ECOSIEVE (Box 1981) is an empirically based model that predicts vegetation types possible on a site based on eight climate variables:

TMAX: Mean temperature of the warmest month

TMIN: Mean temperature of the coldest month

DTY: Annual range of mean monthly temperatures

PRCP: Mean annual precipitation

MI: A moisture index calculated by MI = PRCP/APE, where APE is annual potential evapotranspiration as estimated by the Thornthwaite method.

PMAX: Mean maximum monthly precipitation

PMIN: Mean minimum monthly precipitation

PMTMAX: Mean precipitation of the warmest month

ECOSIEVE has 93 vegetation cover types defined on the basis of the eight climate variables.  Data for a site is checked against a lookup table of the vegetation types.  If all eight climate values fall within the range limits of a vegetation type, that type is flagged as possibly occurring on the site.

In the “Possible ECOSIEVE model vegetation types are:” section of the results, several columns are listed.  The first, “Num,” lists the number of the vegetation types listed.  The second column, “ECOSIEVE vegetation type,” gives the name of the vegetation unit.

“Dom,” the third column, gives a dominance score for the vegetation type; the higher the score, the more likely the particular type will be a dominant type at that location.  However, if the site is near a climatic limit (“LimVar”) for a particular vegetation type, fitness scores (“Fit”) will be low.  Fitness scores run from 0.0 (very stressed), to 1.0 (very healthy).  ECOSIEVE ignores those possible sites that have fitness scores less than 0.01.

The final column, “Biome,” is provided to aid in correlating the 93 ECOSIEVE vegetation types with the following biomes: tropical forest, savanna, desert, chaparral, deciduous forest, coniferous forest, grassland, ice desert.

Copyright © 2003-2011, David M. Lawrence

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