Island restoration

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The ecological restoration of islands, or island restoration, is the application of the principles of

Islands, endemism and extinction

Isolated islands have been known to have greater levels of endemism since the 1970s when the theory of

The field of island restoration is usually credited with having been started in New Zealand in the 1960s, but other smaller projects, such as the restoration of

One important aspect of island restoration is the removal of invasive alien species. Since these species are most often the reason that native fauna and flora is threatened, their removal is essential to the restoration project. From 1673 until 2009, 786 successful invasive vertebrate eradication have been recorded and in the last few decades the frequency of eradications and the size of islands from which invasive vertebrates have been eradicated has increased. A definitive list of past island restoration efforts exists as the Database of Island Invasive Species Eradications.^[2] In addition a list of the current invasive species present on the world's islands exists as the Threatened Island Database^[3]

Islands are particularly suitable for restoration as once cleared of an introduced species they can be kept cleared of these species by virtue of being an island. Species removal is intensive and expensive, and methods used must be carefully chosen as to not create too much impact on non-target species. Feral cats, goats and three species of rats are among the most damaging species introduced to islands (Moors & Atkinson 1984). The differences in size, lifestyle and behaviour preclude the use of the same techniques for all of them, but with many species a range of techniques needs to be used in order to ensure success. Larger animals, such as goats and pigs, can be effectively hunted; in the case of

Invasive vertebrate eradication has many benefits besides conservation of species and has been found to align with 13 UN Sustainable Development Goals and 42 associated targets encompassing marine and terrestrial biodiversity conservation, promotion of local and global partnerships, economic development, climate change mitigation, human health and sanitation and sustainable production and consumption.^[6][7]

Strategies

There are three strategies to reduce the numbers of the introduced animals in order to lighten the problems caused by them: exclusion, control, and eradication. Exclusion is removal of introduced species in limited areas and focused on a local impact. Control has a meaning of mitigation by reducing the numbers of introduced species down to ecologically and economically less harmful level. Since it is not complete wiping out strategy, this has to be taken constantly and repeatedly. This strategy is said to be feasible but less cost effective due to its incompleteness. Eradication is the complete removal of all the individuals of the population, down to the last potentially reproducing individual, or the reduction of their population density below sustainable levels^[8] (J. H. Myerset al., 2000). For islands, it is usually the best strategy as it gives permanent effects, which potentially means most cost effective. However, it is still logistically and economically high cost. Also, this strategy is sometimes hard to accomplish depending on the environment of island and the alien species.^[9] Island Conservation exclusively focuses on the eradication of invasive vertebrate species from islands. Up until 2021, the organization had deployed teams to protect 1,195 populations of 487 species and subspecies on 64 islands.^[10]

Methods

Fencing is used for excluding the alien mammals. This method intends to limit the area for the mammals before control or eradication. Shooting is often used for large animals to control them. This method has meanings of gaining food supply and recreation. It requires accessibility in the field and experience for the hunters. Also, to maintain the effect, it requires good amount of manpower for long time, so it can be costly. Trapping is designed for medium-sized mammals which are hard to shoot at. This method is usually only for reduction not eradication. The advantage of this method is that it can be selective since it is possible to exclude or reduce the possibility of trapping native animals. However, trapping requires limited area to cover and limited population to capture.

Poisoning is very effective for small species. However, there are some disadvantages of this method. It is possible that untargeted animals take the poison. It is also necessary to consider the secondary poisoning that other animals are affected by poisoned species. This method can be costly if the area to cover is large.^[11]

Pathogen Introduction (parasitism) is one of the biological methods to eradicate alien species. It is very effective for limited species, but the viruses and bacteria need to be specified clearly for use.^[11]

Predator introduction is another biological method to eradicate the introduced species. It is less costly and environmentally clean, but it can cause greater problems, because it is possible that the introduced predator targets the native animals instead of alien species and its existence and its parasites can be new problems.^{[citation needed]}

Competitor introduction is also a biological method to eradicate introduced carnivores. It can be very effective with good amount of information. In the end, the competitor has to be removed as well. Virus vectored immune-contraception is one of the newest method that is to infect introduced animals with genetically engineered viruses. This method is considered environmentally clean, low cost, selective, and ethical. However, it is not fully operational and the effect comes slowly.^[9]

Restoration of former habitat

In many cases the removal of introduced species is sufficient to allow a return to a pre-disturbance state, but generally active management, often in the form of replanting native flora and reintroduction of extirpated fauna is needed to achieve restoration goals. Planting of native species helps to replenish species that were either grazed or out competed. Species of animal can be translocated either from existing populations, or from captive bred populations. These reintroductions need to be carefully managed, particularly in the case of endangered species, where the potential benefits need to be weighed against the possibility of failure. Not all translocations succeed, and it may be necessary to help the reintroduced animals along with supplementary feeding or other kinds of management.

One other important aspect of restoration is prevention, that is, keeping invasive species from returning to a cleared island. This can be achieved by restricting access to the island in question (reducing possible instances of invasion) to more stringent quarantine methods. For example, in order to prevent invasive weeds from returning to Laysan, people working on the island must bring entirely new clothes to the island, which must be frozen prior to arrival.

Opposition to island restoration

Prior to the initial efforts to remove rats from New Zealand's offshore islands there was a great deal of skepticism as to the feasibility of island restoration amongst ecologists and conservation workers. However, as the techniques have improved and larger islands have been restored, most of the initial criticisms from within the field have been dropped, in particular as the costs of eradication are often much lower than continuous pest control.

Outside of the field of conservation there has been some opposition from other interested groups, particularly from the

Opposition to island restoration has not led to the abandonment of many projects but has delayed several, particularly through court action. Groups sometimes adopt different approaches; opponents of hedgehog removal in the Outer Hebrides offered bounties for live hedgehogs removed from the islands and relocated in their natural habitat. Invasive plants can also generate strong feelings. The removal of Eucalyptus trees from Angel Island in San Francisco Bay faced considerable opposition.

Island restoration projects

Island restoration has been attempted in many countries since the 1960s, and has met with varying degrees of success. The following examples highlight some of the factors that influence projects. A comprehensive list of projects can be found on the Database of Island Invasive Species Eradications.^[12]

Round Island

Round Island (Île Ronde in French) is a tropical island 22.5 kilometres north of Mauritius, with an area of 1.69 square kilometres and a maximum elevation of 280 metres.^[13] Compared to other Mascarene islands and islets, Round Island remained relatively pristine until goats and rabbits were introduced in the 19th century (goats were introduced between 1846 and 1868, whilst rabbits were present in large numbers before 1810).^[14] These herbivores, along with other factors, such as sporadic logging and frequent cyclones, led to the eventual dwindling of the island's forests and dependent fauna. In turn, this led to soil erosion by wind and rain, impeding forest regeneration, acting as a positive feedback mechanism that caused rapid deforestation of the island. In 1957, however, Round Island was officially made a nature reserve, and in 1979 and 1986 was rid of goats (shooting) and rabbits (poisoning), respectively, after several unsuccessful attempts.^[14]

Since removal of the introduced herbivores, the Round Island plant community has recovered dramatically. This is especially stark for three of the endemic tree species, Latania loddigesii, Pandanus vandermeerschii and Hyophorbe lagenicaulis, which constituted a large portion of the Round Island forest historically. This has led to six reptile species (five of which were

The Round Island restoration program represents one of the longest-running projects of its kind in the world, since its conservation status was confirmed in 1957. Much of the current conservation work on Round Island is conducted by the Mauritian Wildlife Foundation^[16] and Durrell Wildlife Conservation Trust^[17] and revolves around maintaining soil levels, reforestation of the island, and eradication of remaining invasive plants and invertebrates.

Aleutian Islands

The Aleutian Islands, prior to the 18th century, lacked any terrestrial predators, but from the mid-18th century Arctic foxes were introduced to act as a source for the fur trade, a practice that continued into the early 20th century. This introduction decimated the birds of the chain, particularly seabirds like the whiskered auklet. The reduction in seabirds, in turn, had effects on the ecology of the islands, as many of the plants were dependent on the guano from nesting birds acting as a fertilizer. In the early 1950s managers of the Aleutian Islands Reservation became aware of the damage, and an eradication program began. Since then over 80 islands have been cleared of non-native foxes (only six islands remain) and bird populations have rebounded. Whiskered auklets, which numbered 25,000 in 1974, had increased to 116,000 in 2003.

Campbell Island