Temperature and precipitation gradients determine biomass in Birch (Betula spp.) and Fir (Abies spp.) in Eurasia.

Forest ecosystems are sinks of atmospheric carbon and maintain annual temperature. On the other hand, climate change entails changes in all the biota structures and functions, including forest cover and biomass. Temperature and precipitation are the main deterministic factors in species biomass change. Therefore, we compared the biomass of Betula spp. and Abies spp. at the stand level along trans-Eurasian hydrothermal gradients. We analyzed the biomass database of Betula and Abies forest stands in Eurasia. Climate variables explained about 14 and 16% of the total biomass variability in Betula and Abies, respectively. Our results showed that increasing temperature and precipitation positively impacted fir biomass. However, a negative impact was reported on needles and branches due to insufficient humidity. In birch forests, positive trends occur from cold to warm climate zones, but only when there is inadequate water supply. A negative correlation was reported in the moist areas. Most of the birch biomass components only increased in the precipitation gradient in cold climate zones. This positive trend transformed to negative in warm zones (except for branches). We modeled the possible temporal biomass change of tree species based on its territorial pattern in Eurasia using the principle of space-for-time substitution. The developments of models for the main forest-forming species of Eurasia allow us to predict changes in the productivity of the forest cover of Eurasia.