Termite mounds mitigate against 50 years of herbivore-induced reduction of functional diversity of savanna woody plants

Abstract

Context Spatially heterogeneous habitats often promote woody plant species and functional diversity (FD). Ungulate herbivory can have the opposite effect. Across the globe, the type and intensity of herbivory is changing, as domestic livestock replace wild ungulates, which are increasingly confined to protected areas. Despite recognition of the importance of FD for ecosystem functioning, the interactive effect of soilrelated fine-scale heterogeneity and larger-scale ungulate herbivory on woody plant FD is little-known.Objectives In miombo woodland of Zimbabwe, we investigated (1) how bottom-up fine-scale heterogeneity created by Macrotermes termitaria interacts with top-down effects of herbivore foraging-guilds on woody plant FD; and (2) whether browsing combined with grazing impacts FD more than grazing alone. Methods The three different herbivore treatments (grazing, combined browsing-and-grazing, and exclusion) had been maintained for 50 years. We surveyed 10 termite mound-matrix plots within three sites per treatment. We assessed woody plant traits and FD across treatments (herbivore feeding-guild) and position (mound or woodland-matrix), and interactive effects between these. Results Woody plant FD was greater on mounds, and lowest overall with browsing-and-grazing. Specific traits were associated with position (e.g. palatability was greater for mounds), and treatment (e.g. spinescence increased with grazing). Conclusions Long-term enclosure of ungulate herbivores (browsing-and-grazing, and grazing alone) decreased woody FD, but this was mitigated by termitaria. The novel finding is that at regional scales, mounds can enhance woody plant FD despite the impacts of herbivory. At broader scales encompassing the miombo system, potential exists for mounds to stabilise woody plant FD from livestock-induced impacts.

Termite mounds house a diversity of taxa in oil palm plantations irrespective of understory management

“…As abundances of species outside the mounds were not examined, we are unable to comment on the preference of termite mounds as nesting sites compared with other microhabitats. However, this study supports previous work that has found termite mounds act as refuges for a range of animals (Choosai, Mathieu, Hanboonsong, & Jouquet, 2009;Joseph et al, 2015;Joseph, Seymour, Cumming, Mahlangu, & Cumming, 2013).…”

Woody encroachment slows decomposition and termite activity in an African savanna

“…Slower decomposition in encroached areas has important implications for the global carbon budget, given the importance of decomposition to global carbon fluxes (Raich & Schlesinger, 1992), as well as for nutrient cycling in these systems. The reduction in termite activity in encroached areas also has important implications for multiple other ecosystem processes since termites are keystone organisms that influence several attributes of savanna ecosystems, including soil properties, hydrology, vegetation communities and the patterns and impacts of herbivory (Davies et al, 2016;Joseph et al, 2015;Sileshi, Arshad, Konate, & Nkunika, 2010).…”

Microclimates mitigate against hot temperatures in dryland ecosystems: termite mounds as an example

“…In addition, in many habitats (e.g., miombo), termite mounds harbor evergreen vegetation (Joseph et al. , ), whereas the surrounding matrix is dominated by deciduous species, so mounds represent year‐round patches of shade. Finally, variation explained by random effects indicates that site and time of day of measurement had some influence on Δ T , because random effects increased variance explained by 5%.…”