Sandra MacFadyen

Relationship between herbaceous biomass and 1‐km2 Advanced Very High Resolution Radiometer (AVHRR) NDVI in Kruger National Park, South Africa

The relationship between multi‐year (1989–2003), herbaceous biomass and 1‐km2 Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) data in Kruger National Park (KNP), South Africa is considered. The objectives were: (1) to analyse the underlying relationship between NDVI summed for the growth season (ΣNDVI) and herbaceous biomass in field sites (n = 533) through time and (2) to investigate the possibility of producing reliable herbaceous biomass maps for each growth season from the satellite ΣNDVI observations. Landsat Enhanced Thematic Mapper Plus (ETM+) and Thematic Mapper (TM) data were used to identify highly heterogeneous field sites and exclude them from the analyses. The average R 2 for the ΣNDVI–biomass relationship at individual sites was 0.42. The growth season mean biomass and ΣNDVI of most landscape groups were strongly correlated with rainfall and each other. Although measured tree cover and MODIS estimates of tree cover did not have a detectable effect on the ΣNDVI–biomass relationship, other observations suggest that tree cover should not be ignored. The ΣNDVI was successful at estimating inter‐annual variations in the biomass at single sites, but on an annual basis the relationship derived from all the sites was not strong enough (average R 2 = 0.36) to produce reliable growth season biomass maps. This was mainly attributed to the fact that the biomass data were sampled from very small field sites that were not fully representative of 1‐km2 AVHRR pixels. Supplementary field surveys that sample a larger area for each field site (e.g. 1 km2 or larger) should account for the variability in biomass and may improve the strength of ΣNDVI–biomass relationships observed in a single growth season.

Plant invasion science in protected areas: progress and priorities

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.

Predicting Incursion of Plant Invaders into Kruger National Park, South Africa: The Interplay of General Drivers and Species-Specific Factors

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 1.0×1.5 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 cost-effectiveness of management, to locate invasive plants and target them for eradication.

Genetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa

Hybridization between domestic and wild animals is a major concern for biodiversity conservation, and as habitats become increasingly fragmented, conserving biodiversity at all levels, including genetic, becomes increasingly important. Except for tropical forests and true deserts, African wildcats occur across the African continent; however, almost no work has been carried out to assess its genetic status and extent of hybridization with domestic cats. For example, in South Africa it has been argued that the long-term viability of maintaining pure wildcat populations lies in large protected areas only, isolated from human populations. Two of the largest protected areas in Africa, the Kgalagadi Transfrontier and Kruger National Parks, as well as the size of South Africa and range of landscape uses, provide a model situation to assess how habitat fragmentation and heterogeneity influences the genetic purity of African wildcats. Using population genetic and home range data, we examined the genetic purity of African wildcats and their suspected hybrids across South Africa, including areas within and outside of protected areas. Overall, we found African wildcat populations to be genetically relatively pure, but instances of hybridization and a significant relationship between the genetic distinctiveness (purity) of wildcats and human population pressure were evident. The genetically purest African wildcats were found in the Kgalagadi Transfrontier Park, while samples from around Kruger National Park showed cause for concern, especially combined with the substantial human population density along the parks boundary. While African wildcat populations in South Africa generally appear to be genetically pure, with low levels of hybridization, our genetic data do suggest that protected areas may play an important role in maintaining genetic purity by reducing the likelihood of contact with domestic cats. We suggest that approaches such as corridors between protected areas are unlikely to remain effective for wildcat conservation, as the proximity to human settlements around these areas is projected to increase the wild/domestic animal interface. Thus, large, isolated protected areas will become increasingly important for wildcat conservation and efforts need to be made to prevent introduction of domestic cats into these areas.

Woody vegetation of a mosaic of protected areas adjacent to the Kruger National Park, South Africa

Abstract Question: How is pattern detected and spatial scale defined in a manner that is meaningful to management? Location: Protected areas to the west of the Kruger National Park, South Africa. Methods: A Two-Way Indicator Species Analysis (TWINSPAN) based on composition and structure was applied to woody survey data. The resulting TWINSPAN classes for individual monitoring sites were used in a supervised classification of Landsat ETM+ imagery across the study area. The training samples co-ordinates were fed into a GIS and the resulting TWINSPAN point-feature shape file was processed using a 1 km theme-buffer function. Results: The supervised classification using the theme-buffer signatures yielded a satisfactory overall accuracy (κ = 0.75; r2 = 0.80; p = 0.05) using a test sample compiled by reserve wardens throughout the study area. The derived vegetation map was smoothed using a majority filter and after on-screen digitizing a small gabbro intrusion, it was accepted as the best representation of the woody vegetation of the study area at a scale of 1:250 000. Seven plant communities were identified in the current study and satisfactorily accommodated within various topographical units of four extrapolated Landscapes of the Kruger National Park. Conclusions: Vegetation patterns are described of the areas under conservation management to the west of the KNP at a spatial scale that allows for the meaningful examination and comparison of the structure, functioning, and ultimately effective management, of these savannas. This contribution thus links to the co-ordinated effort extending into the Trans-Frontier National Park in Mocambique. A key objective is to better understand the functioning of these savanna systems for effective management and we discuss some of the key ecological issues within the plant communities of each landscape. The latter illustrate the usefulness of the technique in practice.

A Cross-Scale Approach for Abundance Estimation of Invasive Alien Plants in a Large Protected Area

Efficient management of invasive alien plants requires robust and cost-efficient methods for measuring the abundance and spatial structure of invasive alien plants with sufficient accuracy. Here, we present such a monitoring method using ad hoc presence-absence records that are routinely collected for various management and research needs in Kruger National Park, South Africa. The total and local abundance of all invasive alien plants were estimated using the area-of-occupancy model that depicts a power-law scaling pattern of species occupancy across scales and a detection-rate-based Poisson model that allows us to estimate abundance from the occupancy, respectively. Results from these two models were consistent in predicting a total of about one million invasive alien plant records for the park. The accuracy of log-transformed abundance estimate improved significantly with the increase of sampling effort. However, estimating abundance was shown to be much more difficult than detecting the spatial structure of the invasive alien plants. Since management of invasive species in protected areas is often hampered by limited resources for detailed surveys and monitoring, relatively simple and inexpensive monitoring strategies are important. Such data should also be appropriate for multiple purposes. We therefore recommend the use of the scaling pattern of species distribution as a method for rapid and robust monitoring of invasive alien plants in protected areas. Not only do these approaches provide valuable tools for managers and biologists in protected areas, but this kind of data, which can be collected as part of routine activities for a protected area, provides excellent opportunities for researchers to explore the status of aliens as well as their assemblage patterns and functions.

Erratum to: Plant invasion science in protected areas: progress and priorities

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 L. C. Foxcroft (&) Conservation Services, South African National Parks, Private Bag X402, Skukuza 1350, South Africa e-mail: Llewellyn.foxcroft@sanparks.org L. C. Foxcroft D. M. Richardson Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa e-mail: rich@sun.ac.za P. Pyšek Department of Invasion Ecology, Institute of Botany, The Czech Academy of Sciences, 252 43 Průhonice, Czech Republic e-mail: pysek@ibot.cas.cz P. Pyšek Department of Ecology, Faculty of Science, Charles University, Viničná 7, 128 44 Prague 2, Czech Republic P. Genovesi ISPRA, Institute for Environmental Protection and Research, and Chair IUCN SSC Invasive Species Specialist Group, Via V. Brancati 48, 00144 Rome, Italy e-mail: piero.genovesi@isprambiente.it S. MacFadyen Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa e-mail: sandramf@live.co.za