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How to bring back our planet’s forests
Current Biology
Magazine Feature
How to bring back our planet’s forests As an increasing number of protesters are keen to remind us, time is running out to avert a global climate catastrophe. Our globalised civilisation has to change direction in a whole range of aspects, but one of the easiest and most costefficient contributions to damage limitation is to plant many billions of trees. Reforestation efforts have already begun, but some have also been misguided. Michael Gross reports. Brightly painted ships with the inscription “Act now!” appeared on trailers blocking roads in five UK cities on July 15th. This was the start of a week of action scheduled by the climate protest group Extinction Rebellion, which was born out of a London-based protest only last October and specialises in non-violent direct action to disrupt the ‘business as usual’ approach that leads to climate catastrophe. Eye-catching and road-blocking ships showed up outside the Royal Courts of Justice in London, as well as in strategic locations in Cardiff, Glasgow, Leeds and Bristol. Protests in each city were focusing on a different ecological threat — rising sea levels, floods, wildfires, crop failures and extreme weather. The actions chime with a rising tide of other environmentalist protests seen across Europe, such as the ‘Fridays for Future’ pupils’ strikes inspired by the Swedish teenager Greta Thunberg, as well as local protests like those against open-cast coal mining in Germany. Demonstrators denounce the government plans still pushing off change to the remote future, with carbon neutrality promised for 2050. Ironically, the threat of climate change was known 30 years ago, so if a 30-year plan had been triggered then, it would be bearing fruit by now. Instead, the economy continues to invest in further fossil fuel extraction and consumption, as an Extinction Rebellion street party at the Oxford branch of Barclays has highlighted. Among European banks, Barclays has been identified as the biggest investor in fossil fuels by the 2019 report ‘Banking on Climate Change’. The topic is a sensitive one in Oxford, as the university is also resisting calls to divest its funds from fossil fuels.
Business as usual means that the energy-intensive western lifestyle is being rolled out to the entire world population, which is bound to escalate the climate catastrophe and biodiversity collapse. Multiple corrections to that course are necessary, but which measures have the best chances of success? Recent studies suggest that planting billions of trees to restore forests could be the biggest single factor to slow down climate change. Global forests It appears to be a trivial answer to the challenges of climate change that planting more trees will help to sequester more carbon dioxide from the atmosphere while also providing additional benefits such as habitat for wildlife and help with watershed management. The difficult questions, however, are how many trees are needed, where should they be planted,
do we have the space for them without endangering food security, and would it be economically feasible? Several research papers have now addressed these questions. Jean-François Bastin from the ETH Zurich, Switzerland, and colleagues have quantified the global potential for forest restoration, taking stock of all land areas where trees would naturally grow given current climate conditions, and which aren’t covered with concrete or otherwise engaged for growing crops (Science (2019) 365, 76–79). The researchers developed a machinelearning approach to predict the Earth’s carrying capacity for trees and tested it on existing protected areas to verify that it predicts their forest cover correctly. In total, if human civilisation ceased to exist, the predictions suggest that the Earth could and likely would have forests on two thirds of its land surface, amounting to 8.7 billion hectares, or 3.2 billion more than are currently forested. Of this differential, 1.4 to 1.5 billion hectares, depending on definitions, is in use as cropland or urban area. That leaves 1.7 to 1.8 billion hectares on which trees could be planted immediately — although this includes land used for grazing animals, so there might be some objections from that part. The forests in this calculation are accounted according to the definition of
Helping hands: Volunteer helpers of the organisation One Tree Planted at a forest restoration project in Guatemala. (Photo: One Tree Planted, onetreeplanted.org)
Current Biology 29, R715–R737, August 5, 2019
R715
Current Biology
Magazine
Urgent repair: Some African countries are conducting restoration projects in a bid to avert imminent environmental disaster. This image shows tree-planting efforts on Mount Rebero (Rwanda). (Photo: Ministry of Environment – Rwanda.)
the Food and Agriculture Organization (FAO) of the United Nations (at least 0.5 hectares in size, at least 10% canopy cover, no agricultural activity or human settlements). Using the more stringent definition of land actually under canopy cover, the authors arrive at the prediction that 900 million hectares worth of tree cover could be planted. If these areas were allowed to grow the natural forests typical of their region, they could store an additional 205 gigatonnes of carbon, according to the authors’ calculations. This matches the amount that the IPCC estimates must be removed from the atmosphere by the end of the century if global temperature rises are to be kept below the 1.5°C threshold. The biggest chunks of this reforestation potential are found in the world’s largest countries, namely Russia, United States, Canada, Australia, Brazil and China. Given that these countries won’t be rushing to give up cattle ranches and golf courses to make way for forests, it is worth asking where on our planet additional forests would yield the biggest benefits. Russia and Canada may have some of the largest areas that could bear forests, but at high latitudes the carbon sequestration by forest growth is less speedy and efficient than in the tropics. Moreover, forests in higher latitudes R716
might reduce the albedo (ability to reflect sunlight back into space) of the land surface and thus contribute to warming. Therefore, experts tend to place their hopes on tropical and subtropical regions around the world. In a recent analysis of restoration opportunities in the tropics, Pedro Brancalion from the University of São Paulo, Brazil, and colleagues have evaluated the specific benefits and costs of planting trees in tropical lowland areas and thus identified numerous hotspots where reforestation would produce the best yields (Sci. Adv. (2019) 5, eaav3223). These authors used four separate variables to evaluate restoration benefits, including biodiversity conservation, climate-change mitigation, climate-change adaptation, and safeguarding water security. To describe the risks and difficulties associated with potential reforestation projects, the authors looked at land opportunity cost, which could be, for instance, the cost of not using the land for agriculture, as well as the implementation costs and the chances of long-term survival. The researchers funnelled these parameters into a unified number, the restoration opportunity score, which they determined for every unit cell (30 arc sec, which is 1 km2 at the
Current Biology 29, R715–R737, August 5, 2019
equator) of the area of interest. The scores ranging from 0 to 1 follow a normal distribution, with roughly 12% exceeding 0.6. These highest-scoring grid cells are referred to as restoration hotspots. Still, the results favour different areas depending on which way these scores are analysed. The countries with the highest mean score are all in Africa and include Rwanda, Uganda, Burundi, South Sudan and Madagascar. So nationwide reforestation programmes in these countries would have the best chances of making a meaningful contribution to the fight against climate change. However, looking for the largest areas of restoration hotspots, one gets a distribution of locations all around the globe, and the top five areas are found in Brazil, Indonesia, India, Madagascar and Colombia. It is also useful to know that some of the factors analysed show synergies. Thus, the potential restoration sites that would be beneficial for biodiversity conservation and climate-change adaptation may also serve water security. Conflicts of interest arise mainly from the economic factors, as landscapes promising the greatest restoration benefits may also be attractive for other, commercial uses. Overall, Brancalion and colleagues highlight restoration as a tool to achieve multiple benefits, as they also explain in a recent comment (Science (2019) 365, 24–25). For any given location, these benefits can be assessed quantitatively and weighed against the costs. Jonah Busch from the Earth Innovation Institute at San Francisco, USA, and colleagues have recently quantified the opportunities of low-cost carbon sequestration by reforestation, confirming that the best opportunities are found in the tropics (Nat. Clim. Change (2019) 9, 463–466). International challenge Some significant efforts at forest restoration have already begun. The Bonn challenge, for instance, launched in 2011 by the German government and the IUCN, aims to bring 150 million hectares of the world’s deforested and degraded land into restoration by 2020, and 350 million hectares by 2030. Net economic benefits of the first target were calculated to amount to 84 billion US dollars. So far, 43 countries
Current Biology
Magazine including Brazil, India and China have made commitments to restore 300 million hectares of degraded land. This international plan incorporates a number of existing commitments, such as the CBD Aichi Target 15, the UNFCCC REDD+ goal, and the Rio+20 land degradation neutrality goal. Updates on the progress of the participating countries are found on the IUCN’s InfoFLR (Forest Landscape Restoration) website, http://infoflr. org. The second ‘barometer report’ on the FLR projects notes that the USA has already achieved its 2020 target of bringing 15 million hectares into restoration. The report includes indepth assessments for five countries, Brazil, El Salvador, Rwanda, Mexico and the USA, which had made commitments totalling 30.7 million hectares, of which 89% (27.4 million hectares) are now under restoration. However, Simon Lewis from University College London and Charlotte Wheeler from the University of Edinburgh, both in the UK, and colleagues have cast doubt on the value of these commitments (Nature (2019) 568, 25–28). They report that, under current plans, nearly half of the area pledged under the Bonn challenge is to be converted into plantations of commercial trees, such as eucalyptus for paper production or spruce for timber. The authors argue that the potential carbon sequestration is only achieved if the reforested areas are allowed to grow the kinds of trees native to their area and are left undisturbed. With model calculations, Lewis and Wheeler show that letting all the 350 million hectares of the Bonn challenge revert to natural forests would sequester 42 billion tonnes of carbon (out of the 200 billion tonnes reduction that is needed to meet the 1.5°C target). Under current plans, assuming that the fraction now assigned as natural forest will remain protected until the end of the century, the carbon sequestration will only amount to 16 billion tonnes. If all of the committed land was turned into commercial plantations, the carbon benefit would shrink to one billion tonnes. Although natural regrowth of native forests is the cheapest and easiest option, the authors note that 45% of the commitments involve industrial
Natural landscape: If humans weren’t interfering, around two thirds of the ice-free land surface would be covered by trees. Restoring a fraction of the missing natural forests would sequester enough carbon to keep climate change within the limit of the Paris accord. (Photo: jarmoluk/ Pixabay.)
plantations, and a further 21% are for agroforestry setups, such as cacao plantations with shade trees. As the current commitments are unlikely to make a big impact on the carbon balance, the authors call for the participating countries to scale up their plans such that the natural forest component covers the 350 million hectares target, while the planned plantations can continue to exist outside that target. National efforts There is no shortage of examples of how misdirected plantations projects can disturb local ecosystems and upset residents while failing to make any contribution to climate-change mitigation. The government of Ireland, for instance, currently one of Europe’s least forested countries, is encouraging commercial spruce plantations in an effort to offset the country’s carbon emissions including those of the booming dairy industry. It has set a target of increasing forest cover from currently 11% to 18% by 2046. Many investors are now using government incentives to plant Sitka spruce (Picea sitchensis), an extremely tall and fast-growing conifer that is native to the Pacific coast of North America but grows well in the mild and
damp climate of Ireland. Critics like the nature writer Mary Colwell have argued that these large monocultures of nonnative trees displace native biodiversity and endanger bird species like the hen harrier (Circus cyaneus) and the curlew (genus Numenius). These birds, as well as many other species, use so-called marginal farmland as habitat — land that is unsuited for large-scale agriculture and thus often left alone or only used for grazing. Obviously, this state of affairs doesn’t bring any financial benefits, so investors are grasping the opportunity to turn it into tree plantations, with a guaranteed revenue after a few decades and little required maintenance in the meantime. Whether this commercial opportunity is also good for the climate is a matter of some doubt. Colwell and others have argued that the natural humid soil in its current state stores as much carbon as the spruce plantations, and that their overall carbon benefits might be negligible to zero. Similarly, China’s afforestation programme known as the Great Green Wall, designed to stop the spread of the Gobi desert, has also been criticised for relying on monoculture plantations and thereby harming biodiversity (Curr. Biol. (2018) 28, R135–R138).
Current Biology 29, R715–R737, August 5, 2019
R717
Current Biology
Magazine Meanwhile, in some parts of Africa, reforestation has been recognised as an urgent necessity to repair damage to natural support systems and avoid further food and water crises. In Ethiopia, for instance, tree cover has shrunk from 35% to 13% in the last 100 years, leaving the land exposed to drought, erosion and the risk of famines. In response to this emergency, the Ethiopian government has now launched a programme to plant 4 billion trees within the current rainy season, or 40 trees per head of the country’s population. The trees are chosen to be ecologically adequate for the given environment. Part of the project will also involve replacing non-native eucalyptus trees with more adequate species. Introduced for commercial reasons, these plants have been notorious for taking up more water than the native vegetation and thus exacerbating drought conditions. In May, the Ethiopian Prime Minister Abiy Ahmed took part in the first tree plantings in this programme, which was also widely publicised by his government. Into the restoration decade Costa Rica has been an early example of a country investing in the restoration of natural ecosystems. After making a conscious decision in the 1980s to invest in its natural environment, the country has been able to increase tree cover from 21% in 1987 to more than 50% by 2005. Functional ecosystems like mangrove swamps were conserved or restored and the small country is now famous as a pioneer in conservation and a destination for ecotourism. It will be an example to the world as the UN launches the Decade of Ecosystem Restoration 2021–2030. Scaling up such approaches to countries the size of Brazil or China will be a challenge and would require a political will that is not necessarily available in the present political situation. It will, however be urgently necessary because, if we are to avert a climate catastrophe endangering the survival of our civilisation, we really do need to act now. Michael Gross is a science writer based at Oxford. He can be contacted via his web page at www.michaelgross.co.uk
R718
Q&A
Geert Kops Geert Kops graduated in Biology from Utrecht University in 2001 and did a PhD in signal transduction with Boudewijn Burgering and Hans Bos at the University Medical Center Utrecht (UMC Utrecht). Inspired by seminars from Conly Rieder and Erich Nigg, he then joined the lab of Don Cleveland at the University of California San Diego (UCSD) to study the spindle checkpoint. He moved back to the Netherlands in 2005 to establish an independent research group at UMC Utrecht, working on molecular mechanisms of chromosome segregation. After ten years at UMC Utrecht, where he became a full professor, and a short sabbatical as an unproductive ‘postdoc’ at the Fred Hutchinson Cancer Research Center in Seattle, he moved to the Hubrecht Institute in Utrecht, where he is a senior group leader. Since the summer of 2018, Geert has been the Scientific Director of the Oncode Institute, a nation-wide virtual cancer research institute with 62 groups aimed at facilitating basic science discoveries in oncology and accelerating their translation for patient benefit. What are you doing at the moment? Right now, I am preparing a lecture on evolutionary dynamics of kinetochores in eukaryotes for a Dutch conference on evolutionary biology. And by ‘preparing’ I mean procrastinating until there is nearly no more time and then frenziedly working to finish the slide deck. Wait a minute! Your bio mentions that you are Scientific Director of a virtual Dutch cancer research institute, so why are you working on the evolution of kinetochores? (And out of curiosity, what do you do when you procrastinate?) Ah, yes, that may indeed seem a little odd. The research in my group is not what you’d call focused. We started out in 2005 working on molecular mechanisms of the spindle checkpoint, the main control mechanism that protects cells from making mistakes in chromosome distribution during cell division. While we still study molecular mechanisms of
Current Biology 29, R715–R737, August 5, 2019
chromosome segregation, our research has also spun out in two different directions. The first is more directly related to cancer: what are the causes of chromosomal instability and what are its consequences for cells and for cancer initiation, development, and progression? The second is about the evolution of some of the molecular mechanisms that we study. This started out as a small project aimed at using evolutionary insights to help us understand an unusual kinase that we were studying, and it quite unexpectedly turned out to uncover very interesting evolutionary dynamics for this kinase. One thing led to another, and seven years later I am still trying to understand the sometimes perplexing diversity in chromosome segregation mechanisms that we see out there in biology. Have you always had an interest in evolution? It is what actually drew me into studying Biology at Utrecht University. I had a Catholic upbringing (not a strict one though), which meant that God was the ‘easy’ answer to most questions about biology and the universe. I remember one day reading an illustrated version of Darwin’s theory of evolution by natural selection, and it was as if a light had been turned on in my head! It is a beautiful concept, and it had an instant impact on me: I was around 12 or 13 years old and I pretty much abandoned religion then, and slowly ‘evolved’ into a scientist I guess. I started reading more and more about evolution, for example, about the Miller–Urey experiment (simulating possible chemical conditions of early Earth and seeing the basic building blocks of life emerge). I think that, if I had to choose any other topic to work on, it would be related to the origin of life on Earth, one of the great remaining mysteries in biology. I greatly admire people like Jack Szostak, who rededicated his research to this question after winning a Nobel prize for his studies of telomeres! So why did you do a PhD in signal transduction? We had a great teacher at university, Johannes Boonstra, who taught a class on growth factor receptor signaling. Basic concepts about the molecular mechanisms of this signaling were being discovered by
Magazine Feature
How to bring back our planet’s forests As an increasing number of protesters are keen to remind us, time is running out to avert a global climate catastrophe. Our globalised civilisation has to change direction in a whole range of aspects, but one of the easiest and most costefficient contributions to damage limitation is to plant many billions of trees. Reforestation efforts have already begun, but some have also been misguided. Michael Gross reports. Brightly painted ships with the inscription “Act now!” appeared on trailers blocking roads in five UK cities on July 15th. This was the start of a week of action scheduled by the climate protest group Extinction Rebellion, which was born out of a London-based protest only last October and specialises in non-violent direct action to disrupt the ‘business as usual’ approach that leads to climate catastrophe. Eye-catching and road-blocking ships showed up outside the Royal Courts of Justice in London, as well as in strategic locations in Cardiff, Glasgow, Leeds and Bristol. Protests in each city were focusing on a different ecological threat — rising sea levels, floods, wildfires, crop failures and extreme weather. The actions chime with a rising tide of other environmentalist protests seen across Europe, such as the ‘Fridays for Future’ pupils’ strikes inspired by the Swedish teenager Greta Thunberg, as well as local protests like those against open-cast coal mining in Germany. Demonstrators denounce the government plans still pushing off change to the remote future, with carbon neutrality promised for 2050. Ironically, the threat of climate change was known 30 years ago, so if a 30-year plan had been triggered then, it would be bearing fruit by now. Instead, the economy continues to invest in further fossil fuel extraction and consumption, as an Extinction Rebellion street party at the Oxford branch of Barclays has highlighted. Among European banks, Barclays has been identified as the biggest investor in fossil fuels by the 2019 report ‘Banking on Climate Change’. The topic is a sensitive one in Oxford, as the university is also resisting calls to divest its funds from fossil fuels.
Business as usual means that the energy-intensive western lifestyle is being rolled out to the entire world population, which is bound to escalate the climate catastrophe and biodiversity collapse. Multiple corrections to that course are necessary, but which measures have the best chances of success? Recent studies suggest that planting billions of trees to restore forests could be the biggest single factor to slow down climate change. Global forests It appears to be a trivial answer to the challenges of climate change that planting more trees will help to sequester more carbon dioxide from the atmosphere while also providing additional benefits such as habitat for wildlife and help with watershed management. The difficult questions, however, are how many trees are needed, where should they be planted,
do we have the space for them without endangering food security, and would it be economically feasible? Several research papers have now addressed these questions. Jean-François Bastin from the ETH Zurich, Switzerland, and colleagues have quantified the global potential for forest restoration, taking stock of all land areas where trees would naturally grow given current climate conditions, and which aren’t covered with concrete or otherwise engaged for growing crops (Science (2019) 365, 76–79). The researchers developed a machinelearning approach to predict the Earth’s carrying capacity for trees and tested it on existing protected areas to verify that it predicts their forest cover correctly. In total, if human civilisation ceased to exist, the predictions suggest that the Earth could and likely would have forests on two thirds of its land surface, amounting to 8.7 billion hectares, or 3.2 billion more than are currently forested. Of this differential, 1.4 to 1.5 billion hectares, depending on definitions, is in use as cropland or urban area. That leaves 1.7 to 1.8 billion hectares on which trees could be planted immediately — although this includes land used for grazing animals, so there might be some objections from that part. The forests in this calculation are accounted according to the definition of
Helping hands: Volunteer helpers of the organisation One Tree Planted at a forest restoration project in Guatemala. (Photo: One Tree Planted, onetreeplanted.org)
Current Biology 29, R715–R737, August 5, 2019
R715
Current Biology
Magazine
Urgent repair: Some African countries are conducting restoration projects in a bid to avert imminent environmental disaster. This image shows tree-planting efforts on Mount Rebero (Rwanda). (Photo: Ministry of Environment – Rwanda.)
the Food and Agriculture Organization (FAO) of the United Nations (at least 0.5 hectares in size, at least 10% canopy cover, no agricultural activity or human settlements). Using the more stringent definition of land actually under canopy cover, the authors arrive at the prediction that 900 million hectares worth of tree cover could be planted. If these areas were allowed to grow the natural forests typical of their region, they could store an additional 205 gigatonnes of carbon, according to the authors’ calculations. This matches the amount that the IPCC estimates must be removed from the atmosphere by the end of the century if global temperature rises are to be kept below the 1.5°C threshold. The biggest chunks of this reforestation potential are found in the world’s largest countries, namely Russia, United States, Canada, Australia, Brazil and China. Given that these countries won’t be rushing to give up cattle ranches and golf courses to make way for forests, it is worth asking where on our planet additional forests would yield the biggest benefits. Russia and Canada may have some of the largest areas that could bear forests, but at high latitudes the carbon sequestration by forest growth is less speedy and efficient than in the tropics. Moreover, forests in higher latitudes R716
might reduce the albedo (ability to reflect sunlight back into space) of the land surface and thus contribute to warming. Therefore, experts tend to place their hopes on tropical and subtropical regions around the world. In a recent analysis of restoration opportunities in the tropics, Pedro Brancalion from the University of São Paulo, Brazil, and colleagues have evaluated the specific benefits and costs of planting trees in tropical lowland areas and thus identified numerous hotspots where reforestation would produce the best yields (Sci. Adv. (2019) 5, eaav3223). These authors used four separate variables to evaluate restoration benefits, including biodiversity conservation, climate-change mitigation, climate-change adaptation, and safeguarding water security. To describe the risks and difficulties associated with potential reforestation projects, the authors looked at land opportunity cost, which could be, for instance, the cost of not using the land for agriculture, as well as the implementation costs and the chances of long-term survival. The researchers funnelled these parameters into a unified number, the restoration opportunity score, which they determined for every unit cell (30 arc sec, which is 1 km2 at the
Current Biology 29, R715–R737, August 5, 2019
equator) of the area of interest. The scores ranging from 0 to 1 follow a normal distribution, with roughly 12% exceeding 0.6. These highest-scoring grid cells are referred to as restoration hotspots. Still, the results favour different areas depending on which way these scores are analysed. The countries with the highest mean score are all in Africa and include Rwanda, Uganda, Burundi, South Sudan and Madagascar. So nationwide reforestation programmes in these countries would have the best chances of making a meaningful contribution to the fight against climate change. However, looking for the largest areas of restoration hotspots, one gets a distribution of locations all around the globe, and the top five areas are found in Brazil, Indonesia, India, Madagascar and Colombia. It is also useful to know that some of the factors analysed show synergies. Thus, the potential restoration sites that would be beneficial for biodiversity conservation and climate-change adaptation may also serve water security. Conflicts of interest arise mainly from the economic factors, as landscapes promising the greatest restoration benefits may also be attractive for other, commercial uses. Overall, Brancalion and colleagues highlight restoration as a tool to achieve multiple benefits, as they also explain in a recent comment (Science (2019) 365, 24–25). For any given location, these benefits can be assessed quantitatively and weighed against the costs. Jonah Busch from the Earth Innovation Institute at San Francisco, USA, and colleagues have recently quantified the opportunities of low-cost carbon sequestration by reforestation, confirming that the best opportunities are found in the tropics (Nat. Clim. Change (2019) 9, 463–466). International challenge Some significant efforts at forest restoration have already begun. The Bonn challenge, for instance, launched in 2011 by the German government and the IUCN, aims to bring 150 million hectares of the world’s deforested and degraded land into restoration by 2020, and 350 million hectares by 2030. Net economic benefits of the first target were calculated to amount to 84 billion US dollars. So far, 43 countries
Current Biology
Magazine including Brazil, India and China have made commitments to restore 300 million hectares of degraded land. This international plan incorporates a number of existing commitments, such as the CBD Aichi Target 15, the UNFCCC REDD+ goal, and the Rio+20 land degradation neutrality goal. Updates on the progress of the participating countries are found on the IUCN’s InfoFLR (Forest Landscape Restoration) website, http://infoflr. org. The second ‘barometer report’ on the FLR projects notes that the USA has already achieved its 2020 target of bringing 15 million hectares into restoration. The report includes indepth assessments for five countries, Brazil, El Salvador, Rwanda, Mexico and the USA, which had made commitments totalling 30.7 million hectares, of which 89% (27.4 million hectares) are now under restoration. However, Simon Lewis from University College London and Charlotte Wheeler from the University of Edinburgh, both in the UK, and colleagues have cast doubt on the value of these commitments (Nature (2019) 568, 25–28). They report that, under current plans, nearly half of the area pledged under the Bonn challenge is to be converted into plantations of commercial trees, such as eucalyptus for paper production or spruce for timber. The authors argue that the potential carbon sequestration is only achieved if the reforested areas are allowed to grow the kinds of trees native to their area and are left undisturbed. With model calculations, Lewis and Wheeler show that letting all the 350 million hectares of the Bonn challenge revert to natural forests would sequester 42 billion tonnes of carbon (out of the 200 billion tonnes reduction that is needed to meet the 1.5°C target). Under current plans, assuming that the fraction now assigned as natural forest will remain protected until the end of the century, the carbon sequestration will only amount to 16 billion tonnes. If all of the committed land was turned into commercial plantations, the carbon benefit would shrink to one billion tonnes. Although natural regrowth of native forests is the cheapest and easiest option, the authors note that 45% of the commitments involve industrial
Natural landscape: If humans weren’t interfering, around two thirds of the ice-free land surface would be covered by trees. Restoring a fraction of the missing natural forests would sequester enough carbon to keep climate change within the limit of the Paris accord. (Photo: jarmoluk/ Pixabay.)
plantations, and a further 21% are for agroforestry setups, such as cacao plantations with shade trees. As the current commitments are unlikely to make a big impact on the carbon balance, the authors call for the participating countries to scale up their plans such that the natural forest component covers the 350 million hectares target, while the planned plantations can continue to exist outside that target. National efforts There is no shortage of examples of how misdirected plantations projects can disturb local ecosystems and upset residents while failing to make any contribution to climate-change mitigation. The government of Ireland, for instance, currently one of Europe’s least forested countries, is encouraging commercial spruce plantations in an effort to offset the country’s carbon emissions including those of the booming dairy industry. It has set a target of increasing forest cover from currently 11% to 18% by 2046. Many investors are now using government incentives to plant Sitka spruce (Picea sitchensis), an extremely tall and fast-growing conifer that is native to the Pacific coast of North America but grows well in the mild and
damp climate of Ireland. Critics like the nature writer Mary Colwell have argued that these large monocultures of nonnative trees displace native biodiversity and endanger bird species like the hen harrier (Circus cyaneus) and the curlew (genus Numenius). These birds, as well as many other species, use so-called marginal farmland as habitat — land that is unsuited for large-scale agriculture and thus often left alone or only used for grazing. Obviously, this state of affairs doesn’t bring any financial benefits, so investors are grasping the opportunity to turn it into tree plantations, with a guaranteed revenue after a few decades and little required maintenance in the meantime. Whether this commercial opportunity is also good for the climate is a matter of some doubt. Colwell and others have argued that the natural humid soil in its current state stores as much carbon as the spruce plantations, and that their overall carbon benefits might be negligible to zero. Similarly, China’s afforestation programme known as the Great Green Wall, designed to stop the spread of the Gobi desert, has also been criticised for relying on monoculture plantations and thereby harming biodiversity (Curr. Biol. (2018) 28, R135–R138).
Current Biology 29, R715–R737, August 5, 2019
R717
Current Biology
Magazine Meanwhile, in some parts of Africa, reforestation has been recognised as an urgent necessity to repair damage to natural support systems and avoid further food and water crises. In Ethiopia, for instance, tree cover has shrunk from 35% to 13% in the last 100 years, leaving the land exposed to drought, erosion and the risk of famines. In response to this emergency, the Ethiopian government has now launched a programme to plant 4 billion trees within the current rainy season, or 40 trees per head of the country’s population. The trees are chosen to be ecologically adequate for the given environment. Part of the project will also involve replacing non-native eucalyptus trees with more adequate species. Introduced for commercial reasons, these plants have been notorious for taking up more water than the native vegetation and thus exacerbating drought conditions. In May, the Ethiopian Prime Minister Abiy Ahmed took part in the first tree plantings in this programme, which was also widely publicised by his government. Into the restoration decade Costa Rica has been an early example of a country investing in the restoration of natural ecosystems. After making a conscious decision in the 1980s to invest in its natural environment, the country has been able to increase tree cover from 21% in 1987 to more than 50% by 2005. Functional ecosystems like mangrove swamps were conserved or restored and the small country is now famous as a pioneer in conservation and a destination for ecotourism. It will be an example to the world as the UN launches the Decade of Ecosystem Restoration 2021–2030. Scaling up such approaches to countries the size of Brazil or China will be a challenge and would require a political will that is not necessarily available in the present political situation. It will, however be urgently necessary because, if we are to avert a climate catastrophe endangering the survival of our civilisation, we really do need to act now. Michael Gross is a science writer based at Oxford. He can be contacted via his web page at www.michaelgross.co.uk
R718
Q&A
Geert Kops Geert Kops graduated in Biology from Utrecht University in 2001 and did a PhD in signal transduction with Boudewijn Burgering and Hans Bos at the University Medical Center Utrecht (UMC Utrecht). Inspired by seminars from Conly Rieder and Erich Nigg, he then joined the lab of Don Cleveland at the University of California San Diego (UCSD) to study the spindle checkpoint. He moved back to the Netherlands in 2005 to establish an independent research group at UMC Utrecht, working on molecular mechanisms of chromosome segregation. After ten years at UMC Utrecht, where he became a full professor, and a short sabbatical as an unproductive ‘postdoc’ at the Fred Hutchinson Cancer Research Center in Seattle, he moved to the Hubrecht Institute in Utrecht, where he is a senior group leader. Since the summer of 2018, Geert has been the Scientific Director of the Oncode Institute, a nation-wide virtual cancer research institute with 62 groups aimed at facilitating basic science discoveries in oncology and accelerating their translation for patient benefit. What are you doing at the moment? Right now, I am preparing a lecture on evolutionary dynamics of kinetochores in eukaryotes for a Dutch conference on evolutionary biology. And by ‘preparing’ I mean procrastinating until there is nearly no more time and then frenziedly working to finish the slide deck. Wait a minute! Your bio mentions that you are Scientific Director of a virtual Dutch cancer research institute, so why are you working on the evolution of kinetochores? (And out of curiosity, what do you do when you procrastinate?) Ah, yes, that may indeed seem a little odd. The research in my group is not what you’d call focused. We started out in 2005 working on molecular mechanisms of the spindle checkpoint, the main control mechanism that protects cells from making mistakes in chromosome distribution during cell division. While we still study molecular mechanisms of
Current Biology 29, R715–R737, August 5, 2019
chromosome segregation, our research has also spun out in two different directions. The first is more directly related to cancer: what are the causes of chromosomal instability and what are its consequences for cells and for cancer initiation, development, and progression? The second is about the evolution of some of the molecular mechanisms that we study. This started out as a small project aimed at using evolutionary insights to help us understand an unusual kinase that we were studying, and it quite unexpectedly turned out to uncover very interesting evolutionary dynamics for this kinase. One thing led to another, and seven years later I am still trying to understand the sometimes perplexing diversity in chromosome segregation mechanisms that we see out there in biology. Have you always had an interest in evolution? It is what actually drew me into studying Biology at Utrecht University. I had a Catholic upbringing (not a strict one though), which meant that God was the ‘easy’ answer to most questions about biology and the universe. I remember one day reading an illustrated version of Darwin’s theory of evolution by natural selection, and it was as if a light had been turned on in my head! It is a beautiful concept, and it had an instant impact on me: I was around 12 or 13 years old and I pretty much abandoned religion then, and slowly ‘evolved’ into a scientist I guess. I started reading more and more about evolution, for example, about the Miller–Urey experiment (simulating possible chemical conditions of early Earth and seeing the basic building blocks of life emerge). I think that, if I had to choose any other topic to work on, it would be related to the origin of life on Earth, one of the great remaining mysteries in biology. I greatly admire people like Jack Szostak, who rededicated his research to this question after winning a Nobel prize for his studies of telomeres! So why did you do a PhD in signal transduction? We had a great teacher at university, Johannes Boonstra, who taught a class on growth factor receptor signaling. Basic concepts about the molecular mechanisms of this signaling were being discovered by