John Healey – The Conversation

UK must grow more of its own wood to meet climate goals – new research

2025-04-29T20:11:01Z

shutterstock ShaunWilkinson/Shutterstock

Wood is often hailed as a low-carbon hero, a natural alternative to steel, concrete and plastic. It’s a vital tool in the UK’s strategy for reaching net zero. But there’s a catch – the country don’t grow nearly enough of it.

The UK has one of the lowest levels of forest cover in Europe, with just 14% of land forested. It is also the second-largest importer of wood in the world, meeting only 20% of its wood demand from domestic sources.

That leaves the UK not only exposed to volatile global markets, but also facing a serious challenge of “wood security”. And our new research shows the problem goes well beyond economics.

Relying heavily on imported timber, especially from boreal forests in Scandanavia and the Baltic States, could actually undermine the carbon-cutting benefits of using wood in place of high-emissions materials.

Boreal forests occurring in colder northerly environments grow slowly. The carbon stored in them takes decades, sometimes centuries, to recover after harvesting through the growth of the next generation of trees.

In contrast, conifer forests in the UK’s warmer temperate climate restock carbon through regrowth more quickly after harvesting. This makes them much better suited for higher yields of sustainable wood production.

So, how can countries such as the UK increase wood use without making the climate crisis worse? To address this, we created a new model that tracks carbon at every stage of a tree’s journey, from how it grows in the forest to how it’s harvested, transported, processed and used. This includes temporary storage of carbon in wood products, and the avoidance of having to use high-emitting materials and energy sources that would be needed in the absence of wood.

We combined this with models of how carbon storage changes in forests under different harvesting intensities. Our analysis showed that it is possible for rising wood demand to make a positive contribution to national and global net zero targets. But that’s only if the domestic production of wood is dramatically increased in temperate countries such as the UK.

Even a modest annual increase in demand (1.1%) would require a 50% expansion in the area of productive forest over the next 50 years. A more ambitious approach, such as doubling productive forest area and increasing tree growth rates by 33%, could boost the overall contribution of wood use to slowing global warming by 175%. But that would require huge changes in forestry practice and land use policy.

In contrast, under a scenario of higher demand growth (2.3% per year), we found that the climate benefit of wood use is reduced. And only a doubling of forest area and a 33% increase in growth rates would be enough to deliver a meaningful contribution to slowing global warming over the next century.

These benefits would be at risk if forest productivity is undermined by increasing incidence of pests, disease or drought as climate change progresses.

Challenges ahead

Our findings point to three major challenges the UK must address if wood is to play a meaningful role in its net zero strategy.

First, the expansion of productive conifer forest in the UK has slowed to a standstill over the past 30 years. The amount of wood available for harvest is projected to fall after 2039. This trend will have to be reversed very soon to rapidly increase the area of conifer forests. This will need a rethink of how the UK balances land for forestry, farming and nature recovery.

Second, forest management must be improved to sustain productivity under increasing stress from pests, pathogens and drought.

Third, wood must be used more efficiently. That includes reducing waste during processing, designing products for longevity and reusing wood products as many times as possible.

So, the UK’s net zero policy must connect the push for using more wood with a clear plan for how it will grow and manage the forests needed to supply it. At the same time, when policymakers assess the climate effects of cutting down trees, they need to look at the whole picture. That means considering not just what’s lost from the forest, but how the wood is used, how long it stores carbon and how much it replaces more polluting materials.

This kind of joined-up, forward-looking analysis – like the one we developed in our study – is essential if wood is to play a truly sustainable role in fighting climate change.

John Healey receives funding from the Natural Environment Research Council, the Centre for Forest Protection, and the Wildlife Trusts. He is affiliated with Woodknowledge Wales, Rainforest Builder and the Institute of Chartered Foresters.

David Styles received funding from the Natural Environment Research Council (UK) and from the Department of Environment, Climate & Communications (Ireland) for research related to this article.

Eilidh Forster received funding from the Natural Environment Research Council (UK) for research related to this article.

What deer poo can tell us about the future of Britain’s woodlands

2025-03-13T13:36:36Z

shutterstock Nowar AlHaj/Shutterstock

Brambles are considered a nuisance by many woodland managers. But we’ve discovered that fallow deer have a surprising taste for it. In our recent research, we found this unexpected preference by analysing plant DNA from fallow deer poo, offering a fascinating glimpse into their diet. And this discovery could help us better understand how deer shape woodland ecosystems and influence conservation efforts.

Historically, UK deer populations declined because of overhunting, but today, hunting is more of a hobby than a necessity. As people continue shaping landscapes into urban-agriculture-woodland “mosaics”, we have created ideal habitats for deer, providing ample food and shelter, and reduced hunting pressure. As a result, our deer populations are thriving.

The UK government has set a target of net zero carbon emissions by 2050, with tree planting playing a crucial role. But growing saplings past knee height is challenging when deer are grazing nearby. If trees can’t grow, they can’t store carbon.

Fallow deer (Dama dama) are a well-loved species often seen in UK parks. As “intermediate grazers” they eat large quantities of fibrous plant materials, such as grasses, with leafy greens when it suits them.

Studies shows that fallow are one of the least fussy deer species on the planet – they eat just about anything. They also form large social groups. So you can imagine how they thrive in a human-transformed mosaic landscape and the amount of damage they can inflict on woodlands.

Our recent study examined the diet of fallow deer in the Elwy Valley, north Wales. These deer came from a captive herd on a large estate, released when the fences were removed during the first world war. Over the past century, the population has grown from a few dozen to several thousand, raising serious concerns among woodland managers.

A part of the Elwy Valley in north Wales. Llywelyn2000/Wikimedia, CC BY-SA

We used a new DNA sequencing technique called “metabarcoding” to reveal what plant species were in around 350 fallow deer poo samples. These were collected from three woodlands in the Elwy Valley every month for two years.

We also surveyed the woodland vegetation to discover how the deer diet related to the seasonal availability of different plants. The nearby Welsh Mountain Zoo kindly provided poo samples from their fallow deer herd to check against our results from the wild deer.

We expected deer to eat plenty of grass all year round and more broadleaf plants in winter and early spring. But the DNA results surprised us. Fallow deer consumed significant amounts of bramble (Rubus fruticosus agg).

Bramble made up 80% of their winter diet, dropping to 50% by late summer. The deer ingested more broadleaf trees in spring and summer while they were in leaf, and consumed large quantities of acorns in autumn. Grasses accounted for only a small portion of their diet, peaking at a mere 6% during the autumn months.

Our woodland vegetation survey had indicated that bramble was the most prevalent plant in the environment. With edible shoots available throughout the year, bramble provides a consistent food source, probably playing a crucial role in the winter diet when other food is scarce.

Consequences for deer, woodlands and net zero

A recent report showed that Britain’s woodland canopies are becoming more open because of severe storms and the spread of tree diseases. This benefits bramble, which can grow back after deer browsing and rapidly colonise woodlands where gaps in the canopy allow more light to reach the ground. But the relationship between bramble, deer feasting and tree regeneration is complex.

Bramble can protect young trees from deer by forming a spiny barrier, but it can also smother saplings and shade out rare woodland plants. In contrast, heavy deer browsing can suppress bramble growth, preventing it from out-competing other vegetation. As deer populations continue to grow while we try to plant more trees and conserve woodland habitats, balancing these factors becomes a problem with no simple solution.

Through plant DNA analysis of deer faeces and stomach contents, we can gain valuable insights for woodland management by discovering what deer are eating across seasons in different habitats. We can also compare the diets of different deer species (we have six in the UK). This approach helps us build a more comprehensive understanding of the ecological role of deer in our woodlands.

For woodland managers, there is no one-size-fits-all solution. Simply culling deer may not achieve the desired outcomes. Instead, we recommend examining what is happening to the bramble, tree saplings and other plants in both light and shady parts of the woodland, along with the effects of deer grazing. Adaptive management – tailored to specific site conditions – is central to achieving long-term woodland health and successful tree regeneration.

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Amy Gresham receives funding from the Natural Environment Research Council.

This research was funded by the Natural Environment Research Council through the Envision Doctoral Training Partnership (Grant code: NE/L002604/1).

This research was funded by the Natural Environment Research Council through the Envision Doctoral Training Partnership (Grant code: NE/L002604/1). John Healey is a member of The Board of Woodknowledge Wales. He is a member of the Institute of Chartered Foresters, the Royal Forestry Society, the Small Woods Association, the North Wales Wildlife Trust, the British Ecological Society and other scientific and forestry organizations.

How to recognise a temperate rainforest in Britain and Ireland when you see one

2023-07-10T15:54:26Z

The term “temperate rainforest”, or “Celtic rainforest”, has rapidly gained public attention in the UK recently.

In February 2023, British insurance company, Aviva, awarded £38 million of funding for the restoration of these rainforests. These restoration efforts have even caught the interest of Prince William, who has announced plans to double the size of Wistman’s Wood, an iconic fragment of ancient woodland on his Dartmoor estate.

Britain was once covered with trees. But over thousands of years, ancient woodland in wetter areas of the country’s west were cleared and converted into pasture for sheep and cattle. By the start of the 20th century, Britain and Ireland had become the least-wooded region in Europe, with only small fragments remaining in both countries’ western coastal rainforest zones.

But how much of this woodland actually counts as rainforest? The complex variation among different types of woodland makes it difficult to classify them as either rainforests or non-rainforests. And while the climate in Britain and Ireland is wet relative to the south and east of Europe, the question remains: how wet is wet enough to support a rainforest?

To understand if an area can support a rainforest, it’s important to consider not just the mean annual rainfall, but also that it rains across the seasons. Some areas in the Mediterranean basin receive the same amount of annual rainfall as parts of Great Britain. But this rain is concentrated in the winter, and prolonged periods of drought during the summer prevent the formation of a recognisable rainforest.

In Britain and Ireland, the climate is characterised by lower seasonality in rainfall, with dry summers being the exception rather than the rule. However, most climate models predict that this will change in the future, meaning that fewer areas of these islands will be able to support rainforests.

Prince William plans to double the size of Wistman’s Wood. Bourne for nature/Shutterstock

But rainfall alone does not determine the presence of rainforests. The availability of water in the soil, which is influenced by factors such as soil depth, texture and organic matter content, plays a crucial role in supporting rainforest trees. Even in areas with high rainfall, thin soils can lead to conditions prone to drought.

So, this leaves us with a dilemma: how can you spot a rainforest in Britain and Ireland?

1. Characteristic types of plant

The most iconic plant types characteristic of temperate rainforests are the epiphytes. These are plants that grow above the ground and attach themselves to the stems of trees or shrubs.

Epiphytes, including orchids, are an important component of biodiversity in tropical rainforests. By contrast, most of the epiphytes in temperate rainforests are “lower plants”, such as ferns and plants lacking a vascular system to move water within them, like mosses, liverworts and lichens.

Plants such as moss are characteristic of temperate rainforests. Alexandr Macovetchi/Shutterstock

2. Horizontal precipitation

Epiphytes gain some of their moisture from water that trickles down the trunks of trees during heavy rainfall (a process called “stem flow”). But these plants do not solely rely on rain.

In upland or coastal environments, where ground-level cloud or mist is common, another important source of moisture for epiphytes is horizontal precipitation (droplets of water that are suspended in the cloud). This moisture source is particularly important for the epiphytes that are most susceptible to drought, such as filmy ferns and some mosses and lichens.

3. Woody climbers

The UK’s temperate rainforests have several other features that are reminiscent of their tropical counterparts. One such feature is woody climbers (or liana) that use trees to ascend to the forest canopy. Classic examples of these plants in Britain and Ireland are ivy, clematis and honeysuckle.

However, the presence of woody climbers alone is not indicative of a temperate rainforest. While ivy, for example, is most abundant in wetter forests, these three liana species can be found across a range of woodland types in Britain and Ireland, even in the drier eastern regions.

4. Tree structure

The species of tree found in rainforests in Britain and Ireland are not good indicators of their rainforest status. The dominant canopy tree in many is sessile oak, which is the same species that dominates many forests producing straight stems of high-quality oak timber in northern France.

What better distinguishes a rainforest in Britain or Ireland is the structural characteristics of the trees. In rainforests near the west coast, such as on Dartmoor, the trees tend to be short, with leaning trunks and low branches.

However, this small tree structure is unlikely to be a direct result of high rainfall. The canopy trees of temperate rainforests in even wetter areas of coastal Oregon, Washington State and British Columbia in North America reach at least twice the height (40 metres or more). The distinctive short stature of trees in Britain’s rainforests is instead probably influenced by a combination of factors, including exposure to high winds and infertile thin soils, both of which are characteristic of the Atlantic coastal and upland environments of western Britain and Ireland.

Rainforest trees in Britain and Ireland tend to be short, with leaning trunks and low branches. Chris JG White/Shutterstock

The temperate rainforests of Britain and Ireland are rapidly assuming an iconic status, conjuring up a vivid image of mist, moss and convoluted trees.

But these woodlands are more than just visually captivating – they are rare habitats that are crucial for many endangered species, especially epiphytes. Unfortunately, they are also vulnerable to the effects of climate change. This makes them a fitting focus for new initiatives targeting their restoration.

John Healey receives funding from the Natural Environment Research Council of the UK Government, Welsh Government, Woodknowledge Wales.

In Jamaica, native trees are being driven further up mountains towards extinction

2022-05-31T10:42:13Z

eric laudonien / shutterstock

The Blue Mountains of Jamaica are frequently covered in a dense blanket of cloud, but when it lifts the first thing you notice is the cloak of forest extending up their steep slopes to the top of the highest peaks. As you walk up through these trees you encounter an incredible diversity of habitats from the high canopies of the lower slopes to the elfin forests of the ridge tops (barely taller than head height).

Yet new evidence shows that two effects of global climate change are combining to threaten these mountain forests. Climate change increases the intensity of the strongest hurricanes in the region, and it’s also slowly shifting the range of plant and animal species into previously colder zones, towards the north and south poles and up the slopes of mountains to higher altitudes.

Together with an international team of scientists, we have just published new research which shows that, in the Blue Mountains, this species migration was accelerated by Hurricane Gilbert in 1988.

Gilbert caused serious damage to the Blue Mountain forests, snapping the branches and trunks of many of the biggest trees. Most resprouted and survived, but the rate of mortality was particularly high for the species that are restricted to the highest altitude forests. The gaps in the canopy opened up by the death of these trees provided the opportunity for new trees to regenerate, but these tended to be species from lower down the mountain slopes. The net result is that the forest is becoming more dominated by lower altitude species, accelerating a process that was already slowly under way due to global warming.

Trees damaged by Hurricane Gilbert resprout their crowns a few months later. John Healey, Author provided

The Jamaican Blue Mountains rise to an altitude of 2,256 metres so, at present, there is still forested land further up the slopes for the rare mountain species to migrate to. However, once they become confined to the highest mountain ridges there will be nowhere else to go. The impact of an increase in severe hurricanes like Gilbert will bring that threat of extinction ever closer.

Brunfelsia jamaicensis: one of the threatened trees found only in Jamaica’s Blue Mountains. Peter Bellingham, Author provided

This has the potential to be a major contributor to the global biodiversity crisis, showing yet again how it is inextricably linked to the climate crisis. Gilbert was one of the most destructive hurricanes to hit Jamaica in the last century, but there is strong modelling evidence that we will see an increasing number of such intense storms across the Caribbean as a result of climate change.

The Caribbean islands are recognised as one of 36 global biodiversity hotspots and their mountain forests that have avoided deforestation (unlike most of the lowlands) are a particularly important habitat for many endangered species. Lots of the species native to the upper slopes of the Blue Mountains exist nowhere else in the world. Some also exist on a few other Caribbean mountains, but there they will be equally threatened by severe storms.

Australian invaders

All this is made even more serious by yet another combination of damaging human impacts on the natural world: the threat of an increase in intense hurricanes and invasion of forests by species we have introduced from other parts of the world.

A degraded area of forest, now dominated by the invasive Pittosporum undulatum. John Healey, Author provided

The Australian tree Pittosporum undulatum (known locally as “mock orange” because of its brightly coloured fruit) was introduced to a botanic garden in the Blue Mountains more than 130 years ago, yet we now know it has become one of the world’s most invasive species.

In Jamaica, its seeds are dispersed far and wide by native birds and the gaps in the canopy of the natural forests across the Blue Mountains caused by Hurricane Gilbert allowed a huge expansion of its invasion. Pittosporum casts a dense shade and our research has shown that it outcompetes many native trees, particularly threatening the high-altitude species that exist nowhere else and are the most vulnerable to global warming.

Forest floor almost completely covered by seedlings of the invasive species, ruining any chance of regeneration by native trees. John Healey

Taken together, this evidence is another strong reason to recognise climate change as a threat to global biodiversity. Stopping climate change will clearly be a long and difficult challenge, yet there are some more immediate steps that would reduce the risk of extinction in Caribbean forests. The most important is to much better regulate the movement between countries of species with any potential to become invasive and to control invasive populations where they have already started to threaten biodiverse natural habitats.

Protecting the remaining high-altitude forests from deforestation and degradation will also buy us more time. But unless we can effectively solve this climate-hurricane-invasive species combination of threats, then conservation in these mountains will fail and we will be reduced to trying to preserve species outside their native habitats in botanic gardens or seed banks.

John Healey receives funding from a diversity of research funding organisations. His research in Jamaica was funded by the UK Natural Environment Research Council, Department for International Development Forestry Research Programme and the Royal Society.

Edmund Tanner does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Sacred sites have a biodiversity advantage that could help world conservation

2018-05-17T10:22:36Z

jokki/Shutterstock

Since the dawn of history, human societies have ascribed sacred status to certain places. Areas such as ancestral burial grounds, temples and churchyards have been given protection through taboo and religious belief. As many of these places have been carefully managed for many years an interesting side effect has occurred – the sites often retain more of their natural condition than surrounding areas used for farming or human habitation. As a result, they are often called “sacred natural sites” (SNS).

Today, as many other natural habitats have become degraded, researchers worldwide are increasingly interested in the role of SNS in biodiversity conservation. Most of the world’s belief systems, including Christianity, give places sacred status. In Mediterranean Europe, for instance, the grounds of churches – with their associated ancient trees – have become important SNS.

One of the best examples is in the mountainous region of Epirus in north-western Greece. In the municipalities of Zagori and Konitsa almost every village has one or more sacred grove. These places have been protected through religious belief systems for hundreds of years.

The groves are either protective forests that lie uphill from the village, or groups of mature trees surrounding outlying churches, monuments or other works of religious art. Activities such as the cutting of trees or livestock grazing have been either prohibited or strictly regulated in these places (and disobeying these prohibitions sometimes led to excommunication).

Greek investigation

We have recently been studying these Greek SNS as part of our SAGE (SAcred Groves of Epirus) project. Our team wanted to find out, using a rigorous research approach, whether SNS are more biodiverse than other forest areas, and, if so, what lessons conservationists could learn from this.

To do this, our international and multidisciplinary group has recently completed the world’s first replicated systematic investigation into the claims that areas conserved as SNS are more biodiverse for different types of plant and animal.

For our recently published study, we selected eight SNS in Epirus that covered a wide range of environmental conditions. Each was closely matched with a nearby non-sacred “control” forest which had been managed conventionally – sometimes through natural regeneration. We then conducted a detailed inventory in each site, of eight different groups of organisms. These ranged from fungi and lichens, through herbaceous and woody plants to nematodes, insects, bats and passerine birds.

We found that SNS do indeed have a small but persistent biodiversity advantage. This is expressed in a number of ways, most clearly through the existence of more distinct communities of species among the sacred groves than in the control sites (this phenomenon is known as beta diversity).

The group with the most notably higher biodiversity in the SNS than in control sites were the fungi. These often grow in dead wood or old trees, which usually get removed in conventionally managed forests. Of the species of passerine birds (a group that includes many songbirds) that are designated as having special conservation importance at a European level, we found twice as many species present in the SNS as in the control sites.

Because these sacred sites are often quite small it is often said that their conservation benefits are marginal. But we found that the influence of size is relatively weak – even small SNS can play a significant role in biodiversity conservation.

Conserving sacred sites

But Epirus’s sacred sites are now in peril. The rules that linked belief and conservation that once protected the SNS have become difficult to enforce, due to changing population and land-use. The value of forests which protect from landslides and floods is no longer being recognised.

The value of SNS is not just on the land that is sacred itself, these places can act as a nucleus, around which biodiversity can expand. In Epirus, forests have regenerated around many of the sites we studied over the past 70 years – despite humans farming the land. It should be noted that this can increase risks such as fire, as dense young Mediterranean forest is very flammable.

Evidently the already well-conserved SNS are of great environmental importance across the world. So the next step is to link these sites into conventional conservation schemes. But it is vital that such strategies are closely aligned with the cultural status of SNS. Local communities are often highly motivated to maintain their sacred sites and associated belief systems but lack the resources to do so. A fully collaborative approach between conservation professionals and local communities could offer a solution that conserves both biodiversity and local cultural values.

John Healey receives funding from the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program Education and Lifelong Learning of the National Strategic Framework (NRSF) (Code 379405) - Research Funding Program: THALIS. Investing in knowledge society through the European Social Fund.

John M Halley has received funding from the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program Education and Lifelong Learning of the National Strategic Framework (NRSF) (Code 379405) - Research Funding Program: THALIS. Investing in knowledge society through the European Social Fund.

Kalliopi Stara has received funding from from the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program Education and Lifelong Learning of the National Strategic Framework (NRSF) (Code 379405) - Research Funding Program: THALIS. Investing in knowledge society through the European Social Fund.

Pistes forestières, un impact environnemental plus limité que prévu

2016-06-20T04:37:02Z

Fritz Kleinschroth, Author provided

L’accès au bois d’œuvre, même dans le cas d’une exploitation sélective, nécessite l’ouverture de pistes forestières. Or la création de ce type de voies d’accès a d’importantes conséquences pour les forêts : les pistes fragmentent les écosystèmes et facilitent l’accès des populations locales, entraînant une augmentation des dégradations ou de la déforestation.

Des travaux menés par les chercheurs du Cirad et de l’Université de Bangor dans le bassin du Congo montrent qu’en 30 ans près de 90 % des pistes aménagées par les exploitants forestiers ont été abandonnées puis recolonisées avec succès par la végétation. Les chercheurs ont analysé l’évolution de ces pistes dans onze concessions forestières, depuis leur création jusqu’à leur disparition.

Récemment publiés dans les revues Journal of Applied Ecology et Frontiers in Ecology and the Environment, deux articles font le point sur ces résultats.

88 % des pistes abandonnées

Premier constat : le défrichage nécessaire à la construction des pistes d’accès a concerné moins de 1 % du couvert forestier global de la zone d’étude, qui s’étend sur plus de 25 000 km² dans l’est du Cameroun et le nord-est de la République du Congo.

Second constat : à la surprise des scientifiques, seuls 12 % de ce réseau routier ont été utilisés en continu durant ces trois décennies, les 88 % restants ayant été abandonnés après quelques années d’exploitation seulement.

Que sont devenues ces pistes désaffectées ? La végétation les a progressivement reconquises. En trois décennies, la forêt s’est reconstituée, jusqu’à ce que la diversité en espèces, la canopée, la litière et la composition de la strate herbacée ressemblent à celles de la forêt avoisinante.

En étudiant ces processus, les chercheurs ont été étonnés de découvrir que la régénération des espèces d’arbres d’intérêt commercial était meilleure à proximité des pistes abandonnées que dans les forêts elles-mêmes : leur densité peut être jusqu’à trois fois plus importante à proximité des anciennes voies d’accès. Cette situation s’expliquerait par un accès à la lumière facilité dans les zones défrichées.

Les pistes ouvertes il y a une trentaine d’années puis abandonnées montrent des signes de régénération continue. Fritz Kleinschroth, Author provided

Capacité de stockage du CO₂ altérée

L’impact des pistes forestières dans le bassin du Congo semble donc moins important que l’on aurait pu le craindre. Il n’est toutefois pas inexistant, en particulier sur le long terme. En effet, les estimations montrent que malgré une régénération continue, la biomasse – qui permet de déduire le carbone stocké dans les arbres – ne s’accumule que lentement sur les anciennes pistes : 15 à 30 ans après leur abandon, la biomasse qui y est stockée ne représente que 6 % environ de celle stockée par les forêts avoisinantes.

À ce rythme, il faudra 300 ans pour que les pistes accumulent la biomasse qui existait avant leur ouverture. La capacité de ces zones à stocker du carbone est donc durablement affectée. La situation est toutefois un peu meilleure sur les bordures des anciennes pistes, où le sol a été moins compacté.

Réduire la largeur des pistes

Cette lente récupération souligne l’importance de réduire la largeur des pistes, qui était en moyenne de 20 m, et de rouvrir celles qui ont été abandonnées, plutôt que d’en construire de nouvelles. En effet, alors que la forêt est généralement réexploitée dans la même zone après une rotation de 30 ans, il est rare que les anciennes pistes soient réutilisées, les exploitants préférant en ouvrir d’autres, parallèles aux précédentes.

Ces travaux montrent enfin que les abords des voies d’accès abandonnées sont propices à la mise en place d’une sylviculture post-exploitation, durant les quelques années où les pistes non entretenues demeurent praticables. Reste toutefois à trouver un équilibre : la fermeture complète des pistes abandonnées permet de limiter l’accès aux écosystèmes forestiers et leur dégradation, par la chasse notamment.

John Healey receives funding from the Natural Environment Research Council, the Biotechnology and Biological Sciences Research Council, the Economic and Social Research Council, the Center for International Forestry Research, and the European Union. He is a member of the Institute of Chartered Foresters, the Commonwealth Forestry Association and the British Ecological Society.

Fritz Kleinschroth received funding from the European commission through the Erasmus Mundus joint doctorate program FONASO. He is affiliated with Bangor University, CIRAD Montpellier and AgroParisTech Montpellier. He is a member of the Ecological Society of America, the Society for Conservation Biology, the Association for Tropical Biology and Conservation and the European Society for Tropical Ecology.

Sylvie Gourlet-Fleury a reçu des financements de l’ANR (Agence nationale de la recherche), de l’AFD (Agence française de développement) et du FFEM (Fond français pour l’environnement mondial). Elle est coordinatrice adjointe pour le IUFRO de la sous-division “1.02.00 Tropical and Subtropical Silviculture”, et membre du conseil scientifique de l’ATIBT (Association technique Internationale des bois tropicaux).

How forests recover rapidly on logging roads in the Congo Basin

2016-06-06T13:24:30Z

Large areas of tropical forest worldwide are used for selective logging which requires extensive road networks to access trees harvested for timber. It is well documented that building roads into intact forest can have consequences for forest ecosystems. This is because they lead to fragmentation and facilitate access for people which can lead to long-term forest degradation or deforestation.

We conducted a study of roads in forests in Central Africa over a period of 30 years. We studied an area of 108 000 km2, which is larger than Sierra Leone. We made some startling findings. The main one is that the vast majority of roads are transient and in fact provide better habitats for the recovery of diverse species of trees than adjacent logged forests. But we also learnt that the recovery of biomass – the total weight of the living trees, which contains their stocks of carbon – on abandoned roads was slow.

These findings provide important evidence for the long-term management of logging road networks in tropical forests. They show that it is important to close roads from further vehicle use after the end of logging operations, but it is a good plan to re-open these same roads for use when the next phase of logging takes place in each area of forest. Our results also show the excellent potential to use the land cleared alongside roads to grow the next crop of timber trees.

Conversion of tropical forests to agricultural crops, like oil palm in Southeast Asia and soya bean in the Amazon, has been the main source of environmental concern elsewhere in the tropics but in the Congo Basin, the main focus has been on selective logging of forests for timber. Back in 2007 Nadine Laporte and colleagues reported that more than 600 000 km2 (30%) of forest in Central Africa had been allocated by governments as concessions for logging.

Recently there has been a trend towards the application of certification standards to improve the environmental performance of these operations. But there have still been many scientific reports about their negative effects on forest wildlife, including primates and birds, through habitat disturbance or increased poaching. The logging roads used to extract timber are often a major focus of this conservation concern.

Logging roads in the Congo Basin

Our recently published paper reports on the fate of roads built for selective logging in the Congo Basin and discusses the implications for forest management. A remote sensing analysis covering an area of more than 100 000 km2 over a time span of 30 years enabled long-term monitoring of roads from the time they were built until they disappeared.

These observations showed that only 12% of the road network has been permanently open. The remaining 88% was abandoned within a few years of timber harvesting. Changes in the satellite images over time clearly indicated the moment when the road surface was fully covered by vegetation.

But how is this vegetation characterised in terms of structure and diversity? How long do different groups of species dominate after road abandonment and how fast is the recovery of biomass?

To answer these questions, an extensive field study was carried out in eastern Cameroon and northern Republic of Congo, covering the full temporal sequence of roads abandoned over the last 30 years.

Fast recovery

The results show that less than 1% of the forest cover has been cleared for road construction to extract timber. Roads abandoned over the last 30 years showed a continuous trajectory of forest regeneration. Tree species diversity, canopy cover, the litter layer and herb composition converged with those in the surrounding logged forests. Trees of commercial species generally showed even higher rates of regeneration on road tracks and edges than in the forest, as they benefit from the high light levels due to a lack of canopy shade.

These results do not mean that there is no long-term negative impact of roads on forest vegetation. But in the study area, they are less than people would have expected. The slowest measured recovery was in the accumulation of tree biomass on road tracks. This is projected to take hundreds of years to reach the same level of carbon storage as old-growth forests, which means that building logging roads causes an increase in carbon emissions and their global warming potential that will take a very long time to recover.

After some time the understorey of vegetation regrowing on roads becomes dominated by herbs. This impedes further tree regeneration, just as in the adjacent logged forests in this part of the Congo Basin. Unregulated hunting also remains a problem. During the early years after abandonment poachers can hardly be stopped from using logging roads. But over time vegetation recovery makes it more difficult for motorised hunters to use abandoned logging roads.

Should abandoned logging roads be reopened?

Reducing the long-term impact of logging roads on forest ecosystems is an important element of sustainable forest management. Their demonstrated habitat potential could make road edges suitable places for growing a future crop of timber trees either by planting seedlings or tending those that regenerate naturally from seed – what the foresters call silviculture. At the same time, the effective closure of roads after logging operations remains crucial to avoid threats to the forest ecosystem, especially through hunting.

But logging operations are typically repeated in the same area every 30 years, which leads to the question: what happens to old roads if the same forest area is logged more than once? Surprisingly, of all the roads in such areas, only one third have been reopened. All the other new roads were built next to the historic network. The first cut is the deepest –- this remains true for roads built into intact forests.

Given the findings of slow biomass recovery, our studies conclude that more old logging roads should be reopened to avoid creating new ones.