356 Introduced Plants, Negative Effects of in any risk analysis However, stochastic processes (e.g., change in land use), complexity of multiple interactions in natural ecosystems (e.g., presence of seed dispersers), and the increasing prevalence of introduced plant species lacking a weed history elsewhere collectively contribute to making weed impact prediction a major challenge Methods for evaluating comparative benefits (e.g., food source for humans and native animals, erosion control) and costs (e.g., loss of crop production, reduced native biodiversity) of introduced invasive weed species are only slowly emerging due to difficulties in assessing qualitative and quantitative elements of these categories in simple economic terms Acknowledgments This article benefited from comments from Stephen Brown, Garry Cook, Curt Daehler, Penny Edwards, Barrie Forrest, Peter Grubb, Simon Fowler, Mic Julien, Richard Mack, Wendy Nelson, Trevor Partridge, Ian Payton, Dave Richardson, Alan Rose, Leslie Seiger, and Peter Williams See also: Fires, Ecological Effects of Introduced Species, Impacts and Distribution of Migration Plant Biodiversity, Overview Plant Invasions References Brock JH, Wade P, Pysek P, and Green D (eds.) (1997) Plant Invasions: Studies from North America and Europe Leiden: Backhuys Cowling RM, Richardson DM, and Pierce SM (eds.) (1997) Vegetation of Southern Africa Cambridge: Cambridge University Press Cronk QCB and Fuller JL (1995) Plant Invaders: The Threat to Natural Ecosystems London: Chapman and Hall Groves RH, Shepherd RCH, and Richardson RG (eds.) (1995, 1998) The Biology of Australian Weeds RG Frankton and FJ Richardson Luken JO and Thieret JW (eds.) (1997) Assessment and Management of Plant Invasions New York: Springer Pysek P, Prach K, Rejmanek M, and Wade M (eds.) (1995) Plant Invasions: General Aspects and Special Problems Amsterdam: SPB Academic Publishing Richardson DM (ed.) (1998) Ecology and Biogeography of Pinus Cambridge: Cambridge University Press Simberloff D, Schmitz DC, and Brown TC (eds.) (1997) Strangers in Paradise: Impact and Management of Non-Indigenous Species in Florida Washington, D.C: Island Press Starfinger U, Edwards K, Kowarik I, and Williamson M (eds.) (1998) Plant Invasions: Ecological Mechanisms and Human Responses Leiden: Backhuys Vitousek PM, D’Antonio CM, Loope LL, Rejmanek M, and Westbrooks R (1997) Introduced species: A significant component of human-caused global change New Zealand Journal of Ecology 21: 1–16 Walker DI and Kendrick GA (1998) Threats to macroalgal diversity: Marine habitat destruction and fragmentation, pollution and introduced species Botanica Marina 41: 105–112