The Use and Potential of Pest-Proof Fencing for Ecosystem Restoration and Fauna Conservation in New Zealand

Chapter 5 The Use and Potential of Pest-Proof Fencing for Ecosystem Restoration and Fauna Conservation in New Zealand Bruce Burns , John Innes , and Tim Day Introduction In New Zealand, fences are commonplace. In a country in which pastoral agriculture is one of the dominant land uses, and in which rotational grazing is a strong management paradigm, barriers to control the distribution of farm animals are present in most landscapes. It is not surprising, therefore, that New Zealand conservation managers have extended and adapted this basic and familiar technology to try and control the distribution of exotic mammalian pests (The term “pest” here is used to denote wild animals that adversely affect indigenous biota and ecosystems; Parkes and Murphy 2003 ) . By this means, they have succeeded in isolating native ecosystems from the impacts of these pests and have made signifi cant conservation gains. Also, the application of pest-proof fencing in New Zealand to local projects has focused and galvanized public involvement in conservation in a profound manner. Since human colonization of the New Zealand archipelago, 31 species of mammals have established naturalized populations following deliberate or accidental introduction by humans (Parkes and Murphy 2003 ) . Many of these introduced mammals have fundamentally changed the nature of New Zealand natural ecosystems as predators and competitors, causing national and local extinctions of many native species, and continuing to cause population declines in others (Forsyth et al. 2010 ; Innes et al. 2010 ; Lee et al. 2010 ) . Many of the most damaging introduced mammals B. Burns (*) School of Biological Sciences , University of Auckland , Private Bag, 92019 , Auckland 1142 , New Zealand e-mail: [email protected] J. Innes Landcare Research, Private Bag 3127 , Hamilton 3240 , New Zealand T. Day Xcluder Pest Proof Fencing, P.O. Box 7135 , Rotorua 3042 , New Zealand M.J. Somers and M.W. Hayward (eds.), Fencing for Conservation: 65 Restriction of Evolutionary Potential or a Riposte to Threatening Processes?, DOI 10.1007/978-1-4614-0902-1_5, © Springer Science+Business Media, LLC 2012 66 B. Burns et al. are almost ubiquitous in New Zealand and continue to degrade even large, legally protected areas such as National Parks, e.g., ship rat Rattus rattus , brushtail possum Trichosurus vulpecula and stoat Mustela erminea (King 2005 ) . Introduced pests are by far the largest conservation problem in New Zealand (Craig et al. 2000 ) . The use of fences designed to exclude all introduced mammals from natural habitats is a recent conservation strategy being applied in New Zealand for ecosystem restoration. It is an extension of the strategy of using pest-free islands for conservation by attempting to create such “islands” on the mainland, with fences rather than the sea as a barrier to pest reinvasion. The lack of native, terrestrial, fl ightless mammals in New Zealand (Gibbs 2006 ; Tennyson 2010 ) means that fences can selectively exclude this introduced guild with limited apparent disruption to native organisms. The areas established are therefore expected to reverse degrading ecological processes, such as fl owering, pollination and regeneration, and regain species diversity (often through conservation translocations) and abundance. Projects centred on these areas hope for the re-emergence of an ecosystem structure close to that of a pre-human New Zealand, although they concede that such a goal is strictly unattainable given the lack of knowledge of what such an ecosystem looked like, extinction of some species, and changes in environment (e.g., climate) since that time (e.g., Karori Wildlife Sanctuary (recently renamed Zealandia), Campbell-Hunt 2002 ) (Simberloff 1990 ; Atkinson 2001 ) . This chapter reviews the development of conservation fencing, the extent and distribution of conservation areas based on fences, the experience of conservation managers with fences and the current contribution of fences to conservation in New Zealand. Areas with pest-proof fences are now considered an important resource for ongoing conservation efforts, although their long-term effectiveness (both practical and fi nancial) is still being evaluated. Discussion is largely limited to specialist conservation (“pest-proof”) fences rather than situations in which standard stock proof fences are used in a conservation setting. History of Conservation Fencing in New Zealand Fences as barriers to animal movement are a characteristic feature of New Zealand landscapes and refl ect its agricultural heritage. As well, many innovations in fencing technology have been developed in New Zealand (e.g., types of electric fencing, Brook 1939 ) . Adapting fences to conservation problems is therefore congruous with existing cultural traditions for land management. Initially, standard ungulate fences were used in New Zealand to protect reserved natural areas from domesticated browsers such as cattle Bos taurus and sheep Ovis aries (e.g., Brown 1994 ) . Browsing by these farm animals is known to cause signifi cant damage to native forest composition, structure and regeneration (Timmins 2002 ; Smale et al. 2005 ; Dodd and Power 2007 ) , and stock-proof fencing (6–9-wire post and batten, or netting) is widely implemented around conservation areas to improve vegetation condition (Smale et al. 2005 ) . Fencing native forest fragments from stock is a necessary 5 The Use and Potential of Pest-Proof Fencing for Ecosystem Restoration… 67 condition of conservation easements on private lands of such organizations as the Queen Elizabeth II National Trust in New Zealand (Porteous 1993 ) . In the 1980s and 1990s, fences started to be investigated and used as a means of protecting populations of highly endangered species from specifi c predators in cases where the species of conservation interest could not be transferred to predator-free habitat. For example, fences were developed around vegetation containing the endangered giant fl ax snail Placostylus ambagiosus at Te Paki to keep out pigs Sus scrofa , an important predator, using netting reinforced with metal stakes (Parrish et al. 1995 ) . In another initiative, the Cromwell Chafer Reserve was fenced to exclude rabbits Oryctolagus cuniculus , with the fence extending 1.1 m above ground and 0.6 m belowground, to prevent vegetation degradation that would threaten the critically endangered Cromwell chafer beetle Prodontria lewisi (Aviss and Roberts 1994 ) . Also, a population of Maud Island frog Leiopelma pakeka on Maud Island was surrounded by a fence designed to exclude the native tuatara Sphenodon punc- tatus , its main predator on that island (Brown 1994 ) . At about this same time, conservation in New Zealand underwent a revolution fuelled by the success of pest eradication projects on small offshore islands (Taylor and Thomas 1993 ; Jansen 1993 ) . Islands have long been a key component of New Zealand’s conservation strategy with those that are pest-free acting as refuges for species vulnerable to pest mammals. In the 1980s, eradication technologies were developed to clear islands previously invaded by pest mammals to increase the area available for conservation purposes (Pryde 1997 ) . The key advances achieved by these means was the ability to remove a suite of mammal species from islands, and the realization that even seemingly entrenched pests such as Norway rats Rattus norvegicus and mice Mus musculus could be eliminated. By 2008, 71 islands had all non-native mammals eradicated (Bellingham et al. 2010 ) and 65 had been cleared of at least rats including at least 2 islands >2,000 ha (Towns and Broome 2003 ) . The residual biodiversity on these islands has often fl ourished following these pest removals (Bellingham et al. 2010 ) . These island experiences led some conservation managers to consider whether programmes targeting multiple pests could be applied in mainland situations. One of the fi rst of these achieved reductions in a range of pest mammals, particularly brushtail possums and ship rats, to near zero densities over several years in central North Island forests, in order to restore populations of North Island kokako Callaeas cinerea wilsoni (Innes et al. 1999 ) . Kokako populations increased dramatically as a result (Innes et al. 1999 ) , but as well, other ecological responses were noted including improvements in populations of invertebrates, plants and other forest birds (Saunders and Norton 2001 ) . The success of this project caused a shift in focus of some conservation management in New Zealand from species-centred to ecosystem-centred, and led to the creation of a series of “mainland islands” based on trying to achieve sustainable management regimes by which all critical pests were con- trolled to extremely low levels and attempts made to limit re-invasion (Saunders and Norton 2001 ) . The Department of Conservation initiated six Mainland Island projects in 1995 and 1996 throughout New Zealand ranging in size from 117 to 6,000 ha using this approach (Saunders and Norton 2001 ) . 68 B. Burns et al. Unfenced Mainland Island projects have resulted in numerous conservation success stories, although few have so far been published; an exception is from Trounson Kauri Park (Gillies et al. 2003 ) . Behind these highlights, however, predator control in some years failed to prevent damage by surviving or invading pests; some pests such as mice and hedgehogs Erinaceus europaeus were mostly not targeted at all; concern about toxin residues in non-target wildlife

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