Trees, global visions & science communication

Trees, global visions & science communication

Does our research contribute to restoring biodiversity and climate?

There is an ongoing discussion around ‘natural solutions’ for climate, and the potential of forest restoration for carbon capture and mitigation of global warming. One of the key papers in this controversial debate was a Science paper in 2019 from Thomas Crowther’s lab at ETH Zurich. It presented a simple number and a map: 0.9 million ha for additional forest cover may be available across the globe outside areas occupied by settlement and ongoing agriculture. This represents about a trillion trees: 1/3 more than we have at present (although still less than there used to be without human impact) (see a previous paper). They estimated that these additional trees could help to remove a significant part of the access carbon from the atmosphere. [This area may be even represent a conservative potential *)]

That particular paper sparked a global political debate, and has contributed to change the goal of global campaigns from billions to a trillion trees (, etc.). Political decisions need such numbers and dimensions, no matter how precise its underlying components. But the paper also raised substantial criticism, mainly that (a) the potential was overestimated and clearly cannot replace other efforts to reduce greenhouse gas emissions (b) several modelled locations on the map had non-forest ecosystems or high altitude or elevation sites that would even face negative impacts if trees were planted here. I know many colleagues that are indeed very sceptic about the message delivered by this paper and/or by the subsequent media coverage. However, this controvery has many facets. It highlights the complex issue of science communication: clear messages with global impact versus specific details, novelty versus existing knowledge, urgent needs for solutions by society versus scientific uncertainties, inaccuracies and details, funding success versus lack of support, brave visions versus scepticism, leaders versus team spirit etc. This is clearly an issue on its own.

Thomas Crowther has reflected the critique. Whether you are among the sceptics or not, or entirely new to the debate: I can highly recommend this TED podcast interview (47 min) – or if you have only 11 min to spare, at least see his TED talk. It is a personal apology for communication errors around the 2019 paper – but much more than this. The interview is a credible appreciation of small, local solutions realized by regional communities and individual people’s responsibilities for such global problems. It reflects important facets of natural regeneration rather than fast-growing timber plantations and monocultures, the importance of biodiversity as well as non-forest ecosystems, the need for other measures to reduce carbon emissions… Being ecologist ourselves, we probably know all this already and there’s nothing new, right? However, it may still be useful to reflect these issues again. And the interview also depicts the challenging trade-off between delivering a clear message, a global vision on the one hand, and the risks of scientific communication inside and outside science on the other.

Recently, Thomas Crowther has been appointed as chair of the advisory board for the ongoing UN Decade on Ecosystem Restoration. His lab and collaborators now released a global platform where many local restoration projects are represented and linked: Some Jocotoco reserves are also included. Again, it is a network of many local initiatives and a global perspective at the same time, worth exploring. There is a lot to learn about the pros and cons and the forms in which the Crowther lab communicates very visibly, and with a lot of support (e.g. seven persons employed for communication and operations alone) and success.

A similar degree of renaturation, conservation and rewilding optimism is communicated by many NGOs and by other scientific initiatives. One international initiative analysed the recovery of secondary forests with a recent flagship article in Science (Poorter et al. 2021). Their findings across 77 secondary tropical forests sites in the Americas and West Africa highlighted a remarkable recovery speed for many functional aspects of forest ecosystems and tree diversity. The article – and its very prominent media coverage – also raised concerns among scientists or conservationists, however, whether this recovery speed can be generalized to heavily deforested regions in many tropical countries.

How does this debate and communication on restoration potential and climate mitigation concern us – our scientific project on reassembly of a rainforest in northwest Ecuador? First of all, our project and Jocotoco’s activities can be seen in a global framework of many regional attempts to restore ecosystems, particularly tropical forests. The need for action is urgent, the UN decade of Ecosystem Regeneration has started, and we take the climate and biodiversity crisis seriously (do we?). Our project has a scientific focus on reassembly of networks in the context of forest recovery, but also contributes to our understanding how and how quickly forest recover, and under which conditions.

What message can we deliver?

It is quite simple to draw a very optimistic picture for our findings: rainforest recover quickly in a few decades even after all trees have been removed and an area has been used as pasture or monoculture. Most parts of the biodiversity come back as well as the carbon storage within few decades. And this is an important point to make: yes, natural recovery and restoration works well, and yes, it is well worth to protect and conserve secondary forests. More than just timber mass, carbon storage or tree diversity, our project will help to understand which animal and plant species or which compounds of the ecosystem are key to successful regeneration, and which taxa particularly profit from it. Network and trait rules will help to understand underlying mechanisms, may facilitate generalization and knowledge transfer towards other recovering rainforests.

Of course, despite such restoration optimism, protecting the remaining old-growth forests is most effective and should have the highest conservation priority. And generalization to other areas is tricky. Huge areas in tropical countries may lack remaining natural forests entirely, or have only small fragments left – vast areas of the lowlands in western Ecuador included, where agriculture prevails. The species pool for forest recovery must come from such forest remnants, and it is obvious that in cleared agricultural landscapes natural regeneration will be much slower if they regenerate at all. This is also true when soils are depleted and land use has been long or too intense. Hoping that such devastated areas can be quickly restored into natural forests can be misleading. Similarly, many regions require active restoration efforts and tree plantings to show a visible success, so the message can be too simple that natural regeneration works as good or even better than active restoration (see also Crouzeilles et al. 2017). In South-East Asia, the most important tree family (dipterocarps) are very poor disperses, strongly hampering natural regeneration (Philipson et al. 2020). Hence, there is always a risk of delivering the wrong message from a simplified scientific insight. However, I do think that we have to face this challenge, be clear but also critical, engaged but sceptic, an put our work in a larger context – otherwise there may be no impact outside our narrow scientific community at all. 

Effective communication and political solutions need both, exposed visionaries and pedantic experts in their specific disciplines. It needs prominent faces, fund raisers as well as researchers and workers in the field. Most of us scientists are doing communication as a “hobby”, risk mistakes as we cannot be expected to be perfect. And there are many ways to contribute to a better society. Communication is key if we want to make an impact.

–> Feel free to share your thoughts, comments, support or contradiction below.


*) If I may add a personal view here: I think a global goal of restoring ecosystems on 0.9 million ha with 1 trillion trees outside the current agricultural and urbanized areas is even too modest and underestimates the global potential. Cities, urban areas and settlements deserve a much higher tree density. Biofuel should not waste huge land areas – instead it should be produced as a by-product of organic waste only. Most importantly, however, we can easily restore nature from agricultural land without even compromising our nutrition: about one third of the Earth’s land area (i.e. an area of North and South America combined!) can be given back to nature, if we reduce our meat and dairy consumption per person and replace it by a more effective and land-saving plant-based diet. That’s the land area we currently use for raising livestock (UBA) – cows, pigs and chicken which already exceed the biomass of all wild mammals and birds together on our planet by a factor of >10 (Bar-On et al. 2018). And and we can still feed the same human population! This seems to be the simplest and most realistic way for our vision to allocate a third ( or even half of the planet for nature ( The area gained increases proportionally with the shift in our diets, so we do not need to become 100% vegetarians or vegans. The newly gained green area for forest and other ecosystems has all environmental benefits: no carbon and methane emissions rather than long-term carbon fixation, no pesticides, antibiotics and fertilizer, but natural vegetation that can maintain a huge biodiversity. Of course, if we reduce meat in our diet by one-half or more, this would greatly increase our health, too – less fat, cholesterol, bacterial or viral risks and other by-products of mass farming. This is a clear win-win solution, very simple, very cheap, and has a huge impact on the environment. But we do have to overcome our personal resistance, convention and comfort and work towards a a more radical transformation of our society.