Justice Muvengwi

Termite mounds may not be foraging hotspots for mega-herbivores in a nutrient-rich matrix

Our study investigated the influence of termitaria on vegetation utilization by elephants in Chewore North, Zimbabwe. Ten termite mounds and ten similar sized control plots were surveyed for soil nutrients, tree species diversity and plant biomass removal by elephants. Termite mounds had higher mean (± SE) concentrations of P, Ca, Mg and Na (0.15 ± 0.01, 48.8 ± 9.32, 5.78 ± 1.59 and 0.47 ± 0.12 meq per 100 g respectively) than control plots (0.05 ± 0.01, 3.33 ± 0.56, 1.53 ± 0.22 and 0.19 ± 0.02 meq per 100 g). However, Shannon Wiener index of tree diversity did not vary significantly between termite mounds (1.13 ± 0.280) and their control plots (0.827 ± 0.469). Contrary to most studies investigating patterns of vegetation utilization by large mammalian herbivores on termitaria, biomass removal was five times more on control plots than termite mounds. No difference in biomass removal was noted for Colophospermum mopane which had enough replicates for statistical analysis both on termite mounds and control plots. Our study negates the hypothesis that nutrient-rich soil patches will act as feeding hotspots for large mammalian herbivores. We concluded that vegetation utilization by elephants may be tree species specific, particularly in nutrient-rich environments.

Termitaria as preferred browsing patches for black rhinoceros ( Diceros bicornis ) in Chipinge Safari Area, Zimbabwe

This study tested the hypothesis that the black rhinoceros browses more on termitaria than off termitaria vegetation due to elevated soil and foliar nutrient levels on termitaria. We investigated the role of termitaria in providing nutrient-rich forage for the black rhinoceros, by comparing the preference (selection ratio) for vegetation occurring on and off termitaria, and then testing its relationship with foliar nutrient concentrations. Soil nutrients, bite intensity, tree species diversity, vegetation density, canopy cover and basal area were also surveyed on and off termitaria. We sampled 25 termite mounds together with their corresponding control plots in Chipinge Safari Area, Zimbabwe. Soil and foliar N, P, K, Ca and Na concentrations were greater on termitaria than off termitaria, with approximately twice the concentration of these nutrients. Browse preference followed the between-site differences in soil and foliar nutrient concentrations, with higher selection ratios and bite intensities for vegetation on termitaria than off termitaria. Diospyros quiloensis was the most preferred browse species whilst Combretum imberbe, Kigelia africana and Strychnos innocua were the least. In conclusion, the black rhino preferred vegetation on termitaria to that in the surrounding matrix, and utilization of vegetation can be influenced by the soil substrate on which tree species grow.

Termite mounds vary in their importance as sources of vegetation heterogeneity across savanna landscapes

Questions Termite mounds are well known to host a suite of unique plants compared with the surrounding savanna matrix. However, most studies testing the significance of mounds for ecosystem heterogeneity have been conducted at single sites. Mound effects on savanna heterogeneity across varying landscapes are less well understood, and how effects might vary across geological types and mounds of different sizes is as yet unknown. Location Gonarezhou National Park, Zimbabwe. Methods We studied effects of termite mounds on vegetation spatial heterogeneity across two geologies (granite and basalt), including effects of mound size and the spatial extent of termite influence. Herbaceous vegetation was sampled on mounds and savanna matrix plots, and along distance transects away from mounds. Soil nutrients on mounds and in the matrix were also compared between geologies. Results Soil nutrients were more concentrated in large mounds compared with the matrix on granite, but not on basalt, with mounds therefore acting as nutrient hot-spots on nutrient-poor granite only. Large and medium sized mounds hosted compositionally different grass species to the matrix on granite, but not on basalt. Large mounds on granite also had significantly lower grass and forb species richness compared with the matrix. However, small mounds on granite, and all mound size categories on basalt, did not have an effect on grass and forb species richness or assemblage composition, an observation attributed to a lack of difference in soil nutrients between the mounds and matrix. Conclusion Our study shows that the significance of termite mounds to ecosystem spatial heterogeneity is strongly influenced by geology and mound size, with mound effects on herbaceous plant species heterogeneity more pronounced in dystrophic geologies and around large mounds. Future studies should take greater cognisance of landscape context and mound size when seeking to understand the contribution of termite mounds to ecosystem structure and function. This article is protected by copyright. All rights reserved.

Contrasting termite diversity and assemblages on granitic and basaltic African savanna landscapes

Termites are recognised soil ecosystem engineers in the tropics and sub-tropics, making the understanding of their distribution a priority. However, there is a poor understanding of how differences in soil properties and plant biomass productivity affect termite species diversity. We compared the diversity of termites between two soils of differing geological provenance (basalt and granite), and consequently contrasting nutrient content, but subject to similar climatic conditions in a semi-arid Zimbabwean savanna. Basaltic soils contained more dead wood, and were more nutrient-rich than granitic soils, with significantly higher exchangeable Ca and Mg, and available P, and a less acidic pH. However, despite this higher soil nutrient status on basalts, functional and taxonomic termite diversity was higher on granites, although termite abundance was similar between the geological formations. Termite assemblages differed between the geological formations, with very little overlap. We conclude that termite diversity is highly influenced by soil productivity, with nutrient-poor soils having higher diversity, potentially due to reduced competitive exclusion or differences in species adaptation to soil conditions.

Diversity and abundance of macro-invertebrates on abandoned cattle kraals in a semi-arid savanna

Abstract Abandoned cattle (Bos taurus) kraals are sources of habitat heterogeneity in dystrophic semi‐arid African savannas with a strong positive effect on soil nutrients and plant productivity. However, little is known regarding how macro‐invertebrate assemblages vary between abandoned kraals and the surrounding savanna matrix. We tested whether herbaceous biomass and basal and aerial covers and soil nutrients have an effect on aboveground and belowground macro‐invertebrate assemblages. Twelve abandoned kraals were contrasted with their paired control plots for soil characteristics, herbaceous productivity, and macro‐invertebrate assemblages in Save Valley Conservancy, Zimbabwe. Abandoned kraals had significantly higher concentrations of soil nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) as well as herbaceous biomass and basal and aerial covers than control plots. Both aboveground and belowground macro‐invertebrate species richness were higher on abandoned kraals. However, only belowground macro‐invertebrate diversity (Shannon H′ and Hill number 1) was significantly higher on abandoned kraals. Soil nutrients and herbaceous productivity had positive and significant correlations with the dominant taxa (Coleoptera, Hymenoptera, Hemiptera, Isoptera, and Myriapoda) on abandoned kraals. These results add to the growing body of evidence that abandoned kraals exert significant effects on savanna spatial heterogeneity years later, with implications on ecosystem processes and functioning.