Terrestrial Laser Scanning Reveals the Effect of Fire Suppression on Vegetation Structure in South-East Asian Deciduous Dipterocarp Ecosystems

Despite sharing similar structural and functional characteristics to savannas, deciduous dipterocarp (DD) ecosystems in SE Asia are relatively understudied with regards to if and how they are maintained and shaped by fire. Understanding how fire affects the structure of DD ecosystems in SE Asia is important for estimating carbon and aboveground biomass and is necessary to inform effective conservation and forest management practices. Here we use terrestrial laser scans collected at 6 0.25-hectare DD plots spanning a fire gradient in northern Cambodia to evaluate the effect of fire suppression on vegetation structure. The plots were divided into four quadrants and scans were collected at the centre of each quadrant. Using single scan methods we quantitatively describe vegetation structure in three ways: stem density, stand structural complexity, and plant area density. We estimate stem density as the total number of stems within a 5 m radius of the scanner in order to limit the effect of occlusion and average at the plot level for comparison over the fire gradient. We compute a stand structural complexity index (SSCI) in R using a fractal dimension scaled with height to quantify forest structural complexity. As well, we estimate vertical distributions of plant area density (PAD) in CompuTree using a voxel-based approach. We compare each metric between plots as well as within plots to assess structural heterogeneity over the fire gradient. Preliminary results indicate that the SSCI decreases with time since fire as stem density increases and woody encroachment occurs. Our results will contribute to an understanding of the role of fire in shaping DD ecosystems within tropical forest mosaics in SE Asia which will aid in informing fire management and conservation practices.