A Simulation Model of the Role of Belowground Dynamics in a Florida Pine Plantation

Abstract

Abstract A model of a 29-yr-old slash pine (Pinus elliottii) plantation on a typical flatwoods site in north Florida evaluates the importance and magnitude of belowground processes in a forest. The model, which comprised 22 differential equations, most of them nonlinear, was parameterized with three sets of climate data and validated with measurements of soil moisture, soil CO2 evolution, root production, and root biomass. Simulated gross primary productivity (GPP) in a year with normal rainfall was 29.5 Mg ha-1 yr-1 (C), which is consistent with measurements of GPP in a variety of north Florida sites. In the model, one-third of GPP was translocated to the roots, where more than 75% was spent on respiration. Root respiration varied little among the three simulations. Root turnover times were more variable. In the low rainfall simulation, root turnover time was 21% longer than in the other two simulations, which were nearly the same. Simulated P concentration in the soil and plant had much less effect on plant processes than soil moisture did. General agreement of transpiration rates with other studies indicated that evapotranspiration is the only major water loss in slash pine flatwoods. Simulated water-borne P losses from the site were therefore insignificant. Simulated foliage biomass varied considerably during the year, decreasing to less than haft its maximum biomass during an annual cycle in one of the simulations. Comparison of the few sites with comparable estimates of C fixation and allocation suggests that 22%-43% of C fixed is used by roots, and that the proportion allocated to roots may be higher on nutrient-poor sites and sites with low temperatures. For. Sci. 37(1):397-438.