Protected areas deliver enormous benefits inside of their boundaries, but what is their contribution to the biodiversity of broader landscapes? This is a really important question to answer because there are limits to how much land conservation can meaningfully protect. Moreover, the 196 governments parties that have signed onto the Convention on Biological Diversity are aiming to protect 17% of the world’s land surface by 2020, but what about the other 83%? Conservation outside of protected areas is critical to ensure that the spaces between parks aren’t devoid of life.
In a new study, we provide among the first empirical evidence that protected areas may disperse biodiversity and ecosystem services into surrounding landscapes. This finding is in fact expected from meta-population theory, which describes how populations in different places will interact. Meta-population theory specifically predicts that bolstering populations of a species in a given habitat patch, such as by controlling predators, should create sources of emigrants to augment populations in neighbouring regions. Sort of like if you have too many people living in a city. At a certain stage, you’ll get a steady stream of people fleeing the overcrowding and moving into the suburbs.
Birds in particular are a great species for testing spill-over effects because they are highly mobile. They also have key roles in ecosystems as pollinators and seed dispersers that are important to understand better. In our study, we found that restoring populations of fruit-eating birds resulted in higher numbers nearer the protected area than further away in the landscape. This pattern was mirrored by the distribution of young trees that produce large fruits and are preferentially consumed by the birds. If the protected area was having no effect, you would expect a straight line across the landscape, but we did not find this.
Our work, carried out in New Zealand at the stunning Orokonui Ecosanctuary also has major relevance for environmental management; read more about our work at Orokonui here and here. New Zealand’s government has committed to eradicating major non-indigenous predators at a national scale by 2050. Predator-free protected area are seen as an integral part of this strategy if they can concentrate conservation action into manageable sites from which benefits will spill over into the surrounding landscape. This idea has been compared to a “halo”, where populations of threatened species disperse from a core population outwards into the surrounding landscape into a heavenly glow.
In New Zealand, the only practical way predator-free protected areas might be presently achieved is by excluding introduced rats, stoats, possums, etc… with fences. Fences are of course very contentious. At the heart of this debate is whether fenced reserves effectively function as zoos – displaying wildlife to the public without any chance that these species could persist outside of the protected area. Moreover, fences are very costly to build. The 2 m tall, 8.7 km fence fence enclosing Orokonui was constructed in July 2007 at a cost of $2.2 million New Zealand dollars. There are also large operation costs for fences that can siphon the few funds that are available to protect species over considerably larger areas in the backcountry. For example, the annual cost of maintaining one 3400 ha fenced reserve in North Island, New Zealand may be as much as the entire budget of the endangered species programme for a 3.8 million ha area. And fences also have large social costs that risk privatising public land and excluding local communities.
Nonetheless, as the global biodiversity crisis deepens, our new study suggests that fenced reserves may play an important role in delivering conservation benefits into wider landscapes.