section. Section lines were drawn to scale on the photo- 

 graph and measured in millimeters. Next, two random 

 numbers were chosen between 1 and the scaled length 

 (about 100 mm, dependent on photo scale) of a section 

 border. The northwestern corner of the section was used 

 as the zero intersection on which to locate the randomly 

 drawn coordinates. The point described by the coordinates 

 was used as the plot center. 



Plots were selected according to two criteria: (1) site 

 must be forested or have once supported forests, and (2) 

 site must be less than 1.6 km from a trail or road. Plots 

 were selected in the order that sections were selected, 

 eight plots per National Forest. If the first selection was 

 unsuitable, then a ninth plot was selected. This process 

 was continued until all 15 sections within a National 

 Forest were used. If eight satisfactory plots were not 

 found, then the first discarded section was used again, 

 with the northeastern corner as the zero intersection for 

 the randomly drawn coordinates. The process continued 

 until eight satisfactory plots were obtained on each of the 

 15 National Forests. 



A line was drawn from the plot point on the photo to a 

 landmark along a road or trail. This became the witness 

 point. The distance between witness point and plot was 

 scaled from the photo. 



In the field, the photo was oriented, and the bearing 

 from the witness point to the plot was obtained from the 

 photo and recorded. A string-line recorder was used to 

 measure (nearest meter) the scaled distance from the 

 witness point to the plot, and a compass was used to 

 follow the designated bearing. If a stream or some other 

 impassable barrier blocked the chosen path to the desig- 

 nated plot, the complementary bearing and distance were 

 taken in the opposite direction. In a few cases, the desig- 

 nated distance was halved for the same reason. Ultimate- 

 ly, the main criterion was that the plot be located at the 

 end of a measured line of predetermined length. The eight 

 randomly chosen plots per National Forest provided a 

 total of 120 plots. An additional 19 aiixiliary plots were 

 taken in areas where Armillaria spp. were not found on 

 random plots. This provided a more encompassing sample 

 for future study of geographic variation of the fungus and 

 enhanced our knowledge of specific occurrence patterns. 



After traveling the designated distance, a plot center 

 was established at a tree or other major feature. Using a 

 compass and a string-Hne recorder, a plot 20 m on a side 

 (400 m^) was laid out with sides parallel and perpendicular 

 to the bearing. Key indicator plants were recorded, as 

 were aspects of topography, so that habitat type (based on 

 potential climax vegetation) of the plot could be deter- 

 mined (Pfister and Arno 1980). The vegetation was photo- 

 graphed. Roots of cut trees, wind-broken trees, and dead 

 trees (from seedling to mature) were inspected for rhizo- 

 morphs, fans, characteristic rotten wood, and root resin- 

 osis. The root systems of at least one living and apparent- 

 ly healthy representative of all major hardwood and 

 conifer species on the site were inspected for fans, rotten 

 wood, and attached rhizomorphs. The inspection consisted 

 of exposing the root collar and major roots to a depth of 

 about 0.3 m and a lateral spread of 0.5 to 1 m, then look- 

 ing for rot and fans by chopping. Living and apparently 

 healthy conifers that were selected for increment boring 



(cores to be used later to study relationships between Ar- 

 millaria activity and site productivity) were also inspected 

 for fans, resinosis, and attached rhizomorphs. These trees 

 were thoroughly inspected around half their root crowns 

 and along all major roots attached to the inspected por- 

 tion. This inspection required 1 to 3 hours to complete. 

 Any insect or disease problems were also noted. 



Sections of rhizomorphs 0.1 to 0.5 m in length were col- 

 lected and their source recorded. They had to be physically 

 attached to the host plant to be recorded as being from 

 that host. Rhizomorphs not so attached were recorded as 

 taken from the soil. The samples were placed in disposable 

 plastic culture tubes and taken to a field laboratory (motel 

 room). Each evening the day's collections (rhizomorphs, 

 bark fans, or rotten wood) were rinsed two times in tap 

 water, then sterihzed for 10 minutes in a 20 percent com- 

 mercial bleach solution. The bleach solution was decanted 

 and collections rinsed by filling the tube with sterilized 

 water, vigorously agitating, and decanting. They were 

 rinsed a second time and allowed to set for 10 minutes. 

 The final rinse was decanted, and sterilized rhizomorphs 

 were removed and cut into 5- to 10- mm segments. These 

 were placed, one each, in 10-mL plastic culture tubes con- 

 taining 1.5 percent malt extract medium. After 1 month, 

 all collections were verified for rhizomorph production in 

 culture as well as other cultural attributes typical of the 

 genus Armillaria. Some fans were taken directly from 

 their imderbark location and placed in the 10-mL tubes. 



All plots were classified by habitat type with dichoto- 

 mous keys based on Usts of indicator plants (Cooper and 

 others in press; Pfister and others 1977; Steele and others 

 1981). This classification was verified by an ecologist 

 through study of the plot photos and plant lists. Habitat 

 type of the few plots that occurred on fresh or regener- 

 ated clearcuts was determined by inspection of adjacent 

 stands. The plots were lumped by climax series for some 

 analyses and by habitat type for others. The proportion of 

 Armillaria occurrence on any host and as epiphytic rhizo- 

 morphs on hardwoods and conifers was calculated. Also 

 calculated was the proportion of epiphytic rhizomorphs 

 found on: (1) healthy conifers by species, (2) healthy hard- 

 woods (including dead parts of healthy plants), and 

 (3) dead conifer materials by plot. 



RESULTS 



Armillaria Distribution 



Chi-square analysis of the climax series revealed signifi- 

 cant heterogeneity regarding the probability of encounter- 

 ing Armillaria on randomly selected 0.04-ha plots 

 (table 1). Heterogeneity seemed to be associated with 

 plot productivity, as measured by average site index 

 (height of dominant and codominant trees at 50 years = 

 SI in table 1). We therefore arrayed the plots by habitat 

 type in order of increasing productivity within climax 

 series (table 2). The two least productive series (ABLA 

 and PSME)(see table 2 footnote for species code defini- 

 tions) showed a definite discontinuous distribution pattern. 

 Hot-dry, cold-dry, and frost-pocket habitat types appeared 

 not to support Armillaria. Two plots on cold-wet habitat 

 types (ABLA/STAM and ABLA/CACA) also faUed to yield 



2 



