Canadian Forest Service Publications
Tree rings provide early warning signals of jack pine mortality across a moisture gradient in the southern boreal forest. 2015. Mamet, S.D.; Chun, K.P.; Metsaranta, J.M.; Barr, A.G.; Johnstone, J.F. Environmental Research Letters 10(8):1-13.
Issued by: Northern Forestry Centre
Catalog ID: 36374
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Recent declines in productivity and tree survival have been widely observed in boreal forests. We used early warning signals (EWS) in tree ring data to anticipate premature mortality in jack pine (Pinus banksiana)—an extensive and dominant species occurring across the moisture-limited southern boreal forest in North America. We sampled tree rings from 113 living and 84 dead trees in three soil moisture regimes (subxeric, submesic, subhygric) in central Saskatchewan, Canada. Were constructed annual increments of tree basal area to investigate (1) whether we could detect EWS related to mortality of individual trees, and (2) how water availability and tree growth history may explain the mortality warning signs. EWS were evident as punctuated changes in growth patterns prior to transition to an alternative state of reduced growth before dying. This transition was likely triggered by a combination of severe drought and insect outbreak. Higher moisture availability associated with a soil moisture gradient did not appear to reduce tree sensitivity to stress-induced mortality. Our results suggest tree rings offer considerable potential for detecting critical transitions in tree growth, which are linked to premature mortality.
Plain Language Summary
Increased tree mortality in Canada’s boreal forest has recently been observed, and it is of great concern for sustainable forest management. Predicting future mortality is an important research challenge. This study used tree ring data to detect early warning signals linked to a greater chance of dying for jack pine trees growing in areas of different moisture status (dry, wet, and intermediate) in the southern boreal forest in Saskatchewan. A change in growth pattern leading to a period of reduced growth, particularly early in the development of a group of trees, was an early warning signal of mortality. These changes in growth pattern were probably caused by a combination of drought and insect outbreak. Competition from neighbouring trees did not predict mortality. This study is important because it shows that if a tree grew slowly in the past, perhaps because of climatic events that occurred years or decades ago, its fate was sealed early on.