Influence of climatic variables on forests condition in Poland in the period 2002-2021

Forest ecosystem stress caused by climate change, in particularly prolonged and severe droughts, has already been manifested in several parts of Europe, including temperate and boreal forests. It is likely that droughts and heatwaves will occur more often, which might result in the ecological transition of the forests and loss of biodiversity. The assessment of climate change impact on forest ecosystems is complex, as response can vary in space (depending on the physiological vulnerability of ecosystems and site conditions), time, and among species (species resilience).

In this project we investigate the influence of several climatic variables (2 m temperature, rainfall, evapotranspiration and climatic water balance) on the forests condition in Poland in the period 2002-2021. To this end we use ERA-5 Land reanalysis data and vegetation indices – NDVI and EVI – derived from the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) – MOD13Q and MYD13Q. The remotely sensed indicators on vegetation consist of 8-day composites and have 250-m spatial resolution, while the climatic data is 0.1° x 0.1° spatial and 1-day temporal resolution.

The spatio-temporal trends of NDVI and EVI were computed for forest areas only, and their statistical significance was assessed. The monthly analyses were carried out for growing season (April-October). Multi-annual trends of climatic variables were prepared not only for the period 2002-2021, but also for the longer period 1971-2021, in order to strengthen the information coming from the climate trend analysis. The influence of the variability of climate elements on vegetation indices was assessed with the methods of linear regressions and spatial correlations. The results were broken down into sub-regions of similar physical-geographical features (nature-forest classification).

Identification of the relation between changing climate and forests condition seems crucial, because forests are the important element in the planetary energy balance and CO2 absorption. In Poland almost 30% of country area (9.2 million ha) is covered with forests, but such research have not been conducted so far.