Modeling the Effects of GeneticImprovement on Diameter andHeight Growth
Greg Johnson
Weyerhaeuser Company
Credits
This work was made possible by the
Vernonia Tree Improvement Cooperative:
BLM, Crown Zellerbach, Hampton,International Paper, Oregon Department of Forestry,Longview Fibre, Stimson Lumber, Willamette Industries
and was supported by Willamette Industries
Study Objectives
•To determine if the growth of improvedgenotypes differs in quantifiable ways fromWoods-Run stock.
•If differences are apparent, to describe thenature and magnitude of the effect.
•Make recommendations for the adjustmentof growth models to account for geneticeffects.
The Vernonia 1st Generation Tree ImprovementProgram
•Initiated by Roy Silen and Joe Wheat in 1968 as acooperative between Longview Fibre, International PaperCompany, Crown Zellerbach Corporation, and the OregonDepartment of Forestry.
•900 trees were selected from wild stands using roadsideselection. The working assumption was that thispopulation approximated woods-run performance - i.e.,there was little, if any, selection pressure during theidentification of the parents.
•Progeny tests consisted of open-pollinated progeny of the900 parents planted on twelve test sites.
Parent Tree Distribution
The Vernonia 1st Generation Tree ImprovementProgram
•Three spacings were used (8.5'x8.5', 12'x12', and 14'x14')with each location receiving a single spacing assignment(spacing confounded with location).
•There are four locations at each of the spacings.
•Test design was reps-in-sets, where sets of approximately50 families (creating 18 sets) were treated as separateexperiments with replication within each experiment.
•Each set was replicated five times at each test location forall but three of the twelve locations, where two replicateswere installed.
The Data
•Sets 8, 10, and 14 were used from 11 of the12 sites. These sets were part of a study onthe long-term stability of family rankings.
•Periodic data from measurements at 7, 10,15, 20, 25, and 30 years were used.
•Only two sites were measured at age 7, withthe remaining nine sites measured at age 10.
The Data
•A common method of selecting parents foradvanced generation breeding using a reps-in-sets design is to pick the top rankingfamilies from each set.
•For this analysis, an elite subset of familieswas defined as the top five families (basedon height at age 15 from seed) from each set(top 10%).
Heights for each Set at Selection Age (15)
NOTE: Test design
does not allow sets
to be compared.
Selection Effect
Selection age
Analytical Procedure
•Fit height and diameter growth equations toentire test population (Woods-Run).
•Test the hypothesis that the Elite subset’sgrowth can be explained by the Woods-Runequations.
•If the hypothesis is rejected, quantify thedifferences.
Height Growth
•Modeled height growth as a function ofheight and CCH:
•Reliable estimates of site index were notavailable. Location was treated as a fixedeffect.
Height Growth Equation Performance -Woods-Run
Woods-Run Height Growth Performance -Elite Subset
Woods-Run
Elite
Elite height growth
is under-predicted
by the woods-run
equation.
Woods-Run Height Growth Performance -Elite Subset
Height Growth
•No significant correlations found between gainand tree, stand, location, or age variables.
•Average ratio of Elite height growth to Woods-Run Prediction: 1.024
•The initial conditions (starting heights) need to beknown prior to growth projection (cannot assumeequal distributions).
•Recommendation: use a simple ratio adjustment toindividual-tree height growth prediction.
Adjusted Elite Height Growth PredictionResiduals
•Modeled diameter growth as a function ofDBH, BA, and BACL:
•Crown ratios were not available.
•Reliable estimates of site index were notavailable. Location was treated as a fixedeffect.
Diameter Growth
Diameter Growth Equation Performance -Woods-Run
Woods-Run Diameter Growth Performance -Elite Subset
Woods-Run
Elite
Woods-Run Diameter Growth Performance -Elite Subset
Woods-Run Diameter Growth Performance -Elite Subset
Diameter Growth
•Elite trees’ diameter growth does not differ fromWoods-Run when tree size, stand density andsocial position are considered.
•Elite diameters are larger than Woods-Run at anygiven age.
•Gain in DBH may be due to trees reaching breastheight earlier, or a genetic effect prior tomeasurements taken in this study.
Diameter Growth
IFuncoupled•Recommendation: do not adjust diametergrowth equations IF diameter growthprediction is uncoupled from height.
•If height growth is increased and diametergrowth is not, improved trees shoulddevelop with less taper (larger height todiameter ratio).
Height - Diameter Relationship at Age 30
What’s Next?
•Realized Gains Trials
–Large plots with an elite family or elitemixture) are being installed.
–Can test the effect of an improved“neighborhood”.
–Allows examination of multiple gain levels.
–Provides an opportunity to observe growth atearly ages (find out where DBH and earlyheight gain come from).
What’s Next?
•Measure additional growth traits:
–Crown length
–Crown width
•Test Genetics X Density interaction.
•“Calibrate” growth models.