Where are the mistletoes? Large declines in mistletoes in a savanna ecosystem over 30 years

Abstract

Large trees are vital hosts for aerial hemiparasites, and their decline likely drives declines in mistletoe abundance. In semi-arid savannas, mistletoes provide ecological and economic benefits, by enriching soil nutrients, enhancing understorey diversity, and supporting livelihoods through the sale of woodroses. However, their persistence is threatened by changes in disperser and pollinator behaviour, overharvesting, host tree loss, and climate change. We assessed ∼30 years of change (1994 to 2024) in woody plant density, mistletoe-infected trees, and two woodrose-forming mistletoe species ( Erianthemum dregei and Pedistylis galpinii ) across communal rangelands (CRs) and protected areas (PAs) in a lowveld savanna of South Africa. Over this period, woody plant densities increased by 61%, with CRs supporting 46% higher densities than PAs. In contrast, mistletoe-infected tree densities and richness declined by 33% and 40%, respectively. Although mistletoe-infected tree height, stem diameter, and canopy area did not differ between time periods, PAs had infected trees that were 19% to 38% taller with larger stem diameter and canopy areas than in CRs. Mistletoe density declined by 43%, with medium and large individuals decreasing by 30% and 86%, respectively, and P. galpinii declining by 79%. These declines appear linked to losses of large trees and megaherbivore herbivory in PAs, whereas increases in woody cover likely reflect the proliferation of disturbance-tolerant, coppicing species under sustained human and megaherbivore pressures. Nonetheless, CRs supported higher densities and a greater diversity of mistletoe-infected trees and mistletoes than PAs, emphasising the conservation value of customary management systems in sustaining vulnerable parasitic plant communities.