Trade-off between height growth and stem diameter growth for an evergreen oak, Quercus glauca, in a mixed hardwood forest.
Patterns of stem growth of a mid-successional evergreen oak species (Quercus glauca) in a secondary mixed hardwood forest near Mt. Daimonji in the National Forest of Kyoto, Japan, were examined to explore the trade-off relationship between stem-diameter growth and height growth. The mean cross-sectional area (and the corresponding mean diameter) of a stem at a point in time was defined as the stem volume divided by tree height. Based on this definition, a simple equation representing the trade-off relationship between the height growth and mean diameter growth was formulated. In the long term, allocation to height growth was encouraged at the seedling stage and it gradually declined with time, with the decline in the suppressed seedlings being more pronounced than in the dominant trees. However, both the suppressed and the dominant trees showed acceleration of height growth at various ages. Such a fluctuation in the allocation of biomass to height growth is likely to have been caused by chronological changes in light conditions, resulting in meandering of the trajectory of allometry between the height and mean diameter. The observed stem growth patterns of the individual trees could explain the chronological changes in the diameter-height relationship of the population.