Coastal fog during summer drought improves the water status of sapling trees more than adult trees in a California pine forest
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Fog water inputs can offset seasonal drought in the Mediterranean climate of coastal California and may be critical to the persistence of many endemic plant species. The ability to predict plant species response to potential changes in the fog regime hinges on understanding the ways that fog can impact plant physiological function across life stages. Our study uses a direct metric of water status, namely plant water potential, to understand differential responses of adult versus sapling trees to seasonal drought and fog water inputs. We place these measurements within a water balance framework that incorporates the varying climatic and soil property impacts on water budgets and deficit. We conducted our study at a coastal and an inland site within the largest stand of the regionally endemic bishop pine (Pinus muricata D. Don) on Santa Cruz Island. Our results show conclusively that summer drought negatively affects the water status of sapling more than adult trees and that sapling trees are also more responsive to changes in shallow soil moisture inputs from fog water deposition. Moreover, between the beginning and end of a large, late-season fog drip event, water status increased more for saplings than for adults. Relative to non-foggy conditions, we found that fog water reduces modeled peak water deficit by 80 and 70 % at the inland and coastal sites, respectively. Results from our study inform mechanistically based predictions of how population dynamics of this and other coastal species may be affected by a warmer, drier, and potentially less foggy future.
KeywordsTree life stage Leaf water potential Bishop pine Water balance model Climate change
This project was supported through a grant from the Kearney Foundation for Soil Science to C. J. S. and J. Y. K., a UC-Natural Reserve System Mildred E. Mathias graduate student research grant to S. A. B., an instrumentation grant from Decagon Devices to S. A. B., and a grant from the Save The Redwoods League to C. J. S. and S. A. B. Mariah Carbone provided helpful guidance in the field. We thank A. Park Williams for assisting with micrometeorological data acquisition in the field. We thank Lyndal Laughrin and Brian Guerrero for logistical support at the UC-Natural Reserve System on SCI. Jared Nohra and Sabrina Wuu provided excellent undergraduate field and laboratory assistance.
Author contribution statement
S. A. B., C. J. S., J. Y. K., and C. M. D. conceived and designed the study. S. A. B. conducted field and laboratory work, analyzed data, and wrote the manuscript with input and support from C. J. S. and J. Y. K.; D. T. F. contributed to parameterizing the water balance model, interpreting the results, and writing related sections of the manuscript. All authors edited the manuscript.
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