7.16 Optional subprogramme FD: Forest damage

• 7.16.1 Introduction
• 7.16.2 Methods
• 7.16.2.1 Selection of sample trees
• 7.16.2.2 Recommended observation method
• 7.16.3 Quality assurance/Quality control
• 7.16.4 Data reporting
• 7.16.5 References

7.16.1 Introduction

The aim of assessing tree defoliation and discolouration annually is to obtain early quantitative indications of changes in the most important photosynthetically active parts of the trees.

7.16.2 Methods

7.16.2.1 Selection of sample trees

Several sampling designs are acceptable. These can range from a large number of small plots to a small number of large plots. However, in all cases, the trees should be chosen objectively. The total number of trees assessed in any given year at an IM site should exceed 100.

The trees may be marked for easier re-location, but this is not essential. If a marked tree has died since the last inventory, then it should be replaced. The replacement should have an identification number that has not been used previously. Plot locations should not be moved between inventories unless the sample size is very large, as such moves will create a large amount of variability in the data.

For a given sample size, the year-to-year variation in a sample of marked trees will be lower than that of a sample of unmarked trees. However, if the same objective system of tree selection is used each year and the plot centres remain the same, the samples of unmarked trees will consist of approximately the same individuals each year.

On regularly distributed plots
If a network of regularly distributed forest plots has been established over the site, sample trees should be selected on the these plots.

On special plots
If sample plots have not and will not be established over the area the following procedure is followed. Select one to three forest stands representing the typical stand type(s) of the site. Determine the dominant tree species of the stand. Choose 20 or more trees of this species from an area not larger than 1 hectare, e.g. a circular plot with radius ca. 50 m.

7.16.2.2 Recommended observation method

Sample trees should meet the following criteria:

• alive   
• predominant, dominant or codominant social class   
• <50% mechanical damage   
• crown at least partly visible (1-4) (see part 4 in Annual Procedure, below)

Only that part of the crown that is exposed to light and not shaded by neighbouring trees - the assessable crown - should be considered. This means that on free-standing trees the whole crown should be included, while in forest stands it is usually only the upper part of the crown. Epicormic shoots on the stem below the crown are excluded from the estimate.

The following types of damage should not be considered as defoliation:

• those parts of the crown directly thinned by competition or other interactions with neighbours, e.g. whipping   
• old, dead branches which have lost their twigs

Annual procedure

1) Determine the social class of the tree to make sure that it is predominant, dominant or codominant.

• Pre-dominant (including free standing) = trees with upper crown standing above the general level of the canopy;   
• Dominant = trees with crowns forming the general level of canopy;
• Co-dominant = trees extending into the canopy and receiving some light from above, but shorter than the first two.

2) Decide which part of the crown will be included in the assessment.

3) Decide what should be excluded as defoliation.

4) Decide on and note the visibility of the crown (important for evaluation of results):

• 1= whole crown visible   
• 2= crown partially visible (parts clearly visible)   
• 3= crown poorly visible (no parts clearly visible)   
• 4= crown only visible with backlight (in outline)

5) Estimate and note defoliation in 5% steps (definition: needle/leaf loss in the assessable crown as compared to an imaginary, fully needled/leafed tree of the same type, regardless of the cause of loss).

6) Estimate and note discolouration (definition: a deviation from the usual colour of the living foliage for that species; dead needles/leaves are excluded) as proportion of needles/leaves affected in 5% classes.

7) Record any cause of damage that could have significantly influenced the defoliation of the tree, e.g. insects, stem rot, deer, wind, frost, drought, fire, snow, neighbouring windthrow.

The observations should be done by two trained observers using binoculars in full daylight and changing points of observation. Both observers must reach a common score. Suitable time periods are July-August for broadleaves and July-September for conifers, depending on the latitude and altitude of the site.

A photo-guide will help to maintain the assessment standards through time. Use of a photo-guide implies that absolute reference trees are being used. These represent the most suitable standard for long-term assessments of tree condition. Absolute reference trees are the best possible trees of a genotype or species, regardless of site conditions or tree age. The use of absolute reference trees in Integrated Monitoring is strongly recommended over the use of local reference trees.

Other assessments

Record stem diameter at breast height, tree height, crown length and crown width of each tree. These measurements should be repeated at least every 5 years. Details of assessment techniques are given in the Increment Sub-Manual of ICP Forests.

7.16.3 Quality assurance/Quality control

As customary in national forest inventories, a proportion (e.g. 5-10%) of the sample plots measured by each survey crew, must be remeasured by an independent check survey crew. This control inventory covers all measurements and assessments made by the field crews. In case of significant discrepancies, adjustments of instruments of clarification of instructions and their application must be arranged immediately to avoid serious systematic errors.

See also an overview data quality management in Chapter 8.

7.16.4 Data reporting

Annually reported parameters:

Other parameters:

Variables are reported by plot and tree (number 1, 2, 3, ...).

Example files

FD example Excel file
FD example ASCII file

• File identifier SUBPROG states the subprogramme.   
• Species code for the tree is reported as MEDIUM using NCC species codes (see Annex 6 and subprogramme TF for a list of common species).  
• The number of the tree is given as TREE.   
• Spatial pool (SPOOL) is here always 1.   
• General information on flags is given in Chapter 4.   
• Sampling year and month are given as YYYYMM, day field is left blank.

7.16.5 References

ICP Forests Manual, 2016 (including older parts)
http://icp-forests.net/page/icp-forests-manual

ICP Forests manual, 1997. Manual on methods and criteria for harmonized sampling, assessment, monitoring and analysis of the effects of air pollution on forests, 4th edition. Edited in 1997 by the Programme Coordination Centre Federal Research Centre for Forestry and Forest Products (BFH), Hamburg, Germany.

Photoguides for crown defoliation:

Ferretti, M. (ed.). 1994. Mediterranean Forest Trees. A guide for crown assessment. CEC, Brussels. Available from: Commission of the European Communities, DG VI, 200 Rue de la Loi (L120-10/197 A), B-1049 Brussels, Belgium, or from PCCW. No charge. (Separate editions in English, French, German, Greek, Italian, Portuguese and Spanish are available).

Innes, J.L. 1990. Assessment of tree condition. Forestry Commission Field Book 12. HMSO, London. Available from Technical Publications Office, Forestry Commission, Forest Research Station, Alice Holt Lodge, Wrecclesham, Farnham, Surrey GU10 4LH, England. Cost £15 + p. & p. (In English, with German, French and Russian summaries)

Müller, E. and Stierlin, H.R. 1990. Sanasilva Kronenbilder, mit Nadel- und Blattverlustprozenten. Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf. Available from: F. Flück-Wirth, Internationales Buchhandlung fur Botanik und Naturwissenschaften, CH-9053, Teufen, Switzerland. (Multilingual: in German, English, French, Italian). Cost: SFr. 24 + p. & p.