Investigating the relationship between water content distribution in tabonuco trees and soil physical properties at the Luquillo Forest Dynamics Plot (Puerto Rico) using near-surface geophysical methods

Abstract:

Tropical forests are structurally complex ecosystems where the interplay of many different factors directly influences its composition and species diversity. For example, tree water usage may be influenced by factors such as depth to bedrock, regolith thickness, soil water availability, and topographic position. At the same time, given the connection between ground and atmospheric water that trees provide, water content distribution is most logically measured along the tree’s vertical axis. For all these reasons, understanding the differences in certain physical properties in trees and associated soils at different landscape positions may provide information on water budgets, soil features and even forest disturbance across scales within the ecosystem. This study uses a combination of ground-penetrating radar (GPR), and capacitance moisture probes constrained with tree cores and soil samples to better understand the spatial distribution of water content across two-meter vertical transects and tomographic images in several trees characterized by specific soil types. Measured trees (Dacryodes excelsa or tabonuco) were chosen based on positioning within the forest in order to explore how specific soil conditions (such as soil thickness or moisture content variability) may affect water uptake. Results show overall consistent ranges in average water content values between sites (between 6-8 % volumetric water content), that increase variability with tree size and soil thickness. This study shows the potential of near-surface geophysical methods to better understand key ecohydrological processes in tropical forests.