Variability of hygro-climatic conditions of forest vegetation in Poland during the period of 1951–2015*

This work presents an assessment of changes in the hygro-climatic conditions determining the vegetation and productivity of forest areas. Selected indices such as the radiant index of climate aridity – RIA, optimal precipitation – Popt, critical value of precipitation – Pkrt and CVP index (Climate, Vegetation, Productivity), which describe annual biomass and wood production under climatic conditions, were used. The analysis is based on standard meteorological measurements taken from 21 stations from the period of 1951–2015. The daily data were employed to calculate the previously mentioned indices, and the next linear trend coefficient was used to assess changes in hygro-climatic conditions. The results show an increasing tendency towards dry climate conditions (positive values of the RIA linear trend coefficient) in a large part of the area consisting of Wielkopolska, the Silesian lowlands, and southern Poland. These areas are also characterized by the fastest increase in the most favourable sum of precipitation Popt and critical precipitation Pkrt for forest vegetation. This means that water resources in the environment and hygro-climatic conditions important for vegetation and the productivity of forest vegetation are deteriorating. On the other hand, the results of the CVP change assessment show an improvement in the climatic conditions influencing vegetation and forest productivity. The greatest positive changes of the CVP index are observed in the areas of south-eastern Poland