Are young trees or old forests more important for slowing climate change?

Jeremy Kieran/Unsplash, CC BY-SA

Tom Pugh, University of Birmingham

Forests are thought to be crucial in the fight against climate change – and with good reason. We’ve known for a long time that the extra CO₂ humans are putting in the atmosphere makes trees grow faster, taking a large portion of that CO₂ back out of the atmosphere and storing it in wood and soils.

But a recent finding that the world’s forests are on average getting “shorter and younger” could imply that the opposite is happening. Adding further confusion, another study recently found that young forests take up more CO₂ globally than older forests, perhaps suggesting that new trees planted today could offset our carbon sins more effectively than ancient woodland.

How does a world in which forests are getting younger and shorter fit with one where they are also growing faster and taking up more CO₂? Are old or young forests more important for slowing climate change? We can answer these questions by thinking about the lifecycle of forest patches, the proportion of them of different ages and how they all respond to a changing environment.

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Using forests to manage carbon: a heated debate

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The forest carbon budget

Let’s start by imagining the world before humans began clearing forests and burning fossil fuels.

In this world, trees that begin growing on open patches of ground grow relatively rapidly for their first several decades. The less successful trees are crowded out and die, but there’s much more growth than death overall, so there is a net removal of CO₂ from the atmosphere, locked away in new wood.

As trees get large two things generally happen. One, they become more vulnerable to other causes of death, such as storms, drought or lightning. Two, they may start to run out of nutrients or get too tall to transport water efficiently. As a result, their net uptake of CO₂ slows down and can approach zero.

Eventually, our patch of trees is disturbed by some big event, like a landslide or fire, killing the trees and opening space for the whole process to start again. The carbon in the dead trees is gradually returned to the atmosphere as they decompose.

The vast majority of the carbon is held in the patches of big, old trees. But in this pre-industrial world, the ability of these patches to continue taking up more carbon is weak. Most of the ongoing uptake is concentrated in the younger patches and is balanced by CO₂ losses from disturbed patches. The forest is carbon neutral.

New trees absorb lots of carbon, old trees store more overall and dead trees shed their carbon to the atmosphere.
Greg Rosenke/Unsplash, CC BY-SA

Now enter humans. The world today has a greater area of young patches of forest than we would naturally expect because historically, we have harvested forests for wood, or converted them to farmland, before allowing them to revert back to forest. Those clearances and harvests of old forests released a lot of CO₂, but when they are allowed to regrow, the resulting young and relatively short forest will continue to remove CO₂ from the atmosphere until it regains its neutral state. In effect, we forced the forest to lend some CO₂ to the atmosphere and the atmosphere will eventually repay that debt, but not a molecule more.

But adding extra CO₂ into the atmosphere, as humans have done so recklessly since the dawn of the industrial revolution, changes the total amount of capital in the system.

And the forest has been taking its share of that capital. We know from controlled experiments that higher atmospheric CO₂ levels enable trees to grow faster. The extent to which the full effect is realised in real forests varies. But computer models and observations agree that faster tree growth due to elevated CO₂ in the atmosphere is currently causing a large carbon uptake. So, more CO₂ in the atmosphere is causing both young and old patches of forest to take up CO₂, and this uptake is larger than that caused by previously felled forests regrowing.

The effect of climate change

But the implications of climate change are quite different. All else being equal, warming tends to increase the likelihood of death among trees, from drought, wildfire or insect outbreaks. This will lower the average age of trees as we move into the future. But, in this case, that younger age does not have a loan-like effect on CO₂. Those young patches of trees may take up CO₂ more strongly than the older patches they replace, but this is more than countered by the increased rate of death. The capacity of the forest to store carbon has been reduced. Rather than the forest loaning CO₂ to the atmosphere, it’s been forced to make a donation.

So increased tree growth from CO₂ and increased death from warming are in competition. In the tropics at least, increased growth is still outstripping increased mortality, meaning that these forests continue to take up huge amounts of carbon. But the gap is narrowing. If that uptake continues to slow, it would mean more of our CO₂ emissions stay in the atmosphere, accelerating climate change.

Overall, both young and old forests play important roles in slowing climate change. Both are taking up CO₂, primarily because there is more CO₂ about. Young forests take up a bit more, but this is largely an accident of history. The extra carbon uptake we get from having a relatively youthful forest will diminish as that forest ages. We can plant new forests to try to generate further uptake, but space is limited.

But it’s important to separate the question of uptake from that of storage. The world’s big, old forests store an enormous amount of carbon, keeping it out of the atmosphere, and will continue to do so, even if their net CO₂ uptake decreases. So long as they are not cut down or burned to ashes, that is.

Tom Pugh, Reader in Biosphere-Atmosphere Exchange, University of Birmingham

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

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The Baltic Forest and Brown Bears

Forest soil needs decades or centuries to recover from fires and logging

David Blair, Author provided

Elle Bowd, Australian National University and David Lindenmayer, Australian National University

The 2009 Black Saturday fires burned 437,000 hectares of Victoria, including tens of thousands of hectares of Mountain Ash forest.

As we approach the tenth anniversary of these fires, we are reminded of their legacy by the thousands of tall Mountain ash “skeletons” still standing across the landscape. Most of them are scattered amid a mosaic of regenerating forest, including areas regrowing after logging.

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Comic explainer: forest giants house thousands of animals (so why do we keep cutting them down?)

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But while we can track the obvious visible destruction of fire and logging, we know very little about what’s happening beneath the ground.

In a new study published in Nature Geoscience, we investigated how forest soils were impacted by fire and logging. To our surprise, we found it can take up to 80 years for soils to recover.

Logging among the charred remains of Mountain ash after the 2009 fires.
David Blair, Author provided

Decades of damage

Soils have crucial roles in forests. They are the basis for almost all terrestrial life and influence plant growth and survival, communities of beneficial fungi and bacteria, and cycles of key nutrients (including storing massive amounts of carbon).

To test the influence of severe and intensive disturbances like fire and logging, we compared key soil measures (such as the nutrients that plants need for growth) in forests with different histories. This included old forests that have been undisturbed since the 1850s, forests burned by major fires in 1939, 1983 and 2009, forests that were clearfell-logged in the 1980s or 2009-10, or salvage-logged in 2009-10 after being burned in the Black Saturday fires.

We found major impacts on forest soils, with pronounced reductions of key soil nutrients like available phosphorus and nitrate.

A shock finding was how long these impacts lasted: at least 80 years after fire, and at least 30 years after clearfell logging (which removes all vegetation in an area using heavy machinery).

However, the effects of disturbance on soils may persist for much longer than 80 years. During a fire, soil temperatures can exceed 500℃, which can result in soil nutrient loss and long-lasting structural changes to the soil.

We found the frequency of fires was also a key factor. For instance, forests that have burned twice since 1850 had significantly lower measures of organic carbon, available phosphorus, sulfur and nitrate, relative to forests that had been burned once.

Sites subject to clearfell logging also had significantly lower levels of organic carbon, nitrate and available phosphorus, relative to unlogged areas. Clearfell logging involves removing all commercially valuable trees from a site – most of which are used to make paper. The debris remaining after logging (tree heads, lateral branches, understorey trees) is then burned and the cut site is aerially sewn with Mountain Ash seed to start the process of regeneration.

Fire is important to natural growth cycles in our forests, but it changes the soil composition.
David Lindenmayer, Author provided

Logging compounds the damage

The impacts of logging on forest soils differs from that of fire because of the high-intensity combination of clearing the forest with machinery and post-logging “slash” burning of debris left on the ground. This can expose the forest floor, compact the soil, deplete soil nutrients, and release large amounts of carbon dioxide into the atmosphere.

Predicted future increases in the number, frequency, intensity and extent of fires in Mountain Ash forests, coupled with ongoing logging, will likely result in further declines in soil nutrients in the long term. These kinds of effects on soils matter in Mountain Ash forests because 98.8% of the forest have already been burned or logged and are 80 years old or younger.

To maintain the vital roles that soils play in ecosystems, such as carbon storage and supporting plant growth, land managers must consider the repercussions of current and future disturbances on forest soils when planning how to use or protect land. Indeed, a critical part of long-term sustainable forest management must be to create more undisturbed areas, to conserve soil conditions.

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New modelling on bushfires shows how they really burn through an area

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Specifically, clearfell logging should be limited wherever possible, especially in areas that have been subject to previous fire and logging.

Ecologically vital, large old trees in Mountain Ash forests may take over a century to recover from fire or logging. Our new findings indicate that forest soils may take a similar amount of time to recover.

Elle Bowd, PhD scholar, Australian National University and David Lindenmayer, Professor, The Fenner School of Environment and Society, Australian National University

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

Comic explainer: forest giants house thousands of animals (so why do we keep cutting them down?)

Wes Mountain/The Conversation, CC BY-ND

Madeleine De Gabriele, The Conversation and Wes Mountain, The Conversation

Giant eucalypts play an irreplaceable part in many of Australia’s ecosystems. These towering elders develop hollows, which make them nature’s high-rises, housing everything from endangered squirrel-gliders to lace monitors. Over 300 species of vertebrates in Australia depend on hollows in large old trees.

These “skyscraper trees” can take more than 190 years to grow big enough to play this nesting and denning role, yet developers are cutting them down at an astounding speed. In other places, such as Victoria’s Central Highlands Mountain Ash forests, the history of logging and fire mean that less than 1.2% of the original old-growth forest remains (that supports the highest density of large old hollow trees). And it’s not much better in other parts of our country.

David Lindenmayer explains how these trees form, the role they play – and how very hard they are to replace.

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Wes Mountain/The Conversation, CC BY-ND

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Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.

Madeleine De Gabriele, Deputy Editor: Energy + Environment, The Conversation and Wes Mountain, Multimedia Editor, The Conversation

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

Native forest protections are deeply flawed, yet may be in place for another 20 years

Current protections for native forests are hopelessly out of date.
Graeme/Flickr, CC BY-NC

David Lindenmayer, Australian National University

State governments are poised to renew some of the 20-year-old Regional Forest Agreements (RFAs) without reviewing any evidence gathered in the last two decades.

The agreements were first signed between the federal government and the states in the late 1990s in an attempt to balance the needs of the native forest logging industry with conservation and forest biodiversity.

It’s time to renew the agreements for another 20 years. Some, such as Tasmania’s, have just been renewed and others are about to be rolled over without substantial reassessment. Yet much of the data on which the RFAs are based are hopelessly out of date.

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Concerns about the validity of the science behind the agreements is shared by some state politicians, with The Guardian reporting the NSW Labor opposition environment spokeswoman as saying “the science underpinning the RFAs is out of date and incomplete”.

New, thorough assessments are needed

What is clearly needed are new, thorough and independent regional assessments that quantify the full range of values of native forests.

Much of the information underpinning these agreements comes largely from the mid-1990s. This was before key issues with climate change began to emerge and the value of carbon storage in native forests was identified; before massive wildfires damaged hundreds of thousands of hectares of forest in eastern Australia; and before the recognition that in some forest types logging operations elevate the risks of crown-scorching wildfires.

The agreements predate the massive droughts and changing climate that have affected the rainfall patterns and water supply systems of southwestern and southeastern Australia, including the forested catchments of Melbourne.

It’s also arguable whether the current Regional Forest Agreements accommodate some of the critical values of native forests. This is because their primary objective is pulp and timber production.

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Why we need environmental accounts alongside national accounts

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Yet it is increasingly apparent that other economic and social values of native forests are greater than pulp and wood.

To take Victoria as an example, a hectare of intact mountain ash forests produces 12 million litres more water per year than the same amount of logged forest.

The economic value of that water far outstrips the value of the timber: almost all of Melbourne’s water come from these forests. Recent analysis indicates that already more than 60% of the forest in some of Melbourne’s most important catchments has been logged.

The current water supply problems in Cape Town in South Africa are a stark illustration of what can happen when natural assets and environmental infrastructure are not managed appropriately. In the case of the Victorian ash forests, some pundits would argue that the state’s desalination plant can offset the loss of catchment water. But desalination is hugely expensive to taxpayers and generates large amounts of greenhouse emissions.

A declining resource

Another critical issue with the existing agreements is the availability of loggable forest. Past over-harvesting means that much of the loggable forest has already been cut. Remaining sawlog resources are rapidly declining. It would be absurd to sign a 20-year RFA when the amount of sawlog resource remaining is less than 10 years.

This is partially because estimates of sustained yield in the original agreements did not take into account inevitable wood losses in wildfires – akin to a long-distance trucking company operating without accident insurance.

Some are arguing that the solution now is to cut even more timber in water catchments, but this would further compromise water yields at a major cost to the economy and to human populations.

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Profits from forests? Leave the trees standing

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Comprehensive regional assessments must re-examine wood supplies and make significant reductions in pulp and timber yields accordingly.

The inevitable conclusion is that the Regional Forest Agreements and their underlying Comprehensive Regional Assessments are badly out of date. We should not renew them without taking into consideration decades of new information on the value of native forests and on threats to their preservation.

Australia’s native forests are among the nation’s most important natural assets. The Australian public has a right to expect that the most up-to-date information will be used to manage these irreplaceable assets.

David Lindenmayer, Professor, The Fenner School of Environment and Society, Australian National University

This article was originally published on The Conversation. Read the original article.

How tree bonds can help preserve the urban forest

City trees don’t just look after themselves.

Joe Hurley, RMIT University; Dave Kendal, University of Tasmania; Judy Bush, University of Melbourne, and Stephen Rowley, RMIT University

Great cities need trees to be great places, but urban changes put pressure on the existing trees as cities develop. As a result, our rapidly growing cities are losing trees at a worrying rate. So how can we grow our cities and save our city trees?

Tree bonds have recently been proposed by Stonnington City Council as a way to stop trees being destroyed in Melbourne’s affluent southeastern suburbs.

Tree bonds are a common mechanism for protecting trees on public land, but have so far had limited use on private land. A tree bond requires a land developer to deposit a certain amount of money with the local authority during development. If the identified tree or trees are not present and healthy after the development, the funds are forfeited.

The size of the bond can be established based on estimated tree replacement costs, and/or set at a level that is likely to achieve compliance (likely to be thousands or tens of thousands of dollars).

Why are trees important in cities?

The concept of an “urban forest” includes all the trees and plants in cities. This includes tree-lined city streets as well as parks, waterways and private gardens. The urban forest contributes substantially to the quality of life of all urban dwellers, both human and non-human, and is increasingly used to adapt cities to climate change.

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Does higher-density city development leave urban forests out on a limb?

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Trees cool the streets, filter the air and stormwater, and create a sense of place and character. They provide food and shelter for insects, birds and animals.

There is growing research evidence for the physical, mental and social health benefits of urban trees and green spaces. Many local councils such as Brimbank and Melbourne are investing substantially in tree planting to increase these benefits.

However, despite new tree planting on public land, tree canopy on private land is declining.

What can we do to protect trees?

There are a range of existing policy and land use planning measures focused on landscaping requirements for new development. Recently, the Victorian government introduced minimum mandatory garden area requirements. Some Melbourne councils, including Brimbank and Moreland, have also included planning scheme requirements for tree planting for multi-dwelling developments.

Other mechanisms for protecting urban trees on private land include heritage and environmental overlays within local planning schemes, and listings of significant trees and heritage trees.

However, penalties, monitoring and enforcement of tree protection bylaws have not kept pace with the pressures of urban change.

If penalties are insignificant relative to development profits, developers can easily absorb the costs. If monitoring is weak and removal has a good chance of going undetected, tree protection is more likely to be ignored. And if enforcement is weak, or there is a history of successful appeal or defeat of enforcement, many trees may be at risk of removal.

Even when it is successfully pursued, after-the-fact planning enforcement action is a particularly unsatisfactory recourse for tree removal. Replacement trees may take decades to match the quality of mature trees that were removed. What is needed, then, are mechanisms that prevent tree removal in the first place.

Increasing use of tree bonds

The advantage of tree bonds is that they place the onus of proof of retention on developers, rather than the onus of proof of removal on local councils. If a tree is removed, the mechanism is already in place to monitor (the developer needs to demonstrate the tree is still there) and penalise (the financial penalty is already with the enforcing body).

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Concrete jungle? We’ll have to do more than plant trees to bring wildlife back to our cities

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However, tree bonds still do not guarantee tree protection. Some mechanisms used to impose tree bonds may be vulnerable to challenge. For example, historically in Victoria, the planning appeals body VCAT has struck out conditions imposing tree bonds, arguing that punitive planning enforcement measures should be used where trees are removed.

Even where bonds can be imposed and enforced, developers may still be able to demonstrate that trees are unsafe or causing infrastructure damage, and thus need to be removed. In these circumstances, it is often hard to prove otherwise once the tree has been removed.

Nurturing an urban forest

Ultimately, if a landowner is hostile to a tree on their land, that tree’s health and survival can be imperilled, whether through illegal removal, neglect, or applications for removal based on health and safety grounds. It is therefore important that building layout and design realistically allow space for trees to flourish and be valued by landowners.

The urban forest needs protecting and enhancing. This calls for a range of policy mechanisms that work together to retain mature trees, maintain adequate spacing around them, and encourage residents to value and protect the trees around their homes.

Tree bonds provide an attractive solution for local governments in the absence of a strong land use policy framework for protecting trees.

Joe Hurley, Senior Lecturer, Sustainability and Urban Planning, RMIT University; Dave Kendal, Senior Lecturer in Environmental Management, University of Tasmania; Judy Bush, Postdoctoral Research Fellow, Clean Air and Urban Landscapes Hub, University of Melbourne, and Stephen Rowley, Lecturer in Urban Planning, RMIT University

This article was originally published on The Conversation. Read the original article.

Found: ‘lost’ forests covering an area two-thirds the size of Australia

A coolabah forest in Western Australia – one of the world’s previously unrecognised dryland forests.
TERN Ausplots, Author provided

Andrew Lowe, University of Adelaide and Ben Sparrow, University of Adelaide

A new global analysis of the distribution of forests and woodlands has “found” 467 million hectares of previously unreported forest – an area equivalent to 60% of the size of Australia.

The discovery increases the known amount of global forest cover by around 9%, and will significantly boost estimates of how much carbon is stored in plants worldwide.

The new forests were found by surveying “drylands” – so called because they receive much less water in precipitation than they lose through evaporation and plant transpiration. As we and our colleagues report today in the journal Science, these drylands contain 45% more forest than has been found in previous surveys.

We found new dryland forest on all inhabited continents, but mainly in sub-Saharan Africa, around the Mediterranean, central India, coastal Australia, western South America, northeastern Brazil, northern Colombia and Venezuela, and northern parts of the boreal forests in Canada and Russia. In Africa, our study has doubled the amount of known dryland forest.

The world’s drylands: forested areas shown in green; non-forested areas in yellow.
Bastin et al., Science (2017)

With current satellite imagery and mapping techniques, it might seem amazing that these forests have stayed hidden in plain sight for so long. But this type of forest was previously difficult to measure globally, because of the relatively low density of trees.

What’s more, previous surveys were based on older, low-resolution satellite images that did not include ground validation. In contrast, our study used higher-resolution satellite imagery available through Google Earth Engine – including images of more than 210,000 dryland sites – and used a simple visual interpretation of tree number and density. A sample of these sites were compared with field information to assess accuracy.

Unique opportunity

Given that drylands – which make up about 40% of Earth’s land surface – have more capacity to support trees and forest than we previously realised, we have a unique chance to combat climate change by conserving these previously unappreciated forests.

Drylands contain some of the most threatened, yet disregarded, ecosystems, many of which face pressure from climate change and human activity. Climate change will cause many of these regions to become hotter and even drier, while human expansion could degrade these landscapes yet further. Climate models suggest that dryland biomes could expand by 11-23% by the end of the this century, meaning they could cover more than half of Earth’s land surface.

Considering the potential of dryland forests to stave off desertification and to fight climate change by storing carbon, it will be crucial to keep monitoring the health of these forests, now that we know they are there.

Ground-based observations were a crucial part of the survey.
TERN AusPlots, Author provided

Climate policy boost

The discovery will dramatically improve the accuracy of models used to calculate how much carbon is stored in Earth’s landscapes. This in turn will help calculate the carbon budgets by which countries can measure their progress towards the targets set out in the Kyoto Protocol and its successor, the Paris Agreement.

Our study increases the estimates of total global forest carbon stocks by anywhere between 15 gigatonnes and 158 gigatonnes of carbon – an increase of between 2% and 20%.

This study provides more accurate baseline information on the current status of carbon sinks, on which future carbon and climate modelling can be based. This will reduce errors for modelling of dryland regions worldwide. Our discovery also highlights the importance of conservation and forest growth in these areas.

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The authors acknowledge the input of Jean-François Bastin and Mark Grant in the writing of this article. The research was carried out by researchers from 14 organisations around the world, as part of the UN Food and Agriculture Organization’s Global Forest Survey.

Andrew Lowe, Professor of Plant Conservation Biology, University of Adelaide and Ben Sparrow, Associate professor and Director – TERN AusPlots and Eco-informatics, University of Adelaide

This article was originally published on The Conversation. Read the original article.

A marine heatwave has wiped out a swathe of WA’s undersea kelp forest

Scott Bennett, Curtin University; Julia Santana-Garcon, and Thomas Wernberg, University of Western Australia

Kelp forests along some 100km of Western Australia’s coast have been wiped out, and many more areas damaged, by a marine heatwave that struck the area in 2011.

The heatwave, which featured ocean temperatures more than 2℃ above normal and persisted for more than 10 weeks, ushered in an abrupt change in marine plant life along a section of Australia’s Great Southern Reef, with kelp disappearing to be replaced by tropical species.

As we and our international colleagues report in the journal Science, five years on from the heatwave, these kelp forests show no signs of recovery.

Instead, fish, seaweed and invertebrate communities from these formerly temperate kelp forests are being replaced by subtropical and tropical reef communities. Tropical fish species are now intensely grazing the reef, preventing the kelp forests from recovering.

Kelp forest before (left) and after (right) the marine heatwave.
Author provided

Assessing the damage

We and our team surveyed reefs along 2,000km of coastline from Cape Leeuwin, south of Perth, to Ningaloo Reef between 2001 and 2015.

Up until 2011, temperate reefs were clearly defined by the distribution of kelp forests which formed dense, highly productive forests as far north as Kalbarri in WA’s Mid West.

Since 2011, the boundary between these temperate reefs of southern WA and the more tropical reefs (including Ningaloo) to the north has become less clear-cut. Instead, the sharp divide has been replaced by an intermediate region of turf-dominated reefs.

Infographic illustrating the impacts of the heatwave, kelp loss and tropicalisation of temperate reefs.
[Produced by Awaroo]((www.awaroo.com))

This has implications for the Great Southern Reef (GSR), which extends more than 8,000km around the southern half of Australia from the southern half of WA all the way to southern Queensland – a coastline that is home to around 70% of Australians.

Kelp forests are the GSR’s “biological engine”, feeding a globally unique collection of temperate marine species, not to mention supporting some of the most valuable fisheries in Australia and underpinning reef tourism worth more than A$10 billion a year.

But our research shows that on the GSR’s western side, kelp forests are being pushed towards Australia’s southern edge, where continued warming puts them at risk of losses across thousands of kilometres of coastline because there is no more southerly habitat to which they can retreat.

While the 2011 marine heatwave affected some 1,000km of Western Australia’s temperate coastline, it was a stretch of roughly 100km extending south of Kalbarri on the state’s Mid West coast that was most severely affected.

In this area alone an estimated 385 square km of kelp forest have been completely wiped out.

Further south, from Geraldton to Cape Leeuwin, the extent of kelp loss was less severe, despite an estimated total area of 960 square km having been lost in the region.

Northern regions towards Kalbarri were more severely affected because these kelp forests were closer to their limit, and also because this area is closer to the tropical regions like Ningaloo Reef, meaning that tropical species could more easily move in.

A school of tropical rabbitfish moves through the affected area.
Thomas Wernberg, Author provided

The problem was exacerbated by the southward-flowing Leeuwin Current, which helps tropical species move south while making it harder for temperate species to move north and recolonise the affected areas of the GSR.

The combination of these physical and ecological processes set within a background warming rate roughly twice the global average, compounds the challenges faced by kelp forests in the region.

The plight of WA’s kelp forests provides a strong warning of what the future might hold for Australia’s temperate marine environment, and the many services it provides to Australians.

Scott Bennett, Marie Curie Fellow at the Spanish National Research Council (CSIC), Curtin University; Julia Santana-Garcon, Postdoctoral research associate in Marine Ecology, and Thomas Wernberg, ARC Future Fellow in Marine Ecology, University of Western Australia

This article was originally published on The Conversation. Read the original article.

Europe’s oldest forest is threatened by a beetle infestation – let nature take its course

Lucinda Kirkpatrick, University of Stirling

Białowieza Forest is the kind of place you imagine from the Grimm fairy tales. Huge firs, oaks and ashes tower over you, woodpeckers and other birds call all around you and the guides who work there know the intimate history, and names, of many individual trees.

For anyone, it is a magical place – and, as a forest ecologist, visiting it was a dream come true. However, the features that make it so unique may be under threat thanks to new plans for large-scale logging.

Straddling the border between Poland and Belarus, Białowieza is the last remainder of the vast primeval forest that once covered most of Europe. It is a hotbed of biodiversity, home to nearly 20,000 plant and animal species including wolves, lynx and the largest remaining population of European bison. Rare birds, including several woodpecker species, provide a glimpse of the bird life that used to exist in European forests before humans transformed the continent.

The forest is home to around 800 bison.
Francesco Carrani, CC BY

Unfortunately, on the Polish side of the border, only one third of Białowieza Forest is protected. Outside of this area as much as 35% has been earmarked for felling and the fear is that this will result in an increasingly isolated small “island” of protected forest surrounded by fragmented and poorer quality woodland, which has already been shown to support lower bird populations than the protected park area.

Felling around Białowieza has been controlled in the past; quotas were set in 2012 to limit how much wood could be removed. However by 2015, 90% of that quota had already been logged – and the new proposals will triple the permitted volume of logging.

The proposal for further logging is controversial. Poland’s state forest department, Lasy Panstwowe, views the felling as necessary to combat outbreaks of spruce bark beetle, the larvae of which burrow under the bark of living spruce trees to lay its eggs. The developing larvae feed on inner woody layers and can eventually kill the tree.

Spruce bark beetles were here…and it didn’t end well for the tree.
Tõnu Pani, CC BY-SA

However, both local scientists and NGOs, such as Greenpeace Polska, argue that removing damaged trees will cause more harm than good and that further logging is driven by economic rather than management interests. Professor Tomasz Wesołowski, who has studied Białowieza’s birds for more than 30 years, told me it would be a disaster, as logging and replanting would completely change the quality of the forest habitat and threaten its UNESCO heritage site status. There is even a suggestion that this violates Poland’s environmental commitments under the EU’s Natura 2000 program.

The newly proposed logging areas cover 20% of the old-growth forest, as well as areas overgrown by endangered bog woodland habitat. Mass logging would dramatically alter the character of both the areas in question and the surrounding habitat – even more than the bark beetles.

In fact, across the world this form of “salvage logging” to recover economic value from damaged forests often causes more damage to ecosystems than the initial natural disturbance. After a bark beetle invasion hit Sumava National Park, that stretches across the border between Bavaria and the Czech Republic, evidence showed that salvage logging delayed forest recovery.

There’s life in dead wood

The proposed increased logging in Białowieza includes removing quantities of dead wood, yet this dead wood plays an important role in the functioning of a healthy forest. Forests are often built from the bottom up, with dead wood as the foundation.

While aesthetically they may not be that pleasing for us, dead trees are a vital habitat for saproxylic insects which feed on dead and decaying matter. Białowieza supports large populations of endangered saproxylic beetles and invertebrates which rely on dead wood and, in turn, these provide food for birds, small rodents such as shrews and voles, and bats including the rare barbastelle. In turn these animals are eaten by larger predators such as owls, wolves and lynx.

The forest food web starts here.
Aleksander Bolbot / shutterstock

Dead and dying spruce stumps are almost exclusively used by some woodpecker species as nests and also act as great hosts for lichens and mosses, some of which are facing extinction in Europe. If the dead wood is removed, the entire forest ecosystem will suffer.

Logging is unnecessary

Logging is not the only solution to the spruce bark beetle problem. Pheromone traps, for instance, effectively attract large numbers of beetles while outbreaks in the UK are controlled by unleashing a specific predator beetle, Rhizophagus grandis, that targets the spruce beetle. Due to its widespread use in commercial forestry, R. grandis is relatively cheap and readily available, and Forestry Commission research showed it was more effective at controlling outbreaks than salvage logging.

In any case, a beetle infestation might be disastrous for individual trees but it won’t necessarily harm the forest itself. Like many ecosystems, Białowieza is vulnerable to climate change. As species such as Norway spruce are weakened by changing climatic conditions, the bark beetle is able to take hold. This is an invaluable part of the forest regeneration process, allowing deciduous trees that are better able to cope with changing climatic conditions to grow in the gaps left by dying spruces. In the long run it may be better for Białowieza Forest to let nature, and regeneration, take its course.

Lucinda Kirkpatrick, PhD Researcher in Forest Ecology, University of Stirling

This article was originally published on The Conversation. Read the original article.

Germany: Forest