Abstract
Alien species that are desirable and commercially important in parts of the landscape, but damaging invaders in other parts, present a special challenge for managers, planners, and policy-makers. Objective methods are needed for identifying areas where control measures should be focussed. We analysed the distribution of forestry plantations and invasive (self-sown) stands of Acacia mearnsii and Pinus spp. in South Africa; these two taxa account for 60% of the area under commercial plantations and 54% of the area invaded by alien trees and shrubs. The distribution of commercial forestry plantations and invasive stands of these taxa were mapped and the data was digitised and stored as Geographic Information System (GIS) (Arc/Info) layers. A series of environmental parameters were derived from GIS layers of climate, topography, geology, land use, and natural vegetation. The current distribution of the two taxa was subdivided into three groups according to the degree of invasion, planting history and the precision of the data collection. We used regression-tree analysis to relate, for each taxon, the distribution of invasive stands with environmental variables, and to derive habitat suitability maps for future invasion. The current distribution of invasive stands in South Africa was largely influenced by climatic factors. At a national scale, the distribution of large commercial plantations was a poor predictor of areas invaded by both taxa. Using environmental factors identified by the regression trees, we found that 6.6% and 9.8% of natural habitats currently not invaded and untransformed by urbanisation or agriculture are suitable for invasion by Pinus spp. and A. mearnsii, respectively. We then derived guidelines for policy on alien plant management based on vegetation type, degree of transformation, extent of invasion, and the risk of future alien spread. These factors were used to identify demarcated areas where these alien species can be grown with little risk of invasions, and areas where special measures are needed to manage spread from plantations.
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References
Cowling RM, Pressey RL, Lombard AT, Heijnis CJ, Richardson DM and Cole N(1999) Framework for a conservation plan for the Cape Floristic Region. Institute of Plant Conservation, Cape Town
Daehler CC and Carino DA (2000) Predicting invasive plants: prospects for a general screening system based on current regional models. Biological Invasions 2: 93–102
De'ath G and Fabricius KE (2000) Classification and regression trees: a powerful yet simple technique for ecological data analysis. Ecology 81: 3178–3192
Fairbanks DHK and Benn GA(2000) Identifying regional landscapes for conservation planning: a case study from Kwazulu-Natal, South Africa. Landscape and Urban Planning 50: 237–257
Fairbanks DHK, Thompson MW, Vink DE, Newby TS, van der Berg HM and Everard DA (2000) The South African land-cover characteristics database: a synopsis of the landscape. South African Journal of Science 96: 69–85
FOA (1998) Abstract of South African Forestry Facts for the Year 1996/97. Forest Owners Association, Johannesburg
Gabriel KR (1971) The biplot graphic display of matrices with application to principal components analysis. Biometrics 58: 453–467
Gower JC and Hand DJ (1996) Biplots. Chapman &: Hall, London, 277 pp
Guisan A and Zimmermann NE(2000) Predictive habitat distribution models in ecology. Ecological Modelling 135: 147–186
Hawkins DM (1995) Formal Inference-based Recursive Modelling. Department of Applied Statistics, University of Minnesota, St Paul
Higgins SI, Richardson DM, Cowling RM and Trinder-Smith TH (1999) Predicting the landscape scale distribution of alien plants and their threats to biodiversity. Conservation Biology 13: 303–313
Higgins SI, Richardson DM and Cowling RM (2000) A dynamic spatial model for managing alien plant invasions at the landscape extent. Ecological Applications 10: 1833–1848
Higgins SI, Richardson DM and Cowling RM (2001) Validation of a spatial simulation model of a spreading alien plant population. Journal of Applied Ecology 38: 571–584
Hobbs RJ and Huenneke LF (1992) Disturbance, diversity, and invasion: implications for conservation. Conservation Biology 6: 324–337
Le Maitre DC (1998) Pines in cultivation. In: Richardson DM (ed) Ecology and Biogeography of Pinus. pp 407–431. Cambridge University Press, Cambridge
Le Maitre DC, Van Wilgen BW, Gelderblom CM, Bailey C, Chapman RA and Nel JL (2002) Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management. Forestry Ecology &: Management 160: 143–159
Low AB and Rebelo AG (1996) Vegetation of South Africa, Lesotho and Swaziland. Department of Environmental Affairs &:Tourism, Pretoria
Nel JL, van Wilgen BW and Gelderblom CM(1999) The contribution of plantation forestry to the problem of invading alien trees in South Africa: a preliminary assessment. Report ENV/S-C 99003, CSIR, Stellenbosch, 26 pp
Pheloung PC, Williams PA and Halloy SA(1999) Aweed risk assessment model for use as a biosecurity tool evaluating plant introductions. Journal of Environmental Management 57: 239–251
Reichard SH and Hamilton CW (1997) Predicting invasions of woody plants introduced to North America. Conservation Biology 11: 193–203
Reyers B, Fairbanks DHK, van Jaarsveld AS and Thompson M (2001) South African vegetation priority conservation areas: a coarse-filter approach. Diversity and Distributions 7: 79–95
Richardson DM (1998) Forestry trees as invasive aliens. Conservation Biology 12: 18–26
Richardson DM and Higgins SI (1998) Pines as invaders in the southern hemisphere. In: Richardson DM (ed) Ecology and Biogeography of Pinus, pp 450–473. Cambridge University Press, Cambridge
Richardson DM, Macdonald IAW and Cowling RM (1992) Plants and animal invasions. In: Cowling RM (ed) The Ecology of Fynbos: Nutrients, Fire and Biodiversity, pp 271–308. Cape Town, Oxford University Press
Richardson DM, Macdonald IAW, Hoffmann JH and Henderson L (1997) Alien plant invasions. In: Cowling RM, Richardson DM and Pierce SM (eds) Vegetation of southern Africa, pp 535–570. Cambridge University Press, Cambridge
Richardson DM, Pysek P, Rejmánek M, Barbour MG, Panetta DF and West CJ (2000) Naturalization and invasion of alien plants – concepts and definitions. Diversity and Distributions 6: 93–107
Richardson DM, Cambray JA, Chapman RA, Dean WRJ, Griffiths CL, Le Maitre DC, Newton DJ and Winstanley T (in press) Vectors and pathways of biological invasions in South Africa – past, present and future. In: Ruiz GM and Carlton JT (eds) Bioinvasions: Pathways, Vectors and Management Strategies. Island Press, Washington, DC
Rouget M, Richardson DM, Milton SJM and Polakow D (2001) Predicting the dynamics of four invasive Pinus species in a fragmented semi-arid shrubland in South Africa. Plant Ecology 152: 79–92
Rouget M, Richardson DM, Cowling RM, Lloyd JW and Lombard AT (in press) Current patterns of habitat transformation and future threats to biodiversity in terrestrial ecosystems of the Cape Floristic Region, South Africa. Biological Conservation
Schulze RE, Maharaj M, Lynch SD, Howe BJ and Melvil-Thomson B (1997) South African atlas of agrohydrology and climatology. Water Research Commission, Pretoria
Tucker KC and Richardson DM (1995) An expert system for screen-ing potentially invasive alien plants in South African fynbos. Journal of Environmental Management 44: 309–338
Underhill LG (1990) The coefficient of variation biplot. Journal of Classification 7: 241–256
Van Wilgen BW, Bond WJ and Richardson DM (1992) Ecosystem management. In: Cowling RM (ed) The Ecology of Fynbos: Nutrients, Fire and Biodiversity, pp 345–371. Oxford University Press, Cape Town
Van Wilgen BW, Richardson DM, Le Maitre DC, Marais C and Magadlela D (2001) The economic consequences of alien plant invasions: examples of impacts and approaches for sustainable management in South Africa. Environment, Development and Sustainability 3: 145–168
Vayssieres MP, Plant RE and Allen-Diaz BH (2000) Classification trees: an alternative non-parametric approach for predicting species distributions. Journal of Vegetation Science 11: 679–694
Versfeld DB, Le Maitre DC and Chapman RA (1998) Alien invading plants and water resources in South Africa: a preliminary assessment. Water Research Council, Pretoria
Woodward FI (1987) Climate and Plant Distribution. Cambridge University Press, Cambridge
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Rouget, M., Richardson, D.M., Nel, J.L. et al. Commercially Important Trees as Invasive Aliens – Towards Spatially Explicit Risk Assessment at a National Scale. Biological Invasions 4, 397–412 (2002). https://doi.org/10.1023/A:1023611713339
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DOI: https://doi.org/10.1023/A:1023611713339