Strassburg et al. 2020
It is of critical importance that multiple different outcomes of ecosystem restoration are considered when deciding where and how to restore; failure to do so can lead to detrimental trade-offs between outcomes. This study assessed the effects of ecosystem restoration on both biodiversity conservation and carbon sequestration, quantifying how this varies at 300x300m resolution for terrestrial land globally. This information was used to identify the optimal areas to restore to gain the greatest benefits for both biodiversity and climate change mitigation.
The authors estimated that restoring 15% of agricultural and pasture lands would avoid 60% of expected extinctions, and sequester 299 GtCO2 (30% of the total atmospheric CO2 increase since pre-industrial times). Optimising for biodiversity and carbon outcomes simultaneously delivers 95% of the maximum potential biodiversity benefit and 89% of the maximum carbon sequestration benefit. If the scenario is also optimised for costs (including opportunity costs), the benefits for biodiversity and carbon are reduced only marginally (91% of potential biodiversity benefits and 82% of carbon benefits would be realised), whilst reducing costs by 27%. The authors estimated that carbon prices of USD 10-15/tCO2 would cover costs for restoration targets of up to 45% of global land converted to pasture/agriculture, making such restoration one of the cheaper mitigation options available.
The maps of priority restoration areas that this paper presents do not aim to indicate precise locations of where restoration ‘should’ take place, since there are other factors that must be taken into account. Perhaps most importantly, social constraints need to be considered. Conversion of farmland to natural ecosystems could in some cases negatively impact food security, health, food prices, people’s livelihood and ways of life; it may also be unpopular with voters making it politically controversial. However, if ecosystem restoration is planned and implemented with full consultation and genuine engagement of local people, then it holds potential to act as a positive force for people and nature.
Nonetheless, there are two crucially important messages from this study. First, that there are strong synergies between biodiversity and carbon benefits of restoration. Second, that international coordination of restoration efforts can greatly increase the global carbon and biodiversity benefits of restoration, because biodiverse, intact and carbon-rich habitats are not evenly distributed between countries (applying the 15% restoration target at the national scale reduces biodiversity benefits by 28% and carbon benefits by 29%). This should help some countries raise international funding for restoration on their own land by showing that it would be of international importance.
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