CROP TREE GROWTH AND QUALITY TWENTY- FIVE YEARS AFTER PRECOMMERCIAL THINNING IN A NORTHERN CONIFER STAND

Leah M. Phillips1, Robert S. Seymour1, and Laura S. Kenefic2

1Department of Forest Ecosystem Science, 5755 Nutting Hall, University of Maine, Orono, ME 044692USDA Forest Service, Northeast Research Station, 686 Government Rd., Bradley, ME 04411

EXPERIMENTAL DESIGN:

Nine 19.5 x 19.5 m measurement plots were utilized for this study; four 2.4 x 2.4 m PCT plots and five unspaced

plots.

The crop tree sample consisted of:20 balsam fir & 17 red spruce in the unspaced plots; and

20 balsam fir & 23 red spruce in the spaced plots, for a total of 80 crop trees.

DATA COLLECTION:

Crop trees were climbed using ladders for stem form measurements up the tree bole. Diameter measurements included: DBH, diameter 1.0 m below bh, and diameter at

1.0 m intervals up to the live crown base. Other measurements included: THT, height to the lowest live

branch (LLB) & lowest live whorl (LLW); and branch diameters between

1.0 - 2.0 m above bh and between LLB & LLW.

KEY OBJECTIVES:

Compare crop tree growth and productivity between species and treatments as determined by growth

efficiency (GE);

Compare stem form of crop trees between species and treatments; and determine the extent of branchiness

and its effect on wood quality.

Table 1.1 ANOVA output with probability values.

Species Treatment Species x Treatment

Dependent Variable

Dbh (cm) 0.0096* < 0.0001* 0.2126

Total height (m)

< 0.0001* 0.5073 0.0981

Crown length (m)

< 0.0001* < 0.0001* 0.00292*

PLA (m2) 0.6597 < 0.0001* 0.0237* CPA (m2) 0.0134* < 0.0001* 0.8758

GEPLA (dm3/ m2)

< 0.0001* 0.5871 0.7556

GECPA (dm3/ m2)

< 0.0001* 0.3229 0.0523*

Tree volume (m3)

0.0049* < 0.0001* 0.0697

Tree LAI 0.0049* 0.1690 0.0399* Ave. branch size (cm)

0.0672 < 0.0001* 0.1845

# branches 0.3196 < 0.0001* 0.1985 Knot volume

ratio 0.0109* < 0.0001* 0.1444

Height/ diameter ratio

0.0656 < 0.0001* 0.9201

Form class 0.0654 0.0005* 0.5401

Table 1.2. Means comparison of selected crop tree characteristics.

Balsam fir unspaced

Balsam fir spaced

Red spruce unspaced

Red spruce spaced

Dbh (cm) 12.84 17.21 12.11 15.15 Total height

(m) 12.65 13.29 11.21 10.94

Crown length (m)

6.49 9.34 6.06 7.25

PLA (m2) 21.09 48.37 25.82 41.40

CPA (m2) 4.91 8.62 7.09 10.55 GEPLA

(dm3/ m2) 0.19 0.18 0.15 0.15

GECPA (dm3/ m2)

0.85 1.05 0.68 0.62

Tree volume (m3)

0.08 0.15 0.07 0.10

Tree LAI 4.57 5.82 4.50 4.25 Ave. branch size (cm)

1.07 1.38 1.10 1.57

# branches 12.05 17.90 12.29 16.00 Knot volume

ratio 0.002 0.004 0.003 0.005

Height/ diameter

ratio 100 78 95 73

Form class 0.79 0.76 0.77 0.73

RESULTS:

Conclusions:

Treatment: projected leaf area (PLA), crown projection area (CPA), total tree volume, stem taper, knot volume,

and the # and size of branches differed between treatments. Growth efficiency (GE) & tree-level LAI

were not affected by treatment.

Species: GE, CPA, total tree volume, tree-level LAI, and knot volume differed between species. PLA, stem taper,

and the # and size of branches did not differ.

Fig. 1.1 Growth efficiency (GE dm3/m2) in relation to projected leaf area (PLA m2) for balsam fir crop trees.

0 20 40 60 80Projected leaf area (m2)

0.05

0.10

0.15

0.20

0.25

0.30

Gro

wth

effi

cien

cy (

dm3 /

m2 )

UnspacedSpaced

Treatment

GE = b0+b1*(PLA)

Fig. 1.2 Growth efficiency (GE dm3/m2) in relation to projected leaf area (PLA m2) for red spruce crop trees.

0 20 40 60 80

Projected leaf area (m2)

0.05

0.10

0.15

0.20

0.25

0.30

Gro

wth

effi

cien

cy (

dm3 /

m2 )

UnspacedSpaced

Treatment

Fig. 1.3 Growth efficiency (GE dm3/m2) in relation to crown projection area (CPA m2) for balsam fir crop trees.

0 10 20 30Crown Projection Area (m2)

0.0

0.5

1.0

1.5

2.0

Gro

wth

Effi

cien

cy (

dm3 /

m2 )

UnspacedSpaced

Treatment

Fig. 1.4 Growth efficiency (GE dm3/m2) in relation to crown projection area (CPA m2) for red spruce crop trees.

0 10 20 30Crown Projection Area (m2)

0.0

0.5

1.0

1.5

2.0

Gro

wth

Effi

cien

cy (

dm3 /

m2 )

UnspacedSpaced

Treatment

GE = b0+b1*(PLA)

GECPA = b0+b1*(CPA) GECPA = b0+b1*(CPA)

Fig. 1.5 Total tree volume (m3) in relation to diameter at breast height (DBH cm) for balsam fir crop trees.

5 10 15 20 25Diameter at breast height (cm)

0.00

0.06

0.12

0.18

0.24

0.30

Tre

e V

olum

e (m

3 )

UnspacedSpaced

Treatment

Fig. 1.6 Total tree volume (m3) in relation to diameter at breast height (DBH cm) for red spruce crop trees.

5 10 15 20 25Diameter at Breast Height (cm)

0.00

0.06

0.12

0.18

0.24

0.30

Tre

e V

olum

e (m

3 )

UnspacedSpaced

Treatment

Tree volume = b0+b1*(DBH)

STUDY AREA:

The Penobscot Experimental Forest (PEF) is located in Bradley, Maine. The study reported here is part of an

ongoing precommercial thinning (PCT) study (STUDY 58) established in 1976 by the USDA Forest Service. The stand was regenerated by a two-stage shelterwood

method; where 46% of the overstory was removed in the establishment harvest in 1957, and the remaining

overstory was removed in 1967.