A PROCESS-BASED GROWTH-MODEL FOR YOUNG RED PINE

A carbon-balance, process-based growth model was developed to simulate the growth of young red pine (Pinus resinosa Ait.). The dry weights o f current, 1-year-old, 2-year-old, 3-year-old needles, stems and branc hes, and roots of individual trees were considered as state variables. The hourly rate of photosynthesis was calculated with solar radiation , air temperature, leaf water potential, and leaf age as driving varia bles by assuming that the needles experience the same incident light d ensity. Maintenance respiration rate was assumed to be a function of s urrounding temperature. The seasonal allocation of assimilates to each compartment was determined by the activity of each compartment and wa s regulated by soilwater potential. The translocation of carbohydrate reserves, litter fall, and root turnover were incorporated in the mode l. The simulated results fit well with observed values from three plan tations in the central Upper Peninsula of Michigan.