1 Délégation à la Recherche, Government of French Polynesia, B.P. 20981 Papeete, Tahiti. jean-yves.meyer@recherche.gov.pf PACIFIC CONSERVATION BIOLOGY Vol. 20(2): 146–164. Surrey Beatty & Sons, Sydney. 2014. Critical issues and new challenges for research and management of invasive plants in the Pacific Islands JEAN-YVES MEYER 1 Invasive alien species are recognized as a major threat to island biodiversity and ecosystem functions worldwide, with well-documented, detrimental impacts on the native biota of Oceania. Despite their high number and rapid increase in the Pacific Islands, invasive alien plants (IAP) have received less attention by researchers, managers, and the general public compared to invasive animals (e.g., predatory mammals). Indeed, although lists of IAP in natural and agro- ecosystems have been set up in most island countries and territories, their ecological and socio-economical impacts are still not well documented and/or popularized. Very few IAP eradication successes have been reported, and post- control monitoring and cost-benefit analysis are often missing. Moreover, most of the published studies have been conducted in the Hawaiian and the Galápagos islands. This essay is a call for more research and management efforts on IAP in Oceania, especially in the small tropical Pacific Islands. Focal areas should not only include species bio- ecology, control strategies and methods and prioritization systems (including risk assessments), but also better understanding of island ecosystems functioning (e.g. forest dynamics and resilience), with the integration of past and present anthropogenic and natural disturbances. The importance of “novel” ecosystems, where natural habitats have been partially or totally modified by humans, and the potential effects of climate change on terrestrial ecosystems should be addressed, and new conservation and management strategies defined in the Pacific Islands, in order to try to halt biodiversity erosion in highly vulnerable island ecosystems. Key words: globalization, invasive alien plants, novel ecosystems, Pacific Islands, prioritization, resilience, restoration INTRODUCTION DUE to their geographic isolation which restricts gene flow among populations, islands are often celebrated as natural laboratories for evolution (e.g., Carlquist 1974; Grant 1998), favoured sites for biogeographical and ecological studies (e.g., Vitousek et al. 1995; Whittaker and Fernandez-Palacios 2007), and recognized as “biodiversity hotspots” (Myers et al. 2000). Islands are also preferential areas to document the global biotic homogenization phenomenon through introduction of non-native species (McKinney and Lockwood 1999; Olden 2006; Castro and Jaksic 2008). Indeed, the number of introduced species in the Pacific Islands is now equalling or exceeding the number of native and endemic species in many islands or archipelagos (Table 1), and is dramatically increasing with time and with recent species inventories. High vulnerability of island ecosystems to biological invasions is attributed to the impoverishment of the native biota (taxonomic disharmony, lack of certain functional groups), evolution in long isolation from outside influences (Loope and Mueller-Dombois 1989; Keppel et al. 2014), competitive advantages of introduced species under particular environmental conditions (Daehler 2003), and by the fact that most introduced species have been introduced without their natural enemies (DeWalt et al. 2004). Invasion by alien (or non-native, exotic) plant and animal species is indisputably recognized as one of the major drivers of change in island ecosystems worldwide (Vitousek et al. 1996; MEA 2005; Ricciardi 2006) and a serious threat to island native biodiversity (IUCN/SSC/ISSG 2000; Reaser et al. 2007). In the Pacific Islands, introduced predatory animal invaders (e.g., cats, Table 1. Comparison between native and alien flora (flowering plants and ferns) in selected Pacific tropical islands (by size of terrestrial area) and number of naturalized and invasive alien plants (including dominant or major IAP). Native flora Alien flora Naturalized Invasive Island or (number of (number of alien plant alien plant Dominant island group Area (km²) indigenous species) introduced species) species species IAP New Caledonia 19 060 3 261 a 2 008 b 597 b 97 c 67 b Fiji 18 270 1 622 d 977 d 461 d 107 e 30 f Hawai’i 16 880 1 138 g 8 134 h 1 104 i 469 i 86 j Galápagos 7 900 550 k 870 l 229 l 109 l 22 l French Polynesia 3 519 885 m > 1 700 n 593 n - 57 n Cook Is. 238 296 o 997 o 333 o 76 p 12 q Rapa Nui (Easter Island) 166 48 r 370 s 180 s - 36 s Wallis et Futuna 142 351 t 338 u 151 u - 18 u a Jaffré et al. 2004, b Meyer et al. 2010, c Hequet et al. 2009, d Brownlie 1977 and Smith 1996, e GISD, f Meyer 2000, g Wagner et al. 1999, h Staples and Herbst 2005, i Staples and Cowie 2001, j Smith 1985, k Mauchamp 1997, Trueman et al. 2010, m Florence et al. 2007, n Fourdrigniez and Meyer 2008, o McCormack 2007, p Space and Flynn 2002, q Meyer 2004, r Dubois et al. 2013, s Meyer 2008, t Morat et al., u Meyer et al. 2010