SUNScholar - Browsing by Author "Van Wilgen, Brian W."

Browsing by Author "Van Wilgen, Brian W."

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An analysis of the recent fire regimes in the Angolan catchment of the Okavango Delta, Central Africa
(SpringerOpen [Commercial Publisher], 2022-07) Van Wilgen, Brian W.; De Klerk, Helen M.; Stellmes, Marion; Archibald, Sally
Background: This paper presents an analysis of fire regimes in the poorly studied Angolan catchment of the Okavango Delta in Botswana. We used MODIS data to examine the frequency and seasonality of fires over 20 years (from 2000 to 2020) in three dominant vegetation types (miombo woodlands, open woodlands and grasslands, and short closed to open bushlands), and in areas where people were present, and where they were absent. Results: The median fire return intervals for both open woodlands and grasslands and short bushlands were relatively short (1.9 and 2.2 years respectively). In miombo woodlands, fires were less frequent (median return periods of 4.5 years). Human population density had no discernible effect on the fire return intervals, but about 14% of the miombo woodlands experienced no fires over 20 years. Ongoing shifting cultivation within miombo woodlands has led to structural changes and the introduction of fire into this vegetation type where fires were rare or absent in the past. About 12% of the miombo did not burn during the period examined where people were present, whereas close to 20% of the sites remained unburnt where people were absent. This suggests that people did not change the fire return interval in any of the vegetation types studied, but that they altered the amount of the landscape that is flammable in miombo vegetation. Fires occurred between June and September, with a peak in the late dry season (August and September). Conclusions: Historical research indicates that late dry-season fires are detrimental to miombo woodlands, and our analysis suggests that degradation in parts of the catchment has led to the introduction of fire to this previously firefree and fire-sensitive vegetation type. Deforestation of miombo woodlands, and the consequent introduction of fire, is a cause for concern with respect to the ecological stability of the Okavango Delta. Managers should therefore aim to protect the remaining closed-canopy miombo stands from further clearing and to attempt to shift the timing of burns to the early dry season to reduce their intensity.
An approach to the development of a national strategy for controlling invasive alien plant species : the case of Parthenium hysterophorus in South Africa
(AOSIS Publishing, 2016) Terblanche, Colette; Nanni, Ingrid; Kaplan, Haylee; Strathie, Lorraine W.; McConnachie, Andrew J.; Goodall, Jeremy; Van Wilgen, Brian W.
Invasive alien species require co-ordinated strategic management if negative impacts are to be effectively avoided. Here we describe a strategy for the management of Parthenium hysterophorus L. (Asteraceae) in South Africa. P. hysterophorus is an annual herb native to tropical America, which has become invasive in over 30 countries. The strategy sets goals for (1) the prevention of spread to new areas; (2) local eradication of isolated populations; (3) containment in areas where eradication is not possible; and (4) actions to protect assets where containment is no longer an option. We developed both a national strategy to set policy and to monitor progress towards goals at a national level and an implementation plan to set goals and timeframes for their achievement at local levels. It is not clear, at this stage, whether or not the goals of the strategy are achievable because implementation will face many challenges arising from ecological features of the target plant, social and cultural practices that will influence management, inadequate levels of funding and multiple political considerations. Our strategy proposes regular assessment using high-level indicators, a practice that is widely recognised as essential but seldom implemented at a national scale. Because the outcomes are uncertain, it is vital that regular monitoring of outcomes should be instituted from the start, so that both appropriate adjustments can be made to the strategy and lessons for the implementation of similar strategies elsewhere can be derived.
Assessing the effectiveness of invasive alien plant management in a large fynbos protected area
(AOSIS Publishing, 2017) Kraaij, Tineke; Baard, Johan A.; Rikhotso, Diba R.; Cole, Nicholas S.; Van Wilgen, Brian W.
Background: Concern has been expressed about the effectiveness of invasive alien plant (IAP) control operations carried out by Working for Water (WfW). South African legislation now also requires reporting on the effectiveness of IAP management interventions. Objectives: We assessed the effectiveness of IAP management practices in a large fynbos protected area, the Garden Route National Park, South Africa. Methods: We undertook field surveys of pre-clearing IAP composition and the quality of treatments applied by WfW during 2012–2015 in 103 management units, covering 4280 ha. We furthermore assessed WfW data for evidence of change in IAP cover after successive treatments, and adherence to industry norms. Results: Despite the development of detailed management plans, implementation was poorly aligned with plans. The quality of many treatments was inadequate, with work done to standard in only 23% of the assessed area. Problems encountered included (1) a complete absence of treatment application despite the payment of contractors (33% of assessed area); (2) treatments not being comprehensive in that select areas (38%), IAP species (11%) or age classes (8%) were untreated; (3) wrong choice of treatment method (9%); and (4) treatments not applied to standard (7%). Accordingly, successive follow-up treatments largely did not reduce the cover of IAPs. Inaccurate (or lack of) infield estimation of IAP cover prior to contract generation resulted in erroneous estimation of effort required and expenditure disparate with WfW norms. Conclusions: We advocate rigorous, compulsory, infield assessment of IAP cover prior to contract allocation and assessment of the quality of treatments applied prior to contractors’ payment. This should improve the efficiency of control operations and enable tracking of both the state of invasions and effectiveness of management.
Assessing the status of biological control as a management tool for suppression of invasive alien plants in South Africa
(AOSIS Publishing, 2017) Zachariades, Costas; Paterson, Iain D.; Strathie, Lorraine W.; Hill, Martin P.; Van Wilgen, Brian W.
Background: Biological control of invasive alien plants (IAPs) using introduced natural enemies contributes significantly to sustained, cost-effective management of natural resources in South Africa. The status of, and prospects for, biological control is therefore integral to National Status Reports (NSRs) on Biological Invasions, the first of which is due in 2017. Objectives: Our aim was to evaluate the status of, and prospects for, biological control of IAPs in South Africa. We discuss expansion of biological control and suggest indicators to be used in the upcoming NSR to assess sufficient growth. Method: We used published literature, unpublished work and personal communication to assess the status of biological control of IAPs. We propose indicators based on the targets for biological control that were proposed in the 2014 ‘National Strategy for dealing with biological invasions in South Africa’. To prioritise targets for future efforts, we used published lists of damaging IAPs and assessed the prospects for their biological control. Recommendations for using biological control as a management tool were made after discussion among the authors and with colleagues. Results: Significant control of several Cactaceae, Australian Acacia species and floating aquatic plants, and many other IAPs has been achieved in South Africa since 1913. Recently, biological control has benefited from improved international collaboration, a streamlined application process for the release of new biological control agents (resulting in the approval of 19 agents against 13 IAP species since 2013), and increased funding and capacity. There is still a need to improve implementation and to better integrate biological control with other control methods. In order to maximise benefits from biological control, increased investment is required, particularly in implementation and post-release evaluation, and in targeting new IAPs. Proposed targets for growth between 2017 and 2020 include an increase in financial investment in research by 29%, implementation by 28% and mass-rearing by 68%. Research capacity should increase by 29%, implementation capacity by 63% and mass-rearing capacity by 61%. New research projects should be initiated on 12 new IAP targets, while post-release monitoring efforts should be expanded to another 31 IAPs. Conclusion: Biological control of IAPs has contributed substantially to their management in South Africa, and continues to do so. Further investment in targeted aspects of IAP biological control will increase this contribution.
An assessment of climate, weather, and fuel factors influencing a large, destructive wildfire in the Knysna region, South Africa
(SpringerOpen, 2018-08-30) Kraaij, Tineke; Baard, Johan A.; Arndt, Jacob; Vhengani, Lufuno; Van Wilgen, Brian W.
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 practic.
An assessment of the distribution and potential ecological impacts of invasive alien plant species in eastern Africa
(Taylor & Francis, 2018) Witt, Arne; Beale, Tim; Van Wilgen, Brian W.
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.
An assessment of the evolution, costs and effectiveness of alien plant control operations in Kruger National Park, South Africa
(Pensoft Publishers, 2017-06-02) Van Wilgen, Brian W.; Fill, Jennifer M.; Govender, Navashni; Foxcroft, Llewellyn C.; Daehler, C.
Alien plants were first recorded in 1937 in the 2 million ha Kruger National Park (KNP, a savanna protected area in South Africa), and attempts to control them began in the mid-1950s. The invasive alien plant control program expanded substantially in the late 1990s, but its overall efficacy has not been determined. We present an assessment of invasive alien plant control operations over several decades in KNP. We based our assessment on available information from a range of control programs funded from various sources, including national public works programs, KNP operational funds, and foreign donor funds. Over ZAR 350 million (~ US$ 27 million) has been spent on control interventions between 1997 and 2016. We found evidence of good progress with the control of several species, notably Opuntia stricta, Sesbania punicea, Lantana camara and several aquatic weeds, often because of effective biological control. On the other hand, we found that over one third (40%) of the funding was spent on species that have subsequently been recognised as being of lower priority, most of which were alien annual weeds. The allocation of funds to non-priority species was sometimes driven by the need to meet additional objectives (such as employment creation), or by perceptions about relative impact in the absence of documented evidence. We also found that management goals were limited to inputs (funds disbursed, employment created, and area treated) rather than to ecological outcomes, and progress was consequently not adequately monitored. At a species level, four out of 36 species were considered to be under complete control, and a further five were under substantial control. Attempts to control five annual species were all considered to be ineffective.
An assessment of the implementation and outcomes of recent changes to fire management in the Kruger National Park
(Open Journals Publishing, 2008) Van Wilgen, Brian W.; Govender, Navashni; MacFadyen, Sandra
ENGLISH ABSTRACT: This paper reviews recent changes in fire management in the Kruger National Park, and assesses the resulting fire patterns against thresholds of potential concern. In 2002, a lightning-driven approach was replaced by an approach that combined point ignitions with unplanned and lightning fires. The approach aimed to burn an annual target area, determined by rainfall and fuel conditions, in point-ignition fires of different sizes. Most of the original fire-related thresholds of potential concern (TPCs) were incorporated into the new approach. The annual target area to be burnt ranged from 12 to 24% of the park between 2002 and 2006. The total area burnt generally exceeded the targets each year, and management fires accounted for less than half of the total area burnt. The fire regime was dominated by very large fires (> 5 000 ha) which accounted for 77% of the total area burnt. New TPCs were developed to assess whether the fire regime encompassed a sufficient degree of variability, in terms of fire intensity and the spatial distribution of burnt areas. After assessment and adjustment, it appears that these TPCs have not yet been exceeded. The point-ignition approach, and its evaluation in terms of variability and heterogeneity, is based on the untested assumption that a diverse fire regime will promote biodiversity. This assumption needs to be critically assessed. We recommend that the practice of point ignitions be continued, but that greater efforts be made to burn larger areas earlier in the season to reduce large and intense dry-season fires.
Biodiversity assessments : origin matters
(Public Library of Science, 2018-11-13) Pauchard, Anibal; Meyerson, Laura A.; Bacher, Sven; Blackburn, Tim M.; Brundu, Giuseppe; Cadotte, Marc W.; Courchamp, Franck; Essl, Franz; Genovesi, Piero; Haider, Sylvia; Holmes, Nick D.; Hulme, Philip E.; Jeschke, Jonathan M.; Lockwood, Julie L.; Novoa, Ana; Nunez, Martin A.; Peltzer, Duane A.; Pysek, Petr; Richardson, David M.; Simberloff, Daniel; Smith, Kevin; Van Wilgen, Brian W.; Vila, Montserrat; Wilson, John R. U.; Winter, Marten; Zenni, Rafael D.
Recent global efforts in biodiversity accounting, such as those undertaken through the Convention on Biological Diversity (CBD) and Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), are vital if we are to track conservation progress, ensure that we can address the challenges of global change, and develop powerful and scientifically sound indicators. Schlaepfer [1] proposes that we should work toward inventories of biodiversity that account for native and non-native species regardless of species origin and ecological context. We strongly disagree with the approach of combining counts of native and non-native species because this will reduce our capacity to detect the effects of non-native species on native biodiversity with potentially devastating consequences. Compelling and abundant evidence demonstrates that some non-native species can become invasive and produce major ecosystem disruptions and even native species extinction. Unfortunately, we still cannot be certain which non-native species will be the most detrimental (e.g., [2]). Combining native and non-native species together into a single biodiversity index would not only inflate biodiversity estimates and risk promoting the spread of invasive non-native species but would also ignore the fundamental ecological differences between the two groups.
Challenges in invasive alien plant control in South Africa
(Academy of Science of South Africa, 2012) Van Wilgen, Brian W.; Cowling, Richard M.; Marais, Christo; Esler, Karen J.; McConnachie, Matthew; Sharp, Debbie
Working for Water owes much to the community of fynbos ecologists who were instrumental in putting forward an argument to government for its initiation in 1996.2 The 33rd Annual Fynbos Forum (attended by over 250 delegates at Cape St. Francis on 17–19 July 2012) included a plenary workshop on the effectiveness of Working for Water, and discussions on ways for the scientific community to assist in the identification and implementation of improvements. This brief report outlines the issues discussed, including the problems faced by Working for Water, and possible ways for the scientific community to assist in addressing them.
Confronting the wicked problem of managing biological invasions
(Pensoft, 2016) Woodford, Darragh J.; Richardson, David M.; MacIsaac, Hugh J.; Mandrak, Nicholas E.; Van Wilgen, Brian W.; Wilson, John R. U.; Weyl, Olaf L. F.
The Anthropocene Epoch is characterized by novel and increasingly complex dependencies between the environment and human civilization, with many challenges of biodiversity management emerging as wicked problems. Problems arising from the management of biological invasions can be either tame (with simple or obvious solutions) or wicked, where difficulty in appropriately defining the problem can make complete solutions impossible to find. We review four case studies that reflect the main goals in the management of biological invasions – prevention, eradication, and impact reduction – assessing the drivers and extent of wickedness in each. We find that a disconnect between the perception and reality of how wicked a problem is can profoundly influence the likelihood of successful management. For example, managing species introductions can be wicked, but shifting from species-focused to vector-focused risk management can greatly reduce the complexity, making it a tame problem. The scope and scale of the overall management goal will also dictate the wickedness of the problem and the achievability of management solutions (cf. eradication and ecosystem restoration). Finally, managing species that have both positive and negative impacts requires engagement with all stakeholders and scenario-based planning. Effective management of invasions requires either recognizing unavoidable wickedness, or circumventing it by seeking alternative management perspectives.
Contributions to the National Status Report on biological invasions in South Africa
(AOSIS Publishing, 2017) Wilson, John R. U.; Gaertner, Mirijam; Richardson, David M.; Van Wilgen, Brian W.
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 invasions in municipalities, protected areas and subAntarctic Islands; assessments of the efficacy of biological control and other control programmes; and recommendations for how to deal with conflict species, to conduct scientific assessments and to improve risk assessments. The papers in this special issue confirm that South Africa is an excellent place to study invasions that can provide insights for understanding and managing invasions in other countries. Negative impacts seem to be largely precipitated by certain taxa (especially plants), whereas invasions by a number of other groups do not, yet, seem to have caused the widespread negative impacts felt in other countries. Although South Africa has effectively managed a few biological invasions (e.g. highly successful biological control of some invasive plants), the key challenge seems to be to establish and maintain a strong link between implementation, monitoring, reporting and planning.
Coordinated approaches to rehabilitating a river ecosystem invaded by alien plants and fish
(Academy of Science of South Africa, 2013-11-27) Impson, N. Dean; Van Wilgen, Brian W.; Weyl, Olaf L. F.
Large sums have been spent on controlling invasive alien species in South Africa over the past two decades, but documented accounts of successes are almost non-existent. This brief account describes progress with a coordinated pioneering project to simultaneously clear invasive alien trees and predatory alien fish from a degraded but ecologically important river ecosystem in the Cederberg region of the Western Cape Province, South Africa. Dense infestations of invasive Australian Acacia and Eucalyptus species were cleared over 2 years (2010–2012) from the riparian zone of the lower reaches of the Rondegat River. This clearance was followed by the local eradication of an alien fish, smallmouth bass Micropterus dolomieu, from the lower reaches of the river in February 2012 and March 2013 using the piscicide rotenone, so that native threatened fish species could re-colonise from the upper reaches of the river. Overall costs of the clearance and eradication amounted to nearly R4.5 million, and early indications are that the native riparian vegetation and fish are recovering well. The project illustrates several aspects of good practice: careful planning; close and enthusiastic collaboration between affected state and private landowners; public participation to address concerns; the simultaneous and coordinated application of mechanical, chemical and biological control of alien plants and chemical control of alien fish; and direction by qualified ecologists. Although it is too early to assess the long-term success, the exercise provides useful lessons for such projects elsewhere, and paves the way for the more widespread use of similar approaches in selected areas that are a priority for conservation.
Distribution and socio-ecological impacts of the invasive alien cactus Opuntia stricta in eastern Africa
(Springer, 2017) Shackleton, Ross T.; Witt, Arne B. R.; Piroris, Francis M.; Van Wilgen, Brian W.
Many cactus species have been introduced around the world and have subsequently become major invaders, inducing social and ecological costs. We recorded the distribution of Opuntia stricta in eastern Africa, and conducted 200 household interviews using semi-structured questionnaires to assess local perceptions of O. stricta in Laikipia County, Kenya. Opuntia stricta was widespread and abundant in parts of Kenya, Tanzania and Ethiopia and present at low densities in Uganda. In Laikipia County, pastoralists identified that O. stricta had been present for more than 10 years, and were of the opinion that it was still spreading and increasing in density. Two-thirds of respondents estimated that 50–75% of valuable grazing land had been invaded, and all felt that it contributed to the ill-health and death of livestock. Other negative impacts included reductions in native plant populations, rangeland condition, human health, and mobility of humans and animals. These negative impacts resulted in economic losses of US$ 500–1000 per household per year for 48% of households. Only 20% of respondents reported actively managing O. stricta, yet all respondents believed a reduction in the abundance of this weed would improve well-being. Management interventions are needed to reduce negative impacts.
Distribution of invasive alien Tithonia (Asteraceae) species in eastern and southern Africa and the socioecological impacts of T. diversifolia in Zambia
(South African National Biodiversity Institute (SANBI), 2019-09-25) Witt, Arne B.R.; Shackleton, Ross T.; Beale, Tim; Nunda, Winnie; Van Wilgen, Brian W.
Background: Many alien plant species, such as Tithonia diversifolia, T. rotundifolia and T. tubaeformis, have been introduced to areas outside of their natural distribution range to provide benefits, but have subsequently become invasive, threatening biodiversity and agricultural productivity. Objectives: The aim of this study was to determine the current distribution and dates of introduction of invasive Tithonia species in eastern and southern Africa and to document the effects of T. diversifolia on rural livelihoods in Zambia. Method: Roadside surveys, and other sources of information, were used to determine the distribution of invasive Tithonia species in eastern and southern Africa. Household interviews were conducted to gauge perceptions and understand the impacts of T. diversifolia on local livelihoods in Zambia’s Copperbelt province. Results: Tithonia diversifolia is widespread in Uganda, Kenya, Tanzania, South Africa, Malawi and parts of Zambia but less so in Zimbabwe. Tithonia rotundifolia was comparatively uncommon in eastern Africa but common in some southern African countries, while T. tubaeformis was invasive in Swaziland, South Africa, Zambia and possibly also Zimbabwe. According to the majority of respondents in Zambia, T. diversifolia has negative impacts on native vegetation, mobility or access, water availability, crop yields and animal health. Conclusion: Invasive Tithonia species are widespread and spreading throughout much of Africa. Livelihood and biodiversity costs have not been considered by those actively promoting the use and further dissemination of T. diversifolia. We therefore recommend that detailed cost–benefit studies should be undertaken to support informed decisions on the future management of these species.
Fire ecology -- Cape fynbos biome
(Fire management -- Cape Fynbos biome, 2013) Van Wilgen, Brian W.
The management of fire-dependent biodiversity hotspots must be based on sound ecological knowledge and a pragmatic approach that accommodates the constraints within which fire managers must operate. South Africa’s fynbos biome (shrubland or heathland vegetation found in the Western Cape of South Africa) is one such hotspot. In this region, the implementation of prescribed burning to conserve biodiversity must take into account the area’s rugged and inaccessible terrain and recurrent wildfires, the presence of fire-adapted invasive alien plants, and the imperatives for ensuring human safety. These constraints limit the potential for prescribed burning to be effective everywhere, and prioritization and trade-offs will be needed to ensure the efficient use of limited funding and management capacity. In such environments, management must be adaptive, based on clearly defined and shared goals, monitoring, and assessment, and should be flexible enough to adjust as new lessons are learned.
Fire management in Mediterranean-climate shrublands : a case study from the Cape fynbos, South Africa
(Wiley Online, 2010) Van Wilgen, Brian W.; Forsyth, Gregory G.; De Klerk, Helen; Das, Sonali; Khuluse, Sibusisiwe; Schmitz, Peter
Summary: 1. Fire is an important process in Mediterranean-ecosystem shrublands, and prescribed burning is often used to manage these ecosystems. Analyses of past fire regimes are required to interpret biotic responses to fire, as well as to assess the degree to which management interventions have been able to influence the fire regime. 2. We used a spatial data base of fires within 10 protected areas covering >720 000 ha to examine the frequency, seasonality, size and cause of fires over four decades. Our study covered five fire climate zones and a range of mountain fynbos shrubland types. We examined whether regular prescribed burning would be necessary to rejuvenate the vegetation, and also to reduce the incidence and extent of wildfires. 3. Cumulative fire frequency distributions indicated that the probability of fire was not strongly affected by post-fire age, with 50% of the area experiencing a successive fire within 10–13 years after the previous fire in most areas. This suggests that the accumulation of fuel did not limit the occurrence of wildfires, and that regular prescribed burning would not necessarily reduce the risk of wildfires. 4. Inland zones experienced more severe fire weather than coastal zones (∼35% vs. 11–19% of days with high to very high fire danger, respectively). Despite these differences, fire return periods were similar (10–13 years), suggesting that the availability of ignitions, and not fuel or weather, limited the occurrence of wildfires. 5. Despite a policy that promoted prescribed burning, a relatively small area (between 4·6% and 32·4% of the area of all fires) burned in prescribed burns. Seasonal restrictions for safety and ecological reasons, the imperative to integrate planned fires with invasive alien plant treatments and unplanned wildfires have all contributed to the relatively small area that burnt in prescribed burns. 6. Synthesis and applications. Recurrent wildfires, and not prescribed burning, are providing sufficient opportunities for fire-stimulated regeneration in fynbos ecosystems. Because of this, and because burning to reduce fuel loads is unlikely to prevent wildfires, there should be less pressure to conduct prescribed burning. The predicted growth in human populations in all areas is expected to increase the number of ignition opportunities and the frequency of fires, with detrimental consequences for biodiversity conservation and the control of invasive alien trees. Fire frequency should thus be monitored and steps should be taken to protect areas that burn too frequently.
Fire regimes in eastern coastal fynbos : imperatives and thresholds in managing for diversity
(AOSIS Publishing, 2013) Kraaij, Tineke; Cowling, Richard M.; Van Wilgen, Brian W.
Until recently, fire ecology was poorly understood in the eastern coastal region of the Cape Floral Kingdom (CFK), South Africa. Rainfall in the area is aseasonal and temperatures are milder than in the winter-rainfall and drier inland parts of the CFK, with implications for the management of fire regimes. We synthesised the findings of a research programme focused on informing ecologically sound management of fire in eastern coastal fynbos shrublands and explored potential east–west trends at the scales of study area and CFK in terms of fire return interval (FRI) and fire season. FRIs (8–26 years; 1980–2010) were comparable to those elsewhere in the CFK and appeared to be shorter in the eastern Tsitsikamma than in the western Outeniqua halves of the study area. Proteaceae juvenile periods (4–9 years) and post-fire recruitment success suggested that for biodiversity conservation purposes, FRIs should be ≥ 9 years in eastern coastal fynbos. Collectively, findings on the seasonality of actual fires and the seasonality of fire danger weather, lightning and post-fire proteoid recruitment suggested that fires in eastern coastal fynbos are not limited to any particular season. We articulated these findings into ecological thresholds pertaining to the different elements of the fire regime in eastern coastal fynbos, to guide adaptive management of fire in the Garden Route National Park and elsewhere in the region. Conservation implications: Wildfires are likely to remain dominant in eastern coastal fynbos, whilst large-scale implementation of prescribed burning is unattainable. Fires occurring in any season are not a reason for concern, although other constraints remain: the need for sufficient fire intensity, safety requirements, and integration of fire and invasive alien plant management.
Genetic insights into the globally invasive and taxonomically problematic tree genus Prosopis
(2020) Castillo, Maria L.; Schaffner, Urs; Van Wilgen, Brian W.; Montano, Noe Manuel; Bustamante, Ramiro O.; Cosacov, Andrea; Mathese, Megan J.; Le Roux, Johannes J.
Accurate taxonomic identification of alien species is crucial to detect new incursions, prevent or reduce the arrival of new invaders and implement management options such as biological control. Globally, the taxonomy of non-native Prosopis species is problematic due to misidentification and extensive hybridization. We performed a genetic analysis on several Prosopis species, and their putative hybrids, including both native and non-native populations, with a special focus on Prosopis invasions in Eastern Africa (Ethiopia, Kenya and Tanzania). We aimed to clarify the taxonomic placement of non-native populations and to infer the introduction histories of Prosopis in Eastern Africa. DNA sequencing data from nuclear and chloroplast markers showed high homology (almost 100%) between most species analysed. Analyses based on seven nuclear microsatellites confirmed weak population genetic structure among Prosopis species. Hybrids and polyploid individuals were recorded in both native and non-native populations. Invasive genotypes of P. juliflora in Kenya and Ethiopia could have a similar native Mexican origin, while Tanzanian genotypes likely are from a different source. Native Peruvian Prosopis pallida genotypes showed high similarity with non-invasive genotypes from Kenya. Levels of introduced genetic diversity, relative to native populations, suggest that multiple introductions of P. juliflora and P. pallida occurred to Eastern Africa. Polyploidy may explain the successful invasion of P. juliflora in Eastern Africa. The polyploid Prosopis juliflora was highly differentiated from the rest of the (diploid) species within the genus. The lack of genetic differentiation between most diploid species in their native ranges supports the notion that hybridization between allopatric species may occur frequently when they are co-introduced into non-native areas. For regulatory purposes, we propose to treat diploid Prosopis taxa from the Americas as a single taxonomic unit in non-native ranges.
A guide to a vanishing flora
(ASSAf, 2021-03-29) Van Wilgen, Brian W.
Renosterveld is a highly endangered vegetation type that once covered over 2 million hectares within the Cape Floristic Region. Today, the estimated 18 000 remaining patches are widely scattered across the landscape, collectively covering less than 4% of the original extent of this once-expansive veld type. Renosterveld differs from the neighbouring and better-known fynbos in that it occurs on nutrient-rich soils derived from shale, as opposed to the nutrient-poor sandstone soils that support fynbos. Fynbos is best known for its tall proteas and showy ericas, as well as reed-like restios. Renosterveld, on the other hand, is more grassy and characterised by shrubs of low to medium height. In the past, and unlike fynbos, renosterveld supported an abundance of large grazing mammals and their accompanying predators. This began to change around 2000 years ago when the Khoekhoen arrived with domesticated livestock whose more selective feeding habits would have differed from those of wildlife, thus impacting on the flora. Large wild mammals were virtually exterminated when European settlers arrived with modern firearms some 300 years ago, and domestic livestock became the dominant grazers. The fate of the renosterveld was finally sealed after World War II, when mechanised farming allowed large tracts of land to be converted to crops such as wheat and canola. Whether the original renosterveld was a shrubby grassland or a grassy shrubland is a topic that ecologists debate today, as the changing grazing pressures and humaninfluenced fire regimes would have affected the proportional contribution of these two important components of the vegetation. Better understanding of this issue would be important for managing this vegetation type correctly, and this book provides some insights into these intriguing questions. Nonetheless, forming an acceptably robust grasp of the functioning and dynamics of such a fractured ecosystem is akin to visualising the image of a 100-piece jigsaw puzzle from four remaining pieces.

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