Preferential browsing impact in an uneven-aged beech forest in Hungary

Abstract

Selective browsing effects of ungulates, e.g. deer species, can both stabilize or destabilize forest ecosystems and influence biodiversity. However, deer impacts on forest biodiversity are generally considered to be negative. It is clear that herbivorous populations impact forest habitat quality, vegetation composition and dynamics, but also habitat quality (especially plant food supply in the understory) impacts the population dynamics and feeding behaviour of large herbivores. The total forest cover of Hungary is 20,7%; most of it (> 90%) is managed by clearcutting or uniform shelterwood method. One of the most important forest tree species for forest management is European beech (5,9%). The long-term sustainability of forests dominated by drought-sensitive native species, such as beech, highly depends on the management practices involved. Diverse uneven-aged forest ecosystems probably will be more resistant to climate change effects and herbivory impacts. We, therefore, investigated the ungulate browsing impact in an uneven-aged beech forest area, which is a rare example in Hungary still overdominated by even-aged forestry system. The study area was in Pilis Mountains at Pilisszentkereszt Forestry, Hungary. There single-tree and group selection dominates the forested area of more than 1500 ha including mainly beech stands. Our seasonal investigations were carried out between 2008 and 2011. We counted the number of sprouts of all woody species available and accessible to large herbivores and the number of browsed ones in the understory layer. We estimated the density of beech saplings and the amount of optimal forage biomass provided in the understory. Density of naturally growing beech saplings was very high (between 30000 and 60000 saplings per hectare), meanwhile browsing impact of ungulates on beech saplings was negligible (94% of saplings was unbrowsed). The proportion of beech sprouts was much larger than that of other woody species in the understory food supply. But calculating the forage biomass provided by different species, ash biomass exceeded beech biomass in several cases. The total estimated seasonal forage biomass in the understory during the study period was between 158 and 1800 kilograms per hectare. The estimated understory biomass consumed by ungulates was generally lower than 5%. Considering the selection of ungulates among understory species browsing on European ash and blackberry were conspicuous, meanwhile beech was avoided. Proportion of beech in the understory biomass removed by ungulate browsing was negligible; mainly ash and sometimes blackberry dominated the consumption. Besides biodiversity conservation close to nature management of beech forest can be profitable by several reasons. Lack of fences against large game species and dense natural regeneration of beech diminish the costs of forest management. The selective browsing of herbivores is a natural supporting mechanism of ungulates saving money to forest managers by retarding the competitor tree and shrub species of beech. Selective impact of ungulates should be essential in the long-term dynamics of both, managed and virgin beech forests.