Trees resilience to drought in forest ecosystems from Eastern Carpathians, Romania

Carpathian forest ecosystems play a major role in providing ecosystem services and ecological stability in Europe. Increasing drought frequency and intensity is a reality in plains and hills regions, becoming a threat also for mountain forest ecosystems. Forests are among the most vulnerable terrestrial ecosystems to these extremes. The impacts of climate change vary from the reduction of productivity and loss of overall ecosystem biodiversity to even the mortality of trees. Our study assessed the growth and drought resilience of three main forest species from the Carpathians: Picea abies, Abies alba, and Fagus sylvatica.
Based on an extensive tree ring data network consisting of over 6000 trees from 158 plots for P. abies, 64 plots for A. alba, and 65 plots for F. sylvatica, distributed along an elevation gradient, we (i) evaluate the basal area increment variability and (ii) quantify the resilience to the most extreme drought years from last 100 years. To assess the tree's capacity to react to water deficit, we used the resilience indices: resistance, recovery, and recovery period.
Our results show an evident growth decline of P. abies from elevation below 1400 m, with a similar trend in the case of A. alba from elevation below 800 m. A. alba and F. sylvatica show an increasing trend of basal area increment in plots from medium and high elevations. F. sylvatica and A. alba have a higher resistance and resilience to water deficit at low elevations than P. abies. Generally, the recovery period from drought events increases with elevation from all species.