Growth Model Runoff II

REVISED 09/10/2005

 

Welcome to the Growth Model Users Group’s GROWTH MODEL RUNOFF II, a follow-up to our first Runoff conducted in 2002.  GMUG is interested in looking at the performance of commonly available Pacific Northwest Douglas-fir growth models in projecting stands with thinning and fertilization treatments.  We are not looking for “truth”; we just want to understand how each model simulates treatment effects.

 

There are three stands (tree lists provided in the attached spreadsheet):

 

Before Thinning

 

 

 

 

 

 

 

 

stand

Kings Site

tpa

ba

Dq

Avg ht

Avg htlc

rd

Bh age

Total age

1

120

608

146.9

6.7

58.2

31.6

56.9

22

29

2

100

732

138.4

5.9

50.1

20.4

57.0

17

25

3

140

384

151.5

8.5

59.7

27.1

51.9

17

19

 

These are actual stands that span a range of site qualities and are relatively young plantations.  Stands were sub-sampled for height and crown ratio.  For trees without field heights and crowns, regressions specific to each stand were used to impute missing values.  The tree lists are provided in the before and after thinning conditions so that we have uniform thinning conditions.  The thinnings are all to 180 trees per acre with a d/D less than 1.0.  The after thinning stand statistics are:

 

After Thinning

 

 

 

 

 

 

stand

Kings Site

tpa

ba

Dq

Avg ht

Avg htlc

rd

1

120

180

63.1

8.0

64.1

32.8

22.3

2

100

180

47.8

7.0

54.3

21.2

18.1

3

140

180

86.3

9.4

62.5

27.5

28.2

 

We invite you to project the no thin and thinned tree lists for 20 years, with and without a fertilization treatment of 200 pounds of N per acre applied at the beginning of the projection.  At minimum, we would like to get back from you trees per acre, basal area, average height (or dominant height) and cubic volume at as fine a time step as your model permits (i.e., annually, every five years, 10 years, etc.).  Optimally, you can provide projected tree lists (with tree number) at the 5, 10, 15, and 20 year projection points.  If you can provide tree lists, please put them in a spreadsheet in a format similar to those provided in the attached spreadsheet.

 

Please submit your projections to us by October 28, 2005.  Results and model comparisons will be compiled and presented at our next GMUG meeting (winter 2005).

 

Thank you in advance for your help with this project.

 

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