FIGURE 3 - available via license: CC BY
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Bar chart representing the species richness (Chao estimate) and diversity (Shannon index) for the different sampling seasons at the different topographical units. The height of each column represents the mean, and the error bar represents the upper portion of the 95% confidence interval.
Source publication
A preliminary study investigated the associations between vegetation communities along catenary soil gradients in 2015. The severe drought of 2016 in South Africa presented the opportunity to study post-drought savanna vegetation changes. This hillslope transect was surveyed for five successive seasons. The Braun-Blanquet method was used, and the d...
Contexts in source publication
Context 1
... Figure 3a, it seems as if the species richness decreased at all the sites during the drought and subsequently increased more-or-less progressively through time as the communities recovered from the drought between 2015 and the onset of the current sampling period. However, pre-versus post-drought richness estimates are only significantly different for the sodic and riparian habitats (non-overlapping 95% confidence intervals between groups); variance in estimates for the crest communities is high and overlaps with the pre-drought estimate. ...
Context 2
... species richness in crest habitats was greater than in both sodic and riparian habitats. Figure 3b represents the changes that took place in diversity over the different sampling seasons. In contrast to richness, species diversity did not differ between pre-and post-drought periods. ...
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... In the drought-release year, especially herbaceous abundance in treated areas was higher compared to untreated areas, whereas this effect was less pronounced in the post-drought year. Since the drought had led to a strong decrease in herbaceous vegetation cover (Figure 3a), annuals and pioneer species dominated the treated areas in the drought release year, where water competition with more drought-resistant woody species was lower compared to the untreated areas (Van Aardt et al. 2020). This was also apparent when comparing the herbaceous composition and indicator species between treatments in the two years. ...
Land degradation due to bush encroachment and drought threatens the well-being of land users and forage
production in the semi-arid savannas of southern Africa. This study aimed to analyse how herbaceous vegetation
in the Kalahari savanna can recover from drought, and how this is affected by previously implemented bush
control measures. We compared plant species composition and diversity of the herbaceous layer across a drought-
release (2021) and post-drought (2022) year within two land use types (game and livestock) in bush-encroached
and controlled areas, respectively. Diversity decreased significantly during the post-drought year. Annual
species dominated in the drought-release year, which were replaced by perennial forbs and dwarf shrubs in the
post-drought year. Selective bush control enhanced herbaceous species abundance and richness due to decreased
competition. The species richness was higher in the game ranch compared to the cattle farm during the drought-
release year. Herbaceous abundance, however, increased on the cattle farm. The management strategies, feeding
behaviour and animal movement may have contributed to these differences in these two contrasting land use types.
This study showed that herbaceous plant communities can recover rapidly after a drought period and in areas
where bush control was applied.
... Drought is characterized as prolonged and extreme below average water availability relative to local mean annual precipitation that extends into one or more wet seasons (Sankaran, 2019) and multi-annual droughts have been shown to occur periodically in savanna ecosystems-especially semi-arid ones (Mason andTyson, 2000, Tyson et al., 2002). Drought has been observed to cause mortality and dieback within juvenile and adult tree communities (Case et al., 2019, Fensham et al., 2009, Sankaran, 2019 and reductions in plant species richness (van Aardt et al., 2020, Sankaran, 2019. Tree mortality was reported in the 2014-2016 drought in the Nkuhlu area, near Skukuza, in the Kruger National Park in South Africa (Case et al., 2019), and also recorded in savannas of north-eastern Australia post the "millennium" drought (Fensham et al., 2009) Fire impacts savanna distribution , Ratnam et al., 2011, Staver et al., 2011, and some of the traits that enable tolerance of fire and seasonal water shortages may also be important in drought resilience. ...
The aim of this study was to understand how communities of adult and juvenile (seedlings and saplings) woody plants were impacted by fire and the 2014–2016 El Niño drought in Kruger National Park, South Africa. We used a landscape‐scale fire experiment spanning 2013–2019 in a semi‐arid savanna in the central west of Kruger National Park (mean annual precipitation, 543 mm). Adult and juvenile woody species composition were recorded during and after the drought in 40 plots that experienced a mix of no fire, moderate fire, and frequent fire treatments. Using multivariate modeling, we related community composition in juvenile and adult woody plants to year of sampling and the experimental fire treatments. Post‐drought, there was significant adult woody plant top‐kill, especially in dominant species Dichrostachys cinerea (81% reduction in abundance), Acacia nigrescens (30%), and Combretum apiculatum (19%), but there was no significant change in adult species richness. Two years post‐drought, abundance of all juveniles decreased by 35%, and species richness increased in juveniles in both the frequent fire (7%) and no fire treatments (32%). Counter‐intuitively, the El Niño drought increased species richness of the woody plant community due to the recruitment of new species as juveniles, a potential lasting impact on diversity, and where different fire regimes were associated with differences in community composition. Drought events in semi‐arid savannas could drive temporal dynamics in species richness and composition in previously unrecognized ways.
... The vegetation structure was also found to differ between the hillslope zones (Janecke 2020), and this led to a variety of habitat types for animals. The impact of the drought on vegetation and the recovery of plants on the catena over a period of 3-4 years were covered in an article by Van Aardt et al. (2020). The variety of habitat types created by different plant communities in the catenal zones were also linked to mammal presence on the catena and at the waterholes in the vicinity (Janecke & Bolton 2020). ...
... During the extreme El Niño event of 2015-2017, the study area appeared to be a refuge island of green vegetation surrounded by the desert-like areas around Skukuza and Lower Sabie where mainly bare soil, leafless trees and dead trees were present during the drought Van Aardt et al. 2020). The long-term (76 years) average annual rainfall total for Skukuza is 550.4 mm. ...
A higher variety of habitats normally result in higher diversity of species. The granite catenas near Skukuza, Kruger National Park (KNP), consist of different soil types along the hillslope, creating different habitats. Objectives were to determine the mammal species present on a catena and surrounding areas; to indicate their main period of activity; and to indicate human visibility in each catenal zone to explain landscape of fear principles. Camera trap surveys were conducted for short periods and repeated over three years. In total, 31 mammal species were observed on the catena, and its nearest waterholes. Small to mega-sized mammals were present, but some species were only observed during one survey period. Small changes were noticed in activity periods between survey periods, probably due to the drought. A severe drought changed vegetation structure and visibility, but the study area appeared to act as a drought forage refuge. The lowest visibility was found at the sodic patch upper-midslope ecotone, and shrub veld. This can possibly explain the lower number of mammal observations in these areas. Different habitats and habitat features were described which can affect the presence of mammals, i.e. the mud wallows that were created and maintained by the mammals. Future studies can focus on the impact of seasonal changes in mammal presence and on mammal diversity during a normal rainfall year.
Conservation implications: To understand the mechanisms of herbivores as ecosystem drivers, aspects such as vegetation, soil and mammals should be combined. Better understanding of mammals, their habitats and associated processes can lead to better conservation actions.
... Acacia nilotica is common on the lower slopes and Euclea divinorium has an association with the duplex sodic soils of the midslopes, whilst Terminalia sericea predominate the crests. More detailed descriptions of the vegetation along the catena are provided in Janecke (2020), Theron et al. (2020) and Van Aardt et al. (2020). ...
The semi-arid conditions in savanna landscapes ensure that ephemeral drainage dominates the hydrological network in these dryland systems. Quantification of their hydrological processes is important to inform ecosystem understanding and future conservation efforts under a changing climate, and to provide guidance for restoration. By combining in situ hydrometric observations, hydrochemistry, remote sensing and a soil water balance model, we characterise the groundwater–surface water interactions in ephemeral low-order catchments of the granitoid regions of the southern Kruger National Park (KNP). Streams at the lowest orders are augmented by lateral interflows from the catena, although the second- and third-order stream reaches are conduits for groundwater recharge to the fractured rock aquifer; the soils of the crests and foot-slopes also show preferential flow, and are truly recharge soils, whilst the duplex soils of the midslopes clearly show their responsive nature to a low soil moisture deficit in the shallow horizons. Actual evaporation (aET) differed between catena elements with surprisingly little variation at third-order hillslopes, with the greatest overall aET at the first order. Meanwhile, soil water balances demonstrated a significant variation in storage of the riparian zones as a result of interflow from upslope and aET losses. Furthermore, data support broader-scale observations that groundwater recharge through the vadose zone to the fractured rock aquifer is dependent upon threshold antecedent precipitation conditions. Moderate precipitation events (5 mm/day – 35 mm/day) over a 2–3 week period initiate groundwater responses with a 2–3 month lag, whilst intense precipitation events (100 mm/day) are expressed within 2–3 weeks.
Conservation implications: Understanding the lateral connectivity of terrestrial ecosystems to the ephemeral drainage network expressed via hydrological processes in these savanna landscapes is important to infer potential impacts of climate variability on the continued conservation of these ecosystems, both within and external to protected areas.
Local environmental gradients on a catenal scale create ecological patterns from the crest to the stream of the hillslope. Bottom-up drivers interact with top-down controls to give rise to these patterns. A multidisciplinary project was conducted to study the processes that govern functioning, structure and heterogeneity on a catena in a third-order catchment in the Southern Granite Supersite in the Kruger National Park. The project included abiotic components (e.g. groundwater-surface water interactions, soil chemical and physical properties) as well as biotic components (e.g. soil microbes, small aquatic organisms in ephemeral pools, plant communities, vegetation structure and mammal diversity). Each of these components was investigated in detail along the catenal gradient and reported on in separate articles in this special issue. The drought of 2015–2016 occurred during the sampling period of the study and information on the response of vegetation and mammals to the drought were included. In this article, a synthesis of findings from the separate components or disciplines is provided to highlight the interactive functioning and ecological patterns of the catena. These findings were then used to develop a framework for multidisciplinary studies in similar environments. The framework highlights the interactive relationships between various components of the ecosystem and the importance of a multidisciplinary approach.
Conservation implications: The findings of this study were used to develop a conceptual framework outlining how a range of biotic and abiotic patterns and processes interact along the catenal gradient. The framework highlights the importance of recognising these interactions in a multidisciplinary approach focused on one supersite.
Spatial heterogeneity is the unequal distribution of landscape features and consists of diversity in vegetation structure, number and size of woody plants, patchiness in grass cover, sub-canopy habitats, etc. A granite catena (hillslope) comprises of a gradient of soils, hydrology patterns and vegetation composition, creating a spatially heterogeneous area with variety in animal habitats. Objectives were to determine small-scale spatial heterogeneity along a catena near Skukuza, such as vegetation structure, patchiness, size and cover of woody and grass components, to describe certain catenal processes. Tree sizes and canopy cover were measured and the point method used on seven 100 m transects representing different catenal zones. Grasses were categorised according to grazing value, ecological status and percentage shade tolerant grasses. A total of 155 tree canopies were present. Large trees ( 5 m) occurred in riparian zone and upper midslope, but were low in number ( 4 per transect). Woody plants ranged in number from 8 to 32, canopy cover 4.5% – 33.6%, and grass cover from 47% to 69% between zones. A strong correlation was found between canopy cover and shade-tolerant grasses. Size of sub-canopy habitats are mostly determined by size of woody plants and both are important to animals. Various factors related to vegetation contributed to heterogeneity and spatial stratification patterns of the catena ecosystem.
Conservation implications: Concerns about the decline in tree numbers inside Kruger National Park are addressed. Mammal habitats and plant communities are impacted by the decline. The research can be linked to the long-term exclosure studies on granites at Nkuhlu.
The Kruger National Park (KNP) research supersites were designed to encourage place-based research in order to geographically focus research activities on known and well described study sites as opposed to ad hoc site selection practiced previously. This was done by (i) delineating sites using a clear rationale, (ii) providing basic meta-data for these sites, and (iii) actively encouraging scientists to conduct research on these sites and share data freely. The underlying concept was that geographically focused research would facilitate data and knowledge exchanges and lead to long-term, multi-scaled and cross-disciplinary studies at these data-rich sites, facilitating an integrated and collectively developed understanding that would be hard to achieve otherwise.
This essay acts as a short-term reflection on the KNP supersites and an introductory text for the special issue focusing on the outcomes from a multi-disciplinary study conducted on the southern granitic supersite. It starts off by briefly introducing the supersite concept, followed by a reflection on the achievements and challenges towards achieving the main objectives of the supersites. In addition, and as part of the “data-begets-data” philosophy underlying the supersites (i.e positive feedback of place-based data attracting further research and hence collection of further data), updated lists of references and available datasets are provided.
Conservation implications: This paper highlights the successes and challenges of geographically focusing research in the KNP to the research supersites in order to facilitate integrative and multi-scaled learning in savanna systems. It also provides updated lists of references and available datasets to further stimulate research at these sites.
