Knowledge of old-growth Juniperus occidentalis woodlands, which occur in central and eastern Oregon, is limited. Wise management of these woodlands necessitates a better understanding of the community ecology. The community structure of woodlands at seven sites in three areas of central Oregon was studied. Measurements taken at nine plots per site included tree density, canopy cover, heights, diameters, and canopy areas; cover of each understory species and other ground covers; density of shrubs by species and condition; density of woody debris as downed pieces and standing dead trees; and topographic and soil parameters. Tree cores were taken for aging, although heartwood rot is pervasive in older trees. Factors of interest included cover and richness in all vegetative layers, variability within and between sites, and comparison of J. occidentalis woodlands to other old-growth communities. J. occidentalis woodlands were found to have a minimum of 80 trees over 200 years old per hectare, canopy cover of 10-35%, and understory cover of less than 20%. Woody detritus was primarily retained aloft and decomposed by weathering. Tree morphology was highly variable, but decadence was common. Outward physical attributes did not appear to be reliable predictors of tree age. Shrub cover was strongly correlated (r��=0.66) with the combination of elevation, ground cover by rock, and clay content of the soil. Perennial grass cover increased with elevation and the sand-sized soil fraction (r��=0.46). Understory cover, dominated by perennial grass, showed a weaker correlation with the same parameters (r��=0.20). Other significant findings included correlation of juniper cover with elevation, sand. and heat load (r��=0.38). Tree cover was found to increase by almost 1% for each 1% increase in sand content of the soil and by almost 8% for each 100m increase in elevation, while heat load, based on aspect. had a smaller effect. Plots grouped strongly by area. suggesting that there is a stronger influence of area than site on community composition for most of the sites and that differences between areas overwhelm the differences within areas. / Graduation date: 1999

Many resource management controversies indicate disagreement about the possible intended and unintended effects of management actions on ecosystems. Researchers have documented a variety of negative effects on specific ecosystems, e. g. the degradation of salmonid habitat due to mass wasting (Hagans et al. 1986). While the effects of some management actions are reversible, others change systems capacities and are therefore irreversible, e.g. the poisoning of Kesterson Wildlife Refuge with selenium due to agricultural practices (Schuler 1987). The difference between reversible and irreversible management effects is often a matter of scale. Management actions that are out of concordance with the properties of a system have the potential to irreversibly change a system if applied over large spatial and temporal scales. Using the method of contextual watershed classification (Warren 1979) the concordance of forest management with the properties of the Yaquina drainage (an Oregon coastal watershed of 220 sq. mi. size) and its environmental class (the North-central Coast Range) are evaluated. For this purpose, the watershed and its environment are classified according to five components: climate, substrate, biota, water, and culture. Properties are selected that are rather invariant and general, and therefore reflect the potential capacities of system and environment. The climatic, geologic, geomorphic, and hydrologic characteristics are compared to trophic relationships and life history traits of selected tree species in an attempt to understand the biophysical relationships in the forest environment that dominates the watershed. It is found that commonly applied harvest regimes are out of concordance with the biophysical environment and thus have the potential to lead to resource loss. Alternative management practices that would be more concordant with resource properties are proposed. The influence of dominant world views (namely mechanism, realism, rationalism, individualism, utilitarianism, and elitism) on the forest planning process and on the opinions of community leaders is evaluated. It is found that forest management practices, although they are out of concordance with the biophysical environment, are in concordance with the larger cultural environment and the perceptions and opinions of local community leaders. Hence, adopting new practices that are more concordant with the biophysical environment will be difficult. The major hindrance is located in the economic sphere. Concerns relating to the economical sphere are discussed and a probable route to more concordant resource use is proposed. / Graduation date: 1989

Graduation date: 2006 / Canopy gap formation is a major factor contributing to maintenance of overstory species diversity and stand structure in forests and may be integral to development of understory shrub and herb layers as well. Acknowledgement of gap formation as a fundamental feature of natural forests has led to consideration of gaps as an option in forest management regimes. This study examined understory vegetation communities across canopy gaps created as a part of the Density Management Study (DMS), which investigates the effectiveness of a thinning regime in promoting late-successional habitat development in young Douglas-fir forests of western Oregon. Patterns in understory vegetation community composition in and around 0.1 and 0.4ha gaps created as a part of the DMS treatment were investigated. The primary goal of this research was to investigate the potential role of canopy gap creation in fostering heterogeneity in understory vegetation communities, and to examine the extent of gap influence on the surrounding thinned forest matrix. Tree species distributions have been shown to partition across gaps in tropical forest systems through differential responses of species to gradients in resource availability, a pattern known as gap partitioning. In temperate forests, understory vegetation communities are much more diverse than the overstories, and display a greater array of habitat requirements. Therefore, understory communities may be more likely than overstories to exhibit gap partitioning in these forests. Patterns in understory community composition across gaps suggest that gap partitioning has occurred. The strength of this partitioning effect appears to differ between gap sizes, as smaller gaps showed a less powerful effect. Abundance of ruderal species was strongly related to gap partitioning in larger gaps, while smaller gaps were dominated by competitor species. Partitioning may be related to an interactive relationship between harvest-related ground disturbance and resource gradients. Therefore, considerations of gap partitioning processes should take into account intensity and spatial distribution of ground disturbance in relation to resource gradients. In addition, conditions necessary for the expression of gap partitioning in understory vegetation communities may be rare in natural gaps in this region. The influence of gaps on understory vegetation communities in the surrounding forest appears to be relatively small. This small influence extent may help explain the lack of a stand level response to gap formation in these stands. Larger gaps exhibit a slight influence on the understory plant community in the surrounding forest to the north of the gap. In small gaps, there seemed to be an influence of the surrounding forest on gap interiors, resulting in an area of influence smaller than the physical gap area. This relationship may indicate that the area of gap influence on understory vegetation may not scale linearly with physical gap size. Species diversity was higher in gap interiors than in surrounding thinned forests. However this effect was partially due to the presence of exotic species, which showed an affinity for gap interiors. Late successional associated species were negatively related to gap interiors, but only in the larger gap size. Gap creation appears to be promoting small scale species diversity in these stands, but creation of large gaps may also promote the establishment of exotic species and may have a negative effect on late successional associated species. However, any and all of these effects may be transient, as understory communities will be strongly affected by overstory re-establishment, and related changes in resource availability. In general, gap formation may influence small-scale stand heterogeneity as evidenced by understory plant communities, but this effect may rely strongly on the nature of gap formation and intensity of disturbance related to this formation.