Validation of Forest Condition Monitoring Programme (ICP-Forests, level 1) cone index scores by measuring cone density using a field-of-view method

Abstract

A measure of annual cone production is needed for evaluating potential seed crops and for the study of population changes of seed-eating species, but is rarely available in long time series or over extensive areas. The Forest Condition Monitoring (FCM) programme, which contributes to the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP-Forests), has been collecting coning data for Scots pine, Norway spruce and Sitka spruce since 1989, from plots located throughout Britain. A visual assessment system is used to measure a coning index at four levels of abundance as part of the overall crown health assessment. This study tested whether the FCM abundance assessment was related to coning density, and therefore its potential for wider use in future research. Data from the survey have been compared with a field-of-view method that assesses cone density, and the cone production represented by the FCM index has thus been determined. A direct relationship between increased cone index and increased cone density was found; the use of a four-level scoring system allows different cone densities to be distinguished with some reliability. Allocation of cone scores by surveyors from year to year was shown to be consistent except in the case of abundantly coning Sitka spruce. These findings indicate that the FCM programme scoring method does reflect cone production levels and that the data can be used to assess variation in coning between sites and between years. The resolution of the coning data is adequate for assessing the potential for natural regeneration of woodlands but not for selecting stands for seed collections. It is also appropriate for use as a measure of food resource to relate to population changes in seed-eating birds and mammals, and the long-term and Britain-wide nature of these data are of particular value. There is potential for the field-of-view method to be used more widely to evaluate the quality of cone data collected at ICP-Forest sites throughout Europe where the same cone index method has been employed.