LARCH is a GIS model based on decision rules.
A vegetation map or an ecotope map. The model consists of a set of decision rules, plus parameters and norms for sustainable populations.
A map depicting all the ecological networks of one species and whether these networks are sustainable and contain a key patch.
LARCH can be used to achieve different aims. Firstly, it can be used to diagnose the current situation, as described in step 2 of “Planning for nature”. At a later stage it can also be used to evaluate and compare the ecological sustainability of different future scenarios.
LARCH works as follows:
You start off by choosing a species whose sustainability you wish to assess. As input, LARCH needs a map of the vegetation relevant for the species in question, and certain species-specific data such as the dispersal distance, the number of individuals needed for a viable population, and the potential density of breeding pairs or reproductive females. These data are available from a database maintained by Green World Research (Wageningen Environmental Research (Alterra)).
Using these data, LARCH selects the suitable habitats and determines which areas together form a network.
LARCH also determines whether the network contains a habitat patch large enough to meet the quality requirements of a key patch.
LARCH model determines which local population is part of the network population; That are the populations located within the dispersion distance. When a local population becomes extinct, the habitat location can be recolonised from another location in the network.
Finally, LARCH works out which network is sustainable.