Influence of Soil Quality on the Browsing Intensity of Ungulate Herbivores on Tree Species in European Forests

Abstract

The impact of ungulate browsing on tree saplings has been found to have a negative effect on the regeneration of temperate forests. However, it remains ambiguous whether a relationship exists between browsing intensity and soil quality in natural forests. Therefore, we conducted a study in Roztoczańskie National Park to investigate the relationship between soil quality and browsing intensity for tree saplings. The aim was to gain a better understanding of how soil quality affects the browsing of ungulates on tree species. Baseline data (sapling height, basal diameter, crown length and width, browsed-shoot diameter, and soil samples) were collected from the 22 belt transects established in the permanent research plots. The soil quality index was calculated using physical and chemical soil properties. Twig dry mass was determined using allometric equations. Species relative density and browsing intensity were assessed through field measurements. Relationships between the variables were established using a linear regression model. The results suggest that browsing intensity is influenced by the gradient of the soil quality index and that it varies between tree species. Along the increasing soil quality gradient, tree species’ relative density (p = 0.012) and twig dry mass m−2 (p = 0.005) significantly decreased for A. pseudoplatanus. In contrast, browsing intensity increased significantly with an increasing species relative density for A. pseudoplatanus (p = 0.00) and C. betulus (p = 0.001) and with an increasing twig dry mass for F. sylvatica (p = 0.034) and C. betulus (p = 0.004). Browsing intensity increased significantly with an increasing soil quality index for F. sylvatica (p = 0.027) and decreased significantly for A. pseudoplatanus (p = 0.036). Notably, there was a significant positive relationship between browsing intensity and species relative density and twig dry mass, indicating that ungulate browsing is concentrated where browsing is abundant. These results provide insights that can be used to improve management and conservation strategies to protect tree species vulnerable to ungulate herbivory.