Spatiotemporal pattern of wild boar rooting in a Central European dry oak forest

Wild boar (Sus scrofa) density has significantly increased worldwide. In Europe, oak acorns are basic diet items for the species. However, regeneration of temperate oak forests has become excessively low. Thus, better understanding of the patterns and dynamics of wild boar rooting and the spatiotemporal relationship between the acorn density and the rooting has special importance. In our study, the acorn density, the presence and intensity of the rooting were measured monthly in a 28-ha oak forest stand between 2016 October and 2019 April. Study site was divided to 400 m2 grid cells to investigate the spatiotemporal patterns of the rooting. Comparing the acorn densities, we stated that in the first 2 years, but not in the third one, the oaks were masting. During the acorn-rich periods (October–April), significant inter-annual differences were found in the proportions of the disturbed area between the non-mast and the other two mast years. Throughout our observations, 9.12% of the cells stayed undisturbed. On average, in 12.59% of the cells new rooted patches appeared, and 15.6% of them was repeatedly disturbed. Rooting were mainly litter disturbances in 71.75% of cases. Throughout acorn fall periods (September–November), the most intensively rooted sites were the poorest in acorns, while the unrooted sites were the richest. Our results demonstrate that wild boars have a great effect on acorn density and on the whole forest by rooting almost the entire ground surface at least once, but also the masting of the oaks has a crucial role in their rooting dynamics.

Do changes in soil properties after rooting by wild boars (Sus scrofa) affect understory vegetation in Swiss hardwood forests?

Recovering from small fragmented populations, wild boars ( Sus scrofa L.) have considerably increased their numbers and their habitat range in many European countries during the past two decades. Although several studies have focused on the impact of wild boar rooting on selected vegetation properties, little is known about effects on entire forest ecosystems. The main goal of our study was to assess how rooting by boars alters soil and vegetation properties. We measured soil chemical and biological properties (C and N concentrations, N availability, and microbial biomass C) as well as several vegetation characteristics (total plant cover, plant species diversity, and number and height of saplings) on paired rooted and non-rooted plots in six hardwood forests in Switzerland. We found that rooting by wild boars led to significant increases in mineral soil C and N concentrations and microbial biomass C, which could lead to improved growth conditions for plants. However, total plant cover and sapling counts were reduced on rooted plots, possibly due to mechanical disturbance or due to reduced plant available N (measured as supply rate in contrast with the observed increase in total stocks of mineral soil N). In view of these results, simple characterizations of wild boar rooting as beneficial or detrimental to forest ecosystems should be handled with care.