Using GPR to analyze regeneration success of cork oaks in the Maâmora forest (Morocco)

de Mahieu, Aurore [UCL] Ponette, Quentin [UCL] Mounir, Fouad [National Forestry School (ENFI), Morocco] Lambot, Sébastien [UCL]

Under limited precipitation, coarse-textured soils may strongly limit tree regeneration success and stand productivity, yet their effective impact depends on layer thickness and the nature of the underlying soil material. Within that context, we have evaluated the performance of two ground-penetrating radar (GPR) techniques to assess the short-scale variability in physical soil properties, using the Ma^amora forest and cork oak as a case study. A frequency-domain GPR was developed to map the soil surface water content of a 1 ha, 18-year old cork oak stand. In addition, a time-domain GPR was used to detect soil textural transitions in depth between the sand and clay textures of the same cork oak stand. Intensive GPR measurements were made along transects, together with detailed local stand and soil characterization. The volumetric water contents (ϴv) varied between 0.01 m3/ m3 and 0.1 m3/m3, which represent available water storage of coarse sands to sandy loams [0.04 m3/m3 - 0.12 m3/m3]. The estimated transition depths detected by the second GPR varied between 1.8 m and 4.0 m deep. Soil water content was found to be a relevant indicator of successful cork oak regeneration as it was strongly related to the dominant heights of the cork oaks. The most successful areas were characterized by higher surface moisture and these higher values were mostly explained by soil texture. Moreover, the layer thickness also influenced cork oak growth. Hence, both radar systems provided useful predictors for the regeneration success of cork oaks. Using GPR for future tree planting would allow foresters to detect the best areas in terms of hydric and edaphic conditions where trees should be installed in order to ensure a successful establishment.