COS 84-3 - Climate-induced growth dynamics and phenology drives the productivity of temperate trees

Abstract: Climate warming causes significant shifts in growing season length and timing as well as in tree growth dynamics in temperate forests. However, how these shifts affect tree productivity and carbon uptake remains poorly understood. To study this issue, we measured stem radial change with 1-hour frequency in 700 trees of 8 common temperate species using automatic dendrometers across a climatic gradient of the Czech Republic from 2020 to 2022. The start, end and duration of the growing season and yearly biomass and carbon production were calculated. The year 2022 was abnormally warm, while the other years were climatically normal. The effects of increased temperatures in 2022 changed with elevation. In the lowest, i.e., warmest elevations, tree productivity and carbon uptake decreased by around 40 %, whereas in mid and higher elevations, the productivity increased by approximately 30 % on average. The main determinant of yearly biomass productivity was the maximum daily growth rate achieved during the growing season around the longest day of the year (summer solstice) and growing season length. Surprisingly, trees ended growth almost 30 days earlier in lower elevations in the warm year; thus, the growing season was significantly shorter in the warm year in comparison with colder years. These results indicate that the climate warming effects on tree productivity vary with elevation from the negative ones in lower areas to positive ones in higher elevations, most likely due to more favourable water balance in higher elevations. The lengthening of the growing season has positive effects on tree growth, but it may shorten with rising temperatures due to decreasing water availability.