By Dr. James D. Arney
What kind of field research trials is your growth model calibrated upon?
If you manage forest stands with mixed species, mixed structure and/or irregular densities (spatial patterns), then you care what kind of growth model is applied and how it was calibrated. If your harvesting regimes have shifted away from even-aged clearcut harvests, then your forest structure is taking on the characteristics identified in the first sentence of this paragraph.
Mixed species, mixed structure stands require a growth model architecture and field research trial design which are based on the Individual Tree as the Experimental Unit, rather than the Plot (or Stand) as the Experimental Unit. This concept was discussed in the SAF E-Forester on February 1, 2019.
The Nelder Plot is a field research design with the underlying concept that the individual tree is the Experimental Unit, not the plot. Many forest biometricians and silviculturists have stayed away from this plot design because they were attempting to use “plot-based” measures of density. They either chose not to use “tree-based” measures of density or where not experienced enough to work this field trials of this design.
The following PDF provides a PowerPoint presentation of the correct application of the Experimental Unit as applied to a series of Nelder plots. Results are compared with growth models calibrated assuming plots as the Experimental Units.
For more about Nelder plots, contact Dr. Jim Arney by using the contact form below.