A case study of rangeland vegetation changes from 1979 to 2016 in the Middle Atlas Mountains of Morocco

Abstract

This case study assessed changes in vegetation composition of a 0.8 ha rangeland site over the past four decades, in relation to changes in temperature and to an increase in grazing pressure. The frequency and standing crop (biomass) of species and functional groups were sampled in the spring of 1979 and 2016. Mean annual temperature increased, whereas changes in frequency varied between species and functional groups. Species that decreased included perennial plants, whereas species that increased were comprised mostly of annuals and unpalatable herbaceous plants. An NMDS ordination showed significant differences in species composition between 1979 and 2016. Total biomass, as well as the biomass of annual and perennial grasses and forbs did not differ between 1979 and 2016. Shrub biomass, however, decreased by 60% between years. Biomass of the ‘graminoids’ (e.g. Carex divisa), on the other hand, increased fourfold between 1979 and 2016. Species richness and the Shannon–Weaver diversity index H′ declined in 2016. This, together with a decline in the frequency of palatable species and a shift in species composition, could signal a decline in resilience over the long term. Changes in vegetation were most likely driven by a combination of higher temperatures and increased grazing pressure.