Design of Experiments for Screening

The aim of this paper is to review methods of designing screening experiments, ranging from designs originally developed for physical experiments to those especially tailored to experiments on numerical models. The strengths and weaknesses of the various designs for screening variables in numerical models are discussed. First, classes of factorial designs for experiments to estimate main effects and interactions through a linear statistical model are described, specifically regular and nonregular fractional factorial designs, supersaturated designs and systematic fractional replicate designs. Generic issues of aliasing, bias and cancellation of factorial effects are discussed. Second, group screening experiments are considered including factorial group screening and sequential bifurcation. Third, random sampling plans are discussed including Latin hypercube sampling and sampling plans to estimate elementary effects. Fourth, a variety of modelling methods commonly employed with screening designs are briefly described. Finally, a novel study demonstrates six screening methods on two frequently-used exemplars, and their performances are compared

Nutrient Limitation in Two Everglades Tree Species Planted on Constructed Tree Islands

The Everglades is a low-nutrient ecosystem occupied by marsh plant species adapted to low availability of phosphorus. Recently, however, tree islands that are scattered throughout the marsh have been recognized as biogeochemical hotspots. The goal of this study was to determine the general patterns of response by common tree species when conditions limiting to optimal growth were improved by fertilization in an experimentally constructed and managed Everglades wetland. Thirty-six trees of two species, Annona glabra and Chrysobalanus icaco, were randomly selected on two peat- and two limestone-based islands. Each tree was treated with one of three nutrient regimes: Nitrogen (N), Phosphorus (P), or Control (no addition of nutrients). Positive highly significant P-treatment effects on leaf total P and leaf N:P were observed in both species in comparison to Control trees, but neither species exhibited a similar response to N-fertilization. However, among the two species, only A. glabra responded to P-fertilization with increased growth. Both fertilized and unfertilized trees of each species exhibited a highly significant growth response to hydrological condition, with growth enhanced on less persistently flooded sites. Our experimental results identify a clear difference in species growth responses to substrate type in the two species, but do not support the idea that a single critical N:P ratio can be used to indicate nutrient limitation for all wetland trees. © Society of Wetland Scientists 2012