Using Ground-Penetrating Radar to Detect Tree Roots and Estimate Biomass

Abstract

Ground-penetrating radar (GPR) is a nondestructive means of detecting buried objects with electromagnetic waves. It has been applied to detect coarse woody roots, estimate biomass, root diameter, and spatial distribution of roots. This chapter discusses the development of root assessment techniques, basic methodology, and examples of field applications where GPR was successful. IntroductionMany root quantification methods are destructive (e.g., soil cores, pit, whole-plant excavation) and prohibit repeated measurements over time. Destructive sampling yields high quality data, though it is expensive and labor intensive. Frequently, this leads to small sample sizes that may not adequately capture spatial variability and lack statistical power to reveal subtle treatment differences. For those who study

Ecosystem carbon stocks in Pinus palustris forests

“…Dead roots varied from being undetectable to marginally detectable, so GPR data were scaled using live root mass. To integrate GPR data with longleaf pine below-stump estimates derived from inventory data, it was assumed that GPR cannot detect fine roots (<2 mm diameter), taproots, or most decaying roots, and GPR has accounted for all lateral roots regardless of species (Butnor et al 2012a). Because of the predominance of large overlapping roots in the excavation pits and potential underestimation by GPR of lateral roots in the pits, coarse root GPR C (taproot not included) was calculated using two different assumptions: (1) GPR captured all lateral root mass in the excavation pit area (coarse root GPR = GPR -predicted longleaf pine lateral roots in pits) or (2) GPR captured no lateral roots in the pits (coarse root GPR = GPR + predicted longleaf pine lateral roots in pits).…”

“…Postcollection data processing was used to remove signal noise and determine the location and relative size of roots using RADAN 7 software (GSSI, Salem, New Hampshire). Image analysis was applied to summarize processed data and quantify root biomass at 65 locations along each transect (1365 total per subplot) using an approach described by Butnor et al (2012a) with SigmaScan Pro Image Analysis software (Systat Software, Point Richmond, California). The relationship between GPR data and actual root mass was assessed at each stand using twenty-five 15 cm diameter validation rootsoil cores, which were scanned with GPR prior to collection and then dry-sieved, washed, and oven-dried at 65°C to a constant mass (Butnor et al 2012a).…”

Coupling Fine-Scale Root and Canopy Structure Using Ground-Based Remote Sensing

“…Soils along transects were scanned with a SIR-3000 radar unit (Geophysical Survey Systems Inc. (GSSI), Salem, New Hampshire) equipped with a 1500 MHz antenna and a measurement cart with an integrated survey wheel to measure distance traveled along the transect. As with the PCL, the design, operation, and validation of the GPR system is described extensively in prior publications [20,37] and has been successfully used to determine orientation, diameter, depth, and density of roots in situ [20,[38][39][40]. Briefly, the GPR pulses electromagnetic energy into soils and records the two-way travel time of signals reflected from roots ( Figure 2).…”

“…Briefly, the GPR pulses electromagnetic energy into soils and records the two-way travel time of signals reflected from roots ( Figure 2). We filtered noise in GPR images using RADAN 7 software (GSSI, Nashua, New Hampshire), determined root location and size with SigmaScan Pro Image Analysis software (Systat Software, Point Richmond, California), and quantified root biomass using the approach employed by Butnor et al [39], summarized briefly here. The GPR system measures lateral roots and thus GPR-derived root biomass estimates do not include roots directly beneath stems/stumps [37].…”

Methods for Sampling Coarse Roots of an Individual Tree in the Field

“…Recently, a new method using ground-penetrating radar has been introduced to detect coarse roots and estimate biomass (Hirano et al 2009(Hirano et al , 2012Butnor et al 2011;Tanikawa et al 2013Tanikawa et al , 2016. Also, for fine-root dynamics, minirhizotron technique and optical scanner method have been developed (Noguchi et al 2005;Dannoura et al 2008).…”