Grounding nature-based climate solutions in sound biodiversity science

The current narrow focus on afforestation in climate policy runs the risk of compromising long-term carbon storage, human adaptation and efforts to preserve biodiversity. An emphasis on diverse, intact natural ecosystems — as opposed to fast-growing tree plantations — will help nations to deliver Paris Agreement goals and much more.


Box 1: What are nature-based solutions? 40
Nature-based Solutions (NbS) involve working with and enhancing nature to help address societal goals. They are "actions to protect, sustainably manage and restore natural or modified ecosystems, which address societal challenges (e.g. climate change, food and water security or natural disasters) effectively and adaptively, while providing human wellbeing and biodiversity benefits" 3 . They have also been described as solutions "inspired and 45 supported by nature, which are cost-effective, simultaneously provide environmental, social and economic benefits and help build resilience. Such solutions bring more, and more diverse, nature and natural features and processes into cities, landscapes and seascapes, through locally adapted, resource-efficient and systemic interventions" 4 . The concept of NbS has recently emerged against the backdrop of our failure to either stabilise the climate or 50 stem the tide of biodiversity loss. However, high level pledges for "nature" tend to translate into targets for afforestation, often monocultures with single non-native species, which can over the long term produce maladaptation to climate change, compromise carbon storage and negatively impact on biodiversity and sustainable development in general.

A focus on forests
When it comes to high level multilateral pledges for nature the current focus is on forests.   Declaration", which encourages all Parties to take action to conserve and enhance sinks and 105 reservoirs of greenhouse gases, emphasising "healthy, biologically diverse, and resilient forests adapted to climate change" 10 . However, the Declaration does not specify that carbon emissions must be drastically cut in parallel with conserving and enhancing forests for mitigation and adaptation. We stress that the implementation of any forest-based agenda needs to coincide with severe cuts in fossil fuel emissions if we are to achieve the goals of 110 the Paris Agreement.

The problem with monocultures
The issue is how these high-level pledges for forests translate into action on the ground.
Existing international frameworks provide a definition of forests created for the purpose of 115 assessing forest carbon stocks alone and as a result pledges tend to focus more on the extent rather than the quality of forest to be protected, afforested or reforested 2,11 . This is problematic not least because intact forests have been estimated to hold more carbon than logged forests 12 . Furthermore, the approach encourages the establishment of monoculture plantations of fast growing species, including exotics. While such plantations may store 120 carbon in the short term, their capacity to do so over the long term is impaired by changing conditions and disturbances 13 that are becoming more rapid and severe under climate change 14 . For forests to sequester carbon long term, they must be able to resist, recover and/or adapt to these changes 14 , and there is growing evidence that such functional resilience is strongly determined by factors such as ecosystem connectivity, heterogeneity, 125 and diversity at multiple ecological levels 15  Therefore, to enable long term carbon storage mitigation, policy must move away from encouraging single species plantations and instead support practices that enhance the ecological attributes that underpin functional resilience. Such policies would be more in 135 line with recent evidence that diversity (of species and/or traits) is key to preserving forest carbon sinks in the face of climate change 19 .

What about the rest?
It is vital that the current emphasis on forests does not detract from other ecosystems, 140 many of which are also very important for storing carbon. A new campaign to raise the profile of natural solutions to climate change advocates that restoring and protecting forest can "deliver 30% of the climate solution needed by 2030" 20 . Although the campaign strongly emphasises forests, it is based on a study showing that conservation actions in all major natural terrestrial habitats including grasslands, wetlands and 145 agricultural lands could help provide up to 30-37% CO2 mitigation needed through to 2030 for >66% chance of keeping warming to < 2 °C 21 .
Mangroves, in particular, are one of the planet's most efficient carbon storehouses, with mean long-term carbon burial rates (i.e. rates at which organic carbon 150 accumulate in sediments) more than 45 times greater than any other terrestrial ecosystem, including boreal and tropical forests 22 . Peatlands also hold vast reservoirs of carbon (25% of world's carbon) but cover only 2-3% of terrestrial areas 23 . Meanwhile, natural grasslands harbour substantial carbon stores within their soil and can be more resilient than forests to drought and wildfires making 155 them the more effective and secure carbon sink in the long term 24 . However, these important carbon stores barely feature in climate change policy. For example, while 42% of signatories to the Paris Agreement include afforestation and/or restoration in terrestrial forest in the mitigation components of their NDCs, only 19% do the same for coastal habitats. Meanwhile, conservation actions in grasslands appear in 160 only 11% of NDCs, and for montane habitats, in only 4% 2 . Moreover, some of these important naturally-treeless habitats are threatened by afforestation, which is particularly troubling given that the original habitat can often provide greater and more resilient carbon storage benefits 25 .

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In other words, forests must not be prioritised at the cost of continuing to destroy or replace other vitally important ecosystems. To achieve this balance there is a need to be more inclusive when discussing the importance of nature-based solutions to climate change and when encouraging policy makers to take them into account.

Diversity is key for human adaptation
In the drive to harness natural ecosystems to slow warming, it is also important not to lose sight of their essential role in supporting human adaptation to climate change. Prioritizing a variety of ecosystems and promoting their functional resilience will also secure a suite of ecosystem services vital for adaptation 26  Ultimately, it is about working with nature in such a way that ecosystems continue supporting human development and well-being in the face of change (Box 1).

Biodiversity and climate change integration
All this highlights the need for much stronger links between ecosystem scientists, social scientists studying human adaptation and resilience, and those designing and implementing climate change policy. While the understanding of the role that biodiversity at all levels, including a diversity of habitats, can play in mitigating and adapting to climate 195 change is growing rapidly, policy development and implementation for climate change and biodiversity remain largely separate. The result is a lack of robust targets for nature in climate pledges, beyond areas of forest to be planted or restored. As climate pledges get revised, it is important that this knowledge is informing the process and helps raise Conference of the Parties formally decided to integrate climate change issues into national biodiversity strategies and vice versa 30 . This rapidly growing recognition of nature's 210 importance in a warming world is to be celebrated. However, as agendas for nature get translated into actions, the importance of diverse, intact natural ecosystems must not be forgotten. In the fight against climate change, forests make excellent allies. However, unless a diversity of species-rich resilient ecosystems are restored and protected -guided by science and implemented through local stewardship -the battle cannot be won. We 215 hope those advocating for action and funding in the wake of the UNFCCC meeting in Poland in December will bear this in mind.