Pest & Disease Risk


Pests and diseases (P&D) are one of the largest causes of forest loss and damage, affecting around 35M hectares of forest a year globally – mainly in temperate and boreal forests (FAO 2010). For example, across Europe between 1950 and 2000, biotic factors as a whole are estimated to have accounted for 16% of the total wood damaged by disturbances of which 8% was attributed to bark beetles (Schelhaas et al., 2003).

Regional trends for P&D show high variability with the percentage of forest areas affected by pests running as high as 5% in North America in the 1990s during the spruce budworm outbreak, although the average had fallen to 3.4% in the latest figures for 2005. Northern Africa, Western and Central Asia and Europe (excluding the Russian Federation) also had affected areas of around 2-3%. Overall insect infestations have shown a decline but again data is variable. Diseases have affected much smaller proportions of forest overall with only Oceania showing high levels up to 3.9%. (FAO 2010). Limited data is available but show in general that: insects are the most frequent pests impacting on forests; in most regions the majority of pests are indigenous and are prevalent in planted as opposed to naturally regenerated forests; and in all regions broadleaf species had a higher number of pests than conifers (FAO, 2009).

Historic trends offer little guidance on the future risks of P&D for a number of reasons: e.g. new P&D can arise;  existing ones can jump species; and most importantly new P&D can arrive from other countries. Climate change can have both positive and negative impacts on P&D, but trees under climatic stress are more vulnerable to them.

Approaches to assessing risk

General – proposal for daily monitoring of general pest and disease impacts via remote sensing

Prof. Lynch has promoted the concept of daily monitoring of the state and health of forests by using optical and radar satellites that work in different parts of the electromagnetic spectrum (Lynch et al., 2013). Optical satellites could detect changes in the amount of chlorophyll, which can help detect the onset and spread of pests and diseases. Images would need processing into datasets for end-users, via an intermediary organisation, including orthorectification. Daily information is needed to identify threats on a timely basis, whereas currently information is typically provided weekly. This could be provided using the latest satellite constellations recently launched including DMC-2 and the radar systems soon to be launched (resolution 1m). Prof. Lynch has discussed this concept with the commercial and public sector, including Defra. Insurers have been receptive to the idea, provided consensus on data interpretation is achieved by providers. In a letter to the Times dated 30 October 2012 under the general head ‘Defra and the timber trade share the blame for ash dieback’, he argued that this could have helped in the detection of Ash Dieback caused by Hymenoscyphus fraxineus (formerly Chalara fraxinea). There is precedence in that precision agriculture already makes significant use of satellite technology e.g. for irrigation and fertiliser application. Contact: Prof. Jim Lynch

Using remote sensing to detect stress factors/forest health indicating possible P&D impact

  • Prof. Juan Suárez (Forest Research) is working with Dr. Jacqueline Rosette and Professor North (University of Swansea) in the development of new techniques for detecting changes in the foliage associated to stress factors. This project is funded by the Royal Society and involves the use of different sensors and the calibration of the radiative transfer model Flight, developed by Peter North and his collaborators. A recently awarded project by DEFRA aims at the adaptation of the system developed by NASA and the US Forest Service to monitor trajectories of change using satellite imagery. This project is due to start in April 2016.
  • Prof. Juan Suárez is leading the participation of Forest Research  in a consortium with the Chinese Academy of Forestry and the University of Swansea in the Focus-Kanlin project. This work is focused on multi-sensor analysis, data assimilation techniques and modelling. The project aims to develop an operational platform to improve forest inventories and monitor forest health and condition. The project is due to start at the end of 2016.

For both projects contact: Prof Juan Suárez-Minguez

Using remote sensing to detect specific P&D (general approach)

Juan Suárez works with Professor Heiko Baltzer and others at the University of Leicester and Dr. Jackie Rosette at the University of Swansea, on identifying and mapping tree physiology from remotely sensed data. Projects aim to identify stress symptoms that can be associated to the characteristics of individual P&D. The physiological activity of trees under stress can be detected through multispectral and hyperspectral scanning from different types of airborne and satellite sensors. At this point, it is not yet possible to detect the spectral ‘signature’ of the disease. Instead, work is focused on the detection of carotenoid and chlorophyll composition of the foliage as well as temperature differences as indicators of stress. Data assimilation techniques between sensor data and an energy balance model allow a guided search for forest condition. The goal is to gain a better understanding of what sensors depict at a point in time compared to expected signal. So, by a better estimation of anomalies, it will be possible to improve the detection of stress in our forests. Projects in this area include:

Using remote sensing to detect: Phytophthora ramorum

  • The Bluesky Project (link), funded by NERC and  supported by Forest Research is led by Prof. Heiko Baltzer, with Juan Suárez-Minguez as a co-supervisor of Chloe Barnes (PhD student). Bluesky is a UK-based company specialising in aerial survey. This project investigates the use of aerial photography, thermal imaging and airborne laser mapping systems to improve the identification of Phytophthora ramorum in larch. It aims to ‘use a state of the art aerial mapping system to collect data for already infected trees and compare this with data for healthy sites nearby and historic, pre diseased, baseline data.’ The project aims to integrate hyperspectral and thermal imagery with LiDAR information to develop a spectral signature of infected vs uninfected larch. Contact: Prof. Heiko Balzter
  • There is also a Forest Research project aiming to construct the spectral signatures of change depicting the progression of P. ramorum in larch since the point of infection. An experiment will be conducted in the spring and summer of 2016 on a group of saplings. They will be infected with the disease in the control environment of a polytunnel. Temperatures and reflectance will be monitored in a group of infected trees and control individuals. In parallel, foliar samples will be analysed using chromatography to determine changes in pigment composition that will be associated to the changes in reflectance. The hypothesis is that the disease will affect pigments due to changes in carotenoid content and will also affect chemical composition as detected by the sensors and lower stomata activity. This information will be used to calibrate airborne campaigns using the Flight radiative transfer model developed at Swansea University. Contact: Prof Juan Suárez-Minguez

Using remote sensing to detect: Dothistroma septosporum (Red Band Needle Blight)

  • Prof. Juan Suárez is co-supervising PhD student Magdalena Smigaj  with Dr. Rachel Gaulton ( University of Newcastle). Magdalena is using a combination of field and airborne sensors aimed at the detection of Dothistroma septosporum in Scots pine. Work is focused on thermal differences between individuals affected by different degrees of defoliation and multispectral characteristics of the foliage. The airborne sensors are mounted on UAV platforms. Other work is looking at the use of the multispectral waveform LiDAR system (SALCA) developed by Professor Danson at Salford University.
  • Prof. Juan Suárez is also co-supervising PhD student William Cornforth, with Dr. Caroline Nichol (University of Edinburgh). William has been undertaking a set of experiments in a polytunnel with Scots pines infected by Dothistroma septosporum and exposed to nutrient and water deficiencies. The aim of this project is the creation of spectral signatures of plant response associated to different stressors.

For both projects contact: Prof Juan Suárez-Minguez

Quantifying losses from P&D via remote sensing

Prof. Balzter previously worked on techniques to detect forest scars from remote sensing and identify which are caused by P&D damage through elimination of other causes. For example, if remote sensing shows no history of heat emissions from these scars then the cause is not fire related and may be due to P&D damage. High resolution of remaining trees and topographical information can also enhance the analysis. This technique could be particularly useful in areas where there is known P&D damage e.g. from pine beetles, and can be used to assess the extent. Whilst the feasibility of this approach was tested some time ago over Siberia the work has not been followed up in depth and was not published. Contact: Prof. Heiko Balzter

Biological control of pests and diseases

Prof. Lynch is an expert in the use of biological control i.e. the use of natural predators and pathogens to control crop plant and tree pest and diseases ( Hokkanen and Lynch , 1986). This can be economically attractive but most importantly it can pose less environmental and human health problems than many chemicals which have been used. Contact: Prof. Jim Lynch

A new approach to assessing the overall threat to woodland and individual tree species

Davies has developed a new approach that supports a systematic, risk-based assessment of the future threat to woodland from all known individual pest and diseases, based on a risk management approach taken from the finance sector (Davies et al, Forestry 2017). As well as a comprehensive assessment of the threat to woodland, it also provides an assessment of the comparative threat to individual tree species. The approach has been demonstrated through a case study of the evaluation of pest and disease threats to projects certified under the UK’s Woodland Carbon Code. It is currently being expanded to look at all threats to the top 5 tree species in the UK: Sitka Spruce, Scots Pine, Oak, Ash and Birch. The approach can be adapted to any woodland resource worldwide – whether managed for timber, carbon, biodiversity, or public enjoyment – provided the requisite data is available. Its novelty lies in the simplification of complex threats, from numerous pests and diseases, to measures that can be used by a range of stakeholders including those involved in policy, forest asset management and investment. Contact: Susan Davies


DAVIES, S.A., PATENAUDE, G., SNOWDON, P. IN PRESS. A new approach to assessing the risk to woodland from pest and diseases. Forestry Journal. Open access article available here.
FAO 2009. Global review of forest pests and diseases. FAO Forestry Paper 156. Rome: Food and Agriculture Organization of the United Nations.
FAO 2010. Global Forest Resources Assessment 2010. FAO Forestry Paper 163. Rome: Food and Agriculture Organization of the United Nations.
HOKKANEN,H.M.T. & LYNCH,J.M. (Eds) 1995. Biological Control Agents. Cambridge University Press.
LYNCH, J., MASLIN, M., BALZTER, H. & SWEETING, M. 2013. Choose satellites to monitor deforestation. Nature, 496, 293-294.
SCHELHAAS, M. J., NABUURS, G. J. & SCHUCK, A. 2003. Natural disturbances in the European forests in the 19th and 20th centuries. Global Change Biology, 9, 1620-1633.