Dynamics of Salix caprea L. populations during forest regeneration after strong herbivore pressure

Abstract

Abstract. Broadleaved forest communities degenerated through strong pressure from large herbivores. Relief of this pressure led to regeneration, in particular of Salix caprea and other light‐seeded pioneer trees: Populus tremula, Betula pendula and B. pubescens. This regeneration proceeded following conservation protection of degenerate stands in a nature reserve and later in Biaowiéza National Park. The emergence and development of the Salix caprea population proceeded following the expansion of Picea abies, which coincided with the period of enhanced animal pressure on the broadleaved forest. Salix caprea filled all the gaps in the tree stand after the destruction of trees and undergrowth by herbivores (in the years 1892–1915). The species also appeared abundantly in old, at the time unforested, clearings and felled areas.Here, S. caprea developed large populations with certain trees in good condition, with a growth form typical of forest trees and attaining considerable heights. The majority of trees were 50 ‐ 60 yr old at the time of death, although some individuals reached 74 yr of age. The process of extinction of the Salix population — observed over 19 yr on permanent plots with marked trees — proceeded very quickly, especially in the first decade of observation. It led to the almost complete disappearance of S. caprea from the forest communities of Biaowiéza National Park. The death of individual trees is preceded by impairment of their health and reduced annual increments in the last 4–9 years of their life.The development of populations of permanent constituents of the forest, notably Carpinus betulus, Tilia cordata, Acer platanoides and Ulmus glabra, under the canopy of light‐seeded trees, and the absence of a new generation of pioneer trees points to the end of the process of regeneration in the forest communities of BiaHwiéza National Park.