Abstract
Climate models predict an increase in the frequency and intensity of drought events in the Acadian Forest Region, with higher risk of tree growth decline and mortality. To accurately predict future species response, we need to better compare drought-coping traits between Acadian tree species, especially at early life stages as young trees tend to display increased sensitivity to small environmental changes than mature trees. Here, we compared the seasonal growth phenology and biomass allocation in seedlings of 13 Acadian tree species in a controlled environment to assess their ability to predict species drought tolerance rankings. We focused on two traits associated with drought tolerance, namely biomass allocation to root systems, which affects water uptake, and phenology of seasonal growth, where earlier growth can avoid the peak drought period in late summer. We find an earlier onset of height growth in drought-tolerant species (P < 0.05), supporting the late-summer drought avoidance hypothesis. The observed biomass allocation patterns did not support the hypothesis of a higher allocation to roots with drought tolerance. In fact, we report an initially higher shoot-to-root ratio in drought tolerant species (P < 0.05), which becomes non-significant as the season progresses. Our results highlight the complexity of drought response strategies, as the developmental traits reported here only account for a fraction of each species overall drought tolerance. Yet, the important differences in growth phenology observed here between species, and their linkage with drought tolerance indices, could help predict species response to future drought regime.
Highlights
Climate models predict an increase in frequency and intensity of drought events throughout large tracts of land across the globe, including North America (Dai, 2011; Xu et al, 2019)
We focused on two traits associated with drought tolerance, namely biomass allocation and seasonal growth phenology, and tested the hypotheses that more drought-tolerant species would (i) complete their growth earlier in the season while conditions are more favorable, and (ii) allocate a higher fraction of their new biomass to their root system as the season progresses and risk of water stress increases
The differing climate and disturbance regimes between the northern, colder boreal forest and southern, warmer temperate forest create varying levels of drought tolerance (Bugmann, 1996; Carnicer et al, 2013), as those adapted to cooler environments are likely less capable of tolerating extreme heat, which was evidenced in the earlier onset of height growth in northern boreal forest conifers
Summary
Climate models predict an increase in frequency and intensity of drought events throughout large tracts of land across the globe, including North America (Dai, 2011; Xu et al, 2019). This climate shift could have severe impact on forest trees, as exemplified by the recent droughtdriven widespread tree mortality reported in the southern Canadian boreal forest (Michaelian et al, 2011). Knowledge of each species drought-coping traits, including their co-variations and trade-offs, are required to enable accurate prediction of their functional responses to drought events and competitive fitness under a warmer, drier climate
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
