CROWN ALTERATIONS INDUCED BY DECLINE - A STUDY OF RELATIONSHIPS BETWEEN GROWTH-RATE AND CROWN MORPHOLOGY IN BEECH (FAGUS-SYLVATICA L)

One of the first symptoms expressed by declining trees is reduced grow th in stem diameter and length increment. The possibility of a relatio nship between length increment and crown thinning in beech (Fagus sylv atica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branc hing beech trees, 70-100 years old, for a range of length increment ra tes. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and bran ch mortality rates for six healthy and declining trees. Shoot growth r ates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/year (healthy). Simulations of branching p atterns in the apical 2 m of trees growing at different rates indicate d that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduc tion in the area explored. Growth rate-related crown thinning could in crease the risk of bark necrosis and secondary pathogen infection duri ng dry and/or hot spells.