Hierarchical approach to forest ecosystem simulation

Predictions of impact of environmental change on forest ecosystems need to utilise available data collected at a range of organisational scales: cell, leaf, tree, and forest. The model FORDYN is designed to scale up biochemical and physiological data to make predictions about forest growth and development over periods of many years. There are four hierarchical levels within the model. Level 1 represents a set of individual trees within the ecosystem, and deals with the establishment, growth and mortality of individual trees. Level 2 deals with the daily allocation of biomass to above- and below-ground parts of each tree, which is determined according to the Thornley transport-resistance method. Level 3 permits physiological data to be drawn into play: it includes hourly calculations of photosynthesis, respiration according to empirical relationships available from the literature, as well as the transpiration rate calculated from a form of the Penman-Monteith equation. Level 4 incorporates the Farquhar model of C3 photosynthesis, which provides the basis for simulating the impacts of temperature and CO2 on the ecosystem. ortant feature of this model is that the user can decide which of the four organisational levels are to be used in the simulation. In mode 1, only level 1 is called. This mode may by appropriate for use by a forest manager. In mode 2, levels 1 and 2 are called; in mode 3, levels 1, 2, and 3 are called, and in mode 4, FORDYN uses all 4 levels of organisation. e between levels is discussed. Generally, results from a low level provide an input to the next higher level (scaling up by integration, whether by summing or by multiplication). Results from a high level frequently feed back to the lower level, by setting a constraint (usually, a state at the higher level influences the rate at the lower level).