Nowadays, one cannot ignore the message of “Plant trees!” when discussing climate change mitigations. Projects like the Trillion Tree Campaign or even the new EU Biodiversity Strategy for 2030 focus on afforestation as the solution to combat climate change. Temperate and tropical grasslands and savannas are often targets of tree-planting projects, even though these habitats constitute great climate and biodiversity benefits themselves. They are often biodiversity hotspots and are less strongly affected by extreme weather events than many forest systems. In their latest paper, Tölgyesi et al. (2022) suggest modifying the catchphrase “tree planting” by including more than trees and forested ecosystems: The slogan “Restore native vegetation” would shift the focus on the habitat condition of an area, increasing the land range for effective climate change mitigations.
While there is recently growing recognition for the importance of grassland restoration in science, the diverse flora, fauna, and ecosystem services these habitats provide are still often undervalued. According to Tölgyesi et al., this is mainly due to a history of forests being considered the ultimate form of nature by the western world. In colonial times, this view was extended to developing countries, mistakenly considering tropical grasslands and savannas as degraded forests. Tölgyesi et al. stress the misfortune of this situation, since we may be not only destroying important biodiversity by afforesting open habitats of high conservation value: By focusing only on mainly aboveground carbon and not the turnover times of carbon (aimed to be drawn down from the atmosphere) or also whether this really leads to climate cooling, we run the danger of destroying biodiversity and not creating much climate cooling, all in the name of ecological restoration of biodiversity and climate mitigation. We can do better than this, and all it will take is a more inclusive view of the science-policy framing.
Tölgyesi et al. point out that the determination what type of habitat to restore in specific areas is well-known: In arid areas, grasslands should be considered rather than the afforestation of closed-canopy forests, as they sustain the native biodiversity better and will be more resilient in drought-prone present and future. Here, the success of afforestation is low and therefore carbon targets are more likely to be missed. Additionally, grasslands in arid areas present advantages when fires happen: Carbon is safely stored in the soil, while above-ground carbon sinks of forests are lost in fires and land degradation is overall higher. In contrast, Tölgyesi et al. stress that historically-forested regions should be reforested if currently cleared, particularly in the tropical and sub-tropical regions, as here tree planting will not interfere with the important albedo effect that occurs when light surfaces (open habitats) reflect solar radiation back into space. To maximize not only carbon storage but also biodiversity in interaction with climate cooling and adaptation, the issue of what we do with which patch of land is the bottleneck we need to pass through to achieve the best possible outcomes as quickly as possible. The EU Commission supporting the EU Nature Restoration Law in June 2022, based on a proposal from a wide range of restoration ecologists from across Europe who are (amongst other things) concerned about the one-sidedness of only focusing on trees as solutions to our complex environmental problems, is an important step in the right direction. This Law, if it is endorsed by the EU Parliament and the Member States could be a major game-changer, since it includes wetlands (grasslands included) and peatlands, pollinators (flower-rich grasslands in the background here too), marine and riverine ecosystems as well as forests and include multifunctional outcomes of restoration interventions.
Many of our endangered species in Europe for example, are adapted to open habitats and have been lost mainly due to the intensification of agriculture and loss of high nature value grasslands and orchards as important cultural landscapes. We can address many of these challenges by restoring open ecosystems with the same verve as we are adding more trees to the landscape, and we will be addressing insect decline, carbon turnover, increasing the albedo effect and including a stronger human involvement in the landscapes in question.
Lastly, the authors address the areas most targeted by tree-planting projects: Areas that lie within the environmental tolerant limits of closed-canopy forests, like savannas or forest steppes. The mosaic structure of such steppes and savannas provides very high biodiversity levels and many provisioning, regulating and cultural ecosystem services. These habitats are one of the globally most threatened habitats due to agricultural intensification or woody species encroachment. In addition, climate change is already intensifying droughts and extreme weather conditions, severely limiting the capacity of forests to lock atmospheric carbon dioxide long-term into their tissues and their overall sustainability. The forests of the Western United States for example, with major forest fires interacting with insect attacks, have partly started changing into alternative vegetation states of shrublands – making their restoration back to forests a difficult goal to have, depending on how frequent future extremes affect the vegetation. This underlines that we now need to include broad regional climate models that include a changing disturbance regime in our restoration plans, wherever possible, so that we can avoid restoring a habitat type that is predicted to no longer be viable in a region in a number of decades. Since what will actually happen also depends (within a feedback loop system) on what we now do and do not do to restore and conserve different habitats (as well as how they respond to increasing weather extremes) the best possible insurance hypothesis will involve a maximization of restoration of different habitats of different ages, creating landscape mosaics that we know have created high diversity and resilience in the past.
Therefore, Tölgyesi et al. recommend a restoration approach that allows to sustain and increase both woody and grassy vegetation in proportions that consider where different kinds of biodiversity have been found in the past and where they may be in the future, such that we do not risk massively reducing biodiversity whilst calling ourselves “climate heroes”.
Ultimately, “tree planting” as a slogan cannot adequately reflect the potential of nature-based climate change mitigation. Tölgyesi et al. emphasize that using “restoring native vegetation” would avoid confusing the public or non-governmental organizations as it illustrates a more adequate picture of effective measurements. Focusing only on trees or forests is not backed up by science if the goals are to gain win-win situations, and by equally focusing on alternative vegetation types the mismatch between actions and goals could be removed. “Restoring native vegetation” would harmonize actions of climate mitigation and biodiversity conservation and not only accomplish seeing the forest for its trees but also expand our sight to nature’s entire potential to aid in mitigating and adapting to climate change. We know it does not sound as sexy or as simple as “plant a trillion trees” but the outcome will be far sexier for all.
To read the paper by Tölgyesi et al. (2022), click here.
Co-written with Prof. Dr Vicky Temperton