Research highlights from the past year

Over the past year we have continued our work on a wide array of research areas, from tree pests and diseases to urban ecosystem services. Here we summarise a selection of recent projects.

Acute oak decline research

Acute Oak DeclineAs part of a programme funded by Defra, Forest Research has been working with scientists from other organisations to better understand the causes, distribution and scale of acute oak decline (AOD). The disease first appeared in the UK in the early 1980s, and to date many thousands of trees are estimated to be affected or dying.
AOD causes decay of the food and water-conducting tissues in oak trees. Working with scientists from Fera and Bangor University, we used a range of conventional and cutting-edge genetic technologies to find out which microbes were involved. The results confirmed that particular bacteria are the most important component in causing decay and that fungi were not consistently present. At the same time, our research is investigating the role of the two-spotted oak borer beetle (Agrilus biguttatus), which is regularly associated with AOD trees.

As part of this work, Forest Research reared A. biguttatus, bringing it through its entire life cycle in captivity – a world first! We carried out experiments testing the effect of temperature on life cycle development and then used this information to model the beetle’s climate preferences and how this might influence its spread. The beetle thrives in the warm but cannot survive low temperatures. With Cambridge University, we have modelled the effect of climate on distribution and used other data to predict current and future risks of AOD in the UK.

As well as studying the influence of climate, we worked with Rothamsted Research to determine why the beetle is attracted to certain oak trees. Chemicals given off by healthy and AOD-affected trees were collected and characterised by gas chromatography. The effects of these chemicals on adult beetles were tested using a method that measures the electrical impulse responses of their antennae, and this work is helping us understand what attracts the beetle to its host tree.

With the spatial epidemiology modellers at Rothamsted Research we also carried out an extensive coordinated survey across England and Wales. We used these results together with ‘citizen science’ reports to record and map AOD’s current presence or absence.

Urban tree canopies and ecosystem services

Tree lined avenue in Princes Street Gardens EdinburghUrban trees and woodlands provide a range of goods and services that benefit society. These ‘ecosystem services’ include climate regulation, flood mitigation and socio-economic benefits. Many of these services have been valued in economic terms enabling a cost–benefit approach to be employed in urban forest management strategies. However, a lack of data on the extent and composition of urban trees and woodlands is constraining the use of the ecosystem services approach and preventing monitoring and evaluation of changes in the urban forest.

Forest Research has been working with a range of tools and collaborators to improve our knowledge on the extent and characteristics of urban trees and woodlands. Building on work last year, we have continued to use i-Tree Eco, part of the i-Tree software suite, as a field-survey validated approach that provides a broad picture of the size and qualities of the entire urban forest. With partners, we have now surveyed seven major towns and cities of the UK using i-Tree Eco.

While field-based surveys provide valuable and detailed information, they can be expensive and time-consuming. We have been examining the use of canopy data as a substitute, where practitioners can gain a broad overview of the urban forest and the ecosystem services it provides more quickly and at lower cost.

i-Tree Canopy, for example, assesses aerial photography to calculate canopy cover and associated confidence limits. As well as enabling monitoring of canopy change over time, this approach can quantify ecosystem services and provide a market value. We have worked with Treeconomics on the Urban Tree Cover website, which shows canopy data for 20 towns and cities of the UK.
In the past year, we have also completed a review of the suitability of remote sensed data for urban canopy cover assessment and the opportunity of verifying the data by comparison to field data. By combining these datasets, we are able to create better quality information on the UK’s urban canopy cover and improve our knowledge of the urban forest and the ecosystem services which it provides.

Using long-term experiments to guide future forestry

The Teindland experimental reserve (ca. 50 ha in NE Scotland) in the 1980’s – the traditional way of doing forest scienceForest Research has a long history of field research, having conducted thousands of experiments throughout Britain over the past few decades. The potential of this unique and valuable resource is now being unlocked to provide answers to the enduring and emerging challenges of 21st century forest management – such as the suitability of various tree species given our changing climate and how forest management practices affect the amount of carbon stored in our forests.
In 2015–16 we completed a review of our long-term experiments, to share the information about them and to consider the best ways to maintain them for the benefit of future generations. Almost 400 experiments have been retained for potential future use. They have been selected to provide a wide geographical coverage of species. New experiments are also being incorporated where it is anticipated that they could be of future value.

The investment of resources to maintain the long-term experiments is particularly important as some are significant globally as well as at European and British scales. They include probably the best-known forest mixtures experiment in the world at Gisburn Forest, Lancashire. Analysis of trees at this site has found that mixed stands of certain species can have higher productivity than pure plots of the same species. This is the longest second rotation experiment exploring this topic in Europe. The long-term experiments are also being used to explore the effects of different tree harvesting methods on the amount of carbon and nutrients stored in forest soil. For British forestry, long-term trials of European silver fir (Abies alba) have proved especially valuable by demonstrating that this previously dismissed species grows well across a range of British sites.

Evaluating the impact of Grow Wild

Grow Wild ManchesterGrow Wild is a programme funded by the UK National Lottery that is encouraging individual and community based wildflower growing projects to provide health and well-being benefits to people and communities. It is particularly trying to engage young people aged between 12 and 25 years and those not involved in environmental and community based activity. The work, led by the Royal Botanic Garden Kew, and running from 2014 to 2017, involves providing funding and support to transform communal spaces, distributing wild seed kits to youth and community groups, and making seed packets available to the general public.

Forest Research is evaluating the impact of the programme on the people and communities taking part. This involves assessing the kind of activities the programme has enabled, the type of people who took part and what, if any, benefits it has had for peoples’ well-being (e.g. by helping them to connect with people, be active or try something new). We are also assessing whether the programme has led to any longer term behaviour changes that are benefiting individuals or communities. The evaluation will help us to understand what increases community involvement in the care and management of our environment, and the potential for urban green spaces to provide benefits that support community and individual well-being.

During 2015 Forest Research carried out online surveys, interviews and focus groups to collect data that will be used to evaluate the programme’s impact. This has involved undertaking 14 case studies of the community wildflower projects funded by the work and of the programme’s national flagship projects in Scotland and England; further case studies will include Wales and Northern Ireland. The online surveys have been sent out to over 250,000 recipients of the seed packets and seed kits. An initial analysis suggests that 85% of community project participants went on to be more active in their community and 65% continued to do more for nature, such as tree planting. Further analysis of impacts is underway and the full evaluation is due to be produced by spring 2017.

Ash trees resistant to Chalara

Grafting of ash. Trial to find ash resistant to Chalara. Location: Nursery at Northern Research Station, Roslin, Midlothian, Scotland.In 2013, in an attempt to identify ash trees (Fraxinus excelsior) with a resistance to Chalara ash dieback (Hymenoscyphus fraxineus), Forest Research planted out 155,000 ash seedlings on 14 sites in areas known to be infected with Chalara. We are now at the end of the project’s third year and, although later than initially predicted, all sites now show clear evidence of Chalara infection.
We noticed a rapid development of the disease over the 2015 growing season and levels of infection on the 155,000 trees were determined using a simple scoring system. Nearly 50% of the trees are still alive with no signs of infection. There are big variations in the amount of infestation from site to site and also in the survival of trees from different source areas (provenances) at each site. Across all sites the most resistant provenances at the moment seem to be from seed zones in Scotland – but it is too early to form firm conclusions. We expect the number of trees that become infected or die to increase over the remaining two years of the research contract.

This is the first time we have assessed each tree in this manner. We plan to repeat the whole assessment process after both the 2016 and 2017 growing seasons and will then identify trees that are showing clear tolerance to Chalara. In collaboration with partners, we will look for common genetic markers in these apparently tolerant trees that can be used in future screening of other ash trees, and grafted copies of selected trees will be future breeding work to produce Chalara-resistant ash seed.

Eradication of the Asian longhorn beetle

Asian longhorn beetleAsian longhorn beetle (Anoplophora glabripennis) is a major international quarantine pest native to China and Korea that can kill a wide range of broadleaved trees. In 2012, a small population was found established at a site just north of Paddock Wood in Kent. This first confirmed outbreak of the pest in the UK prompted a rapid eradication programme and research to determine which tree species were most at risk and how fast the beetle was spreading.

Forest Research scientists have now completed these studies and they show that the outbreak did not increase and spread as rapidly as was at first feared. A detailed tree ring analysis of the sample material brought back from the outbreak site shows that the beetle had been present for about 10 years before it was discovered, but had spread no further than 234 metres from the original point of introduction.

The relatively slow rate of increase and spread of the outbreak probably reflects the fact that the beetle is near the edge of its climatic range in southern England. Our analysis suggests that several factors combined to allow the beetle to become established, in particular the presence of a highly favourable host species (sycamore, Acer pseudoplatanus) close to the industrial unit where the beetles were introduced, multiple introductions of adult beetles over several years, and a run of particularly warm and dry years while the infestation was becoming established.

Since 2012, the Animal and Plant Health Agency has carried out annual surveys at Paddock Wood, but no further signs of the beetle have been detected. Regrowth from the stumps of the trees that were cut down and burnt during the original eradication programme was cleared and inspected by Forest Research staff and contractors in September 2015, but again there was no sign of any residual infestation. Consequently, even though surveys and monitoring will continue at Paddock Wood until 2018, it seems that we can be increasingly optimistic that this particular infestation has been successfully eradicated.

Release of improved wind risk management tool

London plane blown over by the gales in October 1987Major storms have damaged over a million cubic metres of timber in Britain at least five times in the past 50 years, causing major economic losses, and every year wind causes damage to forests in exposed locations.

During 2015 Forest Research released a new version (2.5) of ForestGALES, its computer-based tool to help foresters improve the resilience of their forests to potentially damaging wind. ForestGALES does this by calculating how the risk of damage changes with species, trees size, soil conditions and silviculture. Forest managers can use this information to adjust their forest management to maintain tree stability and reduce storm damage across the forest.

The original ForestGALES was based on over 30 years of research exploring tree stability and the effects of wind across forests. Since its last upgrade in 2006, our ongoing research, in collaboration with colleagues at INRA in Bordeaux, France, has led to advances in the underpinning science.
ForestGALES 2.5 incorporates the results of field measurements of how trees respond to strong winds, and improved understanding of root anchorage based on a new analysis of almost 2,000 trees across Britain. It predicts that most stands of trees are more stable than indicated by previous versions of the tool, and we verified the improved accuracy of its estimates by comparing them with damage observed in Forestry Commission forests in Cowal and Trossachs following a major storm that crossed central Scotland in 2012.

ForestGALES 2.5 is the recommended wind risk decision support tool for forest management in Britain. In addition, the latest version of ForestGALES incorporates a research mode that will allow researchers to examine the effects of changing the many physical characteristics of trees and forests on the likelihood of wind damage. This will help improve guidance on forest wind risk management.