Abstract
Understanding the extent to which climate limitations drive elevation stratification among species is integral to predicting the impacts of climate change. Zonation patterns of species within moun-tains have been well documented, and shifts in these patterns have been correlated with recent warming. However, the physiological mechanisms that explain these zonation patterns are not well understood. We used a system of broadly sympatric oak species within semi-arid mountains to (1) investigate the extent to which species elevation ranges correlate with climate, (2) test for associations of cold and drought resis-tances with upper and lower elevation limits, and for trade-offs between resistance mechanisms with eleva-tion, and (3) examine the extent to which species-wide climatic ranges predict traits that drive local community assembly along an elevation gradient. We found that aridity gradients but not winter mini-mum temperatures predict oak stratification. Species differed in drought resistance, demonstrating a trade-off between drought avoidance and drought recovery. At lower elevations, species avoided drought stress during the dry season through leaf abscission; at upper elevations, they maintained transpiration but recovered from daily desiccation via higher leaf water storage capacity, rather than tolerating desiccation via lower turgor loss points. Freezing resistance, measured as stem electrolyte leakage, was not correlated with elevation differences. Taken together, these results indicate that elevation stratification is linked to drought resistance rather than freezing resistance. We also found evidence of niche partitioning among clo-sely related oaks linked to contrasting leaf phenology. The functional, phenological, and physiological traits important for elevation stratification were correlated with species' range-wide mean annual precipi-tation and precipitation seasonality, but not aridity. Our findings indicate that drought resistance along a leaf avoidance-recovery trade-off is integral to species stratification within this semi-arid montane system. Additionally, the mechanism of stratification acts upon traits and strategies conserved at the species level. Species within this system are likely vulnerable to range retraction under increased drought as a conse-quence of this phenological avoidance-physiological tolerance trade-off.
| Original language | English (US) |
|---|---|
| Article number | e02149 |
| Journal | Ecosphere |
| Volume | 9 |
| Issue number | 3 |
| DOIs | |
| State | Published - Mar 2018 |
Bibliographical note
Funding Information:All field studies took place on the traditional, unceded homelands of the Chiricahua Apache Nation. The University of Minnesota is within the traditional homelands of the Anishinaabe and Dakota peoples. This research was done with funding to B. Fallon from the Southwestern Research Station-American Museum of Natural History (SWRS), the University of Minnesota Charles J. Brand, Carolyn Crosby, and Dayton Bell Fellowships, and the Department of Plant and Microbial Biology. Additional funding was provided by a National Science Foundation Award 1146380 (J. Caven-der-Bares PI). We performed all data collection under permit with the Coronado National Forest, Douglas Ranger District, managed by the United States Forest Service (USDA). We thank Sally Ratliff, Christopher Walker, and Chip Blackburn for extensive help with fieldwork, and are grateful for the generous support of the SWRS staff and volunteers.
Publisher Copyright:
© 2018 The Authors.
Keywords
- Climate limitations
- Community assembly
- Drought resistance
- Ecophysiology
- Freezing resistance
- Niche partitioning
- Range limits
