The use of ground penetrating radar for remote sensing the organic layer – mineral soil interface in paludified boreal forests

Abstract

Black spruce forests that are located in the Clay Belt, within the boreal region of eastern North America, are prone to paludification. Paludification is a natural process where organic layer accumulates on the forest floor, leading to substantial decreases in forest productivity. This study assessed the ability of using ground penetrating radar (GPR) to remotely sense the organic layer – mineral soil (OL–MS) interface (representing organic layer thickness (OLT)), which has a major influence on the occurrence of paludification in this region. The two chosen sites for this study represented different types of soil and organic layer thicknesses that are linked to different degrees of paludification: low to moderately paludified (site A) and highly paludified (site B). At each site, GPR measurements were collected along three 40 m parallel transects at 20 cm intervals with 200 MHz antenna. GPR interpretations were compared with field manual probing measurements. Detection of this continuous interface was successful at site A (r = 0.93, P < 0.001), but mesic and humic horizon clay content limited radar depth penetration, rendering the OL–MS undetectable at site B. However, we found that GPR data, coupled with ground truth information, were effective in mapping the thickness of the organic fibric horizon (r = 0.79, P < 0.001) at site B, which could be considered as an indicator of the OLT in highly paludified areas. Overall, GPR appeared effective for mapping the OL–MS interface in the low to moderately paludified site, which is attractive for implementing forest management strategies that will help to stop the advance of paludification.