Montane forest vegetation as it occurs on the east flank of the central Oregon Cascades has provided excellent conditions for a "natural experiment" in the use of various methodologies in studying vegetational distribution. This "experiment" has reflected on some theory and practice for the discipline of plant synecology. Detailed descriptions, analysis, and interpretation of the data also document present conditions in relation to the past and allow prognostication of future changes, which in turn may be of silvicultural importance for a portion of this forest type found extensively on the east flank of the Sierra Nevada-Cascades cordillera. A major objective of this study was to determine the relative merits and deficiencies of attempting to transpose to this vegetation the methods of analyzing vegetation based on the individualistic or continuum philosophy of phytosociology that has developed and been practiced principally in the north-central United States. These attempts have been contrasted to strengths and short-comings of poly-climax theory, the most widely used basis of vegetational classification in the Pacific Northwest, in relation to the analysis of this and other vegetation types. The influences on and of these varying interpretations have been outlined and presented in tabular form. The study area is nearly ideal for posing these questions because edaphic and topographic factor complexes remain surprisingly uniform. The vegetation is superimposed in apparent primary response to the condensed gradient of total precipitation due to the orographic "rain shadow" effect from the Cascades intervening in this region of prevailing westerly winds. The stability of the vegetation concomitant with this nearly ideal set of "naturally controlled" physical conditions, minimized variations in successional status, except that due to fire exclusion. This latter variation, however, paralleled the complex gradient studied, a happenstance which allowed silviculturally important interpretations to be made. Stable vegetation occurring in general contiguity allowed stands to be sampled systematically, leaving little doubt concerning the validity of interpolation between stands and the areal representation of the samples. Another main objective of the study was to obtain and analyze data to substantiate the hypothesized influence of light periodic ground fires in initiating and maintaining the characteristic mosaic of size-age class distribution of ponderosa pine. The data also yielded a quantitative indication of the shift in species composition and dominance that is in largest measure due to the continued exclusion of fire by man for approximately the past 50 years. From these data the future appearance of the forest can be surmised, and silvicultural manipulations can be suggested that are best in harmony with the ecology of these forests. The circumstances that provided this "natural experiment" have allowed the author to demonstrate certain limitations to direct transposition of methods widely used in other areas of the United States, or even the Pacific Northwest, when description and analysis in closest feasible parallel to the nature of the patterns of vegetational distribution found in this area are attempted. This finding catalyzed the development of a method incorporating cluster analysis of matrices of relative parameter-weighted coefficients of association into a means of making very objective synecological delimitations. The dendrograms derived from this analysis allow a "sliding scale" of stratification to be made in this vegetation of most realistically intermediate, yet of more continuously variable than unit-association nature.

This study was conducted to describe variation of riparian vegetation in an Oregon Coast Range system according to geomorphic characteristics and in relation to streamflow. Specific objectives of this study were to: I) examine if the vegetation composition and structure of the riparian forest varied among channel-reach morphologies, 2) examine how the composition and structure of the riparian forest changed with distance from the stream, and 3) extract major underlying environmental gradients explaining riparian forest community from riparian vegetation data. A 30 m x 30 m sample site was randomly located on each side of upper Camp Creek in each of 19 reaches, and within each site three consecutive 30 m x 10 m belt-transects established perpendicular to the stream flow. Overstory and understory vegetation was sampled in each belt transect. Environmental variables sampled included slope, aspect, height above summer low flow, elevation above sea level. Non-metric Multidimensional Scaling and Indicator Species Analysis was used to describe characteristics of riparian plant communities. Distinct riparian vegetation patterns were observed in upper Camp Creek with increasing distance from stream. Both overstory and understory vegetation quickly changed with increasing distance from stream. Areas within ten meters from stream were characterized as mesic riparian environments while areas twenty meters away from stream were characterized as upland conifer forest environments. Vegetation composition was ordered along an inferred moisture gradient from streamside to hillslope, and distance from stream and height above summer low flow were almost equally correlated to the gradient. Tall shrubs including salmonberry, sword fern and vine maple are important component of riparian vegetation. Channel-reach morphology little differentiated riparian vegetation. A few species were significantly abundant in a specific reach of channel morphology. However, results of this study about relationships between channel-reach morphology and riparian vegetation were inconclusive.

Riparian areas that can be used as reference sites on which to base goals of vegetation restoration have not been documented in the Oregon Coast Range. I examined the composition and distribution of unmanaged riparian overstories in the central Oregon Coast Range along nine streams which have experienced minimal disturbance from Native Americans and no detectable disturbance since Euro- American settlement. I systematically located transects along nine streams, alternating sides of the streams. Each transect ran perpendicular to the stream and was subjectively divided into different vegetative and/or topographic units called landscape units (LU's). Rectangular plots were placed in each LU for characterization. LU l's were units that were closest to the stream, and LU2's were farther from the stream. Red alder was the most frequently found tree species on both terraces and slopes, and on all LU1 's. On LU2 terraces, alder was also the most frequently found species, but on LU2 slopes, Douglas-fir had the highest frequency. Red alder, Sitka spruce, and bigleaf maple were most commonly found occupying terrace sites, although bigleaf maple might be best adapted to conditions on terraces towards the base of slopes. Conversely, western hemlock and Douglas-fir were most commonly found occupying slope sites. Western redcedar was infrequently found, likely due to seed source limitations. Age distributions and tree frequencies indicate that near-stream communities (LUI 's) and terraces experience both intense and minor disturbances, and they experience both types of disturbances more frequently than communities farther from the stream (LU2's) or on slopes. According to fire records and reconnaissance, all streams appear to have been burned about 145 years ago. When equating a shade-intolerant tree age that was younger than this last catastrophic fire date with a disturbance, calculations of disturbance frequency using four different approaches indicate that between 2.6 and 4.5 disturbances per km per century large enough to regenerate trees occurred since the last stand-resetting fire along the nine creeks sampled. Fifty-two percent of near-stream communities (LU1's) and 23% of communities farther from the stream (LU2's) contained no trees. This could be due to small plot size and/or high shrub competition. The No Tree overstory type was most similar in topographic conditions to the Pure Hardwood overstory type, suggesting that red alder and/or bigleaf maple might have previously occupied the No Tree sites and have since died leaving no or little evidence. It appears that a large-scale, intense disturbance such as fire is needed to allow the recruitment of trees into the shrub-dominated, No Tree areas, especially shade-intolerant trees such as Douglas-fir. Any single definition of natural riparian vegetation is nearly impossible to construct, mainly because most ecosystems are composed of vegetation mosaics that are always changing in time and space. This change is associated with environmental variability, disturbance, and inter- and intra-specific competition. Also, differences in exogenous environmental conditions between pre-settlement times (circa 1850) and today, suggest that historic vegetation, ecological conditions, and resulting successional pathways might not mirror the vegetation, ecological conditions, and successional pathways of currently unmanaged riparian areas. Instead, results from this study, revealing the existence of mixtures of hardwoods, conifers, and no-tree areas over lengths of a stream, should be perceived as just one of many possibilities for a riparian overstory reference model.