Stem form responses to differing areas of weed control around

planted Douglas-fir trees

Robin Rose, Douglas A. Maguire, and Scott Ketchum

Department of Forest Science

Oregon State University

Introduction

Discerning differences in stem form and volume among silvicultural treatments.

Introduction

DBH and height respond to control of competing vegetation.

Consequently stem volume also responds to vegetation control.

Introduction

As trees develop under intensive management:Form differs from a cone

(/12)D2H,Trees large enough for existing

volume or taper equations.

Introduction

Application of volume and taper equations:Regional development;May not include intensively managed

stands;Averages lose subtle differences;

Introduction

Volume and taper equations:Most are functions of only DBH and

HT.Consequences:

Insufficient for detecting treatment differences.

One solution

Measure upper stem diameters.Assess existing volume or taper

equations.Develop new site-specific

equations.

Past work

Upper stem measurements were made at sites near Marcola and Summit:Fit Kozak’s variable-exponent taper

equation:Tested parameters across treatments;No treatment effect was found.

Past work

Compared empirical volumes to Bruce and DeMars (1974) volume estimates.Bias increased with progressively

more weed control.

Past work

Compared volumes to a coneControl:

Cone underpredict volume,Trees more parabolic.

Weed control:Cone overpredicts volume,Tree more neiloid.

Objective

Compare upper stem measurements to those predicted by Jim Flewelling’s taper system.

Methods

SitesSummit, OR:

Central region of the Oregon Coast Range.

Marcola, OR:Western Cascade Mountain

foothills.

Summit

Marcola

Methods

Experimental design Completely randomized design, 8 treatments, 3 replicates, Plot area = 0.112 ac, 49 seedlings planted at 9.8 ft square

spacing.

Methods

Treatments No herbicide, 4 ft2 full control, 16 ft2 full control, 36 ft2 full control, 64 ft2 full control, 100 ft2 full control, 100 ft2 woody vegetation control, 100 ft2 herbaceous vegetation control.

1-ft 2-ft 3-ft

4-ft 5-ft

4 ft2

64 ft2

16 ft2

36 ft2

100 ft2

Methods

Diameter outside bark was collected at tree base, breast height, 8 ft, and every 4 ft above 8 ft.

Observed DOB’s were compared to those predicted by Flewelling system. Consistent bias – inferences unaffected Changing bias – inferences questionable

Results

Average differences:Summit:

DOB overpredictedAcross most of stem profile

Marcola:Low at upper and lower stem positions.High at middle stem positions.

Difference = observed - predicted

0

5

10

15

20

25

30

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3

Difference (in)

Hei

gh

t (f

t)

Marcola

Summit

positive difference--model underpredicts diameternegative difference--model overpredicts diameter

Results

Averages by treatment:General overprediction over stem

profileLargest overpredictions:

Upper stem positionsGreater for more intensive control

Difference = observed - predictedSummit and Marcola averaged

0

5

10

15

20

25

30

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2

Difference (in)

Hei

gh

t (f

t)

4

1636

64

1000

herbwoody

positive difference--model underpredicts diameter

negative difference--model overpredicts diameter

100

0

4

DiscussionIf Flewelling predictions are

regional averages:More intensive weed control

Narrower upper stem profiles.Less intensive weed control

Slightly narrower lower stem profiles.

Results

Treatment differences by site:Marcola:

Underpredicts near base (greater weed control);

Underpredicts near top;Overpredict near middle of tree.

Difference = observed - predictedMarcola site only

0

5

10

15

20

25

30

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

Difference (in)

Hei

gh

t (f

t)

4

1636

64

1000

herbwoody

positive difference--model underpredicts diameternegative difference--model overpredicts diameter

1000

4

Results

Treatment differences by site:Summit:

Overpredicts over entire stem profile;

Overpredictions increase with greater weed control.

Difference = observed - predictedSummit site only

0

5

10

15

20

25

30

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2

Difference (in)

Hei

gh

t (f

t)

4

1636

64

1000

herbwoody

positive difference--model underpredicts diameter

negative difference--model overpredicts diameter

100

4 0

Conclusions

Biases in predicted DOB’s are small.

Systematic bias among treatments.Bias the estimated effects of

treatments on stem profiles.Formal statistical analyses on

implications are continuing.