Current applications of GPR in forest research
Forests, both naturally regenerated stands and plantations are complex, long-lived systems, which can be difficult to assess and monitor over time. This is especially true of belowground biomass and internal features of trees which are inaccessible except by destructive sampling. Traditional methods are expensive, destructive, time-consuming, usually yield a small sample size and are not conducive to long-term monitoring. Since GPR was first used to map tree roots ten years ago, a variety of new applications have been introduced. On soils suitable for radar studies, root biomass surveys have been valuable means to quantify belowground biomass, spatial distribution of roots, measure root diameters and even map individual roots. Methods include collecting linear transects in reflection mode, interlacing grids of transects in order to create 3D reconstructions of roots and applying high frequency borehole antennas used in transmission mode to model vertically oriented roots. One of the more difficult problems we are currently considering is how to analyze permanently marked transects over time to monitor root development while soil moisture, temperature and surface conditions change seasonally. In a departure from subsurface analysis, we have recently employed a method using GPR to detect defects and moisture gradients in stems.