E-Thesis 145 views
Sitka spruce (Picea sitchensis (Bong.) Carr) drought monitoring using remotely sensed Vegetation Indices (VI) at multiple spatiotemporal scales / GERRARD ENGLISH
Swansea University Author: GERRARD ENGLISH
DOI (Published version): 10.23889/SUThesis.69869
Abstract
The environmental threats to UK forests due to the changing climate are unprecedented. However, the potential for remote sensing to assess, model, and monitor these threats at previously unattainable spatiotemporal scales has never been greater. Drought stress is among the greatest threats to forest...
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Swansea University, Wales, UK
2025
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Rosette, J., and Suarez, J. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa69869 |
| Abstract: |
The environmental threats to UK forests due to the changing climate are unprecedented. However, the potential for remote sensing to assess, model, and monitor these threats at previously unattainable spatiotemporal scales has never been greater. Drought stress is among the greatest threats to forests, and Sitka spruce (Picea sitchensis (Bong.) Carr.), UK forestry’s most important conifer species, can be susceptible to it. The present thesis explores potential ways that the UK forestry sector could adopt remotely sensed Vegetation Indices (VI) and transition towards more drought-resilient management. In the analysis presented in this thesis, VI associated with the xanthophyll cycle and anthocyanin concentrations (PRI, ARI,ARI2) detected early drought responses in Sitka spruce needles after about 10 days of mild drought stress. At the stand level, the xanthophyll cycle-associated VI (CCI and GPPVI) detected drought-induced annual reductions during the 2018 drought year. Depending on the time interval, these reductions ranged between 5% and 15%,compared to the 5% GPP reduction estimated by the flux tower. Gross Primary Productivity (GPP) (within 0.5% of flux tower GPP) which were delectable from space. These VI also act as Vcmax proxies to improve model realism in process-based biophysical models. Traditional VI such as NDVI generally performed poorly at the needle and canopy scale for drought detection however, successfully tracked seasonal GPP patterns (R2 > 0.80) when combined with a measure of PAR in the Light Use Efficiency Model (LUE). For the first time, intraspecific clonal differences in drought responses were detected with VI in conifers. This demonstrated the possibility of high-throughput phenotyping for drought tolerance and highlighted potential discrepancies in the drought tolerance of existing breeding population Sitka spruce trees. The results demonstrate how VI can directly aid in transitioning UK forestry to a drought-resilient sector. Xanthophyll reflectance, detectable with MODIS satellites at countywide scales, could facilitate Sitka spruce health monitoring and stress assessments, as well as be incorporated into the breeding program to future-proof progeny. |
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| Item Description: |
A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information. |
| Keywords: |
Remote sensing, Forest Health, Drought Stress |
| College: |
Faculty of Science and Engineering |
| Funders: |
Royal Society and Forest Research |