Land: tree mapping
A landscape under threat?
21 March 2014
The recent completion of what is thought to be the UK’s first National Tree Map is a welcome tool to help those charged with managing woodlands. Faith Clark reports
The St Jude storm that swept the south of England on 28 October last year is estimated to have felled, or fatally damaged, around 10 million trees, with the Forestry Commission calculating that 64% of southern England’s 109,000 woodlands are likely to have been affected. Severe weather conditions have continued through the winter, with gale force winds bringing down trees, disrupting road and rail networks and even causing loss of life.
Meanwhile, millions more trees are facing an 'unprecedented level of threat' from pests and diseases, according to the commission. Then Environment Secretary Caroline Spelman launched the Tree Health and Plant Biosecurity Action Plan in October 2011 to address the issue.
An outbreak of ash dieback (Chalara fraxinea) in 2012 again focused attention on the UK's woodlands. This fungal disease causes leaf loss and crown dieback in affected trees, and usually leads to tree death. Although widespread across Europe, with large numbers reported in Poland in 1992, the first infected trees in the UK were found in February 2012 in a consignment sent from the Netherlands to a nursery in Buckinghamshire. Other infected sites have since been confirmed.
The St Jude storm that swept the south of England on 28 October last year is estimated to have felled, or fatally damaged, around 10 million trees
In October 2012, a small number of cases were identified in East Anglia in the wider natural environment, including established woodland, with no recent supply from nursery stock. In May 2013, the first case in the wide environment was confirmed as far west as in south-west Wales, and Chalara fraxinea is now treated as a quarantine pest under national emergency measures and any suspected sighting must be reported.
Phytophthora ramorum, also known as 'sudden oak death', is a disease that has been causing extensive devastation to larch trees in the south east. The latest outbreak at Wentwood Forest, near Newport in Wales, will see nearly 200ha of ancient wood – home to rare wildlife including dormice, adders and nightjars – cut down and destroyed in an attempt to prevent further losses.
The invasive fungus-like disease was first discovered in the UK in 2002 at a garden centre in Sussex and in 2003 on a mature, 100-year-old red oak. In 2009, the disease was found to be killing large numbers of Japanese larch trees in south-west England and by 2011 infections had been reported in Wales, Northern Ireland and Scotland, with cases in more than 120 Forestry Commission sites, 20 National Trust properties and two Woodland Trust reserves.
The Woodland Trust, which owns the majority of the 1,000ha Wentwood Forest, said the destruction of larch was the largest felling it had to undertake in the 1,200 woods it manages. Plans are already underway to replant the wood with oak and cherry in the hope of preserving other flora such as bluebells and wood anemone.
So, what information is available to track the spread of these diseases and manage and protect what is undoubtedly a valuable resource and part of the UK’s national heritage?
Mapping the threat
In 2012, NASA released the first map of tree population of the US. Depicting the concentration of biomass, the map was created over a six-year period by researchers at the Woods Hole Research Center, the US Forest Service and Geological Survey using space-based radar, satellite imagery, advanced geospatial processing and lots of groundwork.
In the UK, a web search for 'maps of UK trees' returns a number of online sites encouraging visitors to record trees in their locality using interactive mapping tools. These crowdsourced maps include the Woodland Trust’s Ancient Tree Hunt, the Natural History Museum's Urban Tree Survey and Treezilla, describing itself as the 'monster map of trees'. However, more scientifically based region-wide – let alone nationwide – resources are few and far between.
National Tree Map
Following previous development work, aerial surveying company Bluesky recently completed what is thought to be the UK's first and only National Tree Map. Created using the most up-to-date aerial photography and colour infrared datasets, combined with detailed height models, the National Tree Map provides a comprehensive assessment of tree heights and canopy cover.
By using innovative algorithms and image-processing techniques, Bluesky has been able to partially automate the production of the National Tree Map, making its creation a reality. A team of experienced professionals then completed an extensive quality assurance process to ensure the quality and accuracy of the data.
Figure 1: Gathering data, with the village of Easton Grey, Wiltshire, in the background
The Bluesky National Tree Map includes three vector map layers: crown polygons, idealised crowns and height points, as well as an attribute table including identification for each crown feature, height attributes and area calculations. The data is available in a range of formats suitable for use in Geographical Information Systems (GIS) and digital mapping environments. The tree map details more than 280 million trees, with a canopy cover in the region of 20,000sq km.
"Previous estimates of tree cover were around 10% for England and 13% for the UK as a whole," comments Bluesky Technical Director James Eddy. "Using our National Tree Map, we have estimated this figure to be marginally higher at around 13.5% for England and Wales. However, what is more significant than the overall figure is the level of detail we are able to provide."
Tree Map data from Bluesky is already helping a number of organisations improve both their understanding and management of trees and woodland across the UK. Authorities across Manchester are using the data to understand the impact of urban trees on the environment, public health and the aesthetic qualities of the region. Purchased by a consortium of organisations headed up by Red Rose Forest and including local authorities, the Homes and Communities Agency and the University of Salford, the information is being used to provide a greater understanding of the benefits trees can provide across the community.
"Tree audit data can be used in a variety of ways – obviously it’s great for mapping trees in parks and open space, but we’re more interested in understanding the benefits trees provide across the whole community," says Mike Savage, Red Rose Forest Operations Manager. "Using Bluesky’s data we aim to come up with plans to maintain existing tree cover and increase this vital resource across Greater Manchester."
Looking after the UK's green spaces better is worth at least £30bn a year in health and welfare benefits, according to a 2011 report in The Guardian, highlighting the findings of the Department for Environment, Food and Rural Affairs' National Ecosystem Assessment. The health benefits of living with a view of a green space were worth up to £300 per person per year, according to the report.
Using Bluesky's tree map, The Ecology Consultancy and the Green Roof Consultancy have undertaken a Green Infrastructure (GI) Audit on behalf of Hammersmith London Business Improvement District to assess the quality and extent of existing GI resources and provide recommendations for enhancing urban green space.
"Working with the London Borough of Hammersmith, we already had access to some information about trees in the public domain," explains Ben Kimpton, Senior Ecologist at The Ecology Consultancy. "But in a dense urban environment this formed only a small fraction of the actual Green Index. In order to fully understand the role and impact of trees in the public and private landscape and to inform future strategy, we needed the full picture and Bluesky’s data provided this."
Applications of the Bluesky National Tree Map include subsidence risk assessment by insurance companies, propagation modelling for telecommunication infrastructure planning, network resilience assessment for utility companies and carbon reduction planning for environmental mitigation projects.
Remotely sensed data such as the aerial photography used to create the National Tree Map can provide further insight into the state and health of the UK's green infrastructure.
"While we generally see vegetation as green, in reality peak reflectance is in the near infrared spectrum, which we can’t see. Up to 60% of infrared is reflected back to the atmosphere and this is why new infrared is invaluable in vegetation studies," says Bluesky's Eddy. "It can easily separate vegetated surfaces from non-vegetated surfaces and can show how vigorously plants are growing. Plant maturity, insect attack or water shortage can also be detected."
The Normalised Difference Vegetation Index (NDVI) is a graphical indicator that is used to analyse characteristics such as peak reflectance to measure vegetation vigour. "We already have CIR [colour infrared imagery] for the whole of England and Wales, so we've created a NDVI map layer. We hope this will become an invaluable tool for benchmarking vegetation health. As we are continuously updating this cover with new flying we can also monitor how our green infrastructure is responding to the threats of climate, disease and pest attacks," Eddy concludes.
Bluesky is also investigating using other wavelengths to provide additional intelligence for tree and vegetation management.
Faith Clark is a marketing communications expert with specialist knowledge of geographic information and systems, mapping and the use of technology in the public and private sectors