Enhancing the understanding of canopy biodiversity: Estimating forest canopy surface temperature by airborne laser scanning, thermal infrared scanning, and 3D radiation modeling
Final Report Abstract
Leaf temperature is directly influenced by both leaf-specific characteristics (morphology, shape, leaf mass, size and reflective properties) which prevent the leaf from overheating and by environmental factors (air temperature, humidity, solar radiation and wind). These complex interrelations make it a challenge to disentangle the contribution of the single factors and to possible establish relationships between leaf surface temperature and other variables, including biodiversity. The result of this project supported the hypothesis that canopy surface temperature is different among the occurring three tree species at the Hainich National Park. However, the differences we found were small (although quite consistent in our time series) and close to the measurable temperature accuracy of the thermal camera. Furthermore, the overall aim of the “LaserTIR” project studying the influence of the forest structure does actually appear over-ambitious due to the multitude of the potentially influencing factors and their interactions and the complexity of tree crowns including the variability of conditions in the crowns. Controlling these factors in a experimental settings within the forest would be extremely laborious. Consequently, the relationship of forest structure / canopy structure and leaf surface temperature could not be covered in this project. During the analyzing of the data of WP1, we came up with further research questions focused on the usage of thermal imagery in forestry. We tested the potential of infrared thermal imaging for different applications, among them as a supporting technique that may assist researchers in the determination of the age of a bamboo culm. Within that study, we found that there is a small difference in the surface temperature for culms of different age; again, the differences are very small, but consistent. Additionally, we had studied how thermal imagery may improve the well-established method of optical hemispherical photography. The extremely complex interactions at the leaf level, through light, wind, solar radiation, and air temperature which themselves interact with each other make the interpretation of thermal photographs difficult. We used high-resolution data, auxiliary variables, like transpiration or stomatal conductance, and complex statistical methods to test whether small differences in leaf surface temperature can be observed between the different tree species. There are significant differences at least for the data collected at the tower site.
Publications
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2014. Thermal canopy photography in forestry - an alternative to optical cover photography. iForest - Biogeosciences and Forestry.8:1
Nölke N, P Beckschäfer, C Kleinn
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2015. Changes in culm surface temperature with maturity of the bamboo species Guadua angustifolia. Journal of Forest Research: 1-7, 03 October 2015
Nölke N, J C Camargo García, C Kleinn and A Polle
