Papers by Brian van Wilgen
Biological Invasions, 2017
Many species in the family Pinaceae are invaders. These species are relatively easy to control be... more Many species in the family Pinaceae are invaders. These species are relatively easy to control because of some of their intrinsic characteristics and because they are highly visible and easy to eliminate. Many Pinaceae species have been well studied because of their use in forestry and their invasive behavior in many countries. The impacts of invasive Pinaceae are not only ecological, but also economic and social. We review the ecology and management of Pinaceae invasions and explore how restoration of invaded areas should be addressed. There are many ways to prevent invasions and to deal with them. Planting less invasive species, better site selection, and invasion monitoring are used successfully in different parts of the world to prevent invasion. Mechanical and chemical methods are used effectively to control Pinaceae invasions. Control is more effective at the early stages of invasion. Old invasions are more problematic as their elimination is more expensive, and the restoration of native vegetation is challenging. In some areas, native vegetation cannot thrive after Pinaceae have been removed, and weeds colonize cleared areas. More attention is needed to prevent the initiation and spread of invasions by focusing control Guest Editors: Andrew Liebhold, Eckehard Brockerhoff and Martin Nun ˜ez / Special issue on Biological Invasions in Forests prepared by a task force of the International Union of Forest Research Organizations (IUFRO).
Bothalia, 2017
South Africa has committed to producing a National Status Report on Biological Invasions by Octob... more South Africa has committed to producing a National Status Report on Biological Invasions by October 2017 and thereafter every three years. This will be the first status report at a national level specifically on biological invasions. As part of soliciting input, a workshop was held in May 2016 that led to this special issue of 19 papers in the journal Bothalia: African Biodiversity and Conservation. This editorial introduces the symposium, discusses the special issue and summarises how each contribution provides an estimate of ‘status’. Papers focus on key pathways, taxa, areas, and evaluations of interventions, specifically the movement of taxa between South Africa and neighbouring countries; the dispersal pathways of amphibians; a review of alien animals; a report on changes in the number and abundance of alien plants; in-depth reviews of the status of invasions for cacti, fishes, fungi and grasses; an assessment of the impact of widespread invasive plants on animals; reviews on i...
Ecology and Society, 2012
The Table National Park is a 265 km 2 protected area embedded within a city of 3.5 million people... more The Table National Park is a 265 km 2 protected area embedded within a city of 3.5 million people. The park contains an extremely diverse flora with many endemic species, and has been granted World Heritage Site status in recognition of this unique biodiversity. Invasive alien plants are arguably the most significant threat to the conservation of this biodiversity, and the past decade has seen the implementation of aggressive programs aimed at the removal of invasions by these plants. These invasive alien plants include several species of trees, notably pines (Pinus species) and eucalypts (Eucalyptus species), which historically have been grown in plantations, and which are utilized for recreation by the city's residents. In addition, many citizens regard the trees as attractive and ecologically beneficial, and for these reasons the alien plant control programs have been controversial. I briefly outline the legal obligations to deal with invasive alien plants, the history of control operations and the scientific rationale for their implementation, and the concerns that have been raised about the operations. Evidence in support of control includes the aggressive invasive nature of many species, and the fact that they displace native biodiversity (often irreversibly) and have negative impacts on hydrology, fire intensity, and soil stability. Those against control cite aesthetic concerns, the value of pine plantations for recreation, the (perceived) unattractive nature of the treeless natural vegetation, and the (incorrect) belief that trees bring additional rainfall. The debate has been conducted through the press, and examples of perceptions and official responses are given. Despite opposition, the policy promoting alien plant removal has remained in place, and considerable progress has been made towards clearing pine plantations and invasive populations. This conservation success story owes much to political support, arising largely from job creation, and a strong body of scientific evidence that could be cited in support of the program.
Fire Ecology, Jan 26, 2021
Background: Fire is an important process that shapes the structure and functioning of African sav... more Background: Fire is an important process that shapes the structure and functioning of African savanna ecosystems, and managers of savanna protected areas use fire to achieve ecosystem goals. Developing appropriate fire management policies should be based on an understanding of the determinants, features, and effects of prevailing fire regimes, but this information is rarely available. In this study, we report on the use of remote sensing to develop a spatially explicit dataset on past fire regimes in Majete Wildlife Reserve, Malawi, between 2001 and 2019. Moderate Resolution Imaging Spectroradiometer (MODIS) images were used to evaluate the recent fire regime for two distinct vegetation types in Majete Wildlife Reserve, namely savanna and miombo. Additionally, a comparison was made between MODIS and Visible Infrared Imager Radiometer Suite (VIIRS) images by separately evaluating selected aspects of the fire regime between 2012 and 2019. Results: Mean fire return intervals were four and six years for miombo and savanna vegetation, respectively, but the distribution of fire return intervals was skewed, with a large proportion of the area burning annually or biennially, and a smaller proportion experiencing much longer fire return intervals. Variation in inter-annual rainfall also resulted in longer fire return intervals during cycles of below-average rainfall. Fires were concentrated in the hot-dry season despite a management intent to restrict burning to the cool-dry season. Mean fire intensities were generally low, but many individual fires had intensities of 14 to 18 times higher than the mean, especially in the hot-dry season. The VIIRS sensors detected many fires that were overlooked by the MODIS sensors, as images were collected at a finer scale. Conclusions: Remote sensing has provided a useful basis for reconstructing the recent fire regime of Majete Wildlife Reserve, and has highlighted a current mismatch between intended fire management goals and actual trends. Managers should re-evaluate fire policies based on our findings, setting clearly defined targets for the different vegetation types and introducing flexibility to accommodate natural variation in rainfall cycles. Local evidence of the links between fires and ecological outcomes will require further research to improve fire planning.
Transactions of the Royal Society of South Africa, 2019
Eucalyptus camaldulensis can be seen as an iconic tree of superlatives. It is the eucalypt with t... more Eucalyptus camaldulensis can be seen as an iconic tree of superlatives. It is the eucalypt with the widest native range, and one of the most widely planted eucalypts around the globe. In South Africa, it is the most widespread and the most aggressively invasive eucalypt. It has many uses, but also causes major impacts. However, little is known about key aspects of its ecology in South Africa, including its invasion history, invasion processes and dynamics, and people's perceptions of its positive and negative effects on ecosystems. Such knowledge is crucial for developing robust and defendable guidelines for sustainable management of the species. This paper provides a comprehensive dossier of the species in South Africa. It reviews what is known of its introduction and planting history, its current distribution, its value for commercial forestry and other uses, its impacts as an invasive species, pests and pathogens associated with the species, people's perceptions of the species and conflicts of interest, and the options for management and restoration. The review reveals that E. camaldulensis is a tree of many contradictions in South Africa, making it a poster-child example of a conflict-generating non-native species. Based on available knowledge, we assess options for improved management. We highlight several knowledge gaps which need to be addressed in more detail through future research. It is hoped that this species profile will serve as a model for the types of information that are needed for developing objective management strategies for non-native tree species in different parts of the world. Keywords: Conflicts of interest; Eucalyptus; impacts; introduction history; invasive species management; pests and diseases; tree invasions BACKGROUND People and trees have an intimate and vital relationship (e.g. Hayman, 2003; Coder et al., 2017). It is therefore not surprising that many tree species were, and still are being, spread around the world by humans, literally following in the footprints of human civilisation (Richardson, 1998). Trees are used by people for multiple purposes (e.g. food, fuel, paper, timber, shelter, etc.) and contribute to diverse ecosystem services, including net primary production, pollination, soil formation, microclimate provisioning, nutrient cycling, and diverse cultural services (Foli et al., 2014; Castro-Diez et al., 2019). Trees provide ecosystem services worth more than $500 million per year to 10 of the world's megacities (Endreny et al., 2017. On the other hand, many alien tree species also have negative impacts by impacting on ecosystem services or creating new ecosystem disservices (Potgieter et al., 2017). The number of introduced tree species recorded as invasive aliens is increasing rapidly several decades after widespread introductions and plantings of hundreds of tree species in many parts of the world (Richardson, 1998; Richardson and Rejmánek, 2011; Richardson et al., 2014; Rouget et al., 2016). Trees are conspicuous and influential components of vegetation. Because of their large size and biomass, and diverse features of their architecture, many tree species have a major
South African Journal of Botany, 2017
Marloth of dispersal by the rock dassie (Procavia capensis). This rock dwelling generalist eats o... more Marloth of dispersal by the rock dassie (Procavia capensis). This rock dwelling generalist eats only the thin, fleshy pericarp of the fruit. Experiments with eaten and control Heeria argentea fruits show lack of germination in control fruits. We show the benefits of this directed dispersal is to ensure establishment and growth in rocky fire refugia. This is a remarkable example of directed dispersal to sites that are rare in these fire-swept landscapes. We suggest that an entire community of trees has converged in distribution and dispersal mechanism due to the selective pressure of fire.
Ecological Studies, 1998
The Cape Floristic Region (CFR) which covers about 90 000 km2 at the southwestern tip of Africa i... more The Cape Floristic Region (CFR) which covers about 90 000 km2 at the southwestern tip of Africa is especially well known for its exceptional species richness and high levels of endemism in vascular plant taxa. The region has been flagged as one of the world’s foremost “hotspots” of plant diversity and endemism (Myers 1990). Although levels of diversity in most other taxonomic groups are generally less impressive than for plants, the CFR also boasts high levels of endemism for some invertebrate groups, amphibia and fish (references in Macdonald and Richardson 1986; Rebelo 1992).
Koedoe, May 21, 2008
This paper provides an assessment of fire regimes in the Table Mountain National Park over the pa... more This paper provides an assessment of fire regimes in the Table Mountain National Park over the past four decades. We compiled a GIS database of all fires between 1970 and 2007 and analysed the fire regime in terms of the frequency, season and size of fires and the relationship between fire occurrence and fire weather. Most fires (90.5% of area burnt) occurred in summer and autumn, the ecologically acceptable season for fires. However, mean fire return intervals declined by 18.1 years, from 31.6 to 13.5 years, between the first and last decades of the record respectively. The area subjected to short (≤ six years) intervals between fires covered > 16% of the park in the last two decades of the record, compared to ~ 4% in the first two decades. A relatively small number of large fires dominated in terms of area burnt. Of the 373 fires recorded, 40 fires > 300 ha burnt 75% of the area, while 216 fires < 25 ha burnt 3.4% of the area. Fires occurred under a wide range of weather conditions, but large fires were restricted to periods of high fire danger. Prescribed burning was a relatively unimportant cause of fires, and most (> 85%) of the area burnt in wildfires. Areas subjected to short fire return intervals should be considered for management interventions. These could include the re-establishment of extirpated fire-sensitive species, the clearing of invasive alien plants and increased precautions for the prevention or rapid suppression of future accidental fires.
Journal of Environmental Management, Jul 1, 2012
Invasions by alien plants are a significant threat to the biodiversity and functioning of ecosyst... more Invasions by alien plants are a significant threat to the biodiversity and functioning of ecosystems and the services they provide. The South African Working for Water program was established to address this problem. It needs to formulate objective and transparent priorities for clearing in the face of multiple and sometimes conflicting demands. This study used the analytic hierarchy process (a multi-criteria decision support technique) to develop and rank criteria for prioritising alien plant control operations in the Western Cape, South Africa. Stakeholder workshops were held to identify a goal and criteria and to conduct pair-wise comparisons to weight the criteria with respect to invasive alien plant control. The combination of stakeholder input (to develop decision models) with data-driven model solutions enabled us to include many alternatives (water catchments), that would otherwise not have been feasible. The most important criteria included the capacity to maintain gains made through control operations, the potential to enhance water resources and conserve biodiversity, and threats from priority invasive alien plant species. We selected spatial datasets and used them to generate weights that could be used to objectively compare alternatives with respect to agreed criteria. The analysis showed that there are many high priority catchments which are not receiving any funding and low priority catchments which are receiving substantial allocations. Clearly, there is a need for realigning priorities, including directing sufficient funds to the highest priority catchments to provide effective control. This approach provided a tractable, consensus-based solution that can be used to direct clearing operations.
The combination of increasing water scarcity and rising temperatures will also regularly A Status... more The combination of increasing water scarcity and rising temperatures will also regularly A Status Quo, Vulnerability and Adaptation Assessment of the Physical and SocioEconomic Effects of Climate Change in the Western Cape 2005
Biological Invasions in South Africa, 2020
Considerable advances have been made since the first estimates of the impacts of invasive alien p... more Considerable advances have been made since the first estimates of the impacts of invasive alien plants on water resources in the early 1990s. A large body of evidence shows that invasive alien plants can increase transpiration and evaporation losses and thus reduce river flows and mean annual runoff. Riparian invasions, and those in areas where groundwater is accessible, have 1.2-2 times the impact of invasions in dryland areas. The magnitude of the impacts is directly related to differences between the invading species and the dominant native species in size, rooting depth and leaf phenology. Information on the impacts has been successfully used to compare the water use of invasive plants and different land cover classes, to quantify the water resource benefits of control measures, and to prioritise areas for control operations. Nationally, the impacts of invasive alien plants on surface water runoff are estimated at 1.44-2.44 billion m 3 per year. The most affected primary catchments (>5% reduction in mean annual runoff) are located in the Western and Eastern Cape, and KwaZulu-Natal. If no remedial action is taken, reductions in surface water runoff could increase to 2.59-3.15 billion m 3 per year, about 50%
The Journal of Applied Ecology, 1996
... Medium tree 5-10 Fast Bird Acacia longifolia (Andr.) Willd. Medium tree 5-10 Fast Bird Acacia... more ... Medium tree 5-10 Fast Bird Acacia longifolia (Andr.) Willd. Medium tree 5-10 Fast Bird Acacia mearnsii De Wild. Tall tree &amp;amp;gt; 10 Slow Bird Acacia melanoxylon R. Br. Tall tree &amp;amp;gt; 10 Slow Bird Leptospermum laevigatum F. Muell. Medium tree 5-10 Slow Wind ...
Transactions of the Royal Society of South Africa, 2018
With a few exceptions, comprehensive lists of alien plants that invade natural ecosystems are lac... more With a few exceptions, comprehensive lists of alien plants that invade natural ecosystems are lacking in sub-Saharan Africa. Some available lists are either preliminary or localised, or focus on agricultural weeds. This study set out to compile a list of alien plant species that are invading natural ecosystems and rangelands in five countries in eastern Africa, and to map the distribution of the species that threaten ecosystem integrity and productivity. The location of all alien plant species seen during surveys between 2008 and 2016 was recorded using a hand-held GPS device, as well as their status in terms of either being present and/or naturalised, or invasive and spreading. Individual occurrence records were summarised at the scale of half degree grid cells (∼55 km × 55 km). The survey covered almost half (522) of the 1063 grid cells in Ethiopia, Kenya, Tanzania, Uganda and Rwanda. We recorded 164 invasive alien species in 110 genera and 47 families. We provide further information on the distribution and impacts of 30 species considered to have the greatest impacts in terms of transforming natural ecosystems, as well as on a further 21 species with limited distributions that could potentially become ecosystem transformers. Invasive alien plants are clearly a widespread and growing problem in eastern Africa, and capacity to manage them effectively remains a problem. A great deal of work needs to be done to raise awareness of the problem, and to identify appropriate responses that will be effective in resource-poor countries.
International Journal of Wildland Fire, 2013
Daily weather data (since 1939) from four localities in the southeastern , coastal part of the Ca... more Daily weather data (since 1939) from four localities in the southeastern , coastal part of the Cape Floral Kingdom ('south-eastern-CFK') were used to calculate daily fire danger indices (FDIs). Cloud-to-ground lightning strike distributions (2006-10) were explored for geographical and temporal trends. Low or moderate fire danger conditions were the norm year round, and even large fires occurred under these conditions. Lightning occurred throughout the landscape at fairly low densities (mean ¼ 0.4 strikes km À2 year À1) and in all seasons, increasing somewhat during summer. Lightning presence increased with increasing rainfall, relative humidity, temperature and wind speed. Lightning seasonality in the southeastern -CFK did not differ from that in the southwestern -CFK. Our results provide evidence of a largely aseasonal fire regime in eastern coastal fynbos shrublands: FDIs peaked in winter (due to low rainfall and hot, dry katabatic winds) but were not associated with a winter fire regime; lightning and the co-occurrence of lightning and elevated FDIs were aseasonal and were correlated with the incidence of lightning-ignited fires throughout the year. The implication for management is that season of burn is largely unimportant. Mean annual FDI increased significantly over the study period, a trend which is likely to manifest in increased frequency and severity of fire, some of which has already been observed.
Koedoe, May 13, 2011
This paper reviews the experience gained in three South African national parks (Kruger, Table Mou... more This paper reviews the experience gained in three South African national parks (Kruger, Table Mountain and Bontebok) with regard to the adaptive management of fire for the conservation of biodiversity. In the Kruger National Park, adaptive approaches have evolved over the past 15 years, beginning initially as a form of 'informed trial and error', but progressing towards active adaptive management in which landscape-scale, experimental burning treatments are being applied in order to learn. In the process, significant advances in understanding regarding the role and management of fire have been made. Attempts have been made to transfer the approaches developed in Kruger National Park to the other two national parks. However, little progress has been made to date, both because of a failure to provide an agreed context for the introduction of adaptive approaches, and because (in the case of Bontebok National Park) too little time has passed to be able to make an assessment. Fire management interventions, ultimately, will manifest themselves in terms of biodiversity outcomes, but definite links between fire interventions and biodiversity outcomes have yet to be made. Conservation implications: Significant challenges face the managers of fire-prone and fire adapted ecosystems, where the attainment of ecosystem goals may require approaches (like encouraging high-intensity fires at hot and dry times of the year) that threaten societal goals related to safety. In addition, approaches to fire management have focused on encouraging particular fire patterns in the absence of a sound understanding of their ecological outcomes. Adaptive management offers a framework for addressing these issues, but will require higher levels of agreement, monitoring and assessment than have been the case to date.
Applied Vegetation Science, May 29, 2012
Additional contributing authors: Lee-Anne Botha, Oupa Chauke, Jennifer Fill, 8 Therese Forsyth Ll... more Additional contributing authors: Lee-Anne Botha, Oupa Chauke, Jennifer Fill, 8 Therese Forsyth Llewellyn Foxcroft, Charles Griffiths, Michelle Greve, Dai 9 Herbert, Pat Holmes, Philip Ivey, Stiaan Kotze, David Le Maitre, Rob Little, 10 Karabo Malakalaka, John Measey, Siyasanga Miza, Bernard Ndou, 11 Khathutshelo Nelukalo , David Richardson, Tammy Robinson, Ian Rushworth , 12 Ross Shackleton, Heather Terrapon Andrew Turner, Ruan Veldtman, Giovanni 13 Vimercati, Costas Zachariades 14
Fire Ecology, 2018
Background: In June 2017, wildfires burned 15 000 ha around the town of Knysna in the Western Cap... more Background: In June 2017, wildfires burned 15 000 ha around the town of Knysna in the Western Cape, destroying > 800 buildings, > 5000 ha of forest plantations, and claiming the lives of seven people. We examined the factors that contributed to making this one of the worst fires on record in the region. Results: One third of the area that burned was in natural vegetation (mainly fynbos shrublands), and more than half was in plantations of invasive alien (non-native) pine trees, or in natural vegetation invaded by alien trees. We used satellite imagery to assess burn severity in different land cover types by comparing pre-and post-fire images to estimate biomass consumed. We used daily weather data from two weather stations to calculate fire danger and drought indices over 70 years, and compared the fire weather conditions during the 2017 Knysna fires to the long-term weather record. The amount of biomass consumed was significantly higher in plantations of invasive alien trees, and in fynbos invaded by alien trees, than in uninvaded fynbos, providing support for the contention that invasion by alien trees increases the impact and difficulty of control of wildfires. Fire danger indices on the days of the fires were in the top 0.1 to 0.2% of days in the historic record, indicating that fire weather conditions were extreme but not unprecedented. The fires were preceded by a prolonged drought, and 18-month running means for two drought indices were the highest on record. Conclusion: The severity of the fires was exacerbated by very high fire danger conditions, preceded by an unprecedented drought, and further worsened by the conversion of natural fynbos vegetation to plantations, and invasion of vegetation by alien trees. Historical fire suppression also resulted in fuel buildups, further aggravating the problem of fire control, while residential development within and adjacent to fire-prone areas increased the risks faced by residents. Our results support calls to control invasive alien plants, reduce commercial planting of invasive alien trees, strictly regulate development in areas of high fire risk, and maintain awareness of the need for fire-wise practices.
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Papers by Brian van Wilgen