Plenary: Land Transformation and Rehabilitation

Grassland degradation leads to the loss of ecosystem services valuable to humans, and causes negative impacts on landscapes and their functional abilities. The severity of degradation means more time and resources required to rehabilitate a landscape and therefore become a serious challenge. Various methods are used to assess ecosystem health and functioning and one such method is the Landscape Function Analysis (LFA). The LFA method is a field based technique which examines the functional status of rangelands. The LFA method is used to determine the impacts of transforming a grassland for crop production in a communal area, where subsistence farming is the dominating form of land use. The objective was to assess the recovery of old crop fields for the restoration of biodiversity in the catchment area. The study was conducted in Okhombe, located in the Bergville district, northern Drakensberg, where five previously cropped (PC) and five adjacent pristine grassland treatments were surveyed as reference sites. The PC treatments are degraded and have not been utilised for approximately 5 years, and are therefore under recovery with no human intervention. On the other hand, the pristine grassland found adjacent to the PC treatments have not had any severe disturbance however, have been used for grazing by livestock. Two 50m transects were laid out to measure landscape organization indices of patches and inter-patches (number, length, width) which characterize the landscape structure. For each plot, eleven soil surface indicators were assessed, recorded and, class ranks were given for each indicator. The classes represented an estimate of the observed patch/ inter-patch surface assessment for each indicator and each class was then grouped into their appropriate landscape index, namely: stability, infiltration and nutrient cycling. Soil samples were also collected to analyse for physical and chemical properties. Moreover, species richness and diversity was assessed using a Braun Blanquet sampling method. An independent samples t-test was used to test for difference between species richness, diversity, landscape organisation and soil surface assessment for each PC treatment. The results indicated that the pristine grassland were significantly more functional compared to degraded areas based on several indices (p< 0.024). However, diversity and richness did not vary as p>0.125. Species found on the PC area were mostly invading weed species such as Bidens pilosa, Conyza floribunda, Senecio madagascariensis and Tagetes minuta, to some extent Cymbopogon caesius and Panicum ecklonii with high clay content, low pH and moderate (50%) infiltration rates and low soil stability. The adjacent grasslands had more grass species, including Aristida junciformis, Diheteropogon amplectans, Eragrostis curvula, Cymbopoon caesius and the herb Chamaecrista grandulosa, with high soil stability, infiltration, 60% and pH. Severe grassland disturbances impacts greatly on vegetation structure and soil stability. Monitoring grassland areas that were previously transformed for agricultural purposes provides adequate information on measures to be taken in order to restore biodiversity.

Acacia mearnsii (black wattle) is an invasive alien plant that was introduced to South Africa in the middle to late 1800s, however since then it has expanded across the landscape particularly into the Eastern Cape grasslands. Black wattle is a high priority taxon for clearing by the Working for Water (WfW) programme as it is the top taxon responsible for reduction of the naturalised mean annual runoff of South Africa. This paper will present the results of an area prioritisation plan for WfW’s clearing of invasive aliens in the Tsitsa River catchment, where Ntabelanga and Laleni Dams are being planned in the Eastern Cape. The plan was developed through feedback obtained during a workshop attended by the Department of Environmental Affairs (DEA), WfW, the Gamtoos Irrigation Board (the implementing agent in the catchment) and other Rhodes University researchers working in the catchment. A Multi-Criteria Decision Analysis (MCDA), an analysis that aims to achieve multiple, conflicting objectives in decision-making, was conduced using spatial datasets (or criteria) entered into ArcMap to output clearing priorities for areas (pixel size 250 m x 250 m) in the Tsitsa catchment. Two of the criteria that were entered into the analysis included disturbed areas (or old cultivated lands) and riparian zones, both of which are particularly vulnerable to invasion; other criteria were soil erodibility and average density of invasive aliens. The criteria included and their weighting in the analysis are informed by the feedback obtained from the workshop participants and the output is therefore relevant for WfW’s work. This research has implications for delivery on Sustainable Development Goals (SDG) #6 (Clean Water and Sanitation) and #15 (Life on Land) because invasive alien plants threaten the ecosystem’s integrity and services provided.

The Matlabas wetland is a mire located in the headwaters of the Matlabas River, Marakele National Park, Limpopo Province. Various seepage zones and artesian peat domes are contained in this system that consists of two tributaries of which the western one is partially channeled. The mire’s two tributaries are located on fairly steep slopes of approximately 4.6% to 6.3% but are well vegetated. The vegetation is dominated by Miscanthus junceus and several sedge species, and can be correlated to different organic and mineral soils. The occurrence of decaying peat domes and desiccated areas of vegetation, as well as the apparent erosion on the western tributary, have raised concerns on the health of this wetland.The purpose of this presentation is to highlight results of our assessment on the hydrology and vegetation of the Matlabas Mire and the implications thereof on the management of this wetland. A network of piezometers was installed in the mire and results confirm that the system is mainly groundwater fed. Chemical analysis and temperature recorded in the transects indicates an isolated water source which does not mix with surface water. This is linked with isotope analysis of the age of peat in various sections of the mire. Results of the analyses found that the mire is primarily sustained by lateral seepage water that hydrates the peat. However, upward movement of deeper, chemically distinct, groundwater was recorded. Erosion was shown to be a natural process in the mire stabilised by the rough structure of the tussocks and rhizomes characteristic of the vegetation. However, since the construction of a road, erosion has become more pronounced. This road intercepts some seepage water from the surrounding slopes. This slightly changes the energy of the water to produce surface water flows with a higher energy than is the case in an undisturbed scenario. This study shows that desiccation of peat and its subsequent physical and chemical breakdown is related to the current erosion channels. The result is that erosion formation accelerates beyond what the mire is able to balance through sediment input and sustained seepage water input from the slopes. Rehabilitation should aim to firstly reinstate the hydrological drivers of the mire (sufficient subsurface lateral input of water to sustain the peat) and secondly to stabilise priority gullies and headcuts.

Restoration ecology is a growing discipline and its application is resulting in numerous commercial start-ups, however, diversity and seed reintroduction at restoration sites remains a constant barrier to successful restoration. Several commercial seed mixes and mechanical planting methods have been developed to overcome these barriers. Whether commercial mixes are sufficiently diverse is understudied while mechanically planting harvested seed often requires clean seed, causing some species to be removed from the mix. Fluid seed drilling techniques have been proposed to overcome these challenges. By suspending the seed in a cellulose based gel matrix which is injected into the soil with a mechanical planter, variably sized naturally harvested seed can be reintroduced to restoration sites. No formal evaluation of fluid seed drilling’s effectiveness and interactive ability with other planting techniques such as smoke water seed priming is known. This study therefore aimed to assess the grass recruitment, biomass production and diversity responses of commercial and harvested seed under different planting methods. Three seed types; Eragrostis tef, commercially obtained Biomosome® grassveld rehabilitation seed mix (BGR) and locally harvested veld seed mix (HVS) were planted under greenhouse conditions using four planting method treatments; seed only, seed and smoke water, fluid seed drilling, and a combination of smoke and fluid seed drilling. These data were analysed using generalised linear modelling and multivariate analysis of variance and ordination techniques. All recruitment proportions differed significantly. Eragrostis tef (0.53 ± 0.02) showed the greatest germination proportion followed by BGR (0.34 ± 0.02) and HVS (0.21 ± 0.02). Biomass production was greatest under HVS whilst BGR and E. tef resulted in similarly lower biomass production. Planting method did not affect seed recruitment proportion or biomass production. Shannon H diversity results for recruitment and biomass distributions were similarly high for BGR (1.10 ± 0.05 – recruitment, 0.76 ± 0.06 – biomass) and HVS (0.96 ± 0.05 – recruitment, 0.52 ± 0.06 – biomass). Eragrostis tef diversity was consistently lower (0.09 ± 0.05 – recruitment, 0.11 ± 0.6 – biomass). Multivariate analyses of BGR and HVS showed spatial separation of seed types and seed type x planting method for recruitment data and seed type for biomass data. BGR showed a higher recruitment similarity than HVS. Greater biomass distribution heterogeneity was detected under HVS than BGR. An overall dissimilarity of 74.79 % between BRG and HVS was calculated. Here Cynodon dactylon (34.15%), E. curvula (21.26%), E. tef (13.28%), Panicum maximum (11.46%), Plantago lanceolata (5.78%), Chloris gayana (3.10%), and Themeda triandra (3.09%) contributing importantly to this dissimilarity. This study showed that planting method effects on seed recruitment, biomass production, and diversity are minimal and so fluid seed drilling techniques should be explored further. Seed type can, however, greatly affect restored community plant density, biomass and diversity. Whilst BRG and HVS showed similar diversities, their species compositions differed. More homogeneous BGR communities suggested that these communities may be less adapted to ecological change compared to HVS communities. Careful restoration seed mix selection is advised.

The spread of toxic substances in opencast coal mines threaten the ecosystem and wellbeing of human beings which necessitates phytoremediation. Phytoremediation is a technique that involves the use of green plants to remove elemental contaminants from the soil into above ground through shoot biomass. This experiment was conducted to examine the salinity tolerance of different forage grasses grown on mine soil. Twenty seeds for each of Eragrostis curvula (L.) cv Ermelo, Lolium multiflorum (L.) cv Archie and AgriBoost, Cynodon dactylon (L.) cv Bermuda and Panicum maximum (L.) cv PUK8 were sown in pots containing mine soil and watered once daily using distilled water. At two leaf stage, seedlings were thinned out to 10 seedlings per pot followed an application of NaCl solutions of 0, 100, 200, 400, 600, 800, 1 000 mS.m-1 or treated mine water (557 mS.m-1). The experimental setup comprised of 3 pots × 5 varieties × 8 treatments × 4 sampling periods (weeks) over 2 runs. At each sampling period, 3 pots/variety/treatment were destructively sampled to determine biomass production. Salinity significantly affected the total biomass over four weeks. Entry × treatment interaction was significant (p< 0.001) on total biomass. In all NaCl solutions, biomass production increased linearly for all entries until week 2, beyond which it declined sharply up to week 4. Despite the decline, Archie, AgriBoost, Ermelo and PUK8 produced fairly high biomass at 400, 600 and 800 mS.m-1 at week 3. Entry × treatment interaction was significant (p< 0.001) on the rate of decline. Post week 2, biomass reduction for Archie, AgriBoost Ermelo and Bermuda declined with increasing salinity. PUK8 biomass reduction increased with increasing salinity. Biomass production for all varieties increased in a quadratic pattern when watered with treated mine water. Archie, AgriBoost, Ermelo and PUK8 showed a potential for phytoremediation of opencast coal mines irrigated with treated mine water.

Vetiver grass (Chrysopogon zizanioides (L.) Roberty) is a densely tufted perennial C4 grass from central India, used worldwide for soil and water conservation. It is a hardy, fast-growing, and densely rooted grass enabling it to withstand most environmental hazards (drought, frost, and floods). Worldwide use of vetiver is grounded in the claims that it does not compete with neighbouring grasses and it is not invasive. Recent studies have demonstrated that nitrogen deposition has dramatically risen after the industrial and agricultural revolution, and is expected to continue rising. Such increase is predicted to alter plant species coexistence, particularly in grasslands, through making limiting resources non-limiting, hence eliminating the competitive trade-off that allows species coexistence. The claims about vetiver competitive ability were investigated using a pot trial examining the competitive interactions between vetiver and four native grasses (Eragrostis curvula, Digitaria eriantha, Panicum maximum and Hyparrhenia hirta) under different soil nutrient levels. Vetiver tufts were growing with one native species per pot and the experiment was a full factorial design, laid out in a completely randomized arrangement with six replicates of each treatment combination, and 24 treatment combinations in total (i.e. N =144). Nutrient addition was achieved using 80% Hoagland’s solution (N=172, P=25, K=188mg/L), and the relative interaction index (RII) and the percentage change in yield (Ry) were used as indices to assess the effect of competition and nutrient status on native grasses. Vetiver exerted a weak competitive effect on all native grass tufts, except for D. eriantha, under low nutrient status. Vetiver exerted a facilitative effect on D. eriantha under low nutrient status. However, vetiver exerted a strong competitive effect on all native grass species under high nutrient status, except for P. maximum, which responded similar under low and high nutrients conditions. This suggests that, generally, vetiver competes directly with native grasses irrespective of soil nutrient status, but its competitive ability increases with increase in soil nutrient status. As expected, all native species benefited from nutrient addition, with D. eriantha gaining substantially greater aboveground biomass (271.9% ± 23.9) compared to E. curvula (181.9% ± 28.27), H. hirta (192.27% ± 24.25), and P. maximum (169.48% ± 10.92), which did not differ significantly from one another. Overall, narrow-leaved grasses (E. curvula and H. hirta) had a weak competitive ability compared to broad-leaved grasses (P. maximum and Digitaria eriantha). Therefore, morphological traits are important to consider in competition studies and could predict species that might coexist with vetiver. As soil nitrogen continues to increase globally, this will affect coexistence between native grasses and vetiver, with vetiver gaining an increased competitive advantage over native grasses. For this reason the claims that vetiver does not compete with neighbouring grasses need to be reconsidered and caution taken when using vetiver for soil and water conservation.