Climate vulnerability of Nothofagus pumilio, Nothofagus dombeyi and Austrocedrus chilensis in northern Patagonia's temperate forests

Rapid climate change is exposing forests worldwide to increasing stress. In the temperate forests of northern Patagonia (Argentina), increased tree mortality and stand-level dieback have been reported in recent time. However, a comprehensive understanding of how climate change is affecting native trees´ growth across this complex mountainous landscape is still lacking. With a dendrochronological analysis of three widespread tree species (the conifer Austrocedrus chilensis, the evergreen broadleaf Nothofagus dombeyi and the deciduous broadleaf Nothofagus pumilio) in 24 stands across a steep precipitation gradient (1900–700 mm year⁻¹ over <80 km) in the eastern Andes, we explore how recent climate trends are affecting the climate sensitivity of tree growth, basal area increment (BAI), growth synchrony and interannual growth variability. In the colline–lower montane belts (500–1100 m a.s.l.), the growth of A. chilensis and N. dombeyi is primarily constrained by high temperatures and low precipitation in late spring/early summer across the whole gradient. Towards higher elevations, growth limitation of N. pumilio has been shifting from cold- to drought- (and heat-) limited during the last four decades. BAI has generally declined in all A. chilensis stands since the late 1970s, partly due to increasing competition in juvenile stands. However, growth synchrony and interannual variability have increased consistently in both juvenile and mature stands since 1980. The BAI of N. dombeyi has recently diverged across sites, with stable or positive trends at the drier sites and negative trends at the moister sites; yet, similar to A. chilensis, growth synchrony and interannual variability have generally increased. At higher elevations, N. pumilio stands revealed contrasting BAI trends in recent decades, with an overall decrease in growth synchrony and interannual variability. Regional trends in BAI, growth synchrony and interannual variability appeared to be largely modulated by elevation and stand characteristics rather than decreasing precipitation in eastern direction. Across the species, a strong relation between recent BAI, growth synchrony and interannual variability trends, and growth rate at young age (reflecting stand history) was detected, indicating that stands with fast growth at young age are more likely to suffer from premature vitality decline at higher age. Future warming most likely will weaken the vitality of A. chilensis in much of its current distribution range, and that of fast-growing N. dombeyi forests especially at low to mid elevations, while N. pumilio stands are only beginning to experience negative climate warming-related effects.