Studies on the Health of Beech Trees in Surrey, England: Relationship between Winter Canopy Assessment by Roloff's Method and Twig Analysis

Abstract

Trees and saplings of all sizes (total 229) were studied at three amenity sites in Surrey representing mixed woodland, beech high forest and open parkland. Roloff's winter assessment of the twig pattern of growth demonstrated an underlying difference between the sites, which was consistent with an association between greater deterioration and more exposure to climate extremes and pollutants. Trees showed deterioration with age but premature ageing was seen in 35–50-year-old parkland trees. Within the woodland the more exposed trees had worse scores. Quantitative twig analysis was carried out on twigs from the upper canopy of 19 trees and saplings. In the most severely suppressed trees yearly growth declined from the 1976 drought. Subsidiary shoot development was markedly reduced in such trees and there were high numbers of distorted and acute angled shoots. The latter two characteristics increased with age with young healthy trees having very few of these types of shoots, but two 35-year-old trees in open parkland showed premature ageing with larger numbers of such shoots. Twig analysis defined categories of twig pattern according to age and deterioration levels. There was generally good correlation between these categories and the Roloff twig canopy score before analysis or with canopy scores of similar sized neighbours. Objective criteria suggested for future studies were: (1) measurement of annual primary shoot growth; (2) total secondary shoot length relative to a standard primary shoot length; (3) mean number of subsidiary shoots per year; and (4) proportion of shoots growing at 40° or less.