The Importance of Weeds in Plant Biosecurity
Weeds constitute a unique biosecurity challenge. We describe the causes of plant invasion and pathways for introduction. The broad and diverse impacts of weeds are described as well as what makes them different from other types of pests for risk assessmen
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The Importance of Weeds in Plant Biosecurity Andy W. Sheppard, Anthony L. Koop, and Richard Hill
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Introduction
Biosecurity represents the array of research and regulatory strategies used to assess and manage the risk of incursion and impact of harmful organisms (Meyerson and Reaser 2002b), including weeds and harmful invasive pest plants (IPPC 2009). Weeds have a broad definition ranging from plant species with very harmful impacts (Esler 1988; IPPC 2009) to species with simple undesirable qualities such as growing where they are not wanted. The term “weed” is generally well understood, but usage in relation to specific impacts may be subjective. The concept of an invasive plant species is more recent and more scientific in definition, but definitions vary. From an ecological perspective, an invasive plant is an alien species that naturalises, spreads and persists (colonizes). In an applied and regulatory context, this definition also implies impacts, through attaining densities that suppress resident species or biodiversity, and/or disrupt ecosystem function and services. The applied terms of weed and invasive plant represent slightly different concepts (Rejma´nek 1994). In this chapter we use the terms interchangeably as they both relate to the IPPC concept of a pest plant (IPPC 2009). Weeds are categorised by National Plant Protection Organisations (NAPPO) and departments under legislation and regulations based on perceived potential to cause harm, current distribution, abundance and impacts. Specific categories invoke different regulatory actions. The term “noxious weed” is often used for weeds that require a regulatory action, but the precise definition varies among regulatory agencies. A.W. Sheppard (*) CSIRO Ecosystem Sciences, GPO Box 1700, Canberra, ACT 2601, Australia e-mail: [email protected] A.L. Koop USDA-APHIS-PPQ-CPHST, 1730 Varsity Drive, Suite 300, Raleigh, NC 27606-5202, USA R. Hill Richard Hill & Associates, Private Bag 4704, Christchurch, New Zealand G. Gordh and S. McKirdy (eds.), The Handbook of Plant Biosecurity, DOI 10.1007/978-94-007-7365-3_20, © CSIRO 2014
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Weeds are often the most costly biosecurity threats for realised social, economic, and environmental impacts (Pimentel et al. 2000; Hulme, Chap. 1). Estimates suggest that weeds cause direct and indirect losses of about $20–34 billion per year in the USA (Gunn and Ritchie 1988; Pimentel et al. 2000; Westbrooks 1998). In Australia, weeds result in agroforestry losses of $3.5–4.5 billion per year, and possibly more (Sinden et al. 2004). In Canada, weeds in 58 crops result in a loss of about $1 billion annually (Swanton et al. 1993). These costs are likely to be underestimated because they usually ignore environmental and social impacts. Because of the long-term impacts and costs associated with pests and invasive species, incursion prevention is often the first priority in a biosecurity strategy (Meyerson and Reaser 2002a; Pimentel et al. 2000; White and Schwarz 1998). The biosecurity threat po
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