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

A measure of annual cone production is needed for evaluatingpotential seed crops and for the study of population changesof seed-eating species, but is rarely available in long timeseries or over extensive areas. The Forest Condition Monitoring(FCM) programme, which contributes to the International Co-operativeProgramme on Assessment and Monitoring of Air Pollution Effectson Forests (ICP-Forests), has been collecting coning data forScots pine, Norway spruce and Sitka spruce since 1989, fromplots located throughout Britain. A visual assessment systemis used to measure a coning index at four levels of abundanceas part of the overall crown health assessment. This study testedwhether 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-viewmethod that assesses cone density, and the cone production representedby the FCM index has thus been determined. A direct relationshipbetween increased cone index and increased cone density wasfound; the use of a four-level scoring system allows differentcone densities to be distinguished with some reliability. Allocationof cone scores by surveyors from year to year was shown to beconsistent except in the case of abundantly coning Sitka spruce.These findings indicate that the FCM programme scoring methoddoes reflect cone production levels and that the data can beused to assess variation in coning between sites and betweenyears. The resolution of the coning data is adequate for assessingthe potential for natural regeneration of woodlands but notfor selecting stands for seed collections. It is also appropriatefor use as a measure of food resource to relate to populationchanges in seed-eating birds and mammals, and the long-termand Britain-wide nature of these data are of particular value.There is potential for the field-of-view method to be used morewidely to evaluate the quality of cone data collected at ICP-Forestsites throughout Europe where the same cone index method hasbeen employed.