B061-0009
Evaluating the effects of plant biodiversity on surface temperature in forest restoration projects using UAV, Landsat, and ECOSTRESS data

Friday, 11 December 2020
Poster
Jonas Hamberg1, Stephen D Murphy1, Derek T Robinson2, Roydon Fraser3, Andrew Trant1, Patrick James4 and Joshua Fisher5, (1)University of Waterloo, School of Environment, Resources and Sustainability, Waterloo, ON, Canada, (2)University of Waterloo, Department of Geography and Environmental Management, Waterloo, ON, Canada, (3)University of Waterloo, Department of Mechanical and Mechatronics Engineering, Waterloo, ON, Canada, (4)University of Toronto, Daniels Faculty’s Forestry program, Toronto, Canada, (5)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
Abstract:
Changes in plant biodiversity can affect surface temperature through changes in transpiration, albedo, plant structure, physical heat capacity and respiration. Ecosystem thermodynamics predicts that an increase in ecosystem complexity results in reduced surface temperatures. Increased complexity in the form of greater biodiversity and biomass can increase use of available energy and its transformation into latent heat fluxes, lowering sensible heat fluxes and hence temperatures. However, to date we do not know the extent of this effect and how it can be enhanced through forest restoration efforts.

Here, we present the results of two experiments from southern Ontario, Canada that aim to quantify the relationship between plant species diversity, plant biomass, and surface temperatures using remotely sensed thermal imaging data and in-situ sampled vegetation data.

The first experiment was conducted on a project where former farm-fields were seeded to restore oak-woodland or left as passive controls. We compared 12 years of thermal imaging data from Landsat 5, 7 and 8, and ECOSTRESS against annual vegetation sampling of this project and found that restoration effort led to an average decrease in summer day-time surface temperature of 4.5 °C. Each additional plant species decreased summer daytime surface temperature by 0.3 °C when controlling for ground and canopy cover. We also found that native species decreased surface temperatures at more than double the rate of non-native species.

Our second experiment used high resolution thermal imaging from UAV of three sites undergoing restoration through the transfer of forest topsoil and its seed bank. We found a mean summer cooling effect of 0.7 and 2.1 °C respectively in two former farm fields and 5.7 °C in a gravel pit site. The cooling effect was significantly correlated with an increase in native forest species richness at all sites. In contrast not all sites showed correlation between temperature and total plant cover, tree size or total plant species richness.

Overall we find evidence for the hypothesis that plant diversity does decrease surface temperature. Beyond the theoretical questions, our results show how thermal imaging could be used as a tool to monitor for issues in, and evaluate the benefit of, large-scale forest restoration projects (see figure for example).

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