Vegetation patterns and processes in semi-natural open habitats and the contribution of wild red deer to their conservation
by Friederike Riesch
Date of Examination:2019-05-29
Date of issue:2019-09-30
Advisor:Prof. Dr. Johannes Isselstein
Referee:Prof. Dr. Johannes Isselstein
Referee:Prof. Dr. Niko Balkenhol
Referee:Prof. Dr. Gert Rosenthal
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Abstract
English
Traditional practices of human land use have shaped semi-natural open habitats over the past millennia, resulting in the typical European cultural landscapes with characteristic, diverse species communities. In the course of agricultural intensi-fication during the twentieth century, however, areas extensively used, e.g. for pastoral farming, have declined immensely. At the same time, agriculturally suitable soils have been widely improved, especially by mineral fertilisation. This has been associated with widespread losses of plant diversity, as increasing nutrient availability promotes plant species that are strong competitors for light and thus increases the exclusion of less competitive species. Little is known about plant community patterns related to soil chemical parameters in open habitats where the soil nutrient status has not been anthropogenically enhanced. In the absence of traditional agricultural land use, conservation management is required to remove biomass from open habitats in order to prevent secondary succession and related changes in plant communities. Extensive grazing with large domestic herbivores has proven beneficial to the maintenance of semi-natural open habitats. Under certain circumstances (e.g. large, inaccessible areas), however, livestock grazing is impossible. Therefore, there is a need to study if wild herbivores that do not require fencing, regular monitoring or veterinary treatment could be an alternative option for conservation grazing. The present work took advantage of a study area where military land use has prevented agricultural intensification during the past century: the Grafenwöhr military training in north-eastern Bavaria, Germany. In this area, abundant wild and free-ranging red deer (Cervus elaphus) use the open land, such as semi-natural grasslands and heathlands, for foraging. Focusing on two exemplary Natura 2000 open habitat types (European dry heaths and lowland hay meadows), this thesis explores (i) the relationship between soil chemical parameters and vegetation patterns under nearly pre-industrialised soil conditions, and (ii) the interplay of grazing by free-ranging red deer and different vegetation processes. Chapter 1 investigates how the naturally occurring variability in phosphorus and other soil chemical parameters relates to plant species community composition and richness in open habitats. In 2014, plant species composition was surveyed in 40 and 54 relevés in heathlands and grasslands, respectively. The insights provide valuable information about the sensitivity of different semi-natural habitats to changes in soil chemical parameters. Plant species richness increased with increasing soil pH in heathlands and decreased with increasing soil phosphorus concentration in grasslands. Therefore, in order to maintain suitable soil conditions for diverse plant communities in semi-natural open habitats, conservation management should take care to prevent further acidification in heathlands and even low phosphorus input in grasslands. Chapter 2 & 3 look into the contribution of wild red deer to the maintenance of semi-natural grasslands and heathlands based on a grazing exclusion experiment running from 2015 to 2017/18 on a subset of the sampling sites used in the 2014 plant survey. In order to assess synergistic effects between wildlife grazing and additional biomass removal measures (i.e. burning, mowing), the sampling sites in grasslands included burnt, mown and untreated treatment areas. Chapter 2 analyses the dynamics of vegetation productivity, forage quality and biomass removal by red deer, using data from movable exclusion cages installed on open, continuously grazed plots and translocated five times per vegetation period. The amount of biomass annually removed by wild red deer was quantitatively similar to the forage removal by domestic grazing animals in stocking rates commonly used in conservation grazing. Despite the different productivity and grazing requirements of semi-natural grasslands and heathlands, biomass removal by red deer, with its habitat-type–specific seasonal variation, proved beneficial in both habitat types. Mowing, enhancing productivity and forage quality in the late season, increased the grassland attractiveness to red deer, and could therefore be a strategy to spatially direct the grazing activities by free-ranging red deer. Comparing the vegetation development in open and permanently fenced plots in grasslands and heathlands, Chapter 3 studies how plant diversity and vegetation structure respond to the exclusion of red deer. Plant community composition diverged in open and fenced blots in both habitat types. In grasslands, plant species diversity was significantly reduced in fenced compared to open plots. Increasing height of sward and litter in both habitat types and, additionally, reduced cover of bare soil and increasing number of woody plant individuals in heathlands indicated beginning succession when red deer were excluded. In grasslands, the most pronounced differences between open and fenced plots occurred in the mown treatment, suggesting that red deer grazing combined with mowing could create particularly favourable conditions for grassland plant diversity. Taken together, Chapter 2 & 3 indicate that grazing by wild red deer could be useful to the conservation management of semi-natural open habitats, quantitatively—in terms of biomass removal—and qualitatively, providing benefits to vegetation structure and diversity. An adapted wildlife management that allows red deer to forage in open landscapes could therefore contribute to maintaining semi-natural open habitats and simultaneously reduce the potential for conflict between red deer and forestry. Integrating wild red deer into the conservation management seems promising and practicable in particular for large areas of conservation interest, such as core zones of national parks, wilderness areas or active and abandoned military training areas. Overall, the insights from this thesis can contribute to developing suitable strategies for the conservation management of semi-natural open habitats to preserve their biodiversity and ecosystem services in times of increasing anthropogenic pressure on ecosystems.
Keywords: Cervus elaphus; European dry heaths; forage; grazing; lowland hay meadows; military training area; mowing; Natura 2000; open habitat conservation; prescribed fire; plant community composition; species richness; rewilding