Economics and diversity of trees and landscape in northern hardwood forests: Implications of deterministic and stochastic models

A density-dependent matrix model of stand growth is presented. The model was calibrated with re-measured plots in the northern hardwood forests in Wisconsin. Trees were divided into shade-tolerant, intermediate, and shade-intolerant species in twelve diameter classes. Model predictions were tested against post-sample observations for short-term (15-year) and long-term (steady-state) accuracy.; The growth model (in deterministic form) was first applied to study stand growth dynamics with and without management. Starting with the current average stand state, the predicted stand basal area of an unmanaged stand rose steadily to a maximum, dropped gradually, and finally reached a steady state. The time paths of basal area and tree size diversity were highly and positively correlated. In contrast, tree species diversity decreased when tree size diversity and basal area increased, and vice-versa. When harvesting was introduced, it was found that more intensive harvest increased the diversity of tree species, while decreasing the diversity of tree size. A 20-year cutting cycle could produce higher economic returns than a 10-year cutting cycle, with similar size and species diversity.; In the second part, a Markov decision process (MDP) model was formulated to investigate the economic and ecological consequences of alternative management regimes, under an uncertain environment. Simulation based on the Markovian model showed that old growth stands with the highest tree size diversity would dominate the whole forest after a long time period. Major natural disturbances, as well as management, tended to increase the steady-state landscape diversity of the maple-birch forests in Wisconsin. Compared with the observed current cutting regimes, the economic harvesting policy could produce much more income, while keeping landscape and tree diversity at about the same level. The economic returns decreased as the desired level of tree diversity increased (especially for size diversity). Maximization of tree diversity would have a high opportunity cost compared with economic management alternatives.; The MDP model is attractive for its simplicity in practice. Its drawback is the coarseness of the system state definition.