In-depth Q&A: How trees benefit nature, people and the climate 

§ How important are trees for climate change and biodiversity? 

Trees are important for both climate mitigation and adaptation. 

They absorb and store CO2 from the atmosphere and help defend against the intensity of some extreme weather events, such as heatwaves. 

Prof Malhi tells Carbon Brief that trees are key for adapting to the effects of climate change, “particularly the restoration of trees and trees in peri-urban and urban landscapes, where they can play an essential role in minimising the effects of peak temperatures or increased flood risk”. 

Trees and woodlands can improve air quality, protect soils and host a range of biodiversity.

But trees can also be challenged by climate change. A 2019 study found that climate change could cause trees to “live fast and die young”, reducing the ability of forests to act as a carbon sink over long timescales.

Dr Cat Scott from the University of Leeds told the conference that the UK’s land management practices are largely focused on what humans can get from the land in the form of products such as food and timber. 

She said there is an “increasing realisation” that this has not led to ecologically diverse landscapes. 

Scott is the director of the Leeds Ecosystem, Atmosphere and Forest centre which helps manage four forest projects in northern England. 

At these sites, researchers can monitor temperature changes in woodlands compared to open fields. During the record-topping UK 2022 heatwave, Scott said temperatures were 15C lower in one project at Hardknott Forest compared to open grassland nearby. 

Trees comprise a prominent part of the UK’s plan to reach net-zero emissions by 2050. There are a number of government tree-planting schemes and grants, including funding for farmers to plant trees on their land. 

But progress on tree planting has been “too slow”, according to the recent Climate Change Committee (CCC) report on the UK government’s progress in reducing emissions. 

Tree-planting rates will need to double by 2025 to reach the government’s target of 30,000 hectares of woodland creation per year, the CCC said. 

The conference heard about the importance of having many different types of trees in a forest to ensure many different types of species can live there. For example, ash trees support 955 different species and oak supports 2,300.

Ross Barnett from the University of Stirling researches how different landscape factors impact the complexity of sounds in a restored woodland. 

This work explores whether woodland planted with just one type of tree supports significantly fewer invertebrates, pollinators and predators than woods with many tree varieties. 

Dr Eleanor Tew from Forestry England, England’s largest forest manager, said six tree species currently make up almost 70% of forest area managed by the organisation. Tew said the government agency is trying to increase the species diversity in its forests. 

§ What are the main threats to tree health?

Alongside climate change and other threats facing trees in the UK and across the world, pests and diseases can have a major impact. 

These diseases include ash dieback which is expected to kill up to 80% of the UK’s ash trees, according to the Woodland Trust. 

Warmer temperatures and changing rainfall patterns have also led to increased tree mortality, according to the Intergovernmental Panel on Climate Change. 

Dr Cecilia Dahlsjo from the University of Oxford explained that ash dieback is a fungal disease native to Asia. It has been present in the UK for more than a decade. 

Dahlsjo described how ash dieback weakens a tree’s canopy, branches and trunk. It has a 70% mortality rate over a period of 10-15 years, she added. 

Rebecca Gosling, conservation evidence officer for tree health at the Woodland Trust, told the conference that a new introduced pest or pathogen has been identified every 1.4 years in the UK. She said it is “quite a serious situation”. 

Ash trees face another threat from emerald ash borer, a beetle that has been “hitchhiking” into Europe from Russia and the US, Gosling said. This insect can cause significant damage to ash trees. 

Prof Lucio Montecchio from the University of Padova said that trade is the main way in which known and unknown plant parasites move between countries. He told the conference: 

“Usually parasites [do] not move through wind from one country to another…fungi, bacteria, viruses – they must be moved.”

Quick response times are important, he said, alongside increasing local nurseries for trees and reducing imports from abroad. 

Gosling told Carbon Brief that pests and diseases are “high up as one of the biggest threats our woods and trees have” in the UK. She said that experts fear climate change will “add another layer of threat” to trees: 

“With climate change, the predictions are that our trees will become more stressed themselves. So, if they are suffering with more frequent droughts, as we’ve been seeing, the trees will be more stressed and, therefore, less able to defend themselves against a pest or pathogen.

“The second arm to that is that actually the pests themselves might find they’re more able to survive in the UK.”

Warming temperatures caused by climate change increase the risk that “more pests from warmer climates will be able to survive” in the UK, Gosling said. 

In terms of current and future threats to UK forest landscapes, Malhi tells Carbon Brief: 

“Pathogens are probably a bigger effect than climate change, and certainly bigger than deforestation and land use in terms of what’s going to shape these ecosystems over the coming decades.”

§ What benefits do trees provide for people? 

A number of experts at the conference discussed research on the impact that trees can have on people. 

Prof Zoe Davis from the University of Kent researches the “wellbeing benefits” people can get from being in nature. 

She co-authored a study published in Nature Sustainability which looked at the human wellbeing response to certain species traits, such as colour and sound. 

The findings showed that many aspects of nature, such as bird song, can bring joy or other positive emotional responses. 

Trees can also have cultural or local significance around the world. Dr Aliyu Salisu Barau from Bayero University described how many neighbourhoods in Kano city, Nigeria are named after trees. They are important for local history, he told the conference, so tree loss can be a “disaster”. 

People, especially Indigenous peoples and local communities, can often help to protect trees and forests. A study found that Indigenous peoples played a “vital role” in the least-deforested areas of the Brazilian Amazon. 

More than 1.6bn people also rely on forests for timber, food, fuel, jobs and shelter. 

Malhi said there should be greater research emphasis to show that “trees are more than just carbon” storage. 

He told Carbon Brief that social science about nature highlights the “whole spectrum of values of trees” – ranging from ecological, cultural, spiritual and psychosocial. He added: 

“There’s a whole frontier of research there about how people benefit from trees… I think much of the world, as the population gets more and more urban, is going through a nature deprivation catastrophe. I think that’s going to have lots of profound consequences for people’s wellbeing and welfare.”