What is LARCH?
LARCH stands for Landscape Assessment using Rules for Configuration of Habitat. LARCH determines ecological networks for specific species in a patchy landscape and assesses the sustainability of these networks. LARCH computes potential sustainability of networks. Therefore results can differ from actual distribution data of species.
LARCH input parameters
LARCH is used for comparing effects on sustainability of different landscape scenarios. A very important decision is the selection of the species to evaluate. Species in LARCH have several parameters that determine the results. The parameters are based on field studies and rules of thumb from species experts. The quality of these parameters can vary dependent on the selected species. A number of recent LARCH analyses use eco-profiles instead of specific species. Eco-profiles form a classification of animals that have parameters within certain limits regarding dispersal capacities and area requirements. In this way results become more general and less specific for a single species. The most sensitive parameter in the model is the carrying capacity. This parameter determines the area of suitable habitat needed for a local population.
LARCH results
LARCH is based on metapopulation theory. It does not model reproduction and mortality processes like METAPHOR. Suitability of a patch for local populations is based on habitat quality and size. Ecological networks are formed using a distance dispersion parameter. Barriers can influence the construction of the networks. The assessment of network sustainability is dependent on appearance of key patches and minimum viable population areas in the network.
LARCH computation
The LARCH analysis consists of two steps: habitat modelling and spatial modelling. Habitat maps are constructed from vegetation maps. Per species a quality percentage is set for different types of vegetation. The habitat map computation selects the appropriate vegetation and computes the number of reproductive units supported by patches using species-specific area requirement parameters. The spatial modelling comes in two flavours: LARCH-classic computes network sustainability using ecologically scaled landscape indices. LARCH-SCAN computes spatial cohesion using a distance dependent dispersal measure.
LARCH-classic
Sustainability of ecological networks
The LARCH-classic model is used to answer questions like:
Which area is suitable for preserving reed birds?
What spatial configuration of landscape is favourable for a viable population of small mammals?
What size should a nature reserve have for red deer or roe deer?
LARCH-classic has been used to compare spatial quality of multiple ecosystems. In these studies, guide species are selected using three criteria: type of habitat, dispersal capacity and area requirements.
The LARCH-classic model is used to determine sustainability of ecological networks for species. It uses different parameters for each species. Habitat is selected from vegetation maps. Suitability for local populations is determined using species-specific area requirements. Ecological networks per species are constructed using dispersal capacity parameters and barrier maps (optionally). The area of the ecological networks is used to evaluate sustainability.
LARCH-SCAN:
Spatial Cohesion of Landscape
The LARCH-SCAN model is used to answer questions like:
Where are important potential ecological corridors connecting nature areas located?
Which landscape scenario has the best spatial cohesion for a certain species?
What effects do barriers or resistance of the landscape have on spatial cohesion?
LARCH-SCAN determines suitable habitat for a species. It calculates a relative measure for spatial cohesion. This measure can be used to determine promising areas for species and connections between these areas. For some species the relative measure of connectivity can be transformed into a classification of good, reasonable and bad spatial cohesion.
LARCH-SCAN can take barrier effects and resistance of the landscape into account. This results in an effect on the spatial cohesion. The results of LARCH-SCAN can be used as input to the sustainability evaluation of LARCH-classic. In this way, the effect of barriers and resistance of landscape on the sustainability of ecological networks can be estimated.
Results LARCH classic
This is the result of a LARCH analysis for small mammals living in forest. The green networks are strongly sustainable and yellow networks are weekly sustainable. The picture on the right shows the networks without taking barrier effects into account. The left picture shows the same analysis with barrier effects. In this way the networks suffering most from barrier effects can be determined.
Results LARCH scan
This is the result of a LARCH-SCAN analysis for red deer in Europe. The second picture shows the input habitat map and roads and city barriers. The roads are modelled as soft barriers in this analyses with a barrier effect of 10%. The first picture shows the resulting connectivity map. This map gives an indication for the possible locations for corridors between suitable habitat in the Netherlands and Germany.
