B.

Cross

Figure 1.--A. Grand fir with 3-year-old dead (spike) top. sections at various heights in the same tree showing associated discoloration and decay.

Figure 3.--A. Grand fir with a forked top caused by tussock moth defoliation 9 years ago. B.

showing the buried original leader.

Figure 5.--Mortality and dead tops
caused by Douglas-fir tussock
moth defoliation during the
1972-74 infestation in the
Blue Mountains.

Many trees with dead tops were available for study in these localities, therefore, trees were selected with a wide range of ages, diameters at breast height, and diameters at the base of dead tops.

Sampling took place at eleven localities near King Mountain, Malheur N.F.--the site of a 1963-65 tussock moth outbreak. Seven stands were sampled near Long Meadows Guard Station, Umatilla N.F. where a severe tussock moth infestation occurred from 1945 to 1947. Past salvage logging had removed many top-damaged trees in the two older infestation areas. Trees sampled in these areas were usually selected as encountered, unless we could determine by observation from the ground that a dead top was caused by recent bark beetle attacks.

Dead and deformed tops of sample trees were examined to establish the year in which the tops were killed (Wickman and Scharpf 1972, also see footnote 1) in order to attribute the probable cause of death to defoliation, secondary insect attack, or other causes. Since trees weakened by defoliation are susceptible to attack by beetles for several years (Wickman 1963), tops killed by secondary insects during, or within 3 years after the known infestation, were considered tussock moth damaged (fig. 6). An exception was in the oldest epidemic in the Long Meadows area, where trees with tops killed from 21-35 years ago (instead of 26-31 years) were considered damaged by tussock moth defoliation. The age range for this infestation was expanded because of the difficulty and probable errors in aging older dead tops. Some of the most recently killed tops probably originated during a spruce budworm outbreak which occurred in the early 1950's.

Figure 6.--Secondary bark beetle attack of grand fir weakened by tussock moth defoliation in the King Mountain infestation from 1963-65.

tussock moth defoliation were studied; 37 in the King Mountain area; and only 14 in the Long Meadows area (table 1). Trees found to be top-killed either before or more than 3 years after the infestation occurred in a given locality were studied for comparative purposes (table 1). Top-killing in these trees was considered to be caused by other (unknown) agents.

TREE DISSECTION AND MEASUREMENT

Selected trees with top-damage were felled at a stump height of 1 foot and dissected into 16-foot logs to a top d.i.b. of 4 inches for cubic

Table 1--Numbers of grand fir study trees top-killed before, during, and after three Douglas-fir tussock moth infestations in the Blue Mountains

1To be considered as tops killed by tussock moths, the age should range from 26-31 years. The age range for this infestation was expanded, however, because of the difficulty of accurately aging older dead tops.

5

volume measurement. Board-foot volumes of trees 11-in d.b.h. and larger were measured to a top d.i.b. of 6 in. Disks were cut immediately above, at the base of, and below the damage. Ring counts were made at these points to determine when the top was killed. D.b.h., tree age at stump height, and location and description of decay indicators were noted for each tree. Logs were dissected further to measure the extent of decay associated with top-damage or other indicators.

We recorded the type of top-damage (i.e. spike top, broken top, fork, crook, etc.), and the height to and basal diameter of the killed top. Also recorded was the length of the dead top, the length and diameter of any new leaders, the year of top-kill, the extent of decay below and above the base of killed tops, and the presence or absence of secondary insect attack.

A program (PACUL) was developed at the Pacific Northwest Forest and Range Experiment Station to compute volumes of trees and decays. Cubicfoot volumes of logs and decay columns were calculated by the Smalian formula. No arbitrary cull rules were used in cubic-volume measurement. Gross board-foot volumes of logs in trees 11-inch d.b.h. and larger were computed by the Scribner log rule. Board-foot deductions for decay, shake, and frost cracks were made by the squared-defect method. In board-foot measurements, logs more than two-thirds defective were considered totally cull.

ISOLATION AND IDENTIFICATION OF DECAY FUNGI

Culture blocks, approximately 3 in3 (7.6 cm3) in size, were taken from disks cut at the base of and just below the dead top in most trees. These samples were always taken when discoloration or decay was present. Additional culture blocks were taken at various intervals from long decay columns. The blocks were placed in plastic bags and stored in an ice chest until taken to the laboratory.

In the laboratory, the blocks were split with a sterile chisel, and small wood chips were removed from freshly exposed discoloration or decay and placed on 2.5 percent malt agar slants in culture tubes. Inoculated tubes were incubated at room temperature.

The types (hymenomycetes, fungi imperfecti, and bacteria and yeasts) of microorganisms which had been isolated were noted. The hymenomycetous fungi were identified by Frances L. Lombard, Center for Mycology Research, Forest Products Laboratory, Madison, Wisconsin.

STATISTICAL METHODS

Regression and covariance analyses were used to test the relationships between cubic- and board-foot decay (as a percent of gross merchantable tree volumes) and top-kill age, base diameter of dead tops, presence of secondary insect attack, and to derive equations which can be used to predict the extent of defect associated with grand fir dead tops. The equations were used to tabulate defect as (1) percentages of gross merchantable tree cubic-foot and Scribner board-foot volumes, and (2) ex