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Modeling the Effects of Genetic Improvement on Diameter and Height Growth. Greg Johnson Weyerhaeuser Company. Credits. This work was made possible by the Vernonia Tree Improvement Cooperative:
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Modeling the Effects of Genetic Improvement on Diameter and Height 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 improved genotypes differs in quantifiable ways from Woods-Run stock. • If differences are apparent, to describe the nature and magnitude of the effect. • Make recommendations for the adjustment of growth models to account for genetic effects.
The Vernonia 1st Generation Tree Improvement Program • Initiated by Roy Silen and Joe Wheat in 1968 as a cooperative between Longview Fibre, International Paper Company, Crown Zellerbach Corporation, and the Oregon Department of Forestry. • 900 trees were selected from wild stands using roadside selection. The working assumption was that this population approximated woods-run performance - i.e., there was little, if any, selection pressure during the identification of the parents. • Progeny tests consisted of open-pollinated progeny of the 900 parents planted on twelve test sites.
The Vernonia 1st Generation Tree Improvement Program • 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 approximately 50 families (creating 18 sets) were treated as separate experiments with replication within each experiment. • Each set was replicated five times at each test location for all but three of the twelve locations, where two replicates were installed.
The Data • Sets 8, 10, and 14 were used from 11 of the 12 sites. These sets were part of a study on the 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, with the remaining nine sites measured at age 10.
The Data • A common method of selecting parents for advanced generation breeding using a reps-in-sets design is to pick the top ranking families from each set. • For this analysis, an elite subset of families was defined as the top five families (based on 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 age Selection Effect
Analytical Procedure • Fit height and diameter growth equations to entire test population (Woods-Run). • Test the hypothesis that the Elite subset’s growth can be explained by the Woods-Run equations. • If the hypothesis is rejected, quantify the differences.
Height Growth • Modeled height growth as a function of height and CCH: • Reliable estimates of site index were not available. Location was treated as a fixed effect.
Woods-Run Height Growth Performance - Elite Subset Elite height growth is under-predicted by the woods-run equation. Woods-Run Elite
Height Growth • No significant correlations found between gain and 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 be known prior to growth projection (cannot assume equal distributions). • Recommendation: use a simple ratio adjustment to individual-tree height growth prediction.
Diameter Growth • Modeled diameter growth as a function of DBH, BA, and BACL: • Crown ratios were not available. • Reliable estimates of site index were not available. Location was treated as a fixed effect.
Woods-Run Diameter Growth Performance - Elite Subset Woods-Run Elite
Diameter Growth • Elite trees’ diameter growth does not differ from Woods-Run when tree size, stand density and social position are considered. • Elite diameters are larger than Woods-Run at any given age. • Gain in DBH may be due to trees reaching breast height earlier, or a genetic effect prior to measurements taken in this study.
Diameter Growth • Recommendation: do not adjust diameter growth equations IF diameter growth prediction is uncoupled from height. • If height growth is increased and diameter growth is not, improved trees should develop with less taper (larger height to diameter ratio).
What’s Next? • Realized Gains Trials • Large plots with an elite family or elite mixture) are being installed. • Can test the effect of an improved “neighborhood”. • Allows examination of multiple gain levels. • Provides an opportunity to observe growth at early ages (find out where DBH and early height gain come from).
What’s Next? • Measure additional growth traits: • Crown length • Crown width • Test Genetics X Density interaction. • “Calibrate” growth models.