Systematic Experimental Designs for Mixed Species Plantings

Systematic experimental designs provide splendid demonstration areas for scientists and land managers to observe the effects of a gradient of species composition. Systematic designs are based on large plots where species composition varies gradually. Systematic designs save considerable space and require many fewer seedlings than conventional mixture designs. One basic design incorporates a large triangular plot; in concept this plot is identical to the well-known soil textural triangle. The intent of the designs is to produce a response surface over species composition, rather than test for significant differences between 2 specific species compositions. Another design superimposes a species composition gradient on a Nelder’s design, which systematically varies planting density. It is possible to study mixtures in multiple strata, such as overstory trees and herbaceous understory. The systematic mixture designs are most effective when considering 2 to 4 species.