More and more the Penguins here at FSD are asked about the usefulness of Nelder plots and if they are worth it. So to answer the broader question this post will try to address this.
Bottom line… YES, Nelder plots are worth it.
John Ashworth Nelder was a British statistician who among other things worked with experimental designs. We recommend checking out Wikipedia for his bio.
The primary source of Nelder Plot discussions all stems from this article published in Biometrics which is one of the journals of The International Biometric Society.
Nelder, J. A. (1962). New Kinds of Systematic Designs for Spacing Experiments. Biometrics, 18, 283-307.
While many people may not have heard of or seen (you would remember) a Nelder plot a keyword search of Treesearch from the USFS comes up with almost 4000 publications that have that as part of the keyword. Do we believe that the search got it right? No, not really but even if it is 10% of those that is a lot of research.
- The research was initially applied to agriculture to determine the ideal spacing.
- Conceptually Nelder plots focus on the lifeform as the experimental unit. Think of this kind of like cruising with a prism where the tree is in or out based on the distance because every tree has its plot and you are determining if you are on the trees plot. Not a great example but it is possible to think of competition in this way too.
While everyone will think of a Nelder plot as a circular plot with spokes and arcs as seen below this is not necessary. Keep in mind that the only requirement is variable spacing in some manner. If you look at the original publication, you can see some variations of shapes. A circle is just easier to set up.
If we look at it plotted out we see…
It is easier to see the spokes and arcs on younger plots or with different spacing however these plots are on public lands and therefore are not promoting trespassing to examine the plot. When you are on the plot, the views are unique as observed in the photosphere below.
Now that we have seen it why are these valuable/worth your time?
Typical good studies are extensive in area and have a lot of repetition. Perhaps a 1-acre plot for each of the levels of stocking the researcher is interested in. Plus you then need replication. Think five levels of stocking. Already 5 acres plus another 5 for replication. Ok, that is 10 acres. The above plot covers 2 acres has 52 replications at 14 densities. Why? Because the tree is the experimental unit, not the acre.
The Nelder plot design can rapidly provide the landowner with survival numbers as well as growth dynamics and interactions while all being on the same site because of its compactness. Some of those values can be:
- Diameter growth
- Height growth
- Crown dynamics
- Understory vegetation
- Years to 20 feet
- Years to 10 meters
- Years to 20 meters
- Years to 30 meters
Remember those are all key values for the model.
Additionally, these plots mean you can “own” your data. There is very little data out there available to validate and calibrate models. Contrary to the overblown comments made by some organizations there is almost no data currently available to do this kind of research with. Universities tend not to share data until projects are done and all possible research has been reported. USFS can be similar or the data is just lost because of turnover and office changes. Some non-profit organizations depend on data that is licensed only to a 3rd party analyst. When that analyst is gone legally so is the data. Also, this makes verification by a 3rd party impossible.
These plots also allow for the use of the current growing stock used in the forest in question. Most nurseries now likely don’t use heirloom species and likely use some kind of “genetically modified” stock.
A Nelder plot is space efficient, economically feasible, rapidly set up and owned by the entity installing it to validate ANY model. Not even discussed here is the ability to try thinning or species mixes because of the high quantity or replication.