The effects of logging and slash‐burning on soil structure were investigated on three Reddish Brown Latosol soils in the Coast Range of Western Oregon. Soil samples of the surface 2 inches were collected at 50‐foot intervals along randomly located transects within the clear‐cut areas. Soil samples were also collected in the adjacent uncut timber. The condition of the surface soil was noted at 10‐foot intervals along the transects and was recorded as follows: lightly burned, severely burned, disturbed and unburned, or undisturbed. Sixty soil samples from each clear‐cut sampling area were analyzed in the laboratory for mechanical composition, organic matter content, and water stable aggregates. The soil surface conditions after logging and slash‐burning were as follows: lightly burned 44.7%, severely burned 8%, unburned 30.1%, and undisturbed 17.2%. Severe burning was the only treatment that had any significant effects upon soil structure, particle size distribution and soil organic matter content. Analysis of variance revealed that there was a significant decrease in the amount of clay present in the severely burned soils as compared with the soils under undisturbed timber. A 20.6% decrease in the degree of aggregation and a 61.1% decrease in organic matter content were also noted in the severely burned soils as compared with soils in the undisturbed timber. Other treatments had no significant effects upon the soils of the logged area. Since only 8% of the soil surface was severely burned, it is concluded that logging by the high lead method and slash‐burning in the fall after rainfall has occurred have had no appreciable detrimental effects upon soil structure in the area studied.

Nodulation, N accretion, and above‐ground biomass production were investigated in Ceanothus velutinus (snowbrush) stands developing following wildfire and salvage logging in second growth ponderosa pine (Pinus ponderosa Laws) and logging and slash burning in old growth Douglas‐fir stands [Pseudotsuga menziesii (Mirb.) Franco]. In the pine site 82% of the Ceanothus plants were nodulated the first year, whereas in the fir site only 42% were nodulated. Above‐ground snow‐brush biomass production at the end of 10 years was 48,000 and 54,000 kg/ha, respectively, for the pine and fir sites. Nitrogen accretion in biomass, litter, and soil for the 10‐year period was 715 and 1,080 kg/ha, respectively, for the pine and fir sites. The higher accretion in the fir site despite slower nodulation is due to more favorable temperature and moisture conditions at the fir site than at the pine site.

Symbiotic associations were established between nitrogen-fixing nonleguminous (actinorrhizal) snowbrush (Ceanothus velutinus Dougl.) seedlings and two categories of microorganisms: vesicular–arbuscular (VA) mycorrhizal fungi and a filamentous actinomycete capable of inducing nodule formation. The actinomycete is housed in nodules where fixation of atmospheric dinitrogen occurs and is made available to the host plant; the mycorrhizal fungus is both inter- and intra-cellular within the root tissue and may be found within the nodules. The two major nutrients, N and P, are made available and can be supplied to the host plant by these two symbiotic microorganisms. The root system of snowbrush seedlings was dually colonized by VA mycorrhizal fungi and a nitrogen-fixing actinomycete and the possibility of a direct interaction between the endophytes in the symbioses was investigated. Dually infected plants showed increases in total dry weight of shoots and roots, number of nodules, weight of nodular tissue, as well as higher levels of N, Ca2+, and P, and an increase in nitrogenase activity as measured by acetylene reduction.

Growth of planted Douglas‐fir seedlings was investigated on Reddish Brown Latosol soils on two cutover areas in the Cascade Mountains of western Oregon. In April 1955, 2‐0 seedlings were planted on tractor roads, in loose berm material adjacent to the tractor roads, and on undisturbed cutover condition. First‐year survival for all conditions was over 90%. Annual height measurements were made at the end of the 1955 and 1956 growing seasons. Differences in height growth between seedlings on the cutover condition and those on the berm and tractor road conditions were highly significant. Seedling growth differences between berm and tractor road conditions were also statistically significant in several instances. Soil analysis data indicated poor growing conditions on the tractor roads, particularly in regard to aeration, moisture, and N relationships.

Amorphous components predominated in the clay size fraction of samples taken across a climatic transect of soils from Mazama pumice in central Oregon. The amounts were greatest in the less intensely weathered horizons, i.e., in lower horizons and at drier sites of the transect. Crystalline minerals were present in relatively small percentages and were unexpectedly complex. The phyllosilicates included beidellite, montmorillonite, vermiculite, a micaceous component, chloritic intergrades, and chlorite. Non‐phyllosilicate minerals of the suite were gibbsite, plagioclase feldspars, and quartz. The amount and distribution of the individual clay size minerals varied within and between profiles.Results of clay mineral identification were evaluated with respect to environmental data available for the transect sites. The factors primarily controlling the processes responsible for 2:1 clay mineral genesis were hypothesized to be the vesicular structure and chemical composition of the pumice material. Other factors such as climate and vegetation were believed to govern local weathering intensity.