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Research highlights 2020-2021

Throughout the past year our scientists have continued their work on a wide array of research topics. These have ranged from very topical research into whether the pandemic has impacted the way people engage with nature, to continuing our work on climate change and revisiting long-term species trials to help inform the choice of tree species for the future. These, and some of our other activities from the year, are summarised below.

Assessing trends in urban tree canopy cover

Trees in towns and cities provide a wide range of benefits to those that live and work there. They make urban areas safer, more pleasant and healthier places to be. They also help cities cope better with the effects of climate change. With more than 80% of Great Britain’s population living in urban areas, it is important to consider whether the extent of tree cover is changing.

In 2020, Forest Research conducted and published research that explored changes in tree cover since the 1940s for 10 urban areas across Great Britain. By examining aerial photography, our study revealed that all 10 areas had a predominant trend of increasing tree cover from the 1940s through to 2018. However, when we considered the past two decades alone, we found that six locations showed no change in canopy cover and three locations had a tentative shift towards a decline in cover. Ongoing monitoring is required to confirm these trends, but such declines would need to be reversed if the benefits of trees are to be enjoyed by future generations.

Many local authorities across Great Britain have established tree-planting or tree-canopy-cover targets in response to the climate emergency. This study also identified those geographic areas where photographic imagery exists, providing an opportunity to expand this research. There is also a need for new, low-cost ways of calculating historic urban tree cover to enable a wider range of locations to be included in analyses. Such low-cost methods could also enable a wider range of historical image types to be assessed, thereby increasing the robustness of the trends identified. It is hoped that the findings from this research will lead to better protection and management of existing tree cover and improved planning for future cover, for example by setting meaningful and realistic canopy-cover targets.

How nature, trees and woodland have supported people during COVID-19

The COVID-19 pandemic has had a major impact on society. Restrictions on what people could do and where they could go have been unprecedented. In response, Forest Research’s social and economic scientists quickly decided to develop a piece of research to understand whether the restrictions had an impact on people’s engagement with nature.

From late spring to early autumn 2020, we carried out an online survey of 2,115 people and conducted 25 interviews. The survey was publicised by Forestry England through its website and newsletters, so those who completed the survey were already interested in nature and, specifically, trees and woodlands.

The survey results showed that two thirds of people reported an increase in time ‘taken to appreciate nature’, ‘levels of happiness when in nature’ and ‘feelings of connection to nature’. The main benefit identified from engagement with nature was a ‘feeling of escape and freedom’, not surprising given the restrictions people faced. We found younger people (aged 16–34) were significantly more motivated to visit nature for ‘mental health and wellbeing’ benefits, ‘exercise’, ‘exploration’ and ‘to take a break from work or from electronic devices’.

Our findings are detailed in a report that highlights the important role that trees, woodlands and wider nature can play as part of people’s everyday lives and in supporting their wellbeing in the very difficult circumstances of a global pandemic. This report and further details of the study are available from our website. We will be reporting on our interview data soon.

This research builds on much of our work in recent years on how people engage with trees and woodlands and any benefits they gain or barriers they face to access. It has been undertaken under the umbrella of the Active Forests Programme Evaluation, supported by Forestry England and Sport England. Active Forests is a partnership between Forestry England and Sport England supported by the National Lottery.

Revitalising forest garden species trials

Long-term forest experiments often experience neglect when the objective of an experiment ceases to be a research priority, followed by renewed interest when the research agenda changes. This is exemplified by the history of three major forest gardens, with collections of species plots, at Kilmun in Scotland, Brechfa in Wales and Bedgebury in England. All three were first planted in the early to mid-twentieth century to trial potential non-native species for use in British forestry.

They played a key role in identifying Sitka spruce, now the dominant productive forestry species in Britain. However, climate change and increasing threats from pests and diseases make reliance on a single species risky. Collectively, Kilmun, Bedgebury and Brechfa contain 194 species in 291 plots and provide invaluable demonstrations of alternative species that could be used to diversify British forests and increase their resilience in a changing world.

Forest Research has been working with Forestry and Land Scotland (FLS), the Welsh Government, Natural Resources Wales and Forestry England to maintain these important trials and publish results to inform the debate about species choice in British forestry. This year, we have prepared a management plan for the future direction of Kilmun and have grown new species at our Roslin nursery for planting out in plots by local FLS staff at Kilmun. We have also carried out a full audit of the plots at Bedgebury and will produce a review detailing future directions for them. We have begun a similar process at Brechfa where we aim to remeasure all existing plots.

Funding the work in these long-term trials has always been a challenge but now that their contribution is being widely acknowledged it is hoped this will no longer be a problem. Detailed management plans for all three sites and new planting will help to ensure provision of an important demonstration and quantitative resource for foresters for the next 50 years across Scotland, Wales and England.

Improving stiffness in Sitka spruce

The grading of construction timber is governed by three mechanical properties: strength, density and stiffness. The majority of British spruce timber is graded as C16 but has density and strength characteristics that could usually achieve higher grades. The factor limiting a greater proportion of sawn spruce from achieving higher construction grades is stiffness.

Since 2019, Forest Research has been engaged in a study to evaluate stiffness in Sitka spruce trees. The goal is to find trees with excellent stiffness properties that can be infused into the general breeding population to provide a major boost to the quality of domestic timber and bring positive impacts for the whole supply chain.

For this work, we made use of an existing 45-year-old provenance trial that had been established as part of an international effort by the International Union of Forest Research Organizations (IUFRO). The provenance trial gave us access to seeds collected from across 25 Pacific Northwest seed sources, covering the native range of the species. We compared trees grown from these seeds.

Early work within the general breeding population of Sitka spruce shows that the stiffness trait is highly heritable, which means that improvement of stiffness through selection and testing should work well.

Our initial results found that some provenances, on average, had better stiffness values than others but there was no geographical pattern of variation. Most variation was held within, rather than between, provenances, suggesting that trees with good stiffness values can be found throughout the range of Sitka spruce.

Trees with the highest stiffness score were grafted onto young rootstock to create an elite population. After five years, these trees will be planted out and, once they have flowered, their genetic material can be introduced by controlled pollination into the current breeding population of Sitka spruce. Because of the high heritability of stiffness, this will increase the stiffness of the subsequent generation. Introducing genetic diversity from a wider range of provenances will be a valuable source of traits other than stiffness. Additionally, broadening the genetic variation will in theory increase the resilience of genetically improved Sitka spruce to changes in climate.

New top height models for major commercial species

Accurately forecasting standing timber stock in our forests is essential for the timber industry and policy-makers. These predictions support decisions across a number of areas, ranging from timber supply to sawmills, to the net-zero-target strategy for climate-change mitigation.

Timber stock is predicted using growth simulators that work in a similar way to meteorological models: given the current situation, a forecast is provided of what is expected to happen in the future. In the case of timber, our simulators are reliable over periods of several decades.

Forest Research holds a privileged position to develop these simulators, with an extensive network of permanent sample plots across Britain available to fit our models. We have previously developed a growth simulator for the main commercial species in Britain. However, this simulator needed some important updates.

Growth simulators usually consist of several modules. When it comes to typical British commercial forests, it is the top-height module that is of greatest importance. It is commonly accepted that silvicultural treatments have little effect on increments in tree height. Consequently, tree height is considered to be a good indicator of site quality. By modelling top height – the average height of the 100 largest diameter trees per hectare – we are building the ‘growth engine’ of our simulators.

Through a collaboration between two of our Science Groups, we developed a set of new top-height models, which are dynamic, robust and accurate. These are now included in our new growth simulator, which is already being used to project timber production at the national level.

This work was reported on in the scientific journal Forestry and was awarded the Editor’s Choice, in recognition of its relevance.

Connecting trees and forest to the Internet of Things

Over the past few years, the use of Internet of Things (IoT) technology has revolutionised the way that data is captured and analysed across a range of sectors and is providing information at speeds and resolution previously unobtainable. Yet in environmental monitoring and forestry, and despite its potential to transform the way that data is collected, viewed and analysed, this technology has not been adopted as quickly as in other sectors.

In 2020, Forest Research worked in partnership with Defra and Vodafone to explore how this new technology can be used to improve environmental and forest monitoring and to test its suitability at remote rural locations. A pilot study which ran at Forest Research’s two long-term carbon flux sites, Alice Holt in Hampshire and Harwood in Northumberland, used IoT technology to monitor tree growth along with a range of associated environmental variables. Specialist sensors attached to the trees and in the soil were connected to the Vodafone Narrowband-IoT (NB-IoT) network and the data transmitted every 15 minutes to an online web portal.

The trial at the Alice Holt site was very successful, demonstrating that this technology has the potential to deliver continuous, high-quality data from forest sites. Although data capture was not as high at the Harwood site, valuable lessons were learned, especially about NB-IoT network penetration in dense conifer stands that will help to inform future research.

This work is now being extended with a Defra-funded follow-on project planned for 2021. The aim of this study is to test how IoT sensors can be used to improve hydrological monitoring and will be based on the Forest Research natural flood management (NFM) trial site in the Pickering catchment, North Yorkshire.

New climate-matching tool

Over the coming decades, climate change is expected to have major impacts on our trees and forests. It is therefore critical that we plan, manage and expand forests appropriately for both current and future climates. To do this we need to carefully consider the choice of tree species and appropriate silvicultural systems.

Over the past year, Forest Research has worked collaboratively with UK and international partners, including partners in the EU H2020 B4EST project, to develop a new climate-matching tool (CMT). This uses UKCP18 European-scale (RCP8.5) climate projections to provide a visualisation of regions with a similar climate to the projected future climate for user-selected locations in Europe and the Pacific Northwest. The goal is to help practitioners to choose better-suited material and silviculture for use in environments that match projected future climates in England, Scotland, Wales, Northern Ireland, all of Europe, and the Pacific Northwest.

This is not a simple matter of matching future climate equivalents 20–50 years from now. It is important that forest resilience under climate change is carefully considered. The early establishment period of forests and woodlands, up to and including canopy closure, is of paramount importance. If material is unsuited to current environmental pressures, there is a risk of large-scale crop failure and the effort and cost of establishment will be wasted. Therefore, the CMT allows users to examine the near climate future to select sources of material better able to establish and form resilient woodlands and forests. It also provides a longer-term view of climate change, which is intended to help policy-makers and practitioners prepare for more extreme climate pressures in the future. In addition, the CMT can match climates where forest pests and pathogens cause tree-health problems, to show users where in the future similar climatic conditions might cause tree-health issues.

The CMT complements our existing Ecological Site Classification tree selection tool, which shows how trees will perform in a future climate. The advanced version of the CMT also extends to the Pacific Northwest, allowing an exploration of site types associated with the exotic species widely used in British forestry.