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Systematic Planting Designs for Assessing the Controls of
Forest Density on Growth
Wade Tinkham Michael Battaglia Chad Hoffman and Seth Ex
Outline
bull Use of Planting Trials in Forestry
bull Understanding Nelder Plots
bull Analytical Challenges
bull Example from South Dakotabull Density Effects on Size and Growthbull Lessons learned in assessing drought
resistance and resilience
Use of Planting Trials in ForestryCompetitionldquoWhen the immediate supply of a single factor necessary for growth falls below the combined demands of the individual plants competition beginsrdquo
~ Clements (Donald CM 1963 Competition among crop and pasture plants Adv Agron 15 1-118)
Use of Planting Trials in ForestryBlock Replicated Experimentsbull There is extensive literature about
the use of block replicated spacing studies
bull Guiding many silvicultural systems in western forests
400 TPH
800 TPH
Use of Planting Trials in ForestryBlock Replicated Experimentsbull These approaches utilize an area based approach to define
the sampling unit (ie each block is 1 sample)bull This study of 2 species
bull ~5 acres per block setbull 6 replicatesbull 12 densitiesbull 110 trees in each
6 x 12 x 110 = 7920 trees to track
~30 acres invested
Add a second species double everything
Understanding Nelder PlotsIndividual Focused ndash Systematic Experimentsbull John Nelder ndash a British Statistician trying to identify
ideal agricultural plant spacingbull Nelder JA 1962 New kinds of systematic designs for spacing
experiments Biometrics 18 283-307
bull Proposed 5 designs for varying spacing and rectangularity
Ia Ib Ic Id II
Density Rectangularity Both Both Both
Understanding Nelder PlotsIndividual Focused ndash Systematic Experimentsbull The Ia design has been the most widely adapted for
forestry applicationsIa
Density
bull Maintains rectangularity at ~11 while varying spacing
bull Each tree along a spoke represents a different density
bull Each spoke represents a replicatebull While this shows one quadrant these are
commonly installed as full circles
Individual Focused ndash Systematic Experiments
Understanding Nelder Plots
bull Full plots can be divided to investigate site prep species providence etc
bull Effects are separated by guard spokes
bull Density is maintained by guard archesbull This scenario produces 4
replicates of 9 densitiesbull Depending on spacing this could
take as little as 1 acre
bull Multiple plots could be used to investigate across site index
Individual Focused ndash Systematic Experiments
Understanding Nelder Plots
bull Example of mixed species planting for assessing intra-species competition
14 densities5 replicates0325 acres
625 ndash 25267 TPH
Individual Focused ndash Systematic Experiments
Understanding NelderPlots
bull Replicated Douglas-fir plots in Oregonbull Done with a modified Nelder Ia design
Douglas-fir - Diameter Breast Height by Age and ArcNewton amp Cole Nelder Plots
000
200
400
600
800
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1200
1400
1600
1800
0 5 10 15 20 25 30 35
Age (years)
Dia
met
er (i
nche
s)
DF 17DF 16DF 15DF 14DF 13DF 12DF 11DF 10DF 9DF 8DF 7DF 6DF 5DF 4DF 3DF 2DF 1
36 years old16 Densities48 Replicates
5 plots