The successful eradication of two blackberry ...

The successful eradication of two blackberry species Rubus megalococcus and R. adenotrichos (Rosaceae) from Santa Cruz Island, Galapagos, Ecuador C. E. BUDDENHAGEN' Eradication programmes were initiated against infestations of the introduced blackberry species R. adenotrichos and R. megaloccocus on Santa Cruz Island, Galapagos, Ecuador in 1999 and 2000 respectively. The species were judged to be likely invaders even though neither produced viable seeds in Galapagos. Prior to eradication in 2003 these infestations occupied an area of less than a quarter hectare. I estimate the time and dollar cost of eradication of R. adenotrichos and R. megaloccocus to be US$11,322 US dollars/1 738 hours. More than half of these costs were sustained in extensive systematic searches of 330 ha surrounding known infestations. Herbicide accounted for less than 1% of total costs. Control was undertaken using the herbicides glyphosate, and a combination of metsulfuron methyl and picloram. I recommend using teams of workers dedicated to eradicating known or potentially invasive species early in the invasion process or prior to establishment in Galapagos. Abbreviations: Global Environment Facility (GEF), United Nations Development Program (UNDP), Charles Darwin Research Station (CDRS), active ingredient (ai). Key words: Eradication success, Santa Cruz, Galapagos, Rubus adenotrichos, Rubus megaloccocus, Invasive plants, Weeds.

INTRODUCTION IN Galapagos, and elsewhere, invasive plants are permanently altering the ecosystems into which they invade and having a negative impact on them; island ecosystems may be particularly vulnerable (Loope el al. 1988; Vitousek et al. 1997; Jager 1999; Lonsdale 1999; Meyers 2004). Approximately 700 plant taxa are known to have been introduced to Galapagos by humans while 550 are native. Of the introduced taxa, at least 230 have naturalized, and at least 100 of these have established in intact native vegetation. Of these, approximately 40 are recognized as "transformers" in native vegetation, and the other 60 taxa being "integrators" (sensu. Richardson et al. 2000) or with limited distributions that have not yet had demonstrable impacts (Tye 2000; Charles Darwin Research Station (CDRS) Galapagos Flora Database 2005; S. Henderson, unpubl. data). A number of species that are present in Galapagos but not yet naturalized or widespread are expected to become a problem in the future as they establish and spread and some may be eradicable from individual islands (Tye 2000; Soria et al. 2001; Tye et al. 2001). Even without considering future introductions naturalization of species currently found in cultivation is expected. Continuous naturalization of this type is occurring elsewhere in the Pacific e.g., Hawaii (Wester 1985), Australia (Virtue et al. 2004), New Zealand (Williams et al. 2000), and in the eastern Pacific (Meyer 2004). Biodiversity protection in the Galapagos requires us to address the threat posed by

harmful invasive plants. A total control plan for invasive species management is required under the Special Law for Galapagos (1998). A draft exists but has yet to be approved by the Institute Nacional de Galapagos (INGALA). If fully implemented this plan could form the basis for future invasive species management in Galapagos. A strategic approach to the management of invasive plants in Galapagos was discussed by Tye et al. (2001). An effective system for the management of invasive species should contain the following components: prevention, rapid response, eradication and control (Species Survival Commission 2001). These various components are to varying degrees already in place in the Galapagos. For example, a system of quarantine was initiated in 1998 (Zapata et al. 2000); various programmes of control and eradication have been implemented by the Galapagos National Park (mainly in response to invasive animals). Where prevention has failed or has been historically non-existent, and potentially invasive species have been introduced, eradication is the best strategy available (Species Survival Commission 2000). As a principal eradication is particularly desirable on islands, and is more highly regarded than control because of its oneoff costs and the ability to prevent reintroductions (Species Survival Commission 2000; Mack and Lonsdale 2001; Meyer 2004). Eradication of invasive species from individual islands must be initiated at an early stage of the plant's establishment in order to ensure success and be cost effective (Panetta 1999; Panetta and

'Botany Department, Charles Darwin Research Station, Santa Cruz, Galapagos. Ecuador. Mail: Fund:Kith-1 Charles Darwin, Casilla 17-01-3891, Quito, Ecuador. Email: [email protected] PACIFIC CONSERVATION BIOLOGY Vol. 12: 272-78. Surrey Beatty & sons, Sydney. 20M.

BUDDENHAGEN: GALAPAGOS PLANT ERADICATIONS

Timmins 2004). Despite billions of dollars being spent on the management of invasive plants worldwide (Pimentel et al. 2001; Pimentel et al. 2004) there are probably less than 15 examples of successful eradications of plants and few of those with detailed accounts of the costs (Rejmanek and Pitcairn 2001; Mack and Lonsdale 2002; Simberloff 2003; Woldenthorp et al. 2004). At least six species have been identified as eradicated from small atolls in the North West Hawaiian Islands, most from Midway Atoll, though these accounts are not published and I was unable to obtain information about costs, methods or the level of certainty (Forest Starr, pers. comm.). Complete eradication (where feasible) should be attempted wherever there is a suspicion that a species could become invasive, since prediction of invasibility is problematic (Lonsdale and Smith 2000). But, actual eradication of plants is particularly difficult, largely because of the difficulty of finding and controlling every last individual of a population, and plants can survive as seeds in the soil where they are effectively invisible to managers and impossible to control (Simberloff 2003; Panetta 2004; Panetta and Timmins 2004). One of the aims of the Global Environment Facility's (GEF) $18 million multi-institutional, six year Project "Control of Invasive Species in the Galapagos Archipelago" was to demonstrate eradication's value within an overall strategic approach to invasive species management through a research by management approach. In this context, programmes of experimental plant eradications were initiated by the Charles Darwin Research Station's Botany Department in 1998 while planning the GEF project (Soria et al. 2001). These are still in progress and were largely funded by the GEF project which started in 2001. These programmes aim to describe the conditions in which eradication is desirable and feasible. This is achieved by identifying priority species and attempting species eradications from individual islands over a range of spatial scales, and by maintaining detailed documentation of the changing status of the target species over time, the methods used and effort invested. The eradications of the plants described in this article are outcomes of this work. Prior to that Pueraria phaseoloides was successfully eradicated (Soria et al. 2001). Species that are included in the current research by management programme for eradication include Rubus ulmifolius, Rubus

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METHODS Study site

Ninety-six per cent of the land area of the 123 islands that make up the Galapagos (Snell et al. 1996) is protected within the Galapagos National Park (Ecuador) and is part of the World Heritage estate. The human population occurs within unprotected designated urban and agricultural zones on four of the six largest islands: Isabela, Floreana, San Cristobal and Santa Cruz. The eradication of Rubus adenotrichos and Rubus megaloccocus occurred within the 10 000 ha agricultural zone on Santa Cruz Island the second largest island (98 555 ha) representing about 12% of the total land area of Galapagos (Fig. 1). The process of selecting invasive plants for eradication

glaucus, Citharexylum gentryi, Aristilochia odoratissima, Lantana montevidensis, Leucaena leucacephela, Acacia nilotica, Cryptostegia grandiflora and Casuarina equisitifolia.

The following steps are used to select species far eradication: (a) identify species with limited distribution following inventories of introduced species; (b) assess their potential to become invasive using criteria similar to those of Pheloung et al. (1999); (c) examine the plant's invasiveness in Galapagos; (d) confirm distribution, abundance and our ability to control plants with available methods; (e) review the plant's biological characters that may affect the feasibility of eradication; (f) determine the feasibility of eradication in terms of the likelihood of success and costs; (g) attempt eradication if it is judged feasible with available resources; (h) monitor the changing status of the target species and the effort invested during the eradication; (i) document the results to improve future predictions and review eradication feasibility. Rubus megalococcus and Rubus adenotrichos were determined to be potentially invasive and feasible to eradicate from Santa Cruz Island and represent the most feasible eradications attempted in the research by management eradication programme run between 1998 and the present (2005). In relation to the selection of potentially invasive species, step (b), we should not be shy about selecting a species for which we have limited evidence of invasiveness. Waiting to see if something will become invasive is not a good strategy while eradication is easily achievable (Panetta 1999; Mack and Lonsdale 2001). The blackberries considered here have not yet been shown to be particularly invasive either in Galapagos or elsewhere but were judged to be likely invaders (see below).

In this paper I document the successful eradication of two species of blackberry (Rubus megalococcus and Rubus adenotrichos) from Santa Cruz Island in Galapagos.

Typically the extent of an infestation is not perfectly understood when a species is first selected for eradication. The field confirmation step (d) often leads to the discovery of new

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Agricultural. zone bound.

Fig. 1. The location on Santa Cruz Island of the eradicated infestations of Rubus megaloccocus (cross) and Rubus adenotrichos (circles) and the area surrounding them that was searched (shaded areas) to confirm their distributions. The location of Santa Cruz Island (dark grey island) and Galapagos Islands are indicated on the right.

patches of the target species as the field crew searches for and treats plants. This was the case with Rubus adenotrichos (see below). The field crew can also make discoveries through input from the public. Our ability to find plants prior to seed set is determined by the plant's time to maturity, growth form and conspicuousness. All areas in which the plant is likely to occur need to be searched in order to confirm with certainty that all plants have been found and treated. The search method we use is quite effective for large scale searches. It involves using a team of four with GPS units following a grid of spatially equidistant points generated in ArcView® to systematically search large areas. Any less than this number of searchers and progress is too slow, and they are likely to get demoralized. Searchers walk along lines between points with a spacing of 10 to 20 m giving an effective search width of 5 to 10 m either side. The spacing between lines is varied depending on the visibility of the target species and the type and density of the vegetation in which the search is being made. There is still a chance that plants could be missed in dense vegetation and difficult terrain and plants can often survive treatments. Regular follow-up search and control is necessary in order to mop up any surviving plants. Such searches should be more frequent than the time it takes the target species to germinate, flower and produce seeds. In our case neither blackberry species produced viable seeds, though vegetative regrowth after treatment did occur.

Continuous review of progress toward eradication and tracking the effort involved (steps (h) and (i)) is necessary to ensure success and may lead to a reassessment of the feasibility of eradication. The collection of georeferenced data about the distribution and abundance of the target species is the best way to track progress and demonstrate the success or failure of an eradication programme.

Rubus megaloccocus and R. adenotrichos' potential to be harmful invasive plants The genus Rubus includes roughly 250 species (Mabberley 1997), approximately 79 (30%) of those are known to be an invasive species in at least one country in the world (Randall 2002). As such almost any introduced Rubus species should be treated as a potential invader. In Galapagos, five introduced Rubus species are known so far, of which two are considered invasive: R. niveus and R. glaucus. There are no native Rosaceae in Galapagos.

Rubus megaloccocus When first seen by CDRS staff in August 2000, the infestation of R. megalococcus was dense, tall (1-2 meters) and dominated over a quarter hectare of an area formerly dominated by elephant grass (Pennisetum purpureum). R. megalococcus plants can grow 30 cm in two months (Chris Buddenhagen, pers. obs.), and form dense stands. We found no evidence in the literature that this species has become a problem


elsewhere. The decision to eradicate it was based on its behaviour in Galapagos and the fact that many Rubus species are invasive. Rubus adenotrichos

This species has not yet become invasive on Santa Cruz. Its ability to grow in shade was confirmed by its presence under a canopy of Cedrela odorata trees. R. adenotrichos was also introduced on Isabela Island where it is restricted to a single farm in two infestations, covering 1.2 hectares. On Isabela it formed dense impenetrable thickets with stems reaching 4 m into the canopy of trees, and excluded ail other vegetation including elephant grass. R. adenotrichos is currently subject to a control effort there. There is every reason to expect that it can be successfully eradicated from Isabela too. R. megalococcus and R. adenotrichos have not produced viable seeds in Galapagos, which makes eradication more feasible (Panetta 2004). Although this makes the invasion less rapid, the species could become serious problems in the long term by forming dense stands and competing with surrounding vegetation. There are many examples of invasive species that have spread and become serious problems without producing seeds, e.g., Tradescantia fluminensis in New Zealand and Tibouchina urvilleana in Hawaii (Standish 2001; Staples and Herbst 2005). Like Tradescantia, R. megalococcus reproduces from broken stem fragments and is fairly resistant to herbicide

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control (Fig. 2). It may have spread short distances by stem fragments attached to cows and other animals but plants were never found more than a few meters from the known infestation. Also the introduction of other live material of these species could lead to successful breeding if for some reason the original stock required out-crossing. The decision to eradicate these species was based on their potential invasibility. Efforts to determine the plants full distribution and history of introduction Rubus megaloccus

In Galapagos Rubus megaloccocus has only been collected from Santa Cruz Island. It was found on a farm currently owned by Fabian Salome. The previous owner, Elevación Aida, planted it in 1983 (Felix Burgos, pers. comm.). When controlled in August 2000 it covered an area of a quarter hectare. In 2002 systematic searching of 103 hectares in the vicinity of the only known infestation did not reveal any other infestations. Rubus adenotrichos

This was first collected on Santa Cruz in 1999 Initially it was thought that there was only one infestation on Santa Cruz, however in June 2002 searching revealed another infestation 100 m from the first (Fig. 1). The plants occupied a total area of about 20 m2 divided between two

200

plants didn't die after treatment new

plants

150

100

50

0

17-Nov-01 26-Feb-02 16-Jul-02 24-June-03 12-April-05 11-Sep-01 10-Jan-02 07-May-02 21-Jan-03 3-Feb-04 DATE

Pig. 2. The number of blackberry plants (Rubus megaloccocus) remaining in the only known infestation on Santa Cruz. Plants were treated with 3% glyphosate, except for the last two treatments where 8% glyphosate was used. Plants surviving treatment are also indicated.

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patches. Both infestations occurred on one property between El Carmen and Santa Rosa (current owner Michel Gouanere). He bought the farm in 1995 from Plutarco Mendoza. The plants were planted prior to 1995. An additional 2 000 hectares of the agricultural zone (20% of the total area) has been repeatedly searched between 2001 and 2005 without finding more plants of either species. Control methods and control history

Rubus megalococcus

In August 2000, the only known infestation was controlled by the farmer on whose land the plants were found (treated with picloram and 2,4 D) and follow-up work was carried out by CDRS staff a few weeks after. Surviving and untreated plants were treated with 2% Combo 0 (1 container of product diluted in 10 L water). One container of Combo contains 267 ml soluble concentrate that contains 64 g ai of picloram and 6.67 g of dispersible salt of which 4 g are the active ingredient metsulfuron. In a November 2000 R. megalococcus was "completely dead", but in need of monitoring (M. Gardener, unpubl. report). Monitoring in September 2001 revealed that almost 200 live plants remained in the same area (Fig. 2). It was impossible to tell if plants had been treated or not. Glyphosate at 3% (Roundup®) was tried due to its low cost and achieved a continual decline in the number of plants. However, some plants withstood repeated treatments (Fig. 2). For this reason the concentration was raised to 8% for the last two treatments (Fig. 2). Most surviving plants did not form new leaves between treatments. Due to the small size of the infestation, and dense elephant grass an intensive monitoring method was instigated to find plants and track

the survival of individual plants after control. A single - quadrat 50 m by 50 m was permanently marked using plastic tubes of about 1 m in height, and divided into 25 smaller sub-quadrats of 10 by 10 meters. The plants were counted in each sub-quadrat and marked with a different colour of flagging tape at each monitoring before being treated with herbicide. In subsequent visits we thus determined whether any of the live plants had been treated previously. "New" plants sprouted from underground roots (Fig. 2). As plants did not produce seeds, we were able to wait 3 to 6 months between treatments until plants had grown sufficiently to be easily spotted. Searching was difficult due to the lush, tall (up to 2 meters) elephant grass. Using sub-quadrats ensured that the area was searched thoroughly. Rubus adenotrichos

One small patch of R. adenotrichos was controlled in 1999 with 4% Roundup. In January 2002 searches revealed a second small infestation approximately 100 m from the first. Control was undertaken in both infestations and later in May 2002 using 5% Combo®. This was considered to be more likely to kill the plants, as picloram has residual properties that may control regrowth over weeks or months (Vencill 2002). Subsequent visits did not reveal surviving plants. In July 2002 and later, more widespread searching did not reveal any other infestations. Costs

Estimated costs of the successful eradications are indicated in Tables 1 and 2. Rubus megaloccocus

The initial cost of treatments by the farmer and CDRS staff involved at least three visits. After this initial knockdown of the population

Annual costs and activities Costs are estimated per annum for activities, equipment and overheads involved in the eradication of Rubus of labour were estimated from work carried out by Charles Darwin Research Station staff. Prices for labour, travel and herbicide are based on rates of $650 per month for the salaries of field staff, $1,100 for technical staff, $12 per trip to the highlands, and $30 per litre for herbicide. (US$).

Table 1.

megalococcus. Hours

Item

Details

Year 1 2000

Year 2 2001

Labour

Search and control for $400.00 known plants Reporting results Search for neighbouring infestations $60.00 Trips to site $36.00 Equipment $100.00 28% $166.88 $762.88

Labour Labour Herbicide Travel Misc. Overhead Total

Year 3 2002

Year 4 2003

Year 5 2004

Year 6 2005

Total

Hours

$110.00

$220.00

$110.00

$55.00

$55.00

$950.00

144

$40.00

$40.00 $2,600.00

$40.00

$40.00

$40.00

$200.00 $2,600.00

24 720

$10.00 $48.00

$10.00 $348.00

$5.00 $50.00

$300.00

$25.00

$58.24 $266.24

$901.04 $4,119.04

$57.40 $262.40

$110.60 $505.60

$33.60 $153.60

$85.00 $807.00 $100.00 $1,327.76 $6,069.76

888

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Table 2. Costs are estimated per annum for activities, equipment and overheads involved in the eradication of Rebus adenotrichos. Costs were estimated as in Table 1.

Year 1 1999

Item

Details

Labour

$115.56 Search and control for known plants Reporting results Search for neighbouring infestations $1.00 Trips to site $36.00 $100.00 Equipment $73.24 28% $325.79

Labour Labour Herbicide Travel Misc. Overhead Total

Year 5 2003

Year 4 2002

Year 3 2001

Year 2 2000

Year 6 2004

$231.11 $206.25

$27.50 $2,600.00

$48.00

$348.00

$10.00 $50.00

$13'.44 $61.44

$825.44 $3,773.44

$94.81 $413.42

follow-up control was re-initiated in September 2001 and monitoring and control was undertaken every 2-6 months (Fig. 2). In addition, 100 ha were searched in the vicinity, which accounted for the majority of the costs. Rubus adenotrichos

Three days of control work were required to eradicate the two known infestations on Santa Cruz. For one infestation three site visits led to eradication and for the other infestation two visits were enough. Systematic searching over 230 ha (as indicated in Fig. 1) accounted for the majority of the costs. DISCUSSION

The eradication of these two species of blackberry from Santa Cruz was relatively straightforward because they did not produce fruit and they occupied small areas. The eradication of R. adenotrichos was achieved with less effort as the infestations were smaller and responded better to treatment. R. megalococcus was relatively difficult to kill and required more searching and follow-up. In both cases more than half of the costs were sustained in searching to confirm if more plants were present nearby. Herbicide cost less than 1% of the total. There remains a small possibility that undiscovered R. megalococcus and R. adenotrichos plants exist in other parts of the agricultural zone. However, we have been working in the community for years and local farmers are aware of what we are looking for. Furthermore, more than 2 000 ha or 20% of the agricultural zone has been the focus of intense systematic searching by our field crew. All farms have been visited by botanists doing introduced plant inventories in the past few years. Successful plant eradications are few, and detailed documentation of them even rarer. Any eradication effort should accumulate sufficient evidence to declare success with confidence.

$300.00

$25.00

$84.00 $384.00

$64.75 $296.00

Total

Hours

$346.67

96

$233.75 $2,600.00

34 720

$40.00 $807.00 $100.00 $1,155.68 $5,252.09

B50

Monitoring is necessary for this. The evidence needed to declare success will vary depending on the history of introductions, the distribution, abundance, find-ability and biology of the target species (Panetta and Timmins 2004). Whether the evidence accumulated is sufficient is a matter of judgement, but will depend on these factors. The successful eradication of R. adenotrichos and R. megalococcus was accepted through good record keeping during the search and control effort, by tracking the locations of infestations and the costs and methods, and by investigations into the biology of the target plants e.g., seed productivity. The bulk of the cost was in searching for plants in extensive delimiting surveys. ACKNOWLEDGEMENTS

The following current and former staff in the Botany Department of the Charles Darwin Research Station have contributed to the project: Dr. Mark Gardener, Miss Monica Soria, Mr. Jose Luis Escandón, Mr. Patricio Yanez, and in particular the field crew Mr. Manuel Orellana, Mr. Kléver Roman, Mr. Gilberth Valle, Mr. Manuel Montalván, Mr. Felix Burgos, Mr. Luis Gil. Dr. Alan Tye provided detailed comments on the manuscript. The bulk of this work was accomplished with the support of Project ECU/ 00/G31 "Control of Invasive Species in the Galapagos Archipelago", a donation from the Global Environment Facility (GEF). The opinions expressed herein belong to the author. Additional support was provided by Tame Airlines. This is Contribution 1027 of the Charles Darwin Foundation for the Galapagos Islands. REFERENCES 1998. Ley Especial para la Provincia de Galapagos. (Ley No. 67. RO/278). Buddenhagen, C. E., Renteria, J. L., Gardener, M., Wilkinson, S. R., Soria, M., Yánez, P., Tye, A. and Valle. R., 2004. The Control of a Highly Invasive Tree Cinchona pubescens in Galapagos. Weed Technology 18: 1194-202.

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