Drought tolerance of western Canadian forests tree species inferred from dendrochronology

Abstract

Western Canadian forests have been subject to periods of drought stress over the last three decades, resulting in growth reductions, dieback, and increased wildfires in the context of climate change. To contribute to adaptive forest management, this study compares drought vulnerabilities of eight common western Canadian tree species based on 392 tree-ring chronologies. Chronologies were grouped into clusters with similar climatologies and assessed for drought resistance, resilience and recovery. The results show that the most severe drought impacts occurred in dry boreal mixedwood ecosystems, east of the Rocky Mountains. The dominant species in these ecosystems (white spruce and jack pine) were most vulnerable in the north, rather than at the southern fringe of the boreal forest, suggesting lack of adaptive traits to cope with drought conditions in northern populations. The same pattern emerges for sub-boreal ecosystems further west. For example, interior Douglas-fir was most vulnerable to drought at the northern edge of its distribution. In moister montane ecosystems, Douglas-fir and limber pine showed the least drought resistance, but all species recovered well from drought events. The results have implications for forest management in western Canada: interior Douglas-fir should not be planted beyond its northern range limitations despite significant regional warming trends. Across large sections of western boreal forests, not just the southern boreal fringe, the most common species such as white spruce and jack pine appear vulnerable in the long term, while submontane forest ecosystems of British Columbia and Alberta may serve as regional climate change refugia.