Forest condition monitoring – Level I network

In the early 1980s, widespread forest decline became a matter of concern for foresters and scientists across Europe. Many countries established annual surveys to assess the health of their trees. The Forest Condition Survey (also known as the Level I programme) is one of these surveys and it has been effective in documenting changes in the condition of trees and forests across Europe.

The tree health assessment in this survey is based on crown density or transparency. Approximately 90 plots were established in the UK covering the five most common species:

• Oak
• Beech
• Scots pine
• Sitka spruce
• Norway spruce.

The Level I network is a subset of the more extensive national forest condition survey, which includes over 300 plots covering the same five species. However, it became evident in the 1990s that detailed assessments which included measurements of environmental drivers were needed to identify the causes of any observed trends.

Intensive forest health monitoring – Level II network

The principal aim of the network was to identify the underlying causes of poor forest condition identified in the more extensive Level I survey. A network of plots for intensive monitoring (the Level II programme) was established in 1994. In the UK, ten long-term intensive monitoring plots were established in 1995 (oak, Sitka spruce and Scots pine), with ten further plots added in 2002 (including beech and Norway spruce).

Data from these plots are being used to support other environmental research programmes, and, also, to provide information for wider Forestry Commission objectives, including the protection of Britain’s forests and woodlands, their long-term sustainability, and soil and water quality.

Further information on intensive monitoring in Europe.

Measurements in the Level II plots include:

• Crown Condition
• Stand growth (height, diameter and volume increment)
• Foliar chemistry
• Soil chemistry
• Vegetation composition
• Soil solution chemistry
• Litterfall and litter chemistry
• Air quality
• Meteorology.

Some of the above measurements are only made at a proportion of the sites.

Level II forest health monitoring is used in:

• Evaluation of long-term trends in acid deposition and its effect on forest ecosystems including soil, soil solution chemistry, ground flora composition, tree health and growth
• Calculation of critical loads, development of critical loads maps and calculating and mapping critical load exceedances for different woodland habitats
• Continuous updating of the critical load calculations and maps (Terrestrial Umbrella project)
• Development of forest soil quality indicators and testing of their thresholds
• Dynamic modelling of ecosystem change (Terrestrial Umbrella project)
• Budgeting studies
• Spatial variability studies.