Gradient analysis is an empirical

Empirical

The word empirical denotes information gained by means of observation or experimentation. Empirical data are data produced by an experiment or observation....

 analytical method used in plant community ecology to relate the abundances of various species in a plant community to various environmental gradients by ordination

Ordination (statistics)

In multivariate analysis, ordination is a method complementary to data clustering, and used mainly in exploratory data analysis . Ordination orders objects that are characterized by values on multiple variables so that similar objects are near each other and dissimilar objects are farther from...

 or by weighted averaging

Weighted mean

The weighted mean is similar to an arithmetic mean , where instead of each of the data points contributing equally to the final average, some data points contribute more than others...

. These gradients are usually variables

Variable (mathematics)

In mathematics, a variable is a value that may change within the scope of a given problem or set of operations. In contrast, a constant is a value that remains unchanged, though often unknown or undetermined. The concepts of constants and variables are fundamental to many areas of mathematics and...

 that are important in plant species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

distributions, and include temperature, water availability, light, and soil nutrients, or their closely correlated surrogates.

Reference

• Mike Palmer, Ordination Methods for Ecologists Botany Department of Oklahoma State University. Retrieved 15 August 2010.