Richardson D.M.,Stellenbosch University |
Richardson D.M.,Center Tecnologic Forestal Of Catalonia |
Iponga D.M.,Stellenbosch University |
Iponga D.M.,Center Tecnologic Forestal Of Catalonia |
And 8 more authors.
Ecography | Year: 2010
Determining the potential range of invasive alien species under current conditions is important. However, we also need to consider future distributions under scenarios of climate change and different management interventions when formulating effective long-term intervention strategies. This paper combines niche modelling and fine-scale process-based modelling to define regions at high risk of invasion and simulate likely dynamics at the landscape scale.Our study species is Schinus molle (Peruvian pepper tree; Anacardiaceae), a native of central South America, introduced to South Africa in about 1850 where it was widely planted along roads.Localities of planted and naturalized trees were mapped along 5380 km of roads - a transect that effectively samples a large part of western South Africa. Correlative modelling was used to produce profiles of present and future environmental conditions characterizing its planted and naturalized ranges. A cellular-automata simulation model was used to estimate the dynamics of S. molle under future climates and different management scenarios.The overall potential range of S. molle in the region is predicted to shrink progressively with predicted climate change. Some of the potential range of S. molle defined based on current conditions (including areas where it is currently highly invasive) is likely to become less favourable. The species could persist where it is well established long after conditions for recruitment have deteriorated. Some areas where the species is not widely naturalized now (notably the fynbos biome) are likely to become more favourable. Our modelling approach allows for the delineation of areas likely to be invaded in future by considering a range of factors at different scales that mediate the interplay of climatic variables and other drivers that define the dimensions of human intervention such as distance from planted trees and the density of planted plants, both of which affect propagule pressure. © 2010 The Authors.
Jarvie H.P.,UK Center for Ecology and Hydrology |
Withers P.J.A.,ADAS Environment Group |
Bowes M.J.,UK Center for Ecology and Hydrology |
Palmer-Felgate E.J.,UK Center for Ecology and Hydrology |
And 10 more authors.
Agriculture, Ecosystems and Environment | Year: 2010
This paper provides an overview of the impacts of rural land use on lowland streamwater phosphorus (P) and nitrogen (N) concentrations and P loads and sources in lowland streams. Based on weekly water quality monitoring, the impacts of agriculture on streamwater P and N hydrochemistry were examined along a gradient of rural-agricultural land use, by monitoring three sets of 'paired' (near-adjacent) rural headwater streams, draining catchments which are representative of the major geology, soil types and rural/agricultural land use types of large areas of lowland Britain. The magnitude and timing of P and N inputs were assessed and the load apportionment model (LAM) was applied to quantify 'continuous' (point) source and 'flow-dependent' (diffuse) source contributions of P to these headwater streams. The results show that intensive arable farming had only a comparatively small impact on streamwater total phosphorus (TP loads), with highly consistent stream diffuse-source TP yields of ca. 0.5 kg-P ha-1 year-1 for the predominantly arable catchments with both clay and loam soils, compared with 0.4 kg-P ha-1 year-1 for low agricultural intensity grassland/woodland on similar soil types. In contrast, intensive livestock farming on heavy clay soils resulted in dramatically higher stream diffuse-source TP yields of 2 kg-P ha-1 year-1. The streamwater hydrochemistry of the livestock-dominated catchment was characterised by high concentrations of organic P, C and N fractions, associated with manure and slurry sources. Across the study sites, the impacts of human settlement were clearly identifiable with effluent inputs from septic tanks and sewage treatment works resulting in large-scale increases in soluble reactive phosphorus (SRP) loads and concentrations. At sites heavily impacted by rural settlements, SRP concentrations under baseflow conditions reached several hundred μg-P L-1. Load apportionment modelling demonstrated significant 'point-source' P inputs to the streams even where there were no sewage treatment works within the upstream catchment. This indicates that, even in sparsely populated rural headwater catchments, small settlements and even isolated groups of houses are sufficient to cause significant nutrient pollution and that septic tank systems serving these rural communities are actually operating as multiple point sources, rather than a diffuse input. © 2009 Elsevier B.V. All rights reserved.