Reflecting on research produced after more than 60 years of exclosures in the Kruger National Park

All data, in this case works of literature reviewed have been summarised in Online Appendix 2.Herbivores are a main driver of ecosystem patterns and processes in semi-arid savannas, with their effects clearly observed when they are excluded from landscapes. Starting in the 1960s, various herbivore exclosures have been erected in the Kruger National Park (KNP), for research and management purposes. These exclosures vary from very small (1 m2) to relatively large (almost 900 ha), from short-term (single growing season) to long-term (e.g. some of the exclosures were erected more than 60 years ago), and are located on different geologies and across a rainfall gradient. We provide a summary of the history and specifications of various exclosures. This is followed by a systematic overview of mostly peer-reviewed literature resulting from using KNP exclosures as research sites. These 75 articles cover research on soils, vegetation dynamics, herbivore exclusion on other faunal groups and disease. We provide general patterns and mechanisms in a synthesis section, and end with recommendations to increase research outputs and productivity for future exclosure experiments. CONSERVATION IMPLICATIONS : Herbivore exclosures in the KNP have become global research platforms, that have helped in the training of ecologists, veterinarians and field biologists, and have provided valuable insights into savanna dynamics that would otherwise have been hard to gain. In an age of dwindling conservation funding, we make the case for the value added by exclosures and make recommendations for their continued use as learning tools in complex African savannas.South African Environment Observation Network (SAEON).http://www.koedoe.co.zaam2023Paraclinical Science

<i>Virgilia divaricata</i> may facilitate forest expansion in the afrotemperate forests of the southern Cape, South Africa

Virgilia divaricata is a fast-growing nitrogen-fixing tree species often found on the margins of forest in the southern Cape of South Africa and is particularly abundant after fire. However, V. divaricatamay invade fynbos even in the absence of fire and it has been described as a forest precursor. We investigated whether V. divaricata enriches soil fertility after its invasion into fynbos areas adjacent to forests. We measured soil organic carbon and soil nutrients at four sites. At each site, three vegetation types (forest, V. divaricata and fynbos) were examined on the same soil type and at the same elevation. Our results showed that, on average, soils taken from V. divaricata stands had higher nitrogen and phosphorus values than the adjacent fynbos soils, with either lower or similar values to the adjacent forest soils. Higher soil fertility under V. divaricata, together with their shading effect, may create conditions favourable for shade-loving forest species dependent on an efficient nutrient cycle in the topsoil layers, and less favourable for shade-hating fynbos species, which are generally adapted to low soil fertility. We suggest that the restoration of the nutrient cycle found in association with forest may be accelerated under V. divaricata compared with other forest precursor species, which has important consequences for the use of V. divaricata in ecosystem restoration. Conservation implications: Alien plantations in the Outeniqua Mountains are being phased out and the areas are being incorporated into the Garden Route National Park. Fynbos areas are increasingly being invaded by forest and thicket species owing to fire suppression in lower-lying areas. An improved understanding of the fynbos–forest boundary dynamics will aid in efficient management and restoration of these ecosystems

Browser impacts in Mapungubwe National Park, South Africa: Should we be worried?

This study explores the impact of browsers on vegetation types within the Mapungubwe National Park and specifically whether rocky outcrops or ridges in the park serve as refugia from browsers, particularly elephants. We sampled 80 transects at 20 sites and recorded 1740 plants comprising 65 species. We found that a high proportion (> 80%) of the woody vegetation sampled indicated browser utilisation. Although certain woody species (e.g. Albizia harveyi, Boscia albitrunca, Lannea schweinfurthii) appeared to be preferred by browsers, browsing levels were relatively high among all woody species. High levels of browsing by herbivores other than elephants suggest that they have a significant impact on the park’s vegetation. We did not find that rocky ridges acted as refugia to browsers, but instead found that vegetation in rocky ridges was more severely impacted by browsers than vegetation in flat areas, despite vegetation being more accessible in flat areas. If elephant numbers continue to increase at the current rate (e.g. elephant numbers doubled between 2007 and 2010), we predict that some of the heavily utilised species will become locally rare over time. Conservation implications: High levels of browsing by both elephant and smaller herbivores contribute to significant impacts on vegetation away from rivers in Mapungubwe National Park. Without management interventions that address both types of impact, structural and species diversity are bound to decrease over the short to medium term

Data from: Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation of Colophospermum mopane savanna by Imbrasia belina larvae

Severe defoliation is expected to affect nutrient cycling of an impacted system. Outbreaks of the lepidopteran Imbrasia belina (mopane worm) affect discrete patches of Colophospermum mopane trees in semi-arid savanna; larvae may completely defoliate trees for up to six weeks during each of the early and late growing seasons. We studied the impact of mopane worm outbreaks on the availability of nitrogen, phosphorus and potassium within mopane savanna by comparing defoliated with non-defoliated savanna patches. Individual studies conducted were production and nutrient content of leaf biomass and worm frass that determine nutrient input to the soil, and soil nutrient concentrations. Within an outbreak area 44 percent of trees supported ±29,000 worms/ha who deposited ±640 kg/ha dry weight of frass at 1.4 g of frass/day (fourth or fifth instar) compared with an average 1645 kg/ha dry weight of leaf on trees most of which should be deposited by litter fall at the end of the growing season. Nutrient concentrations in frass compared with senescent mopane leaves were two-fold higher for phosphorus, 10 percent higher for potassium, and 20 percent less for nitrogen. Soil nutrient content beneath defoliated trees was higher for phosphorus and potassium but there was no difference for nitrogen. Invertebrate herbivory appears to be an important driver for mopane savanna but has been largely neglected

Dryad_Spine_dens_BI

This file includes spine length, spine density and branching density

Bark_recovery

Recovery rates of the species in the pape

Dryad_Woody_leaf_traits

This file includes the leaf traits included in this publicati

Bark nutrients_Dryad

Nutrient content of species in the stud