespectively to the mean (#months).(#months).64.3243.691.861.104.24 annual aa flow;DXLowDXLow 17.9517.130.50unitless),0.980.54 and and DT2:DT2: respectively; 97.5540.86du1.86du3.211.02rationration b b ofTMaxMof extremeextreme37.1430.550.360.582.40 and lowlow TMinM: flowflow138.6146.603.385.296.94 cond condtiming c c itionsitions of the andand11.5244.082.921.165.71 maximum ofof 2-year2-year and recurrencerecurrence106.493.8738.424.332.78 mini c d mum flowflow monthly 23.1742.092.82 6.212.06eventsevents flows, (#days);(#days); respectively FMRev, FMRev, FDRev,FDRev, (being respectivelyrespectively (standardized(standardizedDMaxMTXLowTT2 toto thethe meanmean annualannual293.6932.371.32 a flow;flow; unitless).unitless).112.2115.260.52 FuFurtherrther298.9361.671.71 detailsdetails a onon hydrologicalhydrological103.7217.470.47 vavariables106.89riables100.125.31 b areare availableavailable94.6227.304.25 inin AnnexAnnex152.77 89.13 6.83 1.1. b 78.3683.613.14 a b ac a,ba,c RrisestRfallst 0.050.13 a a 0.080.03 0.070.04 b,cb a 0.06 0.150.14 cac b 0.060.07 0.10 a,b,ca,ba,cc b 0.09 1andrecurrence1 MayMay FXLow: andand flow1212 frequency April).April). (standardized DXLow TXLowFMRevFXLowFDRevRrisestTXLow of the monthly and andto the TT2:TT2: mean flow timing37.65timing43.690.131.104.24 annual reversals, a ofof theflow;the dailyextremeextreme13.43 17.13unitless),0.980.540.08 flow lowlow reversals, respectively; flfl13.30ows40.86ows3.211.020.07 ba and and and of TMaxMofextreme 2-year2-year16.3837.140.582.400.06 and low recurrence recurrence TMinM:flows138.61 3.210.15(#5.296.94 flow flowtimingper ac year), (Julian(Julian of the respectively; days);44.082.49days);1.165.710.07 maximum DMaxMDMaxM Rriand106.493.870.104.336.65sest andminiand ac and DMinDMinmum Rfallst: M:M:monthly42.095.99 6.210.092.06 durationduration daily flows, rate ofof of therespectivelythe flow maximummaximum rise and (being andfall,and and FXLow: frequencyDMaxMDMinM TT2of the monthly flow32.371.321.86 reversals, a daily15.260.520.50 flow reversals,61.671.711.86 b and extreme17.470.470.36 low flows100.123.385.31 (# per c year), respectively;27.304.252.92 Rri152.772.786.83sest dand Rfallst:78.362.823.14 daily rate of flow rise and fall, a b c a,c Table 1 footer:Rfallst Reg: percentage 0.05of regulation a a (%);0.03 MMaxMst,0.04 MMi b a nMst, and0.06 MT2st: magnitude0.14 acc b of maximum0.06 monthly0.10 a,b,c a,ba,cflow,c b minimum0.09 monthly flow, and 2-year minimum1 May and monthly 12 April). flows,DXLow FXLowFDRevRrisestTXLowRfallstDT2 respectively and TT2: (#months). 37.6564.32timing43.690.050.131.10 a a of theDXLow extreme13.4317.9517.130.030.540.08 and lowDT2: fl13.30 97.5540.86duows0.041.020.07ration ab,c and of extreme2-year16.3830.5537.140.062.40 recurrence low flow138.6146.60 3.210.150.146.94 condflow ac itions(Julian and 11.5244.082.49days);0.065.710.07 of 2-year DMaxM recurrence106.493.8738.420.106.65 and ac DMin flowM:23.17 42.095.996.210.09events duration (#days); of the FMRev, maximum FDRev, and respectivelyminimumrespectively monthly (standardized(standardized flows,DMaxMDMinM respectivelytoto thethe meanmean annual(#months).annual1.321.86 a flow;flow; DXLow unitless).unitless).0.520.50 and FuFu DT2:rtherrther 1.711.86du detailsdetailsration b onon of hydrological hydrologicalextreme0.470.36 low va vaflowriablesriables3.385.31 cond c areareitions availableavailable and4.252.92 of inin 2-year AnnexAnnex recurrence 2.786.83 1.1. c flow2.823.14 events (#days); FMRev, FDRev, recurrenceTable flow 1 (standardized footer: Reg: percentage to the mean of annual regulationaa flow; (%);unitless), MMaxMst, respectively; MMibb nMst, TMaxM and and MT2st: TMinM: magnitude timingcac ofof themaximum maximum monthly and minia,b,c a,ca,ba,cflow,mum minimum monthly mont flows,hly respectively flow, and (being2-year Table 1 footer:FMRevFXLowRrisestRfallstDT2 Reg: percentage64.324.24 0.050.131.10of regulation a 17.950.98(%);0.030.540.08 MMaxMst,97.553.210.041.020.07 MMi b,cb nMst, 30.55and0.580.062.40 MT2st: magnitude46.605.290.150.146.94 c c of maximum11.521.160.065.710.07 monthly3.8738.424.330.10 c cflow, minimum23.172.066.210.09 monthly flow, and 2-year andminimumand FXLow:FXLow: monthly frequencyfrequency flows,DMinMDXLow ofof thethe respectively monthlymonthly flow flow(#months).37.651.86 reversals,reversals, a DXLow dailydaily13.430.50 flowand flow DT2: reversals,reversals,13.30 1.86duration a and and ofextremeextreme extreme16.380.36 low low low flowsflows flow 3.38 3.21 (#(# cond perper a year),year),itions respectively;respectively;and2.492.92 of 2-year RriRri recurrence2.786.65sestsest a andand Rfallst: Rfallst:flow2.825.99 events dailydaily rate(#days);rate ofof flowflow FMRev, riserise andand FDRev, fall,fall, FDRevRrisest 43.690.13 aa 17.130.08 40.860.07 b ba 37.140.06 138.610.15 cac b 44.080.07 106.490.10 a,ca,ba,c b 42.090.09 recurrence1recurrence May andTable flowflow12 April). 1 (standardized(standardized footer: FMRevTXLowRfallst Reg: percentageand toto thethe TT2: meanmean timing4.24 0.05of annualannual regulation a of flow;theflow; extreme unitless),0.98(%);unitless),0.03 MMaxMst, low respectively;respectively; flows3.210.04 MMi b,cband nMst, TMaxMofTMaxM 2-year and0.580.06 andand recurrenceMT2st: TMinM:TMinM: magnitude5.290.14 flow timingtiming cc (Julian ofofof the themaximum days);1.16 0.06 maximummaximum DMaxM monthly andand4.330.10 miniandmini ccflow, DMinmummum minimum M:monthlymonthly2.06 0.09duration mont flows,flows, ofhly respectivelytherespectively flow, maximum and (being(being2-year and respectivelyandrespectively FXLow: (standardized(standardizedfrequencyDXLow DT2of the toto themonthlythe meanmean flow annualannual37.6564.32 reversals, flow;flow; unitless).unitless). daily13.4317.95 flow FuFu rtherreversals,rther13.3097.55 detailsdetails and onon extreme hydrologicalhydrological16.3830.55 low flows vavariablesriables46.60 3.21 (# per areare year), availableavailable respectively;11.522.49 inin AnnexAnnex Rri38.42 6.65 1.1.sest and Rfallst:23.175.99 daily rate of flow rise and fall, FXLowRfallst 1.100.05 aa 0.540.03 1.020.04 bba 2.400.06 6.940.14 cc b 5.710.06 3.870.10 a,b,c a,cb 6.210.09 minimum1recurrence May andTable monthly flow12 April). 1 (standardized footer: flows, FMRevFDRevTXLow Reg: respectively percentageand to the TT2: mean (#months). timing43.694.24 of annual regulationa a of theflow;DXLow extreme 17.13 0.98(%);unitless), and MMaxMst, lowDT2: respectively; fl 40.86owsdu3.21 rationMMi b band nMst, ofTMaxM 2-yearextreme 37.14and0.58 and recurrenceMT2st: low TMinM: flow magnitude138.615.29 flowcond timing c c itions(Julian ofof the maximumand 44.08days);1.16 maximum of 2-year DMaxM monthly and recurrence106.494.33 andmini a,c cflow, DMinmum flowminimum M:monthly42.09 2.06 eventsduration mont flows,(#days); ofhly therespectively flow,FMRev, maximum and FDRev, (being2-year and 1respectively May and 12 (standardized April). TXLowDT2 to theand mean TT2: annual64.32timing flow;of the unitless). extreme17.95 Fulowrther fl97.55ows details and on of hydrological2-year30.55 recurrence variables46.60 flow are (Julian available 11.52days); in DMaxMAnnex38.42 1. and DMinM:23.17 duration of the maximum and Rrisest 0.13 a 0.08 0.07 b 0.06 0.15 ac 0.07 0.10 a,b,ca,b 0.09 recurrenceTable flow 1 (standardized footer:FXLow Reg: percentage to the mean1.10 of annual regulationaa flow; 0.54(%);unitless), MMaxMst, respectively;1.02 MMi ba nMst, TMaxM and2.40 and MT2st: TMinM: magnitude6.94 timing c b ofof themaximum5.71 maximum monthly and3.87 mini a,c flow,b mum minimum monthly6.21 mont flows,hly respectively flow, and (being2-year minimumandminimum1 May FXLow: and monthlymonthly 12 frequency April). flows,flows, FMRevFDRevTXLow of the respectivelyrespectively monthly and TT2: flow (#months).(#months). 43.69timing4.24 reversals, of theDXLowDXLow dailyextreme17.130.98 and flowand lowDT2: DT2:reversals, fl 40.86 du3.21owsdurationration and and ofofextreme extreme2-yearextreme37.140.58 low recurrence lowlow flows flowflow138.61 5.29(# cond flowcondper year), itionsitions(Julian respectively;andand 44.081.16days); ofof 2-year2-year DMaxM Rri recurrence106.49recurrence4.33sest and and DMin Rfallst: flowflowM:42.09 2.06 events eventsduration daily (#days);rate(#days); of of the flow FMRev, FMRev, maximum rise and FDRev,FDRev, fall,and a b c a,c RrisestRfallst 0.050.13 a 0.080.03 0.070.04 b 0.06 0.150.14 ac 0.060.07 0.10 a,b,ca,b 0.09 recurrence1 May and flow12 April). (standardized FXLowFDRevTXLow andto the TT2: mean 43.69timing1.10 annual a of flow;the extreme17.13 0.54unitless), low respectively; fl40.861.02ows a and TMaxMof 2-year37.142.40 and recurrence TMinM:138.616.94 flowtiming b (Julian of the 44.085.71days); maximum DMaxM and106.493.87 miniand b DMinmum M:monthly42.096.21 duration flows, of respectivelythe maximum (being and andrespectivelyminimumand FXLow:FXLow: monthly (standardizedfrequencyfrequency flows, ofof thethe respectivelyto monthlythemonthly mean flow flowannual(#months). reversals,reversals, flow; DXLow unitless). dailydaily flowandflow Fu DT2: reversals,rtherreversals, du detailsration andand on ofextremeextreme hydrological extreme lowlow low flowsflows va flowriables (#(# cond perper are year),year),itions available respectively;respectively;and of in 2-year Annex RriRri recurrence 1.sestsest andand Rfallst: Rfallst:flow events dailydaily rate(#days);rate ofof flowflow FMRev, riserise andand FDRev, fall,fall, Table 1 footer:Rfallst Reg: percentage 0.05of regulation a (%);0.03 MMaxMst,0.04 MMi b nMst, and0.06 MT2st: magnitude0.14 ac of maximum0.06 monthly0.10 a,ba,cflow, minimum0.09 monthly flow, and 2-year minimum1 May and monthly 12 April). flows, FXLowRrisestTXLow respectively and TT2: (#months). timing0.131.10 a of theDXLow extreme0.540.08 and lowDT2: fl 1.020.07owsduration b and of 2-yearextreme2.400.06 recurrence low flow0.156.94 flowcond c itions(Julian and 5.710.07days); of 2-year DMaxM 3.87recurrence0.10 and a,b,c DMin flowM:6.210.09 eventsduration (#days); of the FMRev, maximum FDRev, and respectivelyandrespectively FXLow: (standardized(standardizedfrequency of the toto themonthlythe meanmean flow annualannual reversals, flow;flow; unitless).unitless). daily flow FuFu rtherreversals,rther detailsdetails and onon extreme hydrologicalhydrological low flows vavariablesriables (# per areare year), availableavailable respectively; inin AnnexAnnex Rri 1.1.sest and Rfallst: daily rate of flow rise and fall, recurrenceTable flow 1 (standardized footer: Reg: percentage to the mean of annual regulationa flow; (%);unitless), MMaxMst, respectively; MMib nMst, TMaxM and and MT2st: TMinM: magnitude timingac ofof themaximum maximum monthly and mini a,ba,cflow,mum minimum monthly mont flows,hly respectively flow, and (being2-year minimum monthly flows,RrisestRfallst respectively (#months).0.050.13 DXLow0.080.03 and DT2: 0.070.04duration of extreme0.06 low flow0.150.14 cond itions and0.060.07 of 2-year recurrence0.10 flow0.09 events (#days); FMRev, FDRev, andrespectively FXLow: (standardizedfrequency of the to monthlythe mean flow annual reversals, flow; unitless). daily flow Fu reversals,rther details and on extreme hydrological low flows variables (# per are year), available respectively; in Annex Rri 1.sest and Rfallst: daily rate of flow rise and fall, recurrence1 May andTable flow12 April).1 (standardized footer: TXLowRfallst Reg: percentage andto the TT2: mean timing 0.05of annual regulation a of flow;the extreme (%);unitless),0.03 MMaxMst, low respectively; flows0.04 MMi band nMst, TMaxMof 2-year and0.06 and MT2st:recurrence TMinM: magnitude0.14 flowtiming c (Julian ofof themaximum days);0.06 maximum DMaxM monthly and0.10 miniand a,cflow, DMinmum minimum M:monthly0.09 duration mont flows, ofhly respectivelythe flow, maximum and (being2-year and andrespectively FXLow: (standardizedfrequency of the to monthlythe mean flow annual reversals, flow; unitless). daily flow Fu reversals,rther details and on extreme hydrological low flows variables (# per are year), available respectively; in Annex Rri 1.sest and Rfallst: daily rate of flow rise and fall, recurrenceminimum1 May andTable monthly flow12 April).1 (standardized footer: flows, TXLow Reg: respectively percentage andto the TT2: mean (#months). timing of annual regulation of flow;theDXLow extreme (%);unitless), and MMaxMst, lowDT2: respectively; fl owsdu MMiration andnMst, TMaxMof 2-yearextreme and and MT2st:recurrence low TMinM: flow magnitude flowcondtiming itions(Julian ofof themaximum and days); maximum of 2-year DMaxM monthly and recurrence miniand flow, DMinmum flowminimum M:monthly eventsduration mont flows, (#days); ofhly respectivelythe flow, FMRev, maximum and FDRev, (being2-year and respectively (standardized to the mean annual flow; unitless). Further details on hydrological variables are available in Annex 1. recurrenceminimum1and May FXLow: and monthly flow12 frequency April). (standardized flows, TXLow of the respectively monthly andto the TT2: mean flow(#months). timing annual reversals, of flow;theDXLow dailyextreme unitless), andflow lowDT2: reversals, respectively; fl owsduration and and TMaxMof extreme 2-yearextreme and lowrecurrence low TMinM: flows flow (# flowcondtiming per year),itions(Julian of the respectively;and days); maximum of 2-year DMaxM Rriand recurrencesest miniand and DMinmum Rfallst:flow M:monthly eventsduration daily flows, (#days);rate of of respectivelythe flow FMRev, maximum rise and FDRev, (being andfall,

minimum1andrespectively May FXLow: and monthly 12 (standardizedfrequency April). flows, TXLow of the respectivelyto monthlytheand mean TT2: flow (#months). annualtiming reversals, flow;of theDXLow unitless). dailyextreme andflow Fu lowDT2: reversals,rther fl owsdu detailsration and and on of extreme hydrological2-yearextreme lowrecurrence low flows vaflowriables (# flowcond per are year),itions(Julian available respectively;and days); of in 2-year DMaxMAnnex Rri recurrence 1.sest and and DMin Rfallst:flowM: eventsduration daily (#days);rate of of the flow FMRev, maximum rise and FDRev, andfall, minimumandrespectively FXLow: monthly (standardizedfrequency flows, of the respectivelyto monthlythe mean flow (#months).annual reversals, flow; DXLow unitless). daily andflow Fu DT2: reversals,rther du detailsration and on ofextreme hydrologicalextreme low low flows vaflowriables (# cond per are year),itions available respectively;and of in 2-year Annex Rri recurrence 1.sest and Rfallst:flow events daily (#days);rate of flow FMRev, rise and FDRev, fall, andrespectively FXLow: (standardizedfrequency of the to monthlythe mean flow annual reversals, flow; unitless). daily flow Fu reversals,rther details and on extreme hydrological low flows variables (# per are year), available respectively; in Annex Rri 1.sest 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. Forests 2020, 11, 518 6 of 18

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 (Table1). 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 Forests 2020, 11, 518 7 of 18 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 (Table1). 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 (Figure2a). 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 (Figure2a). 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 (Figure2a). 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 (Figure2b). 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 (Figure2b). Across all functional groups, the relative presence of most species correlated negatively with the degree of flow regulation (Figures3a and4; 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 (Figure3a). 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) (Figure3a). The strength of the relationship did not di ffer 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 (Figure3a). 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 (Figure3b 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 (Figure3b and Annex 3). No woody species were restricted to reaches with a higher flow regimes. Forests 2020, 11, 518 8 of 18 Forests 2020, 11, x FOR PEER REVIEW 8 of 18 Forests 2020, 11, x FOR PEER REVIEW 8 of 18

250 250 a) a) Woody Woody Graminoid 200 Graminoid 200 Forb Forb

150 150

100 100 Species richness (#) Species richness (#) 50 50

0 0 Free-flowing Low Moderate High Free-flowing Low Moderate High

100% 100% b)b) 90% 90% 80% 80% 70% 70% 60% 60% 50% 50% 40% 40% 30% 30% Realtive abundance (%)

Realtive abundance (%) 20% 20% 10% 10% 0% 0% Free-flowing Low Moderate High Free-flowing Low Moderate High Regulation group Regulation group

FigureFigure 2. 2.( a()a Species) Species richness richness within within each each life formlife form group gr foroup each for flow each regulation flow regulation group and group (b) relativeand (b) Figure 2. (a) Species richness within each life form group for each flow regulation group and (b) abundancerelative abundance of eachlife of each form life group form for group each for flow each regulation flow regulation group. group. Regulation Regulation groups groups involve involve the relative abundance of each life form group for each flow regulation group. Regulation groups involve followingthe following levels levels of regulation: of regulation: free-flowing free-flowing (<0%), (<0%), low (> 0%low and (>0%<15%), and moderate<15%), moderate (>15% and (>15%<60%), and the following levels of regulation: free-flowing (<0%), low (>0% and <15%), moderate (>15% and and<60%), high and (>60%). high (>60%). <60%), and high (>60%).

100 Woody 100 a)a) Woody 90 Graminoid 90 Graminoid 80 Forb 80 Forb 70 70 60 60 50 50 40 40 30 30 20

Relative number of species (%) 20 Relative number of species (%) 10 10 0 0 Negative Positive Impassive Negative Positive Impassive

Figure 3. Cont. Figure 3. ContCont.. Forests 2020, 11, 518 9 of 18 Forests 2020, 11, x FOR PEER REVIEW 9 of 18

100 b) 90 80 70 60 50 40 30 20 Relative Relative number species of (%) 10 0 Disappear (Reg>15%) Disappear (Reg>60%) Appear (Reg>15%) Appear (Reg>60%) Species response to flow regulation

Figure 3. Fraction of species separated by their response to flow regulation for each life form group. 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 (increasinga) Fraction degrees of the oftotal regulation. species pool (b) A which specification showed of negative, the above positive, showing or the impassive fraction of responses total species to increasingthat disappeared degrees or of appeared regulation. at reaches(b) A specification with beyond of moderate the above flow showing regulation the fraction (>15%) of or total in the species high thatflow disappeared regulation category or appeared (>60%). at reaches with beyond moderate flow regulation (>15%) or in the high flow regulation category (>60%). The three CCA models (i.e., for woody species, graminoids, and forbs) were statistically significant (TableThe2). Thethree first CCA two models CCA components (i.e., for woody were significant species, ingraminoids, each CCA model,and forbs) whereas were the statistically third and significantfourth components (Table 2). were The significantfirst two CCA for the components woody and were forb significant species but in not each for CCA the graminoid model, whereas species the(Table third2). Theand highestfourth components cumulative variancewere significant was observed for the in woody woody and species, forb species for which but the not selected for the graminoidhydrological species variables (Table explained 2). The uphighest to 52% cumulative of the variance variance in thewas first observed three axes, in woody whereas species, 49% andfor which40% variance the selected was explainedhydrological by variables the first three explained axes forup graminoidsto 52% of the and variance forbs, in respectively the first three (Table axes,2). whereasWoody species 49% and showing 40% variance positive, was negative, explained and impassiveby the first trends three inaxes response for graminoids to increased and degrees forbs, respectivelyof flow regulation (Table 2). were Woody well species segregated showing in CCA posi space.tive, negative, Negative and trends impassive were trends found in for response toSalix increased glauca L., degrees mosses of (Lycopodium flow regulation selago were(L.) Bernh. well segregated ex Schrank in & CCA Mart. space. and L., Negative annotinum trendsL.), heaths were found(Vaccinium for willow microcarpum Salix glaucaAiton, LVaccinium., mosses ( oxycoccosLycopodiumL., selagoAndromeda (L.) Bernh. polifolia exL., Schrank and Ledum & Mart. palustre andL.), L. annotinumBetula nana LL.,.), heathsLinnaea (Vaccinium borealis L., microcarpum and Rosa majalis Aiton,Herrm., Vaccinium whereas oxycoccos most L., Andromeda (Salix polifolia herbacea L., andL., LedumSalix lapponum palustre L.L. and), BetulaSalix nana pentandra L., LinnaeaL., Salix borealis lanata LL.,., Salixand Rosa triandra majalisL., Salix Herrm hastata., whereasL., and Salixmost cinerea willowsL.) (alongSalix herbacea with other L., Salix shrubs lapponum such as L the. and black Salix and pentandra red currants L., Salix (Ribes lanata ningrum L., SalixL. triandra and Ribes L., Salix rubrum hastataL.), Lraspberry., and Salix (Rubus cinerea idaeus L.) alongL.), and with trees other such shrubs as birches such as(Betula the black pendula andRoth red andcurrants Betula (Ribes pubescens ningrumEhrh.) L. andshowed Ribes marked rubrum positive L.), raspberry or impassive (Rubus trends idaeus with L.), regulationand trees such (Figures as birches4 and5; (Betula Annex 5).pendula Hydrological Roth and Betulavariables pubescens that were Ehrh strongly.) showed correlated marked topositive woody or species impassive arrangement trends with in CCA regulation space were(Figures related 4 and to 5;the Annex percentage 5). Hydrological of regulation, variables extreme that low were flow strongly conditions correlated (duration, to frequency,woody species and timing), arrangement monthly in CCAflows space (magnitude were related of maximum to the and percentage minimum), of regu and dailylation, flows extreme (frequency low flow of reversals conditions and (duration, fall rates) frequency,(Figure5 and and Table timing),2). In general,monthly woody flows (magnitude species with of positive maximum and impassiveand minimum), trends wereand daily separated flows (frequencyalong the second of reversals axis that and aligned fall rates) with (Figure a higher 5 and percentages Table 2). In of general, regulation woody and species related with hydrological positive andcharacteristics impassive suchtrends as were shorter, separated more frequent, along the and second earlier axis extreme that aligned low flow with periods; a higher lower percentages maximum of regulationbut higher and minimum related monthlyhydrological flows; characteristics and more frequent such as and shorter, faster more daily frequent, flow reversals. and earlier These extreme latter lowtwo flow had highestperiods; loading lower maximum on the second but higher axis (Figure minimum5 and monthly Table2). flows; The opposite and more was frequent true for and species faster dailycharacterized flow reversals. by negative These trends. latter two had highest loading on the second axis (Figure 5 and Table 2). The opposite was true for species characterized by negative trends.

Forests 2020, 11, 518 10 of 18 Forests 2020, 11, x FOR PEER REVIEW 10 of 18

20 a) 15 10 5 0 -5 -10 -15

Slope of the fitted line fitted of the Slope -20 -25 Fral Satr Potr Pisy Saci Sala Rini Piab Sagl Alin Riru Aral Juco Prpa Lycl Libo Saca Saau Vaul Lyse Vavi Saha Ruid Sape Sahe Lepa Soau Lyan Bena Aruu Bepe Cavu Bepu Vaox Anpo Vami Salap Myga Roma Dame Vamy Samyr Emnih Samyrt Woody

20 15 b) 10 5 0 -5 -10 -15

Slope of the fitted line -20 -25 Jutr Jufi Glli Just Jual Potr Cali Scla Cafl Eqfl Fevi Elac Pagl Cast Ersc Poal Defl Fepr Cate Phar Cael Elpa Alpr Feru Cala Nast Calo Alae Popr Cadi Jubu Vaat Eqar Cabi Scsy Eran Lupi Cani Erva Agst Cagl Scce Mief Cary Casa Caor Alge Cabr Caro Eqpr Cace Poan Aggi Lusu Lusp Feov Caec Schu Popa Caac Caca Eqsy Caaq Cade Cach Caep Dece Lupa Capa Caoe Phlal Cave Cava Eqpa Capu Eqhy Cabu Agca Caliv Phlpr Elyre Jubul Hovu Anod Calas Cadis Elyca Moca Came Phrau Cama Menu Lupar Eqvar Cadio Agme Spspp Cacap Cacan Capan Capau Cacho Agcap Elymu Cacapi Camag Hihi+od Graminoid

20 c) 15 10 5 0 -5 -10 -15 Slope of the fitted line -20 -25 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 160 163 166 169 172 175 178 181 184 187 190 193 196 199 202 205 208 211 214 217 220 Forb

FigureFigure 4. 4. RegressionRegression coefficients coefficients of of the the species-specific species-specific linear linear regressi regressionsons between between the the relative relative presence presence of of a a species species and and the the mean mean perc percentageentage of of regulation regulation separated separated forfor each each life formform groupgroup (Woody(Woody species species (a (a),), graminoids graminoids (b (b)) and and forbs forbs (c )).(c)). Di Differentfferent regression regression coe coefficientsfficients are indicatedare indicated with wit a lineh a belowline below and withand arrowswith arrows at the at top the of topeach. of Theeach. full The names full names of the of species the species are in are Annex in Annex 1. 1. Forests 2020, 11, 518 11 of 18

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 Table1 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) CCA1 CCA2 CCA3 CCA1 CCA2 CCA3 CCA1 CCA2 CCA3 Reg 0.29 0.56 0.17 0.46 0.09 0.00 0.14 0.08 0.47 − − − MMaxM_std 0.07 0.46 0.11 0.22 0.07 0.06 0.11 0.19 0.27 − − − − MMinM_std 0.17 0.55 0.03 0.11 0.18 0.13 0.17 0.04 0.40 − − − − − MT2_std 0.08 0.28 0.10 0.28 0.04 0.14 0.03 0.25 0.07 − − − − TMaxM 0.29 0.13 0.30 0.37 0.01 0.22 0.21 0.06 0.24 − − − − TMinM 0.01 0.22 0.03 0.04 0.39 0.05 0.22 0.21 0.53 − − − − − TXLow 0.01 0.46 0.29 0.04 0.18 0.20 0.10 0.22 0.32 − − − − − TT2 0.30 0.39 0.50 0.72 0.26 0.11 0.30 0.22 0.56 − − − − DMaxM 0.00 0.35 0.33 0.14 0.01 0.25 0.09 0.07 0.07 − − − − − − DMinM 0.41 0.35 0.34 0.04 0.11 0.32 0.29 0.24 0.04 − − − − − − DXLow 0.46 0.14 0.04 0.40 0.14 0.67 0.54 0.29 0.41 − − − − − DT2 0.10 0.28 0.21 0.27 0.32 0.32 0.20 0.38 0.36 − − − − − FMRev 0.15 0.17 0.59 0.31 0.13 0.47 0.12 0.64 0.05 − − − − FDRev 0.03 0.63 0.01 0.21 0.30 0.27 0.01 0.17 0.64 − − − FXLow 0.43 0.66 0.15 0.45 0.18 0.34 0.18 0.09 0.53 − − − − RRise_std 0.17 0.15 0.13 0.02 0.17 0.33 0.08 0.26 0.34 − − RFall_std 0.34 0.60 0.04 0.41 0.14 0.26 0.24 0.07 0.53 − − − − Eigenvalue 0.10 0.07 0.05 0.14 0.12 0.08 0.18 0.13 0.09 Proportion 0.23 0.17 0.12 0.20 0.17 0.12 0.18 0.13 0.09 Explained Significance of axis p = 0.001 p = 0.001 p = 0.027 p = 0.049 p = 0.072 p = 0.113 p = 0.001 p = 0.001 p = 0.003 Forests 2020, 11, 518 12 of 18 Forests 2020, 11, x FOR PEER REVIEW 11 of 18

(a) Woody - Hydrological variables (d) Woody species 1 4

FDRev Rfall FXLow 3 MMinM Reg 0.5 2

1 0 -1 -0.5 0 0.5 1 0 DXLow -2.5 -1.5 -0.5 0.5 1.5 2.5 3.5 4.5 -1 -0.5 MMaxMTXLow Negative -2 Impassive

-1 -3 Positive

(b) Graminoid - Hydrological variables (-9, 10) (e) Graminoids (-2, 7) 1 4

3 0.5 2 TT2 FXLow Reg 1 0 -1 -0.5 0 0.5 1 0 -2.5-2-1.5-1-0.500.511.522.5 -1 -0.5

-2

-1 -3

(c) Forb - Hydrological variables (f) Forbs 1 4

FMRev 3 0.5 2

1 0 -1 -0.5 0 0.5 1 0 -2.5-2-1.5-1-0.500.511.522.5 DXLow -1 -0.5

-2

-1 -3 Figure 5. Biplots of the canonical correspondence analyses (CCA) (CCA) on on woody ( aa,,d),), graminoid graminoid ( (bb,,ee),), and forbforb ( c,(fc),f presence–absence) presence–absence species species data. data. (a–c) represent(a–c) represent the canonical the canonical loadings for loadings the hydrological for the variables,hydrological and variables, (d–f) show and species (d–f) scores.show species For a better scores. visualization, For a better onlyvisualization, hydrological only variables hydrological with variablesloadings ofwith>0.5 loadings are labeled. of >0.5 Each are point labeled. is one Each species, poin witht is one the fillspecies, color representingwith the fill speciescolor representing response to speciesincreased response flow regulation to increased being: flow negative regulation (white being: dots), negative positive (white (black dots), positive and impassive (black (greydots), dots) and impassivetrends. The (grey two dots) dots trends. at the topThe lefttwo cornerdots at inthe (e top) represent left corner two in species(e) represent outside two the species range outside of the x-the and range y-axes; of the their x- and coordinates y-axes; their are indicated coordinates between are indicated parentheses. between An explanation parentheses. of An the explanation codes of the ofhydrological the codes of variables the hydrological are in Table vari1 andables Annex are in 1.Table 1 and Annex 1.

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 (Figure5). 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. (Figures4 and5, Annex 5). Positive and impassive trends were frequently observed in the genus Poa sp., Carex sp, and 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., Forests 2020, 11, 518 13 of 18

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 (Figures4 and5; 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 (Figure5). 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 (Figure5). 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 (Figure4), but all were scattered throughout the biplot (Figure5 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 (Figure5 and Table2). 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 (Table2).

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 [29–31]. 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 Forests 2020, 11, 518 14 of 18 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 , and other studies on the effect of river regulation on species diversity have frequently associated reduced species richness with difficulties in germination and establishment [32–35]. 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 [30,32,38–40]. 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 [43–45]. 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 Forests 2020, 11, 518 15 of 18 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: http://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 Figure4). 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. Forests 2020, 11, 518 16 of 18

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