Examining the impact of invasive tree Psidium cattleianum on canopy structure in tropical wet forests of Hawai’i Island: An application of terrestrial LiDAR

Abstract:

Tropical forests play a critical role within the hydrologic cycle, mediating water fluxes such as infiltration and evapotranspiration. Consequently, shifts in species composition and structure of these forests have the capacity to alter hydrologic function. Anthropogenically-introduced invasive tree species, which can change the structure of tropical forests, are therefore poised to create cascading effects on hydrologic processes. Motivated by the need to understand invasive species impact on tropical forest structure and function, we studied the effect of invasive tree Psidium cattleianum on the canopy of native wet forests in Hawai’i Island, where forested uplands are a crucial source of water for residents. We quantified canopy structural metrics along a gradient of species invasion (three 40m transects) at four different forested sites in the fall of 2019. Each transect was scanned with a terrestrial LiDAR instrument, producing a 3-dimensional point cloud from which canopy metrics, such as leaf area index and rugosity were quantified. Additionally, we characterized canopy cover and species composition along each transect using a tube densiometer and quantified stem basal area by species using a prism. In addition to quantifying the impact of P. cattleianum on forest canopy structure, our data anchors the results from a novel application of terrestrial LiDAR to results from conventional forest sampling methods. This validation of terrestrial LiDAR data is invaluable to understanding the viability of using terrestrial LiDAR technology in future tropical forest canopy studies. Our study improves understanding of the impact of invasive tree species on tropical forest canopy structure, ultimately informing management decisions aimed towards preserving the hydrologic function of forests.