Biodiversity loss could considerably undermine the provision of regulating and non-material NCPs 20–22 and coordinated global responses that simultaneously mitigate global change impacts on biodiversity and NCP loss are increasingly important 2,3,16,22. While our work did not aim at establishing causality between biodiversity presence and NCP provision, we did find high spatial congruence between high biodiversity value and high NCP provision under global environmental change both in the present and in the future.
Levels of air quality and climate regulation will increase in the future, and such increase will be higher within biodiversity regions (especially under higher emission scenarios). Water availability instead will slightly decrease in the future, especially within high value biodiversity regions. Areas of high biodiversity value in South and central America will face decreasing value of mean water availability (indicator for NCP 6), except for the Southeast coast of Brazil while on the other hand area of central Africa, Indonesia and Malaysia will be characterized by increasing WA values. High biodiversity value regions play an increasingly important role in ensuring high LAI under increasing levels of climate change (as the difference in LAI is higher under scenarios of higher emission), meaning that the conservation of these areas will be even important to preserve their air quality regulation role especially if carbon emission level will surpass the Paris targets. Our results also demonstrate that high biodiversity value regions will overlap with critical carbon sinks even if global warming surpasses 2°C above pre-industrial levels, as cVeg increases more under the two more distant scenarios, SSP1-2.6 and SSP5-8.5, compared to the others.
The discrepancies between the cVeg and LAI trends, with more consistent differences between biodiversity vs control areas seen in cVeg across scenarios, is probably due to a mix of factors. Changes in cVeg result from changes in NPP but also from the carbon residence time in living vegetation 23,24. Residence time responds to CO2 levels, which vary across scenarios, and vegetation biomass is influenced by natural disturbances, such as natural fires, which are also simulated interactively in CMIP6 for each scenario. Instead, LAI results from the carbon balance of the leaves 25,26, which is projected to increase “linearly” under each scenario (see Fig. S13). This is different from cVeg, which does not increase much under intermediate scenarios SSP2-4.5 and SSP3-7.0. This is likely related to the influence of land-use change on cVeg. In fact, while all scenarios project some increase in cropland extent, scenario SSP3-7.0 also projects substantial increase in grazing land 27. Thus, the land use of this particular scenario is dominated by a type of vegetation with higher leaves carbon content, but lower amount of carbon stored belowground and in woody parts above ground, leading to lower total carbon in vegetation (cVeg).
The global loss of water availability under each scenario, which is even more pronounced in the high biodiversity value regions, is due to the combination of reduced precipitation and increased evapotranspiration (AET). This is especially true in the Amazon (which contains large extents of high biodiversity value regions), meaning that one of the currently most important areas for biodiversity will not be able to preserve its current freshwater quantity regulation ability in the future 28,29. However, it is also important to recognize the contribution the evapotranspiration from the Amazon (and other extensive tropical forested regions like the Congo and Indonesia) makes in generating precipitation elsewhere. This vegetation-mediated moisture recycling accounts for a substantial portion of the precipitation in downwind systems 30, and increased evapotranspiration in these sending ecosystems could actually increase the resilience of the receiving systems, and all the NCP they generate.
Understanding the relationship between NCP and biodiversity, and their potential conservation synergies, is essential for sustaining human well-being and securing Earth’s life support systems 14,31. Nevertheless, even as the number of studies focused on biodiversity–ecosystem-functioning relationship has increased in recent years 20,32,33, many remaining uncertainties hinder clear conclusions 21,22,34. In fact, the relationship between biodiversity and NCP provision can be very hard to define due to the complexity of processes and interactions present in ecosystems that are seldom fully described and have remained inadequately investigated 35–37. The fact that important biodiversity areas are strongly associated with the provision, and increase, in biomass-related NCP might be related to the fact both processes are ultimately driven by the same underlying environmental drivers. In fact, it has been found that the correlation between species richness and carbon content is higher when both variables can be independently predicted by climate, soil, and topography 31. This is not always the case, as many open ecosystems (grasslands, savannahs) are important for biodiversity conservation but have limited carbon content; however, our delineation of high biodiversity value regions mainly include forested environments where there is high correspondence between higher diversity and higher biomass content. The pattern observed with water availability, where areas of high biodiversity value face higher risk of increased evapotranspiration than control areas, is linked to a potential overestimation of LAI, due to CO2 fertilization effects and their impact on the hydrologic cycle. The CO2 fertilization effects is considered the main driver of the projected increment of global LAI, which is partly offset by the negative effects of global warming, but all CMIP6 models are known to overestimate global mean LAI 38,39. Such overestimation will lead to overestimation of carbon input to the terrestrial ecosystem (gross primary production) 40, transpiration and canopy evaporation 41. The AET increase induced by vegetation greening through an extended area of leaves performing transpiration ,will then reduce soil moisture and runoff, which can intensify droughts at the catchment scale42.
Analysing how the increases or decreases in potential NCP coincide with current and future human population centres is an important next step for ultimately mapping realized NCP, the actual flow of NCP that humanity receives, which could better inform policies that drive national mitigation and adaptation actions. This is especially important given the heterogeneity found in the changes in potential NCP provision between countries even within the same subregion. How future changes in population might interact with and intensify these ecological changes is a key consideration for future policy. For example, strong differences in NCP values are seen between high biodiversity value regions and control areas in Indonesia, while in Malaysia the difference is less evident. Nevertheless, population density is projected to increase strongly under all future scenarios in areas outside high biodiversity value regions in both countries, making differences in realized NCP even larger. Other countries are projected to suffer a reduction of NCP provision while population simultaneously increases: a reduction of cVeg is seen in Cameroon, Gabon, Zambia, and South Africa under various scenarios as population grows in all these countries. In contrast, despite overall declines in water quantity regulation globally, a few countries are characterized by an increase in water availability, such as Zimbabwe, Venezuela, Suriname and Sri Lanka. In particular in these countries, both precipitation and AET decreased, but AET decreased more substantially leading to positive change of water availability (WA), while in Sri Lanka there was a higher increase of precipitation compared to the increase of evapotranspiration. Sri Lanka is also projected to go towards a major population increase compared to other countries characterized by a WA increase for which is projected a smaller increase in population. On the other hand, there are also countries such as China, where a reduction in human population will offset (to some extent) the increase of potential NCP. Thus, fully accounting for realized NCP requires an examination of not only population but demand (or need) for NCP, which may vary among countries or different social groups based on their vulnerability, and this is an important area for further work.
While both land-use change and climate change play a role in determining the change in NCP levels predicted under alternative scenarios, we found a dominant role of climate over land-use. This means that area-based conservation interventions must be coupled with bold climate mitigation policies, or risk being ineffective at preserving the crucial NCP provision role played by several important biodiversity areas. However, we found a risk of reduced water availability in these areas even under the most optimistic scenario considered in our analysis, which is compliant with the 2°C Paris target. This suggests that adaptation to climate change will assume increasing importance even under sustainability scenarios where local communities and nations will need to safeguard water resources, increase water-use efficiency, and change practices and behaviours where necessary to continue to thrive under changing precipitation patterns. Indeed, trade-offs will need to be weighed in the role of nature to provide mitigation vs. adaptation benefits for coping with climate change 43.
Spatial guidance is needed to identify areas of potential co-benefits between conserving biodiversity and NCP, in order to promote the implementation of global climate and biodiversity commitments at local levels. General conclusions have been difficult to draw from past work in which ‘biodiversity’ has generally been based on subset of global biodiversity, typically mammals and birds 44, often to the exclusion of reptiles, invertebrates and plant species, as well as other dimensions of biodiversity 3,16,31,45. Our work synthesizes high biodiversity value regions resulting from the combination of published biodiversity conservation maps focusing on different taxa as well as phylogenetic and functional diversity 17, thus representing many different elements of biodiversity.
Our results show spatial congruence between biodiversity value and NCP value.
Regardless of whether this spatial congruence is due to correlation (via underlying environmental mechanisms) or causation, the areas we identified are important from a conservation policy perspective, allowing us to identify the relative contribution of high biodiversity value regions to NCP provision. Our results show the existence of substantial synergies between the achievement of goals set under different convention (for example, CBD and the United Nations Framework Convention on Climate Change) and different Sustainable Development Goals. Conserving areas of high biodiversity value would protect life on land (SDG15), while delivering a high contribution to good health and wellbeing (SDG3), availability of clean water (SDG6) and mitigation of climate change (SDG 13). Thus, it is now fundamental to improve the mapping of other (less studied) NCP to understand whether other synergistic patterns (similar to those we describe here) emerge 46. Under accelerating climate change, and under high risk of global geo-political instability from recent humanitarian catastrophes (such as COVID-19, the war in Ukraine, and many regional-scale extreme weather events) it is imperative to quickly consolidate an integrated human–nature paradigm shift incorporating NCP into the assessment of SDGs, while guiding investments and implement Nature Based Solutions for climate change adaptation and mitigation policies 47. Here we show that spatial options for win-win strategies that achieve human and nature benefits are available, and rather substantial, and should be pursued before being eroded by human-induced environmental change.