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?