The significance of connectivity by livestock for restoration and conservation of calcareous grasslands

Connecting remnants of calcareous grasslands (Festuco-Brometea) by (rotational) grazing livestock is considered to be an important tool for the restoration and conservation of these ancient and species-rich habitats. The planning of conservation measures is, however, difficult due to the lack of information on the specific potential that typical calcareous grassland grazers (e.g., cattle, goats and sheep) may provide for the spatial dispersal of diaspores between isolated and fragmented habitat patches. Moreover, information on the long-term success of livestock-based restoration measures is hardly available. Consequently, the thesis at hand aims to fill these gaps. Chapter 1 provides a general introduction to the history of calcareous grasslands, briefly summarizing the development and the traditional management of these nutrient-poor, species-rich habitats. Furthermore, current problems regarding the continuity of calcareous grassland are addressed and the significance of spatial connectivity as well as the implementation of restoration measures aiming to increase the cover area of calcareous grasslands are emphasised. Chapter 2 deals with investigating the epi- and endozoochorous dispersal capability of the historically three most important calcareous grassland grazers – cattle, goats and sheep. Epizoochorous dispersal was shown to be best realized with sheep. The analysis of endozoochorous dispersal showed that cattle were superior in terms of dispersed species richness, in particular for Red List species, indicating the significance of rotational cattle grazing for maintaining species-rich calcareous grassland networks alongside rotational grazing with sheep. The importance of rotational sheep grazing was further explored in the next two chapters. Former calcareous grasslands, which had been abandoned and overgrown or afforested in the past, were restored by clearance in the early 1990s and were subsequently managed by extensive sheep grazing. Since restoration was initiated, the vegetation composition has been continuously monitored over a period of 25 years at seven different study sites with different initial vegetation conditions located in the Swabian Alb. In Chapter 3, the floristic changes of these restored grasslands were analysed in a comparison with adjacent ancient grasslands. The vegetation composition of the restored grasslands distinctly developed towards the reference Festuca-Brometea grasslands but after 25 years differences in terms of nutrient content, rare species and habitat characteristic species were still detected between both grassland categories. Overall, the restoration of former calcareous grasslands by clearance and subsequent grazing proved to be a successful measure, but the reestablishment of the floristic composition was not yet completed after 25 years. Since functional plant traits were suggested as a more appropriate tool for tracking changes in the vegetation composition, the functional composition was investigated in Chapter 4 for one of the clear-cut study sites from Chapter 3 (‘Haarberg-Wasserberg’). Covering the observation period of 25 years, ecological meaningful functional trait attributes were compared between restored and reference grasslands and the development of plant functional groups was investigated. Most functional traits converged quickly towards references values. Dispersal- and establishment-related traits recovered within the first years after restoration, while persistence-related traits showed differences for more than 20 years after initial restoration. Differences that could be detected after 25 years were mostly related to the composition of plant species. Moreover, three functional groups were identified which were characterised by traits that correspond to the classification into competitives, stress-tolerators and ruderals according to Grime’s CSR-strategy. After 15 years, the plant functional group of ruderal species could no longer be found, while the group of competitive species became less important containing mostly woody shrub and tree species. Stress tolerators dominated the restored and the reference grassland after 20 years showing no differences between both grassland categories, which indicated that the functional composition of the restored vegetation recovered over a period of less than 25 years. Chapter 5 shortly summarises the results of the previous chapters and evaluates, based on these results, the potential of grazing livestock for connecting calcareous grasslands and their importance for habitat restoration. Finally, the general advantage of zoochorous dispersal vectors for conservation measures is addressed and recommendations for the implementation of restoration measures concerning calcareous grasslands are given

Functional rather than structural connectivity explains grassland plant diversity patterns following landscape scale habitat loss

Context: Functional connectivity is vital for plant species dispersal, but little is known about how habitat loss and the presence of green infrastructure interact to affect both functional and structural connectivity, and the impacts of each on species groups. Objectives: We investigate how changes in the spatial configuration of species-rich grasslands and related green infrastructure such as road verges, hedgerows and forest borders in three European countries have influenced landscape connectivity, and the effects on grassland plant biodiversity. Methods: We mapped past and present land use for 36 landscapes in Belgium, Germany and Sweden, to estimate connectivity based on simple habitat spatial configuration (structural connectivity) and accounting for effective dispersal and establishment (functional connectivity) around focal grasslands. We used the resulting measures of landscape change to interpret patterns in plant communities. Results: Increased presence of landscape connecting elements could not compensate for large scale losses of grassland area resulting in substantial declines in structural and functional connectivity. Generalist species were negatively affected by connectivity, and responded most strongly to structural connectivity, while functional connectivity determined the occurrence of grassland specialists in focal grasslands. Restored patches had more generalist species, and a lower density of grassland specialist species than ancient patches. Conclusions: Protecting both species rich grasslands and dispersal pathways within landscapes is essential for maintaining grassland biodiversity. Our results show that increases in green infrastructure have not been sufficient to offset loss of semi-natural habitat, and that landscape links must be functionally effective in order to contribute to grassland diversity

Dispersal limitation, eutrophication and propagule pressure constrain the conservation value of grassland green infrastructure

Semi-natural grasslands harbour many of Europe's species of conservation interest. Although larger grasslands are the focus of most conservation activity, many grassland fragments are scattered across landscapes –in small patches or along linear elements– which can form Grassland Green Infrastructure (GGI). GGI has the potential to enhance landscape diversity by creating functioning metacommunities comprising of large semi-natural grasslands and these surrounding fragments. While often highlighted in conservation policy, little is known about the biodiversity supported by green infrastructure itself and thus its conservation potential. To address this issue, we contrasted plant communities in 36 ‘core’ grassland sites across three European countries with communities in the surrounding GGI. We related compositional differences to amount and type of GGI habitat (patches or linear), and the distances for seed dispersal by livestock from core sites. We found substantial differences between the GGI and the core sites, with a mean 54% species turn-over. These differences indicated filtering of stress tolerant species characteristic of low nutrient conditions, and semi-natural grassland specialists. Species with poorer dispersal abilities declined strongly with increasing distances from the core sites. The many additional species in the GGI, not found in the core sites, were predominantly those with a competitive strategy and high seed dispersal ability. We conclude that the biodiversity-supporting role of GGI across Europe is severely constrained by eutrophication, dispersal limitation and external propagule pressure. Actions to improve the quality of GGI might include enhancing dispersal by livestock combined with more type-diversification and less intensively used grassland habitats

Green infrastructure can promote plant functional connectivity in a grassland species around fragmented semi‐natural grasslands in NW‐Europe

Species may benefit from green infrastructure, i.e. the network of natural and anthropogenic habitat remnants in human-dominated landscapes, if it helps isolated populations in remaining habitat patches to be functionally connected. The importance of green infrastructure is therefore increasingly emphasized in conservation policy to counter biodiversity loss. However, there is limited evidence, particularly in plants, that green infrastructure promotes functional connectivity, i.e. supports the colonization of habitat patches across a landscape. We applied landscape genetics to test whether the green infrastructure supports structural and functional connectivity in the grassland perennial Galium verum, in 35 landscapes in Belgium, Germany and Sweden. We used multivariate genetic clustering techniques, nestedness analyses and conditional inference trees to examine landscape-scale patterns in genetic diversity and structure of plant populations in the green infrastructure surrounding semi-natural grasslands. Inferred functional connectivity explained genetic variation better than structural connectivity, yielding positive effects on genetic variation. The road verge network, a major structural component of the green infrastructure and its functional connectivity, most effectively explained genetic diversity and composition in G. verum. Galium verum ramets occupying the surrounding landscape proved to be genetic subsets of focal grassland populations, shaping a nested landscape population genetic structure with focal grasslands, particularly ancient ones, harbouring unique genetic diversity. This nested pattern weakened as road network density increased, suggesting road verge networks enable high landscape occupancy by increased habitat availability and facilitates gene flow into the surrounding landscape. Our study proposes that green infrastructure can promote functional connectivity, providing that a plant species can survive outside of core habitat patches. As this often excludes habitat specialist species, conservation practice and policy should primarily focus on ancient, managed semi-natural grasslands. These grasslands both harbour unique genetic diversity and act as primary gene and propagule sources for the surrounding landscape, highlighting their conservation value

Calcareous grassland restored by clearance and subsequent sheep grazing show fast recovery of plant functional traits – Results from a 25-year-long experiment

In this study, the long-term restoration success of calcareous grasslands was investigated using a functional trait approach. The study site is located in the Swabian Alb, Germany, where a former calcareous grassland patch was restored in the 1990s by clearance of a spruce (Picea abies (L.) H. Karst.) afforestation and subsequent reintroduction of sheep grazing as mobile dispersal vector. Vegetation development was monitored over a period of 25 years, both on the restored and an adjacent never afforested ancient grassland which is still managed by traditional sheep grazing. Changes in the functional composition of fifteen ecological meaningful traits were investigated by comparing the respective attribute expressions of the restored with the ancient reference grassland for each year of observation. A RLQ-analysis was conducted in order to identify plant functional groups. The comparison of attribute expressions showed that differences between restored and ancient grassland decreased rapidly over time. The greatest differences were found in persistence-related traits (e.g., life span and growth form) while dispersal- and establishment-related traits recovered faster. The clustering of plant functional groups showed similarities with Grime’s CSR-strategy, as cluster analysis grouped species with either ruderal, competitive or stress-tolerant trait attributes. 20 years after restoration, stress-tolerators dominated, while the ruderal cluster could not longer be detected and only a small group of competitive, mostly woody species remained. In 2018, RLQ analysis revealed no differences in the functional composition between restored and ancient grassland. The quick functional recovery is most likely attributed to the reestablishment of the traditional low-intensive grazing management but also to the close vicinity of the ancient grassland as no spatial isolation prevented dispersal of plant species. Hence, the functional trait approach showed that restoration by clearance and subsequent sheep grazing was a suitable management in our study

Calcareous grassland restored by clearance and subsequent sheep grazing show fast recovery of plant functional traits – Results from a 25-year-long experiment

In this study, the long-term restoration success of calcareous grasslands was investigated using a functional trait approach. The study site is located in the Swabian Alb, Germany, where a former calcareous grassland patch was restored in the 1990s by clearance of a spruce (Picea abies (L.) H. Karst.) afforestation and subsequent reintroduction of sheep grazing as mobile dispersal vector. Vegetation development was monitored over a period of 25 years, both on the restored and an adjacent never afforested ancient grassland which is still managed by traditional sheep grazing. Changes in the functional composition of fifteen ecological meaningful traits were investigated by comparing the respective attribute expressions of the restored with the ancient reference grassland for each year of observation. A RLQ-analysis was conducted in order to identify plant functional groups. The comparison of attribute expressions showed that differences between restored and ancient grassland decreased rapidly over time. The greatest differences were found in persistence-related traits (e.g., life span and growth form) while dispersal- and establishment-related traits recovered faster. The clustering of plant functional groups showed similarities with Grime’s CSR-strategy, as cluster analysis grouped species with either ruderal, competitive or stress-tolerant trait attributes. 20 years after restoration, stress-tolerators dominated, while the ruderal cluster could not longer be detected and only a small group of competitive, mostly woody species remained. In 2018, RLQ analysis revealed no differences in the functional composition between restored and ancient grassland. The quick functional recovery is most likely attributed to the reestablishment of the traditional low-intensive grazing management but also to the close vicinity of the ancient grassland as no spatial isolation prevented dispersal of plant species. Hence, the functional trait approach showed that restoration by clearance and subsequent sheep grazing was a suitable management in our study

Functional rather than structural connectivity explains grassland plant diversity patterns following landscape scale habitat loss

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Could green infrastructure supplement ecosystem service provision from semi-natural grasslands?

Ancient semi-natural grasslands in Europe are important for ecosystem service (ES) provision. Often, the surrounding matrix contains ‘Grassland Green Infrastructure’ (GGI) that contain grassland species which have the potential to supplement grassland ES provision across the landscape. Here we investigate the potential for GGI to deliver a set of complementary ES, driven by plant composition.We surveyed 36 landscapes across three European countries comprising core grasslands and their surrounding GGI. We calculated community-level values of plant species characteristics to provide indicators for four ES: nature conservation value, pollination, carbon storage and aesthetic appeal.Inferred ES delivery for GGI was substantially lower than in core grasslands for conservation, pollination and aesthetic appeal indicators, but not for carbon storage. These differences were driven by the GGI having 17% fewer plant species, and compositional differences, with 61% of species unique to the core grasslands. In addition, connectivity to the core, the amount of GGI and inferred seed dispersal distances by livestock, were strongly positively correlated with conservation value, pollination and aesthetic indicators. All ES indicators showed similar responses to the GGI spatial structure and distance to the core, suggesting robust effects of these drivers on ES. We projected that improved landscape-wide delivery of nature conservation value and pollination could be achieved through targeted GGI management. Reductions in the distances seeds would need to disperse, more GGI, along with a diversification of the GGI elements, were predicted to enhance service credits.We conclude that for vegetation-related ES, species surveys can be employed to assess potential ES delivery. Creating and enhancing GGI is a useful landscape management strategy to supplement the ES delivered by ancient grasslands.A-rapport, A2645</p