COS 152-1 - High drought vulnerability of three conifer species under future climates in northern temperate forests: Insights into hydraulic safety margins

Background/Question/Methods

The future climate of northern temperate forests is expected to be drier and warmer by 2071–2100.Therefore, more events of drought-induced forest dieback are anticipated in northeastern North America. Consequently, we urgently need to assess the vulnerability of dominant tree realistic species to drought. During a greenhouse experiment, we exposed two-year-old seedlings of Picea glauca, Picea mariana and Pinus strobus to three future climate conditions for southern Quebec, Canada, and evaluated their survival, growth and water status responses to soil water availability and atmospheric drought. Climate conditions (treatments) emulated drought periods of different frequency, duration and intensity. Treatments closely simulated one growing season, with changes of air temperature and relative humidity every six hours and daily adjustment of soil water availability.

Results/Conclusions

The three species experienced high mortality (75%) in all water-limited treatments compared to controls (unlimited water treatment; 0% mortality). The biomass of seedlings that survived was 40% lower than control seedlings. Midday water potentials and percent loss of hydraulic conductivity were highly variable between seedlings within a species, especially during the driest and hottest periods of the growing season, despite the use of seedlings from the same genetic provenance. Hydraulic failure was the main mechanism leading to seedling death during drought. We conclude that the hydraulic safety margin is a good indicator of tree mortality risk, especially when defined as the difference between seasonal minimum water potential and the xylem water potential leading to 12% hydraulic conductivity loss. Our study further shows that three of the dominant conifer species of northern temperate forests in southern Quebec are highly vulnerable to drought in futures climates; climate simulations forced by RCPs 8.5 W m^-2 forecast a one in two chance of experiencing a more intense water deficit than our water-limited treatments. Adapting forests to climate change will be critical in warmer and drier climates.