Browsing by Author "MacFadyen, S."
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- ItemAn assessment of the implementation and outcomes of recent changes to fire management in the Kruger National Park(Open Journals Publishing, 2008) van Wilgen, B.W.; Govender, N.; MacFadyen, S.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.
- ItemDefining optimal sampling effort for large-scale monitoring of invasive alien plants: a Bayesian method for estimating abundance and distribution(2011) Hui, C.; Foxcroft, L.C.; Richardson, D.M.; MacFadyen, S.1. Monitoring the abundance and spatial structure of invasive alien plant populations is important for designing and measuring the efficacy of long-term management strategies. However, methods for monitoring over large areas with minimum sampling effort, but with sufficient accuracy, are lacking. Although sophisticated sampling techniques are available for increasing sampling efficiency, they are often difficult to implement for large-scale monitoring, thus necessitating a robust yet practical method. 2. We explored this problem over a large area (c.20 000 km2), using ad hoc presence–absence records routinely collected over 4 years in Kruger National Park (KNP), South Africa. Using a Bayesianmethod designed to solve the pseudo-absence (or false-negative) dilemma, we estimated the abundance and spatial structure of all invasive alien plants inKNP. Five sampling schemes, with different spatially weighted sampling efforts, were assessed and the optimal sampling effort estimated. 3. Although most taxa have very few records (50% of the species have only one record), the more abundant species showed a log-normal species-abundance distribution, with the 29 most abundant taxa being represented by an estimated total of 2Æ22 million individuals, with most exhibiting positive spatial autocorrelation. 4. Estimations from all sampling schemes approached the real situation with increasing sampling effort. An equal-weighted (uniform) sampling scheme performed best for abundance estimation (optimal efforts of 68 records per km2), but showed no advantage in detecting spatial autocorrelation (247 records per km2 required). With increasing sampling effort, the accuracy of abundance estimation followed an exponential form, whereas the accuracy of distribution estimation showed diverse forms. Overall, a power law relationship between taxon density (as well as the spatial autocorrelation) and the optimal sampling effort was determined. 5. Synthesis and applications. The use of Bayesian methods to estimate optimal sampling effort indicates that for large-scale monitoring, reliable and accurate schemes are feasible. These methods can be used to determine optimal schemes in areas of different sizes and situations. In a large area like KNP, the uniform equal-weighted sampling scheme performs optimally for monitoring abundance and distribution of invasive alien plants, and is recommended as a protocol for large-scale monitoring in other protected areas as well.
- ItemErratum to: Plant invasion science in protected areas: progress and priorities(Springer, 2017) Foxcroft, L.C.; Pysek, P.; Richardson, D.M.; Genovesi, P.; MacFadyen, S.Erratum to: Biol Invasions (2017) 19:1353–1378 DOI 10.1007/s10530-016-1367-z Unfortunately, the plant species Opuntia ficus-indica and Opuntia stricta were listed incorrectly as ‘‘Submerged aquatic plant’’; both should be listed as ‘‘Succulent shrub’’.
- ItemInto the great wide open: do alien plants spread from rivers to dry savanna in the Kruger National Park?(2020) Pyšek, P.; Hejda, M.; Čuda, J.; Zambatis, G.; Pyšková, K.; MacFadyen, S.; Storch, D.; Tropek, R.; Foxcroft, L.C.Protected areas play an important role as refuges from invasive species impacts on biodiversity. Within the MOSAIK (Monitoring Savanna Biodiversity in the Kruger National Park) project, plant species were recorded in a representative set of 60 plots, 50 × 50 m in size, across the entire KNP, distributed so as to cover a range of savanna habitats, i.e. perennial rivers, seasonal rivers and dry crests, and two main bedrock types (granite and basalt). The data were used to assess the role of rivers in the dispersal of alien plants and study whether the alien plant species spread from rivers to open dry savanna. The resulting dataset provided the first thorough information on the spatial distribution of naturalised alien plants in KNP. In total, we recorded 20 plant species that are alien to the park, four of them considered invasive: Parthenium hysterophorus, Opuntia stricta, Xanthium strumarium and Zinnia peruviana. The most widespread species in KNP was Tridax procumbens, recorded in 11 plots (i.e. 18% of all sampled), four other species were found in > 10% of the plots. One species, Bidens bipinnata, was not previously reported from the park and represents a new record. The majority of aliens were concentrated along perennial rivers (60% of all occurrences), but some were repeatedly recorded at seasonal rivers as well and two of the most invasive species in KNP, Opuntia stricta and Parthenium hysterophorus, occurred also on dry crests away from water. The average number of alien species per plot was low (1.6), as was their mean percentage contribution to all species in a plot (2.2%), but some plots harboured as many as seven species and contributed up to 11.9%. Moreover, only 21 plots (35%) were alien-species free. In terms of the total species number per habitat, perennial rivers had significantly more aliens than crests and were marginally significantly richer than seasonal rivers. By recording all naturalised alien species occurring in the plots – many of them are not invasive but may become so in the future – and by using the GloNAF database of global distribution of naturalised species, we assessed the invasion potential of the recorded species.
- ItemPatterns of alien plant distribution at multiple spatial scales in a large national park: implications for ecology, management and monitoring(Blackwell Publishing Ltd, 2009) Foxcroft, L.C.; Richardson, D.M.; Rouget, M.; MacFadyen, S.Aim Spatial scale is critical for understanding and managing biological invasions. In providing direction to managing alien plant invasions, much emphasis is placed on collecting spatially explicit data. However, insufficient thought is often given to how the data are to be used, frequently resulting in the incompatibility of the data for different uses. This paper explores the role of spatial scale in interpreting, managing and monitoring alien plant invasions in a large protected area. Location Kruger National Park, South Africa. Methods Using 27,000 spatially-explicit records of invasive alien plants for the Kruger National Park (> 20,000 km2) we assessed alien plant species richness per cell at nine different scales of resolution. Results When assessing the patterns of alien plants at the various scales of resolution, almost identical results are obtained when working at scales of quarter-degree grids and quaternary watersheds (the fourth level category in South Africa’s river basin classification system). Likewise, insights gained from working at resolutions of 0.1–0.5 km and 1–5 km are similar. At a scale of 0.1 x 0.1 km cells, only 0.4% of the Kruger National Park is invaded, whereas > 90% of the park is invaded when mapped at the quarter-degree cell resolution. Main conclusions Selecting the appropriate scale of resolution is crucial when evaluating the distribution and abundance of alien plant invasions, understanding ecological processes, and overationalizing management applications and monitoring strategies. Quarter-degree grids and quaternary watersheds are most useful at a regional or national scale. Grid cells of 1 to 25 km 2 are generally useful for establishing priorities for and planning management interventions. Fine-scale data are useful for informing management in areas which are small in extent; they also provide the detail appropriate for assessing patterns and rates of invasion.
- ItemPlant invasion science in protected areas: progress and priorities(Springer, 2017) Foxcroft, L.C.; Pysek, P.; Richardson, D.M.; Genovesi, P.; MacFadyen, S.Invasive alien species are a major problem for managers of protected areas (PAs) worldwide. Until the 1980s biological invasions were widely considered to be largely confined to anthropogenically disturbed sites and the widespread disruption of ecosystems in PAs by invasive species was not globally perceived as a major threat. A working group of the SCOPE program on biological invasions in the 1980s showed that PAs are not spared from major disruptive effects of invasions. Early research focused on descriptive studies of the extent to which PAs were invaded. More recent research explored drivers of invasion, and in the last decade much work has focused on understanding the impacts of invasions. We review the current understanding of alien plant invasions in PAs, focusing on four themes: (1) the status and macroecological patterns of alien plant invasions; (2) the threats that invasive alien plants (IAPs) pose and the impacts detected to date; (3) the current focus of invasion science in PAs; and (4) research priorities for advancing science-based management and policy. Of a sample of 59 widespread IAP species from a representative sample of 135 PAs globally, trees make up the largest proportion (32%), followed by perennial herbs (17%) and shrubs (15%). About 1857 papers have been published on alien species in PAs; 45% have focused on alien plants. Some textbook examples of impacts by IAPs originate from PAs, illustrating the severe threat to the core function of PAs. Impacts have been quantified at the species and community levels through the displacement and alteration of habitats. In some cases, native species abundance, diversity and estimated species richness have been altered, but reversed following control. At an ecosystem level, invasive plants have radically altered fire regimes in several PAs, in some cases causing regime shifts and transforming woodlands or savannas to grasslands. Invasions have also had a major impact on nutrient cycles. Protected areas are performing an increasingly important part of the global response to stem the rate of environmental change. Despite this, integrated efforts involving science, management and policy that are sufficiently resourced to generate insights on the status and dynamics of IAPs in PAs are insufficient or even lacking. Such efforts are needed to pave the way for monitoring trends, revising legislation and policies, and improving management interventions to reduce the extent and magnitude of impacts of invasive plants in PAs. While policy instruments to support management of non-native species date back to the 1930s, there has been a substantial increase in legislative support and general awareness since the early 2000s. Still, opportunities to improve research for PAs need to be created. Towards this goal, the establishment of a global PA research network could provide a unique vehicle to explore questions across species or functional groups and systems, at a scale currently beyond existing abilities. Developing an integrated global database with standardized, quantitative information could form part of such a networks function.
- ItemPredicting incursion of plant invaders into Kruger National Park, South Africa : the interplay of general drivers and species-specific factors(PLOS, 2011-12) Jarosik, V.; Pysek, P.; Foxcroft, L. C.; Richardson, David M.; Rouget, M.; MacFadyen, S.Background: Overcoming boundaries is crucial for incursion of alien plant species and their successful naturalization and invasion within protected areas. Previous work showed that in Kruger National Park, South Africa, this process can be quantified and that factors determining the incursion of invasive species can be identified and predicted confidently. Here we explore the similarity between determinants of incursions identified by the general model based on a multispecies assemblage, and those identified by species-specific models. We analyzed the presence and absence of six invasive plant species in 1.061.5 km segments along the border of the park as a function of environmental characteristics from outside and inside the KNP boundary, using two data-mining techniques: classification trees and random forests. Principal Findings: The occurrence of Ageratum houstonianum, Chromolaena odorata, Xanthium strumarium, Argemone ochroleuca, Opuntia stricta and Lantana camara can be reliably predicted based on landscape characteristics identified by the general multispecies model, namely water runoff from surrounding watersheds and road density in a 10 km radius. The presence of main rivers and species-specific combinations of vegetation types are reliable predictors from inside the park. Conclusions: The predictors from the outside and inside of the park are complementary, and are approximately equally reliable for explaining the presence/absence of current invaders; those from the inside are, however, more reliable for predicting future invasions. Landscape characteristics determined as crucial predictors from outside the KNP serve as guidelines for management to enact proactive interventions to manipulate landscape features near the KNP to prevent further incursions. Predictors from the inside the KNP can be used reliably to identify high-risk areas to improve the costeffectiveness of management, to locate invasive plants and target them for eradication.