Reactions of the herb and moss layer, tree saplings and the shrub layer to tree deaths in forests of the Wielkopolska National Park (Western Poland)

Abstract

This study examines the impact of canopy and canopy gaps on the development of lower forest layers in five protected phytocoenoses of oak-hornbeam habitats (natural and regeneration stands) and oak-pine habitats in the Wielkopolska National Park (WPN). In the studied forests the most common form of dead trees are those which are uprooted (45–59%), while the most frequently dying tree is pine (40–88%). The total area of gaps in relation to the studied forest area ranges from 329 to 2356 m2/ha. The study reaches the following key conclusions. Gaps do not affect bryophyte richness and cover. The impact of gaps on the herb layer is not uniform for the investigated forests. Gaps often, though not in all cases, cause a significant increase in the total herb layer cover, vascular antrophophyte cover, vascular species richness and a greater H′ diversity. Change in the cover of grasses and lianas to the thinning are not statistically significant. The greatest increase was observed in perennial herbs (mainly dicotyledones). In tree stands under regeneration change gaps are characterized by a rising cover of woody perennials and pioneer species of the Rubus genus. The increase in the herb layer cover does not diminish the cover of tree seedlings. To generalize: differences in the herb layer between the canopy and gaps are greater for forests of oak-hornbeam habitats than for oak-pine forest. The strength of the influence of light gaps on the herb layer is determined by such traits of the pytocoenoses as: density, species composition of tree stand, overshadowing abilities of species present in the canopy, domination or co-domination of one or two species in the herb layer.