Effects of seed and seedling predation by small mammals on seedling recruitment of Protea neriifolia in Swartboskloof, Cape Province

Seed and seedling predation by small mammals, thought to be significant factors controlling the recruitment of Proteaceae in fynbos shrublands, were studied in a fynbos shrubland before and after a fire in March 1987. Seeds of Protea neriifolia R.Br. were planted inside and outside 14 mm mesh exclosures. The abundance of small mammals was recorded at two fynbos and five forest sites before the fire and at an additional forest and fynbos site after the fire. Seed predation reduced seedling recruitment from seeds planted in March 1986 in mature fynbos, but the reduction was significant only at the site with the highest abundance of small mammals. Seed predation did not significantly reduce seedling recruitment from seed planted in July, August and September 1986 in mature fynbos. The primary cause of seedling mortality before the fire was wilting, presumably owing to moisture stress. After the fire small mammal abundance decreased in burnt fynbos and increased in unburnt forest refuges until eight months after the fire when it increased again in the fynbos to a maximum of 41 animals per 100 trapnights two years after the fire. Seedling predation by small mammals had a limited impact after the fire probably because their numbers dropped soon after the fire. The effects of seed predation did not decrease with increasing distance from a forest refuge. Fungal pathogens and herbivory by insects were the primary causes of seedling mortality after the fire. Small mammal abundance in mature fynbos 25-30 years after a fire may have been too low to prevent the recruitment of a second cohort of P. neriifolia seedlings

Selective predation on Protea neriifolia (Proteaceae) seeds by small mammals

The ability of small mammals to select Protea neriifolia seeds containing embryos (full seeds) was examined. Full and empty seeds were glued to wooden boards and placed at three sites in young fynbos. Small mammals were able to select and remove significantly more full seeds than expected. Seed removal rates varied between the study sites but this was not related to the density of small mammals trapped at those sites. Selective feeding greatly increases the feeding efficiency of small mammals because 90% or more of the seed dispersed after fires may be empty

Propagating uncertainty from catchment experiments to estimates of streamflow reduction by invasive alien plants in southwestern South Africa

Abstract Long-term catchment experiments from South Africa have demonstrated that afforestation of grasslands and shrublands significantly reduces surface-water runoff. These results have guided the country’s forestry policy and the implementation of a national Invasive Alien Plant (IAP) control programme for the past few decades. Unfortunately, woody IAP densities continue to increase, compounding existing threats to water security from population growth and climatic change. Decision makers need defensible estimates of the impacts of afforestation or invasions on runoff to weigh up alternative land use options, or guide investment of limited resources into ecosystem restoration through IAP clearing versus engineering-based water-augmentation schemes. Existing attempts to extrapolate the impacts observed in catchment afforestation experiments to broad-scale IAP impacts give no indication of uncertainty. Globally, the uncertainty inherent in the results from paired-catchment experiments is seldom propagated into subsequent analyses making use of these data. We present a fully reproducible Bayesian model that propagates uncertainty from input data to final estimates of changes in streamflow when extrapolating from catchment experiments to broader landscapes. We apply our model to South Africa’s catchment experiment data, estimating streamflow losses to plantations and analogous plant invasions in the catchments of southwestern South Africa, including uncertainty. We estimate that regional streamflow is reduced by 304 million m3 or 4.14% annually as a result of IAPs, with an upper estimate of 408 million m3 (5.54%) and a lower estimate of 267 million m3 (3.63%). Our model quantifies uncertainty associated with all parameters and their contribution to overall uncertainty, helping guide future research needs. Acknowledging and quantifying inherent uncertainty enables more defensible decisions regarding water resource management. This article is protected by copyright. All rights reserved

Effects of land use change on streamflow and stream water quality of a coastal catchment

This study aimed to link land cover/use change to water quality in an important water supply coastal catchment. The approach followed a spatial and temporal analysis of historical catchment land use change to assess how changes influenced water quality and river flow in the Touws and Duiwe Rivers, southwestern Cape, South Africa. Each sub-catchment has unique characteristics which influence land use and water quality and the purpose was to analyse each one separately. Historical water quality and flow analysis were based on the records available (Duiwe River: 1998-2013; Touws River: 1980-2013) together with rainfall data. Records were analysed to detect trends over time, which were linked to changes in land use activities. Agriculture intensified rapidly in the Duiwe River catchment with most arable land cultivated by 1960 and water storage as farm dams escalating. Concentrations of nutrients and electrical conductivity were higher in the Duiwe River than in the more natural Touws River, and were positively correlated to river flows. Mean values for total nitrogen and electrical conductivity were 0.03 mg/L and 16.7 mg/L, respectively, in the Touws River and 0.25 mg/L and 127 mg/L, respectively, in the Duiwe River. Nutrient concentrations decreased in the Duiwe River after 2006 as fertilizer applications to pastures were reduced. The South African Target Water Quality Ranges were exceeded at times and in the Touws catchment this appears to have been due to extensive fires. For instance, sodium concentrations reached a maximum of 1 874.5 mg/L in 1996 compared to a usual average concentration of 20.8 mg/L where the guidelines are between 0 and100 mg/L. The link between land cover/use and water quality was demonstrated and when spatial heterogeneity of the catchments was altered by human or natural events, this was reflected in changes in the water quality.IS

Characterising the water use and hydraulic properties of riparian tree invasions: A case study of Populus canescens in South Africa

Invasive alien plants (IAPs) pose a serious threat to the already limited water resources in dry countries like South Africa which are facing increasing water shortages. Much of South Africa is expected to get drier in future due to climate change. In addition, the future climatic conditions are also predicted to accelerate the rate at which IAPs will spread, due to favourable growing conditions, further disrupting the provision of goods and services. Previous studies on tree water use in South Africa focused on commercial forests of introduced genera mainly Pinus, Eucalyptus, and Acacia. This study sought to expand these observations by quantifying water use and its drivers in riparian Grey Poplar (Populus canescens) invasions in the Berg River catchment of South Africa. Whole tree hydraulic resistance ranged from ~ 1.4 MPa·h·g-1 for large trees to ~14.3 MPa·h·g-1 for the small ones. These resistances are higher than those found for poplars in temperate climates, suggesting substantial hydraulic constraints to transpiration. Daily peak transpiration varied from 5 to 6 L·tree-1 in small trees (~9.2 cm DBH) to between 35 and 40 L·tree-1 for large trees (~24 cm DBH). Stand-level transpiration peaked at ~4 mm·d-1 in summer (Jan– Feb). However, the annual total transpiration was only 338 mm due to the deciduous nature of the species and also the high hydraulic resistance in the transpiration stream. Daily transpiration was strongly correlated to solar radiation (R2 > 0.81) while the air vapour pressure deficit (VPD) constrained transpiration at high VPD values. We conclude that the water use of the poplar invasions is significantly lower than that of other riparian invasions. The impact of these invasions on the water resources is therefore likely quite low, warranting less priority in alien plant clearing operations aimed at salvaging water

A biome-scale assessment of the impact of invasive alien plants on ecosystem services in South Africa

This paper reports an assessment of the current and potential impacts of invasive alien plants on selected ecosystem services in South Africa. We used data on the current and potential future distribution of 56 invasive alien plant species to estimate their impact on four services (surface water runoff, groundwater recharge, livestock production and biodiversity) in five terrestrial biomes. The estimated reductions in surface water runoff as a result of current invasions were >3000 million m3 (about 7% of the national total), most of which is from the fynbos (shrubland) and grassland biomes; the potential reductions would be more than eight times greater if invasive alien plants were to occupy the full extent of their potential range. Impacts on groundwater recharge would be less severe, potentially amounting to approximately 1.5% of the estimated maximum reductions in surface water runoff. Reductions in grazing capacity as a result of current levels of invasion amounted to just over 1% of the potential number of livestock that could be supported. However, future impacts could increase to 71%. A ‘biodiversity intactness index’ (the remaining proportion of premodern populations) ranged from 89% to 71% for the five biomes. With the exception of the fynbos biome, current invasions have almost no impact on biodiversity intactness. Under future levels of invasion, however, these intactness values decrease to around 30% for the savanna, fynbos and grassland biomes, but to even lower values (13% and 4%) for the two karoo biomes. Thus, while the current impacts of invasive alien plants are relatively low (with the exception of those on surface water runoff), the future impacts could be very high. While the errors in these estimates are likely to be substantial, the predicted impacts are sufficiently large to suggest that there is serious cause for concern.Centre of Excellence for Invasion Biolog

An assessment of the effectiveness of a long-term ecosystem restoration project in a fynbos shrubland catchment in South Africa

The long-term effectiveness of ecological restoration projects is seldom reported in the scientific literature. This paper reports on the outcomes of ecosystem restoration following the clearing of alien Pinus plantations and associated alien plant invasions over 13 years from an 8000 ha mountain catchment in the Western Cape Province, South Africa. We examined the goals, methods and costs of management, and the ecological outcomes in terms of reduced alien plant cover and native vegetation recovery. While the goals were not explicitly formulated at the outset, they were implicitly focussed on the conservation of water resources, the restoration of biodiversity, and the provision of employment. Initially, most (>90% of the area) was occupied by Pinus and Acacia invasions, mostly at low densities. The cost of control (initial clearing and up to 16 follow-up visits to remove emergent seedlings) amounted to almost ZAR 50 million (14 ZAR ~ 1US$). Although the cover of alien plants was greatly reduced, over 1000 ha still support dense or medium invasions (>25% cover), and the area occupied by scattered Pinus plants increased by over 3000 ha to >5700 ha. A reliance on passive restoration had not yet resulted in full recovery of the natural vegetation. The mean number of species, and total projected canopy cover on 50 m2 plots was lower in cleared than in comparable reference sites with pristine vegetation (21 vs 32 species/plot, and 94 vs 168% cover respectively). While the project is ongoing, we conclude that the entire area could revert to a more densely-invaded state in the event of a reduction of funding. Several changes to the management approach (including the integrated use of fire, a greater use of power tools, and active re-seeding of cleared areas with indigenous shrubs) would substantially increase the future effectiveness of the project and the sustainability of its outcomes

Determining the feasibility of harvesting invasive alien plant species for energy

Woody invasive alien plants (IAPs) are a threat to South Africa’s water resources, biodiversity and land productivity. The impacts of IAPs were the main reason for the South African government to embark on a natural resource management public works programme called Working for Water (WfW), which was aimed at controlling IAPs in a cost-effective yet labour-intensive way. At the same time, the high biomass of these species presents opportunities for synergies between the clearing of IAPs and the generation of biomassbased energy. The purpose of this study was to determine the cost of harvesting and extracting, chipping, and transporting the biomass, and also to determine the financial and economic feasibility of such an exercise from a commercial perspective. Sampling of the biomass was done at 31 representative sites within the Nelson Mandela Metropolitan Municipality, South Africa. The cost of the operation was carefully monitored, documented and reported at each stage, and compared to the cost of replacing the thermal coal currently used by industry within this municipality. The project proved to be financially viable, but only when the energy entrepreneur forms a partnership with the WfW programme, and then only under specific conditions. The project has, however, very high socio-economic returns with respect to a reduction in environmental externalities and job creation.Working for Water and the Industrial Development Corporationhttp://www.sajs.co.zahb201

Determining the feasibility of harvesting invasive alien plant species for energy

Woody invasive alien plants (IAPs) are a threat to South Africa’s water resources, biodiversity and land productivity. The impacts of IAPs were the main reason for the South African government to embark on a natural resource management public works programme called Working for Water (WfW), which was aimed at controlling IAPs in a cost-effective yet labour-intensive way. At the same time, the high biomass of these species presents opportunities for synergies between the clearing of IAPs and the generation of biomassbased energy. The purpose of this study was to determine the cost of harvesting and extracting, chipping, and transporting the biomass, and also to determine the financial and economic feasibility of such an exercise from a commercial perspective. Sampling of the biomass was done at 31 representative sites within the Nelson Mandela Metropolitan Municipality, South Africa. The cost of the operation was carefully monitored, documented and reported at each stage, and compared to the cost of replacing the thermal coal currently used by industry within this municipality. The project proved to be financially viable, but only when the energy entrepreneur forms a partnership with the WfW programme, and then only under specific conditions. The project has, however, very high socio-economic returns with respect to a reduction in environmental externalities and job creation.Working for Water and the Industrial Development Corporationhttp://www.sajs.co.zahb201

Interdisciplinary and multi-institutional higher learning : reflecting on a South African case study investigating complex and dynamic environmental challenges

Complex social-ecological problems need sustained interdisciplinary engagements across multiple disciplines, yet academic offerings continue to reflect disciplinary silos. To address this, a five-year program, within a developing country context, was conceived to follow an interdisciplinary research mode using a team of students and supervisors from various institutions across the disciplines of ecology, hydrology and economics. By using a flexible student training model, regional/ site specific knowledge was developed while simultaneously developing a shared vision and a model to combine information from each student project. Graduates felt enabled by the program that actively encouraged interdisciplinary interactions and engagements while simultaneously furthering disciplinary development. Cross disciplinary communication, was achieved through multiple engagement opportunities and common research outputs, all facilitated by an external boundary organization. While lengthy time frames are required for such collaborative interdisciplinary programs, researchers, higher learning institutions and funding agencies should not avoid this type of program and investment.The Water Research Commission of South Africahttp://www.journals.elsevier.com/current-opinion-in-environmental-sustainability2017-04-30hb2016Economic