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

The relationship between multi-year (1989-2003), herbaceous biomass and 1-km 2 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 (SNDVI) and herbaceous biomass in field sites (n5533) through time and (2) to investigate the possibility of producing reliable herbaceous biomass maps for each growth season from the satellite SNDVI 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 SNDVI-biomass relationship at individual sites was 0.42. The growth season mean biomass and SNDVI 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 SNDVI-biomass relationship, other observations suggest that tree cover should not be ignored. The SNDVI 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 50.36) 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-km 2 AVHRR pixels. Supplementary field surveys that sample a larger area for each field site (e.g. 1 km 2 or larger) should account for the variability in biomass and may improve the strength of SNDVI-biomass relationships observed in a single growth season.

This paper describes recent changes to the fire management policy of the 1.9 million ha Kruger National Park in South Africa. It provides a real-life example of adaptive learning in an environment where understanding is incomplete, but where management nonetheless has to proceed. The previous policy called for the application of fire to meet burnt area targets that were set for administrative subdivisions, and that were assessed at the scale of the entire park. This was problematic because the park is large and heterogeneous, and because sound ecological motivations that could link burning prescriptions to ecological objectives were missing. The new policy divides the park into five fire management zones on the basis of differences in mean annual rainfall, historic fire return periods, and geology. In addition, it proposes fire management actions designed to achieve specified ecological objectives in each zone, and includes fire-regime related thresholds and associated ecological outcomes against which to assess the effectiveness of management. The new policy is an improvement over previous iterations, but several challenges remain. Most important among these would be to continually improve the understanding of the effects of fire, and to develop frameworks for assessing the impacts of fire together with other ecosystem drivers that interact strongly with fire to influence the attainment of ecological objectives.

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 km 2 ) 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 × 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 conclusionsSelecting the appropriate scale of resolution is crucial when evaluating the distribution and abundance of alien plant invasions, understanding ecological processes, and operationalizing 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.