Simulating the dynamics of carbon and nitrogen in litter-removed pine forest

Abstract

The model TREEDEV is developed based on the TREEDYN and TREEGROW models. In TREEDEV model the characteristics and available data of Masson pine ( Pinus massoniana) forest in Dinghushan Biosphere Reserve are taken into account as a demonstration. The model was validated by plantation forest and natural forest data. Calculation of tree growth is based on carbon and nitrogen balance, which depends on the photoproduction of its needles, respiration, nitrogen content of all organisms and that in soil, and other losses due to respiration, litterfall and renewal of stem, branch, needle and root. The model includes four aspects: (1) Exogenous driving force solar radiation, which is a function of latitude, specific meteorological conditions and seasonal time. (2) Canopy photoproduction, in this submodel the influence of temperature, solar radiation, seasonal time and nitrogen content of the soil are taken into account. (3) Biomass compartment into needles, fine roots, coarse roots, branches and stems, enabling us to calculate the appropriate respiration demands for the maintenance of the living biomass fractions, fine roots and needles renewal more accurately. (4) The cycle of carbon and nitrogen in soil, which is related to the decomposition and humification of soil organic matter and litter, nitrogen mineralization from litter, and nitrogen leaching. The dynamics of nitrogen include nitrogen uptake demand of the tree, the loss of nitrogen, and nitrogen relocation before litter shedding and the nitrogen supply from soil. Combined with field condition, scenarios involving litter removal and protective fencing were taken into account. Sensitivity analysis was performed in which 43 model independent variables were varied and analyzed in respect to their influence on 22 dependent variables describing forest state. Simulation results showed that litter removal has an influence on the growth of vegetation, which changes the environment, and retards the renewal of litter and reduces the uptake and fixation of available nitrogen, especially to needle and fine root. The forest with low intensity disturbance can be restored if it is fenced within an appropriate time (30 years in this paper), but this retards the maturation time of stands and depreciates the economic value of the wood. In this paper carbon and nitrogen cycles are analyzed in view of physiological processes with the goal of improving forest management planning.