Game exclosure experiment in an endangered endemic Pannonian oak wood community: composition, productivity and reproductive success
Abstract
The species-rich oak wood (Cirsio pannonici-Quercetum pubescenti-petraeaé), endemic to dolomite rocks in Bükk Mts., is recently subject to intensive disturbance from overpopulated big game (especially mouflon). In a field experiment, initiated in 1991, response to long-term protection from grazing was studied in order to assess regeneration potential of the community. Vegetation of a large exclosure (20x20 m) was compared to that of an unfenced, grazed control plot. Species composition, diversity, biomass production and reproductive success of species were sampled during the vegetation period in 2004.
Number of flowering shoots of generative species were counted, whereas three abundant herbaceous species (Symphytum tuberosum, Anthericum ramosum and the poisonous Vincetoxicum hirundinaria) were thoroughly studied by measuring the height of 20 randomly chosen flowering shoots. Presence of herb layer species was recorded in 12 plots (lxl m) within and out of the exclosure. We sampled total aboveground biomass in further 12 plots of 25x25 cm size. Biomass samples were dried and sorted as dead, herbaceous (dicots plus Liliaceae, Orchidaceae) and graminoid (Poaceae, Cyperaceae).
We found no significant difference between Shannon diversity of exclosure and control. To assess the degree of disturbance, we applied CSR values completed and adapted to the Hungarian flora. Species indicating disturbance were slightly more frequent in the grazed plot (p<0.05). The amount of living and dead biomass was higher in exclosure (£><0.01 and p<0.05, respectively). Reproductive success of herbaceous species was higher in exclosure concerning both the number of flowering shoots (£><0.001) and the height of flowering shoots of S. tuberosum (£><0.05) and A. ramosum (£><0.001). In contrast, V hinmdinaria and graminoids had greater reproductive performance in grazed plot (£?<0.01). Species indicating undisturbed site conditions showed higher reproductive performance in exclosure (£><0.05). An explanation for selective grazing of dicots can be their higher nitrogen content.
Our results indicate that the level of disturbance exerted on the community by game favours ruderal species and graminoids, while the reproductive success of a number of species is depressed, and so is biomass production. Reducing the present stock of game can be an effective tool to preserve outstanding species richness and prevent unwanted degradation of the community.
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