Growth strategy of trees related to successional status I. Architecture and extension growth

The architecture and growth pattern of early (Alnus nepalensis and Schima khasiana) and late (Machilus kingii, Quercus dealbata and Q. griffithii) successional tree species in a sub-tropical montane, humid, evergreen forest at Upper Shillong (1900 m) in north-east India were analyzed and related to their ecological strategy for niche occupancy in the forest ecosystem. In the early successional species the architectural development pattern and growth design are geared to maximize production under high light environments. These trees have an indeterminate pattern of shoot growth, a prolonged growth period with greater extension growth and rhythmicity (except for A. nepalensis with continuous growth) and branch mainly by syllepsis. These species emphasize vertical growth at the expense of lateral spread. In contrast, the late successional species make modest growth under a determinate scheme, the growth being confined to preformed bud primordia for a brief period of the growing season. There is less rhythmicity in growth and branch productin is by prolepsis. These species emphasize lateral spread, as an adaptation to highly competitive environments. In forest situations these species have one determinate flush of shoot growth only but in open situations there were two such flushes. Bifurcation ratio values are found to vary in forest and open situations, suggesting the capacity of the species to adjust their architecture to changed light conditions.