Tag Archives: trees

There are likely over 9,000 species of trees we haven’t discovered yet. But can we find them before they disappear?

Rainforests are home to the rarest tree species in the world, as well as contain the most species waiting to be discovered by scientists. Credit: Pixabay.

Sure, you’ve heard about the oak and sycamore trees, but do you know about New Zealand’s kauri tree, Madagascar’s traveler’s tree, or Canada’s rhododendron shrub? You may be surprised to learn that there are about 73,000 different species of trees growing on Earth, according to estimates from the most thorough analysis of its kind to date involving more than 140 scientists across the globe and the largest forest databases assembled thus far. Of these, it is thought that nearly 9,200 species have yet to be discovered, making the global estimate about 14% higher than the current number of known tree species.

Many of these tree species are likely rare and extremely localized to specific ecosystems, making them vulnerable to extinction. Some may disappear for good before scientists get the chance to identify and describe them. This is precisely why this latest study is so important — it provides the tools to identify rare and threatened species that require immediate action to prevent them from becoming extinct, as well as map out the most likely locations where new species may be found.

“It is well known that tree species are going extinct due to deforestation and climate change, and understanding the value of that diversity requires us to know what is there in the first place before we lose it. Thus if we were successful in estimating the number of species, it would establish a quantitative benchmark to help us to prioritize conservation efforts,” University of Michigan forest ecologist Peter Reich told ZME Science.

For their study, Reich and over a hundred other international colleagues combined two massive global datasets — one from the Global Forest Biodiversity Initiative and the other from TREECHANGE — to establish tree abundance and occurrence across 90 countries. This data took many years to gather, often requiring researchers to get their boots wet in the field where they would collect samples, measure trees, and count each individual tree in the forest.

This is not the first attempt to quantify the species of trees in the world. Previously, Botanical Gardens Conservation International (BGCI) compiled a list of 60,065 species using data gathered from its network of over 500 member organizations. The new study, however, went the extra mile. It used a vastly more extensive dataset, which makes the estimates more reliable, and the study also estimated unknown species using novel statistical methods.

“Given our enormous data set (more than 40 million trees, 64,000 species in our sample, 9,300 grid cells across the globe) we have sufficient data to address a lot of questions impossible to answer previously,” Professor Reich said.

“Really smart statistically savvy ecologists figured out that there is a lot of information hidden in the numbers of species that show up only once or twice or three times in a large sample, such as the one we put together.  If among a million individual trees we found 800 species, but all of them at least 17 times (I just made up those numbers as an illustration), it is unlikely that there are many additional species out there (because the rarest in our sample have already been encountered quite a few times). By contrast, the greater the number of species that are found only once (and we found a lot of those), the greater the number of species that are similarly rare but that we by accident likely did not yet encounter. And the greater the ratio of species we found once versus twice, and that we found twice versus three times, the more likely is it that there are lots of species we simply did not yet encounter,” the scientist explained.

The analysis of the combined databases yielded a total of 64,100 tree species worldwide. With another estimated 9,200 species yet to be discovered, the total number of tree species on Earth is believed to hover around 73,000.

Nearly 40% of these undiscovered species are likely waiting to be discovered in South America, particularly in biodiversity hot spots like the Amazon basin and the Andean forests. This makes sense since the continent is home to the highest number of rare tree species (nearly 8,200). What’s more, nearly half of all tree species in South America are endemic to the continent, meaning they can’t be found anywhere else in the world.

Up to two-thirds of all already known tree species are found in tropical and subtropical moist forests, which are inaccessible and difficult to study. Dry forests in the same regions also likely hold high numbers of undiscovered species.

But these same hotspots are also the most threatened at the moment by deforestation, climate change, and devastating fires. The new findings show tree diversity is even richer than previously thought, which makes the case for preserving and cherishing these natural treasures all the more important.

“Understanding the value of that diversity requires us to know what is there in the first place before we lose it. By establishing a quantitative benchmark, our study can contribute to tree and forest conservation efforts. Plus, we discovered that one-third of known species are rare, and a much larger fraction of unknown species are rare as well.  Rare species are far more likely to go extinct from deforestation and climate change, so our results highlight the vulnerability of global forest biodiversity.  It is also difficult to manage or conserve resources without a good understanding of what exists, so our data will help us assess where biodiversity is the most threatened (see above), based on the global hotspots of known and unknown rare species, and thus help us to prioritize conservation efforts,” said Reich.

The findings appeared in the Proceedings of the National Academy of Sciences.

Can’t cope with the urban heat? More trees could save the day

When it comes to temperatures, there’s a big gap between tree-rich and tree-less green spaces. Researchers studying data from Europe found that areas with an abundance of trees are two to four times cooler than those without them. With two-third of the population in Europe living in urban areas, it might be about time to plant a few extra trees.

Image credit: Flickr / Colin.

From preventing erosion to filtering the air we breathe, trees provide a large range of environmental services – including regulating urban temperatures. They cool the air through a process known as transpiration cooling and also reduce the amount of sunlight that hits buildings and pavement, lowering the amount of energy absorbed into the air. 

But these benefits can be difficult to find in big cities with a lot of concrete instead of green areas filled with trees. This is because concrete and asphalt act as heat magnets, producing the so-called urban heat island effect. Paved surfaces also block plants and trees from breathing properly, increasing the chances of high temperatures in cities. 

It’s most common for researchers to study temperature reductions by urban trees for a specific city or small region. But this makes a comparison between regions sometimes difficult, as each study in each city follows a different methodology. With this in mind, a group of researchers decided to explore using the same approach for many cities. 

“It would be nice if we knew by how much different heat mitigation measures can reduce temperatures in different cities. If we knew this, decision-makers would be able to select the most appropriate strategy for reducing heat in a specific city. This include increasing the albedo, for example,” study author Jonas Schwaab, told ZME Science. 

Studying trees

Schwaab and his colleagues used land surface temperature data derived from satellites and detailed data on land cover in European cities to compare the temperatures on different land-covers, looking at whether this temperature difference was the same in different regions. The assumption was that trees had a high cooling potential in cities.

The findings showed that tree-covered areas in and around cities are cooler than dense built-up areas during the day in all European regions. However, in central Europe, the temperature difference is higher than in Southern Europe. This is because trees in central Europe usually have more water than they can transpire, the authors suspect. 

“In southern Europe, overall drier than central Europe, less water is available and there’s less transpiration from trees. However, while the cooling effect of trees in Southern Europe through transpiration may be lower than in central Europe, trees are of course very important in providing shade in dry and wetter regions,” Schwaab said. 

While the study could have implications for urban development, the authors warned it has a set of limitations. Schwaab said that the land surface temperature data they used is not ideal for studying the potential reductions in air temperature and that they only focused on the effects of trees on temperature via transpiration rather than on other influences. 

The study was published in the journal Nature Communications. 

Human activities are driving wild trees species to extinction

The world is facing a biodiversity crisis and trees are no exception — a third of the world’s wild tree species are currently threatened with extinction, a concerning new report finds. The researchers said agriculture and grazing are the greatest threats for trees and urged conservation measures to avoid devastating consequences.

Image credit: Flickr / Jon Bunting.

Botanic Gardens Conservation International (BGCI), a plant conservation charity, carried out a five-year assessment of the status of wild tree species around the world. They looked at 60,000 tree species and found that 30% are at risk of extinction. That’s twice the number of threatened mammals, birds, amphibians, and reptiles combined. 

Of those, over 440 tree species are especially at risk, with fewer than 50 individuals remaining in the wild. These can be found all over the world, from the Menai whitebeam (Sorbus arvonensis) in North Wales, with just 30 trees remaining, to the Mulanje cedar (Widdringtonia whytei) in Malawi, with just a few remaining individuals.

“Every tree species matters — to the millions of other species that depend on trees, and to people all over the world. For the first time, we can pinpoint exactly which tree species need our help, so policymakers and conservation experts can deploy the resources and expertise needed,” Paul Smith, Secretary General, BGCI, said in a statement. 

Trees are of vital importance ecologically, culturally, and economically. They are highly significant components of biodiversity and carbon storage in many other ecosystems such as woodlands, grasslands, as well as artificial and urban environments. Most wild species are in Central and South America, followed by Southeast Asia and Africa. 

The report found that one in five tree species are directly used by humans, mainly for timber, medicines, food, and fuel. Their over-exploitation and mismanagement are what’s driving many to extinction. The greatest threats come from agriculture and grazing, followed by logging, harvesting, and a growing influence of climate change.

As global temperature increases, many species could lose areas of suitable habitat, both in temperature and tropical areas. The researchers found that at least 180 tree species are directly threatened by sea-level rise and extreme weather events. This is especially the case for island species, such as the magnolias in the Caribbean.

“Trees are vital for our future and for a healthy world we need tree species diversity. Each tree species has a unique ecological role to play. With 30 percent of the world’s tree species threatened with extinction we need to urgently scale up conservation action,” Sara Oldfield, Co-chair of the Global Tree Specialist Group, said in a statement. 

The road ahead

Despite the challenges faced by trees around the world, the report authors are hopeful for the future of conservation if efforts continue and are scaled up. We have seen some progress in some parts of the world, and there is still time to act. Alongside the actual report, they also launched an online database to track conservation effort for trees. This helps understand which trees need the most protection and in which countries. 

The authors also recommended a set of actions for policymakers and experts to protect and bring back threatened species. They suggested extending the protected area coverage for threatened species, ensuring that they are also conserved in botanic gardens and seed bank collections, and increasing availability of government and corporate funding. 

Individuals and organizations can also support tree planting programs, they argue, which support the planting of native and threatened three species. Through such efforts there’s a “huge opportunity to change this dire picture”, Jean-Christophe Vie, Director General of the Swiss Foundation Franklinia, said in a statement. 

The full report can be accessed here

Even a single urban tree can make a big difference during the summer heatwaves

Even a single tree planted on a street can help urban dwellers cope with urban heat, a new study reports. Researchers found that temperatures were 1.4ºC cooler around 6-7 pm in neighborhoods where at least half the area was covered by a canopy from trees, and even a single tree can make a significant difference for a bloc.

Image credit: Flickr / Steven Penton

Trees provide a remarkable number of environmental services. From filtering the air to preventing erosion and regulating stormwater runoff, there’s no denying trees don’t get enough credit for all the help they provide. Trees also play a role in regulating urban temperatures: they reduce the amount of sunlight striking buildings and pavement, which lowers the amount of energy absorbed and re-radiated into the air.

They also cool the air through a process known as transpiration cooling. As they release water into the atmosphere from the leaves, the surrounding air is cooled as water goes from liquid to vapor. 

But these benefits can be lost as cities expand and get filled with concrete instead of parks and forests. Dark surfaces absorb more heat from the sun, and concrete and asphalt (think roads and buildings) are excellent heat magnets, producing the so-called urban heat island effect, where cities are hotter than their surroundings. Paved surfaces also mean that plants and trees can’t breathe properly, reducing the important evapotranspiration

Urban heat can cause a range of human health problems, and we know that green areas can help reduce these issues. But the exact positive impact of trees has not been quantified. Now, a new study finds that even a couple of trees can make a difference.

“There are plenty of good reasons to plant trees, but our study shows we shouldn’t underestimate the role that individual trees can play in mitigating heat in urban areas,” Michael Alonzo, lead author of the new study, said in a statement. “City planners can take advantage of the small spaces that abound in urban areas to plant individual trees.” 

In the study, Alonzo and colleagues looked at air temperature readings from one hot summer day in 2018 across different areas in Washington DC. They collected 70,000 air temperature readings from multiple days throughout the day. In their analysis, they examined tree canopy over paved and unpaved surfaces as well as distributed trees, such as those planted in the back yard. 

While urban parks provided mid-day cooling, individual trees helped tackle heat especially in the evening, the findings showed. The researchers recorded lower temperatures in neighborhoods that were covered by canopy from distributed trees (trees that stand “by themselves”, not in a forest or a park. Even places with 20% of canopy cover were cooler than those with no trees, showing that the evening cooling effect lasts well into the night. 

In urban areas, people are more likely to live near distributed trees rather than parks. In Washington DC, where the study was carried out, there are many places where individual trees could be planted, such as streets with family homes and streets with rowhouses. This could increase the racial and socio-economic equity of tree planting, the researchers wrote. 

“Evenings are not quite the respite from heat that we once had,” Alonzo said. “These distributed trees do help the city cool off in the evening and that’s important for human health.”

The study was published in the journal Environmental Research Letters. 

Planting trees can increase rainfall across Europe — and this is important for climate change

Expanding the forest cover in Europe could enhance rainfall and partly counteract future drying trends expected with climate change, according to a new study. Researchers found that converting agricultural land to forest would increase summer rains by 7.6% on average, based on observations of existing patterns. 

Image credit: Flickr / iyoupapa

Many countries around the world have started planting more trees in an effort to tackle rising global temperatures. The Bonn Challenge, signed and backed by 48 nations, pledged to restore 350 million hectares of forest by 2030. China has already spent $100 billion on trees in the last decade alone, with 22% of the country now covered in forest. The idea is that a large-scale reforestation effort could influence the local climate and rainfall patterns by altering the transfer of water, energy, and momentum between the land surface and the atmosphere, while also providing shade and numerous other environmental services. Nevertheless, the extent to which reforestation may affect rainfall is largely unknown. With this in mind, a group of researchers decided to explore the issue further. 

They considered the impact of converting rain-fed agricultural land to forests across Europe. They used an observation-based statistical model to assess how changes to forests would impact rainfall across the continent. They found that converting agricultural land to forests triggers substantial changes, tending to increase rainfall in most areas. 

More trees, more rain

Researchers analyzed the effects a 20% increase in forest spread uniformly across Europe would have — a change they described as a realistic figure. They found that it would boost local rainfall, especially in winter and with greater impacts in coastal regions. Planting trees would also cause impacts downwind of the reforested areas, as the rainfall in these locations was increased especially in the summer months. 

Taking the two impacts together, the reforestation campaign could increase summertime rainfall in Europe by an average of 7.6%, partly offsetting drying trends that are expected with climate change, the researchers found. But on the other hand, the expansion of forests would worsen climate-induced intensification of rainfall in winter.

“Probably the most threatening climate change signal that we expect in relation to percipitation, is this decrease in summer precipitation that is expected in the southern parts of Europe like the Mediterranean,” Ronny Meier, lead author and researcher at ETH Zurich, told BBC News. 

The conclusions get even more complex, as the authors note that increased rainfall could also have negative impacts, boosting rainfall patterns that have already been affected by climate change — especially in the Atlantic region. The reasons aren’t fully clear yet, but the team points out that the cloudy air that produces the rain tends to stay longer over forested areas. 

“A forest is a much rougher surface than agricultural land. So, it induces more turbulence at the land-atmosphere interface, and also, the forest exerts more drag on to the atmosphere than agricultural land,” said Meier. “This higher turbulence over the forests is probably the main reasons for the fact that we find more precipitation in regions with more forests.”

Overall, the impact of trees on rainfall is expected to be positive, but it can have complex ramifications.

Although humans have massively expanded their reach across the planet, there is still enough room to accommodate 0.9 billion hectares of forest, according to a study from 2019. Currently, there are an estimated three trillion trees sucking CO2 from the atmosphere all around the globe, with enough room to plant between 1 to 1.5 trillion more trees — a possible growth of up to 50%. However, it’s important to note that trees alone won’t save us from climate change, and the only thing that is guaranteed to help us is reducing our greenhouse gas emissions.

The study was published in the journal Nature

Why keeping one mature street tree is far better for humans and nature than planting lots of new ones

Thanks to Victorian street planners, many British streets were designed to be full of big trees and, with 84% of the population living in urban areas, most people are more likely to encounter trees in the streets than they are in forests.

The UK is one of the least densely wooded countries in Europe (at 13% coverage compared to the EU average of 38%) and, as such, its street trees are even more valuable.

This became all too clear as the UK first entered lockdown in spring 2020, when many people spent more time on their local streets and in parks. Online tree app Tree Talk saw a 50-fold increase in users as people fell in love with their local “street trees”.

They were quite right to do so. The wood of street trees stores carbon, while their roots and crowns support wildlife and slow rainfall, reducing urban flooding. Transpiration and shade from their canopies reduces temperatures in heatwaves, while pollution-trapping leaves lower the prevalence of asthma.

If these ecosystem services weren’t enough, having trees on our streets reduces crime rates and improves mental health and wellbeing. One mature street tree can have a net ecosystem service value of thousands of pounds.

Big trees are being felled

Sadly, the UK has an unhealthy street tree-felling habit. Up to 60 trees per day are chopped down to make way for buildings and infrastructure, such as roads or sewers. Felling rates could also rise as development accelerates and governments relax planning rules to aid post-pandemic economic recovery.

It is larger street trees which are most often the victims of development because they are a challenge for city planners.

Large species like London planes, beech and oak need expensive, carefully engineered tree pits to help them grow safely surrounded by concrete and to prevent their roots from pushing up pavements. Such costs are more than offset, though, when we value nature – a single mature oak produces hundreds of thousands of litres of oxygen per year and supports thousands of species of birds, insects, lichen and fungus.

Residents and councils regularly clash over urban tree-felling. However, when Sheffield City Council entered into a contractor programme a few years ago, which felled more than 5,000 trees, the protests made international news.

Councils are wary of street tree issues now, and often try to manage PR by claiming felling is mitigated by planting several smaller trees to replace each large one removed. When local authorities like Swansea City Council claim development will result in “more trees” they are of course right, but it is not the full story.

Just as any child would understand they were being ripped off if given a 2p piece and a 1p piece to replace a pound coin, removing large species trees and replacing them with small ones results in a net loss of ecosystem services.

Joe Coles, the urban tree campaigner responsible for conservation charity Woodland Trust’s work in Sheffield, describes this as a form of greenwashing. “If we value green infrastructure to the same level as grey then large street trees will become far too valuable to lose”, he tells me. “Until there is acceptance that large trees, taking decades to reach maturity, have significant value – a fact based on scientific evidence – we will continue to see spurious but convenient assertions that higher numbers of small replacement trees are adequate compensation to facilitate development.”

Size really matters with trees. The annual net ecological benefit of planting a large species tree is 92% greater than planting a small one. Mature street trees do everything from having a positive effect on infant birth weight in lower socio-economic demographics, to increasing resilience to major life events among people who live within sight of them. Consumers spend more on streets that are lined with large trees.

Large street trees are the most valuable green infrastructure asset cities have and when that value is overlooked, disasters happen. Even winning the UK’s “tree of the year” competition in 2020 couldn’t save Hackney’s Happy Man Tree from being felled in 2021 to make way for a new housing development.

More than 25,000 petitioners objected to the removal of the healthy, 150-year-old London plane, with even the developers admitting it would have been avoidable had earlier consultation taken place.

There is hope for change in the form of tree strategies which set policies to guide development and planning and which require community consultation. They are a valuable tool for stewarding urban trees for future generations.

Bristol, perhaps the UK’s flagship green city, has adopted a tree replacement standard to ensure planting new trees meaningfully offsets the loss of carbon and ecosystem services where felling cannot be avoided. Tree replacement standards ensure an adequate number of trees are planted to offset each lost and quantifies the financial contribution developers must make if they choose to fell.

Even tree-war epicentre Sheffield has moved forwards, bringing people together to develop a new street tree partnership working strategy that values street trees for the benefits they bring to people, the city and the environment.

These strategies allow local authorities to mandate that developers value tree size and the total canopy cover in a city. The idea is to prevent the use of “stem counts” to hide the removal of large trees and their replacement with smaller trees that are less valuable in terms of carbon storage, ecosystem services and even human wellbeing.

Mary Gagen, Professor Of Physical Geography, Swansea University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The Bosco Verticale In Milan in spring, West side. Credit: Wikimedia Commons.

The urban forest of the future: how to turn our cities into Treetopias

The Bosco Verticale In Milan in spring, West side. Credit: Wikimedia Commons.

The Bosco Verticale In Milan in spring, West side. Credit: Wikimedia Commons.

The 21st century is the urban century. It has been forecast that urban areas across the world will have expanded by more than 2.5 billion people by 2050.

The scale and speed of urbanisation has created significant environmental and health problems for urban dwellers. These problems are often made worse by a lack of contact with the natural world.

With research group the Tree Urbanistas, I have been considering and debating how to solve these problems. By 2119, it is only through re-establishing contact with the natural world, particularly trees, that cities will be able to function, be viable and able to support their populations.

Future cities

The creation of urban forests will make cities worth living in, able to function and support their populations: Treetopias.

This re-design will include the planting of many more urban trees and other vegetation – and making use of new, more creative methods. Although we didn’t fully realise it at the time, the 1986 Hundertwasserhaus in Vienna, a building that incorporated 200 trees in its design, was the start of more creative urban forestry thinking.

The Hundertwasserhaus in Vienna, designed by Friedensreich Hundertwasser. Credit: Wikimedia Commons.

This has been carried on in Stefano Boeri’s Bosco Verticale apartments in downtown Milan, which incorporates over 800 trees as part of the building. Similar structures are being developed around the world, such as in Nanjing in China and Utrecht in The Netherlands.

The urban forest needs to be designed as a first principle, part of the critical infrastructure of the whole city, not just as a cosmetic afterthought. We know for example that in 2015, urban forest in the UK saved the NHS over £1 billion by helping to reduce the impact of air pollutants. In 2119, we may well look back on this present time as the equivalent of the Victorian slum.

Trees can create places which can greatly improve our health and well-being. Our urban forest can give us the spaces and places to help manage our mental health and improve our physical health. Research has indicated for example that increasing the canopy cover of a neighbourhood by 10% and creating safe, walkable places can reduce obesity by as much as 18%.

Cities built on trees

As rural areas become less productive as a result of climate change, cities – which previously consumed goods and services from a large hinterland – will have to become internally productive. Trees will be at the centre of that, contributing to the city energy balance through cooling, regulating and cleaning our air and water flows, and ensuring that our previously neglected urban soils function healthily.

Urban forests could also provide timber for building. We have a history of productive woodlands in the UK, yet alternative construction materials and a growth in an urban population with less knowledge of forest management means that the urban forest is rarely viewed as productive. We are now recognising the potential productivity of the urban forest, as campaigns to stimulate homegrown timber markets and achieve more efficient management efficiencies are proving to be successful.

Furthermore, economic growth is still deemed to be the prime symbol of the effectiveness of a city, but we need to be equally aware of other invisible values. This will open up new approaches to governance. Governance needs to embrace all forms of value in a balanced way and facilitate a new vision, considering how trees can help create liveable cities.

New opportunities

As the urban population rises, we need to get better at understanding the breadth and diversity of the values held about our urban forest. Individual people can hold several distinct values at once, as urban forests may contribute to their wellbeing in different ways.

The current guardians of our urban forest, mainly local authority tree officers, spend much of their time managing risks rather than maximising the opportunities of trees. They often receive complaints about trees and tree management, and it can sometimes be difficult to remember that people do care about trees. We need to develop viable partnerships between tree managers, community members and businesses to support trees in our cities.

Although the canopy cover of cities worldwide is currently falling, this is not the case in Europe, where it is increasing. Many European countries are acknowledging the fact that we have over-designed our towns and cities to accommodate the car, and now it is time to reclaim the public realm for our people – either pedestrians on foot or on bicycles.

Creative developments like the Hundertwasserhaus are not the only answer to creating Treetopia. We are and will continue to plant more street trees, urban groves and informal clusters of trees in our parks and green spaces. Treetopia has begun.

Alan Simson, Professor of Landscape Architecture and Urban Forestry, Leeds Beckett University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

In 10 to 20 years, it will be so hot that tropical trees live shorter lives

It’s not the best time to be a tropical tree, as rising average temperatures risk impacting their lifespan.

Image credits Roel Brienen.

A new study explains that the longevity of trees at the tropics is shortened by higher temperatures. The findings help further our understanding of how climate change will impact ecosystems in the area and its effects on the rest of the planet. The team argues this is the first direct evidence that tropical trees experience shorter lives in hotter environments, and that forests all around the world will be affected.


“Many regions in the tropics are heating up particularly rapidly and substantial areas will become warmer, on average, than approximately 25 °C,” says Professor Manuel Gloor at the University of Leeds, a co-author of the paper.

“Our findings – which are the first to demonstrate that there is a temperature threshold – suggests that for trees in these regions, their longevity is likely to be negatively affected.”

The temperature above which trees become affected is 25 °C, the paper explains. This result is based on four years’ worth of tree ring data recovered worldwide. Roughly 100,000 trees from 400 species in 3,000 sites across the planet formed the dataset. All in all, the team reports that although tropical trees grow twice as fast as those in cold areas, they also live shorter lives (186 years vs 322 years on average).

Average temperatures in tropical forests today sit between 21 °C and 30 °C depending on location. These averages will rise alongside the rest of the world to around 2.5 °C above pre-industrial levels over the next 10 to 20 years. The effect this will have on trees varies depending on exactly how much hotter it gets. Changes in precipitation patterns (another effect of climate change) are going to exacerbate this ever further.

Substantial areas of today’s rainforests will see significantly lower tree longevity. They only cover 7% of the Earth’s surface, but harbor around 50% of its species of plants and animals, and a corresponding 50% of the planet’s carbon stocks. Any change here will have strong, global echoes for habitats, air quality, and carbon scrubbing ability.

“These results are a warning sign that, along with deforestation, global warming adds extra stress on the Earth’s tropical forests,” says Dr Roel Brienen from Leeds, paper co-author.

“If tropical trees die earlier, this will affect how much carbon these forests can hold, raising concerns about the future potential of forests to offset CO2 emissions from fossil fuel burning. It could also cause changes in biodiversity and a decrease in the number of species on the planet.”

Tropical forests in South America are closest to this threshold, but they’re not the only ones at risk. Even the Congo Forest in west Africa, the world’s second largest but with lower average temperatures, will be affected.

The saddest finding here, in the words of co-author Marcos Buckeridge, Director of the Biosciences Institute of the University of São Paulo, is that it’s “unavoidable”. It’s too late to stop average temperatures from passing this threshold “even if we were to take drastic emissions reductions measures”.

The paper “Global tree-ring analysis reveals rapid decrease in tropical tree longevity with temperature” has been published in the journal Proceedings of the National Academy of Sciences.

Larger, older trees can store more carbon and help tackle climate change

Older trees with a large diameter can store disproportionally massive amounts of carbon compared to smaller trees, according to a new study with trees in the United States. This shows the importance trees have in reducing greenhouse gas emissions amid the climate emergency, the researchers argued.

Dr. Milddrexler is seen measuring the trees. Credit Frontiers

Forest carbon accumulation is crucial for mitigating ongoing climatic change, with individual large trees storing a substantial portion of the overall carbon in living trees. Globally, forests store about 862 gigatons of carbon in live and dead vegetation and soil.

Large-diameter trees constitute about half of the mature forest biomass worldwide and are key to the ability of forests to accumulate substantial amounts of carbon. On average, 50% of the live tree biomass carbon in all types of forests globally is stored in the largest 1% of trees.

Researchers looked at the above-ground carbon storage of large-diameter trees (more than 21 inches or 53.3 centimeters) in Oregon and Washington. Although they account for just 3% of the total trees on the studied plots, large trees stored 42% of the total above-ground carbon within the forests, the findings showed.

The study was prompted by a policy proposal that could alter carbon storage in forest ecosystems. In the Pacific Northwest region of the US, a rule was set in 1994 to slow the loss of large and older trees in national forests by setting a 21-inch diameter rule. But a proposed amendment would allow harvesting trees of up to 30 inches.

Dr. David Mildrexler, who led the study, said in a statement: “Large trees represent a small proportion of trees in the forest, but they play an exceptionally important role in the entire forest community — the many unique functions they provide would take hundreds of years to replace.”

Mildrexler and his team used species-specific equations to relate tree diameter and height to the aboveground biomass in the stem and branches. They also looked at the proportion of large trees of the total forest stand, their aboveground carbon storage and the consequences of removing these large trees.

The findings showed that trees of more than 30 inches (76.2 cm) in diameter only constituted 0.6% of the total stems. But they accounted for over 16% of the total aboveground carbon stored across the forests examined. Once trees reach a large size, any increase in diameter can result in a significant addition to the tree’s carbon stores.

“If you think of adding a ring of new growth to the circumference of a large tree and its branches every year, that ring adds up to a lot more carbon than the ring of a small tree,” said Mildrexler. “This is why specifically letting large trees grow larger is so important for climate change because it maintains the carbon stores in the trees.”

For Mildrexler, the study showed the importance of strengthening the 21-inch rule so that additional carbon is accumulated as 21-30″ diameter trees are allowed to continue to grow. Meanwhile, states should allow a good number of sub-21-inch trees to grow further and become additional large and effective carbon stores.

“Large trees are the cornerstones of diversity and resilience for the entire forest community. They support rich communities of plants, birds, mammals, insects, and micro-organisms, as well as act as giant water towers that tap into groundwater resources and cool our planet through evaporation,” the researcher argued.

The study was published in the journal Frontiers.

It’s greener than you thought: New tree count in Sahara shows surprising results

Using satellite imagery and a new AI algorithm, scientists were able to perform the first tree count in the Sahara area. Normally, it’s nigh impossible to count individual trees over a large region, but the method represents an important advance that could be used in other areas to answer this question.

The number of trees in the Western Sahara area exceeds 1.8 billion, the analysis shows.

Trees and shrubs play a crucial role in arid areas. They offer shelter and resources for local wildlife, and protect the environment from degradation (such as erosion). But assessing and monitoring the number of trees in these remote areas is no easy feat.

Separating individual trees from their canopy was thought to be impossible. But Martin Brandt and colleagues weren’t discouraged. They used high-resolution remote sensing data along with satellite images and then applied an artificial intelligence pattern recognition algorithm.

It’s the first time anything like this has ever been done.

“Previous assessments were estimations or extrapolations of the canopy area without any information on the numbers, here we have a wall-to-wall identification of each tree and shrub,” Brandt, associate professor at the University of Copenhagen tells ZME Science.

According to the study, the area comprising of Western Sahara, the Sahel, and Sudanian zone features an impressive number of trees. Even as the study only focused on trees with a crown size greater than 3m², they found that isolated trees cover about 1.3 million km² (an area 6 times larger than the UK). It’s hard to draw any immediate conclusions about what this means for Western Africa, but what really stands out is the method itself, which highlights the potential to create a global tree inventory.

Large-scale tree mapping. Image credits: Brandt et al..

“We cannot really say that the environment is in a better state than we thought, because local studies have shown that there are trees, so this is not a secret, but now we have a tool to precisely map the number and crown area of each tree, which certainly will help to better understand the environment and carbon cycle of dry areas,” Brandt adds.

The method can be applied in other settings, Brandt notes. Anywhere you have satellite data with 0.5 meters resolution, it could be applied — although the algorithm does need to be retrained for every particular objective.

“Generally, deep learning works as follows: we show the algorithm how a tree looks, and it will search the satellite images and mark the tree crowns as it has learned it from the training. That works surely with everything that we can identify with our eyes, like houses or cars, or even cows. The requirement is satellite imagery which is normally very expensive.”

Niall Hanan is a community and ecosystem ecologist who published a commentary article on the study, is also excited about the prospects.

“I was particularly interested in the study by Brandt and colleagues, because it provides a clear demonstration of our growing ability to measure terrestrial vegetation at the scale of individual trees. They mapped individual trees in some 1.3 M km² of West Africa, but the study shows the potential for mapping individual trees worldwide,” Hanan tells ZME Science.

This represents an important advance because unlike previous generic descriptions that analyzed “tree cover”, this can also provide information on tree density, canopy size, and the number and location of individual trees. This could be transformative for how we model and manage global ecosystems, Hanan notes. But he’s not so sure about applying the approach to different ecosystems just yet.

Before we can do that, we need better, cheaper access to satellite data, as well as more efficient algorithms. But the groundwork has been laid down.

“The deep learning approach used by Brandt and colleagues won‘t be easy to apply at global scales, in part because of the data and computational size of the task, but more particularly because of the overhead in terms of providing sufficient training data. Further advances in efficient deep learning methods are probably needed to make global mapping of trees feasible, but this study demonstrates the possibility.”

Journal Reference: Brand et al, An unexpectedly large count of trees in the West African Sahara and Sahel. Nature, 14 october 2020. DOI : 10.1038/s41586-020-2824-5

Pollution is impairing the growth of trees in Siberia and the Arctic

Industrial pollution in the Arctic is way worse than we’ve assumed, according to a new paper, and it’s affecting the life of trees.

Norilsk, Russia. Image credits Flickr / Ninara.

The findings are based on the analysis of tree-rings and wood chemistry around the city of Norilsk in the Russian Arctic. According to the authors, ecosystems in this region have been “devastated” by decades of nickel and copper mining, and the effects extend far enough to disrupt the global carbon cycle. They also explain that die-offs have spread to almost 100 kilometers away from the city.

Trouble in the north

“Using the information stored in thousands of tree rings, we can see the effects of Norilsk’s uncontrolled environmental disaster over the past nine decades,” said Professor Ulf Büntgen from Cambridge’s Department of Geography, who led the research.

“While the problem of sulfur emissions and forest dieback has been successfully addressed in much of Europe, for Siberia, we haven’t been able to see what the impact has been, largely due to a lack of long-term monitoring data.”

Norilsk is the northernmost city in the world, housing around 100,000 people. It’s also one of the most polluted places on Earth due to intensive mining operations for nickel, copper, and palladium which have been ongoing since the 1930s under very little environmental regulations. A spill in May 2020, which involved around 17,500 tons of diesel oil making its way into local rivers, further destroyed local ecosystems.

Airborne emissions from the city’s industries are directly responsible for the destruction of around 24,000 square kilometres of boreal forest in the last six decades, the team explains. However, even those areas of the forest that have survived are struggling. Tree growth is impaired by the polluted air, as it reduces the plants’ ability to absorb carbon from the atmosphere.

However, these links are well documented. What the team studied is the ‘divergence problem’ in dendrochronology (the study of tree rings). The size of each tree ring is a great indicator of the environmental conditions during the year they developed in, including precipitation levels and average air temperatures. But researchers have noticed that the width of tree rings has become independent of (i.e., that it’s ‘decoupling’ from) air temperatures ever since the 1970s.

The team used data on tree ring and wood chemistry from both living and dead trees in the area to quantify the ecological damage caused by industrial emissions from Norilsk. They report that this damage peaked in the 1960s, but is still affecting the forests and trees around the city. Furthermore, the team explains that industrial emissions are at least partially responsible for the phenomenon of ‘Arctic dimming‘. This is the phenomenon where (natural or man-made) pollution particles block incoming sunlight, affecting plant growth and other natural processes such as evaporation and precipitation.

Wide-scale tree death caused by pollution in the Norilsk region began in the 1960s, the team explains. Dimming in the Arctic also began having a noticeable effect on the growth rate of local trees since the 1970s. Given that atmospheric circulation tends to accumulate pollution in the arctic area, not disperse it as in other regions, the researchers also looked at arctic areas farther away from the city. They report finding that “trees across the high-northern latitudes are suffering as well.”

All in all, the findings give us a glimpse into how trees in the Arctic region will likely fare in the future. Shifts brought about by climate change should make plants grow faster, but the team says that the trees of Siberia are actually growing slower than before. This is mainly caused by atmospheric pollution, which is impeding their ability to photosynthesize. Such changes reflect global trends, the team adds, giving us cause for concern in regards to the health of trees in the future.

“What surprised us is just how widespread the effects of industrial pollution are — the scale of the damage shows just how vulnerable and sensitive the boreal forest is,” said Büntgen. “Given the ecological importance of this biome, the pollution levels across the high-northern latitudes could have an enormous impact on the entire global carbon cycle.”

The paper “Ecological and conceptual consequences of Arctic pollution” has been published in the journal Ecology Letters.

Trees that live fast die young and this is bad news for the climate crisis

There’s a universal trade-off between early growth and lifespan in trees, according to a new study, which showed faster growth has a direct and negative effect on the lifespan of trees. This could mean bad news for the climate crisis, challenging the idea that greater growth would mean greater carbon storage.

Credit Franz Jachim. Flickr (CC BY-NC-ND 2.0)

Trees grow faster in warmer areas of the planet and this should help stop global warming, as they can absorb more carbon dioxide from the air as they grow. But this apparently beneficial cycle was questioned by a new study, which showed the faster trees grow, the sooner they die — no extra carbon included.

“While it has been known for a long time that fast-growing trees live shorter, so far this was only shown for a few species and at a few sites,” Roel Brienen, lead author, said in a statement. “We started a global analysis and were surprised to find that these trade-offs are incredibly common. It occurred in almost all species we looked at.”

For decades forests have provided an important carbon sink, especially as global warming started to kick in. However, Brienen and his team recently found that carbon accrual in the Amazon had declined by a third since the 1990s. This led them to explore the link between tree growth and longevity in as many species as possible.

Their new study is the largest one so far to look at the link between the growth and lifespan of trees. The researchers looked at more than 200,000 tree-ring records from 82 tree species from sites around the globe. They confirmed that the accelerated growth led to a shorter lifespan and that this happened in all species and climates.

The researchers suggested that the growth-lifespan trade-off is due to a higher risk of dying, as trees reach their maximum potential tree size sooner. But other factors also play a role. For example, trees that grow faster invest less in defenses against diseases or insect attacks.

“Our findings, very much like the story of the tortoise and the hare, indicate that there are traits within the fastest growing trees that make them vulnerable, whereas slower growing trees have traits that allow them to persist,” said co-author Steve Voelker. “Carbon uptake rates of forests are likely to be on the wane as slow-growing and persistent trees are supplanted by fast-growing but vulnerable trees.”

This would eventually reverse any carbon storage gains and diminish hopes for the future capacity of the terrestrial carbon sink, requiring the world to reduce its emissions much faster.

However, this doesn’t mean trees aren’t relevant in mitigating the climate crisis. Keith Kirby, woodland ecologist at the University of Oxford, not involved in the study, told The Guardian that despite the world can’t rely as much on the growth of trees to enhance forest carbon sink potential, this could be offset by slowing deforestation and expanding forests.

The study was published in the journal Nature Communications.

Planting trees is not a simple solution to climate change

While continuously questioning climate action, US President Donald Trump surprised a few at this year’s State of the Union speech by announcing the US would join a global initiative to plant a trillion trees around the world.

US President Trump plants a tree with French President Macron. Credit White House

The idea is that tree planting is a nature-based solution to climate change since trees and soil can take in and store the heat-trapping CO2 gas from the atmosphere. Nevertheless, the claim that trees alone can fix the issue might not be that accurate.

Restoration ecologist Karen Holl published a commentary with Brazilian professor Pedro Brancalion, endorsing the benefits of trees but questioning the simplistic view of tree-planting as a panacea for environmental degradation. “We can’t plant our way out of climate change,” Holl said.

“Trees are deeply entrenched in the human psyche. It’s very satisfying to go out and put a tree in the ground. It’s a concrete, tangible thing to do,” said Holl. But broad-scale tree planting initiatives must be undertaken carefully and with a commitment to long-term management, if the benefits are to be fully realized, she said.

“Planting trees is not a simple solution. It’s complicated, and we need to be realistic about what we can and cannot achieve. We need to be thoughtful and plan for the long term.”

Planting trees can improve biodiversity, water quality, and provide shade. But depending on where and how it is done, tree planting can also harm native ecosystems and species, reduce water supply, dispossess local landholders, and increase social inequity.

In their commentary, Holl and Brancalion presented a set of principles that should guide forest enhancement initiatives. Such efforts should focus on protecting and maintaining intact forests instead of planting new ones, they should be seen as only one part of the carbon reduction measures that are needed, and they should balance social and ecological goals.

At the same time, tree planting initiatives should work with local stakeholders to resolve conflicting land-use goals and ensure maximum effectiveness over the long term, the authors claimed. Planting trees doesn’t ensure they will survive, as seen in many countries.

To be successful, tree-planting initiatives need to engage local stakeholders and confront conflicting goals for land use. “Much of the land proposed for tree planting is already being used to grow crops, harvest timber, and other subsistence activities, so tree planting initiatives need to consider how landowners will earn income,” said Holl. “Otherwise, activities such as agriculture or logging will just move to other lands”

“The first thing we can do is keep existing forests standing, and the second is to allow trees to regenerate in areas that were formerly forests,” said Holl, who specializes in tropical forest restoration. “In many cases, trees will recover on their own—just look at the entire eastern United States that was deforested 200 years ago. Much of that has come back without actively planting trees.”

The commentary was published in the journal Science

The secret behind Ginkgo biloba’s near-immortal lifespan

Considered the oldest surviving tree species, the Ginkgo biloba has been on the planet for around 200 million years and has stayed relatively unchanged. Remarkably, the tree has a lifespan of more than 3,000 years. Seeking answers, a study has now revealed what could be the key to its longevity.

Credit Wikipedia Commons

The research by experts from China and the United States — the most comprehensive study on plant aging to date — analyzed thin cores from 34 ginkgo trees in Anlu, in China’s Hubei province, and Pizhou, in Jiangsu province. The procedure employed by the researchers did not harm the trees.

When examining the rings, the researchers realized that the growth of the trees didn’t slow down after hundreds of years. Actually, it even sped up in some cases. The size of the leaves and the trees’ photosynthetic ability and seed quality – which are indicators of health – didn’t change with age.

The researchers, led by Li Wang, a plant molecular biologist at Yangzhou University, started wondering about what was going on at the genetic level. They compared the gene expression in leaves and the cambium, which is a layer of stem cells between the internal wood and external bark.

Collecting enough material was tricky as older trees only have some layers of cambial cells left. The researchers sequenced the trees’ RNA, looked at their hormone production and screened the miRNA (molecules that turn some genes on and off) in trees from 3 to 667 years old.

Unsurprisingly, the expressions of the genes associated with senescence, which is the final stage of a cell’s life, increased predictably in dying leaves. But when the team looked at the expression of the same genes in the cambium, they didn’t find a difference between young and old trees.

This would mean that despite some organs such as leaves perish, the tree itself won’t likely ever die of old age, the study concluded. Instead, ginkgo trees seem to die from stressors such as pests or droughts.

“In humans, as we age, our immune system begins to start to not be so good,” said Richard Dixon, a biologist at the University of North Texas, told the New York Times. But in a way, “the immune system in these trees, even though they’re 1,000 years old, looks like that of a 20-year-old.”

Nevertheless, ginkgo trees do go through changes over time. Older trees were found to have lower levels of a growth hormone called indole-3-acetic acid and higher levels of a growth-inhibiting hormone called abscisic acid. Also, older trees had decreases in gene expression associated with cell division, differentiation, and expansion.

The researchers also looked at whether the trees were more vulnerable to certain stressors as they age. To do so, they examined genes related to pathogen resistance and the production of protective antimicrobial compounds called flavonoids. But they didn’t find a difference in gene expression for trees of different ages.

Not needing to worry about growing old is “something that for humans is difficult to understand,” plant physiologist Sergi Munné-Bosch of the University of Barcelona, who was not involved in the study, told Science. “Aging is not a problem for this species,” he said. “The most important problem that they have to deal with is stress.”

Origin and description

Native to China, the ginkgo has been planted since ancient times in Chinese and Japanese temple gardens and is now valued in many parts of the world as a fungus- and insect-resistant ornamental tree. It tolerates cold weather and can survive the adverse atmospheric conditions of urban areas.

But despite is widely cultivated, the tree is listed as an endangered species by the red list of the International Union for Conservation of Nature (IUCN), mainly because of the rarity in the wild. Only two populations are found to grow in the wild today, both in the Tian Mu Shan Reserve, the Zhejiang province in eastern China

Ginkgo has been much used in traditional Chinese medicine. Toward the end of the 20th century, ginkgo extract became popular in many countries for its purported memory-enhancing properties. The nut of the tree is also valued in many countries as a delicacy.

Oldest fossilized forest discovered under New York

If you took a stroll through an abandoned quarry in Cairo, New York, it’s easy to think that the spiderweb-like features on the ground are just some ore waiting to be extracted. To the trained eye, however, this is a scientific gold mine — the intricate pattern is, in fact, a huge fossilized forest dating back 386 million years. It’s the earliest forest that scientists have discovered yet.

Archaeopteris root system at the New York site. Credit: Charles ver Straeten.

Scientists first started investigating the site in the foothills of the Catskill Mountains, in the Hudson Valley, around a decade ago. Since then, various research groups have painstakingly mapped over 3,000 square meters of forest, which used to be made up of some of the earliest types of trees.

This includes Cladoxylopsids — leafless trees with short celery-like branches and shallow roots that could grow to up to 10 meters in height — and Archaeopteris — ancient pine-like trees. The new study also identified a third type of tree that has yet to be described properly.

All three types of trees would have reproduced through spores rather than seeds — indicative of their ancient nature. The authors of the new study, which includes researchers from Binghamton University, New York State Museum, and Cardiff University, claim that the extensive network of trees would have spread from New York all the way to Pennsylvania around 386 million years ago.

This forest was one of the earliest in the world but even back then, trees exhibited a modern feature: long, woody roots that transported water and nutrients from the soil. Until this point in time, primitive trees only had ribbon-like, mostly unbranched roots that had to be constantly replaced as the tree above grew.

“It is surprising to see plants which were previously thought to have had mutually exclusive habitat preferences growing together on the ancient Catskill delta,” said co-author of the study Dr. Chris Berry from Cardiff University’s School of Earth and Ocean Sciences.

“This would have looked like a fairly open forest with small to moderate sized coniferous-looking trees with individual and clumped tree-fern like plants of possibly smaller size growing between them,” he added.

The site marks a transition in the planet’s history from a relatively barren landscape to a lush, green world covered in trees. In time, the success of trees would have soaked a lot of carbon dioxide (CO2), completely altering the climate and the ecosystem around them. Over just a few million years, the CO2 levels in the atmosphere dropped 15-fold, reaching levels similar to those recorded today.

“In order to really understand how trees began to draw down carbon dioxide from the atmosphere, we need to understand the ecology and habitats of the very earliest forests, and their rooting systems,” Dr. Berry said in a statement.

Eventually, the ancient forest in New York was wiped out by a flood, as evidenced by fish fossils found on the surface of the quarry.

The Cairo forest is only 2-3 million years older than the previous record-holder for the title of the world’s oldest forest, a site a Gilboa, also in New York State.

“These remarkable findings have allowed us to move away from the generalities of the importance of large plants growing in forests, to the specifics of which plants, in which habitats, in which types of ecology were driving the processes of global change. We have literally been able to drill into the fossil soil between the trees and are now able to investigate geochemical changes to the soil with our colleagues at Sheffield University,” Berry said.

“We are really getting a handle on the transition of the Earth to a forested planet.”

The findings appeared in the journal Current Biology.

Tree-planting campaign raises $8 million in five days

In just five days, more than $8 million have been raised by a global tree-planting campaign, with the participation of US entrepreneur Elon Musk and YouTuber Jeffree Start among many others.

The project has a website through which donations can be made

The project called “Team Trees” seeks to plant 20 million trees around the globe by 2020, with each $1 donation “planting” one tree. The donations go to the Arbor Day Foundation, a US organisation dedicated to planting trees.

It all started in May, when a YouTuber called Jimmy Donaldson, known online as “Mr Beast,” asked what he should do to celebrate his 20 millionth subscriber. One of his fans responded urging him to plant 20 million trees to represent each of his subscribers.

Since then, the YouTuber has collaborated with other content creators and the Arbor Day Foundation to create the #TeamTrees campaign. The idea is simple – for each $1 donation, the Arbor Day Foundation will plant one tree. The trees will reportedly be planted on every continent except Antarctica.

Planting trees across the world is a cheap and easy solution to reducing carbon dioxide (CO2) levels, which is seen as a major factor in climate change. As trees grow, they absorb and store CO2 from the atmosphere, and emit oxygen.

The Arbor Day Foundation says over their lifespan, 100 million trees could absorb eight million tons of carbon – the equivalent of taking more than six million cars off the road for a year.

“The average person can’t afford $150,000 or a million, but we’ve been getting spikes of between 5 and 20 trees every time a large donation comes in and every tree matters, every single donor is important,” Arbor Day Foundation spokesman Danny Cohn told CNN.

Over the past five days, the campaign has gained significant attention online. Elon Musk, co-founder and CEO at Tesla, donated $1m to the project. He also changed his Twitter handle to “Treelon.” The name of Twitter CEO Jack Dorsey has also appeared on the campaign website’s “most trees” leader board, pledging to plant 150,000 trees.

At the same time, Beauty YouTuber Jeffree Star, who has over 16.4m subscribers, also donated $50,000 to the campaign. YouTube has promised to match the next million dollars of donations.

In a video announcing the launch of the project “Mr Beast” said: “I personally haven’t always been the most environmentally friendly. We only have one Earth, and it’s important we take care of it. People just keep making fun of our generation for ‘retweet activism’ and not actually doing something.”


Vikings cut down all of Iceland’s forests — the country is planting them anew

Iceland is trying to heal its Viking-induced wounds — by reforesting.


The Icelandic countryside; soon to also feature trees.
Image credits Monica Volpin.

Iceland is currently considered the least forested country in all of Europe, but this wasn’t always the case. At the end of the ninth century, as Vikings from Norway first set foot on the island, a quarter of it was covered in lush birch forests. The Vikings, however, cut down almost 97% of these trees to obtain building materials and make room for crops and pastures.

Today, less than 0.5% of Iceland is forested, according to the United Nations Food and Agriculture Organization (FAO). Locals joke that, because the forests here are so rare and so young, all you need to do to find your way around them is to stand up. Partly as a way to address climate change, partly as a way to prevent environmental degradation, and partly out of a desire to simply see the island blanketed in forests again, Iceland is now trying to reforest itself, according to AFP.


Iceland, sadly, isn’t a very welcoming place for trees. Its harsh climate and active volcanoes (which periodically cover the soil in layers of lava and ash) make it hard for trees to take root and grow here. However, the lack of trees is particularly bad news for Iceland; without their roots to support it, the soil here erodes quickly and can’t store water very well. All in all, this means Iceland is experiencing extensive desertification despite its northern latitude

The country has made reforesting one of the priorities in its 2018 climate action plan, citing carbon uptake by trees as an important avenue for Iceland to mitigate climate change.

Reforestation efforts that began in the 1950s and the 1990s have helped replant some of these forests, but there is still much to do. For example, the Icelandic Forest Service (IFS) has been tasked to turn the alien landscape of Hafnarsandur, an 8,000-hectare area of basalt and black sand in Iceland’s southwest, into a forest. This is meant both as a way to increase forest cover in Iceland as well as a method to protect the nearby town of Thorlakshofn from recurring dust storms. The IFS is now busy planting lodgepole pines and Sitka spruces in the area

“This is one of the worst examples of soil erosion in Iceland on low land,” Hreinn Oskarsson, the IFS head of strategy, explains about Hafnarsandur. “We are planning an afforestation project to stabilise the soil,” Oskarsson added.

Iceland’s only domestic tree is the birch. However, the IFS focuses its afforestation efforts on other species. The problem with the native birch, according to Adalsteinn Sigurgeirsson, deputy director of the IFS, is that it isn’t a “productive species”. For objectives such as fast carbon sequestrations or timber production, it just doesn’t cut it — so the IFS is branching out from monocultures using this single native species.

Iceland is now peppered with nursery gardens that feed the country’s afforestation efforts with young poplars and pines. These are grown indoors for three months and are afterward moved outside.

“Originally, they come from Alaska but now we have 30, 40, 50 year-old trees giving us seeds, so we collect that and we use that for forest seedlings production,” Holmfridur Geirsdottir, a 56-year-old horticulturist and greenhouse owner, told AFP.

Once in the wild, these trees have an uphill battle to fight. Iceland’s soils are very poor in nitrogen, an essential element for plants, limiting the average growth rate of trees here to around one-tenth the rate observed in the Amazon rainforests. However, climate change might offer an unexpected boost in these trees’ growth rates.

“What has mainly been hampering growth of forest here has been the low temperatures and the coolness of the summers, but we are realising changes in that because of climate change,” said forest service deputy director Sigurgeirsson.

“Warming appears to be elevating tree growth in Iceland, and therefore also the carbon sequestration rate,” he continued.

Since 2015, Iceland has planted around 1,000 hectares of forest (between three and four million trees).

Rainforest canopy.

NASA creates first 3D model of Amazon rainforest canopy to estimate the effects of droughts, climate change

In an effort to estimate the effect of drought on the Brazilian Amazon, NASA has created the first ever 3D model of its canopy.

Rainforest canopy.

Image credits Robert Kerton / CSIRO.

Rainforests are some of the most complex and rich ecosystems on the planet (see here and here). One striking feature of such forests is that their canopies — which can rise up to 15 or even 20 stories high — form ecosystems unto themselves. However, they are in danger.

Climate projections suggest that the Amazon basin will experience warmer and drier conditions in the future. We’ve learned from periods of drought that rainforests don’t handle dryness well. When faced with long periods without rain, rainforest trees risk drying out because there’s not enough water in the soil for them to pump up to the canopies — so they starve.

However, we’re not quite at the point where we can estimate — based on our climate and precipitation projections — exactly how rainforests will react in the future. Simply put, estimating the number of dying or damaged trees (for example, where only branches are falling) is almost impossible. Rainforests are vibrant but chaotic, abundant but densely-packed places, and getting any kind of accurate data on tree health has long been an elusive goal for researchers.

When in doubt, LiDAR the sample

Traditionally, researchers attempted to record this data by hiking through rainforests and surveying a few acres of trees in spots along the way. They would count how many trees were alive, how many were dead, looked at the quantity and types of debris on the ground, and used these readings to estimate forest-wide averages.

Since that has traditionally not-worked-very-well, Doug Morton from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, decided to use an eye in the sky. He and his team used an airplane-mounted light detection and ranging (LiDAR) device to create a 3D model of the Brazilian Amazonian canopy, drawing data from three separate flights in 2013, 2014 and 2016.

LiDAR works largely the same as radar, only it substitutes light in lieu of radio waves. Firing some 300,000 laser pulses a second, LiDAR can provide an incredibly detailed model of an object — much more accurate than what hiking researchers could achieve.

The team flew over two 30-mile (50 km) stretches near the city Santarém in the state of Pará, Brazil: one over the Tapajós National Forest (also in Brazil), and one over privately-owned stretches of the rainforest — most of which are strongly fragmented by human land-use. This region of the Amazon basin typically has a three-month dry season from October through December, the team writes, the same period when surface temperatures peak in the Pacific Ocean (during the El Niño event). El Niño delays the start of the rainy season in the central Amazon, leading to an extended dry season that stresses the trees.

The team used the LiDAR readings to detect gaps in the canopy — areas where a tree or branch had fallen in the months between each survey. They write that between 2013-2014 (a non-El Niño period), falling branches and trees altered around 1.8% of the forest canopy in the examined area. Scaled up over the whole Amazon basin, that would be equivalent to losing canopy trees or branches over 38,000 square miles (98,000 square km).

During the El Niño drought period from 2014 to 2016, branch morality rose by 65%, equivalent to 65,000 square miles (168,000 square km) over the whole basin.

Even subtle changes add up in the Amazon, Morton says, because it’s such a huge forest. So a subtle shift in precipitation patterns during an El Niño year ends up having a huge impact on the forest’s ability to sequester carbon. Dry periods, in other words, alters the balance between how much carbon the trees store as they grow versus how much they give off when they die and decompose.

However, the drought didn’t selectively affect more tall trees than smaller ones, as previous experiments suggest. This, Morton says, is good news.

“Large trees hold most of the carbon in any forest. If droughts were to preferentially kill large trees, it would boost the total amount of carbon that’s lost from drought as opposed to other disturbance types.”

The team says that understanding the effects of prolonged drought will give us a better sense of what might happen to atmospheric carbon levels if drought events become more common due to climate change.

The paper “El Niño drought increased canopy turnover in Amazon forests” has been published in the journal New Phytologist.

Tree park.

The US lost roughly 1 in every 100 urban trees between 2009 and 2014

The USDA Forest Service estimates that the country has lost approximately 36 million urban/community trees per year between 2009 and 2014.

Tree park.

Image credits Albrecht Fietz.

If you’re an American who likes stepping out in the street right under the shade of a tree, the USDAFS has bad news for you — the country’s cities and towns are running slim on trees. Roughly 0.7% of the nation’s urban trees have been felled between 2009 and 2014, which equals approximately 36 million trees, or 175,000 acres of tree cover lost annually over that period.

Fewer trees

Overall national urban tree cover declined from 42.9% to 42.2% over that period, the report states. However, the losses weren’t spread uniformly across the US; 23 states had a statistically significant decrease in urban tree cover, while 45 states showed a net decline.

“Urban forests are a vital part of the nation’s landscape,” said co-author Tony Ferguson, Director of the Forest Service’s Northern Research Station and the Forest Products Laboratory. “Forest Service research puts knowledge and tools into the hands of urban forest managers that supports stewardship and the wise allocation of resources.”

Trees help filter air and water, improving their quality, which is especially nice in urban areas, that tend to see the highest levels of pollution. They also help keep down energy bills in the summer by keeping buildings cool. Other benefits urban trees provide include noise reduction, mitigation of runoff and flooding, as well as enhancing our mood and mental well-being, and having a positive effect on health. Overall, the benefits derived from urban forests in the US is estimated at some $18 billion annually, in the form of air pollution removal, carbon sequestration, and lowered building energy use.

The states or districts with the greatest annual net loss in urban tree cover were Rhode Island and the District of Columbia (0.44%), Georgia (0.40%), and Alabama and Nebraska (0.32% each). The states that lost the most tree cover per year were Georgia (18,830 acres/year), Florida (18,060 acres/year) and Alabama (12,890 acres/year).

Mississippi, Montana, and New Mexico saw slight (statistically non-significant) increases in urban tree cover. Maine recorded the highest percentage of urban tree cover across the US — 68%. North Dakota, with just 10%, ranked the lowest.

“Urban forests are an important resource,” said Dave Nowak of the USDA Forest Service’s Northern Research Station, co-author of the study. “Urban foresters, planners and decision-makers need to understand trends in urban forests so they can develop and maintain sufficient levels of tree cover — and the accompanying forest benefits — for current and future generations of citizens.”

Over the same period, urban/community impervious cover (concrete, buildings, so on) saw a statistically-significant increase, from 14.5% to 15.1%. States that saw the greatest annual net percent increase in impervious cover were Delaware (0.28%), Iowa (0.26%), Colorado, Kansas and Ohio (with 0.24% each). States with the greatest net increase in impervious cover were Texas (17,590 acres/year), Florida (13,900 acres/year), and Ohio (8,670 acres/year).

The study comes to flesh out previous research of the USDAFS, looking into the role urban forests will play in future cities.

The paper “Declining urban and community tree cover in the United States” has been published in the journal Urban Forestry & Urban Greening.

Violet ground beetle.

Without tree husks to house them, Europe’s beetles are dying out

As Europe is running out of trees, beetles are running out of time.

Violet ground beetle.

Image credits Bernard Dupont.

The International Union for the Conservation of Nature (IUCN) has assessed the status of 700 European species of beetle that live in old and hollowed wood — and the results aren’t good. Almost a fifth of these species (18%) are at risk of extinction due to the decline in ancient trees, according to the report, European Red List of Saproxylic Beetles.

Saproxylic beetles (meaning beetles somehow related to dead and/or rotting wood) have a key role to play in environments, as they help decomposition do its thing and cycle nutrients back into use. They’re also quite plump, and are an important food source for birds and mammals. Finally, some are even involved in pollination.

However, Europe is running out of them. Logging, tree loss, and deforestation are taking a huge toll on the insects’ habitats, the IUCN reports. Other major threats include urbanization, development of the tourism industry, and an increase in wildfires in the Mediterranean region.

“Some beetle species require old trees that need hundreds of years to grow, so conservation efforts need to focus on long-term strategies to protect old trees across different landscapes in Europe, to ensure that the vital ecosystem services provided by these beetles continue,” said Jane Smart, director of the IUCN Global Species Programme.

Luc Bas, the director of IUCN’s European Regional Office, says it’s “critical for the Common Agricultural Policy to promote the appropriate management of wood pasture habitats containing veteran trees across Europe”. One of the measures proposed as part of this new management approach is to create inventories of ancient and veteran trees from each European country, to enable local and national governments to protect them adequately across landscapes.

The report further points out that each landscape needs to be populated with trees of different ages, including saplings, mature and ancient trees, as well as some that are past their ‘best before’ date — such as standing dead trees, fallen tree trunks, and stumps. The forestry sector in many countries has made progress regarding the last category, which is traditionally treated as a nuisance and something that should be removed to clear space for newer plants.

A beetle’s life

There are 58 families of beetles spread across Europe, totaling some 29,000 species, of which some can explode. Out of these, some 4,000 are believed to be saproxylic. However, data is lacking for many of these species: for half of the saproxyls, “the population trend [remains] unknown”. The IUCN suggests that more monitoring is needed, and sooner rather than later, so we can keep accurate tabs on the beetles’ health.

“Some of these beetles are incredibly beautiful interesting things – if people stopped and looked at them and appreciated them, they’d realise they’re just as worthy of conservation as elephants and tigers,” Keith Alexander, IUCN Saproxylic Beetles Specialist Advisor, told the BBC.

“And these things live in the countryside on our doorstep.”