A strategy for Galapagos weeds A. Tye, M. C. Soria, and M. R. Gardener Charles Darwin Research Station, Galapagos. Postal address: CDRS, AP 17-01-3891, Quito, Ecuador. E-mail: [email protected] Abstract Galapagos has a native vascular flora of some 500 species, 60 more species that are doubtfully native, and more than 600 introduced species. Introduced species are the most serious problem facing the native biota. The worst invasive plants are trees and other woody species, vines and grasses, and most of them were introduced deliberately. Many have invaded the Galapagos National Park and are also invasive in agricultural zones. A strategy for tackling the weeds problem includes prevention, control, eradication and restoration, the research required to develop and prioritise these management actions, and development of a legal framework for their implementation. Given limited resources for control, a risk assessment system for prioritising problem species and key sites is essential and is being developed. It will evaluate both species that are already present, and proposed introductions. A quarantine system for Galapagos has been designed and implementation commenced. Quarantine is essential if the balance between introduction and eradi- cation is to be tipped towards the latter. Research includes investigations of the ecology and distribution of introduced plants, to determine factors (such as reproduction and dispersal rates and longevity of plants and their soil seedbanks) essential for the design of successful management programmes. Research on control techniques is also essential, since many Galapagos invasives are useful species that have not been subject to control elsewhere. Restoration research is beginning, focussing on methods of control combined with active restoration, such as seeding with native species. Invasive plants have only recently been widely recognised as high priority in Galapagos, and the first projects investi- gating the ecology of serious weeds are now yielding results. Control trials are leading to the development and adoption of effective field methods. Attempts have begun to eradicate species with still-small populations, but which are known as invasive elsewhere. A pilot project is also beginning, to assess the feasibility of eradicating a well-established inva- sive tree species. These measures, aside from their scientific and conservation value, also act as confidence builders, demonstrating to the public and land managers both the dangers of introduced species and the possibilities for their control and eradication. Resumen Galápagos cuenta con una flora vascular nativa de algunas 500 especies, más 60 especies que son dudosamente nativas y más de 600 especies introducidas adicionales. Los organismos introducidos constituyen el problema más grave que enfrenta la biota nativa. Las peores plantas invasoras son árboles y otras especies leñosas, trepadoras y pastos, y la mayoría de las especies que están causando o podrían causar problemas fueron introducidas a propósito. Muchas de estas especies han invadido el Parque Nacional Galápagos, y son igualmente agresivas en las zonas agrícolas. Una estrategia para enfrentar este problema incluye prevención, control, erradicación y restauración, las investigaciones necesarias para desarrollar y priorizar estas acciones de manejo, y el desarrollo de un marco legal para su implementación. El primer paso es desarrollar medidas para priorizar los problemas, tomando en cuenta los recursos limitados para el control. Un sistema de evaluación de riesgos se está desarrollando, para evaluar tanto especies que ya se dan en las islas y para introducciones propuestas. Este último forma parte de la prevención: un sistema de cuarentena para Galápagos ha sido diseñado, y su implementación iniciado. La cuarentena puede reducir pero jamás parar las introducciones, pero es necesario para cambiar el equilibrio entre la introducción y la erradicación. El control y erradicación tienen dos componentes: investigación y manejo. Las investigaciones de la ecología y distribución de las plantas introducidas nos permiten determinar los factores necesarios para diseñar programas de control y erradicación que sean exitosos, tales como tasas de reproducción y dispersión, longevidad de plantas y semillas etc. La investigación para desarrollar nuevos métodos de control también se necesita, por lo que muchas especies invasivas en Galápagos son especies útiles y no han sido sujetos del control en otras partes. La investigación para la restauración ya empieza, con su enfoque en combinar acciones de restauración positivos en combinación con el control, tales como siembra de especies nativas. El programa de plantas introducidas en Galápagos esta creciendo rápidamente, por lo que las plantas invasoras han sido solo recién ampliamente reconocidas como de alta prioridad. Los primeros proyectos para investigar la ecología de las malezas más graves ya son produciendo resultados. Los ensayos de control llevan al desarrollo y uso de métodos de campo eficientes. Se han iniciado intentos para erradicar especies aun representadas únicamente por pequeñas poblaciones, pero las cuales están conocidas como invasoras graves en otros lugares. También ha comenzado un proyecto piloto para evaluar la factibilidad de erradicar un árbol invasora bien establecido. Estas medidas, aparte de su valor científico y para la conservación, además pueden aumentar la confianza y cambiar la opinión general sobre el peligro de las especies introducidas y la factibilidad de su control. Keywords Environmental weeds; strategic planning; Galapagos; prevention; control; eradication; restoration; research; islands. Pages 336-341 In Veitch, C. R. and Clout, M. N. (eds.). Turning the tide: the eradication of invasive species. IUCN SSC Invasive Species Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK. Tye et al: A strategy for Galapagos weeds THE PROBLEM species are found in the more humid, higher altitudes of the four larger inhabited islands, and the settled areas are Galapagos is an isolated oceanic archipelago of volcanic the major source of invasion into the Galapagos National islands lying 1000 km west of Ecuador, straddling the equa- Park. tor (Fig. 1). The date of discovery of the archipelago is The Galapagos islands support a native vascular flora of usually recognised as 1535. The islands were uninhabited about 500 species, with an additional 60 doubtfully native at that time, and no evidence proving earlier human pres- species, principally pantropical ruderals, which may have ence has been found (Slevin 1959; Hickman 1985). The arrived naturally or may have been introduced by the ear- first visitors after discovery were mainly buccaneers, pass- liest human visitors to the islands. In this paper, “intro- ing sailors, whalers and sealers (Hickman 1985). Settle- duced” and “alien” are used interchangeably to mean in- ment began on Floreana Island in the early 1800s, but Santa troduced deliberately or accidentally due to the actions of Cruz Island was only settled as late as the 1920s (Slevin man. “Naturalised” means reproducing in natural or semi- 1959; Schofield 1989). natural habitat without the further assistance of man (be- The pirates and whalers deliberately or accidentally intro- yond habitat disturbance). “Invasive” means invading natu- duced some alien species, including goats, rats and, prob- ral (undisturbed) habitats. “Weed” means a naturalised ably, insects and plants. Even before permanent settlement, species. Floreana had large areas dominated by introduced plants Porter (1822) mentioned the first alien species (pumpkins such as Citrus spp. (Slevin 1959; Hamann 1984). The rap- Cucurbita sp. and potatoes Solanum tuberosum), which idly increasing settled population, growing at 8% per year were introduced about 1807. Numbers increased slowly in the 1990s through both immigration and births, has been until the 1960s, although true numbers are unknown, since accompanied by an enormous number of new introduc- earlier references (especially Wiggins and Porter 1971; tions of alien plants and animals (Mauchamp 1997). Al- Porter 1984) took into account only naturalised species. though agricultural development began at the time of set- The list continued to increase, reaching 438 in 1995 tlement, the process has been uneven, leading to different (Mauchamp 1997) and over 600 by November 2000 (Da- rates of introduction of alien species. Floreana has the long- tabase of the Galapagos Flora, Charles Darwin Research est history of the presence of a large introduced flora, while Station). The minimum detection rate has thus been more agriculture on Santa Cruz was minimal until about 1960 than 10 per year in the last 30 years (Fig. 2), and more (Moll 1990). than 120 during 2000. However, the recent apparent rate The Galapagos National Park forms 96.4% of the land of increase is obviously affected by increased interest in area of Galapagos; inhabited areas (urban and agricultural recent years in the introduction process, as well as increased zones, military bases and airports) make up the rest. Alien sampling effort and individual research projects, and the plants that have escaped from cultivation are mostly found inclusion of cultivated, non-naturalised species in more on the five inhabited islands, especially the four with agri- recent lists (Tye 2001b). cultural and urban zones (Floreana, Isabela, San Cristóbal, The principal threat to the terrestrial biota of Galapagos is Santa Cruz: Fig. 1); the fifth,