Management Of Invasive Alien Plants Research Articles

Clearing of invasive alien plants under different budget scenarios: using a simulation model to test efficiency

Clearing of invasive alien plants (IAPs) is a necessary but expensive exercise. Typically, insufficient resources are available to clear all areas simultaneously. Consequently areas need to be prioritized for clearing. The financial resources available determine the extent of the area which can be cleared, while the prioritization identifies the location of the areas to be cleared. We investigate the following questions: (1) How does a change in the budget impact on the efficiency of the clearing operations over time? (2) How does this differ for different sites? (3) Can we identify pattern which make it possible for managers to determine if their budget is sufficient to achieve a management goal (e.g. clearing 95% of the area of IAPs) in a given time? (4) Can we draw general rules about how the time needed of achieving a management goal is changing when increasing the budget? We use a spatio-temporal explicit simulation model (SpreadSim) to simulate the spread of major woody IAPs over time, using a random prioritization strategy as a null model. This strategy requires no understanding or assumptions about the factors influencing spread; it is thus a reasonable baseline prioritization strategy. Our results confirm that a reduction of the budget increases the time needed to reach a management goal of 95% non-invaded areas and simultaneously increases the overall budget needed to achieve this goal. In addition, for each site, we can identify three values. Firstly, a “lower critical limit” of the budget, below which the IAP spread is only slowed down and management does not result in a reduction of the area invaded by IAPs, which is independent of the management goal. Secondly, the “critical budget”, at which we have a chance of more than 50% of achieving our management goal in a given time. Thirdly, an “upper critical limit” for the budget, above which no substantial change in the time needed to reach the management goal can be observed. For all our three sites, the “upper critical limit” is located at approximately 1.7 times the “critical budget”. The variability of the temporal trajectories of the area covered by IAPs for different simulations for the same input parameter and highly non-linear change in IAP cover over time indicate that an identification of the “critical budget” based on few years of IAP management is nearly impossible and that the use of simulation models is imperative. Nevertheless, the general pattern observed can be generalized to other prioritization strategies and provide important guidance for budget allocations.

An economic assessment of the contribution of biological control to the management of invasive alien plants and to the protection of ecosystem services in South Africa

This study is a first attempt at a holistic economic evaluation of South African endeavours to manage invasive alien plants using biological control. Our focus was on the delivery of ecosystem services from habitats that are invaded by groups of weeds, rather than by each individual weed species. We established the net present value of the weed biological control efforts, and derived benefit:cost ratios by comparing this value (a cost) to the estimated value of ecosystem services protected by weed biological control. We identified four major functional groupings of invading alien plants, and assessed their impact on water resources, grazing and biodiversity. We estimated the area that remained free of invasions due to all historic control efforts in South Africa, and the proportion that remained free of invasion as a result of biological control (which was initiated in 1913). The estimated value of potential ecosystem services amounted to 152 billion South African rands (ZAR—presently, about US$ 19.7 billion) annually. Although an estimated ZAR 6.5 billion was lost every year due to invading alien plants, this would have amounted to an estimated additional ZAR 41.7 billion had no control been carried out, and 5–75% of this protection was due to biological control. The benefit:cost ratios ranged from 50:1 for invasive sub-tropical shrubs to 3,726:1 for invasive Australian trees. Benefit:cost ratios remained positive and our conclusion, that biological control has brought about a considerable level of protection of ecosystem services, remains robust even when our estimates of the economic impacts of key variables (i.e. sensitivity analyses of indeterminate variables) were substantially reduced.

Plant invasions in arid areas: special problems and solutions: a South African perspective

Management of invasive alien plants in arid areas is complicated by the cryptic and stochastic nature of the invasion process, the low density of researchers, extension officers and farmers in these areas, the complex, delayed and sometimes, indirect, effects of alien invasive plants on these ecosystems, and by high and shifting values placed on goods and services derived from invasive alien plant species. Fluctuating vegetation cover together with convergent adaptations for dispersal and facilitation enables some desert aliens to invade intact vegetation. Invasive plants in arid areas are not all arid-adapted: the most problematic species globally are phreatic, wetland or oasis specialists that can colonise remote wetlands and springs through a combination of wind-dispersed seeds and vegetative reproduction. Their success is often linked to disturbance and facilitated by agricultural activities including water extraction, cropping and livestock management. Invasive alien plants in arid region wetlands have an impact on forage, water resources and biodiversity in these key resource areas, that is disproportionately great relative to the area they occupy. Management of arid region aliens could include pre-introduction biocontrol planning that makes it possible to use aliens while reducing invasion risks. An alternative is to replace the aliens with extralimital indigenous plants that can supply the rangeland services perceived to be absent from arid environments—but such interventions may carry even greater risks.

Spatially‐explicit sensitivity analysis for conservation management: exploring the influence of decisions in invasive alien plant management

AbstractAim Decision‐support models have considerable potential for guiding management strategies when problems are complex. The robustness of such decision‐making processes is rarely evaluated, and the influence of decision criteria (or factors) in management decisions is seldom considered. We present a framework for a spatially‐explicit sensitivity analysis by using a scheme developed to provide objective guidelines, in the form of static priority maps, for managing woody invasive alien plants (IAPs).Location The Cape Floristic Region, South Africa.Methods The model included seven factors related to management history, fire risk, and the age, identity, density and spread of IAPs. Each factor had a weight associated that reflected its relative importance in prioritizing areas for clearing. We changed these factor weights using three approaches of sensitivity analysis and assessed the effect of these changes on the spatial structure of the resulting priority maps in three different management regions.Results Different outcomes arose depending on the importance given to different factors. Priority maps were most sensitive to the fire‐related factors, suggesting that fire is both a crucial driver of invasion in fynbos and an overriding determinant of management options. The factor ‘area burnt recently’ provided crucial information for the effective clearing of IAPs. The sensitivity of the model to changes in other factors was more context specific: levels of sensitivity were highly dependent on different features of the landscape, especially the spatial heterogeneity of particular factors.Main conclusions By clarifying the importance of factors in shaping priority maps, the sensitivity analysis framework enabled us to identify the necessary factors to produce outcomes matching a pre‐selected management strategy. This is important for cost‐efficient management, as acquisition and curation of data is expensive. This spatially‐explicit sensitivity analysis is, thus, recommended to evaluate the robustness and generality of selected management strategies, and validate the assumptions derived from decision‐making protocols.

The evolution of fire and invasive alien plant management practices in fynbos

The history and development of fire and invasive alien plant management policies in fynbos during the 20th century are reviewed. Fire was initially condemned outright as a destructive force, but as its vital role became better understood, management policies switched from protection to active burning in 1968. During the 1970s, large, coordinated research programmes were established, resulting in a solid basis of knowledge on which to develop fire management policies. Despite policies of prescribed burning, wild fires remain the dominant feature of the region, fortunately driving a variable fire regime that remains broadly aligned with conservation objectives. The problem of conserving fire-adapted fynbos is complicated by invading alien trees that are also fire-adapted. Research results were used to demonstrate the impacts of these invasions on water yields, leading to the creation of one of the largest alien plant control programmes globally. Despite improvements in control methods, alien trees, notably pines, continue to spread almost unchecked. Biological control offered some hope for controlling pines, but was ruled out as too high a risk for these commercially-important trees. Failure to address this problem adequately will almost certainly result in the severe degradation of remaining fynbos ecosystems.

Normes OEPP/EPPO Standards Phytosanitary procedures Procédures phytosanitaires

Normes OEPP/EPPO Standards Phytosanitary procedures Procédures phytosanitaires

Identifying priority areas for the management of invasive alien plants in the Cape Floristic Region

introduced alien species. However, this is the first study on the topic in South Africa and specifically in the Western Cape, where A. mellifera capensis the Cape Honeybee is endemic to the region. De Hoop Nature Reserve and Marine Protected Area was the site where we introduced 24 managed hives (8 per replicate site) during the winter season. We determined the change in insect guild abundance and number of visits between three treatments namely before (control), during and after the presence of the honeybee hives. Initial results suggest that honeybee abundance do increase and some insect guild abundances decrease during the presence of the hives.

Prioritising areas for the management of invasive alien plants in the CFR: different strategies, different priorities?

Prioritising areas for the management of invasive alien plants in the CFR: different strategies, different priorities?

Effects of Weed‐Management Burning on Reptile Assemblages in Australian Tropical Savannas

Fire is frequently used for land management purposes and may be crucial for effective control of invasive non-native plants. Nevertheless, fire modifies environments and may affect nontarget native biodiversity, which can cause conflicts for conservation managers. Native Australian reptiles avoid habitat invaded by the alien plant rubber vine (Cryptostegia grandiflora) and may be susceptible to the impacts of burning, a situation that provides a model system in which to examine possible conservation trade-offs between managing invasive plants and maintaining native biodiversity. We used replicated, experimental fire treatments (unburned, dry-season burned, and wet-season burned) in 2 habitats (riparian and adjacent open woodland) to examine the short- (within 12 months of fire) and longer-term (within 3 years of fire) changes of reptile assemblages in response to wet- and dry-season burning for weed management in tropical savannas of northern Australia. Within 12 months of fire, abundances of the skink Carlia munda (Scincidae) were higher in the burned sites, but overall reptile composition was structured by habitat type rather than by effects of burning. Within 3 years of a fire, the effects of fire were evident. Reptiles, especially the gecko Heteronotia binoei (Gekkonidae), were least abundant in dry-season burned sites; litter-associated species, including Carlia pectoralis (Scincidae), were rarely observed in burned habitat; and there were fewer species in the wet-season burned sites. Reptile abundance was associated with vegetation structure, which suggests that fire-induced changes detrimentally altered the availability of resources for some reptiles, particularly leaf-litter species. Invasive alien plants, such as rubber vine, have severe effects on native biodiversity, and control of such species is a fundamental land management objective. Nevertheless, fire management of invasive alien plants may adversely affect native biodiversity, creating a conservation conundrum. In such scenarios, land managers will need to identify the most desired conservation goal and consider the consequences for native biota.

Restoration of water resources (natural capital) through the clearing of invasive alien plants from riparian areas in South Africa — Costs and water benefits

Working for Water forms part of the Expanded Public Works Programme of the South African Government, aimed at the sustainable management of natural resources through the control and management of invasive alien plants while enhancing socio-economic empowerment in South Africa. The programme's name was taken from one of the original motivations: namely, reducing the impacts of invasive alien trees on water resources. A number of studies have looked at the potential impacts of the programme but only one or two have used actual management data to quantify its costs and benefits. This paper is the first, in hopefully a series of papers, on the costs and impacts of the programme over recent years. The paper focuses on the extent, costs and impacts of clearing invasive alien plants from riparian areas. Data were extracted from the Working for Water Information Management System (WIMS) and analysed to assess clearing costs and estimated impacts of clearance on water resources. Some of the most significant findings of the study again illustrate the need to treat invasions as early as possible. Very scattered (1–5%) invasions of selected species for example were between 3 and 25 times cheaper to clear than closed canopy stands (75–100%). On the other hand, unit reference values, used to compare clearing operations in terms of cost efficiency in generating extra water yield, were much higher for low levels of invasion than denser invasions, to the extent that the former's viability could be questioned by the uninformed. However, this was only assessed in terms of extra water generated and not in terms of volumes of water secured, as invasive alien plants spread and become denser if not actively controlled. If left unchecked, water losses increase, which makes the clearing of light infestations much more viable. Overall, it is estimated that around 7% of riparian invasions have been cleared, resulting in significant yield increases. The increased estimated yield of 34.4 million m 3 is about 42% of the yield of the new Berg River Scheme in the Western Cape (81 million m 3). The investment in clearing species known for excessive water use from riparian areas, at a cost of R116 million, was found to be a very good investment. However, it is important to note that the clearing of invasive alien plants will seldom result in the total elimination of shortfalls in water supply and should be seen as part of a package of water resource options to optimize supply, aimed at minimizing wastage of water.

Normes OEPP EPPO Standards Phytosanitary procedures Procédures phytosanitaires

Normes OEPP EPPO Standards Phytosanitary procedures Procédures phytosanitaires

Guidelines for the management of invasive alien plants or potentially invasive alien plants which are intended for import or have been intentionally imported

Guidelines for the management of invasive alien plants or potentially invasive alien plants which are intended for import or have been intentionally imported

Hydrocotyle ranunculoides

<i>Hydrocotyle ranunculoides</i>