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A plant distribution shift: temperature, drought or past disturbance?
Dylan W Schwilk1, Jon E Keeley
1Biological Sciences, Texas Tech University, Lubbock, Texas, United States of America. dylan.schwilk@ttu.edu
Plos One
|February 21, 2012
Summary
Plant distribution shifts upslope may not be due to climate warming. A study on Ceanothus greggii in California found that differing fire histories, not warming, explained changes in plant mortality and elevation. This highlights the role of disturbance history.
Area of Science:
- Ecology
- Climate Change Biology
- Plant Ecology
Background:
- Climate change models predict vegetation shifts to cooler, wetter areas, often upslope in mountains.
- Species-specific responses to climate change can be complex and influenced by factors beyond temperature and precipitation.
- A previously reported upslope vegetation shift in California's Santa Rosa Mountains warrants re-examination of underlying mechanisms.
Purpose of the Study:
- To investigate the mechanisms behind a reported upslope shift in plant distribution in the Santa Rosa Mountains.
- To re-evaluate the assumption of uniform fire history across elevations in prior studies.
- To determine if observed mortality patterns in Ceanothus greggii are driven by climate warming, drought, or ecological succession.
Main Methods:
- Focused on five elevational zones within the Santa Rosa Mountains' chaparral ecosystem.
- Utilized tree-ring analysis of live and dead Ceanothus greggii individuals to determine past per-capita mortality rates.
- Calculated mortality time series and tested hypotheses related to climate warming, drought indices, and self-thinning (age since last fire).
Main Results:
- Discovered significant differences in the age of sites since the last fire across the studied elevations.
- Found that higher recent mortality at lower, younger elevations explained the apparent upward shift in Ceanothus greggii distribution.
- Concluded that mortality patterns were best explained by self-thinning dynamics (peaking 40-50 years post-fire) rather than gradual climate warming or drought.
Conclusions:
- The observed upslope shift in Ceanothus greggii distribution in the Santa Rosa Mountains is likely an artifact of differing disturbance histories (fire frequency and age).
- This study suggests that ecological succession and self-thinning, influenced by fire history, are more significant drivers of this species' distribution changes than direct climate warming effects.
- Re-evaluating assumptions about disturbance regimes is crucial for accurately interpreting vegetation responses to environmental change.
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