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Drought prone, arid and semi-arid ecosystems are challenging to restore once degraded due to low levels of natural recruitment and survival of reintroduced plants. This is evident in the restoration of degraded succulent thicket habitats in the Albany Subtropical Thicket Biome located in South Africa. The current restoration practice for this ecosystem focuses predominantly on reintroducing Portulacaria afra L. Jacq., which is naturally dominant in terms of cover and biomass, but largely absent in regions degraded by domestic livestock. This has been achieved by planting unrooted cuttings with limited consideration of soil water availability in a drought-prone ecosystem. This study tests the effects of the timing of water availability after planting on the root development of P. afra cuttings. Cuttings were harvested from seven individual plants and grown in a glasshouse setting. Eighty four cuttings were taken from each individual, twelve for each of the seven watering treatments per individual plant. The treatments represented a time-staggered initial watering after planting, including: on the day of planting, 4 days, 7 days, 14 days, 21 days, and 28 days after planting. After 32 days, all treatments were watered on a bi-weekly basis for two weeks; a control treatment with no watering throughout the experiment was included. The proportion of rooted cuttings per treatment and dry root mass were determined at the end of the experimental period (day 42). The early onset of watering was associated with a higher percentage of rooting (X2(5)D11.352, pD0:045) and had a weak, but non-significant, impact on the final dry root mass (F5,36 D 2.109, pD0:0631). Importantly, no clear rooting window within 28 days was detected as the majority of cuttings exhibited root development (greater than 50% of cuttings rooted for each individual parent-plant); this suggests that watering at the time of planting P. afra cuttings in-field for restoration may not be necessary. An unexpected, but important, result was that parent-plant identity had a strong interaction with the accumulation of root mass (F36,460 D 5.026, p < 0:001; LR7 D 122.99, p<0:001). The control treatment, which had no water throughout the experiment, had no root development. These findings suggest that water availability is required for the onset of rooting in P. afra cutting. However, the duration of the experiment was insufficient to detect the point at which P. afra cuttings could no longer initiate rooting once exposed to soil moisture, and thus no rooting window could be defined. Despite harvesting material from the same source population, parent-plant identity strongly impacted root development. Further work is required to characterise the rooting window, and to explore the effect of parent-plant condition on in-field and experimental restoration results; we urge that experiments using P. afra closely track the parent-source at the individual level as this may be a factor that may have a major impact on results. [ABSTRACT FROM AUTHOR]

Drought prone, arid and semi-arid ecosystems are challenging to restore once degraded due to low levels of natural recruitment and survival of reintroduced plants. This is evident in the restoration of degraded succulent thicket habitats in the Albany Subtropical Thicket Biome located in South Africa. The current restoration practice for this ecosystem focuses predominantly on reintroducing Portulacaria afra L. Jacq., which is naturally dominant in terms of cover and biomass, but largely absent in regions degraded by domestic livestock. This has been achieved by planting unrooted cuttings with limited consideration of soil water availability in a drought-prone ecosystem. This study tests the effects of the timing of water availability after planting on the root development of P. afra cuttings. Cuttings were harvested from seven individual plants and grown in a glasshouse setting. Eighty four cuttings were taken from each individual, twelve for each of the seven watering treatments per individual plant. The treatments represented a time-staggered initial watering after planting, including: on the day of planting, 4 days, 7 days, 14 days, 21 days, and 28 days after planting. After 32 days, all treatments were watered on a bi-weekly basis for two weeks; a control treatment with no watering throughout the experiment was included. The proportion of rooted cuttings per treatment and dry root mass were determined at the end of the experimental period (day 42). The early onset of watering was associated with a higher percentage of rooting (X2(5) = 11.352, p = 0.045) and had a weak, but non-significant, impact on the final dry root mass (F5,36 = 2.109, p = 0.0631). Importantly, no clear rooting window within 28 days was detected as the majority of cuttings exhibited root development (greater than 50% of cuttings rooted for each individual parent-plant); this suggests that watering at the time of planting P. afra cuttings in-field for restoration may not be necessary. An unexpected, but important, result was that parent-plant identity had a strong interaction with the accumulation of root mass (F36,460 = 5.026, p

Introduction. Over-grazing by livestock has resulted in the widespread degradation of South Africa's succulent thicket ecosystems. This is characterised by a significant reduction in the cover of the dominant succulent shrub, Portulacaria afra. Because this species is unable to regenerate naturally in degraded habitat, active reintroduction is required to restore ecosystem function. However, reintroduction success is relatively low, and the recruitment barriers for this species are poorly understood. Methods. By conducting pairwise plot surveys in actively restored and adjacent degraded succulent thicket habitats, the extent of P. afra seedling abundance in these contrasting ecosystem conditions is quantified. Results. Seedling abundance was significantly greater in restored ecosystems (W = 23,p = 0.03225). Additionally, seedlings found in restored habitats were strongly associated with open habitat, whereas seedlings in degraded ecosystems were more restricted to nurse sites (X² = 122.84, df = 2, p-value < 2.2e-16). A weak (R² = 0,237), but significant (p = 0,0295) correlation between P. afra cover and seedling abundance was recorded. Conclusion. Active restoration of succulent thicket habitat through P. afra reintroduction appears to overcome recruitment barriers. This may suggest that, despite the poor survival of introduced individuals, natural recruitment could contribute to the regeneration of restored succulent thicket ecosystems. [ABSTRACT FROM AUTHOR]

Introduction Over-grazing by livestock has resulted in the widespread degradation of South Africa’s succulent thicket ecosystems. This is characterised by a significant reduction in the cover of the dominant succulent shrub, Portulacaria afra. Because this species is unable to regenerate naturally in degraded habitat, active reintroduction is required to restore ecosystem function. However, reintroduction success is relatively low, and the recruitment barriers for this species are poorly understood. Methods By conducting pairwise plot surveys in actively restored and adjacent degraded succulent thicket habitats, the extent of P. afra seedling abundance in these contrasting ecosystem conditions is quantified. Results Seedling abundance was significantly greater in restored ecosystems (W = 23, p = 0.03225). Additionally, seedlings found in restored habitats were strongly associated with open habitat, whereas seedlings in degraded ecosystems were more restricted to nurse sites (X2 = 122.84, df = 2, p-value < 2.2e–16). A weak (R2 = 0,237), but significant (p = 0, 0295) correlation between P. afra cover and seedling abundance was recorded. Conclusion Active restoration of succulent thicket habitat through P. afra reintroduction appears to overcome recruitment barriers. This may suggest that, despite the poor survival of introduced individuals, natural recruitment could contribute to the regeneration of restored succulent thicket ecosystems.

Ecosystem restoration and reforestation often operate at large scales, whereas monitoring practices are usually limited to spatially restricted field measurements that are (i) time- and labour-intensive, and (ii) unable to accurately quantify restoration success over hundreds to thousands of hectares. Recent advances in remote sensing technologies paired with deep learning algorithms provide an unprecedented opportunity for monitoring changes in vegetation cover at spatial and temporal scales. Such data can feed directly into adaptive management practices and provide insights into restoration and regeneration dynamics. Here, we demonstrate that convolutional neural network (CNN) segmentation algorithms can accurately classify the canopy cover of Portulacaria afra Jacq. in imagery acquired using different models of unoccupied aerial vehicles (UAVs) and under variable light intensities. Portulacaria afra is the target species for the restoration of Albany Subtropical Thicket vegetation, endemic to South Africa, where canopy cover is challenging to measure due to the dense, tangled structure of this vegetation. The automated classification strategy presented here is widely transferable to restoration monitoring as its application does not require any knowledge of the CNN model or specialist training, and can be applied to imagery generated by a range of UAV models. This will reduce the sampling effort required to track restoration trajectories in space and time, contributing to more effective management of restoration sites, and promoting collaboration between scientists, practitioners and landowners. [ABSTRACT FROM AUTHOR]

Ecosystem restoration and reforestation often operate at large scales, whereas monitoring practices are usually limited to spatially restricted field measurements that are (i) time- and labour-intensive, and (ii) unable to accurately quantify restoration success over hundreds to thousands of hectares. Recent advances in remote sensing technologies paired with deep learning algorithms provide an unprecedented opportunity for monitoring changes in vegetation cover at spatial and temporal scales. Such data can feed directly into adaptive management practices and provide insights into restoration and regeneration dynamics. Here, we demonstrate that convolutional neural network (CNN) segmentation algorithms can accurately classify the canopy cover of Portulacaria afra Jacq. in imagery acquired using different models of unoccupied aerial vehicles (UAVs) and under variable light intensities. Portulacaria afra is the target species for the restoration of Albany Subtropical Thicket vegetation, endemic to South Africa, where canopy cover is challenging to measure due to the dense, tangled structure of this vegetation. The automated classification strategy presented here is widely transferable to restoration monitoring as its application does not require any knowledge of the CNN model or specialist training, and can be applied to imagery generated by a range of UAV models. This will reduce the sampling effort required to track restoration trajectories in space and time, contributing to more effective management of restoration sites, and promoting collaboration between scientists, practitioners and landowners.

Restoration of degraded subtropical succulent thicket, via the planting of Portulacaria afra (spekboom) truncheons, is the focus of a public works programme funded by the South African government. The goals of the programme, which started in 2004, are to create jobs, sequester carbon, restore biodiversity, reduce erosion, improve soil water holding capacity and catalyse private sector investment for upscaling of restoration. Here we report on a region-wide experiment to identify factors that can improve project success. Measures of success were survivorship and annual aboveground biomass carbon sequestration (ABCsr) of spekboom truncheons some 33–57 months after planting—starting in March 2008—into 173 fenced plots (0.25 ha) located throughout the global extent of spekboom thicket vegetation. We also collected data for 18 explanatory variables under the control of managers, and an additional 39 variables reflecting soil physical and chemical characteristics and rainfall patterns post restoration, all beyond the influence of managers. Since the latter covariates were available for only 83 plots, we analysed the two data sets separately. We used a prediction rule ensemble to determine the most important predictors of restoration success. There was great variation in percentage survivorship (median = 24, range = 0–100%) and ABCsr (median = 0.009, range = 0–0.38 t C ha−1 yr−1). The model using management variables explained less variance (53%) in survivorship than the model incorporating additional soil and rainfall covariates (62%). ABCsr models were better fits (78 and 88% variance explained, respectively). All model configurations identified browse intensity as a highly influential predictor of restoration success. Predicted success was highest for plots located in target habitat; however, only 45% were thus located, suggesting the need for expert input and habitat modelling for improving target habitat identification. Frost exposure was another important predictor influencing all models but was likely a consequence of locating sites off target habitat. Sites planted on equatorward slopes during the warm season showed reduced carbon sequestration, possibly due to elevated soil moisture stress associated with high radiation loads. Physiographic factors associated with improved restoration success were location on sloping ground (reduced frost exposure), increasing longitude (more warm-season rainfall) and increasing latitude (less frost coastwards). Few trends were evident among post-restoration climatic factors beyond the control of managers. Higher rainfall during the year post restoration had a negative impact on carbon sequestration while higher rain during the early months post restoration had a positive effect on both carbon sequestration and survivorship. Soil factors showed little importance for the survivorship model, whereas silt content, % K and Mg CEC emerged as predictors of carbon sequestration. Our results have direct relevance for improving the success of landscape-scale restoration projects envisioned for the ca. 8,930 km2 of degraded spekboom thicket.

Restoration of degraded subtropical succulent thicket, via the planting of Portulacaria afra (spekboom) truncheons, is the focus of a public works programme funded by the South African government. The goals of the programme, which started in 2004, are to create jobs, sequester carbon, restore biodiversity, reduce erosion, improve soil water holding capacity and catalyse private sector investment for upscaling of restoration. Here we report on a region-wide experiment to identify factors that can improve project success. Measures of success were survivorship and annual aboveground biomass carbon sequestration (ABCsr) of spekboom truncheons some 33–57 months after planting—starting in March 2008—into 173 fenced plots (0.25 ha) located throughout the global extent of spekboom thicket vegetation. We also collected data for 18 explanatory variables under the control of managers, and an additional 39 variables reflecting soil physical and chemical characteristics and rainfall patterns post restoration, all beyond the influence of managers. Since the latter covariates were available for only 83 plots, we analysed the two data sets separately. We used a prediction rule ensemble to determine the most important predictors of restoration success. There was great variation in percentage survivorship (median = 24, range = 0–100%) and ABCsr (median = 0.009, range = 0–0.38 t C ha−1 yr−1). The model using management variables explained less variance (53%) in survivorship than the model incorporating additional soil and rainfall covariates (62%). ABCsr models were better fits (78 and 88% variance explained, respectively). All model configurations identified browse intensity as a highly influential predictor of restoration success. Predicted success was highest for plots located in target habitat; however, only 45% were thus located, suggesting the need for expert input and habitat modelling for improving target habitat identification. Frost exposure was another important predictor influencing all models but was likely a consequence of locating sites off target habitat. Sites planted on equatorward slopes during the warm season showed reduced carbon sequestration, possibly due to elevated soil moisture stress associated with high radiation loads. Physiographic factors associated with improved restoration success were location on sloping ground (reduced frost exposure), increasing longitude (more warm-season rainfall) and increasing latitude (less frost coastwards). Few trends were evident among post-restoration climatic factors beyond the control of managers. Higher rainfall during the year post restoration had a negative impact on carbon sequestration while higher rain during the early months post restoration had a positive effect on both carbon sequestration and survivorship. Soil factors showed little importance for the survivorship model, whereas silt content, % K and Mg CEC emerged as predictors of carbon sequestration. Our results have direct relevance for improving the success of landscape-scale restoration projects envisioned for the ca. 8,930 km² of degraded spekboom thicket. [ABSTRACT FROM AUTHOR]

Restoration of subtropical thicket in South Africa using the plant Portulacaria afra (an ecosystem engineer) has been hampered, in part, by selecting sites that are frost prone—this species is intolerant of frost. Identifying parts of the landscape that are exposed to frost is often challenging. Our aim is to calibrate an existing cold-air pooling (CAP) model to predict where frost is likely to occur in the valleys along the sub-escarpment lowlands (of South Africa) where thicket is dominant. We calibrated this model using two valleys that have been monitored during frost events. To test the calibrated CAP model, model predictions of frost-occurrence for six additional valleys were assessed using a qualitative visual comparison of existing treelines in six valleys—we observe a strong visual match between the predicted frost and frost-free zones with the subtropical thicket (frost-intolerant) and Nama-Karoo shrubland (frost-tolerant) treelines. In addition, we tested the model output using previously established transplant experiments; ∼300 plots planted with P. afra (known as the Thicket-Wide Plots) were established across the landscape—without consideration of frost—to assess the potential factors influencing the survival and growth of P. afra. Here we use a filtered subset of these plots (n = 70), and find that net primary production of P. afra was significantly lower in plots that the model predicted to be within the frost zone. We suggest using this calibrated CAP model as part of the site selection process when restoring subtropical thicket in sites that lie within valleys—avoiding frost zones will greatly increase the likelihood of restoration success.

Restoration of subtropical thicket in South Africa using the plant Portulacaria afra (an ecosystem engineer) has been hampered, in part, by selecting sites that are frost prone—this species is intolerant of frost. Identifying parts of the landscape that are exposed to frost is often challenging. Our aim is to calibrate an existing cold-air pooling (CAP) model to predict where frost is likely to occur in the valleys along the sub-escarpment lowlands (of South Africa) where thicket is dominant. We calibrated this model using two valleys that have been monitored during frost events. To test the calibrated CAP model, model predictions of frost-occurrence for six additional valleys were assessed using a qualitative visual comparison of existing treelines in six valleys—we observe a strong visual match between the predicted frost and frost-free zones with the subtropical thicket (frost-intolerant) and Nama-Karoo shrubland (frost-tolerant) treelines. In addition, we tested the model output using previously established transplant experiments; ∼300 plots planted with P. afra (known as the Thicket-Wide Plots) were established across the landscape—without consideration of frost—to assess the potential factors influencing the survival and growth of P. afra. Here we use a filtered subset of these plots (n = 70), and find that net primary production of P. afra was significantly lower in plots that the model predicted to be within the frost zone. We suggest using this calibrated CAP model as part of the site selection process when restoring subtropical thicket in sites that lie within valleys—avoiding frost zones will greatly increase the likelihood of restoration success. [ABSTRACT FROM AUTHOR]

Orientation: There is growing interest in how international climate change mitigation and adaptation programmes play out at the local level. Research purpose: The aim of this study was to investigate the link between land restoration and carbon sequestration projects in the Eastern Cape, using Portulacaria afra (Spekboom), and market-based approaches to address global climate change. Motivation for the study: The Eastern Cape is one of the poorest areas of the country, and there is great emphasis on the establishment of economically and environmentally sustainable, as well as socially just, local economic development (LED) initiatives. However, LED projects are often not sustainable in the long run. Research design, approach and method: A mixed methods design, using data on international carbon markets, and key stakeholder interviews with those involved in LED land restoration programmes, was used. Qualitative results were analysed using Connelly’s (2007) framework for sustainable development, which included indicators for environmental protection, economic growth and social justice. Main findings: Stakeholders perceive the long-term financial sustainability of such projects as resting on their ability to earn carbon credits, despite the current very low international carbon prices. Practical/managerial implications: The long-term success of carbon-based restoration projects may depend on the establishment of a local carbon market or continued public funding. Upfront costs of land restoration projects are high and return only starts years later. Contribution/value-add: The establishment of a South African carbon market that helps carbon sequestration LED projects to meet the technical and administrative requirements needed to sell carbon credits will be an important determinant of their sustainability.

Intensive goat farming has transformed more than a million hectares of subtropical thicket in South Africa from a dense closed-canopy shrubland into an open savanna-like system. Restoration of the degraded thicket landscapes can be achieved by planting truncheons of spekboom ( Portulacaria afra ). The sale of carbon sequestered by spekboom can potentially fund restoration projects. Maximising the rate of spekboom growth at the outset of such projects will be critical for covering upfront costs. To investigate the potential effects of watering on restoration projects, we applied 16 different watering treatments to 320 spekboom truncheons in a nursery environment over eight months. The application of 4 L of water over eight watering events per month achieved the maximal mean increase in basal stem diameter for unrooted truncheons, namely 5.6 ± 1.8 mm. By comparison, application of 6 L of water over four watering events per month resulted in a maximal mean increase of 5.0 ± 3.7 mm for rooted truncheons. The estimated total cost of manually watering truncheons in the field ranged from ZAR560 to ZAR4840 per month for truncheons planted 2 m apart (i.e. 2500 truncheons per hectare), and was ZAR59 per month for truncheons planted in micro-basins 20 m apart (i.e. 25 micro-basins per hectare). The former costs would not be affordable for restoration projects financed through sale of sequestered carbon, but the latter costs would be. Dense planting of truncheons in shallow trenches and/or micro-basins – which would collect rainwater – is a promising new protocol for increasing the rate of carbon sequestration at the start of restoration projects. [ABSTRACT FROM AUTHOR]

An accepted criterion for measuring the success of ecosystem restoration is the return of biodiversity relative to intact reference ecosystems. The emerging global carbon economy has made landscape-scale restoration of severely degraded Portulacaria afra (spekboom)-dominated subtropical thicket, by planting multiple rows of spekboom truncheons, a viable land-use option. Although large amounts of carbon are sequestered when planting a monoculture of spekboom, it is unknown whether this is associated with the return of other thicket biodiversity components. We used available carbon stock data from degraded, restored, and intact stands at one site, and sampled carbon stocks at restored stands at another site in the same plant community. We also sampled plant community composition at both sites. The total carbon stock of the oldest (50 years) post-restoration stand (250.8 ± 14 t C ha−1) approximated that of intact stands (245 t C ha−1) and we observed a general increase in carbon content with restoration age (71.4 ± 24 t C ha−1 after 35 and 167.9 ± 20 t C ha−1 after 50 years). A multiple correspondence analysis separated degraded stands from stands under restoration based on ground cover, floristic composition, and total carbon stock. Older post-restoration and intact stands were clustered according to woody canopy recruit abundance. Our results suggest that spekboom is an ecosystem engineer that promotes spontaneous return of canopy species and other components of thicket biodiversity. The spekboom canopy creates a cooler micro-climate and a dense litter layer, both likely to favor the recruitment of other canopy species. [ABSTRACT FROM AUTHOR]

Is the maximum rate of carbon sequestration reported for the CAM-C3 plant Portulacaria afra (spekboom), viz. 15.4 t CO2 ha−1 yr−1, unusual in comparison with other plants with similar physioliogies, or could such rates be expected routinely in restoration with P. afra? Private sector investors in thicket restoration need an answer to this question in order to assess the feasibility of using carbon finance as the main income stream from their investments. A literature review showed that 15.4 t CO2 ha−1 yr−1 is not an unusual rate of carbon sequestration for CAM plants in arid and semi-arid environments, which suggests that investors in thicket restoration should not consider this an outlier value. The results also suggest that carbon finance could be used to fund restoration using other CAM plants in degraded xeric thickets in countries such as Argentina, Chile, Mexico, and Madagascar. [ABSTRACT FROM AUTHOR]