Skip to main content
2023 ESA Annual Meeting Main banner
Icon Legend
This session is not in your schedule.
This session is in your schedule. Click again to remove it.
Back

Contributed Talk

Session: : Communities: Spatial Patterns And Environmental Gradients 5

COS 100-3 - The transition between energy and water limited systems promotes co-occurring thresholds in tree growth and stable isotope ratios

Tuesday, August 8, 2023
2:00 PM – 2:15 PM PDT
Location: B119
Abstract: Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Though growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by shifts in the primary climatic constraints on tree growth. Here we used generalized additive mixed models to test whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation. Further, we tested whether stemwood growth thresholds were associated with multiple thresholds in source and sink processes that limit tree growth. We extracted 772 tree cores, 1,398 needle length records, and 1,075 stable isotope samples from 27 sites across whitebark pine’s (Pinus albicaulis Engelm.) climatic niche in the Sierra Nevada. Our results indicated that a temperature threshold in stemwood growth occurred at 8.4 °C (7.12 - 9.51°C; estimated using fall-spring temperature). This threshold was significantly correlated with thresholds in foliar growth, as well as carbon (δ13C) and nitrogen (δ15N) stable isotope ratios, that emerged during drought. These co-occurring thresholds likely reflected the transition between energy and water limited tree growth (i.e., the E-W limitation threshold), which may lead to important differences in growth-defense tradeoffs and drought-adaptations. Further, threshold drought responses suggested that trees growing in energy limited regions may continue to experience elevated growth in response to climate change. The positive effect of warming, however, will likely be offset by growth declines in water limited regions, which threatens the long-term sustainability of the recently listed whitebark pine species.