Richard L. Everett

Fire history in the ponderosa pine/Douglas-fir forests on the east slope of the Washington Cascades.

We collected 490 and 233 fire scars on two ponderosa pine (Pinus ponderosa)/Douglas-fir (Pseudotsuga menziesii) dominated landscapes on the east slope of the Washington Cascades that contained a record of 3901 and 2309 cross-dated fire events. During the pre-settlement period (1700/1750‐1860), the Weibull median fire-free interval (WMFFI) and the mean firefree interval (MFFI) were 6.6‐7 years at both sites. The MFFI during the settlement period (1860‐1910) varied within 3 years of the pre-settlement value, but increased to 38 and 43 years for a truncated fire suppression period between 1910 and 1996. Increased variation in MFFI among aspect polygons suggests fire regimes have become more complex since Euro-settlement. In the pre-settlement period, an area equal to approximately 50‐60% of the study areas burned every 6‐7 years, an amount of fire disturbance apparently in balance with landscape and stand vegetation structure. Overlapping fires have created a complex mosaic of different fire histories on these forested landscapes. Mapped fire events from the 1700‐1910 showed 134 and 157 separate fire history polygons (FHP) at the two sites. Fire disturbance rates and patterns are suggested as ecologically defensible reference points for landscape heterogeneity to reduce the potential for catastrophic fires and to establish vegetation disturbance management guidelines. # 2000 Elsevier Science B.V. All rights reserved.

Seed Reserves in Soils of Successional Stages of Pinyon Woodlands

Seedlings emerging from soil, duff and litter samples from four microsites (duff, transition, interspace, shrub) and four successional stages (grass-forb, shrub-tree, tree-shrub, tree) were recorded for 6 weeks. Seed reserves in soils decreased in number and species diversity from early to late successional stages. Of seedlings emerging, 890% were annuals. The shrub microsite from the shrub-tree stage had the highest total and perennial seed reserves. As shrub cover decreased, the transition microsite between the duff and interspace became the most important source of total seed reserves, and the duff microsite became the most important source of perennial seed reserves. INTRODUCTION The temporal and spatial variation in seed reserves in soils is an important component in modeling succession (Major and Pyott, 1966; Livingston and Allessio, 1968; Kellman, 1970). Previous studies found that seed reserves decline from early to late stages of succession (Oosting and Humphreys, 1940; Olmsted and Curtis, 1947; Quick, 1956; Livingston and Allessio, 1968). In southwestern shruband grasslands, seed reserves are concentrated under or around shrubs and grasses, with few seeds in the barren area in between (Knipe and Springfield, 1972; Nelson and Chew, 1977). Seed reserves also vary with soil depth, with most of the reserves concentrated in the top 2-3 cm of soil (Floyd, 1966; Wesson and Wareing, 1969; Childs and Goodall, 1973; Strickler and Edgerton, 1976). The objective of this study was to determine variation in amounts and species of seed reserves in the soils from various stages of pinyon woodland succession. The most commonly identified stages of pinyon-juniper succession are: (1) annual grass-annual forb stage; (2) perennial grass-perennial forb stage; (3) shrub-perennial grass-perennial forb stage; (4) shrub-perennial grass-perennial forb-young tree stage; (5) mature treeshrub stage, and (6) climax tree stage (Arnold et al., 1964; Erdman, 1970; Barney and Frischknecht, 1974; Stager, 1977; Tausch and Tueller, 1977). In addition, distribution of seed reserves among seedbed components of the woodlands was examined. This seedbed consists of a mosaic of shrub litter, pinyon duff, bare ground (interspace) and transition microsites. SITE DESCRIPTION The study was conducted in April 1979 on the N-facing foothill slopes of the Sweetwater Mountains, 0.5 km SE of Walker, California (T. 8 N., R. 23 E., Sec. 27). The study area has a slope of 15 % and an elevation of approximately 1890 m. Average annual precipitation is 250 mm and mean annual temperature is 9.8 C. The soils are well-drained typic torripsamments of granitic parent material. The area is characterized by variations in understory and pinyon (Pinus monophylla) cover resulting from a combination of past use of wood products, livestock grazing, wildfires and disease or insect attacks. Within a recent burn and adjacent woodland area, four sites in different successional stages were identified as grass-forb, shrub-tree, tree-shrub and tree. The grassforb site is located on the 1973 Rock Creek burn. The burn was aerial-seeded in the 1Stationed at the Renewable Resources Center, University of Nevada, Reno 89512.

Structure of northern spotted owl nest stands and their historical conditions on the eastern slope of the Pacific Northwest Cascades, USA

Abstract The northern spotted (Strix occidentalis caurina) uses a wide array of nesting habitat throughout its current range and successfully reproduces in a variety of stand types on the eastern slope of the Pacific Northwest Cascades. The species has the ability to utilize dynamic forest stands that continue to undergo significant changes in tree density, proportion of tree size classes, and tree species composition. Current stand structure and composition reflect the results of timber harvest, reduced fire effects and ongoing successional and stand development processes. In nest stands, multi-layered canopy was more strongly expressed in numbers of both small ( 41 cm DBH) trees than in unoccupied stands of the same type within the owl neighborhoods. Tree density and the proportion of shade-tolerant tree species have increased significantly in spotted owl nest sites in both dry and wet forests since Eurosettlement. Barring disturbance, further increases in the dominance of shade-tolerant species should occur over time with continual change in nest stand structure and composition. The development of dense forest stands and ‘old-forest structural attributes’ as a result of reduced fire effects could be potential mitigating factors to the loss of old-forest habitat from harvest and should be considered in determining the available owl habitat in the eastern Cascades. However, old-forest structural attributes in dense, overstocked stands are at high fire hazard and should be viewed as transitional until old-forest habitat with improved sustainability becomes available.

Continuity in fire disturbance between riparian and adjacent sideslope Douglas-fir forests

Abstract Fire-scar and stand-cohort records were used to estimate the number and timing of fire disturbance events that impacted riparian and adjacent sideslope Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) forests. Data were gathered from 49 stream segments on 24 separate streams on the east slope of the Washington Cascade Range. Upslope forests had more “traceable” disturbance events than riparian forests in each of the valley types with a mean difference of 8–62%. Approximately 55–73% of the total traceable fire disturbance for a stream segment occurred on either sideslope and 24–27% in the riparian forest. Plant association groups in the riparian forest had 25–42% fewer fire disturbance events than the same plant association group upslope. Fewer traceable disturbance events in riparian forests may indicate a reduced disturbance frequency or a more severe disturbance regime or both. The two sideslopes on either side of the riparian forest shared the same fire event in 65 and 54% of the recorded fire events on east/west and north/south sideslopes, respectively. Riparian forests shared fire events with adjacent sideslope forests 58–79% among valley types, and 64–76% among aspects. Shared fire events indicate significant continuity in fire disturbance between riparian and adjacent sideslope forests. Fire disturbance regimes of sideslope and riparian forests are quantitatively different, but interconnected through shared fire disturbance events. Disturbance events play a role in maintaining ecosystem integrity and we suggest that disturbance may need to be planned for in administratively defined riparian buffer strips to protect long-term ecological integrity of riparian and adjacent upslope forests.

Deer mouse preference for seed of commonly planted species, indigenous weed seed, and sacrifice foods.

Highlight: Captive deer mice from pinyon-juniper, sagebrushbitterbrush, and Jeffrey pine-ceanothus plant associations were fed a variety of shrub, grass, forb, and tree seeds. Mice ate or destroyed an amount of seed equal to approximately one-third their body weight daily. Seed of bitterbrush, singleleaf pinyon, balsamroot, and small burnet were the most preferred food items tested while seed of Utah juniper, smooth brome, fourwing saltbush, and big saltbush were least preferred. Planting valuable forage species whose seeds are not preferred by deer mice would appear to improve seeding success on sites where seed predation by deer mice is a problem.

Monoterpene concentrations in fresh, senescent, and decaying foliage of singleleaf pinyon (Pinus monophylla Torr. & Frem.: Pinaceae) from the western Great Basin

Senescent foliage from pines is potentially a large contributor to the total monoterpene content of the litter layer, and the availability of these compounds as phytotoxins may result from release of these compounds into the vapor phase. In order to determine the fate of several monoterpene hydrocarbons in the natural environment, we examined their concentrations in fresh, senescent, and decaying needles from 32 single-leaf pinyon pine (Pinus monophylla Torr. & Frem.: Pinaceae) trees growing at two different locations. Total monoterpene content was highest in the fresh needles (mean=5.6 ± 2.2 mg/g extracted air dry weight), but also remained relatively high in senescent needles (mean=3.6 ±1.8 mg/g extracted air dry weight), either still attached to the tree or forming the freshest layer of understory litter. Decaying needles within a dark decomposing layer of litter material 5–20 cm from the surface were found to contain much lower amounts of total monoterpenes (average: =0.12 ±0.06 mg/g extracted air dry weight). Further investigation of the fate of these compounds in the pinyon understory is required to determine if these hydrocarbons are indeed exerting phytotoxic characteristics.

Cavities in snags along a wildfire chronosequence in Eastern Washington

We sampled occurrence of bird-excavated cavities in snags in a chronosequence of 26 wildfire burns (ages 1-81 years) on the east slope of the Washington Cascade Range, USA. Cavities occurred in 5.5% of the 1,867 recorded snags; most (69%) were in burns 250) of subalpine fir (Abies lasiocarpa; 0.2%) and lodgepole pine (Pinus contorta; 0.0%) snags. Cavities occurred in about 4% of the small samples (n 34 cm diameter at breast height [dbh]) snags >2 m tall and located in middle-age to older burns (>19 years old). Cross-validated accuracy of the classification tree model was 97% for cavity snags and 82% for snags without cavities. Cavity-bearing Douglas-fir snags were best characterized as large-diameter snags (>33 cm dbh), or as smaller soft snags (Class 4, 5) at elevations <1,200 m. Accuracy of the classification tree model was 88% and 73% for snags with and without cavities, respectively. In burns <20 years old, Douglas-fir snags with broken tops had higher cavity excavation rates (6%) than snags with whole tops (0.25%). Aspect, slope, slope position, and elevation had negligible or no value for classification. To ensure good post-fire snag habitat, manage pre-fire green stands for tree species, large size, defect (e.g., broken tops), and spatial pattern that will provide cavity snags in short and long terms. When salvaging burns, retain snags with defects incurred prior to fire, especially broken tops, and large-diameter snags of species known to be most suitable for cavity excavation in that area.

Pinyon-juniper woodland understory distribution patterns and species associations

Peuplement de Pinus monophylla-Juniperus osteosperma au Nevada. Mode de croissance des especes de sous-bois, interaction entre ces especes, types de successions observes

Measurement of monoterpene hydrocarbon levels in vapor phase surrounding single-leaf pinyon (Pinus monophylla Torr. & Frem.: Pinaceae) understory litter.

A headspace air-sampling experiment was performed in the laboratory to determine the identity and concentrations of monoterpene hydrocarbons that could be attained in the vapor phase surrounding single-leaf pinyon pine (Pinus monophylla Torr. & Frem.) understory litter using controlled air collection conditions at a simulated field temperature of 37.8°C. The total monoterpene hydrocarbon content in 21 sequential samples of air collected from a sealed glass carboy packed with 1.44 kg of single-leaf pinyon litter equivalent to a bulk density of 0.15 g/cm3 averaged 3.56 ± 1.04 mg/liter. The monoterpenesα-pinene and camphene were present in the vapor phase at the highest concentrations, averaging 2.40±0.64 and 0.68±0.22 mg/ liter, respectively. Myrcene,β-pinene, 3-carene,β-phellandrene, andγ-terpinene were all present at average concentrations below 0.30 mg/liter. The first two traps of the sequential air samples yielded the highest concentrations for the monoterpene hydrocarbons; however, the average total levels were relatively stable throughout the remaining 19 traps. Therefore, the data indicate that these hydrocarbons volatilize from the source pinyon litter and maintain an equilibrium in the vapor phase. Although this analysis was conducted using an artificial system, combined with results from our previous studies, mounting evidence indicates that monoterpene hydrocarbons present in the vapor phase of the single-leaf pinyon understory may be toxic to a variety of native plant species and thus further implicates allelopathy as a significant contributor to the observed patterning of associated vegetation in these forests.

Development of current stand structure in dry fir-pine forests of eastern Washington

Abstract Stand reconstruction, using live trees and deadwood, provided a four to five hundred year recruitment history for the current stand structure in dry fir-pine forests of northern Washington, USA. The lengthy structural record indicated these dry fir-pine forests were resilient to change, that all forest conditions were transient, and that forests were currently transitioning away from maximum tree density levels. Historically, frequent fires maintained low tree abundance, but fire cycles lengthened in the 1860s as Euro-settlement progressed. Average stand density had already increased to 194% (SD  =  116) of 1860 levels by the start of effective fire suppression in 1915. From the 1930s to 1960s, average stand density peaked at 258% (SD  =  98) of 1860 levels. By 2000, tree mortality in these overstocked stands had reduced average stand densities to 68% (SD  =  19) of maximum levels. However, tree densities in 2000 still averaged 173% (SD  =  64) above historical levels. Although there had been significant tree recruitment and a century without fire, the trees present in the historic stands provided 75% (SD  =  13) of the basal area in 2000. Numerous understory (< 7.6 cm dbh) trees (252 trees/ha, SD  =  97) were present in 1860 stands and these trees contributed more basal area than the historic overstory in 2000. In the absence of fire and without human intervention, the sampled stands have decreased in overall tree density from maximum levels while representation of shade-tolerant species, range and evenness of age-class structure, and abundance of old forest (live tree and deadwood) legacies have increased.