Western Cascades Research Articles

MICROSITE CONTROLS ON TREE SEEDLING ESTABLISHMENT IN CONIFER FOREST CANOPY GAPS

Tree seedling establishment and growth were studied in experimental canopy gaps to assess the effect of heterogeneity of regeneration microsites within and among gaps in mature conifer forests. Seedlings were studied for two years in closed-canopy areas and in recently created gaps ranging in size from 40 to 2000 m2 in four stands of mature (90–140 yr) and old-growth (>400 yr) Douglas-fir forest in the western Cascade Range of central Oregon and southern Washington, USA. We examined the relative importance of substrate type, shade from logs and shade cloth, density of understory vegetation, gap size, and forest age on the success of Pacific silver fir (Abies amabilis), Douglas-fir (Pseudotsuga menziesii), and western hemlock (Tsuga heterophylla). Seedlings originating from seed sown on experimental microsites were compared with seedlings regenerating naturally on a range of microsites. Seedling establishment was greater on decayed wood than on forest floor or mineral soil in closed-canopy areas, particula...

Morphological and molecular variation among populations of octoploid fragaria virginiana and F. chiloensis (rosaceae) from North America

Relationships among 37 North American octoploid strawberry populations were studied by evaluating 44 morphological traits and 36 randomly amplified polymorphic DNA (RAPD) markers. Both data sets were analyzed by principal components analysis and UPGMA clustering based on genetic distances. Morphological data defined five groups: east of the Missouri River (Fragaria virginiana ssp. virginiana), the Black Hills (F. virginiana ssp. virginiana and ssp. glauca), from the eastern Cascades to the eastern Rocky Mountains (F. virginiana ssp. glauca), the western Cascades and Olympic Peninsula (F. virginiana ssp. platypetala), and the Pacific coast (F. chiloensis). Canonical discriminant analysis clearly discriminated populations into these provenances, suggesting that these groups are morphologically distinct. RAPD data defined three groups, one with F. virginiana ssp. virginiana and ssp. glauca, another with F. chiloensis, and a third with F. virginiana ssp. platypetala. The latter was more similar to F. chiloensis than F. virginiana, suggesting it is likely a subspecies of F. chiloensis. All octoploid North American strawberries have likely derived from a common ancestor and have differentiated into F. chiloensis and F. virginiana by adapting to moister and drier environments, respectively.

Species Replacement During Early Secondary Succession: The Abrupt Decline of a Winter Annual

The factors that contribute to species establishment and decline determine the rate and pattern of successional change. We tested a commonly held assumption that competitive displacement is responsible for the loss of species during succession. Manipulative field experiments were used to examine the effects of interspecific competition on the population dynamics of Senecio sylvaticus, a winter annual that briefly dominates postharvest sites in the western Cascade Range of Oregon. Senecio increased in density 400-fold from the first to the second growing season after disturbance but decreased precipitously in year 3 to 10% of the density and 0.5% of the biomass per plot of the previous year. Although interspecific competition reduced the cover and biomass of Senecio during its peak year, it had little or no effect on either the population increase or decline; the pattern of change was similar among all treatments. These counterintuitive results underscore the importance of testing, not simply assuming, that interspecific competition is responsible for the replacement of a species during succession.

SPECIES REPLACEMENT DURING EARLY SECONDARY SUCCESSION: THE ABRUPT DECLINE OF A WINTER ANNUAL

The factors that contribute to species establishment and decline determine the rate and pattern of successional change. We tested a commonly held assumption that competitive displacement is responsible for the loss of species during succession. Manipulative field experiments were used to examine the effects of interspecific competition on the population dynamics of Senecio sylvaticus, a winter annual that briefly dominates postharvest sites in the western Cascade Range of Oregon. Senecio increased in density 400-fold from the first to the second growing season after disturbance but decreased precipitously in year 3 to 10% of the density and 0.5% of the biomass per plot of the previous year. Although interspecific competition reduced the cover and biomass of Senecio during its peak year, it had little or no effect on either the population increase or decline; the pattern of change was similar among all treatments. These counterintuitive results underscore the importance of testing, not simply assuming, that interspecific competition is responsible for the replacement of a species during succession.

Green-Tree Retention: Consequences for Timber Production in Forests of the Western Cascades, Oregon

National Forest management in the Pacific Northwest is adopting ecosystem management, in which the entire forest ecosystem is considered, as well as commodity production. Silvicultural prescriptions in ecosystem management often include retention of some live trees following timber harvest (green-tree retention) with the primary goal of maintaining biodiversity. How green-tree retention will affect growth and tree species composition of future forests is an important question. We took a retrospective approach to this question by using past disturbance as an analogue to green-tree retention following timber harvest. We used United States Department of Agriculture (USDA) Forest Service timber inventory plot data from the Cascade Mountains of Oregon and southwest Washington (western hemlock zone). We selected 132 unmanaged stands with a tree cohort of 70–110 yr old (regeneration) or a tree cohort of 70–110 yr old with an overstory of large trees 200+ yr old (remnants), representing clearcuts and stands harvested with green-tree retention, respectively. Regeneration basal area (BA) across species and for Pseudotsuga menziesii tended to decline with increasing remnant density (R2 = 0.51 and 0.60, respectively), but only after remnant densities reached ≈15 trees/ha; the relationships were roughly sigmoidal. Part of the effect of remnants on regeneration results from remnants’ occupation of space, making it unavailable to the regeneration. After adjusting regeneration BA to account for remnants’ space occupation, the relationship between regeneration BA and remnant density weakened by about half, implying that remnant effects resulted from both space occupancy and other factors associated with remnants. Total-stand BA was relatively constant across remnant densities. Remnant density was not related to tree-species diversity in the regeneration.

Reply to the comment by D. D. Blackwell and G. R. Priest on “ heat flow from four new research drill holes in the Western Cascades, Oregon, U.S.A.” by S. E. Ingebritsen, M. A. Scholl and D. R. Sherrod [ Geothermics 22, 151–163 (1993)

Reply to the comment by D. D. Blackwell and G. R. Priest on “ heat flow from four new research drill holes in the Western Cascades, Oregon, U.S.A.” by S. E. Ingebritsen, M. A. Scholl and D. R. Sherrod [ Geothermics 22, 151–163 (1993)

Comment on “ heat flow from four new research drill holes in the Western Cascades, Oregon, U.S.A.” by S. E. Ingebritsen, M. A. Scholl and D. R. Sherrod [ Geothermics 22, 151–163 (1993)

Comment on “ heat flow from four new research drill holes in the Western Cascades, Oregon, U.S.A.” by S. E. Ingebritsen, M. A. Scholl and D. R. Sherrod [ Geothermics 22, 151–163 (1993)

CHANNEL NETWORK EXTENSION BY LOGGING ROADS IN TWO BASINS, WESTERN CASCADES, OREGON1

ABSTRACT: Based on field surveys and analysis of road networks using a geographic information system (GIS), we assessed the hydrologic integration of an extensive logging‐road network with the stream network in two adjacent 62 and 119 km2 basins in the western Cascades of Oregon. Detailed surveys of road drainage for 20 percent of the 350 km road network revealed two hydrologic flow paths that link roads to stream channels: roadside ditches draining to streams (35 percent of the 436 culverts examined), and roadside ditches draining to culverts with gullies incised below their outlets (23 percent of culverts). Gully incision is significantly more likely below culverts on steep (< 40 percent) slopes with longer than average contributing ditch length. Fifty‐seven percent of the surveyed road length is connected to the stream network by these surface flowpaths, increasing drainage density by 21 to 50 percent, depending on which road segments are assumed to be connected to streams. We propose a conceptual model to describe the hydrologic function of roads based on two effects: (1) a volumetric effect, increasing the volume of water available for quickflow and (2) a timing effect, altering flow‐routing efficiency through extensions to the drainage network. This study examines the second of these two effects. Future work must quantify discharge along road segments connected to the stream network in order to more fully explain road impacts on basin hydrology.

Isotope hydrology of voluminous cold springs in fractured rock from an active volcanic region, northeastern California

The more than 1550 km2 (600 mi2) Hat Creek Basin in northeastern California is host to several first magnitude cold springs that emanate from Quaternary basaltic rocks with individual discharge rates ranging from 1.7 to 8.5 m3 s−1 (60–300 ft3 s−1). Stable isotope (δ18O, δD, δ13C) and 14C measurements of surface and groundwater samples were used to identify recharge areas, and to evaluate aquifer residence times and flow paths. Recharge locations were constrained from the regional decrement in meteoric water δ18O values as a function of elevation, determined to be −0.23‰ per 100 m for small springs and creek waters collected along the western Cascade slope of this region. In general, the large-volume springs are lower in (δ18O than surrounding meteoric waters, and are inferred to originate in high-elevation, high-precipitation regions up to 50 km away from their discharge points. Large spring 14C abundances range from 99 to 41 % modern carbon (pmc), and most show evidence of interaction with three distinct carbon isotope reservoirs. These reservoirs are tentatively identified as (1) soil CO2 gas equilibrated under open system conditions with groundwater in the recharge zone [δ13CDIC ≈ −18‰, 14C > 100 pmc], (2) dissolved carbon equilibrated with atmospheric CO2 gas [δ13CDIC ≈ +1‰, 14C > 100 pmc], and (3) dissolved carbon derived from volcanic CO2 gas emissions [δ13CDIC≈0‰, 14C=0 pmc]. Many regional waters show a decrease in 14C abundance with increasing δ13C values, a pattern indicative of interaction with dead carbon originating from volcanic CO2 gas. Several lines of evidence suggest that actual groundwater residence times are too short (⩽ 200 years) to apply radiocarbon dating corrections. In particular, water temperatures measured at springs show that deep groundwater circulation does not occur, which implies an insufficient aquifer volume to account for both the high discharge rates and long residence times suggested by 14C apparent ages. The large springs also exhibit rapid decreases in flow during periods of drought that suggests a high level of aquifer interconnectivity to the recharge area. The estimated amount of volcanic CO2 dissolved in surface and groundwater originating from the Lassen highlands is consistent with the conversion of approximately 10% of the geothermal CO2 flux into dissolved inorganic carbon.

Peak Flow Responses to Clear‐Cutting and Roads in Small and Large Basins, Western Cascades, Oregon

This study quantified long‐term changes in streamflows associated with clear‐cutting and road construction and examined alternative hydrologic mechanisms to explain stream hydrograph changes in the Cascades Range, western Oregon. We examined differences in paired peak discharges for 150 to 375 storm events for five basin pairs, using 34‐year records from two pairs of 60‐to‐101‐ha experimental basins in the H. J. Andrews Experimental Forest, and 50‐to‐55‐year records from three pairs of adjacent basins ranging from 60 to 600 km2. Forest harvesting has increased peak discharges by as much as 50% in small basins and 100% in large basins over the past 50 years. These increases are attributable to changes both in flow routing due to roads and in water balance due to treatment effects and vegetation succession.

Riparian Bryophytes of the H. J. Andrews Experimental Forest in the Western Cascades, Oregon

The knowledge of the distribution and habitat demands for bryophytes in the Pacific Northwest is scarce, and few published quantitative accounts of the flora are present. The present paper includes habitat description, elevational range, substrate preference, and frequency estimates for more than 130 riparian mosses and liverworts found in old-growth Pseudotsuga-Tsuga forests of the H. J. Andrews Experimental Forest, Oregon. The data are based on 360 samples distributed among 42 sites covering 1st to 5th order streams and 420 to 1250 m. TWINSPAN analysis resulted in 6 sample groups, representing samples from different elevations, geomorphic surfaces, and stream sizes. The most common mosses are Eurhynchium oreganum, Isothecium stoloniferum, Hypnum circinale, and Dicranum fuscescens. Among the hepatics Scapania bolanderi, Cephalozia lunulifolia, and Porella navicularis are the most abundant species. Most species are rare at both site and sample plot level, and this is especially true for acrocarps where more than one-third of the observed species occurred in only one or two sites or/and samples. Four of the occurring species (i.e., Antitrichia curtipendula, Buxbaumia piperi, Douinia ovata, and Ptilidium californicum) are listed for special management and/or regional surveys. Bryophytes constitute an important and conspicuous component of old-growth forests in the Pacific Northwest (Lesica et al. 1991; McCune 1993; Schofield 1988); however, few studies on the abundance and distribution of mosses and liverworts have been conducted. The epiphytic flora, composed of bryophytes and lichens, of old-growth Douglas-fir has been shown to be species rich and influences nutrient dynamics and overall production in old-growth stands (Pike et al. 1975, 1977). Besides these studies, however, there has been until now no published account of factors influencing the distribution of individual species within old-growth forests (see however Peck et al. 1995; Schofield 1976). Dispite this lack of study, many bryophytes are considered to be dependent of old-growth conditions (FEMAT 1993; Soderstrom 1988). Thus, effective management of the bryophyte flora, which is an important forest product of the region (Peck 1990; Schlosser et al. 1992) and a significant part of forest biodiversity, is constrained by lack of knowledge. Riparian zones are thought of as key elements in the forested landscape, and preservation of these is a major goal of forest management (FEMAT 1993). Of the mosses and liverworts considered as vulnerable in the Pacific Northwest (USDA 1994), many occur in riparian areas. This association is dependent on many factors, but the occurrence of a wide range of different substrates, disturbance patterns, and a moist microclimate are important contributors to the diversity in these zones (Glime & Vitt 1987; Vitt et al. 1986). The present paper reports habitats and frequencies of species found in riparian areas of old-growth Pseudotsuga-Tsuga forests in the western Cascades of Oregon. A general treatment of the bryophyte community patterns will be published elsewhere.

Crown structure in western hemlock, Douglas-fir, and grand fir in western Washington: trends in branch-level mass and leaf area

Extensions of a basic allometric equation applied in predicting total foliage of individual trees were developed to estimate foliage and woody components of individual branches in western hemlock (Tsugaheterophylla (Raf.) Sarg.), Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), and grand fir (Abiesgrandis (Dougl. ex D. Don) Lindl.). Nine initial equations were fitted on both nonlinear and log-transformed scales to data collected in the western Cascade Mountains of Washington. In all cases, the logarithmic form of each equation provided the best fit to the data based on a modified likelihood criterion and residual patterns. Branch diameter was the overall best predictor of branch foliage and woody mass; however, significant (p = 0.05) improvements in fit were obtained when other structural and positional variables were included in the equations (e.g., foliated branch length and depth into crown). The effects of fertilization and site (locality) differences were explored using indicator variables for western hemlock branches. Significant site effects were observed for intercept terms for all three branch components (total foliage area, total foliage mass, and total woody mass), while fertilization effects were observed in interaction with relative height above crown base for both foliage components.

Origin of freshwater-diatom-rich pyroclastic-debris-flow deposit in a shallow-marine Tertiary forearc basin, NW Oregon

ABSTRACT An unusual freshwater-diatom-bearing pyroclastic-debris-flow deposit is present within the shallow-marine upper Eocene to Oligocene Pittsburg Bluff Formation of northwestern Oregon. The subaerially generated pyroclastic-debris flow rapidly debouched into the shallow-marine environment. The flow formed a wedge-shaped deposit, up to 3.5 m thick, that is mappable over several square kilometers. Thickness and maximum clast size decrease offshore; near the distal margins the debris flow mixed with seawater and became a high-density shelf turbidity current. Where emplaced above storm wave base, the deposit was locally reworked to form a thin lag conglomerate. Thalassinoides burrows are present in the upper 30 cm of the deposit. The rhyodacite chemical and mineral composition, regional geologic setting, and thickness and clast-size variations indicate a nearby highly explosive calcalkaline volcanic source to the northeast (i.e., Western Cascade are). This deposit documents the earliest known Cascade arc explosive event that directly affected sedimentation in the Tertiary forearc basin of western Oregon. A sanidine- and biotite-bearing ash fall tuff 3 m above the debris-flow deposit was derived from a backarc eruptive source (e.g., Oligocene John Day Formation). This tuff yielded an 40Ar/39Ar date of 29.83 Ma. The well-preserved diatom flora within the debris-flow deposit matrix extends the geologic range of some genera (e.g., Gomphonema) and widens the geographic distribution of others (e.g., Gomphopleura). Possible scenarios to explain the presence of exclusively freshwater diatoms in the debris-flow deposit in this shallow-marine section include: (1) a primary pyroclastic debris flow may have passed through a diatom-rich lake between the site of eruption and its entrance into the sea; (2) freshly erupted pyroclastics temporarily blocked a river drainage, creating an alpine lake that produced the debris flow upon dam failure; (3) primary pyroclastic debris may have been vented directly through a caldera or crater lake rich in diatomaceous sediment.

Postglacial Vegetation and Climate of the Cascade Range, Central Oregon

Pollen data from two sites provide information on the postglacial vegetation and climate history of the Cascade Range. Indian Prairie in the western Cascade Range was colonized by subalpine forests of Pinus, Picea, and Tsuga and open meadows prior to ca. 12,400 14C yr B.P. The treeline lay 500 to 1000 m below its modern elevation and conditions were cooler than at present. From ca. 12,400 to ca. 9950 14C yr B.P. Abies became important and the forest resembled that presently found at middle elevations in the western Cascade Range. The pollen record implies a rise in treeline and warmer conditions than before. From ca. 10,000 to 4000-4500 14C yr B.P., conditions that were warmer and effectively drier than today led to the establishment of a closed forest composed of Pseudotsuga , Abies, and, at lower elevations, Quercus and Corylus . During this period, Gold Lake Bog in the High Cascades was surrounded by closed forest of Pinus and Abies. The early-Holocene pollen assemblages at both Indian Prairie and Gold Lake Bog lack modern analogues, and it is likely that greater-than-present summer radiation fostered unique climatic conditions and vegetation associations at middle and high elevations. In the late Holocene, beginning ca. 4000-4500 14C yr B.P., cooler and more humid conditions prevailed and the modern vegetation was established. A comparison of these sites with others in the Pacific Northwest suggests that major patterns of vegetational change at individual sites were a response to large-scale changes in the climate system that affected the entire region.

Tertiary Facies and Paleoenvironments Along the Coast Range and Western Cascade Margin, Western Oregon: ABSTRACT

Tertiary Facies and Paleoenvironments Along the Coast Range and Western Cascade Margin, Western Oregon: ABSTRACT

Distribution of coarse woody debris in a mountain stream, western Cascade Range, Oregon

The distribution of coarse woody debris in a fifth-order Cascade Range (Oregon) stream system was examined from a geomorphic point of view. The number, volume, location, orientation, decay class, and pool formation roles of coarse woody debris were investigated. The processes of coarse woody debris production, transport, and storage, which vary with channel and valley floor geomorphology, are responsible for the pattern of coarse woody debris distribution on valley floors. Channel width and sinuosity are the main factors that control production, storage sites, and hydrologic effects of coarse woody debris. The amount of coarse woody debris and the number of pool-forming pieces are relatively high in wide, sinuous reaches, where a complex structure of floodplains and riparian forests develops in association with a braided channel pattern. These relations are transferable to other systems with similar relations of coarse woody debris piece length to channel width.

Extent of partial melting beneath the Cascade Range, Oregon: Constraints from gravity anomalies and ideal‐body theory

The spatial correlation between a horizontal gradient in heat flow and a horizontal gradient in residual gravity in the Western Cascades of central Oregon has been interpreted by others as evidence of the western edge of a pervasive zone of high temperatures and partial melting at midcrustal depths (5–15 km). Both gradients are steep and relatively linear over north‐south distances in excess of 150 km. The Western Cascades gravity gradient is the western margin of a broad gravity depression over most of the Oregon Cascade Range, implying that the midcrustal zone of anomalous temperatures lies throughout this region. Ideal‐body theory applied to the gravity gradient, however, shows that the source of the Western Cascades gravity gradient cannot be deeper than about 2.5 km and is considerably shallower in some locations. These calculations are unique determinations, assuming that density contrasts associated with partial melting and elevated temperatures in the crust do not exceed 500 kg m−3. Consequently, the gravity gradient and the heat flow gradient in the Western Cascades cannot be caused directly by the same source if the heat flow gradient originates at midcrustal depths. This conclusion in itself does not disprove the existence of a widespread midcrustal zone of anomalously high temperatures and partial melting in this area, but it does eliminate a major argument in support of its existence. The gravity gradient is most likely caused by lithologic variations in the shallow crust, perhaps reflecting a relict boundary between the Cascade extensional trough to the west and Tertiary oceanic crust to the west. The boundary must have formed prior to Oligocene time, the age of the oldest rocks that now conceal it.

Growth Rates of Two Epiphytic Cyanolichen Species at the Edge and in the Interior of a 700-Year-Old Douglas Fir Forest in the Western Cascades of Oregon

Thalli of two epiphytic lichens, Lobaria oregana (Tuck.) Miill. Arg. and Pseudocy- phellaria rainierensis Imsh., were collected from the canopy of an old-growth forest. Thalli were individually attached to nylon monofilament and transplanted into the crowns of four trees, two growing in the forest interior and two growing on the edge of a clearcut, at heights between 35 and 45 m above the ground. Half of the transplants in each tree were derived from thalli collected in the interior and half were derived from thalli collected on the edge. After one year, L. oregana transplants grew significantly less on the edge than they grew in the interior. The source of P. rainierensis thalli significantly affected transplant growth rate. Thalli that came from the interior and were transplanted to the edge did not grow, on average, while thalli that came from the edge and were transplanted back to the edge grew well.

Heat flow from four new research drill holes in the Western Cascades, Oregon, U.S.A.

Conceptual models of the thermal structure of the Oregon Cascade Range propose either (1) a narrow zone of magmatic heat sources, flanked by shallow heat-flow anomalies caused by lateral ground-water flow; or (2) a wide zone of magmatic heat sources, with localized, generally negligible ground-water effects. The proposed narrow heat source coincides with the Quaternary volcanic arc, whereas the wider heat source would extend 10–30 km west of the arc. To test the models, four new heat-flow holes were sited west of the Quaternary arc but within the area of the proposed wide heat source. The sites are separated from the Quaternary arc by topographic divides and (or) major river valleys, so that heating by regional-scale ground-water flow seems unlikely. Measured heat flow (76±5 mW mm −2) was significantly lower than the values predicted by interpolation from an existing heat-flow contour map (95±7 mW m −2). The lower values are consistent with a narrow zone of magmatic heat sources. The complete heat-flow data set consists mostly of shallow (100–200 m) data and defines lobate highs around hot-spring groups in the Western Cascades. However, all of the deepest holes in the study area (44°–45°15′N) show hydrologic gradient disturbances extending to depths >200 m, so the shallow data must be extrapolated with caution.

Gradients in Epiphyte Biomass in Three Pseudotsuga-Tsuga Forests of Different Ages in Western Oregon and Washington

Epiphyte biomass on branches and trunks was estimated for 42 individual felled trees, distributed among three Pseudotsuga menziesii-Tsuga heterophylla stands aged 95, 145, and 400+ years, in the western Cascade Range of Oregon and Washington, then extrapolated to the whole stands by regression techniques. Epiphytes were sorted into four groups defined by ecological roles rather than taxonomy: cyanolichens, alectorioid lichens, lichens, and bryophytes. In general the spatial sequence of dominance of these four groups, from upper canopy to forest jloor, was: other lichens, alectorioid lichens, cyanolichens, and bryophytes. The zones of these functional groups of epiphytes apparently migrate upward in forests through time. For example the Hypogymnia and Platismatia that dominate throughout canopies in young forests are found primarily in the upper canopies of old forests. Similarly, bryophytes enter a stand near the forest jloor and gradually expand their dominance upwards. Epiphyte biomass was greatest in the old-growth stand, with about 2.6 t/ha. In the two younger stands total epiphyte biomass was about 1 t/ha. The old-growth stand differed from the younger stands in having over 1 t/ha of cyanolichens, while this group was essentially absent from the younger stands. As a synthesis of these and previous results, a similar gradient hypothesis is proposed: epiphyte species are ordered similarly on three distinct spatial and temporal gradients: 1) vertical differences in species composition within a given stand, 2) species compositional differences among stands differing in moisture regime but of the same age, and 3) changes in species composition through time in a given stand.