Total Plant Species Richness Research Articles

Distribution and richness of aquatic plants across Europe and Mediterranean countries: patterns, environmental driving factors and comparison with total plant richness

AbstractQuestionsWhat are the geographic patterns of γ‐diversity of aquatic plants and what are the main driving factors? Are richness trends for aquatic plants similar to total plant richness? Is the Mediterranean area a hot spot for aquatic plants?LocationEurope and the Mediterranean Basin.MaterialWe listed vascular aquatic plant presence or absence for 44 countries. We also compiled total plant species richness and geographic and environmental variables for each country.MethodsWe first analysed country ordination based on their aquatic flora constrained by environmental variables (dbRDA), and selected the environmental variables best explaining species patterns (BEST analysis). Total species richness patterns were studied using maps and latitudinal gradients. We used generalized additive models (GAM) to detect the main environmental factors driving species richness, both for aquatic plants and total plants.ResultsThe BEST analysis identified a single variable that best explains aquatic plant species distribution: evapotranspiration. However, richness of aquatic plants vs latitude varies and no clear trend was observed. No relation was found between total plant and aquatic plant richness. Aquatic and total plant richness peak between 40° and 50°N, and values were intermediate at low latitudes. GAM related aquatic plant richness with water resources and rainfall, while total plant richness is mainly driven by evapotranspiration and temperature. Hydrophytes were relatively more abundant at higher latitudes than helophytes and the ratio correlated with evapotranspiration.ConclusionSouthern and western Europe hold the highest aquatic plant diversity, although no clear latitudinal species richness patterns were found. Aquatic plant richness is mainly driven by water‐related variables. Total plant richness exhibits a latitudinal pattern influenced by the Sahara desert, which depresses richness at low latitudes. Best predictors of total plant richness patterns are water–energy variables.

Modeling plant species richness using reflectance and texture data derived from QuickBird in a recently burned area of Central Spain

Species richness increases markedly during the first years after fire, driven mainly by the increase in the number of herbaceous species. However, such increase is variable in space and time, due to the role that the different plant life-forms can play after the fire disturbance. In addition, the absence of reliable species richness information can be a limitation for decision making when postfire management actions are needed. In this study we used QuickBird imagery to develop multiscale, spatially explicit predictive models of species richness in a burned area 1year after a fire. The study area is an abandoned dehesa (a Quercus suber (cork oak) open woodland with shrubs) of central Spain, which had been affected by a large summer fire. Two 90×180m macroplots were established, where species richness and percentage cover of various plant life-forms were measured at three spatial scales (1, 25, and 100m2). Total plant species richness was related to reflectance and spectral contrast derived from the multispectral bands of QuickBird and to the Normalized Difference Vegetation Index (NDVI), by using regression tree analysis (RTA) and boosted regression trees (BRT). Furthermore, for the biophysical support of such models, plant species richness was related to field-based compositional data, and life-form percentage cover to satellite data. Results indicated that the relationship between species richness, reflectance and spectral contrast was strong and scale-dependent (1m2: adjusted R2=0.50; 25m2: adj. R2=0.65; 100m2: adj. R2=0.79), whereas NDVI played a minor role at all scales. At the finest sampling scale, a low range of species richness was related to a high variability of spectral and texture responses, due to the excess of spatial detail of the pixel size. At 25m2, a higher range of species richness was related to a low variability of spectral and texture responses; this was probably due to the fact that the sampling size only captured certain portions of plant individuals or life-form associations. At the largest sampling scale (100m2), the highest variability of species richness was adequately related to the spectral and texture responses, due to the spatial fit between the sampling plot size and both the pixel- and plant-sizes. Species richness was closely linked to life-form percentage cover (mainly to herbaceous plant cover), and life-form cover was adequately explained by satellite data, giving a biophysical support to our predictive models. Reflectance and spectral contrast were good predictive tools of total plant species richness at the largest sampling scale, but their predictive power diminished at the smaller scales. This was explained by the range of species richness measured at each scale, the spatial arrangement of species, and the ratio of the spatial resolution (both for pixels from satellite data and for ground sampling plots) to the size of the objects. These results contribute to improve our knowledge about the link between high spatial resolution remotely sensed data and species richness at different sampling scales.

Environmental determinants of woody and herb plant species richness patterns in Great Britain

There is evidence that broad-scale species richness patterns of woody plants correlate with contemporary gradients of environmental energy inputs and water availability. However, climate—richness relationships for herbaceous species are less well known. Here we analyze the seed-bearing flora of Great Britain, quantifying the relationships between total, herb, and woody plant species richness and 14 environmental predictors measuring levels of energy, water, or combined energy and water. PCAs of the environmental variables identified the primary trends of environmental variation across Great Britain related to mean annual temperature and annual precipitation. OLS multiple regression and partial regression analyses identified mean annual temperature as the strongest driver of richness for all species groups. Similarly, reparameterized versions of published energy-water models for woody plant species richness and for angiosperm family richness gradients also identified energy variables as the primary predictors of the richness of all, woody, and herb species.

Fairy rings caused by a killer fungus foster plant diversity in species‐rich grassland

AbstractQuestionsDoes the fairy ring fungus Agaricus campestris affects spatial distribution of co‐existing plant species? Is ring development related to changes of soil physical, chemical, enzymatic and microbiological properties? What are the causes of weakening and subsequent luxuriance of vegetation during fairy ring dynamics in the soil?LocationSpecies‐rich, mowed calcareous grassland, central Italy (43° 17′26″ N, 12° 51′29″ E).MethodsFairy rings were monitored for total plant biomass, species richness and composition in four zones: external grassland (OUT), fungal front (FF), area with flourishing vegetation (BELT) and internal grassland (IN). In each zone, 17 soil parameter were analysed: physical and chemical properties (water‐holding capacity, pH, electrical conductivity, organic C, Olsen P, total N, NH4+, NO3−, hydrophobicity and cyanide concentration), total enzyme activity (FDA) and microbiological features (community‐level physiological profile using BIOLOG EcoPlates™, microbial biomass, fungal mycelium, culturable actinomycetes, bacteria and fungi). A bioassay was performed to evaluate responses of three co‐existing species (Bromus erectus, Cynosurus echinatus and Centaurea ambigua) growing on soil collected from different fairy ring zones.ResultsPlant species composition dramatically changed in response to fairy ring development, with disappearance of most grassland species in the ring‐affected area. Plant biomass and species richness were higher in OUT and IN areas, and lowest in FF. Profound changes in soil properties occurred after fungal passage, with consistent reductions of C and N content and increases of FDA and microbial physiological profiles. Soil from the FF zone had remarkable increases of mineral N forms, electrical conductivity and hydrophobicity, with no trace of cyanide. The bioassay showed species‐specific responses to different soil types.ConclusionsThis study provides evidence that the spread of fairy ring fungi, coupled with a reduction of perennial plant cover, creates empty niches for many short‐lived species.

Influence of limnology on temporal changes in species diversity of aquatic vegetation in two tropical ponds (Kolkata, India)

Monthly changes in species diversity of aquatic macrophytes (richness and Simpson’s diversity index) were studied in relation to various limnological predictors (including their time lag effects) of two tropical ponds, over a period of three years, using regression analysis with correction for temporal autocorrelation.The monthly mean ± SD number of total plant species was 6±2 and 2±1 in Pond 203 and Pond 206, respectively, with significant pond effect. Immediate and 2-months lag of water temperature in the ‘species rich’ pond (Pond 203) appeared to be the significant predictors for Simpson’s diversity index and total plant species richness, respectively. Secchi depth (1-month lag) was found to be the significant predictor for Simpson’s diversity index in ‘less species rich’ pond (Pond 206), while total plant species richness was not found to be influenced by any limnological predictor. Comparative literature review on maximum number of plant species per pond revealed low richness in tropical and subtropical ponds than their temperate counterparts. Among different growth forms, maximum number of emergent and submerged plant species per pond was also less in tropical climates.

Do biogeographic parameters matter? Plant species richness and distribution of macrophytes in relation to area and isolation of ponds in NW Polish agricultural landscape

Effects of pond size and isolation on total vascular plant species richness and number of obligate wetland species were compared. Subsequently, the potential for the presence of spatial patterns in wetland species distribution among ponds in an agricultural landscape was explored. Relationships between species richness and two main biogeographic parameters were analysed using simple and multiple linearised regression models. Spatial patterns were looked for by means of analyses carried out with the R CRAN software (join-count statistics). Simple regression analyses performed on the regional scale (n = 50) revealed the significance of the effect of pond size only (r = 0.46 for total plant species richness and r = 0.28 for wetland species richness vs. pond area). Further analyses conducted on the local scale identified the best multiple regression models in the largest pond cluster (n = 20); the models showed statistical significance of relationships between the species richness and both independent variables (r = 0.80 for total plant species richness and r = 0.70 for wetland species richness vs. pond area and isolation, including mean distance to the nearest ten ponds). Spatial analyses were performed for 26 obligate wetland species selected from 149 species recorded in all the 50 ponds. Exploratory spatial data analysis revealed the presence of significant positive spatial autocorrelation in the distribution of 8 species. In such cases, it is possible to reject the random distribution hypothesis, which justifies exploration of spatial regimes. In practice, correct spatial model specifications may have implications for predicting species occurrences under changing environmental conditions, e.g. changes in the number of ponds.

Responses of Prairie Vegetation to Fire, Herbicide, and Invasive Species Legacy

We evaluate prairie plant community variation in a matrix of restoration treatments in the south Puget Lowland, WA. Native and exotic plant community diversity and composition were measured across areas that differed in burning history and grass-specific herbicide application, having received one to several treatments since 2002. All plots were also variable in historical proximity to a key invasive exotic species (Cytisus scoparius - Scotch broom), a nitrogen-fixing shrub. Three trends were readily apparent from our data: 1) total plant species richness was higher following a prescribed fire. This trend was associated with increases in both native and exotic plants; 2) areas treated with a grass-specific herbicide generally had lower exotic and higher native cover; and 3) using a combination of GIS modeling and community analysis, we found that historical proximity to C. scoparius across all treatment areas was associated with suppressed native species richness. In fact, the magnitude of the effect of historical proximity to C. scoparius was as large as the differences among fire treatment areas. These data suggest that restoration treatments such as fire and herbicide application affect species richness and diversity in prairies, but the changes were neither rapid nor large. Further, exotic species legacies may interact with treatment effects to variably alter restoration outcomes.

Tree diversity and environmental context predict herb species richness and cover in Germany's largest connected deciduous forest

Abstract In temperate deciduous forests, the herb layer contributes most to total vascular plant species richness. The diversity of the tree layer can influence herb layer diversity by modifying resource availability and environmental conditions relevant to herb layer plants. Here, we explore the relationship between tree layer diversity and herb layer species richness and cover. Also, we address the question how different environmental factors that are potentially modified by the tree layer influence herb layer characteristics. Our study area is located in the Hainich National Park, one of the largest continuous stretches of broad-leaved deciduous forest in Central Europe. We recorded herb and tree layer composition on 79 plots selected along a tree diversity gradient ranging from two to nine tree species. In addition, canopy cover, soil pH, mass of the humus layer, soil C:N ratio, soil moisture and distance to the forest edge were determined. We used generalized least square models to analyse effects of tree diversity, environmental variables, and spatial plot positions on herb layer species richness and cover. Species richness and cover of the herb layer increased with increasing tree diversity. In addition, both species richness and cover showed a negative response to increasing canopy cover and mass of the humus layer. Herb layer species richness was also positively related to increasing soil pH and the distance to the forest edge. The proportion of forbs increased with increasing tree diversity, whereas the proportion of tree saplings decreased and the proportion of graminoids was not affected. The proportion of true forest species increased with increasing canopy cover. We conclude that forest stands with a high tree diversity feature a more diverse herb layer and a higher herb cover. Furthermore, the environmental variables humus layer mass, light availability and pH also strongly affect herb layer species richness and cover.

Frequent burning promotes invasions of alien plants into a mesic African savanna

Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning.

Vegetation development in sown field margins and on adjacent ditch banks

The creation of temporal and newly sown field margins for 6 years is a common agri-environment scheme (AES) in the Netherlands. Conservation profits resulting from AES vary over different areas and need further studying. We examined plant species richness in such field margins and adjacent ditch banks in the province of Zeeland, where these linear elements do not experience plant biomass removal after mowing as management strategy. First, during 2 years, we inventoried field margins sown with a wildflower mixture and related the species composition and richness to the age of the margins. In a second assessment, we studied plant species richness on ditch banks protected from arable fields by these margins. Major clusters in a principal component analysis (PCA) on species composition in the field margins showed a succession from sown and ruderal annual species (year 1), to sown perennial species (year 2) and ending with a dominance by tussock forming grass species and Urtica dioica (year 5–6). Total plant species richness decreased with increasing age of the margins, and this was caused by the combination of a decline in sown species and a stable number of not-sown species. The presence of field margins during several years did not result in an increase in plant species richness on adjacent ditch banks. In both the field margins and on the ditch banks, mowing management is not followed by the removal of the cuttings. For plant conservation, the results of these field margins are disappointing, probably due to the lack of a proper management. Therefore, we recommend implementing a hay-making and opening management, to increase plant richness and to reduce noxious weeds in the margins and on the ditch banks.

Effects of agricultural intensification on plant diversity in Mediterranean dryland cereal fields

Summary 1. Agricultural intensification, at field and landscape scales, has caused a decrease in weed richness and changes in species composition. In order to prevent this loss of diversity and develop efficient management regimes, it is important to understand how both aspects of intensification affect plant diversity and the way in which they interact. 2. This study assessed plant diversity at the centre, edges and boundaries of 29 organic and 29 conventional cereal fields distributed in 15 agrarian localities of the NE Iberian Peninsula. We focused on the composition of plant assemblages and on the specific richness at the field level, which was calculated for the whole set of species and for that of characteristic arable weeds. The percentage of arable land together with human settlements was used as a surrogate for landscape complexity and the amount of nitrogen inputs for land‐use intensity. 3. Our results show that both scales of agricultural intensification have a similar negative effect on the total plant species and characteristic arable weed richness, and they also affect plant assemblages. Furthermore, we found no strong interaction between landscape and land‐use intensity for explaining total plant richness. 4. The relative importance of farming intensity and landscape varies depending on the location within the field, which can be attributed to differences in the agricultural impact and limited seed dispersal from adjacent habitats. Management is the main factor in explaining differences among field centres, whereas changes at boundaries are mainly due to landscape characteristics, and at edges both factors are relevant. 5. Synthesis and applications. To preserve agricultural plant diversity it is equally important to prevent agricultural intensification at field and landscape scales. Policies enhancing low‐intensity management techniques, such as organic farming, are the main way to promote diversity inside the fields and will be equally beneficial in simple and complex landscapes for total plant species richness. To maintain diversity within agricultural areas, it is also important to reduce farming intensity at the edges, which would favour characteristic arable weeds and margins’ overall plant diversity.

Plant species richness–environment relationships across the Subantarctic–Patagonian transition zone

AbstractAim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition.Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W).Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data.Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition.Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships.

Estimating total plant species richness in depressional wetlands in the longleaf pine ecosystem

We evaluated methodology for estimating total plant species richness in seasonally inundated depressional wetlands of the longleaf pine (Pinus palustris Mill.) ecosystem. Our objectives were to assess non-parametric estimators of plant species richness based on species incidence plot samples and to determine the minimum sampling requirement for accurate extrapolation of species richness. We quantified species accumulation in varying sample plot areas and spatial distribution within nine depressional wetlands. We recorded species presence on 1 m2, 4 m2, and 100 m2 plots along transects extending across each wetland. Increasing sample area from 1 m2 to 4 m2 plots resulted in an increase in mean species richness up to 33%. EstimateS was used to estimate total species richness for each wetland and sampling method. Species accumulation curves did not reach a plateau and none of the estimates showed a convergence of estimated and observed richness. Due to the large number of unique species and the heterogeneous distribution of species in these hyperdiverse wetlands, we conclude that the most commonly used non-parametric estimators are not effective as tools to obtain accurate estimates of total species richness.

Beneath the veil: plant growth form influences the strength of species richness–productivity relationships in forests

ABSTRACTAim Species richness has been observed to increase with productivity at large spatial scales, though the strength of this relationship varies among functional groups. In forests, canopy trees shade understorey plants, and for this reason we hypothesize that species richness of canopy trees will depend on macroclimate, while species richness of shorter growth forms will additionally be affected by shading from the canopy. In this study we test for differences in species richness–productivity relationships (SRPRs) among growth forms (canopy trees, shrubs, herbaceous species) in small forest plots.Location We analysed 231 plots ranging from 34.0° to 48.3° N latitude and from 75.0° to 124.2° W longitude in the United States.Methods We analysed data collected by the USDA Forest Inventory and Analysis program for plant species richness partitioned into different growth forms, in small plots. We used actual evapotranspiration as a macroclimatic estimate of regional productivity and calculated the area of light‐blocking tissue in the immediate area surrounding plots for an estimate of the intensity of local shading. We estimated and compared SRPRs for different partitions of the species richness dataset using generalized linear models and we incorporated the possible indirect effects of shading using a structural equation model.Results Canopy tree species richness increased strongly with regional productivity, while local shading primarily explained the variation in herbaceous plant richness. Shrub species richness was related to both regional productivity and local shading.Main conclusions The relationship between total forest plant species richness and productivity at large scales belies strong effects of local interactions. Counter to the pattern for overall richness, we found that understorey herbaceous plant species richness does not respond to regional productivity gradients, and instead is strongly influenced by canopy density, while shrub species richness is under multivariate control.

Impacts of regional urbanization development on plant diversity within boundary of built-up areas of different settlement categories in Jinzhong Basin, China

The impact of regional urbanization development on the plant species richness was studied in this paper by taking Jinzhong Basin of Chinese Shanxi Province as the example. 54 villages, 38 towns, 8 county seats and 4 cities within the region were taken out randomly to form the samples I, II, III and IV as the investigation objects, according to the data collected from the said samples, the impact of regional urbanization development on the plant species richness was analyzed through Gleason index and ANOVA. The results show that the species richness of indigenous plants was lowest in cities and highest in villages; the species richness of neophytic plants was highest in cities and lowest in villages. Total plant species richness was the highest in the cities and lowest in towns.

Agrotolerant and high nature-value species—Plant biodiversity indicator groups in agroecosystems

Abstract We analysed the effect of agricultural land use intensity and landscape structure on the plant diversity and improved the monitoring methodology by classifying plant species into two emergent agrotolerance groups: (i) species that occur frequently on agricultural land – common agrotolerant species, and (ii) all other species – so-called nature-value species, including habitat specialists and rare weed species. We tested the hypothesis that the species richness (alpha-diversity at habitat scale) of those species groups has differential response to changes in agricultural land use intensity, landscape structure and habitat characteristics. The proportion of (semi-)natural elements in the landscape enhanced species richness at habitat and landscape scale. Higher fertilisation rate predicted the reduction in small-scale species richness in both species groups. High species richness of agrotolerant species was associated with the vicinity of agricultural land, i.e. open field boundaries, small-area habitat patches and road verges, while it was suppressed by tree or shrub layer. The alpha-diversity of nature-value species was higher in large-area habitat patches and ditch verges. The classification of plant species based on their tolerance to agricultural disturbances is very useful in the evaluation of the effects of agricultural practices on biodiversity. The distinction between agrotolerant and nature-value plant species, and the estimation of habitat structure would increase the effectiveness of biodiversity monitoring in agricultural landscapes in comparison with classical methodology based on the assessment of total plant species richness.

Forest vascular plants as indicators of plant species richness: A data analysis of a flora atlas from northwestern Germany

Our study had the objective to examine whether the number of forest vascular plants in a forest-poor region may be indicative of total plant species richness and of the number of threatened plant species. We also related forest plant species richness to geological and soil variables. The analysis was based on a regional flora atlas from the Weser-Elbe region in northwestern Germany including incidence data of species in a total of 1109 grid cells (each ca. 2.8 × 2.8 km2). All taxa were classified either as forest or non-forest species. Total species richness in the grid cells ranged from 65 to 597, with a mean value of 308. The number of forest species varied between 20 and 309 (mean 176). Grid cells with or without particular geological units differed in total and forest species richness, with those containing peatland and marshland being particularly species-poor. Indicator value analysis showed that both total and forest species richness in the grid cells were related to soil acidity and nitrogen in a hump-backed manner, with the highest number of species found at moderately low values for nitrogen and at intermediate values of pH. Forest species richness was highly positively correlated with the number of non-forest species and threatened non-forest species. Indicators for high species richness were primarily those species that are confined to closed semi-natural forests with a varied topography and relatively base- and nutrient-rich soils. Grid cells including historically ancient forest exhibited a higher species richness than grid cells lacking ancient forest, indicating the importance of a long habitat continuity for a high phytodiversity. The “habitat coincidence” of high species richness is best explained by similar responses of forest species and species of other habitats to the main environmental gradients. It is suggested that the regional patterns found for the Weser-Elbe region can be transferred also to other forest-poor regions in Central Europe.

The effect of logging on vegetation composition in Western Massachusetts

Forest harvesting is one of the most significant disturbances affecting forest plant composition and structure in eastern North American forests, yet few studies have quantified the landscape-scale effects of widespread, low-intensity harvests by non-industrial private forest owners. Using spatially explicit data on all harvests over the last 20 years, we sampled the vegetation at 126 sites throughout central and western Massachusetts, one-third of which had not been harvested, and two-thirds of which had been harvested once since 1984. Seedling and sapling densities increased with increasing harvest intensity, but decreased to levels similar to unharvested sites by year 20 for all but the most intensive harvests. The composition of understory trees appears to be only slightly changed by harvesting, and was strongly correlated with adult tree composition. Regeneration was dominated by Betula lenta followed by Pinus strobus; Quercus spp. exhibited little sapling recruitment, even in Quercus-dominated stands. Total vascular plant species richness increased substantially with harvesting on low C:N sites (i.e., rich soils), but was only slightly increased on high C:N sites. While harvesting was associated with a statistically significant change in vascular plant composition, non-metric multidimensional scaling revealed that climate (temperature, precipitation) and C:N ratios were the major correlates of composition. Overall, the compositional impacts of harvesting were minor, perhaps because of the low-intensity of harvesting. However, our results support observations from elsewhere in the northeastern U.S. of limited oak regeneration on both harvested and unharvested sites. In addition, our results suggest that increased harvest intensity may be expected to alter forest composition, particularly on rich sites where invasive species may increase as a result of harvesting.

Validation of plant diversity indicators in semi-natural grasslands

The use of plant biodiversity indicators in a nationwide survey of semi-natural grasslands in Sweden was examined by comparing results from the survey with additional in-depth studies of plant diversity at the same 30 sites in southern Sweden. Additional grasslands, that were not subjected to the nationwide survey (i.e. rejected after an initial site selection), were also investigated in order to examine the quality of the initial site selection and to assess to what extent they harboured species rich plant communities. Results showed that grasslands that were not included in the nationwide survey were generally smaller in size and that they contained significantly lower plant diversity than sites that were included by the survey. However, some indicator species, including indicators for poor management, were abundant in both types of sites. Biodiversity indicators correctly indicated both plant species richness and plant species density when using data from the in-depth study. However, by comparing indicator species found by the nationwide survey and by the in-depth study, it was shown that the survey overlooked 42% of all indicator species occurrences, which removed the significant relationship between indicator richness and total plant species richness. Furthermore, a null model showed that the chosen indicator species did not perform significantly better than species chosen at random from the available species pool. The conclusion was that validation of indicators is crucial, because even though real correlations exist between taxa or between a subset of species and overall diversity, poor precision of surveys might make these indicators useless. This also suggests that the effort put into searching for the indicator species may have to be so high, that it may be more efficient to go directly into assessing the biological values they are supposed to indicate.

Rapid deterioration of Aquatic Warbler Acrocephalus paludicola habitats at the western margin of the breeding range

In the last German breeding area of the rapidly declining ''Pomeranian'' population of the Aquatic War- bler (Acrocephalus paludicola), the Lower Oder Valley National Park, we investigated changes in habitat suit- ability between 1993 and 2006 by combining monitoring results with repeated assessments of vegetation structure and composition, site conditions, and land use. Sites with recent Aquatic Warbler records showed shorter and sparser vegetation, a thinner litter layer, and a higher total plant species richness and cover of small and least competitive (CSR) species than abandoned or unoccupied sites. On a long-term study plot, during a period of late mowing and subsequent cessation of land use, vegetation height increased, the cover of CSR species decreased, and the site became abandoned by Aquatic Warblers. The probability of Aquatic Warbler occurrence was dependent on elevation and increased with the proportion of early mown or grazed area in the preceding year, with early use being most important on slightly higher elevated sites. This rapid deterioration of eutrophic habitats by delayed or discon- tinued land use is atypical for the majority of Aquatic Warbler breeding habitats. We conclude that both late or no land use and land use during the breeding season nega- tively affect the Pomeranian breeding sites and that a more sophisticated and flexible land management is urgently needed.