Growing evidence suggests short-duration climate events may drive community structure and composition more directly than long-term climate means, particularly at ecotones where taxa are close to their physiological limits. Here we use an empirical habitat model to evaluate the role of microclimate during a strong El Niño in structuring a tropical montane cloud forest's upper limit and composition in Hawai'i. We interpolate climate surfaces, derived from a high-density network of climate stations, to permanent vegetation plots. Climatic predictor variables include (1) total rainfall, (2) mean relative humidity, and (3) mean temperature representing non-El Niño periods and a strong El Niño drought. Habitat models explained species composition within the cloud forest with non-El Niño rainfall; however, the ecotone at the cloud forest's upper limit was modeled with relative humidity during a strong El Niño drought and secondarily with non-El Niño rainfall. This forest ecotone may be particularly responsive to strong, short-duration climate variability because taxa here, particularly the isohydric dominant Metrosideros polymorpha, are near their physiological limits. Overall, this study demonstrates moisture's overarching influence on a tropical montane ecosystem, and suggests that short-term climate events affecting moisture status are particularly relevant at tropical ecotones. This study further suggests that predicting the consequences of climate change here, and perhaps in other tropical montane settings, will rely on the skill and certainty around future climate models of regional rainfall, relative humidity, and El Niño.
Bibliographical noteFunding Information:
Acknowledgments this work was supported by the usgs Biological resources Discipline global Change research Program, the usgs Pacific Island ecosystems research Center, us Fish and Wildlife service in support of the Pacific Islands Climate Change Cooperative (PICCC; award number 12170-B-g100), and a national science Foundation Dissertation Improvement grant (award number DeB-0808466). Partial support of halenet field observations and data management was provided through nsF ePsCor 0903833 (J. gaines, PI). We thank haleakala¯ national Park, the hanawī natural area reserve, Corie yanger, gregor schuurman, michael nullet, John Delay, lloyd loope, sarah Bogen, and Janice Poehlman for assistance. anonymous reviewers, Jennifer schmitz, gregor schuur-man, monica turner, michael tweiten, and Jack Williams provided helpful comments on this manuscript. Data collection complies with the current laws of the usa in which the collection was performed.
Copyright 2014 Elsevier B.V., All rights reserved.
- El Niño/Southern Oscillation
- Habitat model