Erosion processes in degraded argan-tree populations in South Morocco

由于农业的扩张和集约化以及过度放牧，摩洛哥地方性艾尔甘树种群的土壤和植被正在日益退化。有树冠覆盖的面积减少，而在阿尔甘树之间没有覆盖的面积增加。由于入渗减少，径流和土壤侵蚀率急剧上升。因此，幼林更难在这些退化的土壤上站稳脚跟，林下植被仍然是斑驳的。我们将研究不同退化阶段的盘根树种群，以建立阈值来描述侵蚀过程的启动和动力，特别是细沟和沟壑侵蚀。在《高地图集》和《反地图集》中的三个研究区，将把用栅栏围起来的重新造林区域与不同斜坡上的无保护区域进行比较。人口密度的发展将使用1968年的高分辨率日冕卫星照片和2017/18年的大规模航空照片进行量化，这些照片将在项目期间使用无人机(UAV)拍摄。特征树冠将被记录下来，并使用运动结构(SFM)技术(来自多视角图像的3D模型)进行分类。粒度、团聚体稳定性、土壤有机质和土壤养分的分析表明，随着树距的增加，树冠覆盖面积对树间面积的影响逐渐减小。通过入渗测量和降雨模拟试验，研究了不同退化阶段林间区的可蚀性和入渗能力。线性侵蚀形式的体积将使用带3D建模的SfM监测进行量化。从无人机的照片中可以辨认出石头覆盖和牛群的踪迹。对牛的计数以及对主要信息提供人的访谈将补充绵羊和山羊对有阿尔甘树种群的地区的放牧压力的知识。通过研究种群密度、树间和树面积的退化，可以将阿尔冈树种群划分为稳定类，这些稳定类由通过这种多方法概念获得的值来定义。阈值描述了阿尔冈树下侵蚀过程的动态化，并证明了某些侵蚀过程与某些退化状态或种群密度有关。这是艾尔干树种群可持续种植的重要先决条件。

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.