Evaluating tree root distribution in a tree-based intercropping system with use of ground penetrating radar

Abstract

Within agroforestry systems, tree root architecture is a driver of important ecological processes such as belowground nutrient flows and C storage. Yet the belowground component of trees remains largely under-studied due to methodological restraints. Conventional subsurface sampling can overlook the heterogeneity of root systems, while complete excavations are destructive and unrepeatable. Thus, there is a need to develop non-intrusive technologies, such as ground penetrating radar (GPR), to measure root systems in situ. In this study we used GPR to detect coarse root distributions below five tree species (Quercus rubra, Juglans nigra, Populus sp., Picea abies, and Thuja occidentalis) at a temperate tree-based intercropping site in Guelph, Ontario. GPR geo-imaged transects were collected in 4.5 _ 4.5m grids that were centered on 15 individual trees. Subsequently, tree roots were identified across all geo-images (visualized as radar signal reflections) providing 3-dimensional root distribution data for each target tree. Roots detected by GPR accounted for approximately 80% of large coarse roots (�1cm) and 40% of small coarse roots (<1cm) that were later exposed in a subset of matched soil profiles. Significant inter-specific variations of coarse rooting depth preferences were detected. Additionally, preliminary analyses indicate different tree rooting patterns below the crop rows. To determine fine root distributions, fine roots were extracted from soil cores collected from the tree root study plots. Preliminary analysis indicates fine root length densities vary across species predominately in the upper 20cm. Limitations will be identified and applications will be discussed of GPR to answer ecological questions within agroforestry systems. Notably, we will highlight results from our complementary study that used the same GPR data to effectively estimate belowground biomass.