forests – Cabot Institute for the Environment blog

Climate change: effect on forests could last millennia, ancient ruins suggest

Posted on February 25, 2022March 29, 2023 by janet.crompton

Jonathan Lenoir, Université de Picardie Jules Verne (UPJV) and Tommaso Jucker, University of Bristol

Forests are home to 80% of land-based biodiversity, but these arks of life are under threat. The rising average global temperature is forcing tiny plants like sidebells wintergreen on the forest floor (known as the understory) to shift upslope in search of cooler climes. Forest plants can’t keep up with the speed at which the climate is changing – they lag behind.

The pace at which forests adapt to changing conditions is so slow that species living in forest understories today are probably responding to more ancient changes in their environment. For instance, the Mormal Forest floor in northern France is, in several places, covered by a carpet of quaking sedge. This long grass-like plant betrays the former settlements of German soldiers who used it to make straw mattresses during the first world war.

Changes in how people managed the land, sometimes dating back to the Middle Ages or even earlier, leave a lasting fingerprint on the biodiversity of forest understories. Knowing how long the presence of a given species can carry on the memory of past human activities can tell scientists how long climate change is likely to have an influence.

A forest carpeted with tall grass. — The wind whispering through Mormal’s sedge evokes the region’s wartime past.
Jonathan Lenoir, Author provided

Ecologists are turning to technologies such as lidar to rewind the wheel of time. Lidar works on the same principles as radar and sonar, using millions of laser pulses to analyse echoes and generate detailed 3D reconstructions of the surrounding environment. This is what driverless cars use to sense and navigate the world. Since the late 1990s, lidar has enabled amazing discoveries, such as the imprints of Mayan civilisation preserved beneath the canopy of tropical forest.

In a new paper, I, along with experts in ecology, history, archaeology and remote sensing, used lidar to trace human activity in the Compiègne Forest in northern France back to Roman times – much later than historical maps could ever do.

Illuminating ghosts from the past

Compared to farm fields, which are ceaselessly disturbed, forest floors tend to be well-preserved environments. As a result, the ground below the forest canopy may still bear the imprints of ancient human occupation.

Archaeologists know this pretty well and they increasingly rely on lidar technology as a prospecting tool. It allows them to virtually remove all the trees from aerial images and hunt artefacts hidden below treetops and fossilised under forest floors.

Using airborne lidar data acquired in 2014 over the Compiègne Forest in northern France, a team of archaeologists and historians found well-preserved Roman settlements, farm fields and roads. Long considered a remnant of prehistoric forest, the Compiègne was, in fact, a busy agricultural landscape 1,800 years ago.

A black-and-white aerial photo of a landscape marked by depressions and boundaries. — Lidar can reveal the terrain hidden beneath forests.
Jonathan Lenoir, Author provided

A closer look at these ghostly images of the Compiègne Forest reveals several depressions within a fossilised network of Roman farm fields. Archaeologists excavated numerous depressions like this across many forests in north-eastern France and found that people from the late iron age and Roman era carved them.

These depressions were made to extract marls (lime-rich mud) to enrich farm fields in carbonate minerals for growing crops and to create local depressions where rainwater collects naturally for livestock to drink. Marling is still a widespread practice in crop production in northern France.

A hillside with a large, white crater in. — A pit for extracting marl in Northern France.
Jonathan Lenoir, Author provided

The long-lasting effects of human activity

These signs of Roman occupation in modern forests provide clues to why some plant species are present where we wouldn’t expect them to be.

On a summer day in 2007 in a corner of the Tronçais Forest in central France, a team of botanists found a little patch of nitrogen-loving species – blue bugle, woodland figwort and stinging nettle – nestled among more acid-loving plants.

Nothing special at first sight. Until archaeologists found that Roman farm buildings had once stood in that spot, with cattle manure probably enriching the soil in phosphorous and nitrogen.

A shrub with bright blue flowers. — Blue bugle heralds an ancient Roman farm.
Kateryna Pavliuk/Shutterstock

If a clutch of tiny plants can betray ancient farming practices dating back centuries or millennia, ongoing environmental changes, such as climate change, will have similarly long-lasting effects. Even if the Earth stopped heating, the biodiversity of its forests would continue changing in response to the warming signal, in a delayed manner, through the establishment of more and more warm-loving species for several centuries into the future.

Just as the Intergovernmental Panel on Climate Change has a mission to provide plausible scenarios on future climate change, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services aims to provide plausible scenarios on the fate of biodiversity. Yet none of the biodiversity models so far incorporate this lag effect. This means that model predictions are more prone to errors in forecasting the fate of biodiversity under future climate change.

Knowing about the past of modern forests can help decode their present state and model their future biodiversity. Now lidar technology is there to help ecologists travel back in time and explore the forest past. Improving the accuracy of predictions from biodiversity models by incorporating lagging dynamics is a big challenge, but it is a necessary endeavour for more effective conservation strategies.

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This blog is written by Jonathan Lenoir, Senior Researcher in Ecology & Biostatistics (CNRS), Université de Picardie Jules Verne (UPJV) and Cabot Institute for the Environment member Dr Tommaso Jucker, Research Fellow and Lecturer, School of Biological Sciences, University of Bristol

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

In the Amazon, forest degradation is outpacing full deforestation

Posted on September 15, 2020March 31, 2023 by janet.crompton

Deforestation in the Brazilian Amazon has increased abruptly in the past two years, after having been on a downward trajectory for more than a decade. With the country’s president Jair Bolsonaro notoriously enthusiastic about expanding into the rainforest, new deforestation data regularly makes global headlines.

But what fewer people realise is that even forests that have not been cleared, or fully “deforested”, are rarely untouched. Indeed, just 20% of the world’s tropical forests are classified as intact. The rest have been impacted by logging, mining, fires, or by the expansion of roads or other human activities. And all this can happen undetected by the satellites that monitor deforestation.

These forests are known as “degraded”, and they make up an increasingly large fraction of the world’s remaining forest landscapes. Degradation is a major environmental and societal challenge. Disturbances associated with logging, fire and habitat fragmentation are a significant source of CO₂ emissions and can flip forests from carbon sinks to sources, where the carbon emitted when trees burn or decompose outweighs the carbon taken from the atmosphere as they grow.

Forest degradation is also a major threat to biodiversity and has been shown to increase the risk of transmission of emerging infectious diseases. And yet despite all of this, we continue to lack appropriate tools to monitor forest degradation at the required scale.

A man chainsaws a tree trunk in Amazon rainforest

Degraded – but not deforested.
CIFOR / flickr, CC BY-NC-SA

The main reason forest degradation is difficult to monitor is that it’s hard to see from space. The launch of Nasa’s Landsat programme in the 1970s revealed – perhaps for the first time – the true extent of the impact that humans have had on the world’s forests. Today, satellites allow us to track deforestation fronts in real time anywhere in the world. But while it’s easy enough to spot where forests are being cleared and converted to farms or plantations, capturing forest degradation is not as simple. A degraded forest is still a forest, as by definition it retains at least part of its canopy. So, while old-growth and logged forests may look very different on the ground, seen from above they can be hard to tell apart in a sea of green.

Degradation detectives

New research published in the journal Science by a team of Brazilian and US researchers led by Eraldo Matricardi has taken an important step towards tackling this challenge. By combining more than 20 years of satellite data with extensive field observations, they trained a computer algorithm to map changes in forest degradation through time across the entire Brazilian Amazon. Their work reveals that 337,427 km² of forest were degraded across the Brazilian Amazon between 1992 and 2014, an area larger than neighbouring Ecuador. During this same period, degradation actually outpaced deforestation, which contributed to a loss of a further 308,311 km² of forest.

The researchers went a step further and used the data to tease apart the relative contribution of different drivers of forest degradation, including logging, fire and forest fragmentation. What these maps reveal is that while overall rates of degradation across the Brazilian Amazon have declined since the 1990s – in line with decreases in deforestation and associated habitat fragmentation – rates of selective logging and forest fires have almost doubled. In particular, in the past 15 years logging has expanded west into a new frontier that up until recently was considered too remote to be at risk.

Map of deforestation and degradation in the Brazilian Amazon, 1992-2014.

The Brazilian Amazon, shaded in grey, covers an area larger than the European Union.
Matricardi et al

By putting forest degradation on the map, Matricardi and colleagues have not only revealed the true extent of the problem, but have also generated the baseline data needed to guide action. Restoring degraded forests is central to several ambitious international efforts to curb climate change and biodiversity loss, such as the UN scheme to pay developing countries to keep their forests intact. If allowed to recover, degraded forests, particularly those in the tropics, have the potential to sequester and store large amounts of CO₂ from the atmosphere – even more so than their intact counterparts.

Simply allowing forests to naturally regenerate can be a very effective strategy, as biomass stocks often recover within decades. In other cases, active restoration may be a preferable option to speed up recovery. Another recent study, also published in the journal Science, showed how tree planting and cutting back lianas (large woody vines common in the tropics) can increase biomass recovery rates by as much as 50% in south-east Asian rainforests. But active restoration comes at a cost, which in many cases exceeds the prices that are paid to offset CO₂ emission on the voluntary carbon market. If we are to successfully implement ecosystem restoration on a global scale, governments, companies and even individuals need to think carefully about how they value nature.

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This blog is written by Cabot Institute member Dr Tommaso Jucker, Research Fellow and Lecturer, School of Biological Sciences, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Tommaso Jucker

Forest accounting rules put EU’s climate credibility at risk, say leading experts

Posted on June 15, 2017April 5, 2023 by janet.crompton

**Article re-posted from EURACTIV **

Forest mitigation should be measured using a scientifically-objective approach, not allowing countries to hide the impacts of policies that increase net emissions, writes a group of environmental scientists led by Dr Joanna I House.

Dr Joanna I House is a reader in environmental science and policy at the Cabot Institute, University of Bristol, UK. She co-signed this op-ed with other environmental scientists listed at the bottom of the article.

From an atmospheric perspective, a reduction in the forest sink leads to more CO2 remaining in the atmosphere and is thus effectively equivalent to a net increase in emissions. [Yannik S/Flickr]

When President Trump withdrew from the Paris Agreement, the EU’s Climate Commissioner, Miguel Arias Cañete spoke for all EU Member States when he said that, “This has galvanised us rather than weakened us, and this vacuum will be filled by new broad committed leadership.” The French President, Emmanuel Macron, echoed him by tweeting, “Make our planet great again”.

But as the old saying goes, ‘If you talk the talk, you must walk the walk,’ and what better place to start than the very laws the EU is currently drafting to implement its 2030 climate target under the Paris Agreement. This includes a particularly contentious issue that EU environment leaders will discuss on 19 June, relating to the rules on accounting for the climate impact of forests.

Forests are crucial to limiting global warming to 2 degrees Celsius. Deforestation is responsible for almost one tenth of anthropogenic carbon dioxide (CO2) emissions, while forests remove almost a third of CO2 emissions from the atmosphere.

In the EU, forests currently grow more than they are harvested. As a result, they act as a net ‘sink’ of CO2 removing more than 400 Mt CO2 from the atmosphere annually, equivalent to 10% of total EU greenhouse gas (GHG) emissions.

New policies adopted or intended by Member States will likely drive them to harvest more trees (e.g. for the bioeconomy and bioenergy), reducing the sink. The controversy is, in simple terms, if forests are taking up less CO2 due to policies, should this be counted?

Based on lessons learnt from the Kyoto Protocol, the European Commission proposed that accounting for the impacts of forests on the atmosphere should be based on a scientifically robust baseline. This baseline (known as the ‘Forest Reference Level’) should take into account historical data on forest management activities and forest dynamics (age-related changes). If countries change forest management activities going forward, the atmospheric impact of these changes would be fully accounted based on the resulting changes in GHG emissions and sinks relative to the baseline. This approach is consistent with the GHG accounting of all other sectors.

Subsequently, some EU member states have proposed that any increase in harvesting, potentially up to the full forest growth increment, should not be penalised. This would be achieved by including this increase in harvesting, and the related change in the net carbon sink, in the baseline.

As land-sector experts involved in scientific and methodological reports (including for the Intergovernmental Panel on Climate Change, IPCC), in the implementation of GHG inventory reports, and in science advice to Governments, we have several scientific concerns with this approach.

From an atmospheric perspective, a reduction in the forest sink leads to more CO2 remaining in the atmosphere and is thus effectively equivalent to a net increase in emissions. This is true even if forests are managed “sustainably”, i.e. even if harvest does not exceed forest growth.

This is further complicated as the issues are cross-sectoral. Higher harvest rates may reduce the uptake of CO2 by forests, but use of the harvested wood may lead to emissions reductions in other sectors e.g. through the substitution of wood for other more emissions-intensive materials (e.g. cement) or fossil energy. These emission reductions will be implicitly counted in the non-LULUCF sectors. Therefore, to avoid bias through incomplete accounting, the full impact of increased harvesting must be also accounted for.

Including policy-related harvest increases in the baseline could effectively hide up to 400 MtCO2/yr from EU forest biomass accounting compared to the “sink service” that EU forests provide today, or up to 300 MtCO2/yr relative to a baseline based on a scientific approach (up to two thirds of France’s annual emissions).

Hamper the credibility of the EU’s bioenergy accounting: Current IPCC guidance on reporting emissions from bioenergy is not to assume that it is carbon neutral, but rather any carbon losses should to be reported under the ‘Land Use, Land-Use Change and Forestry’ (LULUCF) sector rather than under the energy sector (to avoid double counting). EU legislation on bioenergy similarly relies on the assumption that carbon emissions are fully accounted under LULUCF.
Compromise the consistency between the EU climate target and the IPCC trajectories. The EU objective of reducing GHG emissions of -40% by 2030 (-80/95% by 2050) compared to 1990 is based on the IPCC 2°C GHG trajectory for developed countries. This trajectory is based not just on emissions, but also on land-sinks. Hiding a decrease in the land sink risks failure to reach temperature targets and would require further emission reductions in other sectors to remain consistent with IPCC trajectories.
Contradict the spirit of the Paris Agreement, i.e., that “Parties should take action to conserve and enhance sinks”, and that Parties should ensure transparency in accounting providing confidence that the nationally-determined contribution of each country (its chosen level of ambition in mitigation) is met without hiding impacts of national policies.
Set a dangerous precedent internationally, potentially leading other countries to do the same (e.g. in setting deforestation reference levels). This would compromise the credibility of the large expected forest contribution to the Paris Agreement.

The Paris Agreement needs credible and transparent forest accounting and EU leaders are about to make a decision that could set the standard. Including policy-driven increases in harvest in baselines means the atmospheric impacts of forest policies will be effectively hidden from the accounts (while generating GHG savings in other sectors). Basing forest accounting on a scientifically-objective approach would ensure the credibility of bioenergy accounting, consistency between EU targets and the IPCC 2°C trajectory, and compliance with the spirit of Paris Agreement. The wrong decision would increase the risks of climate change and undermine our ability to “make the planet great again”.

Disclaimer: the authors express their view in their personal capacities, not representing their countries or any of the institutions they work for.

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Signatories:

Joanna I House, Reader in Environmental Science and Policy, Co-Chair Global Environmental Change, Cabot Institute, University of Bristol, UK
Jaana K Bäck, Professor in Forest – atmosphere interactions, Chair of the EASAC Forest multifunctionality report, University of Helsinki, Finland
Valentin Bellassen, Researcher in Agricultural and Environmental Economics, INRA, France
Hannes Böttcher, Senior Researcher at Oeko-Institut.
Eric Chivian M.D., Founder and Former Director, Center for Health and the Global Environment Harvard Medical School
Pep Canadell, Executive Director of the Global Carbon Project
Philippe Ciais, scientist at Laboratoire des Sciences du Climat et de l’Environnement, Gif sur Yvette, France
Philip B. Duffy, President and Executive Director Woods Hole Research Center, USA
Sandro Federici, Consultant on MRV and accounting for mitigation in the Agriculture and land use sector
Pierre Friedlingstein, Chair, Mathematical Modelling of Climate Systems, University of Exeter, UK.
Scott Goetz, Professor, Northern Arizona University
Nancy Harris, Research Manager, Forests Program, World resources Institute.
Martin Herold, Professor for Geoinformation Science and Remote Sensing and co-chair of Global Observations of Forest Cover and Land Dynamics (GOFC-GOLD), Wageningen University and Research, The Netherlands
Mikael Hildén, Professor, Climate Change Programme and the Resource Efficient and Carbon Neutral Finland Programme, Finnish Environment Institute and the Strategic Research Council, Finland
Richard A. Houghton, Woods Hole Research Centre USA
Tuomo Kalliokoski University of Helsinki, Finland
Janne S. Kotiaho, Professor of Ecology, University of Jyväskylä, Finland
Donna Lee, Climate and Land Use Alliance
Anders Lindroth, Lund University, Sweden
Jari Liski, Research Professor, Finnish Meteorological Institute, Finland
Brendan Mackey, Director, Griffith Climate Change Response Program, Griffith University, Australia
James J. McCarthy, Harvard University, USA
William R. Moomaw, Co-director Global Development and Environment Institute, Tufts University, USA
Teemu Tahvanainen, University of Eastern Finland
Olli Tahvonen, Professor forest economics and policy, University of Helsinki, Finland
Keith Pausitan, University Distinguished Professor, Colorado State University, USA
Colin Prentice, AXA Chair in Biosphere and Climate Impacts, Imperial College London, UK
N H Ravindranath, Centre for Sustainable Technologies (CST), Indian Institute of Science, India
Laura Saikku, Senior Scientist, Finnish Environment Institute
Maria J Sanchez, Scientific Director of BC3 (Basque Center for Climate Change), Spain
Sampo Soimakallio, Senior Scientist, Finnish Environment Institute
Zoltan Somogyi, Hungarian Forest Research Institute, Budapest, Hungary
Benjamin Smith, Professor of Ecosystem Science, Lund University, Sweden
Pete Smith, Professor of Soils & Global Change, University of Aberdeen, UK
Francesco N. Tubiello, Te Leader, Agri-Environmental Statistics, FAO
Timo Vesala, Professor of Meteorology, University of Helsinki, Finland
Robert Waterworth
Jeremy Woods, Imperial College London, UK
Dan Zarin, Climate and Land Use Alliance

Why forests are about more than just climate change

Posted on December 1, 2014April 14, 2023 by janet.crompton

It’s National Tree Week, and there is a plethora of talk about all the great things that trees do: encouraging biodiversity, providing a pleasant space for humans, and providing numerous ecosystem services. As well as this, there is some reference to how trees take in carbon dioxide, and the benefits of this for helping to prevent climate change. But what if trees didn’t help prevent climate change? What if actually, they increased climate change?

Afforestation (planting forests) is one of many suggestions as a way to deliberately change the earth’s climate to attempt to reverse the effects of climate change (known as ‘geoengineering’). Planting more trees seems like a an obvious, natural solution. Carbon offsetting, RED+ and lots of other schemes around the issue of climate change have been based on the preservation or increase of forests. But does it work?

We’ve known for some time that boreal forests contribute to climate change rather than help prevent it, because of changes in the surface reflectance (the albedo). But thus far, forests in other places have been thought to be beneficial, storing up carbon and not affecting the albedo so much.

But our recent study suggests that globally, preserving and expanding forests actually causes a net global warming. We used the Met Office’s latest climate model and did simulations of future climate change, with and without afforestion/forest preservation, and we found that though the deforestation has no discernable effect on the climate, the afforestation does.

Does this mean that we are advocating chopping down forests? No. As National Tree Week says, forests are about more than climate change. However much climate change is a key challenge for the future, we can’t forget that other things are important too. The climate effect of the forest preservation and expansion is small – only about 0.1 °C. How do you value that against the mass loss of biodiversity, irrelplaceable ecosystems and ecosystem services that would be lost?

Saving or planting forests is not a panacea for climate change, but neither is it the enemy. Conserving forest is worthwhile for lots of other reasons, but we shouldn’t kid ourselves that there won’t be difficult decisions to make about protecting the unique forest habitats, especially tropical forests like the Amazon, and preventing climate change.
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This blog was written by Cabot Institute member, T Davies-Barnard, University of Exeter.