Ecological stability in the face of climatic disturbances: a case study of a dryland ecosystem in the Moroccan High Atlas Mountains

Abstract

Drylands suffer from land degradation due to increasing anthropogenic pressure and climate change. This threatens the existence of these valuable ecosystems and the people that live in them. The ecological stability of an ecosystem determines how it responds to disturbances. Understanding ecological stability is, therefore, crucial in preventing land degradation and designing strategies for restoration. In this study, the ecological stability of a dryland ecosystem in the Moroccan High Atlas Mountains, in the face of both a drought and a heavy flooding period, was determined. The Breaks For Additive Seasonal and Trend (BFAST) change detection methodology was used to determine breakpoints and trends in a time-series of Landsat NDVI data between 1984 and 2019. The breakpoints were classified using a newly developed typology based on the trend before and after the breakpoint. The improved typology that is introduced in this thesis, considers the statistical significance of trends and subdivides them in categories of abrupt changes that lead to an improvement of ecosystem functioning (positive breakpoints) and abrupt changes that lead to a deterioration of ecosystem functioning (negative breakpoints). Ecological stability was quantified using the resistance to abrupt changes that lead to a deterioration in ecosystem functioning and the response to climatic disturbances (i.e. the drought and the flood) as indicators. The resulting data on resistance and response to climatic disturbances were compared to data of land cover classification, overall change in vegetation cover and initial vegetation cover. The results show that ecological stability is higher in the northern part of the Ounila watershed. Ecological stability is lowest in lower-lying bare areas in the east and south of the watershed. Areas with higher initial NDVI exhibited higher ecological stability. In the upper part of the watershed, there are some areas that have shown overall greening or browning. The areas that have experienced greening, had low resistance and showed an improvement in ecosystem functioning in response to the drought. These areas were identified as locations with high potential for land restoration.