Systematic Experimental Designs for Mixed Species Plantings

The role of species mixtures in plantation forestry

“…There are also innovative plot designs that are designed to be so efficient in land area that they can be used as species trials, and yet still allow quantitative analysis of species interactions at the individual tree-level. These have been described for two species (Nester, 1994, described in Kelty andCameron, 1995), three species (Goelz, 2001) and four species (Vanclay, 2006b). …”

Experiment designs to evaluate inter- and intra-specific interactions in mixed plantings of forest trees

“…This leads to the suggestion that multi-species trials, rather than binary trials, may be more efficient for examining competition and facilitation amongst forest tree species. Goelz (2001a) has established a series of triangular plots in which the relative density of each of three species varies systematically from each corner, and has reported the 7-year results (Goelz, 2001b). His design was inspired by the simplex lattice (Cornell, 1973(Cornell, , 1990, and represents an optimal design for three species, provided that species interact only with their immediate neighbours.…”

“…4 may be criticised for a lack of randomisation. While it is possible to randomize the placement of species in such a design (Goelz, 2001a), it is not always desirable to do so (cf. Observation 5).…”

“…Observation 2). This may be addressed by employing a series of triangles with different spacings (Goelz, 2001a), or by ensuring that the experiment employs two components: one which varies species composition systematically (e.g., a Goelz triangle), and another that varies spacing systematically (e.g., a clinal plot or Nelder fan as advocated by Goelz, 2001a). Fig.…”

“…The Goelz design provides for all possible combinations of three species in a seven-tree hexagon (a central subject tree surrounded by six neighbours), including 0:0:7, 0:1;6, 1:1:5, etc., in a compact design involving only 210 trees of each species. Goelz (2001a) discussed how the design can be expanded to accommodate more than three species, and randomization can be introduced into the design without compromising the range of species composition. His design is near perfect for small trees, but suffers a weakness because as trees grow, the zone of influence of each tree may extend beyond one spacing unit, and may affect the next concentric hexagon of trees.…”