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Landis 4.0

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HETEROGENEITY

In LANDIS, heterogeneity of vegetation, disturbance, and management activities is modeled at multiple hierarchical levels from the landscape to the pixel. For vegetation heterogeneity, LANDIS stratifies the heterogeneous landscape into land types (also called ecoregions for broad-scale studies), which are generated from GIS layers of climate, soil, or terrain attributes (slope, aspect, and landscape position). Land types capture the highest level (coarse grain) of spatial heterogeneity caused by various environmental controls. Within a land type, a somewhat uniform suite of ecological conditions that results in similar species establishment patterns is assumed, but the stochastic processes such as seed dispersal can result in intermediate level (fine grain, within land type) heterogeneity of a species distribution. Finally, succession, competition, and probabilistic establishment may result in heterogeneity of species presence and age cohorts even among pixels that were initially identical. Disturbance heterogeneity refers to various regimes a disturbance may have on the simulated landscape. For disturbance heterogeneity (except for wind and biological disturbances), LANDIS stratifies the heterogeneous disturbance regimes using disturbance regime maps (fig. 1). For example, fire regimes are characterized by ignition frequency and fire cycle (mean fire return interval) in the fire regime map (Yang et al. 2004). Within-regime heterogeneity is further simulated by the stochastic process of each disturbance regime, and pixel level heterogeneity is simulated through the interaction of disturbance and vegetation in the particular pixel. Furthermore, land types or disturbance regimes can be defined by users to partition the landscape into strata that are most relevant for a particular application.

 

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