Fire and plants Bond, W.J; Wilgen, B.W. van (Department of Botany, University of Cape Town (South Africa))
1996, 1995, 1996., Letnik:
14
eBook, Book
Large regions of the world are regularly burnt either deliberately or naturally. However, despite the widespread occurrence of such fire-prone ecosystems, and considerable body of research on plant ...population biology in relation to fire, until now there have only been limited attempts at a coherent conceptual synthesis of the field for use by students or researchers.
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
m
3 (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 pre-modern 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.
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.
► Invasive alien plant control was prioritized in a large number of water catchments. ► A goal and criteria were agreed at workshops involving multiple stakeholders. ► Stakeholder decision models were combined with spatial data to compare catchments. ► Control operations are not currently optimally aligned with priorities. ► The agreed priorities should guide the reallocation of available resources.
Studies addressing the economic impacts of invasive alien species are biased towards ex-post assessments of the costs and benefits of control options, but ex-ante assessments are also required to ...deal with potentially damaging invaders. The polyphagous shot hole borer Euwallacea fornicatus (Coleoptera: Curculionidae) is a recent and potentially damaging introduction to South Africa. We assessed the potential impact of this beetle by working across economic and biological disciplines and developing a simulation model that included dynamic mutualistic relations between the beetle and its symbiotic fungus. We modeled the potential growth in beetle populations and their effect on the net present cost of damage to natural forests, urban trees, commercial forestry, and the avocado industry over 10 yr. We modeled high, baseline, and low scenarios using discount rates of 8, 6, and 4%, and a plausible range of costs and mortality rates. Models predicted steady growth in the beetle and fungus populations, leading to average declines in tree populations of between 3.5 and 15.5% over 10 yr. The predicted net present cost was 18.45 billion international dollars (Int. $), or about 0.66% of the country's GDP for our baseline scenario ($2.7 billion to $164 billion for low and high scenarios). Most of the costs are for the removal of urban trees that die as a result of the beetle and its fungal symbiont, as has been found in other regions. We conclude that an ex-ante economic assessment system dynamics model can be useful for informing national strategies on invasive alien species management.
This paper uses five inter-related topics (the management of rivers, fire regimes, invasive alien species, rare antelope and elephants) to assess 15
years of adaptive management in the Kruger ...National Park (KNP), South Africa. The importance of adaptive planning (a process for developing achievable objectives, which is adaptive because objectives are revised as understanding grows), has been highlighted by this assessment, and the KNP’s track record of adaptive planning is better than that of adaptive management. Adaptive management has identified important issues with regard to biodiversity conservation, and resulted in a shift in management focus to these issues. Because the conservation outcomes of management shifts will only manifest themselves in the longer term, the relative success of adaptive management should be measured by the degree to which management has been refocused onto priority issues, and by the rate at which new understanding is generated. Some issues previously seen as important (fire, rare antelope), are now regarded as less so, while others remain important and difficult to solve, although there has been some progress (rivers, alien plants and elephants). It has also proved difficult to implement active adaptive management (large-scale, replicated trials using different approaches), because of local variation and logistical problems. Adaptive management will remain the approach of choice because there is some progress, and no known alternative to managing this complex ecosystem. It is simply not an option to return to the easily-understood “implementable” solutions (such as culling, regular prescribed burning, or artificial water provision) that demonstrably did not work.
Globally, invasions by alien plants are rapidly increasing in extent and severity, leading to large-scale ecosystem degradation. Weed biological control offers opportunities to arrest or even reverse ...these trends and, although it is not always effective or appropriate as a management strategy, this practice has an excellent record of safety and many notable successes over two centuries. In recent years, growing concerns about the potential for unintended, non-target damage by biological control agents, and fears about other unpredictable effects on ecosystems, have created an increasingly demanding risk-averse regulatory environment. This development may be counter-productive because it tends to overemphasize potential problems and ignores or underestimates the benefits of weed biological control; it offers no viable alternatives; and it overlooks the inherent risks of a decision not to use biological control. The restoration of badly degraded ecosystems to a former pristine condition is not a realistic objective, but the protection of un-invaded or partial restoration of invaded ecosystems can be achieved safely, at low cost and sustainably through the informed and responsible application of biological control. This practice should therefore be given due consideration when management of invasive alien plants is being planned. This discussion paper provides a perspective on the risks and benefits of classical weed biological control, and it is aimed at assisting environmental managers in their deliberations on whether or not to use this strategy in preference, or as a supplement to other alien invasive plant control practices.
Mesquite (Prosopis species) were introduced to South Africa to provide fodder and shade for livestock, but some have become invasive, impacting on water and grazing resources. Mesquite’s net economic ...effects are unclear and their unequal distribution leads to conflict. We estimated the value of mesquite invasions in the Northern Cape Province for different scenarios, differentiating between productive floodplains and upland areas. The estimated net economic value of mesquite in 2009, covering 1.47 million ha, was US$3.5–15.3 million. The value will become negative within 4–22 years, assuming annual rates of spread of 30 and 15%, respectively. The estimated 30-year present value (3% discount rate) of the benefits of control in the floodplains exceeded that of costs but the opposite was true in the uplands. Control efforts should therefore focus on floodplains while preventing spread from uplands into cleared or uninvaded floodplains. More efficient control methods are needed as estimated control costs (>US$9.5 million yr−1) exceed financial capabilities of Public Works programmes. Control in the floodplains was not economically justifiable using an 8% discount rate, because this substantially discounted future costs. We conclude that more effective control methods, such as biological control, are needed to prevent substantial economic losses.
► Mesquite provides net benefits today but switches to negative within 4–22 years if not controlled. ► Control costs exceed public funds; cheaper, more effective methods such as biocontrol are needed. ► Benefits of control are the avoided pasture and water losses, so control should focus on productive lands. ► Farmers must be convinced of the future private benefit of control & incentives created to fund this. ► Control must also focus on upland sources of invasion of productive or high water-yielding regions.
Approaches to fire management in the savanna ecosystems of the 2-million ha Kruger National Park, South Africa, have changed several times over the past six decades. These approaches have included ...regular and flexible prescribed burning on fixed areas and a policy that sought to establish a lightning-dominated fire regime. We sought to establish whether changes in management induced the desired variability in fire regimes over a large area. We used a spatial database of information on all fires in the park between 1957 and 2002 to determine elements of the fire regime associated with each management policy. The area that burned in any given year was independent of the management approach and was strongly related to rainfall (and therefore grass fuels) in the preceding 2 years. On the other hand, management did affect the spatial heterogeneity of fires and their seasonal distribution. Heterogeneity was higher at all scales during the era of prescribed burning, compared with the lightning-fire interval. The lightning-fire interval also resulted in a greater proportion (72% vs. 38%) of the area burning in the dry season. Mean fire-return intervals varied between 5.6 and 7.3 years, and variability in fire-return intervals was strongly influenced by the sequencing of annual rainfall rather than by management. The attempt at creating a lightning-dominated fire regime failed because most fires were ignited by humans, and the policy has been replaced by a more pragmatic approach that combines flexible prescribed burning with lightning-ignited fires.
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.
We review the current state of knowledge of quantified impacts of invasive alien plants on water quality, with a focus on South Africa. In South Africa, over 200 introduced plant species are regarded ...as invasive. Many of these species are particularly prominent in riparian ecosystems and their spread results in native species loss, increased biomass and fire intensity and consequent erosion, as well as decreased river flows. Research on the impact of invasive alien plants on water resources has historically focused on water quantity. However, although invasive alien plants also affect the quality of water, this aspect has not been well documented. Alien invasive plants increase evaporation rates, and reduce stream flow and dilution capacity. The biomass inputs of alien invasive plants, especially nitrogen fixers such as Acacia spp., alter nutrient cycles and can elevate nutrient concentrations in groundwater. Alien plant invasions alter the fire regimes in invaded areas by changing the size, distribution and plant chemistry of the biomass. More intense fires increase soil erosion and thereby decrease water quality. In contrast to riparian invasions, aquatic invasive plants have been more extensively studied in South Africa and their impacts on water quality have been relatively well monitored. Water quality in South Africa is rapidly deteriorating, and all factors that influence this deterioration need to be taken into account when formulating actions to address the problem. The changes in water quality brought about by alien plant invasions can exacerbate the already serious water quality problems. PUBLICATION ABSTRACT
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