Interacting effects of fertilization, mowing and grazing on plant species diversity of 1500 grasslands in Germany differ between regions

Basic and Applied Ecology 14 (2013) 126–136

Interacting effects of fertilization, mowing and grazing on plant species diversity of 1500 grasslands in Germany differ between regions Stephanie A. Sochera,∗ , Daniel Pratia , Steffen Bocha , Jörg Müllerb , Henryk Baumbachb,c , Sonja Gockele,l , Andreas Hempb,j , Ingo Schöningd,e , Konstans Wellsf,g , Franc¸ois Buscoth,k , Elisabeth K.V. Kalkof,1 , Karl Eduard Linsenmairi , Ernst-Detlef Schulzed , Wolfgang W. Weissere,l , Markus Fischera,b a

Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland Institute of Biochemistry and Biology, University of Potsdam, Maulbeerallee 1, D-14469 Potsdam, Germany c Institute of Botany, Herbaria Haussknecht, Botanical Garden, University Jena, Philosophenweg 16, D-07743 Jena, Germany d Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745 Jena, Germany e Institute of Ecology, Friedrich-Schiller-University Jena, Dornburgerstr. 159, D-07743 Jena, Germany f Institute of Experimental Ecology, University of Ulm, Albert-Einstein Allee 11, D-89069 Ulm, Germany g Biodiversity and Climate Research Centre (BiK-F), D-60325 Frankfurt (Main), Germany h Helmholtz Centre for Environmental Research – UFZ, Department of Soil Ecology, Theodor-Lieser-Strasse 4, D-06120 Halle, Germany i Theodor-Boveri-Institute for Biosciences, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany j Department of Plant Systematics, University of Bayreuth, Universitätsstr. 30, D-95447 Bayreuth, Germany k Chair of Soil Ecology, Institute of Biology, University of Leipzig, Johannis-Allee 21-23, D-04103 Leipzig, Germany l Department of Ecology and Ecosystem Management, Terrestrial Ecology, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, D-85350 Freising, Germany b

Received 25 January 2012; accepted 20 December 2012 Available online 20 January 2013

Abstract The relationship of different types of grassland use with plant species richness and composition (functional groups of herbs, legumes, and grasses) has so far been studied at small regional scales or comprising only few components of land use. We comprehensively studied the relationship between abandonment, fertilization, mowing intensity, and grazing by different livestock types on plant diversity and composition of 1514 grassland sites in three regions in North-East, Central and SouthWest Germany. We further considered environmental site conditions including soil type and topographical situation. Fertilized grasslands showed clearly reduced plant species diversity (−15% plant species richness, −0.1 Shannon diversity on fertilized grasslands plots of 16 m2 ) and changed composition (−3% proportion of herb species), grazing had the second largest effects and mowing the smallest ones. Among the grazed sites, the ones grazed by sheep had higher than average species richness (+27%), and the cattle grazed ones lower (−42%). Further, these general results were strongly modulated by interactions between the different components of land use and by regional context: land-use effects differed largely in size and sometimes even in direction between regions. This highlights the importance of comparing different regions and to involve a large number of plots

∗ Corresponding

author. Tel.: +41 31 631 4923; fax: +41 31 631 4911. E-mail address: [email protected] (S.A. Socher). 1 Deceased. 1439-1791/$ – see front matter © 2012 Gesellschaft für Ökologie. Published by Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.baae.2012.12.003

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when studying relationships between land use and plant diversity. Overall, our results show that great caution is necessary when extrapolating results and management recommendations to other regions.

Zusammenfassung Der Einfluss unterschiedlicher Grasland-Nutzungstypen auf den Artenreichtum und die Zusammensetzung der Pflanzen (Kräuter, Leguminosen und Gräser) wurde bisher nur auf kleiner regionaler Skala oder nur mit wenigen Landnutzungtypen getestet. In einer vergleichenden Studie zeigen wir die Effekte von Verbrachung, Düngung, Mahd und Beweidung durch unterschiedlichen Tierbestand auf Artenreichtum und Zusammensetzung der Pflanzen auf 1514 Grasländern in drei unterschiedlichen Regionen in Nordost, Zentral und Südwest Deutschland. Zusätzlich wurden standortbedingte Umweltfaktoren wie Bodentypen und topographische Daten mit einbezogen. Gedüngte Graslandflächen hatten klar reduzierte Artendiversität (−15% Artenzahl, −0.1 Shannon Diversität auf gedüngten Flächen von 16 m2 ) und veränderte Zusammensetzung (−3% Anteil an Kräutern), die Effekte der Beweidung waren am zweitgrößten und die der Mahd am kleinsten. Mahd mit mittlerer Intensität (2 Schnitte pro Jahr) und Schafbeweidung erhöhten die Artenzahl (+27%), während Rinderbeweidung die Artenzahl verringerte (−42%). Diese allgemeinen Muster wurden durch Wechselwirkungen zwischen Landnutzungstypen und durch verschiedene regionale Kontexte moduliert: die Größe und teilweise sogar Richtung der Unterschiede zwischen Landnutzungstypen unterschied sich zwischen den Regionen. Das verdeutlicht die Bedeutung, verschiedene Regionen miteinander zu vergleichen und viele Untersuchungsflächen einzubeziehen, um verläßliche Aussagen über Beziehungen zwischen Landnutzung und Artendiversität machen zu können. Zusammenfassend ist also grosse Vorsicht geboten, wenn Ergebnisse und Nutzungsempfehlungen über Regionen hinweg verallgemeinert werden sollen. © 2012 Gesellschaft für Ökologie. Published by Elsevier GmbH. All rights reserved. Keywords: Biodiversity exploratories; Functional groups; Land use type; Livestock type; Shannon diversity

Introduction Agricultural management has a strong effect on biodiversity (Houghton 1994; Sala et al. 2000; Poschlod 2005; Ellenberg & Leuschner 2010; Maskell, Smart, Bullock, Thompson, & Stevens 2010). In Germany, half of the landscape is dedicated to agriculture (47%) and 30% of the agricultural area is used as meadows or pastures. Most of these grasslands are intensively used for haymaking or cattle herding and only 5% are used in organic farming at low intensity (Statistisches Jahrbuch 2009). Highly intensively used grasslands are characterized by the application of large amounts of fertilizer (up to 400 kg/ha/year), high mowing frequencies (four to five times per year), and high stocking rates (70 livestock units/ha). On less intensively used grasslands fertilizer applications are lower or absent, sheep replace cattle as main grazers, and the first and often only cut is done late in the year to ensure successful plant recruitment (Rook et al. 2004). In Central Europe, grasslands are among the most speciesrich ecosystems, but during the last century increasing intensification has led to a species decline across many taxa. Fertilization, in particular of semi-natural and nutrient-poor grasslands, has led to a drastic decline of the diversities of plants and other taxa (Kölliker, Stadelmann, Reidy, & Nosberger 1998; Hansson & Fogelfors 2000; Fischer & Wipf 2002; Jacquemyn, Brys, & Hermy 2003; Hautier, Niklaus, & Hector 2009; Kleijn et al. 2009). Clearly, the gradient of land use intensity reflects the opposed interests between high productivity and maintenance of diversity (Klimek, Richter, Hofmann, & Isselstein 2007). In addition, as Central

European grasslands were established largely from woodlands during a long history of low-intensity anthropogenic land use, the currently ongoing abandonment of uneconomical sites and the subsequent succession threaten these systems and their diversity. A recent meta-analysis by Kleijn et al. (2009) across 130 grasslands in six European countries showed that plant species richness generally decreases with higher nitrogen input (Kleijn et al. 2009). However, other studies reported highest plant species richness at moderate levels of fertilizer application (Zechmeister, Schmitzberger, Steurer, Peterseil, & Wrbka 2003). Furthermore, fertilization intensity is often confounded with mowing intensity. A study across 84 Austrian farms showed that plant species richness decreased with simultaneously increasing mowing and fertilization intensity (Schmitzberger et al. 2005), but could not disentangle the contributions of both management factors to the observed species richness decline. In addition to fertilization and mowing, grazing intensity is a major factor influencing grassland plant diversity. Reviews suggest negative effects of more intense grazing on plant species diversity in mesotrophic grasslands (Stewart & Pullin 2008) but positive effects at higher levels of productivity (Proulx & Mazumder 1998). Such dependence of grazing effects on nutrient availability and moisture suggests that the level of grazing supporting high diversity increases with site productivity (Kondoh 2001). In addition to grazing intensity, grazing effects may differ between sheep, cattle and other livestock, although the effect of livestock type is considered less important than that of grazing intensity (Stewart & Pullin 2008). Moreover, within livestock species body size matters

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more for effects on biodiversity than breed does (Rook et al. 2004). Interpreting studies on diversity effects of land use type (fertilization, type of livestock, and grazing intensity) is often complicated by simultaneous variation of further environmental site conditions, such as slope, elevation, or soil type, and because farmers manage marginally suited sites less intensively (Klimek et al. 2007). A comprehensive analysis of land use effects on plant diversity should therefore include such site variation in order to distinguish land use effects from those of environmental factors. Most previous studies were restricted in scope by either focusing on single aspects of land use, on habitats of high conservation value, or on single regions. However, the interacting effects among different aspects of land use, such as fertilization, grazing, and mowing intensities, have not yet been addressed by a large scale study across different regions. Plant species diversity can be assessed by several measures. Clearly, species richness is the most commonly used index (Magurran 2004). Shannon’s evenness includes information on the dominance structure within communities, and Shannon diversity combines species richness and evenness. Along similar lines, many other indices have been described (see Smith & Wilson 1996). However, these measures of diversity indices do not capture whether and how different functional plant groups respond distinctly to different aspects of land use. Functional plant groups were defined according to several morphological or physiological characteristics (Roscher et al. 2004; Ellenberg & Leuschner 2010). The most commonly used classification into herbs, grasses, and legumes is of both agricultural and conservation interest. In this paper, we study land use effects on vascular plant species diversity (plant species richness, Shannon index, and evenness) and functional group composition of about 1500 grassland sites. We studied three distinct regions in Germany, the so-called Biodiversity Exploratories (Fischer, Kalko, et al. 2010), with different geographic background to cover a broad variety of landscape types including post-glacial lowlands, hilly lands, and low mountain ranges, together representative for large parts of Germany. In each region the study covers fertilized and unfertilized grasslands of different land use types (fallows, meadows, pastures, and mown pastures). Pastures were grazed by the typical livestock types for Germany, i.e. sheep, cattle, and horse. We also considered several environmental parameters including soil type, elevation, and slope. In particular we address the following questions: (i) How do different components of land use affect plant species diversity? (ii) How do different functional plant groups respond to land use? (iii) How consistent are land use effects on plant species diversity and composition across the three study regions?

Materials and methods Study area We studied vascular plant diversity in the context of a large research program on the relationships between land use, biodiversity, and ecosystem processes, the German Biodiversity Exploratories project (www.biodiversity-exploratories.de). The three Biodiversity Exploratories are situated in three regions, each with a variety of differently used grasslands and forests (Fischer, Bossdorf, et al. 2010; Fischer, Kalko, et al. 2010). The exploratory Schorfheide-Chorin in the lowlands of NE Germany forms part of the UNESCO Biosphere Reserve Schorfheide-Chorin. The exploratory Hainich-Dün is situated in the hilly lands of Central Germany and includes the National Park Hainich. The exploratory Schwäbische Alb in a low mountain range of SW Germany is situated in the UNESCO Biosphere Reserve Schwäbische Alb. All three Biodiversity Exploratories cover different grasslands: from semi-natural forms used at very low intensity to very intensively managed ones. In each of the three exploratories, grasslands are scattered among arable fields, forests, and settlement areas. To study the effect of land use on grassland as comprehensively as possible, we assessed plant diversity on circa 500 grassland plots in each Biodiversity Exploratory. Plots were selected to cover the whole range of land use types characteristic for that region. Plots had a minimum distance of 500 m from each other when the land use type was the same and of 200 m when it was different (see Fischer, Bossdorf, et al. 2010 for details on plot selection).

Land use, soil, and topographic information We obtained information on the current land use of the plots from questionnaires answered by farmers and land owners, including the land use type (fallow, meadow, pasture, and mown pasture), livestock type (cattle, horse, horse and cattle, or sheep), fertilization (fertilized and unfertilized plots), and mowing intensity (number of cuts; Fischer, Kalko, et al. 2010). Whereas fallows were abandoned sites of formerly managed grasslands, mown pastures designate grasslands mown once per year either before or after they were grazed, hence they experience biomass removal by grazing and mowing within the same year. In contrast, pastures and meadows refer to exclusive biomass removal by either grazing or mowing within a year. We also inferred the history of land use by asking the farmers how long the sites had been used as grassland and whether land use intensity changed recently. However, as this information was not available for all plots and because time used as grassland showed neither a main effect on species richness nor an interaction effect with the regions, we excluded it from the final models. Furthermore, most of the grasslands had the same land use for the last 5 years.

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For each plot, a soil sample had been taken and soil type classified according to the World Reference Base of Soil Resources (IUSS Working Group WRB 2007; Fischer, Bossdorf, et al. 2010; Fischer, Kalko, et al. 2010). The main soil groups were Histosols in Schorfheide-Chorin (318 plots), Cambisols in Hainich-Dün (235), and Cambisols (205 plots) and Leptosols (194 plots) in the Schwäbische Alb. Finally, topographic information on elevation and slope of each plot was derived from digital terrain models. Full information on land use and soil type was available for 1292 out of 1514 grassland plots.

Vegetation relevés From 25 May to 15 August 2007 we recorded vegetation relevés in 1514 plots in the three exploratories. We re-assessed 138 plots in May 2009 and discarded the earlier relevés because of unreliable data mainly from species-rich grassland that had been recorded too late in the season. In all plots vegetation relevés were taken in an area of 4 m × 4 m situated next to the position where the soil core had been sampled. Moreover, we recorded the ground cover by each vascular plant species to the nearest percent following the nomenclature of Wisskirchen & Häupler (1998). For each plot we determined vascular plant species richness (S), Shannon Index of diversity (H ) and Evenness (J ) as   H = − pi × ln pi , and J = H /ln S, where pi is the proportion of total abundance of the ith species. We also classified vascular plant species according to the functional groups herbs, grasses, and legumes and determined the absolute and relative species richness for each class.

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To examine the effect of fertilization we ran a model including land use type (pasture, meadow, mown pasture), fertilization, and the interactions land use type × fertilization, exploratory × land use type, exploratory × fertilization, and exploratory × land use type × fertilization. To examine the effect of mowing intensity we ran a model including land use type (excluding fallows and pastures), the number of cuts, the interaction between them, and their interactions with the respective exploratory. To examine the effect of sheep, cattle, and horses we ran a model including land use type (excluding fallows and meadows), fertilization, livestock type, and the two-way and three-way interactions between exploratory, land use type, fertilization, sheep, and other livestock type. Because we expected larger differences between sheep grazing and the other livestock types than between cattle and horse grazed plots, we split the livestock type effect by first testing the effect of sheep grazing and then the remaining effect of the other livestock types (cattle, horses, or cattle and horses). The sequence of fitting the land use variables turned out not to change statistical significances and therefore we just present the sequence outlined above for each model. It turned out to be highly necessary to include environmental site conditions (soil type, elevation, and slope) as they were significant in all tested models. We also tested for temporal effects (year and date of recording), but these were not significant and therefore excluded from the models. We performed all statistical analyses with the software R version 2.10.0 (R Development Core Team 2009).

Results

Statistical analyses

Differences between the biodiversity exploratories

To test the effect of the different components of land use on measures of vascular plant diversity we used generalized linear models. We analyzed six response variables: species richness and diversity indices (S, H and J ) of vascular plants, and the relative species richness of herb, legume, and grass species (in percent). As our comparative data set was unbalanced with respect to the distribution of specific combinations of land use types over exploratories (Fischer, Bossdorf, et al. 2010), we used separate models for more balanced subsets of data (see following paragraphs) to examine differences between (i) fallows and managed grasslands, (ii) fertilized and unfertilized grasslands, (iii) mowing effects in meadows and mown pastures, and (iv) livestock type effects of sheep, cattle, and horses. In all models we fitted the exploratory and the covariates (soil type, elevation, and slope) first, followed by the components of land use. Because there were no fallows in the Schwäbische Alb we examined the effect of fallows for the other two exploratories. For all further analyses, we excluded fallows.

On all 1514 plots we recorded a total of 623 vascular plant species, ranging from 365 vascular plant species in the 465 plots in the Schwäbische Alb, to 353 in the 515 plots in Hainich-Dün, to 318 in the 534 plots in Schorfheide-Chorin. Vascular plant species richness per 16 m2 , Shannon diversity and the proportions of herb and legume species were highest in the Schwäbische Alb, lower in the HainichDün exploratory and lowest in the Schorfheide-Chorin exploratory (see Appendix A: Table 1). Mean evenness was quite similar in all three exploratories. Thus, while the sizes of the regional species pools were not very different between the three exploratories, there was pronounced regional variation in plant community diversity and composition at the plot level. Accordingly, the factor exploratory strongly affected species diversity per plot in all models. Variation in species richness per plot among regions was much larger than the corresponding variation in total richness per region (coefficient of variation, CV = 25.1% for plot species richness vs. CV = 7.1% for total species richness),

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Table 1. Summary of analyses of variance of effects of exploratory, covariates (soil type, elevation, and slope), and fallow on vascular plant species diversity and composition on 16 m2 plot for the two exploratories with fallows. Df

Exploratory (E) Soil type Elevation Slope Fallow yes/no (Fa) E × Fa Residuals Residual mean squares

1 11 1 1 1 1 917

Vascular plant species richness F

Shannon diversity F

Evenness F

Proportion of herb species F

Proportion of grass species F

Proportion of legume species F

157.60*** 7.53*** 21.81*** 46.47*** 9.41** 27.66***

46.95*** 2.49** 7.78** 29.67*** 1.53 21.27***

0.01 1.62 0.40 6.46* 6.06* 4.62*

47.59*** 5.40*** 0.54 14.74*** 3.70 1.95

63.33*** 6.30*** 0.45 27.49*** 11.76*** 0.14

96.01*** 26.79*** 5.19* 2.51 5.79* 1.17

50.80

0.191

0.011

0.013

0.013

0.004

* p < 0.05. ** p < 0.01. *** p < 0.001.

indicating that differences between the regional species pool contributed only little to variation in local richness.

Differences between fallows and managed grasslands Overall, the 52 fallow plots in Schorfheide-Chorin (37 plots) and Hainich-Dün (15 plots) had lower evenness (−0.04), proportion of grass (−10.8%), and proportion of legume species (−30%) than managed grassland plots, but similar number of vascular plants (+49%) and Shannon diversity (−0.24). However, these relationships varied strongly depending on the exploratory (Table 1, Fig. 1). Whereas in Hainich-Dün fallow plots had higher vascular plant species richness (+49%) and higher Shannon diversity (+0.3) than managed plots, whereas evenness was very similar (−0.001) there were slightly fewer vascular plant species (−4%), lower Shannon diversity (−0.2), and evenness (−0.057) for fallow

Fig. 1. The difference between fallows (N = 52) and managed (N = 1355) grasslands in vascular plant species richness (number of species per 16 m2 ) for Hainich-Dün and Schorfheide-Chorin, the two exploratories where fallows occurred and for both exploratories combined. Error bars denote 1SE.

plots than for managed plots in Schorfheide-Chorin. Overall, this indicates that the relationship between abandonment and grassland diversity differs very much between study regions.

Differences between fertilized and unfertilized grasslands Fertilization of plots decreased vascular plant species richness (−15%), Shannon diversity (−0.1), and a small decrease in the proportion of herb species (−3%), but increased the proportion of grass species (+6%; Table 2). Differences between fertilized and unfertilized grasslands differed between exploratories for vascular plant species richness (Fig. 2), proportion of legume species, and proportion of grass species, as indicated by significant fertilization-byexploratory effects (Table 2, Fig. 3). Whereas the differences between fertilized and unfertilized sites were more pronounced in the Schwäbische Alb and Hainich-Dün, they were

Fig. 2. The difference between fertilized (N = 614) and unfertilized (N = 792) grasslands in vascular plant species richness (number of species per 16 m2 ) in all exploratories combined, in the Schwäbische Alb, Hainich-Dün, and Schorfheide-Chorin. Error bars denote 1SE.

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Table 2. Summary of analyses of variance of effects of exploratory, covariates (soil type, elevation, and slope), land use type (meadows, pastures, and mown pastures), and fertilization on vascular plant species diversity and composition on 16 m2 plot. Df

Exploratory (E) Soil type Elevation Slope Land use type (LUT) Fertilization (F) LUT × F E × LUT E×F E × LUT × F Residuals Residual mean squares

2 11 1 1 2 1 2 4 2 4 1261

Vascular plant species richness F

Shannon diversity F

Evenness F

Proportion of herb species F

Proportion of grass species F

Proportion of legume species F

264.95*** 5.86*** 61.52*** 143.35*** 65.49*** 93.76*** 10.15*** 5.59*** 22.84*** 6.83***

152.42*** 2.67** 36.94*** 48.02*** 30.35*** 28.37*** 11.66*** 16.13*** 2.15 8.90***

24.89*** 1.89* 5.08* 2.64 8.60*** 1.05 6.77** 19.19*** 1.60 6.80***

72.48*** 6.49*** 2.12 26.31*** 22.73*** 4.32* 2.70 12.79*** 1.99 3.44**

78.63*** 7.32*** 3.58 48.88*** 26.24*** 7.20** 2.11 13.09*** 3.01* 4.13**

71.14*** 33.27*** 4.10* 0.35 8.85*** 1.14 2.24 22.96*** 5.24** 11.36***

51.30

0.157

0.010

0.010

0.010

0.003

* p < 0.05. ** p < 0.01. *** p < 0.001.

not significant in the Schorfheide-Chorin exploratory, if analyzed separately by exploratory (data not shown). The three land-use types meadow, mown pasture, and pasture differed in all measured variables, but again with pronounced differences among the exploratories (Table 2, Fig. 4). In the Schwäbische Alb, pastures had higher vascular plant species richness and Shannon diversity, followed by meadows and mown pastures, whereas evenness and functional group composition was remarkably similar across land-use types. In Hainich-Dün, pastures had higher vascular plant species richness, Shannon diversity, and a higher proportion of herbs, followed by mown pastures and meadows. Finally, in Schorfheide-Chorin land-use types were overall very similar in diversity and composition, with only a slightly higher number of vascular plants on pastures (Fig. 4).

Furthermore, differences between fertilized and unfertilized sites interacted with the land use types for species richness, Shannon diversity, and evenness. Fertilized mown pastures and meadows had more vascular plant species than unfertilized ones, whereas fertilized pastures had fewer vascular plant species than unfertilized ones. Shannon diversity and evenness were higher for fertilized meadows than for unfertilized ones, whereas they were lower for fertilized mown pastures and pastures than for unfertilized plots. Finally, significant three-way interactions between exploratory, land-use types, and fertilization indicate that the effect of fertilization is strongly context dependent: it not only depends on the land-use types which are fertilized but this interaction between fertilization and land use varies across the three study regions (Table 2).

Fig. 3. The difference between fertilized (N = 614) and unfertilized (N = 792) grasslands in the proportion of species number of grasses, legumes, and herbs in all exploratories combined, in the Schwäbische Alb, Hainich-Dün, and Schorfheide-Chorin.

Fig. 4. The difference between the three land use types (meadow N = 496, mown pasture N = 361, and pasture N = 498) in vascular plant species richness (number of species per 16 m2 ) for all exploratories combined, and for the Schwäbische Alb, Hainich-Dün, and Schorfheide-Chorin. Error bars denote 1SE.

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Table 3. Summary of analyses of variance of effects of exploratory, covariates (soil type, elevation, and slope), land use type, and the number of cuts on vascular plant species diversity and composition on 16 m2 plots for mown grasslands. Df

Exploratory (E) Soil type Elevation Slope Land use type (LUT) Number of cuts (NC) LUT × NC E × LUT E × NC E × LUT × NC Residuals Residual mean squares

2 11 1 1 1 1 1 2 2 1 780

Vascular plant species richness F

Shannon diversity F

Evenness F

Proportion of herb species F

Proportion of grass species F

Proportion of legume species F

135.28*** 1.91* 31.40*** 12.62*** 1.84 5.92* 0.16 6.02** 15.43*** 8.06**

94.03*** 2.46** 16.93*** 2.56 5.00* 0.39 0.48 15.98*** 5.15** 1.11

30.11*** 1.79 3.39 0.03 13.93*** 0.02 0.14 16.63*** 2.15 0.001

43.14*** 2.72** 3.25 2.45 0.63 2.30 7.48** 18.42*** 2.86 0.39

41.73*** 2.79** 4.16* 3.72 0.38 2.96 7.54** 17.90*** 3.31* 0.38

76.29*** 12.65*** 0.44 0.04 4.24* 5.85* 0.02 26.12*** 1.29 0.28

35.90

0.15

0.01

0.01

0.01

0.00

* p < 0.05. ** p < 0.01. *** p < 0.001.

In summary, the generally negative relationship of fertilization and the positive relationship of pastures with plant species diversity and proportion of herb species differed between exploratories.

Relationship of mowing frequency with grassland diversity Analyzing mowing frequency for meadows and mown pastures revealed an increase of vascular plant species richness and a decrease of the proportion of legume species with the number of cuts (Table 3) with pronounced variation among the exploratories. Whereas increased mowing frequency decreased vascular plant species richness (−19%, Fig. 5) and Shannon diversity (−0.45), and increased the proportion of grass species (+26%) from one to three cuts in Hainich-Dün, it increased vascular plant species richness (+12%), Shannon diversity (+0.17) and the proportion of grass species (+10%) in Schorfheide-Chorin. In the Schwäbische Alb vascular plant species richness and Shannon diversity were highest on plots mown twice per year, and the proportion of grass species decreased by 13% with increasing cutting frequency. Together, these results, too, illustrate that relationships between land use and diversity differ between regions. Furthermore, the effect of mowing frequency on the proportion of herb and grass species differed between meadows and mown pastures (Table 3). Meadows cut twice per year had the highest proportion of grass and the lowest proportion of herb species, whereas mown pastures cut twice had the lowest proportion of grass species and the highest proportion of herb species, which indicates that species composition responded differently to mowing, depending on land use type. Overall, the differences between grasslands of different cutting frequencies and the interactions between land use

Fig. 5. The difference between mowing frequency (cut once N = 421, twice N = 286, or three times a year N = 149) in vascular plant species richness (number of species per 16 m2 ) in all exploratories combined, in the Schwäbische Alb, Hainich-Dün, and Schorfheide-Chorin (meadows and mown pastures only). Error bars denote 1SE.

components and cutting frequency were rather small, whereas the interaction between exploratory and cutting frequency was pronounced (Fig. 5).

Differences between grasslands grazed by different livestock types Analyzing the effect of livestock type on pastures and mown pastures showed that vascular plant species richness (+27%) and Shannon diversity (+0.3) were significantly higher on plots grazed by sheep than by other livestock (cattle and cattle and horse). Plots grazed by cattle and horses had higher vascular plant species richness (+12%) and a higher

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Discussion Abandonment of management and plant diversity

Fig. 6. The difference between grasslands grazed by different live stock types (sheep N = 289, cattle N = 461, cattle and horse N = 33, and horse N = 76) in vascular plant species richness (number of species per 16 m2 , pastures and mown pastures only). Error bars denote 1SE.

proportion of grass (+15%), but a lower proportion of herb species (+9%) than plots grazed by cattle only (see Appendix A: Table 2, Fig. 6). Pastures grazed by sheep had higher vascular plant species richness (+38%) and proportion of herb species (+8%) but lower proportion of grass species (−18%) compared with mown pastures. In addition, unfertilized plots grazed by sheep had higher Shannon diversity (+0.26), evenness (+0.015), and proportion of herb species (+6%) compared with fertilized plots (see Appendix A: Table 2). In contrast, unfertilized plots grazed by cattle and horses had a lower number of vascular plants, Shannon diversity, and proportion of herbs, but a higher proportion of grasses than fertilized plots. Thus, differences between grasslands grazed by different livestock types largely depended on whether grasslands were additionally mown and fertilized or not. Finally, in the Schwäbische Alb the differences between sites grazed by sheep and by other livestock were higher for Shannon diversity (+0.17), evenness (+0.02), and proportion of herb species (+9%) but lower for the proportion of legume species (−32%) than in Hainich-Dün. Sheep pastures in the Schorfheide-Chorin differed from the ones in the two other exploratories, but this type of land use was too rare (number of plots = 8) to allow statistically robust comparisons. In summary, the differences in diversity and composition between grasslands grazed by different livestock types were mainly driven by differences between sheepgrazed and other pastures, whereas differences between the other livestock types (cattle, horses, or cattle and horses) were comparatively small. In contrast to other aspects of land use (see above), relationships of livestock type with land use were rather consistent across exploratories.

It has been suggested that abandonment of grassland use leads to a decline in plant species diversity due to the competition for light that follows decreased occurrence of vegetation gaps as safe sites for germination, or due to increased litter accumulation (Jacquemyn, van Mechelen, Brys, & Honnay 2011). Such an effect was absent in SchorfheideChorin with its typically wetter soils. This might be due to more similar species composition between fallows and managed grasslands in the Schorfheide-Chorin, or due to unknown differences in time since abandonment. In contrast, fallows in Hainich-Dün showed increased diversity, probably because abandonment occurred only recently and the increase in diversity is caused by a temporary effect of bush encroachment. Moreover, we cannot exclude the possibility that species-rich grasslands were more often abandoned than poorer grasslands in Hainich-Dün, thus reversing the cause-effect relationship between management and diversity. From a conservation point of view our results indicate that plant species may decline after grassland management abandonment in some sites, as suggested by other studies (Rook et al. 2004; Maurer, Weyand, Fischer, & Stöcklin 2006), but this effect may be absent or even opposite elsewhere. Because abandonment effects may change over time, long-term observational studies are better suited to assess its consequences for diversity than our comparative approach is.

Fertilization and plant diversity The generally lower vascular plant species richness of fertilized grasslands (Stevens, Dise, Mountford, & Gowing 2004; Crawley et al. 2005; Silvertown et al. 2006; Kleijn et al. 2009) differed between land use types (meadows, mown pastures, and pastures) and exploratories. Fewer vascular plant species and lower Shannon diversity on fertilized plots was possibly caused by a competitive advantage of taller grasses, which increased with fertilization, over smaller herbs. This general trend was due to the findings in the Schwäbische Alb and Hainich-Dün, while patterns differed in the SchorfheideChorin, possibly due to its wetter soils (Table 2). We could not test for a unimodal fertilization-diversity relationships (Grime 1973; Wilson & Tilman 2002; but see Adler et al. 2011), because we did not have information on the amount of fertilizer for all the plots. In a subset of 150 plots we found a linearly negative instead of a hump-shaped relationship between productivity and diversity (Socher et al. 2012). On pastures, fertilization was most detrimental for vascular plant species richness, Shannon diversity and evenness, whereas on meadows, its effects were less pronounced or even positive. Possibly this was due to different species compositions and larger heterogeneity of the species composition

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on pastures compared with meadows. Moreover, it may result from differences in light availability, which may be higher in meadows due to cutting and may thus allow more species to persist (Hautier et al. 2009) and more seedlings to germinate. The small increase of species diversity with fertilization on meadows is surprising and likely caused by fertilization in meadows of lower initial species diversities and a decrease of meadows at higher initial diversities. Our results indicate a generally high sensitivity of pasture vegetation in HainichDün and the Schwäbische Alb to fertilization. However, our results also show that this did not apply to all regions, as fertilization effects differed in the Schorfheide-Chorin. This prevents us from generalizing our results on fertilization and simultaneously confirms the advantage of including three distinct regions in this study. Also, the omnipresence of interactions of fertilization effects with effects of land-use types and of exploratories highlights the importance of studying different aspects of land use simultaneously across several geographical regions.

Mowing and plant diversity Pooled over the meadows and mown pastures of the exploratories vascular plant species richness was highest at intermediate cutting frequency (two cuts per year), supporting predictions based on the intermediate disturbance hypothesis (Grime 1973; Kondoh 2001). Mowing may initially increase light availability, thereby promoting subdominant species and germination rates (Collins 1998; Hautier et al. 2009), but at higher cutting frequencies only few species are able to cope with such a degree of disturbance and thus diversity decreases. Effects of mowing frequency differed between meadows and mown pastures. Mowing twice per year favored grass over herb species on meadows, but not on mown pastures. In meadows, grasses may be favored due to their cuttingtolerant growth form and herbs may suffer from low seedling recruitment due to the absence of safe sites for recruitment in relatively homogenous swards. In mown pastures, however, mowing reduces the cover of those species that are avoided by grazers, which are often herbs, and thus mowing has an equalizing effect on the competitive balance of the species. The effects of mowing frequency varied considerably in direction depending on region, with an optimum in Schwäbische Alp, a reduction in Hainich-Dün and a stimulation of species richness in the Schorfheide grasslands (Table 3). From a conservation point of view these results indicate that mowing at intermediate levels generally enhances plant species richness, but that this general pattern is modified in several ways. It strongly depends on geographic region, differs between functional plant groups, and the latter effect additionally depends on whether sites are additionally grazed. This suggests that there is no best universal mowing frequency to promote plant species richness, but that mowing

regimes need to be adapted to regional and local circumstances.

Livestock type and plant diversity Among the pastures and mown pastures we recorded higher diversity, evenness and proportion of herbs at sites grazed by sheep than by cattle or horses. The promotion of herb species on sheep pastures could be due to the ability of sheep to create high fine-scale sward heterogeneity (Proulx & Mazumder 1998; Klimek, Marini, Hofmann, & Isselstein 2008) offering higher niche diversity (Maurer et al. 2006). However, as we did a comprehensive comparative study in the field and not an experiment, it may also be that sheep grazed pastures had been established at nutrient-poorer sites of initially higher species diversity. Our results indicate that promoting plant species richness by grazing calls for careful selection of livestock types and stocking densities, according to regional conditions, because livestock types may differ in their effects on species diversity and composition. In our case, based on detailed land use information for a subset of 150 plots, grazing intensity (number of livestock × grazing duration per ha) did not differ between sheep and cattle grazed plots and only slightly among regions (Blüthgen et al. 2012). However, it is likely that in other regions grazing intensity varies between livestock types and may have contributed to idiosyncratic grazing effects in different regions (Rook et al. 2004; Stewart & Pullin 2008).

Differences between regions To assess whether results – and derived conservation recommendations – can be generalized, we included many different land use types and environmental site conditions in three distinct geographic regions. Repeatedly, relationships between land use and plant species diversity and composition differed between regions, although all regions comprised the same basic land use varieties. Most likely the regional differences may be explained by the prevalent soil types in the three regions, with many wet, organic Histosols in Schorfheide and dry, shallow Leptosols in the Schwäbische Alb (IUSS Working Group WRB 2007). The differences in relationships between land use type and plant diversity in the different exploratories demonstrate that results and conservation conclusions cannot simply be generalized across regions, but that their interpretation requires careful consideration of regional peculiarities.

Conclusions Our study suggests that, among the land use types applied to German grasslands, fertilization has the largest and negative effects on plant species diversity and composition,

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followed by positive effects of grazing and mixed effects of mowing. Conserving high vascular plant species richness calls for avoiding fertilization especially of pastures. Among the grazed sites, sheep grazed pastures had higher species richness, while cattle grazing decreased species richness. An important message of our study is that these general results are strongly context dependent, in particular the effect of mowing, highlighting the importance of comparing different regions and involving a large number of study plots when studying land use effects on plant diversity. It calls for carefully comparing environmental conditions before extrapolating results and management recommendations between regions.

Acknowledgements We dedicate this article to the memory of our friend, colleague and co-author Elisabeth K.V. Kalko, who very sadly passed away during the final stage of this work. We thank all local teams supporting us during the vegetation period, especially Metke Lilienthal, Ralf Lauterbach, Martin Fellendorf, Jörg Hailer, Uta Schumacher, Ulf Pommer, and Claudia Seilwinder. Further, we thank Jens Nieschulze for providing topographic data, Simone Pfeiffer and Ilka May for project infrastructure. We thank Prof Hövemeyer and three anonymous reviewers for helpful comments on the manuscript. We thank the DFG for funding in the framework of the DFG Priority Program 1374 “Infrastructure-BiodiversityExploratories” (FI1246/6-1, FI1246/9-1) and the University of Bern. Field work permits were given by the responsible state environmental offices of Baden-Württemberg, Thüringen, and Brandenburg (according to § 72 BbgNatSchG).

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10. 1016/j.baae.2012.12.003.

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