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1 January 2012 Management of the Invasive Hill Raspberry (Rubus niveus) on Santiago Island, Galapagos: Eradication or Indefinite Control?
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Abstract

The eradication of an invasive plant species can provide substantial ecological and economic benefits by eliminating completely the negative effects of the weed and reducing the high cost of continuing control. A 5-yr program toward the eradication of hill raspberry (Rubus niveus Thunb.) in Santiago Island is evaluated using delimitation and extirpation criteria, as well as assessment of the ecological community response to management techniques. Currently, hill raspberry is located in the humid zone of Santiago island. It is distributed over three main infestations, small patches, and many scattered individuals within an area of approximately 1,000 ha. New infestations are constantly being found; every year, new detections add an area of approximately 175 ha. Adult and juvenile individuals are still found, both beyond and within known infestations. Both plant and seed bank density of hill raspberry decreased over time where infestations were controlled. Species composition in the seed bank and existing vegetation were significantly different between areas under intensive control and adjacent uninvaded forest. After 5 yr of intensive management, delimitation of hill raspberry has not been achieved; new populations are found every year, increasing the infested area that requires management. Off-target effects on native species resulting from control efforts seem to be substantial. Although a vast increase in economic investment would allow intensive searching that might enable all individuals to be found and controlled, the resultant disturbance and off-targets effects could outweigh the conservation benefits of eradication.

Nomenclature: Hill raspberry, Rubus niveus Thunb.

Management Implications: During the last two decades, the Galapagos National Park Directorate and the Charles Darwin Foundation have been carrying out control and eradication programs to restore natural areas that have been degraded by invasive plant species. Control has proved to be costly and perennial and at best has slowed the spread of invasives. Similarly, eradication has had limited success, with only four (targeting weeds with small distributions and transient seed banks) out of 30 programs reaching the goal. Hence, there is an obvious need to evaluate the current 5-yr eradication program targeting hill raspberry in Santiago Island. Eradication does not seem feasible with the current search methodology, primarily because of the failure to find all plants before they fruit. Therefore, one of the fundamental requirements for successful eradication is not being met. Increase in the frequency and extent of search and control operations would be needed to meet this requirement, with all known and potential sites being visited at 4- to 6-month intervals to prevent fruit production. Although larger infestations can be seen from a helicopter, the discovery of all individual plants would require cutting a very closely spaced network of paths through nearly impenetrable low spiny forest. This more effective search methodology would need to be implemented and maintained until the elimination of the seed bank has been achieved (a minimum of 4 yr and up to 10 yr). It is estimated that it would cost USD 10 million (USD 1 million yr−1) over 10 yr to achieve eradication, a 6.7-fold increase in investment from the current level. Additionally, although herbicide control successfully kills individual plants, it has also affected natural vegetation, and opening a tight network of tracks would also cause concomitant disturbance. If the increased investment is not available or the off-target effects are considered greater than the benefits of eradication, or both, alternative objectives and methodologies (e.g., biocontrol) must be considered for the management of hill raspberry.

Weed Science Society of America
Jorge Luis Renteria, Mark R. Gardener, F. Dane Panetta, and Mick J. Crawley "Management of the Invasive Hill Raspberry (Rubus niveus) on Santiago Island, Galapagos: Eradication or Indefinite Control?," Invasive Plant Science and Management 5(1), 37-46, (1 January 2012). https://doi.org/10.1614/IPSM-D-11-00043.1
Received: 7 June 2011; Accepted: 1 November 2011; Published: 1 January 2012
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