Impact of climate change on the growth of main tree species in Romania using dendrochronological data
The objective of this study is to identify and estimate the impact of the change in climate on the annual growths of the three main forest species from Romanian forests: Norway spruce, European beech, and sessile oak. We have used more than 6500 increment cores of the National Forest Inventory in combination with the Romanian homogenized climatic data. To ensure more than 30 observations per time step, we have used quinquennials rather than years. Using a longitudinal autoregressive mixed model, we found that the average radial growth changed significantly since 1960 for all three species and almost all ecoregions. The response of each species in respect to the climate variables considered in the study differs notably, as Norway spruce exhibited a radial growth unaffected by climate change, but sensitive to the previous quinquennial growth, the ecoregion, and the calendar quinquennial. European beach, however, had a radial growth that depends on the precipitations and temperatures during the summer and growing season as well as to the previous quinquennial growth, the ecoregion, and the calendar quinquennial. The radial growth of sessile oak was similar to the European beech, except for the growing season temperature, which seems to have an insignificant impact. While the ecoregions were already proven to play a significant role in radial growth for all the tree species, the inclusion of climate distilled evermore the differences among the ecoregions. Consequently, when considering the quinquennial calendar and climate, the data suggest the existence of two distinct growth areas for Norway spruce and six different growth areas for European beech and Sessile oak.