Impact of insects on tree growth

Summary

This programme carries out research on a number of insect pests that cause defoliation or other types of non-lethal injury to forest trees. The objective is to determine the impact of these insects on tree growth and timber production, and to estimate the economic costs of damage.

The most detailed research has focussed on the impact of green spruce aphid (Elatobium abietinum) on Sitka spruce. Long-term experiments on the effect of defoliation by this aphid on young Sitka spruce were undertaken in Hafren Forest, Wales, during 1993-2000, and comparative work on mid-rotation Sitka spruce is currently being undertaken in Radnor Forest (2000-2006). Research on the green spruce aphid is linked to the potential impacts of climate change programme, as global warming is likely to have a major influence on the prevalence of this pest.

Other current research projects include studies on the impact of horse chestnut leafminer (Cameraria ohridella), the biology and ecology of leaf weevils (Phyllobius species), and the relationship between hornet clearwing moth (Sesia apiformis) and dieback in mature poplars. Previous studies have quantified the impact of pine looper moth (Bupalus piniaria) on Scots pine, and damage caused by insects and disease to poplars and willows grown as short-rotation coppice.

Research objectives

The main objective of the programme is to quantify the effects of phytophagous insects on the growth of forest trees, and to use this information to estimate the economic costs of non-lethal damage. The main parameters used to describe growth loss are reductions in height, diameter and volume increment. However, an important part of the research is to understand the mechanisms that determine the response of trees to insect attack. This involves detailed assessment of insect populations, patterns of shoot growth, and canopy biomass, in order to establish relationships between insect densities, rates of damage and changes in tree performance.

Specific objectives:

• Determine the impact of green spruce aphid on Sitka spruce by quantifying relationships between aphid population densities, defoliation and tree height and volume increment.
• Obtain field data on populations of the green spruce aphid in relation to key climate variables (e.g. temperature, rainfall, humidity, wind speed) to determine the likely response of the aphid to climate change.
• Monitor the spread of horse chestnut leafminer in the UK and determine its impact on horse chestnut trees in urban and rural situations.
• Develop an understanding of the ecology and impact of leaf weevils in the genus Phyllobius, in particular the circumstances under which they cause significant defoliation of young broad-leaved trees.
• Investigate the long-term interactions between hornet clearwing moth and dieback and recovery in poplars.

Funders and partners

This research is funded by the Forestry Commission Alternative management approaches programme.

Research on green spruce aphid has been part funded by European Union research and development programmes AIR-3-CT94-1883 ‘The spruce aphid in Western Europe’ and FAIR-3-CT96-1792 ‘Improving protection and resistance of trees to the spruce aphid’.

Status

The programme started in April 1989 and is ongoing. Current research on green spruce aphid in Radnor Forest commenced in 1999