CONCEPTUAL DESIGN OF LANDIS

In LANDIS, a landscape is modeled as a grid of cells (or sites) with vegetation information stored as attributes for each cell. At each cell, the model tracks a matrix containing a list of species by rows and the 10-year age cohorts by columns. The temporal scales of LANDIS are largely dictated by the current 10-year age-cohort structure, and the 10-year time step makes the model suitable for simulating long-term dynamics (10¹-10³ years). The spatial scales of LANDIS are within 10³ - 10⁷ ha, depending on the simulation cell size. Since LANDIS tracks only the presence absence of species age cohorts, not individual trees, computational loads are greatly reduced. In addition, the essential information of presence/absence is relatively independent of cell size, and therefore LANDIS is capable of simulating forest succession at cell sizes ranging from 10 to 500 m (He et al. 1999a).

The LANDIS model can be represented conceptually as a repeating cycle of processes that operate on the initial input map and subsequent time steps. Major model dynamics include (a) successional dynamics, (b) species-site quality interactions, and (c) disturbance and management. Succession occurs within a cell based on species life history attributes such as shade tolerance and longevity. Species-site quality interactions involve filtering species based upon their ability to establish on a particular cell based on propagule availability (seed or sprouting ability) in relation to the land type, a spatial landscape input that may correspond to soils, slope, or other physical characteristics. Disturbance and management simulate wind, fire, insect and disease, forest harvesting, and fuel management activities that interact with species/age cohorts in both spatial and temporal dimension (Mladenoff 2004).

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