Remote measurement of canopy water content in giant sequoias (Sequoiadendron giganteum) during drought

FOREST ECOLOGY AND MANAGEMENT

卷:419

Article

Martin, Roberta E.¹  Asner, Gregory P.¹  Francis, Emily¹  Ambrose, Anthony²  Baxter, Wendy²  Das, Adrian J.³  Vaughn, Nicolas R.¹  Paz-Kagan, Tarin¹  Dawson, Todd²  Nydick, Koren⁴  Stephenson, Nathan L.³ 

[1] Carnegie Inst Sci, Dept Global Ecol, Stanford, CA 94305 USA

[2] Univ Calif Berkeley, Dept Integrat Biol, Berkeley, CA 94720 USA

[3] US Geol Survey, Western Ecol Res Ctr, Three Rivers, CA 93271 USA

[4] Sequoia & Kings Canyon Natl Pk, Three Rivers, CA 93271 USA

关键词: California;    Carnegie Airborne Observatory;    Giant sequoia;    Sierra Nevada mountains;   

DOI  :  10.1016/j.foreco.2017.12.002

来源: Elsevier

【 摘 要 】

California experienced severe drought from 2012 to 2016, and there were visible changes in the forest canopy throughout the State. In 2014, unprecedented foliage dieback was recorded in giant sequoia (Sequoiadendron giganteum) trees in Sequoia National Park, in the southern California Sierra Nevada mountains. Although visible changes in sequoia canopies can be recorded, biochemical and physiological responses to drought stress in giant sequoia canopies are not well understood. Ground-based measurements provide insight into the mechanisms of drought responses in trees, but are often limited to few individuals, especially in trees of tall stature such as giant sequoia. Recent studies demonstrate that remotely measured forest canopy water content (CWC) is a general indicator of canopy response to drought, but the underpinning leaf- to canopy-level causes of observed variation in CWC remain poorly understood. We combined field and airborne remote sensing measurements taken in 2015 and 2016 to assess the biophysical responses of giant sequoias to drought. In 49 study trees, CWC was related to leaf water potential, but not to the other foliar traits, suggesting that changes in CWC were made at whole-canopy rather than leaf scales. We found a non-random, spatially varying pattern in mapped CWC, with lower CWC values at lower elevation and along the outer edges of the groves. This pattern was also observed in empirical measurements of foliage dieback from the ground, and in mapped CWC across multiple sequoia groves in this region, supporting the hypothesis that drought stress is expressed in canopy-level changes in giant sequoias. The fact that we can clearly detect a relationship between CWC and foliage dieback, even without taking into account prior variability or new leaf growth, strongly suggests that remotely sensed CWC, and changes in CWC, are a useful measure of water stress in giant sequoia, and valuable for assessing and managing these iconic forests in drought.

【 授权许可】

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