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Title: Interactions between vegetation and microclimate in a heterogeneous tropical landscape
Author: Hardwick, Stephen Robert
ISNI:       0000 0004 6422 6332
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Land use change and forest fragmentation threaten biodiversity in the tropics. One important mechanism by which species are affected by land use change is the change in microclimate that occurs with modifications to the vegetation cover. We quantified the link between vegetation and microclimate in the tropics for the first time, finding strong relationships between leaf area index and five key microclimate variables. The mean daily maximum air temperature 1.5 m above the ground was up to 6.5 °C hotter in oil palm plantations and up to 2.5 °C hotter in logged forest than in primary forest, which could have large impacts on the organisms living in these habitats. We also developed a process based microclimate model designed for use across this range of land use types. The model reproduced the direction of the observed trends, and performed well in predicting mean climate variables as well as inter- and intraday variability. Model results suggested that changes in canopy height associated with logging and agricultural conversion have a more important influence on the near-surface microclimate than changes in leaf area index. The hotter, drier and windier microclimate found near a forest edge could drive an increase in tree transpiration. For the first time, transpiration rates were measured in six trees before and immediately after the creation of a forest edge by monitoring sap flow. After edge creation, mean daily sap flow rates increased in all trees, with the increases ranging from 4-61%. The magnitude of the change in mean daily sap flow was found to be positively correlated with diameter at breast height and negatively correlated with the distance to the forest edge. These increases in tree water use near forest edges, particularly by large trees, could create water shortages and drive increased tree mortality.
Supervisor: Toumi, Ralf ; Ewers, Robert Sponsor: Imperial College London ; European Union
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral