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D E M O
Demonstration of Ecosystem Management Options Study

A Large-Scale Experiment in Structural Retention Harvests in Pacific Northwestern Forests

 

Effects of Varying Levels and Patterns of Green-Tree Retention on Amount of Harvesting Damage

John R. Moore1, Douglas A. Maguire2,
David L. Phillips2, and
Charles B. Halpern3

1Department of Forest Resources
John.Moore@ForestResearch.co.nz

2Department of Forest Science
Oregon State University
Corvallis, Oregon 97331

3College of Forest Resources
Box 352100
University of Washington
Seattle, WA 98195-2100

We provide a brief overview of this work below. For full text see:

Moore, J. R., D. A. Maguire, D. L. Phillips, and C. B. Halpern. 2002. Effects of varying levels and patterns of green-tree retention on amount of harvesting damage. Western Journal of Applied Forestry 17:202-206.

In this study, we assessed the magnitude and distribution of tree bole damage resulting from implementation of the retention harvest treatments that comprise the DEMO experiment (see Treatment Implementation and Experimental Design).

Among the six study blocks (see Study Area), Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) comprised 75% of all measured trees (55 and 20%, respectively), and the proportion of trees damaged was similar for both species. Suppressed trees tended to be more susceptible to damage than were trees in other crown classes (Table 1).

Table 1.  Distribution of fresh scars by crown class.

Crown class

All Trees

Damaged Trees

% of total trees

% within crown class

% of all damaged trees

Dominant

4.1

3.5

2.2

Co-dominant

42.3

6.0

39.6

Intermediate

19.2

5.8

17.3

Suppressed

32.7

8.1

40.9

Unknown/dead

1.7

0.0

0.0

A greater proportion of trees in the dispersed retention treatments were damaged than in the aggregated treatments (Table 2). Only in the two dispersed retention treatments were levels of damage significantly different from the controls (p<0.05). The greatest proportion of damaged trees occurred in the 15% dispersed retention treatment and was likely due to the wider dispersion and higher intensity of felling and yarding operations associated with this treatment. The pattern of damage across treatments was similar for both small ( £25 cm DBH) and large (>25 cm DBH) trees. Some evidence was also found that sites with gentler slopes had less damage than those with steeper topography.

Table 2.  Proportion (%) of trees with fresh scars among the six experimental treatments.  Means with an asterisk differ significantly (p<0.05) from the control.  Fresh scars in the control treatment may reflect wind damage.

   Treatment

All trees

Trees £25 cm DBH

Trees >25 cm DBH

   100% control

0.8

1.1

0.6

   75% aggregated

2.2

3.4

1.3

   40% dispersed

17.0*

18.1*

15.4*

   40% aggregated

2.4

2.7

2.3

   15% dispersed

27.2*

25.0*

29.3*

   15% aggregated

1.6

1.7

1.8

Given these initial patterns of harvest-related damage, we expect that the future incidence of stem rot and growth reductions will be greatest in the dispersed retention treatments.