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Prva nadba uši Cinara curvipes (Patch, 1912)(Homoptera, Aphididae) v Sloveniji in njen morebitni gospodarski pomen

Multiple forest health variables were examined in an eastern Sierra Nevada mixed conifer stand, principal among them bark beetle demography. As indicated by pitch tube counts, California white fir (Abies concolor var. lowiana [Gord.] Lemm.), the predominant species, was colonized prodigiously compared to Jeffrey pine (Pinus jeffreyi Grev. and Balf.) and sugar pine (Pinus lambertiana Dougl.). Across host species, pitch tube abundance was positively related to white fir prevalence and negatively related to tree species diversity. Bark beetles preferentially attacked trees of small to medium DBH in white fir and sugar pine. Attack intensity in small Jeffrey pine was positively correlated with stand basal area and biomass and that in sugar pine of medium size was positively correlated with basal area also. Minor mistletoe infestations were detected in white fir along with incense-cedar (Libocedrus decurrens Torr.) and California red fir (Abies magnifica A. Murr.), with bark beetle colonization in the smallest and largest white fir positively related to the percentage of this fir thus infested. Mortality in white fir and Jeffrey pine irrespective of size was positively correlated with the pitch tube count in the largest white fir regarding the former and with total tree count regarding the latter.

Thinning implemented with a cut-to-length system accompanied by on-site slash mastication and dispersal and followed by prescribed underburning were evaluated for their influences on individual tree and stand level growth in eastern Sierran mixed conifer. California white fir (Abies concolor var. lowiana [Gord.] Lemm.) dominated stand composition with Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and sugar pine (Pinus lambertiana Dougl.) moderately represented while incense-cedar (Libocedrus decurrens Torr.) and California red fir (Abies magnifica A. Murr.) were exceedingly minor constituents. One decade after treatment, trees in the thinned stand subunit exhibited large height and DBH gains irrespective of fire treatment, responses attributable to the thinning protocol and to enhanced growth of residual stems, while minimal dimensional changes prevailed in the unthinned subunit. Diminished board feet and cubic volumes prevailed in the thinned subunit, and especially in its burned portion, through the end of the study, however, reflecting a reduction in stocking exacerbated by further loss caused by the underburn. Steep reductions in white fir volumes were responsible for the overall losses in the thinned and burned treatment combination. Jeffrey pine responded favorably to thinning but not to underburning, while sugar pine volume responses were unaffected by either treatment.

During the late fall of 2002 we administered three burns in mixed conifer forest sites in the north-central Sierra Nevada. Eight months later we measured fire-induced injury and mortality in 1300 trees. Using logistic regression, an array of crown scorch, stem damage, fuels, and fire-behavior variables were examined for their influence on tree mortality. In Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), white fir (Abies concolor (Gord. & Glend.) Lindl.), and incense cedar (Calocedrus decurrens (Torr.) Florin), smaller trees with greater total crown damage had higher mortality rates. Smaller stem diameters and denser canopies predicted mortality best in ponderosa pine (Pinus ponderosa Dougl. ex P. Laws. & C. Laws). Duff consumption and bark char severity increased model discrimination for white fir and incense cedar and California black oak (Quercus kelloggii Newberry), respectively. In tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.), greater total crown damage in shorter trees resulted in higher mortality rates. Along with tree diameter and consumption of large (>7.6 cm diameter at breast height, DBH) rotten downed woody debris, fire intensity was a significant predictor of overall tree mortality for all species. Mortality patterns for white fir in relation to crown damage were similar among sites, while those for incense cedar were not, which suggests that species in replicated sites responded differently to similar burns. Our results demonstrate actual fire-behavior data incorporated into mortality models, and can be used to design prescribed burns for targeted reduction of tree density in mixed conifer forests.

Summary 1 Restoration of wildland fire to forests is a challenge when historical fire regimes have been altered. We studied four fires that burned over approximately 7865 ha on an altitudinal gradient in Grand Canyon National Park, USA, in 2003. The fires met criteria for the current USA policy allowing the restoration of fire's ecological role in forest landscapes: Wildland Fire Use for Resource Benefits. 2 After the fires burned out, we remeasured 82 permanent pre-established monitoring plots burned by the fires plus 43 additional plots on unburned companion sites. 3 The maximum height of charring of tree boles and basal area mortality increased in mean value and variability with altitude. At a low-altitude Pinus–Quercus site, tree density declined significantly but basal area was unchanged. At a mid-altitude mixed-conifer site and a high-altitude Picea/Abies/Populus site, both density and basal area declined. 4 The thinning effect of fire was concentrated on smaller, shorter, fire-susceptible trees. Small-diameter trees (

In Sierra Nevada forests, shrubs are considered strong soil moisture competitors with regenerating trees, reducing seedling establishment, and slowing growth. Recent studies, however, suggest that in some circumstances shrubs can facilitate tree establishment and growth by modifying harsh microclimate conditions; increasing acquisition of water, carbon, and/or nutrients via shared mycorrhizal connections; or enhancing soil fertility, particularly under nitrogen-fixing shrubs such as Ceanothus spp. We examined the establishment dates and growth rates and patterns of white fir saplings growing in greenleaf manzanita, whitethorn ceanothus, and bare patches to examine whether establishment was correlated with past wet years, whether saplings growing in ceanothus had nitrogen-enriched foliage or faster growth rates than in the other two patches, and whether saplings in shrub patches experienced competition for light. Sapling establishment was not correlated with high precipitation or heavy snowpack years, suggesting shade-tolerant saplings do not need wet yearstobecome established.Soilsunderceanothus werenitrogen enriched,butwhitefirsaplingfoliagedidnothavehighernitrogenconcentrations and saplings did not grow faster in ceanothus than in the other two patches. Because growth rates of saplings were comparable in all patch types examined despite significantly different edaphic and abiotic conditions, we inferred that the various competitive and facilitative interactions affecting tree growth are in net balance across the patch types examined. However, competition for light is important—a significant percentage of growth release events occurred after saplings emerged above their host shrubs. Where shrubs are present, shade-tolerant species (i.e., white fir) are favored over drought-tolerant (pine) species. Our results may help interpret changes in understory conditions that are contributing to mixed conifer’s compositional shift toward more shade-tolerant species after a century of fire-suppression. # 2006 Elsevier B.V. All rights reserved.

The snowshoe hare (Lepus americanus) is a habitat specialist with a broad geographic range associated with boreal and subalpine forests in North America (Hall 1981, Hodges 1999a,b). It reaches southern range limits in the Southern Rocky Mountains in northern New Mexico, USA. Here, scant and mostly anecdotal evidence suggests that it is restricted to high-elevation, subalpine conifer forests dominated by Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa; Findley et al. 1975, DeVelice et al. 1986, Pase and Brown 1994). These southwestern forests lack several plant species, including lodgepole pine (Pinus contorta), jackpine (Pinus banksiana), black spruce (Picea mariana), birch (Betula spp.), and balsam poplar (Populus balsamifera), that, in more northern latitudes, are considered important habitat elements for snowshoe hare, especially in terms of cover (Bittner and Rongstad 1982, Litvaitis et al. 1985, DeVelice et al. 1986, Ferron and Ouellet 1992, Bryant et al. 1994, Pase and Brown 1994, Moir and Fletcher 1996). Methods for managing subalpine forests for snowshoe hare in the Southern Rocky Mountains are particularly important because of a current effort to reintroduce Canada lynx (Lynx canadensis), which is a specialized predator of snowshoe hare (Hodges 1999a,b, Colorado Division of Wildlife 2002). Another leporid, the mountain cottontail (Sylvilagus nuttallii), occurs throughout the intermountain region of western North America, also reaching the southern extent of its range in the American Southwest (Hall 1981). Throughout this broad zone of sympatry, the two leporids segregate in ecological distribution with no reports of syntopy (Bittner and Rongstad 1982, Chapman et al. 1982, Chapman and Wilner 1986). The mountain cottontail typically is associated with lower-elevation sagebrush (Artemisia spp.)–dominated habitats (Orr 1940, Chapman 1975, 1999, Chapman et al. 1982). However, it is a habitat generalist and at more southern latitudes it also occurs in higher-elevation habitats including juniper (Juniperus spp.) and pinon pine (Pinus spp.) woodlands and middle-elevation montane conifer forests, which are dominated by ponderosa pine (Pinus ponderosa), white fir (Abies concolor), Douglas-fir (Pseudotsuga menziesii), and blue spruce (Picea pungens; Bailey 1931, Durrant 1952, Findley et al. 1975, Hoffmeister 1986, Fitzgerald et al. 1994, Frey and Yates 1996). Mountain cottontails also occur in subalpine conifer forest in areas of the Southwest and Southern Rocky Mountains where snowshoe hare are absent, such as the White Mountains in eastcentral Arizona and the Pikes Peak massive in central Colorado (Warren 1910, Armstrong 1972, Hoffmeister 1986). Findley et al. (1975) reported a specimen each of mountain cottontail and snowshoe hare from Goose Lake, Taos County, New Mexico, USA. This locality is at 3,542 m elevation, which is in the subalpine conifer forest zone. These records suggested that less ecological segregation between snowshoe hare and mountain cottontail might occur in the American Southwest, including the potential for local syntopy. Thus, the purpose of our study was to assess habitat use of snowshoe hare and mountain cottontail in subalpine conifer forests at their southern point of sympatry in the Southern Rocky Mountains.

In this study we analyzed the spatial structure of ectomycorrhizal fungi present in the soils as resistant propagules (e.g. spores or sclerotia) in a mixed-conifer forest in the Sierra Nevada, Califor- nia. Soils were collected under old-growth Abies spp. stands across approximately 1 km and bioassayed with seedlings of hosts that establish best in stronger light (Pinus jeffreyi) or that are shade-tolerant (Abies concolor). Ectomycorrhizal fungi colonizing the roots were characterized with molecular techniques (ITS- RFLP and DNA sequence analysis). Wilcoxina, five Rhizopogon species and Cenococcum were the most frequent of 17 detected species. No spatial structure was detected in the resistant propagule community as a whole, but P. jeffreyi seedlings had higher species richness and associated with seven Rhizopogon species that were not detected on A. concolor seedlings. We drew two conclusions from comparisons between this study and a prior study of the ectomycorrhizal community on mature trees in the same forest: (i) the resistant propagule community was consider- ably simpler and more homogeneous than the active resident community across the forest and (ii) Cenococcum and Wilcoxina species are abundant in both communities.

To elucidate broad-scale environmental controls of coniferous forest reproduction in the Sierra Nevada, California, we monitored reproduction for 5 years in 47 plots arrayed across a steep elevational (climatic) gradient. We found that both absolute seedling densities (stems < 1.37 m) and seedling densities relative to overstory parent tree basal area declined sharply with elevation. Rates of seedling turnover (the average of birth and death rates) also declined with elevation. In contrast, seed production was not predicted by elevation and was highly variable from year to year. During a mast year of seed production, the intensity of masting was uneven among plots. Seedling densities were elevated only during the single year immediately following the mast year, suggesting reproduction in our forests may be primarily limited by abiotic factors such as the availability of suitable sites and weather. Disturbance also clearly affected reproduction; plots that had recently burned had significantly higher seedling to parent tree ratios for Abies species, suggesting that even though established Abies concolor may be relatively susceptible to fire, the species can recover rapidly through prolific reproduction. Since reproductive failures may be our earliest signal of changing forest conditions, seedling dynamics could provide a sensitive, if variable, indicator of environmental changes.

Site index curves for white fir (Abies concolor) in Arizona, New Mexico, and southwestern Colorado were developed using height-age measurements and an estimated guide curve and 95% confidence intervals for individual predictions. The curves were developed using height-age data for 1,048 white firs from 263 study sites distributed across eight national forests. These site index curves can be used with standard inventory data for estimating potential site productivity for white fir in the southwestern United States.

Riparian vegetation plays an integral role in the ecology of the streams it borders, and in many western US forests, is subjected to frequent wildfire disturbances. Many questions concerning the role of natural fire in the dynamics of riparian zonevegetation remain unanswered. This case study explores the relationships between wildfire burn patterns, stream channel topography, and the short-term response of riparian vegetation to fire along two creeks in the northern Sierra Nevada mixed-conifer forest. Post-fire sampling along 60, 3 m wide transects across riparian zones was used to document the topography, species distribution, sprouting response, and seedling recruitment 1 year after the Lookout fire in the Plumas National Forest, CA. Our results indicate that larger riparian zones acted as natural fire breaks, limiting the progression of the predominantly backing fire downhill toward the stream. On Fourth Water creek’s steeper first terraces, where crownfires occurred, the percentage of burned plants that sprouted was higher than in the less-severely burned and more extensive first terraces of Third Water creek (93% versus 33%, P < 0.05). Total seedling recruitment was higher along Fourth Water creek (69 versus 35 seedlings, P < 0.05), while plant regeneration along Third Water creek was primarily vegetative. Along Fourth Water creek, the percent of burned hardwoods that sprouted increased with proximity to the water’s edge from 33% onthe slopeabove the riparian zone to 95% onthegravelbar, suggesting that moisture content plays a role in riparian species response to fire. An influx of white fir (Abies concolor Gordon & Glend. (Lindl.)) seedlings on the second terraces of Third Water creek may indicate a shift in species composition iffuture fires are suppressed and regeneration trends do not change significantly in the next few years. These results contribute to the limited research on natural fire in riparian zones, and can inform management strategies designed to restore and maintain riparianvegetation in the fire-prone forests of the Sierra Nevada. # 2005 Elsevier B.V. All rights reserved.

We studied use of day roosts by adult, female long-legged myotis (Myotis volans) in 4 watersheds dominated by ponderosa pine (Pinus ponderosa) forest east of the Cascade Crest in Washington and Oregon, USA, 2001–2003. To investigate maternity habitat in managed, xeric forests we radiotracked 87 bats to 195 snag roosts and 34 rock crevices totaling 842 roost-days. Bats changed roosts every 2.7 ± 0.1 (SE) days and averaged 3.6 ± 0.3 roosts per bat. Roosts were 2.0 ± 0.1 km from capture sites, and bats moved 1.4 ± 0.1 km between successive roosts. Six bats (6.9%) day-roosted in rock crevices exclusively, 9 bats (10.3%) used snags and rock crevices, and the remaining bats (82.8%) day-roosted in snags exclusively. Most snag roosts were thick-bark ponderosa pine (n = 103; 52.8%) or thin-bark grand fir (Abies grandis) and white fir (Abies concolor) (n = 74; 37.9%). Over half of all snag roosts (n = 101; 52%) were used by solitary bats; 28 snag roosts (14%) housed >50 bats (large-flyout roosts). Ninety-three percent of large-flyout roosts were in ponderosa pine snags. Large-flyout roosts were larger, taller, and retained more exfoliating bark and total bark than small-flyout roosts (P 25 cm diameter, and were lower in elevation than random snags (P < 0.05). Pregnant bats divided roost-days almost evenly between thick and thin-bark snags (52.7 vs. 47.3%), whereas lactating bats roosted in thick-bark snags more often than they did in thin-bark snags (80.3 vs. 19.7%, P < 0.0001). Pregnant bats roosted in both upslope and riparian zones (57.5 vs. 42.5%), but lactating bats spent more days roosting upslope than in riparian zones (73.1 vs. 26.9%, P < 0.0001). These findings suggest that reproductive female long-legged bats choose roosts relative to their changing physiological needs. We recommend that management of forests for sustaining habitat of female long-legged myotis in the east Cascades ensure the continued availability of both thick- and thin-bark snags in early stages of decay, in both riparian and upslope positions.

The unambiguous identification of closely related species is useful for many practical purposes in forest tree species. For example, international laws require timber identification and the control of the origin of forest reproductive material. In this paper, we present a mitochondrial DNA marker which can be used to differentiate among groups of fir species (Abies spp.). Eight Mediterranean and one North American fir species (used as reference) were analysed at the fourth intron of the NAD subunit 5 gene. A total of six different haplotypes was identified, one in the American Abies concolor, the other five in Mediterranean species. Two different haplotypes were found each in the widespread A. alba and in A. cephalonica, one haplotype being shared among the two species. A single species specific haplotype was found in the near-eastern A. cilicica. The two southwestern species A. pinsapo and A. numidica shared one haplotype. The fifth haplotype was shared by all remaining eastern Mediterranean firs, A. cephalonica, A. bornmuelleriana, A. equi-troiani, and A. nordmanniana. Differences in haplotype sequences were mainly due to large insertions/deletions. Agarose gel electrophoresis thus provides a fast, cheap and reliable diagnosis method for species or species group identification.

Tree mortality is an important process causing forest structural and compositional change. In this study, we investigate the influence of drought and topography on recent patterns of tree mortality in old-growth mixed conifer forests in Yosemite National Park, located in the Sierra Nevada Mountains of northern California, USA. The surveyed stands have experienced a century of fire exclusion and are dominated by associations of Pinus ponderosa, Calocedrus decurrens and Abies concolor. The average age of trees in the stands was 88 years. We sought answers to the following questions: (1) Do periods of high tree mortality correspond with drought? (2) Do spatial and temporal patterns of high tree mortality vary by slope aspect? and (3) Do different tree species exhibit similar temporal and spatial patterns of tree mortality? We identified temporal patterns of tree mortality on three north- and south-facing slopes by determining the death date of trees using dendrochronology. Tree death date frequency was then compared by slope aspect and to Palmer Drought Severity Index (PDSI), and April snowpack depth as measures of growing season water availability. The frequency of tree death dates was negatively correlated with annual and seasonal PDSI and April snowpack depth, and more trees died in years with below normal PDSI and snowpack. Correlations between tree mortality and drought were evident only for multi-year periods (2‐5 years). Temporal patterns of tree death were similar on north- and south-facing slopes and among species, but the density of dead trees was higher on north than south slopes. Dense stand conditions caused by fire suppression, and the coincident outbreak of bark beetles during drought, may have limited any buffering effect of topography on tree mortality. Drought induced tree mortality in mixed conifer forests in Yosemite National Park highlights the importance of both historical legacies such as fire suppression and exogenous controls such as climate as drivers of vegetation change. # 2005 Elsevier B.V. All rights reserved.

In order to obtain information on the genetic structure of Abies concolor and the genetic variation among 11 populations introduced from America to China, allozyme analysis based on starch gel electrophoresis technology was used. 24 loci of 10 allozyme systems were mensurated, and the genetic structure and genetic diversity of the 11 populations of A. concolor evaluated. The results show that the genetic variation among is significant, and the genetic variation within A. concolor populations is more important. In contrast with other conifers, the variation of A. concolor is above the average level of conifers, and higher than the same level of Abies. The percentage of polymorphic loci (P) was 62.5%, the number of alleles per locus (A) 2.08, the number of effective alleles per locus (A e) was 1.37, the expected heterozygosity (H) 0.204, and the Shannon information index (I) 0.351 7. There is a short genetic distance (D=0.061) and a low gene flow (N m=0.839 4) among the 11 introduced populations of A. concolor with high genetic variation. The genetic differentiation coefficient (G st) was 0.229 5, which is higher than that of the mean in Abies or Pinus.

We simulated forest dynamics of the regional ponderosa pine–white fir conifer forest of the San Bernadino and Sierra Nevada mountains of California to determine the effects of high ozone concentrations over the next century and to compare the responses to our similar study for loblolly pine forests of the southeast. As in the earlier study, we linked two models, TREGRO and ZELIG, to consider both physiological effects within individual trees and competitive interactions within forest communities. We represented regional effects by simulating at three sites in California, Lassen National Park, Yosemite National Park, and Crestline in the San Bernardino Mountains. At each of these locations, we simulated the response to altered pollutant conditions of 0.5, 1.5, 1.75, and 2 times ambient ozone. Of the two major dominant species in this forest, white fir showed little response, but ponderosa pine was predicted to show large effects. Ambient ozone at Crestline (approximately 110 ppm h, and larger than twice the ambient concentration at either of the other sites) was predicted to decrease individual tree carbon budgets by 10%. This effect was predicted to lead to a decrease in ponderosa pine abundance under average climatic conditions by 16% were these concentrations to continue over the next century. A doubling of ozone at Crestline over the next 100 years was predicted to decrease this budget by an additional 11%, leading to a decline in abundance of 41%. Effects at the other sites were predicted to be smaller (effects of current ambient ozone on abundance of 10% at Yosemite and 0% at Lassen) in proportion to the smaller exposures at those sites. Decreases in chronic moisture availability at all three sites were predicted to reduce these effects, particularly if ozone exposures rise.

We analyzed attributes of tree encroachment on montane meadows and subalpine grasslands on the North Rim of Grand Canyon National Park. Species composition, age, density, height, diameter, condition class, and patterns of tree establishment were examined on belt transects at 12 meadow sites. Of the 3481 live and dead trees sampled, 52% of all trees were Populus tremuloides, 20% were Picea spp., 11% were Abies lasiocarpa, 10% were Abies concolor, and 7% were Pinus ponderosa. Tree densities averaged 4703 trees ha � 1 . Sixtytwo percent of the trees sampled were less than 20 yr of age, although some species established in the early and mid-1800s. Ninety-one percent of all trees, however, established after the mid-1930s, with the greatest establishment occurring after the early 1970s. Of this 91%, Populus tremuloides composed the majority (90%) of recent tree recruitment, with a mean establishment date of 1983–1984. A general pattern of progressively younger trees from the closed forest toward the meadow interiors was detected for some species, and together with little evidence of historical tree occurrence (e.g., large standing dead, downed logs, etc.) on the transects, indicated that trees had been encroaching on these meadows since the 1800s. These trends suggest a loss of important meadow habitat and landscape biodiversity within Grand Canyon National Park during the past century.

Knots, i.e. branch bases inside tree stems, in fir trees contained remarkably higher concentrations of lignans, oligolignans, and juvabiones than the adjacent stemwood. Eight fir species were analysed (Abies sibirica, A. lasiocarpa, A. balsamea, A. alba, A. amabilis, A. veitchii, A. sachalinensis, and A. concolor). The amount of lignans could in some knots exceeds 6% (w/w) and the knots generally contained 20–50 times more lignans than the stemwood. However, there were large variations, not only between species but also even between knots in the same tree. Secoisolariciresinol was the predominant lignan in all knots. The lignans occur in free form in the knots and are easily extracted with polar solvents. In addition to the lignans, oligomeric aromatic substances, mainly sesquineo- and dineolignans, and juvabiones were accumulated in the knotwood. Secoisolariciresinol, but also lariciresinol (Abies alba) and 7-hydroxymatairesinol (A. amabilis), could be extracted in large scale from fir knots at pulp and paper mills. The ready availability of large amounts of lignans and oligolignans now enables research to assess their bioactivity and provide the base for applications in medicine and nutrition, or as natural antioxidants and antimicrobial agents in various technical products.

The fisher (Martes pennanti) is a forest mustelid that historically occurred in California from the mixed conifer forests of the north coast, east to the southern Cascades, and south throughout the Sierra Nevada. Today fishers in California occur only in 2 disjunct populations in the northwestern mountains and the southern Sierra Nevada. We studied the ecology of fishers in both populations (the north coast [Coastal] and southern Sierra Nevada [Sierra]) to characterize the size and composition of their home ranges, and to compare features between locations. Twenty-one (9 Coastal, 12 Sierra) of 46 radiocollared fishers were relocated frequently enough (>20 times) to estimate home ranges. The home ranges of males (X = 3,934.5 ha) were significantly greater than those of females (980.5 ha), and the home ranges of females were significantly greater in the Coastal than in the Sierra area. The smaller home ranges in the Sierra were probably due to productive habitats rich in black oak (Quercus kelloggii). Midseral Douglas-fir (Pseudotsuga menziesii) and white fir (Abies concolor) types composed the greatest proportion (42.8%) of home ranges in the Coastal study area. The greatest proportion of home ranges in the Sierra study area were in the intermediate tree size class (60.7%), had dense canopy closure (66.3%), and were in the Sierran Mixed Conifer type (40.1%). These measures provide guidelines for managers who wish to influence landscape features to resemble occupied fisher habitat. The recovery of fishers in the Pacific States, however, will also require the consideration of microhabitat elements and characteristics of landscapes that might affect metapopulation dynamics.

Crown symptoms and other aboveground variables were examined on 36 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco.) (40–209 years old), 46 white fir (Abies concolor (Gord. & Glend.) Lindl.) (36–165 years old), and 97 ponderosa pine (Pinus ponderosa Dougl. ex Laws.) (64–220 years old) trees in northern New Mexico and southern Colorado. Root systems of all trees were excavated to determine extent of root disease. Symptoms observed on infected trees, including reductions in height growth, changes in foliage characteristics, and crown dieback, worsened as the number of infected roots increased. Trees with aboveground symptoms had a significantly higher (p < 0.05) number of infected lateral roots than trees without symptoms. In mixed conifer stands on the Archuleta Mesa, Colo., four qualitative crown symptoms were used to accurately detect Armillaria ostoyae (Romagn.) Herink and (or) Heterobasidion annosum (Fr.) Bref. infection of Douglas-fir (21/22, or 95%) and white fir (19/28, or 68%). Similarly, 61% (48/79) of the A. ostoyae infected ponderosa pine trees on the Jemez site, N.M., were detected using the qualitative Thomson vigor rating system. Discriminate analysis, using more thorough variables and analysis, resulted in correct infection classifications of 82%, 85%, and 78% for Douglas-fir, white fir, and ponderosa pine, respectively, suggesting that aboveground variables are reasonable indicators of root disease.

We synthesize current information on input, accumulation, and decay of coarse woody debris (CWD) compared with other aboveground litter to assess the role of CWD in the nutrient cycles of northern coniferous forests. CWD contributes between 3% and 73% of aboveground litter input, but -1. Nitrogen or P concentrations in CWD increase during decay, depending on the initial N/P ratio, which eventually converges at about 20. CWD is initially a sink for N and (or) P, whichever is least available, but becomes a source later in decay. CWD contributes

Replicated circular openings ranging in size from 0.1 to 1 ha were cleared in 1996 at Blodgett Forest Re- search Station, California, and planted with seedlings of six native species. After 5 years of postharvest growth, heights were measured and analyzed according to species, opening size, and location within opening. The sequence of mean height from tallest to shortest, according to species, was as follows: giant sequoia (Sequoiadendron giganteum (Lindl.) Buchholz) > incense-cedar (Calocedrus decurrens (Torr.) Florin) > Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) ≈ ponderosa pine (Pinus ponderosa Dougl. ex Laws.) > sugar pine (Pinus lambertiana Dougl.) ≈ white fir (Abies concolor (Gord. & Glend.) Lindl.). To describe the influence of openings size on seedling height, we use an information-theoretic approach to select from competing models that predicted fifth-year height from group selection opening size. Asymptotic fits (modeled with Michaelis-Menton curves) were selected for giant sequoia, ponderosa pine, sugar pine, and incense-cedar. Quadratic fits were selected for white fir and Douglas-fir. Linear models predicting increasing growth with opening size were consistently ruled out for all species. Although a marked depression in seedling-height growth occurred along the edges within the openings, mean annual radial increment of the 90-year-old border trees surrounding the openings increased by 30%, compared with other canopy trees in the forested matrix be- tween openings. Resume : Des ouvertures circulaires repetees dont la dimension variait de 0, 1a1h a ont etecoupees a blanc en 1996

This research analyzes patch development and determines tree spatial patterns along the lower mixed-conifer ecotone on the North Rim of Grand Canyon National Park in Arizona U.S.A.. Patterns of patch development were interpreted from spatial analyses, based on tree age and size, and past records of disturbance and climate. Five plots in the ecotone between mixed conifer forests and monospecific stands of ponderosa pine Pinus ponderosa were studied for patterns of patch development. The methods used include: 1 size-structure analyses, to compare species patch development; 2 dendrochronological dating of tree establishment; 3 tree ring master chronology, to determine periods of suppressed growth, compared to a Palmer Drought Severity Index; and 4 spatial analyses by species composition, size and age, with univariate and bivariate analyses of spatial association and spatial autocorrelation. We found an increased density of shade-tolerant and fire-intolerant species namely clusters of pole-sized white fir, and fewer large ponderosa pine.

Replicated circular openings ranging in size from 0.1 to 1 ha were cleared on a Sierran mixed conifer forest in 1996 at the Blodgett Forest Research Station, California and planted with seedlings of six native species. After 3 years of growth, heights of all trees were measured and analyzed according to species, opening size, and location within the opening. To determine the cause of the edge influence on height, we measured differences along north‐south transects in extension growth, pre-dawn water potential, and light availability for three species of trees: giant sequoia (Sequoiadendron giganteum), ponderosa pine (Pinus ponderosa), and Douglas-fir (Ptseudotsuga menziesii var. menziesii). The sequence of mean height from tallest to shortest based on species was: giant sequoia > incense cedar > Douglas-fir > ponderosa pine > white fir > sugar pine. For all species combined, a ten-fold increase in the area of the opening corresponded to a 34% increase in mean height. Trees were tallest on average in the north rows and shortest in the south rows. There was no difference in height between trees in the east and west rows. As expected, resource availability was greatest near the center and least near the edges with north edges receiving significantly more light than southern edges. In general, observed edge effects on sapling height growth were correlated with light and water supply. However there were important differences between species in the nature of the co-limitation. Giant sequoia growth was most sensitive to light and water availability. Together they explained more than 47% of the observed variation in giant sequoia height. In contrast, only light was a significant predictor of ponderosa pine performance. Douglas-fir heights were significantly related to both light and water but there was more unexplained variability in the Douglas-fir model compared to the other species. These highly controlled experimental group openings provide a standard reference for silviculturalists using the group selection method of regeneration. # 2002 Elsevier Science B.V. All rights reserved.

Tree mortality is often the result of both long-term and short-term stress. Growth rate, an indicator of long- term stress, is often used to estimate probability of death in unburned stands. In contrast, probability of death in burned stands is modeled as a function of short-term disturbance severity. We sought to narrow this conceptual gap by deter- mining (i) whether growth rate, in addition to crown scorch, is a predictor of mortality in burned stands and (ii) whether a single, simple model could predict tree death in both burned and unburned stands. Observations of 2622 unburned and 688 burned Abies concolor (Gord. & Glend.) Lindl. (white fir) in the Sierra Nevada of California, U.S.A., indicated that growth rate was a significant predictor of mortality in the unburned stands, while both crown scorch and radial growth were significant predictors of mortality in the burned stands. Applying the burned stand model to unburned stands resulted in an overestimation of the unburned stand mortality rate. While failing to create a general model of tree death for A. concolor, our findings underscore the idea that similar processes may affect mortal - ity in disturbed and undisturbed stands. Resume : Chez les arbres, la mortalite est souvent le resultat de stress a long et a court termes. Le taux de croissance, un indicateur de stress a long terme, est souvent utilise pour estimer les risques de mortalite dans les peuplements qui n'ont pas ete endommages par le feu. Par contre, dans les peuplements endommages par le feu, le risque de mortalite est modelise en fonction de la severite d'une perturbation a court terme. Nous avons tente de reconcilier cet ecart conceptuel en determinant (i) si le taux de croissance, en plus du roussissement de la cime, pouvait servir a predire la mortalite dans les peuplements endommages par le feu et (ii) si un modele simple et unique pouvait predire la morta- lite tant dans les peuplements endommages par le feu que non endommages. Les observations faites sur 2622 tiges de Abies concolor (Gord. & Glend.) Lindl. (sapin argente) non endommagees et 688 tiges endommagees par le feu dans la Sierra Nevada en Californie, aux Etats-Unis, montrent que le taux de croissance peut servir a predire la mortalite dans les peuplements non endommages par le feu alors que le roussissement de la cime et la croissance radiale peuvent ser- vir a predire la mortalite dans les peuplements endommages par le feu. L'application du modele concu pour les peuple- ments endommages par le feu aux peuplements non endommages entraine une surestimation du taux de mortalite dans les peuplements non endommages. Bien que nous n'ayons pas reussi a elaborer un modele general de mortalite des ti- ges de A. concolor, nos resultats soulignent la notion que des processus similaires peuvent affecter la mortalite dans les peuplements perturbes et non perturbes.

Lymantria monacha (L.) (Lepidoptera: Lymantriidae), the nun moth, is a Eurasian pest of conifers that has potential for accidental introduction into North America. To project the potential host range of this insect if introduced into North America, survival and development of L. monacha on 26 North American and eight introduced Eurasian tree species were examined. Seven conifer species (Abies concolor, Picea abies, P. glauca, P. pungens, Pinus sylvestris with male cones, P. menziesii variety glauca, and Tsuga canadensis) and six broadleaf species (Betula populifolia, Malus x domestica, Prunus serotina, Quercus lobata, Q. rubra, and Q. velutina) were suitable for L. monacha survival and development. Eleven of the host species tested were rated as intermediate in suitability, four conifer species (Larix occidentalis, P. nigra, P. ponderosa, P. strobus, and Pseudotsuga menziesii variety menziesii) and six broadleaf species (Carpinus caroliniana, Carya ovata, Fagus grandifolia, Populus grandidentata,...

Aim We addressed four objectives: (1) Determine the regional responses of species, size classes and a vegetation type to climate and parent material predictors, including their distributions in environmental space and the relative contributions of the predictors to explained variation. (2) Determine whether size classes of a species respond similarly to climate and parent material. (3) Assess the extent to which the predicted regional distribution of a vegetation type can be approximated by the distribution of its diagnostic species and vice versa. The establishment of a consistent relationship between the distribution of a vegetation type and its diagnostic species would facilitate change detection, management and conservation planning by allowing the use of one distribution to generate the other when data availability is limited. (4) Examine landscape-scale environmental variability in predicted species and vegetation type distributions. Location South-western USA (Arizona, New Mexico and southern Colorado). Methods Ecological response surface models were developed using a data base of 1409 vegetation plots to analyse biotic–environmental relationships of (1) Pinus ponderosa P. & C. Lawson and Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr. size classes, (2) P. ponderosa, A. concolor and Quercus gambelii Nutt. combined size classes, and (3) a P. ponderosa forest type widely distributed in the south-western USA. Results and main conclusions Pinus ponderosa and A. concolor models generally were judged to be successful. Quercus gambelii models were judged unsuccessful, which may result from the influence of variables not modelled, such as soil moisture, disturbance, biotic factors and other site limiting factors. Size classes differed in the range of environmental conditions associated with high occurrence probabilities within and between species, reflecting differences in the effects of climate variability and anthropogenic changes, such as fire suppression, on the distribution of each size class. Pinus ponderosa alliance was predicted to be distributed over a narrower range of environmental conditions than P. ponderosa species models, therefore limiting the use of this vegetation type as a surrogate for the distribution of the dominant species, and vice versa. Maps of combinations of environmental variables that produced a high probability of P. ponderosa occurrence showed that some landscapes predicted to contain the species exhibited diverse environmental conditions over short distances. The use of regional environmental relationships to characterize areas with high local environmental variability may facilitate identification of areas of potential rapid biotic change.

Heretofore, only regression models using average RGC as the independent variable were available to predict the survival of planted seedlings. Now, however, Critical RGC-Expected Survival models are available. Each model predicts the survival of a population on sites with the same Critical RGC as specified by the model. Survival is predicted to equal the percent of the seedlings in the population that have RGCs≥ that Critical RGC. These models are validated by a chi-square goodness of fit test which determines the probability that the survival predictions made by a model agree with the survivals observed on a planting site. In validating a model, the harshness of the planting site is also quantified in terms of its Critical RGC. In this paper, three Critical RGC-Expected Survival models are validated, demonstrating that RGC controls survival on both harsh and gentle sites. On the harsher sites, the Critical RGC for survival was 40 cm; whereas on the gentler sites, it was 20 cm.

Fire regime characteristics of high-elevation forests on the North Rim of the Grand Canyon, Arizona, were reconstructed from fire scar analysis, remote sensing, tree age, and forest structure measurements, a first attempt at detailed reconstruction of the transition from surface to stand-replacing fire patterns in the Southwest. Tree densities and fire-/non-fire-initiated groups were highly mixed over the landscape, so distinct fire-created stands could not be delineated from satellite imagery or the oldest available aerial photos. Surface fires were common from 1700 to 1879 in the 4,400 ha site, especially on S and W aspects. Fire dates frequently coincided with fire dates measured at study sites at lower elevation, suggesting that pre-1880 fire sizes may have been very large. Large fires, those scarring 25% or more of the sample trees, were relatively infrequent, averaging 31 years between burns. Four of the five major regional fire years occurred in the 1700s, followed by a 94-year gap until 1879. Fires typically occurred in significantly dry years (Palmer Drought Stress Index), with severe drought in major regional fire years. Currently the forest is predominantly spruce-fir, mixed conifer, and aspen. In contrast, dendroecological reconstruction of past forest structure showed that the forest in 1880 was very open, corresponding closely with historical (1910) accounts of severe fires leaving partially denuded landscapes. Age structure and species composition were used to classify sampling points into fire-initiated and non-fire-initiated groups. Tree groups on nearly 60% of the plots were fire-initiated; the oldest such groups appeared to have originated after severe fires in 1782 or 1785. In 1880, all fire-initiated groups were less than 100 years old and nearly 25% of the groups were less than 20 years old. Non-fire-initiated groups were significantly older (oldest 262 years in 1880), dominated by ponderosa pine, Douglas-fir, or white fir, and occurred preferentially on S and W slopes. The mixed-severity fire regime, transitioning from lower-elevation surface fires to mixed surface and stand-replacing fire at higher elevations, appeared not to have been stable over the temporal and spatial scales of this study. Information about historical fire regime and forest structure is valuable for managers but the information is probably less specific and stable for high-elevation forests than for low-elevation ponderosa pine forests.

Summary The seed pathogen fungus Geniculodendron pyriforme (teleomorphic state: Caloscypha fulgens) was isolated from imported seeds (USA and Canada) of the following tree species: Picea sitchensis, Piceaengelmannii, Abies grandis and Abies concolor glauca. This is the first report of G. pyriforme on imported conifer seeds in continental Europe. A description of typical culture characteristics of the fungus is given. Resume La parasite des semences Geniculodendron pyriforme (teleomorphe: Caloscypha fulgens) a ete isole de graines importees des USA et du Canada. Les graines concernees appartenaient aux especes suivantes: Picea sitchensis, P. engelmannii, Abies grandis et A. concolor glauca. C'est la premiere mention de G.pyriforme sur graines de coniferes importees sur le continent europeen. Une description des caracteristiques culturales du champignon est fournie. Zusammenfassung Der Saatgut-pathogene Pilz Geniculodendron pyriforme (Teleomorphe: Caloscypha fulgens) wurde aus importierten Samen (USA und Kanada) folgender Nadelholzarten isoliert: Picea sitchensis, P.engelmannii, Abies grandis und A. concolor glauca. Dieser Nachweis ist der erste Bericht uber das Auftreten von G. pyriforme an importiertem Nadelholzsaatgut auf dem europaischen Festland. Es wird eine Beschreibung der typischen Kulturmerkmale des Pilzes gegeben.

Urban areas emit significant amounts of pollutants that impact forest ecosystems. One of the most important of these is nitric acid vapor (HNO3), a nitrogen-containing gas that deposits efficiently to forest canopies. Since measuring HNO3 fluxes directly is often impractical and costly in remote forest locales, inferential techniques are most often used to estimate HNO3 flux. Given the highly efficient deposition of HNO3, many of these inferential models assume that leaf surfaces are a ‘perfect sink’ for HNO3 (i.e., that resistance to HNO3 deposition is negligibly small or zero). This study tests the ‘perfect sink’ assumption in an open gas exchange system by exposing Abies magnifica, Abies concolor, and Pinus jeffreyi seedlings to concentrations of 1–13 ppb at 4–20% relative humidity. We find that, at these humidities and concentrations, cuticles are not perfect sinks for HNO3, with cuticular resistance values ranging from 20 to 184 s m−1. In addition, our results indicate that accumulating HNO3 on leaf cuticles at these concentrations leads to higher cuticular resistance over 8–12 h exposure periods. Based on this laboratory data, we then parameterized cuticular resistance using a single-layer inferential model for semi-arid forests in the Lake Tahoe Basin. Modeled fluxes using this modification were 33% lower during well-mixed daytime conditions than the fluxes from an identical model run using the perfect sink assumption. Since HNO3 can often account for more than half of atmospheric deposition, we conclude that inferential models that assume foliage to be perfect HNO3 sinks are inaccurate, especially in semi-arid forests where significant amounts of HNO3 can accumulate on leaf surfaces during dry periods.

Logistic regression equations of prescribed fire mortality were developed for white fir (Abies concolor [Gord. and Glend.] Lindl.), sugar pine (Pinus lambertiana Dougl.), ponderosa pine (Pinus ponderosa Laws.), incense-cedar (Calocedrus decurrens [Torr.] Floren.), and giant sequoia (Sequoiadendron giganteum [Lindley] Buchholz) in the southern Sierra Nevada, California. A total of 1025 trees were analyzed in this study. Variables included in the mortality equations are diameter at breast height, percent crown volume scorched, crown scorch height, and local forest floor consumption. The likelihood ratio χ2 was highly significant (P

Maloney, P. E., and Rizzo, D. M. 2002. Dwarf mistletoe–host interactions in mixed-conifer forests in the Sierra Nevada. Phytopathology 92: 597-602. We determined the spatial pattern of dwarf mistletoe (Arceuthobium spp.) associated with two different conifer hosts, white fir (Abies concolor) and Jeffrey pine (Pinus jeffreyi), in forests around the Lake Tahoe Basin and at the Teakettle Experimental Forest, both located in the Sierra Nevada. We also examined a number of host variables and bark beetle incidence to determine how these factors might be involved in the Arceuthobium–conifer interaction. There was no significant relationship between dwarf mistletoe-infected trees and associated bark beetles. We found the highest incidence of dwarf mistletoe on Jeffrey pine in Lake Tahoe (87%), followed by dwarf mistletoe on white fir in Lake Tahoe (30%), with the lowest incidence on white fir at Teakettle (27%). Dwarf mistletoe incidence on white fir in our Lake Tahoe grid was not correlated to density but the dwarf mistletoe rating (DMR) was positively correlated to host size. At the Teakettle Forest, dwarf mistletoe incidence on white fir was not correlated with host density but the DMR was correlated with host size. Dwarf mistletoe incidence and DMR on Jeffrey pine were correlated with host density. Individuals, of both conifer species, in all diameter size classes were susceptible to dwarf mistletoe, with the lowest infection rate in the seedling-10-cm-diameter class. Arceuthobium on white fir in Lake Tahoe showed spatial dependence to a range of 20 m. However, Arceuthobium on Jeffrey pine in Lake Tahoe and on white fir at Teakettle showed no clear pattern of spatial structuring. The degree of infection and stand history appear to be important in the spatial dynamics of Arceuthobium spp.

We determined the incidence of pathogens and insects across mixed-conifer stands in the Sierra San Pedro Martir (SSPM) of northern Baja, Mexico, to assess the role of pests in a pristine forest ecosystem. We also determined the spatial distribution of the two most common pests, mistletoe, Phoradendron pauciflorum Torrey, and the fir engraver, Scolytus ventralis LeConte, of white fir (Abies concolor (Gord. & Glend.) Lindl.) across a 25-ha grid to assess spread and what host and pest variables were related. In these open parklike stands the mean tree density was 160 trees/ha, of which 58% were trees >20 cm diameter at breast height (DBH). In these low-density, mixed-aged stands we found that mixed-conifer species were well represented with no one species being completely dominant. Percent cumulative mortality for the SSPM was 12.7%, ranging from 2 to 24%, with the greatest amount of mortality occurring in the larger size classes, trees [Formula: see text]50 cm DBH. Multiple linear regression analysis showed that 78% of the mortality we observed was explained by pathogens and bark beetles (r2 = 0.78, P = 0.0001, F = 84). Mean pest incidence for Jeffrey pine (Pinus jeffreyi Grev. & Balf. in A. Murray), white fir, and sugar pine (Pinus lambertiana Dougl.) was 21, 88, and 2%, respectively. We found a number of relationships among host and pest variables, as well as a pathogen– insect interaction, and across the SSPM we found that nonhost species may be interfering in certain host–pest interactions. Spatial patterns from the 25-ha grid survey revealed that both P. pauciflorum and S. ventralis incidence were widespread. Phoradendron pauciflorum showed no spatial structure across the 25 ha but S. ventralis showed some degree of spatial structuring across the survey area. We also found that mistletoe severity was negatively correlated with regeneration of white fir. In pristine forests, pathogens and insects influence mortality and regeneration success, affecting stand structure and composition.

Aim In this study, we evaluated the fire-forest mosaic of a mixed conifer forest landscape by testing the hypothesis that pre-fire suppression fire regime parameters vary with species composition (tree species), and environment (i.e. slope aspect, slope position, elevation). Location Our study was conducted in the 1587 ha Cub Creek Research Natural Area (CCRNA), Lassen National Forest, CA, USA. Methods We quantified the return interval, seasonal occurrence, size, rotation period, and severity of fires using dendroecology. Results Slope aspect, potential soil moisture, forest composition, and fire regime parameters in our study area co-vary. Median composite and point fire return intervals (FRI) were longest on higher, cooler, more mesic, north-facing (NF) slopes covered with white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii)‐white fir, and red fir (A. magnifica)‐white fir forests, shortest on the dry, south-facing (SF) slopes covered with ponderosa pine (Pinus ponderosa)‐white fir forests and intermediate on west-facing slopes dominated by white fir‐sugar pine (P. lambertiana)‐incense cedar (Libocedrus decurrens) forests. The spatial pattern for length of fire rotation (FR) was the same as that for FRI. Fires in CCRNA mixed conifer forests occurred mainly (90%) in the dormant season. Size of burns in CCRNA mixed conifer forests were generally small (meana 106 ha), however, during certain drought years widespread fires burned across fuel breaks and spread throughout the watershed. Fire severity was mainly high on upper slopes, low on lower slopes and moderate and low severity on middle slopes. Patterns of fire severity also varied with slope aspect. Fire frequency decreased dramatically in CCRNA after 1905. Conclusions In CCRNA, fire regime parameters [e.g. FRI, fire extent, FR, fire severity] varied widely with species composition, slope aspect and slope position. There was also temporal variation in fire extent with the most widespread fires occurring during drought years. The important contributions of topography and climate to variation in the fire regime indicates that exogenous factors play a key role in shaping the fire-forest structure mosaic and that the fire-forest structure mosaic is more variable, less predictable and less stable than previously thought. Finally, some characteristics of the fire regime (i.e. fire severity, season of burn) in CCRNA are different than those described for other mixed conifer forests and this suggests that there are geographical differences in mixed conifer fire regimes along the Pacific slope.

We studied vegetation composition and structure in a mixed conifer–oak ecosystem across a range of fire severity 10 years following wildfire. Sample plots centered on focal California black oaks (Quercus kelloggii) were established to evaluate oak and neighboring tree and shrub recovery across a gradient of fire severity in the southern Cascade Range, USA. Shrub and oak resprouting was strongest around focal oaks where conifer mortality was greatest. Linear modeling revealed negative relationships between California black oak sprout height or basal area and residual overstory tree survival, primarily white fir (Abies concolor). The two dominant competing species, California black oak and white fir, showed opposite responses to fire severity. Sprouting California black oak and associated shrubs dominated in severely burned areas, while surviving, non-sprouting white fir maintained dominance by its height advantage and shading effects in areas that burned with low fire severity. Our results indicate that high-severity fire promotes persistence and restoration of ecosystems containing resprouting species, such as California black oak, that are increasingly rare due to widespread fire exclusion in landscapes that historically experienced more frequent fire. We present a conceptual model based on our results and supported by a synthesis of postfire resprouting dynamics literature. Our results and conceptual model help illuminate long-term postfire vegetation responses and the potential ability of fire to catalyze formation of alternate vegetation community structures that may not be apparent in studies that evaluate postfire effects at shorter time-since-fire intervals or at coarser scales.

International audience; The Douglas-fir tussock moth (DFTM), Orgyia pseudotsugata McDunnough (Lepidoptera:Erebidae:Lymantriinae), is a native western North American defoliator of true fir, Abies spp. Mill., and Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. We investigated the population genetics and impact associated with the first recorded outbreak of DFTM in southern California (USA), and report the first collection of DFTM in Baja California Norte, Mexico. This latter population is similar genetically to populations from Washington, USA and British Columbia, Canada. We assessed forest stand characteristics, levels of defoliation, and mortality of white fir, Abies concolor Lindl., associated with the DFTM outbreak in the Transverse Mountain Ranges of southern California. We compared these data to those from southern California non-outbreak stands of A. concolor, and from virgin stands with an A. concolor component in the Sierra San Pedro Martir National Park (Mexico). Total stand density (ha−1) was significantly higher (22%) in non-outbreak stands than in outbreak stands. However, outbreak stands had significantly higher mortality of A. concolor than non-outbreak stands [whether expressed as density (70%) or basal area (m2 ha−1) (32%)]. Total stand and A. concolor density and basal area for living and dead trees were significantly lower in the Sierra San Pedro Martir National Park than in southern California. Dead A. concolor comprised >95% of all tree mortality in both outbreak and non-outbreak areas in southern California, which corresponded to a mean 20% basal area loss of A. concolor associated with DFTM feeding injury within the outbreak area. The mean level of defoliation of A. concolor by DFTM was 39%, and 62% of all dead A. concolor were associated with DFTM defoliation. In stands with high levels of defoliation, larval feeding and tree mortality were also noted in Jeffrey pine, Pinus jeffreyi Grev. & Balf. The amount of dead A. concolor basal area associated with the fir engraver, Scolytus ventralis LeConte (Coleoptera: Scolytidae), in non-outbreak stands was 96% greater than in outbreak stands. Using the U.S.D.A. National Insect and Disease Risk Map software, a total of 13,534 ha were predicted to be at risk to basal area loss from future DFTM outbreaks on national forest lands in southern California. Changes in forest management practices and fire suppression policies likely led to an increase in the density and continuity of DFTM’s preferred host in southern California and to a southward shift in the historic range of DFTM outbreaks.

Xylem water potential of the midelevation conifers Pinus jeffreyi, Pinus lambertiana, Abies concolor, and Calocedrus decurrens, the higher elevation Pinus monticola and Abies magnifica, and co-occurring evergreen angiosperm shrubs, together with soil moisture under these plants, were monitored at three sites on the Kern Plateau in the southernmost Sierra Nevada Range of California. Site locations spanned the ecotone between the mid- and upper montane forests at elevations of 2230-2820 m. Measurements were made through a low-snowfall year and a heavy-snowfall year.In the Mediterranean climate of the Sierra Nevada, the heavy winter snowpack persists into late spring, after precipitation has effectively stopped. We found the subsequent depletion of soil moisture due to plant water uptake to result in predawn xylem water potentials for conifers more negative by 0.6-1.4 MPa than those for shrubs or inferred soil potentials. Shrubs generally depleted soil moisture more rapidly and ultimately extracted a greater fraction of the available soil moisture than did the conifers. This depletion of soil moisture by shrubs, particularly Arctostaphylos patula, may limit conifer growth and regeneration by prematurely terminating growth on the shallow soils studied. The conifers all generally showed similar patterns of soil moisture use, except that A. magnifica extracted moisture more rapidly early in the season.

Growth and xylem water potential of the lower elevation conifers Pinus jeffreyi and Abies concolor and the higher elevation Pinus monticola and Abies magnificawere monitored in their montane Mediterranean habitat of the southernmost Sierra Nevada mountains of California. Measurements were made across the ecotone between the midmontane and upper montane forests and through light and heavy snowfall years. Radial stem growth, averaging ;1.5 mm/yr, started 2 wk after snow melt, providing that maximum air temperatures had reached 218C, and ended when predawn water potentials fell rapidly at the onset of the summer drought. Leader growth started on or after a fixed date, providing that minimum air temperatures were above 248C for Pinus species or 12.58C for Abies species. The cue for leader growth was inferred to be photoperiodic. Leader growth ended when either a determinate internode length of ; 1m m was reached or predawn water potentials fell rapidly. Abies magnificagrew more rapidly than the low-elevation species, but had a shorter growth period; its annual leader growth, as a consequence, was only 35 mm/yr vs. 50 mm/yr for the low-elevation species. Needle growth was similarly determinate in the absence of early drought. This growth phenology contributes to determining species distribution across the ecotone. The montane Mediterranean climate of the Sierra Nevada range of California is characterized by heavy winter precipitation—rain and snow in the midmontane forest and snow in the upper montane forest—and an extended period of summer drought (Oosting and Billings, 1943; Axelrod, 1976; Major, 1990). The ecotone between the midmontane forest and upper montane forest is marked by a major discontinuity in the distribution of conifer and other species (Mellmann-Brown and Barbour, 1995; Barbour and Minnich, 2000). In the southernmost Sierra Nevada this ecotone occurs at elevations between ;2400 and 2700 m. The overall objective of the work reported in this and in a companion paper in this issue (Royce and Barbour, 2001) was increased understanding of environmental factors and their interactions affecting conifer species distribution across this ecotone. The midmontane (mixed conifer) forest of the southernmost Sierra Nevada is dominated by yellow pine (Pinus ponderosa Laws or Pinus jeffreyi Grev. & Balf.), Sierra white fir (Abies concolor Gordon & Glend. var. lowiana (Gordon) Murray), sugar pine (Pinus lambertiana Douglas), incense cedar (Calocedrus decurrens (Torry) Florin), and black oak (Quercus kelloggii Newb.). The upper montane (red fir) forest is dominated by Shasta red fir (Abies magnificaMurray, var. shastensis Lemmon) and western white pine (Pinus monticola Douglas). Trees found within the ecotone include P. jeffreyi, P. monticola, A. concolor, and A. magnifica(Barbour and

Peroxidase activity was monitored during somatic embryogenesis of white fir (Abies concolor Gord. et Glend) starting from a non-embryogenic callus. Results revealed profound differences between non-embryogenic and embryogenic calli with an elevated level of enzyme activity in non-embryogenic ones. Precotyledonary, early cotyledonary and late cotyledonary stages of somatic embryogenesis were characterized by a substantially reduced peroxidase activity compared to callus tissues and regenerated plantlets. Changes in peroxidase activity are as a rule paralleled by variation in isoenzyme composition. The utility of the enzyme in the induction stage of somatic embryogenesis in white fir is proposed.

Species distribution and abundance patterns in the southern Cascades are influenced by both environmental gradients and fire regimes. Little is known about fire regimes and variation in fire regimes may not be independent of environmental gradients or vegetation patterns. In this study, we analyze variation in fire regime parameters (i.e., return interval, season, size, severity, and rotation period) with respect to forest composition, elevation, and potential soil moisture in a 2042 ha area of montane forest in the southern Cascades in the Thousand Lakes Wilderness (TLW). Fire regime parameters varied with forest composition, elevation, and potential soil moisture. Median composite and point fire return intervals were shorter (4-9 yr, 14-24 yr) in low elevation and more xeric white fir (Abies concolor)-sugar pine (Pinus lambertiana) and white fir-Jeffrey pine (P. jeffreyi) and longest (20-37 yr, 20-47 yr) in mesic high elevation lodgepole pine (Pinus contorta) and red fir (Abies magnifica)-mountain hemlock (Tsuga mertensiana) forests. Values for mid-elevation red fir-white fir forests were intermediate. The pattern for fire rotation lengths across gradients was the same as for fire return intervals. The percentage of fires that occurred during the growing season was inversely related to elevation and potential soil moisture. Mean fire sizes were larger in lodgepole pine forests (405 ha) than in other forest groups (103-151 ha). In contrast to other parameters, fire severity did not vary across environmental and compositional gradients and >50% of all forests burned at high severity with most of the remainder burning at moderate severity. Since 1905, fire regimes have become similar at all gradient positions because of a policy of suppressing fire and fire regime modification will lead to shifts in landscape scale vegetation patterns.

Piperidine alkaloids are reported for the first time from Picea omorika (Serbian spruce), Abies balsamea (balsam fir), and Abies concolor (Rocky mountain white fir). The alkaloids of P. omorika and P. sitchensis were similar, but not identical, and very different from those reported from P. breweri, a species with which they have been taxonomically linked. We were not able to detect alkaloids in A. procera, A. lowiana, or A. grandis. The total base fraction of A. bifolia yielded a nonbasic monoterpenoid known as Muller's lactone, presumed to be an artifact of the isolation procedure.

Aim Spatial and temporal variation in fire regime parameters and forest structure were assessed. Location A 2630-ha area of mid- and upper montane forest in Lassen Volcanic National Park (LVNP). Methods Two hypotheses were tested concerned with fire-vegetation relationships in southern Cascades forests: (1) fire regime parameters (return interval, season of burn, fire size, rotation period) vary by forest dominant, elevation and slope aspect; and (2) fire exclusion since 1905 has caused forest structural and compositional changes in both mid- and upper montane forests. The implications of the study for national park management are also discussed. Results Fire regime parameters varied by forest compositional group and elevation in LVNP. Median composite and point fire return intervals were shorter in low elevation Jeffrey pine ( Pinus jeffreyi ) (JP) (4‐6 years, 16 years) and Jeffrey pine‐white fir ( Abies concolor ) (JP-WF) (5‐10 years, 22 years) and longer in high elevation red fir ( Abies magnifica )— western white pine ( Pinus monticola ) (RF-WWP) forests (9‐27 years, 70 years). Median fire return intervals were also shorter on east-facing (6‐9 years, 16.3 years) and longer on south- (11 years, 32.5 years) and west-facing slopes (22‐28 years, 54-years) in all forests and in each forest composition group. Spatial patterns in fire rotation length were the same as those for fire return intervals. More growing season fires also occurred in JP (33.1%) and JP-WF (17.5%) than in RF-WWP (1.1%) forests. A dramatic decline in fire frequency occurred in all forests after 1905. Conclusions Changes in forest structure and composition occurred in both mid- and upper montane forests due to twentieth-century fire exclusion. Forest density increased in JP and JP-WF forests and white fir increased in JP-WF forests and is now replacing Jeffrey pine. Forest density only increased in some RF-WWP stands, but not others. Resource managers restoring fire to these now denser forests need to burn larger areas if fire is going to play its pre-settlement role in montane forest dynamics.

The structure of Heterobasidion annosum populations was studied in 15 mixed-conifer sites in central and northern California. Study sites displayed mortality of white fir trees in enlarging discrete patches (mortality centers). At each site, fungal genotypes were defined by somatic compatibility tests. In two sites, further genetic and molecular analyses were performed on field genotypes and on homokaryons obtained by dedikaryotization of field heterokaryons. Isolates were found to be colonizing mostly the roots and the bole sapwood of white fir trees, and no significant infections of other tree species were observed. Each mortality center was characterized by the presence of several fungal genotypes, all belonging to the S intersterility group. Both homokaryotic and heterokaryotic strains were present in all sites. Multiple genotypes were retrieved in individual trees or stumps. Out of 228 fungal genotypes, 86% were found only within a single tree or stump, while 14% had spread to adjacent trees. The two largest genotypes had diameters of 9 and 10 m, and had colonized five and nine trees, stumps, or both, respectively. The maximum distance between two adjacent trees colonized by the same genotype was 6 m, and a highly significant correlation was found between tree diameter and distance of fungal “vegetative” spread. The largest clones were found in areas characterized by high tree and stump densities, and secondary spread of the fungus was more significant in denser stands. In most cases, original infection courts of existing genotypes could be traced to standing trees and not to stumps. The genetic analysis performed in two mortality centers revealed that most local genotypes had different mating alleles, and thus originated from unrelated basidiospores. In a few cases, the same mating allele was shared by two heterokaryons (n+n genome) or by a homokaryon (n genome) and a heterokaryon. Molecular analysis showed that nuclei bearing the same mating allele were identical, providing evidence that the two nuclei forming heterokaryons can act independently in the field and can be shared among isolates, presumably via di-mon mating or by separate matings of different portions of widespread homokaryons.

We compared abundances of seven species of forest rodents among three types of fir ( Abies concolor and A. magnifica ) forest: unlogged old-growth, unlogged mature, and shelter-wood-logged old-growth. Small mammals were livetrapped during summers 1991 and 1992 in four grids within each type of forest; grids were located in the Lassen National Forest in northeastern California. Shelterwood-logged forests had been logged 6–7 years previously. Differences in capture rates between unlogged, old-growth and shelterwood-logged, old-growth forests suggest that logging led to significant increases in populations of golden-mantled ground squirrels ( Spermophilus lateralis ), yellow pine chipmunks ( Tamias amoenus ), and lodgepole chipmunks ( Tamias speciosus ) but may have led to reduced populations of western red-backed voles ( Clethrionomys californicus ). Capture rates of Douglas' squirrels ( Tamiasciurus douglasii ), Allen's chipmunks ( Tamias senex ), and deer mice ( Peromyscus maniculatus ) did not differ significantly between unlogged and shelterwood-logged forests. Capture rate of T. douglasii was significantly greater in mature forests than in old-growth forests in 1992, but we did not detect significant differences between old-growth and mature forests for the other six species. These results illustrate how opening of the canopy and disturbance of the forest floor can lead to significant changes in patterns of abundance of forest rodents.

Studies were conducted to determine whether herbivore-induced synthesis of monoterpenes occurs in the needles of ponderosa pine (Pinus ponderosa Lawson), lodgepole pine (P. contorta Douglas var. latifolia Engelmann), white fir (Abies concolor Lindl. and Gordon) and Engelmann spruce [Picea engelmanii (Parry) Engelm.]. In the needles of all species except Engelmann spruce, simulated herbivory significantly induced the activity of monoterpene cyclases 4-8 days after wounding. In ponderosa pine, real herbivory by last-instar tiger moth larvae (Halisdota ingens Hy. Edwards: Lepidoptera) induced a significantly larger response (4.5-fold increase in monoterpene cyclase activity) than did simulated herbivory (2.5-fold increase). To our knowledge, this is the first report of herbivore-induced increases in monoterpene synthesis in needle tissue. Despite this increase in monoterpene synthesis, we observed no significant increase in total monoterpene pool size in wounded needles compared to controls. Large increases in the rate of monoterpene volatilization were observed in response to wounding. We conclude that the volatile losses caused by tissue damage compensate for herbivore-induced monoterpene synthesis, resulting in no change in pool size. Tiger moth larvae consume ponderosa pine needles in a pattern that begins at the tip and proceeds downward to midway along the needle, at which point they move to an undamaged needle. Constitutive monoterpene concentrations and monoterpene cyclase activities were highest in the lower half of ponderosa pine needles. The monoterpene profile also differed between the upper and lower needle halves, the lower half possessing an additional one to four monoterpene forms. We propose that the increasing gradient in monoterpene concentrations and number of monoterpenes along the needle from tip to base deters feeding beyond the midway point and provides time for the induction of increased cyclase activity and production of new monoterpenes. The induction of new monoterpene synthesis may have a role in replacing monoterpenes lost through damage-induced volatilization and preventing extreme compromise of the constitutive defense system.