This is part 1 of a 3-part series highlighting our work testing the effectiveness of fenced sanctuaries for biodiversity conservation
We’ve just wrapped our trip to New Zealand, primarily helping to re-measure permanent vegetation monitoring plots. The work is part of a one-year project, primarily supported by a British Ecological Society Research Grant, and smaller grants from the JS Watson Trust and Robert Bruce Trust. Our aim is to predict whether eco-sanctuaries restore habitat for threatened fauna.
As many of us already know, conservationists are urgently deriving strategies for protecting the world’s most threatened species. One approach that is quickly gaining traction is fencing large areas of land and managing these as “sanctuaries”, which maintain ecological processes and species that could not otherwise survive in the surrounding landscape because of pressures such as predation or poaching. Whether this is akin to a “modern” zoo has been hotly debated. Paul Scofield et al. have been critical of the costs of establishing sanctuaries in New Zealand, but as John Innes and some of our friends have pointed out, there are small successes being made. Part of the reason for debate is that there there are few data measuring the effectiveness of fenced sanctuaries towards achieving biodiversity goals. Ideally, data must be collected prior to and following the establishment of a sanctuary and compared to trends in unprotected habitat.
Offshore island offer a good comparator for sanctuaries, which we can think of as being “islands” in human-dominated landscapes. On islands, conservationists have been tremendously successful at eradicating non-indigenous mammals and restoring viable populations of native fauna and flora, with many examples from archipelagos, especially for ungulates and smaller mammals. But there is almost no information on whether the positive responses of native species to the removal of all introduced mammals can be replicated on larger continental land masses. Partly, complete eradication of introduced mammals on mainland sites has been impossible to achieve without fencing. This is where New Zealand fits in…
New Zealand offers an ideal opportunity to test the benefits of sanctuaries. Much of the country’s native fauna is threatened from introduced mammals, particularly stoats and rodents. Thus, predator-free sanctuaries are increasingly used for protecting birds, reptiles, and lizards found only in this part of the world. Exclusion of introduced mammals not only reduces pressures upon fauna but also modifies vegetation by reducing seedling mortality and seed predation.
To measure how well sanctuaries are working, we have been capitalizing on an internationally-unique experiment within the 307 ha Orokonui Ecosanctuary, located outside of Dunedin, New Zealand. Billed as one of New Zealand’s only “Cloud Forests” (not because it is a true cloud forest, but because it is in the clouds most of the time!), the sanctuary has proved a remarkable home to many bird species on the brink of extinction. It houses free-roaming tuatara (reptiles that are evolutionarily so old they roamed the world with dinosaurs), ca. 30-40 kākā (endangered forest parrots that are absent through much of the South Island), a population of Haast tokoeka, and even gets occasional visitors from Sirocco, the superstar of the parrot world. Vegetation in the sanctuary is key, however, to allowing these animals to thrive. Much of the property is undergoing secondary succession from former livestock grazing and now forming some of the last remaining stands of regenerating podocarp-broadleaved forest along the eastern South Island, outside of the Catlins.
Despite this remarkable array of life, it is a 2 m tall, 8.7 km fence that makes Orokonui special. This fence was constructed in July 2007 to the cost of $2.2 million New Zealand Dollars (1 NZD = 0.50 GBP), and is intended to keep out all introduced mammals, including mice (which is really difficult to do!). Once the fence was built, the charitable trust spent the next six years trying to eradicate all the mammals inside the fence. This is a continual battle, and as we discovered in our work, there are 64 km of trapping lines regularly monitored throughout the EcoSanctuary to ensure there are no re-invasions.
Using this predator-proof fence as an experimental treatment, our collaborator Kelvin Lloyd (Wildland Consultants, Landcare Research), established a network of 52 vegetation monitoring plots between 2005 and 2007 -immediately prior to construction of the fence and subsequent pest eradication. We have been working to re-measure these plots to test whether exclusion of introduced mammals has improved habitat for native fauna.
Baseline measurements show that seedlings of ecologically important emergent tree species, particularly the fleshy-fruited Podocarpaceae that dominate New Zealand’s cool temperate forests, were almost entirely absent. Of 21,397 seedlings <10 cm tall recorded between 2005 and 2007, only 14 were podocarps! This is despite the fact that many of these species are mast seeders that produced thousands of seeds during their most recent reproductive event just a few years prior. Why might they be absent then? Well, the fruits of these species are found to be highly nutritious not only by rare native taxa, such as Sirocco and his kākāpō mates, but also by introduced rodents, whose populations erupt in response to mast seeding events.
In part 2 of 3, I will being to highlight some of our findings from the plot re-measurement. These are suggesting that seed predation may be declining, allowing a number of ecologically-important tree species to regenerate and re-establish in the forest.