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Plant diversity differs between young and old mesic meadows in a central European low mountain region
Agriculture, Ecosystems and Environment 129 (2009) 457–464
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Plant diversity differs between young and old mesic meadows in a central European low mountain region Gunnar Waesch a, Thomas Becker b,* a b
University of Goettingen, Albrecht-von-Haller Institute for Plant Sciences, Department of Vegetation Analysis and Phytodiversity, Untere Karspu¨le 2, 37073 Goettingen, Germany University of Marburg, Department of Biology, Plant Ecology, Karl-von-Frisch-Str. 8, 35034 Marburg, Germany
A R T I C L E I N F O
A B S T R A C T
Article history: Received 18 April 2008 Received in revised form 28 October 2008 Accepted 29 October 2008 Available online 11 December 2008
Effects of habitat age on species diversity are an important issue in plant conservation. However, effects of habitat age on mesic meadows are poorly investigated. Here we compare plant species richness between old mesic meadows (>150 years) and young mesic meadows (40–60 years) in a low mountain region (Thuringian Forest, Germany). Species richness and species traits were determined in 20 old and 20 young mountain meadows (alliances Polygono-Trisetion, Violion caninae) which were defined using historical maps and compared using species indicator analysis and ANOVA. Additionally we quantified changes in the extent of the area of young and old meadows using a Geographical Information System. Species richness of vascular plants on 20 m2 plots was significantly higher in old than in young meadows, while evenness did not differ between young and old meadows. Endangered plant species were restricted to old meadows, which also contained a higher proportion of habitat specialists. The terminal velocity index of seeds was lower and seed weight was higher in old meadows, indicating a lower importance of wind dispersal in old meadows. This was also indicated by a higher proportion of species with seeds adapted to wind dispersal in young meadows. In old meadows there was a higher proportion of species with seeds adapted to ant dispersal and a lower proportion of species with seeds adapted to animal dispersal. In a representative sub-area of the study region, the total area of meadows has increased by 88% during the 20th century due to transformation of arable fields into meadows, while the area of old meadows declined by 36% during the same time due to abandonment and afforestation. We conclude that the age of the habitat is highly important in order to maintain plant diversity of mesic meadows. Therefore, higher priority should be given to old meadows. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Biodiversity Dispersal Grassland Habitat age Habitat continuity Land use history Species diversity
1. Introduction In agricultural regions throughout Europe, land use has changed considerably within the past 100 years. Among the semi-natural habitats that have been particularly affected by these changes, meadows on moderately fertile soils, denoted as mesic or mesophilous meadows, have often been subject to more intensive management or have been abandoned, and as a consequence, the area covered by mesic meadows has dramatically declined in Europe (Burel et al., 1998; MacDonald et al., 2000). In Germany, for example, mesic meadows were widespread and abundant until 1950 and have declined to 11% of the agricultural area in 2000. This decline is continuing: between 1999 and 2003 the area of meadows has declined from 2.1 to 1.9 million ha, i.e. a 10% loss in only 4 years (Bundesamt fu¨r
* Corresponding author. Tel.: +49 6421 2822053; fax: +49 6421 2822093. E-mail address: [email protected] (T. Becker). 0167-8809/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2008.10.022
Naturschutz, 2004). However, in marginal regions such as low mountain areas new mesic meadows on moderately fertile soils have been created after crop production was no longer economically feasible at many sites (MacDonald et al., 2000; Olsson et al., 2000; Tasser and Tappeiner, 2002; Waldhardt and Otte, 2003). Such regions offer an ideal opportunity for studying effects of habitat age on species diversity in meadows. Extensively managed mesic meadows contain a high number of plant species including many rare and endangered taxa (Korneck et al., 1998), and therefore, species-rich mesic meadows were included in the European Habitats Directive (92/43/EEC; European Union, 1992; NATURA 2000-Codes 6520 and *6230). Because mesic meadows are species-rich and declining, a better understanding of the effects of habitat age on species diversity is very important for their conservation. In general, the absence of plant species at a site can be due to limitation of propagule dispersal and recruitment or subsequent establishment (Mu¨nzbergova´ and Herben, 2005; Stein et al., 2008). Recruitment limitation is due to the actual environmental
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conditions, e.g. nutrient concentration of the soil (Myklestad and Sætersdal, 2004), and management regime (Maurer et al., 2006; Critchley et al., 2007). In meadows, a high nutrient concentration favours competitive plant species and therefore, in strongly fertilized meadows species diversity is often reduced (Janssens et al., 1998; Klimek et al., 2007; Wellstein et al., 2007). In contrast, seed limitation and dispersal limitation of species are a result of the propagule abundance and dispersal potential; however, the importance of both factors declines with time (Ozinga et al., 2005). Of course, a newly created meadow can hardly harbour the full set of typical species, but if seed sources occur abundantly in the vicinity, colonisation might be expected to be advanced some decades after creation. A number of studies have investigated the importance of habitat age for forests and most of them found large differences in plant species diversity and composition between recent and ancient stands (reviewed in Hermy and Verheyen, 2007). In contrast, effects of habitat age on mesic meadows or pastures are poorly investigated (but see Wells et al., 1976; Austrheim et al., 1999; Bissels et al., 2004; Gustavsson et al., 2007), and we do not know of any study that has investigated plant functional characteristics, e.g. mode and ability of dispersal, as an explanation of differences between new and old meadows. Moreover, grasslands and forests differ considerably in many attributes, e.g. in wind influence and management intensity, and hence probably in the importance of wind dispersal and human dispersal (Luftensteiner, 1982). Therefore, results of studies in forests cannot easily be applied to meadows. Here we study plant diversity of young and old mesic meadows in a low mountain region in central Germany. We ask the following
questions: (1) Are old meadows (>150 years) more species-rich than young meadows (40–60 years)? (2) Are there differences between old and young meadows regarding species traits and the abundance of habitat specialists and endangered plant species? (3) Has the area of old meadows changed during the 20th century in the study region? 2. Methods 2.1. Study region and assessment of changes in meadow area Our comparison of young and old meadows encompasses the whole high altitude area of the Thuringian Forest in central Germany, i.e. an area ca. 45 km in length and ca. 15 km in width (508310 –508530 N, 108220 –108560 E) (Fig. 1). In this area meadows are sparsely distributed within a matrix of spruce forests. The meadows studied are located between 430 and 790 m above sea level (mean: 585 m a.s.l.). Mean annual temperature at these sites ranges between 5.2 and 7.0 8C and mean annual precipitation from 634 to 1099 mm (Deutscher Wetterdienst, 2007). The geological substrate is formed from siliceous bedrock (Upper Permian period) resulting in nutrient-poor, moderately acidic brown podzolic soils and rankers (Andreas et al., 1996). The pH of the soils ranges from 4.1 to 5.8 (Waesch, 2003). Changes in the area of young and old meadows were quantified in the 11 km2 biosphere reserve ‘Vesser valley’ (350–848 m a.s.l.), a representative part of the Thuringian Forest (Waesch, 2003) (Fig. 1). For the Vesser valley we determined in a spatially explicit manner the area of meadows which already existed in 1905, and which have been created between 1905 and 1994, and of fields,
Fig. 1. Study region. The comparison of young and old meadows encompasses the whole high altitude area of the Thuringian Forest (A): white dots represent sites with young and black dots those with old meadows. Changes in the extent of young and old meadows were studied in the Vesser valley (B). Different shades of grey correspond (from lighter to darker) to altitudes of 300–500 m, 500–700 m and >700 m a.s.l.
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forests and built-up areas using 1:25,000 topographical maps (see below) with the programme TOPOL (TopoL Software Company, 2007). 2.2. Meadow age assessment The age of the meadows was assessed from historical topographical 1:25,000 maps from 1854 to 1856 (‘Ko¨niglichPreußische Generalstabsaufnahme’) and 1905 to 1939 (‘Preussische Landesaufnahme’). Additionally, we interviewed farmers and landowners and made observations of former agricultural land use in the field, such as agricultural terraces which were built by the farmers at many sites in the Thuringian Forest in order to establish fields. Meadows were defined as old if they had existed in both time layers and thus were older than 150 years and as young if they have not yet existed in 1939 and thus were younger than 60 years. Young meadows were established on former arable land between 1950 and 1960 when crop farming was given up at many sites in the region. 2.3. Selection of study sites and record of vegetation Selection of study sites is based on a previous survey of the meadow vegetation of the Thuringian Forest (Waesch, 2003; 462 plots of 4 m 5 m; cover of each vascular plant species recorded according to the Braun-Blanquet method; Dierschke, 1994). From this data set we excluded all plots with more than two indicator species for wet conditions (species with moisture value >7 according to Ellenberg et al., 2001) and all plots with indicator species for wet conditions above 5% cover in order to reduce effects of different abiotic conditions. Furthermore, we excluded intensively managed meadows with more than two indicator species for high nitrogen concentrations (nitrogen value >7) and all plots with indicator species for high nitrogen concentrations above 5% cover. Moreover, we excluded all grasslands not managed for more than one year. For the remaining plots we defined age of the meadows (see above), and included all 20 meadows younger than 60 years into our study. From the remaining 47 old meadows we randomly selected 20 meadows in order to receive a balanced design. The nomenclature of the vascular plant species follows Wisskirchen and Haeupler (1998), and of the plant communities Rennwald (2000). 2.4. Assessment of species diversity and species traits For the assessment of species richness and species traits we excluded ruderal species also growing in fields (species assigned to the classes Artemisietea, Agropyretea, Plantaginetea, Agrostietea stoloniferae, according to Ellenberg et al., 2001), tree and shrub species growing in meadows only as seedlings, non-indigenous plant species, and species neither characteristic for meadows nor fields from the comparison of species richness and species traits of young and old meadows. This reduction onto a species set characteristic for meadows allows more robust conclusions with respect to this vegetation type (compare e.g. Hermy and Verheyen, 2007, for forests). Finally, we included 115 species characteristic for meadows (and referred to as ‘‘meadow plant species’’ in the following) of the total number of 147 vascular plant species, respectively 90% of all species records. We compared the species richness, Shannon’s diversity, evenness, proportion of different modes of dispersal and clonal growth, terminal velocity and weight of the seeds, seed bank type, proportion of habitat specialists i.e. species with narrow niche, and number of endangered plant species between young and old meadows. Habitat specialists comprise species characteristic of the alliances Polygono-Trisetion and Violion caninae according to Ellenberg et al. (2001), while
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species diagnostic for the order Arrhenatheretalia and the class Molinio-Arrhenatheretea were considered as habitat generalists. The Polygono-Trisetion and V. caninae comprise mesic to nutrientpoor montane meadows, while the Arrhenatheretalia and MolinioArrhenatheretea comprise all types of mesic grasslands or cultural grassland, respectively, i.e. plants characteristic of these syntaxa mostly occur in a wide range of grassland communities and are mostly widespread and common (for hierarchical classification system and more details on syntaxa see Waesch, 2003). The seed bank type was assigned for each species following Thompson et al. (1997), with the exception of Meum athamanticum (transient seed bank; K. Lieberum, pers. comm.) and Alchemilla vulgaris agg. (persistent seed bank; Waesch, 2003). Mode of dispersal was assigned following Mu¨ller-Schneider (1986) with the exception of Carex pilulifera, Dianthus deltoides, and Thymus pulegioides (dispersal by ants; Kjellsson, 1985, and Dosta´l, 2005, respectively), Calluna vulgaris (dispersal by wind; Soons and Bullock, 2008). Mode of clonal growth (stolons, rhizomes) and seed weight were taken from the BIOLFLOR database (Klotz et al., 2002). Indices of terminal velocity, which reflect wind dispersal potential of the seeds according to Tackenberg et al. (2003), were taken from the databases DIASPORUS (Bonn et al., 2000) and LEDA (The LEDA traitbase, 2007), and from O. Tackenberg (unpubl. data). Endangered plant species were identified in the plots according to the German red list (Korneck et al., 1996). 2.5. Statistical analysis Species indicator analysis (Dufreˆne and Legendre, 1997) based on all 147 species determined in the plots was carried out using the software package PC-ORD 4 (McCune and Mefford, 1999), and was used to assess characteristic species for young and old meadows. The values obtained were tested for significance by Monte-CarloPermutation tests with 9999 runs. Shannon’s index, which weights number of species by their abundances (median percent value of corresponding Braun-Blanquet class), was calculated as H0 = Spi lnpi, where pi is the proportion of the ith species of the total abundance of all species (Magurran, 1988), and evenness as E1/D = (1/D)/S. This evenness index based on a diversity index derived from Simpson’s index of dominance D (D ¼ Si p2i , pi = relative abundance of species i) is independent of species richness (Smith and Wilson, 1996). We calculated the following variables per plot and compared differences between young and old meadows with ANOVA: mean unweighted Ellenberg indicator values (based on all 147 species; according to Ellenberg et al., 2001), species richness and Shannon’s diversity, evenness, proportion of different modes of dispersal and clonal growth, terminal velocity index and weight of the seeds, proportion of seed bank types, and four phytosociological categories (see above) as a measure of the degree of specialization of meadow species. Slope, altitude, soil pH, and cover of herb layer of the plots were also compared with ANOVA between young and old meadows, while slope position, i.e. the proportion of plots on upper, middle and lower slopes, was compared with logistic regression. Levels of significance on comparison of the proportions of stoloniferous and rhizomatous plants between young and old meadows were corrected using Bonferroni corrections for the number of tests (Miller, 1981). Variance component estimates using the restricted maximum likelihood method (Sokal and Rohlf, 1995) was used to partition the total variation in the proportion of dispersal types and indicator value for nitrogen between old and young meadows and into the residual variation. This allowed us to compare the relative importance of dispersal limitation, recruitment limitation and environmental conditions for differences in species composition between young and old meadows. Deviation of the proportion of
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endangered plant species from zero was analysed using t-statistic and calculated as t = 0 x/SEx, where x is the mean proportion of endangered plant species of old meadows. Values of seed weight were log-transformed prior to analysis. Homogeneity of variance was tested and residuals were checked for normal distribution. Statistical analyses (apart from species indicator analysis) were performed with SPSS 14 (SPSS Inc., Chicago, USA, 2005). 3. Results 3.1. Environmental conditions in young and old meadows In order to ensure comparability of young and old meadows regarding the questions stated, we first tested differences in abiotic conditions between both meadow types. There were no significant differences in mean species indicator values for moisture and soil reaction between young and old meadows, but indicator values for nitrogen were higher in young meadows (Table 1). Inclination of the slope and altitude did not differ significantly between young and old meadows. There were no significant differences in the position of plots on a slope between young and old meadows. Soil pH and cover of the herb layer did also not differ between young and old stands. Differences in intensity of present management between young and old meadows were not determined. Most meadows were mown once a year in summer followed by cattle grazing in late summer and autumn. 3.2. Plant species diversity Overall, we counted a total of 147 plant species. Of those, 115 species were characteristic for meadows and hence referred to as
Table 1 Environmental characteristics of the meadows investigated. Mean and 1SE. ANOVA, and simple logistic regression, n = 20, each for young and old meadows.
Indicator value for moisture Indicator value for soil reaction Indicator value for nitrogen Inclination of the slope (8) Altitude (m a.s.l.) Upper slope position (% sites) Middle slope position (% sites) Lower slope position (% sites) Soil pH Cover of herb layer (%)
Young meadows
Old meadows
F/(x2)
p
5.2 0.06 4.8 0.18 4.9 0.22 11 2.7 567 22 0 75 25 5.0 0.16 93 3
5.0 0.07 4.4 0.14 4.0 0.19 7 1.2 599 21 10 60 30 4.9 0.08 92 2
1.6 2.4 9.2 2.7 1.0 (2.8) (1.0) (0.1) 0.4 0.2
0.207 0.126 0.004 0.111 0.316 0.090 0.310 0.723 0.516 0.669
‘‘meadow plant species’’ here (Table 2, and Appendix). Both the total species richness of meadow plants (28.7 vs. 15.4 species per 20 m2) and the number of habitat specialists (11.5 vs. 3.0 species per 20 m2) were significantly higher, and the proportion of habitat generalists was significantly lower in old meadows compared to young meadows (Fig. 2a and b). Furthermore, Shannon’s diversity of meadow plants was higher in old than in young meadows (2.5 vs. 1.9, F = 15.7, p < 0.001) while evenness did not differ significantly between young and old meadows. Indicator species analysis resulted in six indicator species for young and 20 indicator species for old meadows (Table 2). 60% of the indicator species of old meadows were habitat specialists characteristic of mesic to nutrient-poor montane meadows, whereas indicator species of young meadows comprised exclusively habitat generalists. Endangered plant species occurred exclusively in old meadows (0.8 vs. 0.0 endangered species per 20 m2, t = 4.1, p < 0.001). These were Alchemilla glaucescens,
Table 2 Indicator species for young and old meadows. Mean percent cover values of occupied plots in superscript. Species diagnostic for: Arrh, Arrhenatheretalia; M-A, MolinioArrhenatheretea; P-T, Polygono-Trisetion; Viol, Violion caninae. Mode of dispersal: ane, anemochory; spei, speirochory; myr, myrmecochory; zoo, zoochory. Mode of clonal growth: stol, stolons; rhiz, rhizomes. Indices of terminal velocity positively reflect wind dispersal potential of the seeds. Seed bank type: tran, transient; pers, persistent. Species
Mode of clonal growth
Terminal velocity index
Indicator species for young meadows Agrostis capillaris, Arrh ane, spei, zoo Rumex acetosella, –a ane, spei, zoo Alopecurus pratensis, M-A ane a Poa pratensis, M-A zoo a Cerastium holosteoides, M-A spei, zoo Rumex obtusifolius/crispus, –a ane, spei, zoo
stol – stol stol stol –
4 0 2 3 2 3
0.1 0.4 0.8 0.3 0.1 1.3
Indicator species for old meadows Meum athamanticum, P-Tb – Luzula campestris, Viol myr, zoo Potentilla erecta, Viol myr Anthoxanthum odoratum, – ane, spei, zoo Knautia arvensis, Arrh spei, myr Plantago lanceolata, – spei, zoo Veronica officinalis, Viol zoo Phyteuma spicatum, P-T myr, zoo Nardus stricta, Viol zoo Lathyrus linifolius, Viol myr Sanguisorba officinalis, – ane Leucanthemum vulgare, Arrh spei, zoo Polygala vulgaris, Viol ane, myr Crepis mollis, P-Tb ane Campanula rotundifolia, Viol zoo Ajuga reptans, M-A myr Anemone nemorosa, P-Ta myr Rhinanthus minor, Arrh – Carex pilulifera, Viol myr Hieracium lachenalii, – ane
– stol, rhiz rhiz rhiz – – stol stol, rhiz rhiz stol rhiz – – – – stol rhiz – rhiz rhiz
0 0 2 2 2 0 2 2 1 0 2 0 2 6 3 ? 0 3 0 5
7.6 0.8 0.5 0.5 4.6 1.8 0.1 0.2 0.7 12.5 2.0 0.4 1.7 0.3 0.1 1.5 2.6 2.9 1.2 0.4
a b
Weak indicator species. Red-listed species.
Mode of dispersal
Seed weight (mg)
Seed bank type
Indicator value
p
Plots occupied (%)
per per per per per per
66.7 52.8 41.9 35.2 29.6 29.6
0.033 0.057 0.047 0.059 0.053 0.056
9022.2 2010.0 505.3 404.7 301.3 301.3
808.8 50.1 252.0 151.7 50.1 50.1
tran per per per tran per per tran tran tran tran per tran tran tran per tran tran per tran
74.0 69.3 66.1 57.6 56.6 51.5 45.0 45.0 43.6 41.3 40.0 39.6 35.0 35.0 47.6 30.0 29.6 25.0 25.0 25.0
<0.001 <0.001 <0.001 <0.001 0.017 0.005 <0.001 0.001 0.005 0.020 0.004 0.013 0.007 0.009 0.018 0.023 0.053 0.045 0.046 0.048
200.7 52.5 52.5 102.5 451.7 152.5 0– 0– 52.5 152.5 0– 50.1 0– 0– 301.7 0– 50.1 0– 0– 0–
7513.8 752.0 703.0 6010.0 851.8 603.8 451.2 450.4 458.3 552.1 404.7 401.3 356.4 351.5 652.1 301.3 301.3 252.5 251.5 251.5
Young (n = 20)
Old (n = 20)
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Fig. 2. (a) Number of total meadow plant species (total) and habitat specialists (special) per plot, and (b) proportions of habitat specialists (P-T, Viol) and habitat generalists (Arrh, M-A) in young and old montane meadows. Habitat specialists represent character species of the syntaxa Polygono-Trisetion (P-T) and Violion caninae (Viol); habitat generalists represent character species of the syntaxa Arrhenatheretalia (Arrh) and Molinio-Arrhenatheretea (M-A). Mean and 1SE, ANOVA, *p < 0.05, **p < 0.01, ***p < 0.001. n = 40, for each pairwise comparison.
Fig. 3. Proportion of types of (a) seed dispersal and (b) clonal growth in young and old montane meadows. ane, anemochory; spei, speirochory; myr, myrmecochory; zoo, zoochory; stol, stolons; rhiz, rhizomes. Mean and 1SE, ANOVA, *p < 0.05, **p < 0.01, ***p < 0.001. The levels of significance on comparison of the proportions of stoloniferous and rhizomatous plants were corrected using Bonferroni corrections. n = 40, for each pairwise comparison.
Arnica montana, Crepis mollis, Lilium bulbiferum, Pedicularis sylvatica, Polygala serpyllifolia and Thesium pyrenaicum. 3.3. Plant species traits Old meadows showed a higher proportion of myrmecochorous (seeds dispersed by ants) plant species, and lower proportions of anemochorous (wind-dispersed), zoochorous (animal-dispersed) and speirochorous (dispersed by agricultural activities) plant species than young meadows (Fig. 3a). There were no differences in the proportion of plant species for which no dispersal agent is known between young and old meadows (19% vs. 16%, F = 1.8, p = 0.19). The terminal velocity index of the seeds was lower (1.8 vs. 2.2, F = 10.1, p = 0.003) and seed weight was higher in old meadows (1.9 mg vs. 1.4 mg, F = 4.6, p = 0.039). Meadow type explained 54% respectively 50% of the variance in proportions of myrmecochorous and speirochorous species, while only 29% variance in nitrogen indicator values were explained by meadow type. Mode of clonal growth differed as follows: in old meadows there was a higher proportion of species growing with rhizomes whereas in young meadows species producing stolons were more abundant (Fig. 3b). Furthermore, in old meadows there was a lower proportion of species which are able to build a persistent seed bank (39% vs. 47%, F = 3.9, p = 0.05) indicating a lower potential of dispersal in time.
3.4. Changes in area of young and old meadows In the Vesser valley, the total area of meadows increased by 88% between 1905 and 1994 due to transformation of arable fields into meadows (Table 3). Within the same time, the area of meadows that already existed in 1905 declined by 36% due to afforestation both spontaneously following abandonment and through planting. Most of the meadows that have disappeared were located at the highest brook valleys or at remote sites within forests. 66% of the total meadow area in 1994 was younger than 90 years.
Table 3 The extent and increase or decrease, respectively, of young and old meadows and other land use forms in the Vesser valley in and between 1905 and 1994.
Old meadows (existing since 1905) Young meadows (created after 1905) Total meadow area Arable land Forests Built-up areas
1905 (ha)
1994 (ha)
1019 – 1019 1413 7754 143
657 1257 1914 189 7643 538
Increase or decrease (ha)
(%)
362 +1257 +895 1224 111 +395
36 – +88 87 1 +276
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4. Discussion The results of this study show that knowledge of habitat age is necessary to understand present day patterns of grassland plants in the agricultural landscape. In the studied landscape, old meadows (>150 years) had a higher plant species diversity, higher numbers of habitat specialists and red-listed species than young meadows (40–60 years). Furthermore, our study shows that old meadows have strongly declined during the 20th century even in a region where the total meadow area has strongly increased. 4.1. Plant species diversity Higher numbers of vascular plant species in old than in young grasslands were also found in sub-alpine pastures in Norway (Austrheim et al., 1999), upland pastures in West Germany (Waldhardt and Otte, 2003) and dry-mesic pastures in Sweden (Gustavsson et al., 2007). Although there were differences in indicator species between those studies and our study, we were able to confirm several of the indicator species for old grasslands found in those studies, e.g. Anemone nemorosa and Polygala vulgaris. Endangered plant species occurred exclusively in meadows older than 150 years. Similar results were found in subalpine pastures in Norway (Austrheim et al., 1999) and Denmark (Ejrnæs and Bruun, 1995). However, endangered plant species can also occur in young meadows as observed in the Thuringian Forest for Silene viscaria and Botrychium lunaria (Brettfeld and Bock, 1994). Old meadows may not be species-rich if they have been intensively managed at some time in the past (Ejrnæs and Bruun, 1995). We found species-poor ‘‘old’’ meadows near the Vesser valley where herbicides were applied during agricultural improvement by the local agricultural cooperative of the German Democratic Republic in the 1960s. Therefore, the term ‘old meadow’ should only be used to describe meadows which have not been agriculturally improved at some time in the past. Very likely, the old meadows in our study were continuously managed as mesic meadows throughout the past 150 years. Until 1950 chemical fertiliser was not applied in high altitude areas in the Thuringian Forest, and after 1950 land owners stated no application of chemical fertiliser for the old meadows. However, we do not know the older history of the meadows, i.e. for how long they existed before 1850 and if there were changes in management including arable land use and abandonment. In a Swedish region, land use 300 years ago was the strongest predictor of today’s species composition and richness of semi-natural grasslands (Gustavsson et al., 2007). Our analyses of diversity are based on a subset of 115 plant species of the total number of 147 vascular plant species found (see Section 2). When all 147 species were included in the analyses, mean species richness was higher in both old (30.7 species per 20 m2) and in young meadows (18.9 species per 20 m2), but overall differences were the same. However, results were slightly clearer when focusing on species characteristic for meadows only. 4.2. Dispersal and recruitment limitation The newly established meadows studied might be colonised by plants due to clonal growth of existing species from adjacent meadows, and by seed dispersal by wind, ants, cattle, and human activities. The higher proportion of myrmecochorous plant species and lower proportions of anemochorous and zoochorous plant species in old meadows may indicate that dispersal limitation causes lower species richness of young meadows. Seed dispersal by ants usually achieves distances of a few decimetres (Go´mez and
Espadaler, 1998). Dispersal by wind is more effective but mainly acts over small distances (Tackenberg et al., 2003). The statement that the higher proportion of anemochores indicates dispersal limitation is also supported by the higher terminal velocities in the old meadows. Therefore, some doubtful cases in the dispersal type classification of Mu¨ller-Schneider (1986) (e.g. the classification of short-distance dispersers like Ranunculus acris and all grasses as wind-dispersed) most likely have no important effect on the results of our study. In general, in grasslands which are (from time to time) grazed by e.g. cattle, zoochory is expected to be most important for long distance dispersal (Couvreur et al., 2005). Our results also confirm that old meadow plant species often do not build a persistent seed bank. Persistent seed banks might enable meadow plant species to survive temporary agricultural land use at least over a few decades. However, persistent seed banks tend to be associated with disturbance and cultivation, and for many meadow plants the ability of re-colonisation from the seed bank is limited (Bekker et al., 1997). In our study old meadow plant species often were rhizomatous, whereas young meadow plant species often had stolons. Stoloniferous species seem to be better adapted for colonisation of new habitats because stolons are often longer than rhizomes and might be transported more easily e.g. in hooves of cattle. However, both strategies normally act on a very small scale. For some anemochores, e.g. C. mollis and Hieracium lachenalii which are strongly confined to old meadows within our study area, high indices of the terminal velocity indicate high dispersal potential. Therefore, these species are probably not limited in their dispersal and therefore might be rather limited in their recruitment in young meadows. In young meadows, fertilization often has led to higher concentration and availability of nutrients. In grasslands, higher nutrient concentrations facilitate competitive plant species and cause higher biomass which also causes increased competition (Myklestad and Sætersdal, 2004; Janssens et al., 1998). Although we used only extensively managed meadows for the comparison, indicator values for nitrogen were higher in young meadows, indicating higher concentrations of nutrients. The variance of indicator values between young and old meadows was smaller than those of the proportions of myrmecochorous and speirochorous species. Furthermore, competitive plant species were largely missing even in young meadows. Therefore, we suggest that effects of recruitment limitation due to increased competition are smaller than effects of dispersal limitation. Ultimately, the impact of the better nutrient supply of the young meadows can only be solved using seed addition experiments. 4.3. Changes in the area of young and old meadows in marginal regions The land use dynamics presented here can be regarded as typical for marginal, agriculturally used regions. An increase in grassland area, caused by transformation of arable land into meadows, has also been reported from other low mountain regions (Waldhardt and Otte, 2003; MacDonald et al., 2000, for a review). However, in the study region the area of old meadows strongly declined due to abandonment and afforestation although the total area of mesic meadows strongly increased. Therefore, the overall situation of meadows in the Thuringian Forest has deteriorated. 4.4. Implications for conservation Our results show that old meadows are more species-rich and contain more endangered plant species than young meadows. Therefore, higher conservation priority should be given to old
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meadows than to younger stands. For old montane meadows our study provides a set of indicator species which can be used for locating old stands (at least in central Europe). Furthermore, for our study region, the locality of old meadows is provided in detail within a map which was given to the local conservation authorities. Such maps would be helpful in identification of potential areas for conservation issues in meadows in other regions, e.g. all regions with high priority in conservation of grasslands according the Habitats Directive of the European Union (European Union, 1992). Young meadows extensively managed as we study here might also be restored by addition of diaspores using cut material from species-rich old meadows (Walker et al., 2004; Donath et al., 2007; Edwards et al., 2007; Stein et al., 2008). Such measures could overcome the dispersal limitation of old meadow plants. Acknowledgements This paper is dedicated to Hartmut Dierschke, Go¨ttingen, a pioneer in research and conservation of montane meadows. We thank all farmers for information about land use and for allowing us to work on their land, Werner Westhus, Jena, for further information, and Friedrich Wulf, Berlin, for field data, and Oliver Tackenberg, Frankfurt, for data on terminal velocities. We thank Erwin Bergmeier, Go¨ttingen, for valuable ideas regarding this study, and Ute Becker, Frankfurt, Ju¨rgen Dengler, Hamburg, Thilo Heinken, Potsdam, Francis Kirkham, Wolverhampton, UK, and Diethart Matthies, Marburg, for valuable comments to earlier drafts of this paper. The first author was funded by a grant by the ‘Evangelisches Studienwerk Villigst’.
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Contents lists available at ScienceDirect
Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee
Plant diversity differs between young and old mesic meadows in a central European low mountain region Gunnar Waesch a, Thomas Becker b,* a b
University of Goettingen, Albrecht-von-Haller Institute for Plant Sciences, Department of Vegetation Analysis and Phytodiversity, Untere Karspu¨le 2, 37073 Goettingen, Germany University of Marburg, Department of Biology, Plant Ecology, Karl-von-Frisch-Str. 8, 35034 Marburg, Germany
A R T I C L E I N F O
A B S T R A C T
Article history: Received 18 April 2008 Received in revised form 28 October 2008 Accepted 29 October 2008 Available online 11 December 2008
Effects of habitat age on species diversity are an important issue in plant conservation. However, effects of habitat age on mesic meadows are poorly investigated. Here we compare plant species richness between old mesic meadows (>150 years) and young mesic meadows (40–60 years) in a low mountain region (Thuringian Forest, Germany). Species richness and species traits were determined in 20 old and 20 young mountain meadows (alliances Polygono-Trisetion, Violion caninae) which were defined using historical maps and compared using species indicator analysis and ANOVA. Additionally we quantified changes in the extent of the area of young and old meadows using a Geographical Information System. Species richness of vascular plants on 20 m2 plots was significantly higher in old than in young meadows, while evenness did not differ between young and old meadows. Endangered plant species were restricted to old meadows, which also contained a higher proportion of habitat specialists. The terminal velocity index of seeds was lower and seed weight was higher in old meadows, indicating a lower importance of wind dispersal in old meadows. This was also indicated by a higher proportion of species with seeds adapted to wind dispersal in young meadows. In old meadows there was a higher proportion of species with seeds adapted to ant dispersal and a lower proportion of species with seeds adapted to animal dispersal. In a representative sub-area of the study region, the total area of meadows has increased by 88% during the 20th century due to transformation of arable fields into meadows, while the area of old meadows declined by 36% during the same time due to abandonment and afforestation. We conclude that the age of the habitat is highly important in order to maintain plant diversity of mesic meadows. Therefore, higher priority should be given to old meadows. ß 2008 Elsevier B.V. All rights reserved.
Keywords: Biodiversity Dispersal Grassland Habitat age Habitat continuity Land use history Species diversity
1. Introduction In agricultural regions throughout Europe, land use has changed considerably within the past 100 years. Among the semi-natural habitats that have been particularly affected by these changes, meadows on moderately fertile soils, denoted as mesic or mesophilous meadows, have often been subject to more intensive management or have been abandoned, and as a consequence, the area covered by mesic meadows has dramatically declined in Europe (Burel et al., 1998; MacDonald et al., 2000). In Germany, for example, mesic meadows were widespread and abundant until 1950 and have declined to 11% of the agricultural area in 2000. This decline is continuing: between 1999 and 2003 the area of meadows has declined from 2.1 to 1.9 million ha, i.e. a 10% loss in only 4 years (Bundesamt fu¨r
* Corresponding author. Tel.: +49 6421 2822053; fax: +49 6421 2822093. E-mail address: [email protected] (T. Becker). 0167-8809/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2008.10.022
Naturschutz, 2004). However, in marginal regions such as low mountain areas new mesic meadows on moderately fertile soils have been created after crop production was no longer economically feasible at many sites (MacDonald et al., 2000; Olsson et al., 2000; Tasser and Tappeiner, 2002; Waldhardt and Otte, 2003). Such regions offer an ideal opportunity for studying effects of habitat age on species diversity in meadows. Extensively managed mesic meadows contain a high number of plant species including many rare and endangered taxa (Korneck et al., 1998), and therefore, species-rich mesic meadows were included in the European Habitats Directive (92/43/EEC; European Union, 1992; NATURA 2000-Codes 6520 and *6230). Because mesic meadows are species-rich and declining, a better understanding of the effects of habitat age on species diversity is very important for their conservation. In general, the absence of plant species at a site can be due to limitation of propagule dispersal and recruitment or subsequent establishment (Mu¨nzbergova´ and Herben, 2005; Stein et al., 2008). Recruitment limitation is due to the actual environmental
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conditions, e.g. nutrient concentration of the soil (Myklestad and Sætersdal, 2004), and management regime (Maurer et al., 2006; Critchley et al., 2007). In meadows, a high nutrient concentration favours competitive plant species and therefore, in strongly fertilized meadows species diversity is often reduced (Janssens et al., 1998; Klimek et al., 2007; Wellstein et al., 2007). In contrast, seed limitation and dispersal limitation of species are a result of the propagule abundance and dispersal potential; however, the importance of both factors declines with time (Ozinga et al., 2005). Of course, a newly created meadow can hardly harbour the full set of typical species, but if seed sources occur abundantly in the vicinity, colonisation might be expected to be advanced some decades after creation. A number of studies have investigated the importance of habitat age for forests and most of them found large differences in plant species diversity and composition between recent and ancient stands (reviewed in Hermy and Verheyen, 2007). In contrast, effects of habitat age on mesic meadows or pastures are poorly investigated (but see Wells et al., 1976; Austrheim et al., 1999; Bissels et al., 2004; Gustavsson et al., 2007), and we do not know of any study that has investigated plant functional characteristics, e.g. mode and ability of dispersal, as an explanation of differences between new and old meadows. Moreover, grasslands and forests differ considerably in many attributes, e.g. in wind influence and management intensity, and hence probably in the importance of wind dispersal and human dispersal (Luftensteiner, 1982). Therefore, results of studies in forests cannot easily be applied to meadows. Here we study plant diversity of young and old mesic meadows in a low mountain region in central Germany. We ask the following
questions: (1) Are old meadows (>150 years) more species-rich than young meadows (40–60 years)? (2) Are there differences between old and young meadows regarding species traits and the abundance of habitat specialists and endangered plant species? (3) Has the area of old meadows changed during the 20th century in the study region? 2. Methods 2.1. Study region and assessment of changes in meadow area Our comparison of young and old meadows encompasses the whole high altitude area of the Thuringian Forest in central Germany, i.e. an area ca. 45 km in length and ca. 15 km in width (508310 –508530 N, 108220 –108560 E) (Fig. 1). In this area meadows are sparsely distributed within a matrix of spruce forests. The meadows studied are located between 430 and 790 m above sea level (mean: 585 m a.s.l.). Mean annual temperature at these sites ranges between 5.2 and 7.0 8C and mean annual precipitation from 634 to 1099 mm (Deutscher Wetterdienst, 2007). The geological substrate is formed from siliceous bedrock (Upper Permian period) resulting in nutrient-poor, moderately acidic brown podzolic soils and rankers (Andreas et al., 1996). The pH of the soils ranges from 4.1 to 5.8 (Waesch, 2003). Changes in the area of young and old meadows were quantified in the 11 km2 biosphere reserve ‘Vesser valley’ (350–848 m a.s.l.), a representative part of the Thuringian Forest (Waesch, 2003) (Fig. 1). For the Vesser valley we determined in a spatially explicit manner the area of meadows which already existed in 1905, and which have been created between 1905 and 1994, and of fields,
Fig. 1. Study region. The comparison of young and old meadows encompasses the whole high altitude area of the Thuringian Forest (A): white dots represent sites with young and black dots those with old meadows. Changes in the extent of young and old meadows were studied in the Vesser valley (B). Different shades of grey correspond (from lighter to darker) to altitudes of 300–500 m, 500–700 m and >700 m a.s.l.
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forests and built-up areas using 1:25,000 topographical maps (see below) with the programme TOPOL (TopoL Software Company, 2007). 2.2. Meadow age assessment The age of the meadows was assessed from historical topographical 1:25,000 maps from 1854 to 1856 (‘Ko¨niglichPreußische Generalstabsaufnahme’) and 1905 to 1939 (‘Preussische Landesaufnahme’). Additionally, we interviewed farmers and landowners and made observations of former agricultural land use in the field, such as agricultural terraces which were built by the farmers at many sites in the Thuringian Forest in order to establish fields. Meadows were defined as old if they had existed in both time layers and thus were older than 150 years and as young if they have not yet existed in 1939 and thus were younger than 60 years. Young meadows were established on former arable land between 1950 and 1960 when crop farming was given up at many sites in the region. 2.3. Selection of study sites and record of vegetation Selection of study sites is based on a previous survey of the meadow vegetation of the Thuringian Forest (Waesch, 2003; 462 plots of 4 m 5 m; cover of each vascular plant species recorded according to the Braun-Blanquet method; Dierschke, 1994). From this data set we excluded all plots with more than two indicator species for wet conditions (species with moisture value >7 according to Ellenberg et al., 2001) and all plots with indicator species for wet conditions above 5% cover in order to reduce effects of different abiotic conditions. Furthermore, we excluded intensively managed meadows with more than two indicator species for high nitrogen concentrations (nitrogen value >7) and all plots with indicator species for high nitrogen concentrations above 5% cover. Moreover, we excluded all grasslands not managed for more than one year. For the remaining plots we defined age of the meadows (see above), and included all 20 meadows younger than 60 years into our study. From the remaining 47 old meadows we randomly selected 20 meadows in order to receive a balanced design. The nomenclature of the vascular plant species follows Wisskirchen and Haeupler (1998), and of the plant communities Rennwald (2000). 2.4. Assessment of species diversity and species traits For the assessment of species richness and species traits we excluded ruderal species also growing in fields (species assigned to the classes Artemisietea, Agropyretea, Plantaginetea, Agrostietea stoloniferae, according to Ellenberg et al., 2001), tree and shrub species growing in meadows only as seedlings, non-indigenous plant species, and species neither characteristic for meadows nor fields from the comparison of species richness and species traits of young and old meadows. This reduction onto a species set characteristic for meadows allows more robust conclusions with respect to this vegetation type (compare e.g. Hermy and Verheyen, 2007, for forests). Finally, we included 115 species characteristic for meadows (and referred to as ‘‘meadow plant species’’ in the following) of the total number of 147 vascular plant species, respectively 90% of all species records. We compared the species richness, Shannon’s diversity, evenness, proportion of different modes of dispersal and clonal growth, terminal velocity and weight of the seeds, seed bank type, proportion of habitat specialists i.e. species with narrow niche, and number of endangered plant species between young and old meadows. Habitat specialists comprise species characteristic of the alliances Polygono-Trisetion and Violion caninae according to Ellenberg et al. (2001), while
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species diagnostic for the order Arrhenatheretalia and the class Molinio-Arrhenatheretea were considered as habitat generalists. The Polygono-Trisetion and V. caninae comprise mesic to nutrientpoor montane meadows, while the Arrhenatheretalia and MolinioArrhenatheretea comprise all types of mesic grasslands or cultural grassland, respectively, i.e. plants characteristic of these syntaxa mostly occur in a wide range of grassland communities and are mostly widespread and common (for hierarchical classification system and more details on syntaxa see Waesch, 2003). The seed bank type was assigned for each species following Thompson et al. (1997), with the exception of Meum athamanticum (transient seed bank; K. Lieberum, pers. comm.) and Alchemilla vulgaris agg. (persistent seed bank; Waesch, 2003). Mode of dispersal was assigned following Mu¨ller-Schneider (1986) with the exception of Carex pilulifera, Dianthus deltoides, and Thymus pulegioides (dispersal by ants; Kjellsson, 1985, and Dosta´l, 2005, respectively), Calluna vulgaris (dispersal by wind; Soons and Bullock, 2008). Mode of clonal growth (stolons, rhizomes) and seed weight were taken from the BIOLFLOR database (Klotz et al., 2002). Indices of terminal velocity, which reflect wind dispersal potential of the seeds according to Tackenberg et al. (2003), were taken from the databases DIASPORUS (Bonn et al., 2000) and LEDA (The LEDA traitbase, 2007), and from O. Tackenberg (unpubl. data). Endangered plant species were identified in the plots according to the German red list (Korneck et al., 1996). 2.5. Statistical analysis Species indicator analysis (Dufreˆne and Legendre, 1997) based on all 147 species determined in the plots was carried out using the software package PC-ORD 4 (McCune and Mefford, 1999), and was used to assess characteristic species for young and old meadows. The values obtained were tested for significance by Monte-CarloPermutation tests with 9999 runs. Shannon’s index, which weights number of species by their abundances (median percent value of corresponding Braun-Blanquet class), was calculated as H0 = Spi lnpi, where pi is the proportion of the ith species of the total abundance of all species (Magurran, 1988), and evenness as E1/D = (1/D)/S. This evenness index based on a diversity index derived from Simpson’s index of dominance D (D ¼ Si p2i , pi = relative abundance of species i) is independent of species richness (Smith and Wilson, 1996). We calculated the following variables per plot and compared differences between young and old meadows with ANOVA: mean unweighted Ellenberg indicator values (based on all 147 species; according to Ellenberg et al., 2001), species richness and Shannon’s diversity, evenness, proportion of different modes of dispersal and clonal growth, terminal velocity index and weight of the seeds, proportion of seed bank types, and four phytosociological categories (see above) as a measure of the degree of specialization of meadow species. Slope, altitude, soil pH, and cover of herb layer of the plots were also compared with ANOVA between young and old meadows, while slope position, i.e. the proportion of plots on upper, middle and lower slopes, was compared with logistic regression. Levels of significance on comparison of the proportions of stoloniferous and rhizomatous plants between young and old meadows were corrected using Bonferroni corrections for the number of tests (Miller, 1981). Variance component estimates using the restricted maximum likelihood method (Sokal and Rohlf, 1995) was used to partition the total variation in the proportion of dispersal types and indicator value for nitrogen between old and young meadows and into the residual variation. This allowed us to compare the relative importance of dispersal limitation, recruitment limitation and environmental conditions for differences in species composition between young and old meadows. Deviation of the proportion of
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endangered plant species from zero was analysed using t-statistic and calculated as t = 0 x/SEx, where x is the mean proportion of endangered plant species of old meadows. Values of seed weight were log-transformed prior to analysis. Homogeneity of variance was tested and residuals were checked for normal distribution. Statistical analyses (apart from species indicator analysis) were performed with SPSS 14 (SPSS Inc., Chicago, USA, 2005). 3. Results 3.1. Environmental conditions in young and old meadows In order to ensure comparability of young and old meadows regarding the questions stated, we first tested differences in abiotic conditions between both meadow types. There were no significant differences in mean species indicator values for moisture and soil reaction between young and old meadows, but indicator values for nitrogen were higher in young meadows (Table 1). Inclination of the slope and altitude did not differ significantly between young and old meadows. There were no significant differences in the position of plots on a slope between young and old meadows. Soil pH and cover of the herb layer did also not differ between young and old stands. Differences in intensity of present management between young and old meadows were not determined. Most meadows were mown once a year in summer followed by cattle grazing in late summer and autumn. 3.2. Plant species diversity Overall, we counted a total of 147 plant species. Of those, 115 species were characteristic for meadows and hence referred to as
Table 1 Environmental characteristics of the meadows investigated. Mean and 1SE. ANOVA, and simple logistic regression, n = 20, each for young and old meadows.
Indicator value for moisture Indicator value for soil reaction Indicator value for nitrogen Inclination of the slope (8) Altitude (m a.s.l.) Upper slope position (% sites) Middle slope position (% sites) Lower slope position (% sites) Soil pH Cover of herb layer (%)
Young meadows
Old meadows
F/(x2)
p
5.2 0.06 4.8 0.18 4.9 0.22 11 2.7 567 22 0 75 25 5.0 0.16 93 3
5.0 0.07 4.4 0.14 4.0 0.19 7 1.2 599 21 10 60 30 4.9 0.08 92 2
1.6 2.4 9.2 2.7 1.0 (2.8) (1.0) (0.1) 0.4 0.2
0.207 0.126 0.004 0.111 0.316 0.090 0.310 0.723 0.516 0.669
‘‘meadow plant species’’ here (Table 2, and Appendix). Both the total species richness of meadow plants (28.7 vs. 15.4 species per 20 m2) and the number of habitat specialists (11.5 vs. 3.0 species per 20 m2) were significantly higher, and the proportion of habitat generalists was significantly lower in old meadows compared to young meadows (Fig. 2a and b). Furthermore, Shannon’s diversity of meadow plants was higher in old than in young meadows (2.5 vs. 1.9, F = 15.7, p < 0.001) while evenness did not differ significantly between young and old meadows. Indicator species analysis resulted in six indicator species for young and 20 indicator species for old meadows (Table 2). 60% of the indicator species of old meadows were habitat specialists characteristic of mesic to nutrient-poor montane meadows, whereas indicator species of young meadows comprised exclusively habitat generalists. Endangered plant species occurred exclusively in old meadows (0.8 vs. 0.0 endangered species per 20 m2, t = 4.1, p < 0.001). These were Alchemilla glaucescens,
Table 2 Indicator species for young and old meadows. Mean percent cover values of occupied plots in superscript. Species diagnostic for: Arrh, Arrhenatheretalia; M-A, MolinioArrhenatheretea; P-T, Polygono-Trisetion; Viol, Violion caninae. Mode of dispersal: ane, anemochory; spei, speirochory; myr, myrmecochory; zoo, zoochory. Mode of clonal growth: stol, stolons; rhiz, rhizomes. Indices of terminal velocity positively reflect wind dispersal potential of the seeds. Seed bank type: tran, transient; pers, persistent. Species
Mode of clonal growth
Terminal velocity index
Indicator species for young meadows Agrostis capillaris, Arrh ane, spei, zoo Rumex acetosella, –a ane, spei, zoo Alopecurus pratensis, M-A ane a Poa pratensis, M-A zoo a Cerastium holosteoides, M-A spei, zoo Rumex obtusifolius/crispus, –a ane, spei, zoo
stol – stol stol stol –
4 0 2 3 2 3
0.1 0.4 0.8 0.3 0.1 1.3
Indicator species for old meadows Meum athamanticum, P-Tb – Luzula campestris, Viol myr, zoo Potentilla erecta, Viol myr Anthoxanthum odoratum, – ane, spei, zoo Knautia arvensis, Arrh spei, myr Plantago lanceolata, – spei, zoo Veronica officinalis, Viol zoo Phyteuma spicatum, P-T myr, zoo Nardus stricta, Viol zoo Lathyrus linifolius, Viol myr Sanguisorba officinalis, – ane Leucanthemum vulgare, Arrh spei, zoo Polygala vulgaris, Viol ane, myr Crepis mollis, P-Tb ane Campanula rotundifolia, Viol zoo Ajuga reptans, M-A myr Anemone nemorosa, P-Ta myr Rhinanthus minor, Arrh – Carex pilulifera, Viol myr Hieracium lachenalii, – ane
– stol, rhiz rhiz rhiz – – stol stol, rhiz rhiz stol rhiz – – – – stol rhiz – rhiz rhiz
0 0 2 2 2 0 2 2 1 0 2 0 2 6 3 ? 0 3 0 5
7.6 0.8 0.5 0.5 4.6 1.8 0.1 0.2 0.7 12.5 2.0 0.4 1.7 0.3 0.1 1.5 2.6 2.9 1.2 0.4
a b
Weak indicator species. Red-listed species.
Mode of dispersal
Seed weight (mg)
Seed bank type
Indicator value
p
Plots occupied (%)
per per per per per per
66.7 52.8 41.9 35.2 29.6 29.6
0.033 0.057 0.047 0.059 0.053 0.056
9022.2 2010.0 505.3 404.7 301.3 301.3
808.8 50.1 252.0 151.7 50.1 50.1
tran per per per tran per per tran tran tran tran per tran tran tran per tran tran per tran
74.0 69.3 66.1 57.6 56.6 51.5 45.0 45.0 43.6 41.3 40.0 39.6 35.0 35.0 47.6 30.0 29.6 25.0 25.0 25.0
<0.001 <0.001 <0.001 <0.001 0.017 0.005 <0.001 0.001 0.005 0.020 0.004 0.013 0.007 0.009 0.018 0.023 0.053 0.045 0.046 0.048
200.7 52.5 52.5 102.5 451.7 152.5 0– 0– 52.5 152.5 0– 50.1 0– 0– 301.7 0– 50.1 0– 0– 0–
7513.8 752.0 703.0 6010.0 851.8 603.8 451.2 450.4 458.3 552.1 404.7 401.3 356.4 351.5 652.1 301.3 301.3 252.5 251.5 251.5
Young (n = 20)
Old (n = 20)
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Fig. 2. (a) Number of total meadow plant species (total) and habitat specialists (special) per plot, and (b) proportions of habitat specialists (P-T, Viol) and habitat generalists (Arrh, M-A) in young and old montane meadows. Habitat specialists represent character species of the syntaxa Polygono-Trisetion (P-T) and Violion caninae (Viol); habitat generalists represent character species of the syntaxa Arrhenatheretalia (Arrh) and Molinio-Arrhenatheretea (M-A). Mean and 1SE, ANOVA, *p < 0.05, **p < 0.01, ***p < 0.001. n = 40, for each pairwise comparison.
Fig. 3. Proportion of types of (a) seed dispersal and (b) clonal growth in young and old montane meadows. ane, anemochory; spei, speirochory; myr, myrmecochory; zoo, zoochory; stol, stolons; rhiz, rhizomes. Mean and 1SE, ANOVA, *p < 0.05, **p < 0.01, ***p < 0.001. The levels of significance on comparison of the proportions of stoloniferous and rhizomatous plants were corrected using Bonferroni corrections. n = 40, for each pairwise comparison.
Arnica montana, Crepis mollis, Lilium bulbiferum, Pedicularis sylvatica, Polygala serpyllifolia and Thesium pyrenaicum. 3.3. Plant species traits Old meadows showed a higher proportion of myrmecochorous (seeds dispersed by ants) plant species, and lower proportions of anemochorous (wind-dispersed), zoochorous (animal-dispersed) and speirochorous (dispersed by agricultural activities) plant species than young meadows (Fig. 3a). There were no differences in the proportion of plant species for which no dispersal agent is known between young and old meadows (19% vs. 16%, F = 1.8, p = 0.19). The terminal velocity index of the seeds was lower (1.8 vs. 2.2, F = 10.1, p = 0.003) and seed weight was higher in old meadows (1.9 mg vs. 1.4 mg, F = 4.6, p = 0.039). Meadow type explained 54% respectively 50% of the variance in proportions of myrmecochorous and speirochorous species, while only 29% variance in nitrogen indicator values were explained by meadow type. Mode of clonal growth differed as follows: in old meadows there was a higher proportion of species growing with rhizomes whereas in young meadows species producing stolons were more abundant (Fig. 3b). Furthermore, in old meadows there was a lower proportion of species which are able to build a persistent seed bank (39% vs. 47%, F = 3.9, p = 0.05) indicating a lower potential of dispersal in time.
3.4. Changes in area of young and old meadows In the Vesser valley, the total area of meadows increased by 88% between 1905 and 1994 due to transformation of arable fields into meadows (Table 3). Within the same time, the area of meadows that already existed in 1905 declined by 36% due to afforestation both spontaneously following abandonment and through planting. Most of the meadows that have disappeared were located at the highest brook valleys or at remote sites within forests. 66% of the total meadow area in 1994 was younger than 90 years.
Table 3 The extent and increase or decrease, respectively, of young and old meadows and other land use forms in the Vesser valley in and between 1905 and 1994.
Old meadows (existing since 1905) Young meadows (created after 1905) Total meadow area Arable land Forests Built-up areas
1905 (ha)
1994 (ha)
1019 – 1019 1413 7754 143
657 1257 1914 189 7643 538
Increase or decrease (ha)
(%)
362 +1257 +895 1224 111 +395
36 – +88 87 1 +276
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4. Discussion The results of this study show that knowledge of habitat age is necessary to understand present day patterns of grassland plants in the agricultural landscape. In the studied landscape, old meadows (>150 years) had a higher plant species diversity, higher numbers of habitat specialists and red-listed species than young meadows (40–60 years). Furthermore, our study shows that old meadows have strongly declined during the 20th century even in a region where the total meadow area has strongly increased. 4.1. Plant species diversity Higher numbers of vascular plant species in old than in young grasslands were also found in sub-alpine pastures in Norway (Austrheim et al., 1999), upland pastures in West Germany (Waldhardt and Otte, 2003) and dry-mesic pastures in Sweden (Gustavsson et al., 2007). Although there were differences in indicator species between those studies and our study, we were able to confirm several of the indicator species for old grasslands found in those studies, e.g. Anemone nemorosa and Polygala vulgaris. Endangered plant species occurred exclusively in meadows older than 150 years. Similar results were found in subalpine pastures in Norway (Austrheim et al., 1999) and Denmark (Ejrnæs and Bruun, 1995). However, endangered plant species can also occur in young meadows as observed in the Thuringian Forest for Silene viscaria and Botrychium lunaria (Brettfeld and Bock, 1994). Old meadows may not be species-rich if they have been intensively managed at some time in the past (Ejrnæs and Bruun, 1995). We found species-poor ‘‘old’’ meadows near the Vesser valley where herbicides were applied during agricultural improvement by the local agricultural cooperative of the German Democratic Republic in the 1960s. Therefore, the term ‘old meadow’ should only be used to describe meadows which have not been agriculturally improved at some time in the past. Very likely, the old meadows in our study were continuously managed as mesic meadows throughout the past 150 years. Until 1950 chemical fertiliser was not applied in high altitude areas in the Thuringian Forest, and after 1950 land owners stated no application of chemical fertiliser for the old meadows. However, we do not know the older history of the meadows, i.e. for how long they existed before 1850 and if there were changes in management including arable land use and abandonment. In a Swedish region, land use 300 years ago was the strongest predictor of today’s species composition and richness of semi-natural grasslands (Gustavsson et al., 2007). Our analyses of diversity are based on a subset of 115 plant species of the total number of 147 vascular plant species found (see Section 2). When all 147 species were included in the analyses, mean species richness was higher in both old (30.7 species per 20 m2) and in young meadows (18.9 species per 20 m2), but overall differences were the same. However, results were slightly clearer when focusing on species characteristic for meadows only. 4.2. Dispersal and recruitment limitation The newly established meadows studied might be colonised by plants due to clonal growth of existing species from adjacent meadows, and by seed dispersal by wind, ants, cattle, and human activities. The higher proportion of myrmecochorous plant species and lower proportions of anemochorous and zoochorous plant species in old meadows may indicate that dispersal limitation causes lower species richness of young meadows. Seed dispersal by ants usually achieves distances of a few decimetres (Go´mez and
Espadaler, 1998). Dispersal by wind is more effective but mainly acts over small distances (Tackenberg et al., 2003). The statement that the higher proportion of anemochores indicates dispersal limitation is also supported by the higher terminal velocities in the old meadows. Therefore, some doubtful cases in the dispersal type classification of Mu¨ller-Schneider (1986) (e.g. the classification of short-distance dispersers like Ranunculus acris and all grasses as wind-dispersed) most likely have no important effect on the results of our study. In general, in grasslands which are (from time to time) grazed by e.g. cattle, zoochory is expected to be most important for long distance dispersal (Couvreur et al., 2005). Our results also confirm that old meadow plant species often do not build a persistent seed bank. Persistent seed banks might enable meadow plant species to survive temporary agricultural land use at least over a few decades. However, persistent seed banks tend to be associated with disturbance and cultivation, and for many meadow plants the ability of re-colonisation from the seed bank is limited (Bekker et al., 1997). In our study old meadow plant species often were rhizomatous, whereas young meadow plant species often had stolons. Stoloniferous species seem to be better adapted for colonisation of new habitats because stolons are often longer than rhizomes and might be transported more easily e.g. in hooves of cattle. However, both strategies normally act on a very small scale. For some anemochores, e.g. C. mollis and Hieracium lachenalii which are strongly confined to old meadows within our study area, high indices of the terminal velocity indicate high dispersal potential. Therefore, these species are probably not limited in their dispersal and therefore might be rather limited in their recruitment in young meadows. In young meadows, fertilization often has led to higher concentration and availability of nutrients. In grasslands, higher nutrient concentrations facilitate competitive plant species and cause higher biomass which also causes increased competition (Myklestad and Sætersdal, 2004; Janssens et al., 1998). Although we used only extensively managed meadows for the comparison, indicator values for nitrogen were higher in young meadows, indicating higher concentrations of nutrients. The variance of indicator values between young and old meadows was smaller than those of the proportions of myrmecochorous and speirochorous species. Furthermore, competitive plant species were largely missing even in young meadows. Therefore, we suggest that effects of recruitment limitation due to increased competition are smaller than effects of dispersal limitation. Ultimately, the impact of the better nutrient supply of the young meadows can only be solved using seed addition experiments. 4.3. Changes in the area of young and old meadows in marginal regions The land use dynamics presented here can be regarded as typical for marginal, agriculturally used regions. An increase in grassland area, caused by transformation of arable land into meadows, has also been reported from other low mountain regions (Waldhardt and Otte, 2003; MacDonald et al., 2000, for a review). However, in the study region the area of old meadows strongly declined due to abandonment and afforestation although the total area of mesic meadows strongly increased. Therefore, the overall situation of meadows in the Thuringian Forest has deteriorated. 4.4. Implications for conservation Our results show that old meadows are more species-rich and contain more endangered plant species than young meadows. Therefore, higher conservation priority should be given to old
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meadows than to younger stands. For old montane meadows our study provides a set of indicator species which can be used for locating old stands (at least in central Europe). Furthermore, for our study region, the locality of old meadows is provided in detail within a map which was given to the local conservation authorities. Such maps would be helpful in identification of potential areas for conservation issues in meadows in other regions, e.g. all regions with high priority in conservation of grasslands according the Habitats Directive of the European Union (European Union, 1992). Young meadows extensively managed as we study here might also be restored by addition of diaspores using cut material from species-rich old meadows (Walker et al., 2004; Donath et al., 2007; Edwards et al., 2007; Stein et al., 2008). Such measures could overcome the dispersal limitation of old meadow plants. Acknowledgements This paper is dedicated to Hartmut Dierschke, Go¨ttingen, a pioneer in research and conservation of montane meadows. We thank all farmers for information about land use and for allowing us to work on their land, Werner Westhus, Jena, for further information, and Friedrich Wulf, Berlin, for field data, and Oliver Tackenberg, Frankfurt, for data on terminal velocities. We thank Erwin Bergmeier, Go¨ttingen, for valuable ideas regarding this study, and Ute Becker, Frankfurt, Ju¨rgen Dengler, Hamburg, Thilo Heinken, Potsdam, Francis Kirkham, Wolverhampton, UK, and Diethart Matthies, Marburg, for valuable comments to earlier drafts of this paper. The first author was funded by a grant by the ‘Evangelisches Studienwerk Villigst’.
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