Changes in diversity of the mountain beech forest herb layer as a function of the forest management method

Abstract

Development of more sustainable forest management methods is heavily reliant on the profound understanding of interactions between management methods and the forest vegetation. This study presents an analysis of changes in the interactions between the diversity of the tree and herb layers over the past 50years in the previously over-exploited Eastern Carpathian beech forests. After the anthropogenic pressure related to large scale forest clearings, intense forestry and agricultural use ceased, the regeneration processes accompanied two distinct routes (1) implementation of more sustainable forest management (shelterwood system) and (2) complete cessation of land use. The vegetation diversity and its dependence on the biotic and abiotic factors has been examined based on the data collected from 62 semi-permanent plots during two sampling periods: 1955–1962 and 2005–2009. The plots were located within the polish part of the “Eastern Carpathian” International Biosphere Reserve. The analysis included forest management methods, diversity indicators specific to different vegetation layers, indicator species groups, individual tree species, canopy density and the height of the forest stand.The main direction in changes indicates an increase in strength of the correlation between the diversity of tree and herb layers, caused by a change in the factor differentiating the diversity of the tree layer from a historical one related to general use of the land by the autochthonous people to an environmental one. Sycamore has been identified as a highly important species responsible for maintaining the stability and diversity of the herb layer structure. It has also been verified that analysis conducted using general diversity indicators does not truly reflect the interrelations between the tree and herb layer vegetation. A better representation of these interactions is provided by an analysis incorporating individual tree species and indicator species groups. Three distinct diversity patterns of the tree and herb layers have been distinguished, depending on the developmental stage of the forest and the management method implemented. First one, specific to heavily disturbed, overexploited maturing forests from the period between 1955 and 1962 is characterised by a weak relationship between the diversity of the tree and herb layer vegetation and a major role of sycamore in development of the herb layer structure. The second pattern was identified in mature forest stands, where more sustainable management methods were implemented. The second pattern is characterised by a strong relationship between the diversity of the tree and herb layer with a concomitant decrease in the importance of sycamore and an increase in the negative effects of beech exerted on the herb layer structure, which consequently undergoes homogenisation due to a decrease in habitat heterogeneity. The third pattern was described for unmanaged, mature forests, in which an emerging relationship between the diversity of tree and herb layers accompanied by a more diverse structure of the herb layer maintained by the presence of sycamore within the forest stand as well as the presence of large quantity of coarse woody debris has been identified.