The role of natural disturbances in the dynamics of protected forests
Zbigniew Maciejewski, Jerzy Szwagrzyk
The topic of our study was process of spontaneous regeneration in secondary mixed forest stand growing on a fertile habitat before and after extensive blowdown. The object of the research was the windfall located in the Roztocze National Park; the windfall of a size of about 2.5 ha was created in August 2008 as a result of hurricane. Inside the current windfall area there was a 0.5-ha permanent research plot, where long-term research on spontaneous regeneration of secondary forest stands has been conducted since 1973. Therefore we could compare trends in natural forest regeneration before and after the windfall. Based on the obtained results it can be concluded that the occurrence of windfall substantially changed the direction of regeneration processes and strongly accelerated the rate of changes. During the last decades before disturbance the tree stand studied was in the phase of spontaneous regeneration towards a potential natural community from Fagetalia sylvaticae order, typical for rich and well-drained habitats of the oak-hornbeam community in the Roztocze National Park. Species with greater light requirements Scotch pine Pinus sylvestris, aspen Populus tremula and oaks Quercus robur and Quercus petraea, ecologically alien to the potential plant community, retreat from the tree and shrub
layers. The share of tree species typical of the potential community European beech Fagus sylvatica, European
hornbeam Carpinus betulus, sycamore maple Acer pseudoplatanus slowly increased in the tree layer. In August 2008 a tornado broke or up-rooted almost 60% of all trees and damaged many others on the area near to 2.5 hectares. There is a group of tree species actually beneft from the blowdown. Apart from a true pioneer species, like willows aspen or Scotch pine, there are also sycamore maple and European beech – the species abundantly present in the forest regenerations before the tornado. To this group belongs also the European hornbeam which rapidly regenerate both in generative
and vegetative way (as offshoots of downed trees). In light of the obtained results the role of light-demanding (pioneer) species in regeneration of the windthrow gaps in a fertile habitat appears to be transient.