Picea abies and Pinus cembra at high altitudes show different growth reaction to rising temperatures: Study from the Western Carpathian subalpine forests

Abstract

The subalpine forests of the Western Carpathian High Tatra Mountains represent a unique, isolated enclave of postglacial refugia. Climate change presents challenges and opportunities for alpine species: while rising temperatures may extend the growing season, potentially boosting growth rates, these changes may also push species closer to their physiological limits. This study examines the impacts of warming on the radial growth of Picea abies Karst. and Pinus cembra L. in Western Carpathian subalpine forests. We hypothesize that in subalpine zones, where tree growth is predominantly limited by low temperatures, Picea abies will experience enhanced growth under warmer conditions, whereas Pinus cembra will reduce growth under associated stress. We identified two pointer years with negative growth responses in P. cembra (1980 and 2014) and two years (1974 and 1993) with negative growth responses observed only in P. abies. The years 1965 and 1996 were found to be common years of negative response. Results indicate a non-linear relationship between temperature and radial increment. While P. abies and P. cembra both respond negatively to cold years (RWI < 1) at lower temperature sums, their responses diverge at higher temperature sums. As the cumulative sum of daily average temperatures above 9°C exceeds 1500 degree-days, spruce’s response remains positive (RWI > 1), whereas stone pine´s becomes significantly negative (RWI < 0.9). We conclude that, with continued climate manifestations, such as heatwaves, the competitive advantage of spruce in subalpine forests could potentially result in a gradual contraction of P. cembra distribution in the High Tatra Mountains.