Rainer Waldhardt

Analysing land-cover changes in relation to environmental variables in Hesse, Germany

Land-use and land-cover changes affect ecological landscape functions and processes. Hence, landscape ecologists have a central interest in a comprehensive understanding of such changes. Our study focuses on the relationships between environmental conditions and agricultural land-cover changes. We present a method to (i) characterise the major spatial-temporal processes of land-cover changes, (ii) identify the correlations between environmental attributes and land-cover changes and (iii) derive potential environmental drivers of land-cover changes in a German marginal rural landscape. The method was applied to study land-cover dynamics from 1945 to 1998 in the districts of Erda, Steinbrücken and Eibelshausen, situated in the marginal rural landscape of the Lahn-Dill Highlands, Germany. We employed land-cover data gained by the interpretation of multi-temporal aerial photographs. Various environmental variables were introduced into the analyses. We identified physical landscape attributes (elevation, slope, aspect, available water capacity and soil texture) and structural landscape dimensions (patch size, patch shape and distance between patch and nearest settlement). With the aid of GIS, K-means partitioning and canonical correspondence analysis, we investigated land-cover trajectory types, land-cover transitions at individual time intervals and their relationships to these environmental variables. Our results show that, between 1945 and 1998, land-cover changes correlated with the physical attributes of the underlying landscape. On the other hand, the structural landscape dimensions correlated with land cover only in periods of minor land-cover changes (1972–98). Greater diversity of physical landscape attributes is correlated with greater land-cover dynamics. Besides the important influence of socio-economic factors, land-cover changes in the study areas took place within the relatively stable physical constraints of the underlying landscape.

Indicators of plant species and community diversity in grasslands

Abstract Parameters which are directly related to both land use change and biodiversity may be useful tools to indicate biodiversity in marginal landscapes. In these landscapes for about five decades abandonment of cultivation, especially in favour of extensive grassland use and succession on abandoned fields, has led to considerable changes in the landscape structure. Regions such as the Lahn-Dill Highlands (Hesse, Germany), formerly characterized by small-parcelled crop and grassland rotation, increasingly feature old grassland communities over large areas. Impacts of changes in the landscape structure on the floristic–phytocoenotic diversity have been studied in two landscape tracts of this region that today are mainly used as grassland. Reconstruction of land use dynamics based on multitemporal aerial photograph interpretations of the period from 1945 to 1997 confirm the predominance of cultivation until ca. 1960 in both areas. On the basis of phytosociological surveys in one stand abandoned 3 years before the survey and in each three grassland stands of different age classes (11–27, 28–38, 39–46 and over 46 years), the floristic–phytocoenotic diversity of these stands is characterized as follows: (i) Flora and vegetation are clearly differentiated in relation to stand age. (ii) The vegetation of the older (>38 years) stands is more comparable among one another than is the vegetation of younger stands. (iii) 19- to 33-year-old stands have the highest number of exclusive species. (iv) Old stands (>46 years) have the highest α-species richness. (v) The stands can be classified into different vegetation types in relation to age. The floristic–phytocoenotic diversity is associated with site differences of the above age classes. Older stands are more frequent at upper slopes and the pH values of their soils are lower. With a small methodological outlay, grassland stands of different age and species diversity can be differentiated by red–green–blue (RGB) colour tonal values from false-colour infrared (FCIR) aerial photographs. The results open up possibilities for the qualitative and quantitative indication of floristic–phytocoenotic diversity in grasslands on the basis of stand age, site factors and also green and blue tonal values from the respective FCIR aerial photographs. Furthermore the results indicate that it is necessary to retain old grassland stands, as well as a mosaic of extensively used grassland stands of different ages to retain plant species and community diversity in the study region.

Estimation and prediction of plant species richness in a mosaic landscape

Traditional agricultural mosaic landscapes are likely to undergo dramatic changes through either intensification or abandonment of land use. Both developmental trends may negatively affect the vascular plant species richness of such landscapes. Therefore, sustainable land-use systems need to be developed to maintain and re-establish species richness at various spatial scales. To evaluate the sustainability of specific land-use systems, we need approaches for the effective assessment of the present species richness and models that can predict the effects on species richness as realistically as possible. In this context, we present a methodology to estimate and predict vascular plant species richness at the local and the regional scale. In our approach, the major determinants of vascular plant species richness within the study area are taken into consideration: These are according to Duellis mosaic concept the number of habitat types and of habitat patches within area units. Furthermore, it is based on the relative frequencies of species within habitat types. Our approach comprises six steps: (i) the determination of present habitat patterns within an observation area, (ii) the creation of a land-use scenario with simulated habitat patterns, (iii) the determination of species frequencies within habitat types of this area, (iv) a grouping of habitat-specific species, (v) the estimation of the probabilities for all species (or habitat specialists) to occur, either in stepwise, exponentially enlarged landscape tracts (local scale), or in the entire observation area (regional scale), and (vi) the validation of the estimated species numbers. The approach will be exemplified using data from the municipal district of Erda, Lahn-Dill Highlands, Germany. The current species numbers to be expected on the basis of probability calculations were compared with those recorded on the basis of extensive field work. This comparison shows that, on the basis of our simple calculations, the current local plant species richness can be predicted well, with a slight underestimation.

Biodiversity and landscape: summary, conclusions and perspectives

Abstract Based on the contributions in this special issue and further references approaches to indicate biodiversity at the landscape scale are summarized and discussed. The complexity of biodiversity, its levels of aggregation and its specific relations to “natural” and “anthropogenic” environmental conditions depending on spatio-temporal scales are emphasized. The necessity of further research is stressed and research fields are differentiated.

Seed bank diversity in mesic grasslands in relation to vegetation type, management and site conditions

Abstract Questions: 1. Do different management types (i.e. hay meadow, silage meadow, meadow-pasture, pasture) have different impact on the size and composition of the seed bank of mesic grassland (Arrhenatheretalia)? 2. How strong is the effect of management on the seed bank in relation to above-ground vegetation, edaphic factors and land-use history? 3. Are there differences in C-S-R plant strategy types and seed longevity under different management regimes? Location: Lahn-Dill Highlands in central-western Germany. Methods: Above-ground vegetation and the soil seed bank of 63 plots (at 21 sites) in mesic grasslands were studied. Differences between management types in quantitative seed bank traits and functional characteristics were tested by ANOVA. The impact of management, above-ground vegetation, site conditions and land-use history on seed bank composition were analysed by partial CCA. Results: Management had no significant impact on species richness and density of the seed bank but significantly influenced their floristic composition and functional characteristics. CCA revealed that even after adjustment for soil chemical parameters and above-ground vegetation management still had significant impact on seed bank composition. ANOVA revealed that silage meadows contained higher proportions of R-strategy compared to hay meadows. In contrast, in hay meadows and meadow-pastures proportions of S-strategy were higher than in silage meadows. Conclusions: The type of grassland management has little impact on quantitative seed bank traits. Management types with a high degree of disturbance lead to an increase of species following a ruderal strategy in the seed bank. Irrespective of management type only a limited proportion of characteristic grassland species is likely to re-establish from the seed bank after disappearance from above-ground vegetation. Nomenclature: Wisskirchen & Haeupler (1998).

Floristic diversity at the habitat scale in agricultural landscapes of Central Europe: summary, conclusions and perspectives

Abstract Referring to the agricultural history in Central Europe determinants of floristic diversity at the habitat scale and the decline in diversity over the last few decades are described. In this context the preservation of floristic diversity is stressed to be one important goal of modern, multifunctional agricultural land use. To reach this goal indicators of diversity are useful tools to evaluate the effects management practices have on floristic diversity in agro-ecosystems. However, “key indicators” that allow an easy assessment and evaluation of diversity are still lacking. Potentially, indicators of biodiversity measures at the habitat scale can be developed from a large number of parameters. An attempt to classify parameters into three major types of indicators and requirements indicators have to meet are presented. Based on the contributions in this special issue and further references recent approaches to indicate floristic diversity at the habitat scale in agricultural landscapes of Central Europe are summarized and discussed. It is concluded that further research should focus on the validation of existing approaches and their integration into a comprehensive set of indicators and on the development of standardized modes of collection for data.

Contrasting weed species composition in perennial alfalfas and six annual crops: implications for integrated weed management

Weed communities are most strongly affected by the characteristics and management of the current crop. Crop rotation may thus be used to prevent the repeated selection of particular weed species. While weed communities are frequently compared among annual crops, little is known about the differences between annual and perennial crops that may be included in the rotations. Moreover, nearly all existing studies (17 articles reviewed) are based on local field experiments rather than commercial fields. We compared the weed composition in perennial alfalfas (Medicago sativa) and six annual crops: winter wheat (Triticum aestivum), oilseed rape (Brassica napus), pea (Pisum sativum), sunflower (Helianthus annuus), maize (Zea mays) and sorghum (Sorghum bicolor) using data from 632 commercial fields in western France. Weed species composition showed the strongest dissimilarities between perennial alfalfas and all annual crops, followed by the well-known differences between autumn- and spring/summer-sown annual crops. Indicator Species Analysis showed that most weed species either preferred perennial alfalfas (including Taraxacum officinale, Veronica persica, Crepis spp., Poa trivialis, Silene latifolia, Capsella bursapastoris and Picris spp.) or annual crops (including Mercurialis annua, Galium aparine, Fallopia convolvulus, Chenopodium album and Cirsium arvense). Perennial alfalfas thus suppressed many weeds that are widespread (and sometimes problematic) in annual crops while favouring other species. Shifted weed composition and reduced frequency of several noxious weeds suggest that perennial alfalfas may be used as a valuable part of integrated weed management, reducing the need for herbicides and sustaining plant and animal diversity in agricultural landscapes.

Estimating Vegetation Cover from High-Resolution Satellite Data to Assess Grassland Degradation in the Georgian Caucasus

In the Georgian Caucasus, unregulated grazing has damaged grassland vegetation cover and caused erosion. Methods for monitoring and control of affected territories are urgently needed. Focusing on the high-montane and subalpine grasslands of the upper Aragvi Valley, we sampled grassland for soil, rock, and vegetation cover to test the applicability of a site-specific remote-sensing approach to observing grassland degradation. We used random-forest regression to separately estimate vegetation cover from 2 vegetation indices, the Normalized Difference Vegetation Index (NDVI) and the Modified Soil Adjusted Vegetation Index (MSAVI2), derived from multispectral WorldView-2 data (1.8 m). The good model fit of R2  =  0.79 indicates the great potential of a remote-sensing approach for the observation of grassland cover. We used the modeled relationship to produce a vegetation cover map, which showed large areas of grassland degradation.

Assessing the spatial distribution of grassland age in a marginal European landscape

Grassland age is increasingly recognised to be an indicator for present-day biodiversity, e.g. plant species richness, and is also important for other landscape functions. We developed a methodological approach to systematically assess the spatial distribution of grassland age in marginal European landscapes. This approach - applied to the Lahn-Dill Highlands (1270 km(2)), a marginal landscape in Hesse, Germany - comprises three steps: (1) in a two-stage stratification process, we pre-stratified the study area according to recent land-cover patterns and their changes between 1955 and 1995 (stratification I) and classified grassland types by combining data on soil moisture, base-richness, and elevation (stratification II). From 50 grassland types, we randomly selected 1000 representative grassland patches. (2) We determined the age of these patches by means of aerial photograph interpretation of a chronosequence dating back to 1953 and classified each patch with respect to the age classes young (<18 years), mid-aged (18-47 years), and old (>47 years). (3) Based on this information, we calculated grassland type-specific probabilities for grassland patches to belong to the respective age classes. These probabilities were projected to districts by direct extrapolation. An exemplary validation of extrapolation results for two test areas was performed. The results revealed that 49% of the investigated patches were old grassland. The remaining patches were mid-aged (36%) or young grassland (15%). The extrapolation results indicated accordingly a predominance of old grassland at the district scale. Occurrences of mid-aged grassland were concentrated in districts with a pronounced land-cover change, whereas young grassland is apparently evenly distributed across the study area. Validation results suggest that our approach is suitable for a realistic estimation of grassland age in marginal European landscapes. The method may be applied in landscape models of various disciplines that rely on large-scale information on grassland age.

Relationships between plant diversity, vegetation cover, and site conditions: implications for grassland conservation in the Greater Caucasus

Overgrazing, land use abandonment and increasing recreational activities have altered the vegetation of high-montane and subalpine grassland of the Caucasus. The failure of previous restoration efforts with unsuitable and exotic plant species indicates the need for information on the present vegetation and in which way it might change. Within the Greater Caucasus, we have described and quantified the mountain grassland which develops under characteristic overgrazed and eroded site conditions. Further, we have proposed potential native plant species for revegetation to restore and conserve valuable mountain grassland habitats. We used non-metric dimensional scaling ordination and cluster comparison of functional plant groups to describe a gradient of grassland vegetation cover. For our study region, we identified four major vegetation types with increasing occurrence of ruderal pasture weeds and tall herb vegetation on abandoned hay meadows within the subalpine zone. Within high-montane grassland a decline of plant diversity can be observed on sites of reduced vegetation cover. Due to a low potential of the grassland ecosystem to balance further vegetation cover damage, the long-term loss of diverse habitats can be expected. We conclude with management recommendations to prevent erosion and habitat loss of precious mountain grasslands.