The impact of seed predation and browsing on natural sessile oak regeneration under different light conditions in an over-aged coppice stand

Abstract: Sessile oak (Quercus petraea (Matt.) Liebl.) is one of the most important commercial species cultivated at low altitudes in the Czech Republic, and over-aged coppices are a significant part of oak stands in the region. In order to secure a high-valuable timber production (e.g., through conversion of such stands into coppices-with-standards), knowledge of the potential and limits of generative regeneration is essential. This study was conducted in three oak-dominated over-aged coppice stands in different stages of conversion into coppices-with-standards and characterized by different basal area (BA, from 9.3 to 14.1 m2 ha-1) and relative diffuse radiation (ISF, from 12.1 to 35.5%). The study stands were compared with respect to seed predation following acorn fall and oak regeneration parameters. At the time of their fall the acorns represented a sought-after source of food for large mammals (particularly wild boar). At the end of acorn fall, 13-67% acorns were lost due to animal predation. A control evaluation conducted the following spring revealed a decrease of 92-97% in fallen acorns. Despite the major animal impact, a high reserve of acorns and saplings remained in the stands (4 600-29 000 acorns and 66 000-310 000 saplings per ha). With increasing light intensity the oak regeneration density decreased, while the height and age variability of oak regeneration increased. Although saplings were capable of surviving several years under unfavorable light conditions (even below 12% ISF), they require a minimum of 20% ISF (i.e., BA < 16 m2 ha-1) to achieve sustainable height increment. Based on our results, for conversion of such stands into coppices-with-standards we recommend a maximum of 200 reserved trees (BA = 16 m2 ha-1) to achieve successful height growth of the understorey.