Hargrove, W. W. and R. J. Luxmoore. 1998.
A New High-Resolution National Map of Vegetation Ecoregions
Produced Empirically Using Multivariate Spatial Clustering.
Conference paper
to be published electronically by Environmental Systems Research
Institute, Redlands CA.
A parallel supercomputer was used to divide the conterminous 48 states
of the United States into 1000, 2000, 3000, 5000, and 7000 ecoregions
with relatively homogeneous values of elevation, edaphic, and climatic
variables using an iterative multivariate clustering
technique. Resolution
of the clustered maps is 1 square kilometer; each national map has over
7.7 million cells. Each cell has nine variables from maps with values for
elevation, soil nitrogen, soil organic matter, soil water capacity, depth to
water table, mean precipitation, solar irradiance, degree-day heat sum,
and degree-day cold sum.
The resultant national maps objectively capture the ecological patterns of
spatial variance in physical, edaphic, and climatic factors relevant for the
distribution and growth of plants and animals. Assignment of red, green,
and blue colors according to the principal component scores associated
with the ranges of the nine variables defining each cluster results in a map
where the ecological similarity of adjacent cluster regions is readily
apparent. Maps with this gradually-changing color spectrum illustrate
ecological relationships for plant growth derived from soil factors,
physiognomy, and climate across the 48 states at user-defined
resolutions. The clustering technique is being used as a way to spatially
extend the results of simulation models by reducing the number of runs
needed to obtain output over a larger area.