Use of diameter increment and basal area increment in tree growth studies

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Abstract
Growth of diameter of individual trees can be expressed as diameter increment or basal area increment. Little work has been done to determine which of these parameters is preferable for use in growth studies. This paper examines growth of trees in pure and mixed stands of even-aged, regrowth forest of Eucalyptus regnans, E. obliqua and E. globulus, aged 6-80 yr, thinned and unthinned, in southeastern Tasmania [Australia]. Weighted least squares regression equations are developed to relate diameter and basal area increments, over 1- to 6-yr increment periods, to initial tree diameter in 29 growth plots. The correlation between basal area increment and initial diameter was always greater than that between diameter increment and initial diameter in these relationships. Despite this, the precision of estimates of future diameter in each plot is the same whether diameter or basal area increment equations are used. Data from a thinning experiment in 38- to 85-yr-old, even-aged Acer saccharum, Fraxinus americana and Prunus serotina stands in southern Ontario [Canada] are also examined and similar results obtained. It is concluded that no a priori reason exists for expressing growth as diameter increment or basal area increment in studies of these types.