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ABSTRACT Forest composition is changing, yet the consequences for terrestrial carbon cycling are unclear. In the eastern United States, water‐demanding “mesophytic” tree species are replacing “xerophytic” oaks (Quercusspp.) and hickories (Caryaspp.), raising concerns that forest productivity will become increasingly sensitive to more frequent and severe drought conditions predicted for the region. However, we have a limited understanding of the extent to which the mortality risk of xerophytes versus mesophytes is coordinated with their growth sensitivity during drought. Here, we evaluated growth and mortality dynamics for 20 abundant eastern United States tree species following a severe drought in the summer of 2012. We synthesized data from ~4500 forest inventory plots and used an approach that quantified relative drought responses between co‐located trees to minimize impacts from environmental heterogeneity. We found that mesophytes were just as likely to perish as co‐occurring xerophytes but were more sensitive to drought in terms of diminished growth. These findings suggest that xerophytic decline is likely to lead to reduced carbon uptake during drought and that management efforts to conserve oak‐hickory stands will be decisive to sustain the carbon mitigation potential of these forests. However, we also found that growth‐mortality relationships differed between functional groups. Among xerophytes, growth and survival during drought were decoupled. Among mesophytes, there was a high degree of coordination, where species that experienced greater mortality also experienced greater growth reductions. Therefore, mesophytes with high growth sensitivity to water deficits are likely to be the most vulnerable to drought‐driven die‐off events moving forward.
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Complex trajectories of tree growth in the southwestern United States after severe drought
Abstract Climate change driven extreme droughts have major impacts on forest ecosystems, including large‐scale mortality and reduced primary production, which feedback to affect the global carbon cycle. The long‐term impacts of extreme drought events on forest mortality, ecosystem responses, and recovery/post‐drought trajectories are poorly understood. In this study, we combine annual tree ring widths of five major species occurring in the southwestern United States and data obtained from long‐term forest inventory and monitoring plots to study the effect of an extreme drought event in 2002 on subsequent tree growth. We quantified the extent to which trees that survived the drought had increased growth due to potential increases in resources from reduced stand density or reduced growth due to lingering impacts of drought stress. We found diverse patterns of post‐drought growth trajectories across species, with drastic increases in growth in some species such as trembling aspen (Populus tremuloides) and clear growth suppression in other species such as ponderosa pine (Pinus ponderosa), reflecting notable drought legacy effects. Total basal area was the best predictor of post‐drought growth responses, though the regression effect (positive or negative) varied by species; for example, ponderosa pine showed less growth than predicted in higher density stands while spruce had greater growth than expected in the higher density stands. Climatic water deficit and stand age also emerged as important drivers of post‐drought growth trajectories for multiple species. The results of this study can help to elucidate how different forest types in the southwestern United States will respond to future drought events and the ramifications for carbon cycling in this region.
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- PAR ID:
- 10677180
- Publisher / Repository:
- Ecosphere
- Date Published:
- Journal Name:
- Ecosphere
- Volume:
- 17
- Issue:
- 3
- ISSN:
- 2150-8925
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/ecs2.70514
