FENDS : a model to investigate growth and nitrogen dynamics in managed stands of Pinus nigra var. maritima (Ait.) Melville
This thesis describes the development and subsequent use of a computer simulation model, FENDS (Forest Ecosystem Nitrogen Dynamics Simulator), designed to investigate growth and nitrogen dynamics in managed stands of Pinus nigra var. maritima (Ait.) Melville. The literature is reviewed as three subject areas. First is the production of biomass, its partition within trees and changes which occur during stand development. Second is the cycling of nitrogen within forest ecosystems including inputs to, and losses from the system. The review ends with a description of the types of model that have been developed in relation to forestry, with emphasis placed upon the computer simulation models. An overview of the model is provided together with an account of its development. The current version is described in detail and assumptions upon which it has been based are discussed. A number of key areas for which information is lacking have been identified including: 1) allocation of growth to tree and ground vegetation components, particularly root systems; 2) turnover rates of root systems; 3) mechanisms controlling storage and remobilisation of nitrogen in trees; 4) changes in opitimum nitrogen concentrations which occur during stand development; and 5) breakdown of recalcitrant organic matter and associated nitrogen dynamics. The model has been used to simulate weeding, fertiliser applications and thinning operations and to examine potential interactions. Results from these simulations are discussed.