Cronk, Q. C. B., and J. L. Fuller. 2001. Plant Invaders: the Threat to Natural Ecosystems. Earthscan Publications, London, UK.

Doria Gordon

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Published: October 24, 2001

Invasive non-native plants pose an increasing threat to the composition and structure of natural communities across the globe. A better understanding of the causes, patterns, predictability, consequences, and management options associated with this threat to biodiversity is necessary to guide managers, policy makers, researchers, and the general public. Plant Invaders: the Threat to Natural Ecosystems (Cronk and Fuller 2001) is part of the People and Plants series, a collaboration between the World Wide Fund for Nature; UNESCO; The Royal Botanic Gardens, Kew; and the Darwin Initiative for the Survival of Species. The goal of the series is to provide background for botanists and others involved in applied conservation efforts. The manual presents a detailed overview of invasion biology and history as well as methods for establishing control efforts. Generalizations about invaders are derived from the literature and a suite of species that have affected several locations, most notably, South Africa, Australasia, Mauritius, and Hawaii. Species invasive in Europe, North America, and elsewhere are also included. The authors synthesize much of the theory and ecology of invasive plants succinctly and clearly for nontechnical readers. In addition, they include a good mix of theoretical and applied information.

The manual is organized into five chapters. The first briefly addresses definitions, the effects of invaders on natural systems and processes, and patterns of invasion by landform, climate, and biome. The second chapter opens with a review of the invasion process, a history of plant translocation, and the biological characteristics of invasive species; the remainder focuses on factors that might make it possible to predict invasiveness, including taxonomy, geographic patterns, and theoretical considerations. The third chapter introduces the more applied issues of education, existing and recommended legislation or procedures to prevent the introduction of invaders, appropriate record keeping, and control approaches. The last two chapters focus on invasive species. The fourth presents fairly detailed case studies of 17 species in 14 families, and the fifth provides more abbreviated (and sometimes minimal) information on roughly 200 species in 67 families. No rationale is offered as to why particular species were included, other than a desire for species with a variety of life histories and growth forms and the greater availability of information on the species covered in the case studies. However, there are certainly sufficient data on others that were not selected for the fourth chapter, such as downy chess (Bromus tectorum), kudzu (Pueraria lobata), and Brazilian pepper-tree (Schinus terebinthifolius).

Some aspects of the discussion on invaders in the first two chapters could have been expanded. For example, the section on patterns of geographical distribution of invasion does warn readers that less information is available for areas such as South America, north and central Asia, and India. However, the effects on distribution of differential selection and the movement of species by humans received no attention other than a discussion of the activities taking place in botanical gardens. In addition, the authors devote little time to genetics or the role of repeated introductions of species in producing more aggressively invasive genotypes. Similarly, although potential nontarget impacts of biocontrol agents on native plants are examined, their possible effects on arthropods or other organisms are not considered.

Cronk and Fuller supplement the literature review on prediction by making generalizations about invader characteristics from the suite of species in the last two chapters. However, deriving patterns of invasiveness from this large but arbitrarily selected group could be misleading. One of the most valuable contributions of this substantial list is that it provides an early warning to natural area managers about species that are likely to become invasive in new areas. Some discussion of this application, including the identification of general areas that might be vulnerable to invasion by the species listed, would have been a useful addition.

This manual may be somewhat less accessible to nontechnical readers because of its exclusive use of Latin binomials rather than common names in the text and examples. Common names are provided in the species lists, but cross-referencing from the examples to the case studies or to the longer listing is inconvenient. In addition, both common names and trade or product names of herbicides are used inconsistently. Because product names vary with manufacturer and location, the consistent use of common names (e.g., triclopyr rather than Garlon) would have been more informative. The costs cited for control efforts are difficult to interpret because they are given in the currency of the country involved (e.g., South African Rand or Mauritian Rs). Conversion to a common currency at a specified date would have been helpful. Finally, after a nice section of definitions early in the manual, the apparently synonymous use of "weed" and "invasive" is confusing.

Invasive species are now receiving so much attention from the research and management communities that the information available at any given time quickly becomes outdated. I was puzzled by the lack of citations after 1993 and by the fact that there were no data for some species with which I am familiar, until I realized that this manual was first published in 1995 by Chapman & Hall. Although the synthesis on the ecology of invaders is still generally a good review of the current understanding, some concepts and information are missing. For example, no mention is made of the threat posed by Lantana camera cultivars to endemic lantana species in Florida through hybridization, the biocontrol agents that have been released to control the bottle-brush tree (Melaleuca quinquenervia), or the documented negative effects of the cactus moth (Cactoblastis catorum), a successful biocontrol agent in some places, on native opuntia cactus. In addition, several of the species included in the fourth and fifth chapters have now been documented in areas that are not included on the list, e.g., strawberry guava (Psidium cattleianum) in Florida and giant salvinia (Salvinia molesta) in the southern United States.

Furthermore, because managers are one of the intended audiences for this manual, it is important to include current information on herbicide application and prohibition. Many of the herbicides mentioned (e.g., Dalapon, Tebuthiuron, Bromacil) are not available in all locations and are labeled for different uses in different countries. Although an appendix warns the reader that 2,4,5-T is highly toxic and banned in several countries, the last two chapters describe it as an effective herbicide for controlling several individual species. Thus, a strong caveat about the examples provided should have been included for less experienced readers.

Overall, this manual is a useful introduction to the important topic of invasive species. Much of the literature has been well synthesized, and there is valuable information on many individual species. Researchers and managers familiar with this issue may be most interested in the list of species, which provides a useful warning about potential invaders in new sites. Technical and nontechnical readers new to the field will find the manual to be informative. However, the latter also need to be aware that more recent information is available, particularly on control efforts.

Cronk, Q. C. B., and J. L. Fuller. 2001. Plant Invaders: the Threat to Natural Ecosystems. Earthscan Publications, London, UK. xiv + 241pp., paperback, U.S. $39.95. ISBN 1 85383 741 4.

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Cronk, Q. C. B., and J. L. Fuller. 2001. Plant invaders: the threat to natural ecosystems. Earthscan Publications, London, UK.