@phdthesis{Tschoepe2007,
  author    = {Tsch{\"o}pe, Okka},
  title     = {Managing open habitats for species conservation : the role of wild ungulate grazing, small-scale disturbances, and scale},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-13218},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {During the last decades, the global change of the environment has caused a dramatic loss of habitats and species. In Central Europe, open habitats are particularly affected. The main objective of this thesis was to experimentally test the suitability of wild megaherbivore grazing as a conservation tool to manage open habitats. We studied the effect of wild ungulates in a 160 ha game preserve in NE Germany in three successional stages (i) Corynephorus canescens-dominated grassland, (ii) ruderal tall forb vegetation dominated by Tanacetum vulgare and (iii) Pinus sylvestris-pioneer forest over three years. Our results demonstrate that wild megaherbivores considerably affected species composition and delayed successional pathways in open habitats. Grazing effects differed considerably between successional stages: species richness was higher in grazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Species composition changed significantly in the Corynephorus and ruderal sites. Grazed ruderal sites had turned into sites with very short vegetation dominated by Agrostis spp. and the moss Brachythecium albicans, most species did not flower. Woody plant cover was significantly affected only in the pioneer forest sites. Young pine trees were severely damaged and tree height was considerably reduced, leading to a "Pinus-macchie"-appearance. Ecological patterns and processes are known to vary with spatial scale. Since grazing by megaherbivores has a strong spatial component, the scale of monitoring success of grazing may largely differ among and within different systems. Thus, the second aim of this thesis was to test whether grazing effects are consistent over different spatial scales, and to give recommendations for appropriate monitoring scales. For this purpose, we studied grazing effects on plant community structure using multi-scale plots that included three nested spatial scales (0.25 m2, 4 m2, and 40 m2). Over all vegetation types, the scale of observation directly affected grazing effects on woody plant cover and on floristic similarity, but not on the proportion of open soil and species richness. Grazing effects manifested at small scales regarding floristic similarity in pioneer forest and ruderal sites and regarding species richness in ruderal sites. The direction of scale-effects on similarity differed between vegetation types: Grazing effects on floristic similarity in the Corynephorus sites were significantly higher at the medium and large scale, while in the pioneer forest sites they were significantly higher at the smallest scale. Disturbances initiate vegetation changes by creating gaps and affecting colonization and extinction rates. The third intention of the thesis was to investigate the effect of small-scale disturbances on the species-level. In a sowing experiment, we studied early establishment probabilities of Corynephorus canescens, a key species of open sandy habitats. Applying two different regimes of mechanical ground disturbance (disturbed and undisturbed) in the three successional stages mentioned above, we focused on the interactive effects of small-scale disturbances, successional stage and year-to-year variation. Disturbance led to higher emergence in a humid and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens establishment was competition, while in the dry year water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. We conclude that wild ungulate grazing is a useful tool to slow down succession and to preserve a species-rich, open landscape, because it does not only create disturbances, thereby supporting early successional stages, but at the same time efficiently controls woody plant cover. However, wild ungulate grazing considerably changed the overall appearance of the landscape. Additional measures like shifting exclosures might be necessary to allow vulnerable species to flower and reproduce. We further conclude that studying grazing impacts on a range of scales is crucial, since different parameters are affected at different spatial scales. Larger scales are suitable for assessing grazing impact on structural parameters like the proportion of open soil or woody plant cover, whereas species richness and floristic similarity are affected at smaller scales. Our results further indicate that the optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. Further, at the landscape scale, facilitation by late successional species may be an important mechanism for the persistence of protected pioneer species.},
  language  = {en}
}