Topographically-mediated variability in fog and belowground moisture and its role in redwood distributions and responsiveness to drought
Abstract/Contents
- Abstract
- Forests cover 30% of the land surface and absorb almost a quarter of annual anthropogenic carbon dioxide emissions, but are vulnerable to increasing drought stress as a result of climate change. Regions of high water availability embedded within topo-climatically diverse forest landscapes could protect forests during drought, but have been understudied. In this dissertation, I sought to develop a nuanced understanding of the role of fine-scale spatial variation in water availability on the habitat distribution and drought responsiveness of coastal redwoods (Sequoia sempervirens), the tallest tree species on earth. In the first chapter, I show that redwood distributions can be mapped at 10 m resolution with demonstrable accuracy over 34,800 hectares and three redwood forests from airborne imaging spectroscopy, field-collected training data, and an optimized machine learning image classification framework. In the second chapter, I found that mapped fog frequency from the MODIS satellite and airborne LiDAR-derived estimates of belowground moisture shaped microscale redwood distributions, and that interpolated height above a stream (IHAS) was consistently negatively related to redwood abundance. These results suggested that fog and topographically-defined gradients of water availability within redwood forests contribute to significant variation in redwood habitat suitability within regions where redwood range contraction has been predicted with coarse resolution data. The third chapter tests the hypothesis that access to moisture from fog and streams have a buffering effect on redwood response to drought. Cores were collected from redwoods across a gradient in fog frequency and at two IHAS positions at Mt. Tamalpais. Annual basal area growth rates calculated from ring width measurements revealed an amplified negative response of redwood annual growth to drought indices at ridge sites with low fog frequency, suggesting that redwoods with access to water from fog and streams were less responsive to drought, as we expected. However, streamside trees under the highest fog frequency regime were the most responsive to precipitation variability, challenging the simple interpretation that redwoods with access to water from fog and streams were always less responsive to precipitation deficits. Analyses of airborne LiDAR-derived tree height data revealed that these trees were significantly taller and therefore exposed to higher leaf water stress. We concluded that biological compensation for higher water availability during mean climate, through increased height growth, might reduce the buffering effect of fog and streams on redwood growth responsiveness to drought.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2019; ©2019 |
| Publication date | 2019; 2019 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Francis, Emily J |
|---|---|
| Degree supervisor | Field, Christopher B |
| Thesis advisor | Field, Christopher B |
| Thesis advisor | Asner, Gregory P |
| Thesis advisor | Fendorf, Scott |
| Thesis advisor | Konings, Alexandra |
| Thesis advisor | Mach, Katharine J |
| Degree committee member | Asner, Gregory P |
| Degree committee member | Fendorf, Scott |
| Degree committee member | Konings, Alexandra |
| Degree committee member | Mach, Katharine J |
| Associated with | Stanford University, Department of Earth System Science. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Emily J. Francis. |
|---|---|
| Note | Submitted to the Department of Earth System Science. |
| Thesis | Thesis Ph.D. Stanford University 2019. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2019 by Emily Jane Francis
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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