In this post Associate Editor Ayesha Tulloch discusses a paper she recently handled from Owen Greenwood and colleagues ‘Using in situ management to conserve biodiversity under climate change’
There is little doubt that over the next 100 years, climate change is likely to become one of the main drivers of biodiversity loss worldwide. The recent 2015 United Nations Climate Change Conference in Paris, France, laid down clear foundations for global progress on tackling climate change. 195 nations approved an historic agreement to set a goal of limiting global warming to less than 2 degrees Celsius compared to the pre-industrial level, and reaching zero net emissions to sometime between 2050 and 2100.
However, tackling climate change is a much more complicated task than simply reducing emissions and limiting global warming. These direct methods of climate change mitigation will fail to save many of the species currently in danger of losing key habitats and resources due to shifts in environmental conditions within their current ranges. Species’ abilities to adapt to changed climates and habitats will depend on a number of factors, including their ability to traverse large distances or hostile land cover. Much discussion of adaptation to climate change by conservationists has therefore focussed on accommodating or assisting these range shifts. An alternative strategy, which has been given much less attention, is to improve species’ abilities to cope with climate change within their existing ranges. Particularly for slow-moving or poorly-dispersing species, these strategies might make the difference between persistence under a changed climate, and local or even global extinction.
Greenwood et al.’s recent paper provides an important synthesis of how habitat management can be used to reduce the negative impacts of climate change on species at a local scale. The actions with the most supporting evidence from existing literature are those involved in mitigating sea-level rise, such as managed realignment and sea-defence creation. There is much less evidence for the effectiveness of terrestrial management techniques to assist species with adapting to global warming or changes in precipitation. Manipulating vegetation structure is one type of terrestrial management response that can alter changed temperature and moisture conditions likely to be experienced by organisms under global warming. For example, the availability of suitable microclimates within particular vegetation structures for the Glanville fritillary butterfly is almost twice as strong a predictor of butterfly abundance as regional air temperature. This suggests that practitioners should implement land management such as afforestation or reduced grazing techniques that result in more preferred vegetation cover for the butterfly. These altered microclimatic conditions are likely to benefit the butterfly and perhaps other species as regional climatic conditions become unsuitable.
One important finding is that almost all habitat manipulation strategies to combat climate change result in trade-offs, and the likely positive effects on some wildlife must be balanced against potential adverse effects on other species. Half of the suggested habitat management responses to climate change were assessed as having strong supporting evidence, but few were “no-regrets” policies, with potential adverse effects ranging from reductions in species diversity to decreased local water availability and off-site erosion. In the example of habitat manipulation to assist the fritillary butterfly, increasing the density of vegetation might increase resource competition with non-target species and lead to their declines.
Despite a range of management alternatives available to manipulate habitats at a local scale and combat the effects of regional climate, Greenwood et al.’s review also includes a key caveat – 80% of these management techniques appear, from the evidence available, to have a medium to high risk of failure. They also discovered four management responses to climate change that have never been demonstrated to work: adding fertilizer to promote vegetation growth, keeping rice fields flooded after harvest, rewetting soils in old arable fields, and raising areas of substrate for nesting birds. Many failures appear to be due to a combination of undesirable side-effects, and either a lack of evidence or contradictory evidence from different systems. This suggests that we not only need more evidence from a wide range of systems about the contexts in which particular management options might be effective, but we also need to know for which species particular actions might be beneficial, and to carefully document the likely negative outcomes for other species. In many cases managers will most likely be faced with triage decisions – giving up on some species locally, to save others.
The climate is changing and will continue to change regardless of all our best efforts to reduce emissions and limit global warming. Successful conservation will increasingly depend on our ability to help species cope with this change. Although many of the adverse effects of climate change might be offset by appropriate management at the local scale, Greenwood et al.’s review highlights that most of the evidence we have for this is indirect and not based on sound empirical studies. Perhaps because of this, the use of habitat management as a tool for manipulating changing climatic conditions has rarely been recommended as a means of helping species cope with climate change, except as a means of countering sea-level rise. I see this as an important opportunity for ecologists, conservationists and practitioners to work together and better evaluate the effectiveness of alternative in situ management interventions through adaptive management and monitoring. Learning about, documenting, and sharing the successes and failures of alternative habitat manipulation strategies is the only way to find effective actions for improving species’ abilities to cope with ongoing climate change. Because many of these actions might take years to have an effect, experiments should start now, supported by government initiatives for institutional collaboration.