Ungulate impact on the regeneration of an uneven-aged dry oak forest
DOI:
https://doi.org/10.56617/tl.3614Keywords:
continuous cover forestry, sustainable forest management, forest regeneration, selective ungulate browsing, wild boar impactAbstract
The regeneration of deciduous oak forests in the Northern Hemisphere have become poor lately. Many researchers think the reason behind this phenomenon is the continuously growing populations of big game species. The proper forest regeneration requires sufficient and healthy acorn crop. Both, the oak acorns and the saplings are sensitive to the effects of the ungulates. The oak acorn is an essential forage for many acorn predators, including wild boar (Sus scrofa). In later life stage the oak saplings could be under significant browsing, however it strongly depends on the actual patterns of the selective ungulate foraging. Based on this, we investigated the impact of big game species on the acorn and sapling density at the main patches of the forest regeneration, within the forest gaps, but also at other control sites. Our study area was a dry oak selection forest near Zánka in Hungary, where the local foresters assumed the regeneration permanently impeded by game impact. In this forest the deliberately generated gaps – to help the regeneration – are fenced, which are only able to exclude wild boars. Meanwhile the gaps evolved in a natural way remain unfenced. During our investigation in 2015, we counted the number of available and browsed shoots of all woody plant species accessible as food to ungulates. According to this, we described the occurrence of different tree and shrub species, and the browsing preferences of ruminants. Moreover, we determined the density of oak saplings and their condition according to browsing and also the density of oak acorns and their condition. Our results showed that the shoots of Turkey oak (Quercis cerris) were only frequent in the fenced gaps and the sapling density of this species was also higher there, than in the unfenced plots. We only found sessile oak (Quercus petraea) saplings in the gaps, but their presence was more pronounced in the unfenced gaps. Neither of the oak species was preferred by the ungulate herbivores. Regarding the acorn production, there was no statistical difference between the two gap types. But considering the absolute value there were almost twice as many acorns in the fenced gaps. However, even there it was at a low density (3.4 pcs/m2). In the unfenced gaps the acorns were usually damaged by small rodents, while in the fenced gaps there were more germinated ones. Our research shows that the impact of ungulates might be locally strong on the forest regeneration. But in our study area, the regeneration is probably not strictly influenced by the browsing on saplings. Wild boars might have a stronger impact on it by their acorn consumption. Nevertheless, besides ungulates we should also consider other factors which could have essential roles (acorn yield, acorn germination, other acorn predators and other sapling consumers).
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