Regional influences of soil available water-holding capacity and climate, and leaf area index on simulated loblolly pine productivity

We simulated loblolly pine ( Pinus taeda L.) net canopy assimilation, using BIOMASS version 13.0, for the southeastern United States (1° latitude by 1° longitude grid cells) using a 44-year historical climate record, estimates of available water-holding capacity from a natural resource conservation soils database, and two contrasting leaf area indices (LAI) (low; peak LAI of 1.5 m 2 m −2 projected, and high; 3.5 m 2 m −2). Median (50th percentile) available water-holding capacity varied from 100 to 250 mm across the forest type for a normalized 1.25 m soil profile. Climate also varied considerably (growing season precipitation ranged from 200 to 1600 mm while mean growing season temperature ranged from 13° to 26°C). Net canopy assimilation ranged from 9.3 to 19.2 Mg C ha −1 a −1 for high LAI and the 95th percentile of available water-holding capacity simulations. We examined the influence of soil available water-holding capacity, and annual variation in temperature and precipitation, on net canopy assimilation for three cells of similar latitude. An asymptotic, hyperbolic relationship was found between the 44-year average net canopy assimilation and soil available water-holding capacity. Shallow soils had, naturally, low water-holding capacity (