Erosion processes in degraded argan-tree populations in South Morocco

点击翻译按钮获取中文摘要

Soil and vegetation in the endemic argan-tree population in Morocco is increasingly being degraded by expansion and intensifying agriculture as well as overgrazing. Areas with canopy cover decrease while areas without cover between the argan trees increase. Due to reduced infiltration, runoff and soil erosion rates rise drastically. Thus, it is more difficult for young stands to establish themselves on these degraded soils, and undergrowth remains patchy. We will study argan-tree populations in different stages of degradation to establish threshold values to describe the initiation as well as the dynamisation of erosion processes, especially rill and gully erosion. In three study areas in the High Atlas and the Anti-Atlas, fenced-in reforestation areas will be compared to unprotected areas on differing slopes. The development of population densities will be quantified with high-resolution CORONA satellite photographs from 1968 and large-scale aerial photographs from 2017/18 that will be taken during the project using unmanned aerial vehicles (UAV). Characteristic tree crowns will be documented and classified using structure from motion (SfM)-techniques (3D models derived from multicopter images). Analyses of grain sizes, aggregate stability, soil organic matter and soil nutrients will show the decreasing influence of the crown covered area, with an increasing distance between trees, on an expanding intertree area. The erodibility and the infiltration capacity of the intertree areas in different stages of degradation will be studied using infiltration measurements and rainfall simulation experiments. Volumes of linear erosion forms will be quantified using SfM-monitoring with 3D-modelling. Stone cover and cattle trails can be identified from the UAV photographs. Cattle counts as well as interviews with key informants will complement the knowledge of the grazing pressure by sheep and goats on the areas with argan-tree populations. By studying the degradation of population densities, intertree and tree areas, the argan-tree populations can be classified into stability classes defined by values acquired through this multi-method-concept. The threshold values describe the dynamisation of erosion processes under argan trees and prove that certain erosion processes correlate with certain degradation states or population densities. This is the vital prerequisite for a sustainable cultivation of the argan-tree populations.