Dry Matter Production in Young Loblolly (Pinus Taeda L.) and Slash Pine (Pinus Elliottii Engelm.) Plantations

The net primary productivity of the pine species and lesser vegetation (herbaceous ground cover) plus turnover rates between the litter layer and soil organic matter were investigated in young loblolly and slash pine plantations in Beaufort County, North Carolina. Estimations of the aboveground tree biomass and production by components were made by applying multiple regression, weight—prediction equations developed from harvest data (15 slash pine and 41 loblolly pine trees) to tree dimensions from 28 permanent, undisturbed plots. Optimal plot size was determined by time—cost analysis. Total biomass for slash pine ranged from 5.2 mt/ha and 9.9 kg/tree (age 4) to 31.7 mt/ha and 29.8 kg/tree (age 8), and loblolly pine ranged from 4.2 mt/ha and 4.7 kg/tree (age 4) to 107.6 mt/ha and 82.7/tree (age 12). Net production for slash pine was greater than loblolly pine and ranged from 3.9 mt/ha per year and 8.0 kg/tree per year (age 4) to 12.3 mt/ha per year and 11.6 kg/tree per year (age 8). Loblolly pine produced from 4.3 mt/ha per year and 4.8 kg/tree per year (age 4) to 4.1 mt/ha per year and 4.3 mt/ha per year (age 8). Net primary production of loblolly pine was 22.3 mt/ha per year and 18.8 kg/tree per year at age 10 and 11 and dropped to 18.4 mt/ha per year and 13.6 kg/tree per year at age 12. The decrease in production rate of loblolly pine at age 12 was correlated with a decrease in branch needle biomass as canopy closure progressed. Five root systems were excavated, and percentage of aboveground tree biomass was used to calculate root biomass and production. Canopy closure also caused a decrease in net primary production of the lesser vegetation from 1.8 mt/ha per year in the open stands to 0.2 mt/ha per year under closed stands. Simultaneously, the ground—litter component increased from 3.7 to 5.8 mt/ha through litter fall, and the turnover rate to the soil decreased. Soil organic matter accounted for 88% (102.0 mt/ha) to 52% (124.0 mt/ha) of total plot biomass in the youngest and oldest stands, respectively. Caloric analysis was done on all plant material and ground litter. The results are presented as net primary production and turnover rates (10⁹ cal/ha per year).