Thneed Weekly – Week 2014 – 23

Nelder Plot Visit….

So you ask yourself what the heck is a Nelder plot.  Well instead of jumping right in to what it is take a look at one.  (this is not the one visited on this trip)

And of course Google has updated there images so the representation isn’t as good.

NELDER, J. A. (1962). New kinds of systematic designs for spacing experiments. Biometrics, 18, 283-307.

These plots were designed to answer questions in agriculture such as optimal spacing and even optimal mixing of planting stock.  This circular design is rare in forestry because of the typical research project that is carried out.  One reason is that each plant is the experimental unit which differs from planting large areas and taking the average.  The system of planting the spokes and arcs can give varying levels of competition.

The above picture is a plot that the Field Penguin got to visit.  It was truly amazing.  This is not a common plot in forestry.  but the theory is each arc (circle) has a planting density which is repeated for each spoke.  So 40 spokes would mean 40 trees at a given density.  Making the tree the experimental unit.  This is a vital concept for individual tree distance dependent models.  The inside and outside arc’s are lost as buffers.  However walking through this particular installation it was clear where the higher density was affecting tree growth and there was no under story vegetation.  As one walked out from the center it could be seen that grasses then woody understory began at specific competition levels.

If you ever have the opportunity to see a Nelder style plot the penguins in the office highly recommend it.

The setup is simple.  after calculating the spacing the planter takes a spike and places it in the center of the plot.  There are a series of knots in a rope for spacing.  The planter plants at each knot.  To move to the next spoke the planter has a piece of rope at a fixed length to space from the last spoke.  No measurements needed after your spacing ropes are setup.

As a side note determining the spacing of a given point in the plot is very similar to the math used for calculating the pieces needed in creating a segmented bowl in woodturning.  If we can get the Head Programming Penguin moving the hope is to have a form on this site to calculate the necessary values to get the spacing of interest.  If you think this would be useful please contact us via the contact form.