Forum News 33 article: Ridding Tristan da Cunha's outer islands of alien plants
Removal of existing invasive alien plant species from and halting the establishment of new species on the three outer islands of Tristan da Cunha.
Alien plants have caused and continue to cause significant environmental changes on oceanic islands. This project aims to enhance the capacity of the Tristan Natural Resources Department to address the problem by instituting quarantine procedures to prevent new alien plant introductions to the outer islands and to eradicate selected species that already occur on them.
The project continues from and builds on two recent Tristan environmental projects: the OTEP-funded project "Eradication of the alien plant, Procumbent Pearlwort Sagina procumbens, at Gough Island" (2005/07), and the FCO-funded project "Clearing invasive Flax Phormium tenax on Inaccessible Island" (2004). These two species (in terms of visible flowering plants) have been essentially removed from those outer islands on which they occur. However, there is now a need to continue eradication and monitoring efforts to remove any new plants that emerge from the existing seed load in the peat soils and to eliminate the seed load itself. In the case of flax on Inaccessible there has been no follow-up since the initial clearing in 2004. Observations on Nightingale indicate some resprouting from flax plants uprooted in 2005.
The project also supports the Tristan Environmental Charter and the requirements of the 2006 Conservation Ordinance.
- Summer surveys of the occurrence, distribution and phenology of alien plant species occurring on all four main islands in the Tristan da Cunha Group.
- Production of an alien plants management plan that will prioritize species on their current and expected future impact, current distribution and phenology, efforts and resources required to control and preferably eradicate them, and the likelihood of success of the latter. Examples of established alien plants that might be prioritized for action include Holcus lanatus, Rumex acetosolla, R. obtusifolius and Mariscus congestus on Nightingale and Brassica rapa, Cynodon dactylon, Sporobolus africanus and Vellereophyton dealbatum on Inaccessible.
- Establishment of an island-based documentation centre within the Tristan Natural Resources Department containing relevant literature (especially the floras of likely source regions), a plant herbarium (duplicated in a suitable off-island locality such as Kew Gardens) that contains examples of both native and alien plant species recorded on all Tristan islands (including the main island), along with an electronic photographic record of native and alien plants on a CD-ROM, supported by identification keys and descriptions.
- Follow-up work towards the eradication of Procumbent Pearlwort Sagina procumbens on Gough and New Zealand Flax Phormium tenax on Nightingale and Inaccessible.
- Production of a quarantine manual to halt the arrival of new alien plant species on the outer islands of Tristan da Cunha.
- Late summer surveys (when plants are flowering) of all four main islands by an experienced botanist and botanical assistant with the support of staff of the Tristan Natural Resources Department. Plants will be collected for identification, photography and addition to the herbarium. Plant distribution, especially of aliens, will be mapped using GPS. Approximately two to three weeks each will be required on the outer islands and a period of two to three months on the much larger main island with its larger suite of alien species.
- Production of an alien plants management plan by the project botanist that prioritises actions to be taken against existing and new alien plants.
- Establishment of the Tristan Alien Plants Documentation Centre by the project botanist.
- Continued eradication efforts directed at Procumbent Pearlwort on Gough and New Zealand Flax on Nightingale and Inaccessible. The former will require visits to Gough at less than annual intervals to treat invaded ground to eliminate the existing seed load; the latter requires regular visits to Nightingale and Inaccessible to remove seedlings. Other species of alien plants will be eradicated when considered feasible and accorded a high priority for action (e.g. when known to belong to a highly invasive species). Post-eradication monitoring will be undertaken during visits of opportunity to the outer islands (e.g. during South African annual relief voyages to Gough and during scientific, management, traditional-take and/or tourist visits to Nightingale and Inaccessible) to assess both whether eradication has been successful and the level of site rehabilitation. TNRD staff will conduct fieldwork with support on site and guidance from project leaders, rope-access experts, Tristan Biodiversity Action Group (T-BAG) members, etc.
- Production of a quarantine manual setting out procedures to be followed to halt the arrival of new alien plants species at the outer islands. This document will include procedures to be undertaken at off-island packing stores and vessel's home ports, aboard ocean-going vessels visiting Tristan da Cunha, and during inter-island movements by small boats and helicopters. It will include procedures to be followed by visitors from outside Tristan da Cunha (such as scientists and tourists) and by Tristan Islanders and others travelling between islands in the group (especially from the main island to Nightingale and to Inaccessible). The manual will be produced under the guidance of the project leaders with input from international experts and T-BAG members.
This project has the support of the Tristan Natural Resources Department and the Tristan Island Council.
Three to-be-appointed members of T-BAG will work closely with the TNRD in co-ordinating, managing and executing the project. These are:
- Dr Niek Gremmen (Southern Ocean island and alien plant expert - The Netherlands)
- Associate Professor Peter Ryan (Leader of the Inaccessible Flax Eradication Project - South Africa)
- Mr John Cooper (Leader of the Sagina Eradication Project - South Africa).
Risk 1: Plant eradication efforts are not successful within the two-year project period.
Probability: Low to Medium depending on species selected for eradication (species with a high likelihood of failure are unlikely to be selected for eradication).
Impact: Medium to High
Management: Reassessment of eradication procedures; extension of eradication time-period, changes in eradication methods, change to a control programme until new eradication methods become available and/or are tested.
Risk 2: Herbarium collection is not sufficiently complete.
Management: Collection of plants should continue after the duration of the project.
Risk 3: Quarantine manual and alien plant management plan prove inadequate to halt arrival, establishment, control or eradication of alien plants.
Management: Manual and plan should be regarded as evolving documents to be updated as inadequacies become noticeable when in use and in the light of world-wide developments in the field.
The broad objective is to work towards a situation whereby the three outer islands of Gough, Inaccessible and Nightingale remain largely free of the deleterious effects of invasive alien plants so that their existing biodiversity and ecological processes can continue to exist in a largely natural and undisturbed state.
The project will indirectly enhance the lives of Tristan Islanders by ensuring their Territory's outer islands remain in as natural a state as possible, thus maintaining their eco-tourism and scientific research potential. Eco-tourism visits to Tristan are increasing and the management of alien plants on the outer islands will support this activity of economic significance to the Territory.
Funded by FCO/DIFD Overseas Territories Environment Programme, 2007, project number TDC403
Multilateral Environmental Agreements
The project is being developed in the context of the Convention on Biological Diversity (CBD), which has been extended to the Territory. It thus supports the Tristan Biodiversity Action Plan (2006-2010), which was developed by the UK Darwin Initiative-funded project "Empowering the people of Tristan da Cunha to implement the CBD", which has as one of its objectives "The impact of invasive alien species is reduced or eliminated".
Together, Gough and Inaccessible form a single World Heritage Site. The project is thus in support of Tristan's commitment to the World Heritage Convention.