A Young Douglas-fir Plantation Growth Model for the Pacific Northwest
Nick Vaughn
University of Washington
College of Forest Resources
Outline• Current status of the model
• A review of the datasets
• Model details
• Predictive abilities
• Timeline
Current Status• Have a model form for height growth
– Base function with H0 and SI as predictors
– Modifiers for Density, Relative height and Veg
• Choosing between forms for DBH– Similar to the height growth function
• Can somewhat predict changes of Veg– Just started, still need to test
Data review• Two datasets
– SMC Type III (5/6 of the data)– RVMM project
• Different design, but similar measurements– All Conifers measured– Multiple measurements– Veg cover optically estimated on subplots– Both are missing a lot of data on Veg treatments
Data review• Some differences
– SMC data is from designed experiment– RVMM from real-world stands– Hardwoods treated different– RVMM data has only one remeasure (2-year)– RVMM veg measured in same year as trees
Data review• Fitting model using data with associated Veg
measures for each tree measurement• Heights measured at both beginning and end of
period• Site Index computed on stands using last
measurements,– Some < age suggested for such calculations (~10 years)
• Useable tree-growth observations– RVMM: 4591
– SMC: 24320
x RVMM Coastal
x RVMM Cascade
x SMC Type III
Data review• Range of stand ages
Model Details• Height growth model:
),,(),(),(),( 043201 THHfTHfVHfSIHfH toptoptop
where:
0H is initial Height (ft)
topH is Top-height of the plot (ft)
SI is Site Index (Flewelling’s curves, base=30)
T is Trees per acre
V is plot Shrub cover (%)
H is 1-year Height growth (ft)
Model Details• Height growth model – Veg. modifier:
– At low Htop:More vegetation = less growth
– As Htop increases, this effect goes to 0
VHvvVHf toptop )exp(1),( 212
Model Details• Height growth model – Density modifier:
– At low Htop:More density = more growth
– As Htop increases, effect lessens.– After Htop reaches about 26 feet:
More density = less growth
TdHddHdTHf toptoptop )()(1),( 23213
Model Details• Height growth model – Relative height mod:
– Relative height = heighti/Htop
– Lower relative ht. = less growth– As Htop and/or Density increase, this effect gets
stronger
)/log()exp(1),,( 010432
toph
toph
top HHHThTHHf
Model Details• Diameter growth model:
),,(),(),(),,( 043201 THHfTHfVHfBASIDfD toptoptop
where:
0D is initial Diameter (in)
topH is Top-height of the plot (ft)
SI is Site Index
T is Trees per acre
V is plot Shrub cover (%)
D is 1-year Diameter growth (in)
BA is Basal Area per acre
Model Details• Shrub vegetation dynamics model:
),,,,( 0 topHTBASIVfV
where:
0V is initial Shrub Vegetation cover (%)
topH is Top-height of the plot (ft)
SI is Site Index
T is Trees per acre
BA is Basal Area per acre
V is 1-year Veg cover change (%)
Predictive Abilities• Height growth model:
R2 = 0.578
Predictive Abilities• Diameter growth model:
R2 = 0.590
Predictive Abilities
Predictive Abilities
Predictive Abilities
Predictive Abilities
Predictive Abilities
Predictive Abilities
Predictive Abilities
Timeline
• “Finish” modelling by June– Done = satisfied with results
• Write-up done and defend by August
• Coding is already underway.
Questions?
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