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1.
Thinnings using cut-to-length or whole-tree harvesting systems followed by underburning were evaluated for their effects on seedling and sapling demography in a pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand containing a minor component of California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Depression of seedling counts due to forest floor disturbance associated with thinning was followed by a recovery largely confined to Jeffrey pine in the whole-tree treatment where final seedling counts exceeded those found initially. The postburn substrate was more favorable for establishment of Jeffrey pine than white fir seedlings, and the largest increase in seedling counts between the initial and final inventories occurred in the burned portion of the whole-tree treatment. Live sapling losses from thinning were greatest in the cut-to-length treatment, while underburning induced complete sapling mortality. Absent treatment, several stand and site variables influenced seedling and sapling abundance, prominent among them a propensity for mahala mat (Ceanothus prostratus Benth.) to elevate counts of white fir within both size classes. These results provide land managers insight into the impacts of six combinations of thinning and burning treatment on natural regeneration in eastern Sierra Nevada Jeffrey pine and similar dry site forest types.  相似文献   

2.
Thinning implemented with a cut-to-length harvesting system coupled with on-site slash chipping and redistribution and followed by prescribed underburning were assessed for their impacts on a shrub understory in an uneven-aged Sierra Nevada mixed conifer stand. Overstory species consisted of California white fir (Abies concolor var. lowiana [Gord.] Lemm.), Jeffrey pine (Pinus jeffreyi Grev. & Balf.), sugar pine (Pinus lambertiana Dougl.), incense-cedar (Libocedrus decurrens Torr.), and red fir (Abies magnifica A. Murr.), while huckleberry oak (Quercus vacciniifolia Kellogg) was predominant among 10 understory shrubs. Herbaceous species were entirely absent from the site for the 4-yr duration of the study. The mechanized treatments exerted minimal detriment effects on overall understory cover and weight, and for prostrate ceanothus (Ceanothus prostratus Benth.) and creeping snowberry (Symphoricarpos mollis Nutt.)—two of the lesser shrubs—were stimulatory. In contrast, losses to the total understory from the underburn amounted to two-thirds of cover and weight in the absence of the mechanized treatments and more than three-quarters where they had been implemented, with huckleberry oak prevalence especially diminished. For almost all of the understory species individually as well as for the total, greater pretreatment abundance predisposed greater posttreatment prevalence. Results of this study provide insight into the understory impacts of restoration treatments that are deemed especially appropriate for sensitive sites in western U.S. forests.  相似文献   

3.
Variability of postfire injury and stand and individual tree factors that affected survival responses of eastern Sierra Nevada conifers to wildfire were examined. Prefire measurements served as a basis of comparison for postfire conditions in a mixed conifer stand located in the eastern portion of the Lake Tahoe Basin and provided insight into predisposing influences on survival. Species composition consisted primarily of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and California white fir (Abies concolor var. lowiana [Gord.] Lemm.) along with a minor component of sugar pine (Pinus lambertiana Dougl.). Postfire survival was higher in Jeffrey pine than white fir but was highest overall in sugar pine. Catastrophic crown loss occurred less frequently in Jeffrey pine than in the fir but was least common in sugar pine. Survival generally increased with tree size, but this relationship did not extend to the largest trees in the stand. Among an array of regression models used to evaluate selected variables for their predictive capacity regarding postfire survival, prefire stand density was found to negatively influence that of Jeffrey and sugar pine, and survival of Jeffrey pine and white fir was negatively correlated with bole char. These results provide natural resource managers guidance in the selection of viable trees for retention during the salvage harvesting operations that often follow wildfire events.  相似文献   

4.
Wildfire effects on understory shrubs and herbs, regeneration of the seedling and sapling size classes, and downed and dead fuels were assessed in a mixed conifer stand located in the Lake Tahoe Basin in which California white fir (Abies concolor var. lowiana [Gord.] Lemm.) was most abundant but with Jeffrey pine (Pinus jeffreyi Grev. & Balf.) also prevalent. In burned and unburned stand portions, prefire measurements served as a basis of comparison for the postfire measurements pertinent to each study component. Fire severely suppressed the understory vegetation, which was dominated by shrubs such as bush chinquapin (Chrysolepis sempervirens [Kellogg] Hjelmqvist) and antelope bitterbrush (Purshia tridentata [Pursh] DC.), while a tepid postfire recovery of most of the preexisting species in the burned stand portion was augmented by new ones, including shrubs such as snowbrush (Ceanothus velutinus Douglas ex Hook.) and whitethorn (Ceanothus cordulatus Kellogg) ceanothus and herbs such as Holboell's rockcress (Arabis holboellii Hornem.). Tree seedling abundance was also substantially reduced in the burned portion, but the postfire population was dominated by Jeffrey pine whereas white fir had been most prevalent originally. Sapling regeneration was eliminated from the burned stand portion regardless of species. Downed and dead fuel loading was severely diminished by the fire, especially regarding fine fuels, permitting subsequent sheet erosion to imperil new seedling regeneration. These results contribute to an understanding of the direction and pace of postwildfire succession on sites occupied by Sierra Nevada mixed conifer and similar forest cover types, which is critical in decisions concerning the need for, and extent of, postfire site rehabilitation measures.  相似文献   

5.
Forest thinnings implemented with cut-to-length and whole-tree harvesting systems followed by underburning were evaluated for their effects on bark beetle prevalence in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) interspersed with isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on pitch tube counts in a stand with a moderate bark beetle population in its pine component, the Jeffrey pine beetle (Dendroctonus jeffreyi Hopkins) generally preferred larger trees before treatment implementation, but after exhibiting mixed pretreatment tendencies concerning stand density demonstrated a posttreatment proclivity toward higher density. Cut-to-length thinning followed by underburning increased the pine beetle population while whole-tree thinning unaccompanied by burning reduced it. Tree mortality was induced by the bark beetle infestation but was not its sole cause. Pitch tube abundance on white fir far exceeded that on Jeffrey pine, and the greatest influence on the fir engraver (Scolytus ventralis LeConte) population was the prevalence of its host tree. The responses presented herein to these thinning and burning practices, which are being increasingly utilized in forest restoration efforts in the western USA, provide natural resource managers insight into potential forest health outcomes when implemented in Jeffrey pine and similar dry site forest types.  相似文献   

6.
An investigation of wildfire effects on water relations of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) along with species comparisons of the water relations of unburned specimens of this pine to those of unburned white fir (Abies concolor var. lowiana [Gord.] Lemm.) were conducted in a mixed conifer stand located in the Lake Tahoe Basin. Xylem water potentials were significantly lower in burned than in the unburned Jeffrey pine as measured in predawn, midday, and evening periods distributed over more than two postfire growing seasons, while soil water potentials were lower in burned than in unburned stand portions during the drier parts of the growing season, but the reverse proved true during the wetter part. Diurnal fluctuation in bole diameter, a measure of stored water recharge capacity, was largely unaffected by wildfire, however. Xylem water potentials were consistently lower in unburned white fir than in unburned Jeffrey pine and DBH fluctuation was often lower in the fir than in the pine as well, but soil water potentials associated with unburned subject trees did not differ significantly between the two species. Demonstrated here are ecophysiological alterations that occur in Sierra Nevada mixed conifer due to wildfire and shifting species composition.  相似文献   

7.
An investigation of wildfire effects on mineral nutrition of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) along with species comparisons of the nutrition of unburned specimens of this pine to those of unburned California white fir (Abies concolor var. lowiana [Gord.] Lemm.) were conducted in an eastern Sierran mixed conifer stand. Foliar Fe and Mn concentrations were frequently higher and Al was consistently so in burned than in the unburned pine as assessed in six sampling periods distributed over more than two postfire growing seasons while base cation/metallic element molar ratios consisting of Ca/Al, K/Al, K/Mn, Ca/Fe, Mg/Fe, K/Fe, and Ca/Zn were often lower in the former. Foliar N, P, Fe, Zn, and Cu were frequently higher in unburned pine than unburned fir while the reverse proved true concerning K, Ca, Mn, B, and Al; and likewise several molar ratios involving Al and Mn were higher in the former while several involving Fe, Zn, and Cu were higher in the latter. At midstudy, mineral soil in the burned stand portion had lower K but higher S, Mn, and Zn than that in the unburned portion, and the former had several molar ratios that were lower as well.  相似文献   

8.
Vertical distribution of leaf area largely governs both tree structure and function. Models of this important tree attribute have been constructed for several commercially important conifers. However, a limited number of studies have compared alternative modeling techniques and inherent species differences. This study used several existing datasets for the five primary conifer species in Maine, namely balsam fir [Abies balsamea (L.) Mill.], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)] to examine species variation in total and vertical distribution of projected leaf area at the individual branch- and tree-levels. In addition, multiple methods for modeling the vertical distribution of leaf area were examined across the species. For a given branch diameter and location within the crown, eastern hemlock branches held the greatest amount of leaf area, followed by balsam fir, northern white-cedar, white pine, and red spruce. At the tree-level, eastern white pine held the greatest amount of leaf area followed by eastern hemlock, balsam fir, red spruce, and northern white-cedar for a given tree size. Across species, the two-parameter, right-truncated Weibull distribution performed the best for predicting vertical distribution of leaf area when compared to the four-parameter beta and Johnson's SB distributions (reduction of root mean square error of 1.7–21.1%). Northern white-cedar had a relative distribution of leaf area distinctly different than other species in this study with a mode shifted towards the upper crown. In contrast to red spruce and white pine, the mode of the relative distribution of leaf area for balsam fir and eastern hemlock occurred lower in the crown. Results of this study suggest that differences in total and vertical distribution of leaf area exist between species, but significant amounts of their variation are largely accounted for by bole and crown size.  相似文献   

9.
This study reports 14th-year response of a boreal mixedwood stand to different harvest intensities (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), spot site preparation treatments (none and scalped), and chemical weeding frequencies (none, single, and multiple) in northeastern Ontario. The response variables include the survival and growth of planted white spruce (Picea glauca [Moench] Voss) and jack pine (Pinus banksiana Lamb.), height and density of natural regeneration and shrubs, and cover of shrubs and non-woody vegetation. Harvesting and weeding generally improved survival and growth of planted trees, although white spruce survival did not significantly differ among the three weeding frequencies. Harvesting tended to increase heights of hardwood (mostly trembling aspen (Populus tremuloides Michx.)) and conifer (largely balsam fir (Abies balsamea (L.) Mill.).) natural regeneration, cover and density of shrubs, and cover of herbs, lichens, and ferns. Chemical weeding reduced height, density and cover of shrubs, height and density of hardwood regeneration, and fern cover, but increased moss and lichen cover. Spot scalping did not significantly affect planted seedling, natural regeneration, or the vegetation.Maximum survival and growth of planted white spruce and jack pine were achieved using a combination of clearcutting and multiple weeding. However, partial cutting followed by a single weeding produced acceptable survival and reasonable growth of planted trees, particularly for white spruce. Partial canopy removal alone substantially reduced the amount of hardwood regeneration, relative to clearcutting, but did not adequately suppress understory shrubs. Significant improvement in seedling growth following multiple weedings was evident primarily in the complete canopy removal treatments: 50% partial cut with removal of residuals after 3 years and clearcut. While the effects of harvesting and weeding on planted crop trees found in the 5th-year assessments generally persisted at year 14, survival decreased, likely due to light competition from developing hardwood and shrubs.  相似文献   

10.
Forest thinnings implemented with cut-to-length and whole-tree harvesting systems followed by underburning were evaluated for their effects on individual tree and stand level growth responses in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) accompanied by isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on both dimension and volume measures, trees of the unburned whole-tree treatment combination exhibited the greatest individual growth responses. At the stand level, a diminished volume growth response in the whole-tree treatment was especially pronounced in the burned portion, mostly attributable to exaggerated stocking losses, while a superior response in the unburned cut-to-length combination likely reflected not only the absence of detrimental fire impacts but also benefits of on-site slash retention. For stand level biomass, diminished growth in the whole-tree treatment was again evident, with that in the burned portion again most pronounced, while biomass accrual in the unburned cut-to-length treatment combination was generally comparable to that in the unthinned control. Increasingly utilized in forest restoration efforts in the western USA, the responses presented herein to these thinning and burning practices provide natural resource managers insight into potential compromised outcomes when implemented in Jeffrey pine and similar dry site forest types.  相似文献   

11.
Quantitative models of crown structure have been developed for several conifer species, but these studies have rarely simultaneously fit the models across multiple species. This study used extensive crown structure data for the five primary conifer species in Maine to test for species differences in maximum branch diameter profile, branch density, and relative branch diameter distribution. The species included balsam fir [Abies balsamea (L.) Mill], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)]. After accounting for key covariates, significant species differences were found in all crown structural attributes examined in this study. Profiles for the mean tree indicated that northern white-cedar had the smallest maximum branch diameters throughout the crown and white pine had the largest, except near the base of the crown where the species switched in rank. The density of live branches in a crown had the widest range of variation of the examined crown structural attributes. Red spruce had a significantly higher density of primary branches than the other conifers, particularly in the upper crown. The relative branch diameter distribution indicated that balsam fir had a distribution more skewed towards larger relative branch sizes, while eastern hemlock and red spruce had distributions shifted towards smaller relative branches. This study highlights the range of variability in key crown structural attributes due to inherent species differences, but indicates that models fit across multiple species can perform quite well as the amount of explained variation was relatively high.  相似文献   

12.

• Introduction  

The accurate estimation of stem taper and volume are crucial for the efficient management of the forest resources. Compatible segmented polynomial taper and volume equations were developed for Brutian pine (Pinus brutia Ten.), Lebanon cedar (Cedrus libani A. Rich.), Cilicica fir (Abies cilicica Carr.), Scots pine (Pinus sylvestris L.), and Black pine (Pinus nigra Arnold.).  相似文献   

13.
Forest thinnings implemented through cut-to-length and whole-tree harvesting followed by underburning were evaluated for their effects on long-term downed and dead fuels accumulations in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) accompanied by isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on an initial inventory consisting of dry weight and fuel bed depth measurements conducted posttreatment, accumulations in the cut-to-length treatment were elevated according to most measures. Burned stand portions exhibited smaller quantities of fuels initially in individual timelag categories and in total as well as reduced fuel bed depths compared to their unburned counterparts except for the 1,000-hr fuels in the whole-tree treatment where postburn mortality of small stems nullified this effect. A linkage between initial mortality resulting from prescribed fire and final 1,000-hr fuels, as measured 8 yr later, was established but was probably attributable to combined thinning and burning effects. Over the course of the study, either greater accruals or diminished reductions in loading were apparent within burned stand portions compared to unburned portions, most notably in the whole-tree treatment. Results presented here provide insight into potentially compromised fuels reduction outcomes when implemented in uneven-aged stands on dry forest sites.  相似文献   

14.
Fire injury was characterized and survival monitored for 5677 trees >25 cm DBH from five wildfires in California that occurred between 2000 and 2004. Logistic regression models for predicting the probability of mortality 5-years after fire were developed for incense cedar (Calocedrus decurrens (Torr.) Florin), white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), sugar pine (Pinus lambertiana Douglas), Jeffrey pine (P. jeffreyi Balf.), and ponderosa pine (P. ponderosa C. Lawson). Differences in crown injury variables were also compared for Jeffrey and ponderosa pine. Most mortality (70–88% depending on species) occurred within 2 years post-wildfire and had stabilized by year 3. Crown length and crown volume injury variables predicted tree mortality equally well; however, the variables were not interchangeable. Crown injury and cambium kill rating was significant in predicting mortality in all models. DBH was only a significant predictor of mortality for white fir and the combined ponderosa and Jeffrey pine models developed from the McNally Fire; these models all predicted increasing mortality with increasing tree size. Red turpentine beetle (Dendroctonus valens) was a significant predictor variable for sugar pine, ponderosa pine, and Jeffrey pine; ambrosia beetle (Trypodendron and Gnathotrichus spp.) was a significant predictor variable for white fir. The mortality models and post-fire tree survival characteristics provide improved prediction of 5-year post-wildfire tree mortality for several California conifers. The models confirm the overall importance of crown injury in predicting post-fire mortality compared to other injury variables for all species. Additional variables such as cambium kill, bark beetles, and tree size improved model accuracies, but likely not enough to justify the added expense of data collection.  相似文献   

15.
The fungal pathogen Heterobasidion irregulare has caused substantial damage to pine species in much of the south‐eastern United States, but the potential for damage from Heterobasidion root disease to forest tree species of the Great Lakes Region has not been thoroughly investigated. In each of three trials in two infested stands, fresh stem discs of six native conifer species were exposed to natural inoculum and examined for the asexual Spiniger stage of H. irregulare after incubation in the laboratory. In the first trial, the fungus was infrequently observed on discs, and differences among species were not found. But in the other two trials, detection of the pathogen was much more frequent on discs of tamarack (Larix laricina), red pine (Pinus resinosa) and white spruce (Picea glauca) than those of northern white cedar (Thuja occidentalis), eastern hemlock (Tsuga canadensis) and balsam fir (Abies balsamea). In a second study, the ability of an isolate of H. irregulare to decay root sapwood of these same species was compared using a soil‐block decay test. After 16 weeks of incubation, weight loss due to decay was greatest for red pine (23.2%) and larch (19.1%) and least for balsam fir (1.3%). Differences in the ability of H. irregulare to infect and saprophytically utilize substrate of these important tree species should prompt additional investigation of the relative risk posed to forests of the Great Lakes Region.  相似文献   

16.
Mature shrubs can provide microhabitats that are beneficial to tree seedling growth and development. Sugar pine trees (Pinus lambertiana) grow in a narrow zone on the eastern slope of the Carson Range in extreme western Nevada, whereas Jeffrey pine (Pinus jeffreyi) is the dominant tree species in the region, an area extensively disturbed by wild fire. This study compares seedling establishment of sugar pine and Jeffrey pine relative to mature shrubs. In the fall of 2002 (cohort 1) and 2003 (cohort 2), 13,600 seeds of both species were planted in wire mesh enclosures, at three sites, under a variety of microhabitat treatments: under shade and in the open, under two species of shrub cover, and with and without plant litter. Seedlings were monitored for survival through two growing seasons. Even though more sugar pine seedlings emerged, more Jeffrey pine seedlings survived, and Jeffrey pine was the more drought tolerant species, better suited for the xeric climate found in the Carson Range. Litter slightly hindered seedling emergence but had no effect on survival and there was no significant species × litter interaction. Supplemental water facilitated survival in all treatments with highest survival in shade treatments. Sugar pine seedlings showed a significant increase in survival over Jeffrey pine seedlings with the addition of water, particularly in open treatments and more of both species survived under manzanita shrubs with water. The highest seedling mortality occurred when shrub canopy was removed, and seedlings experienced the effect of full sun and competition for soil water. For either species, microhabitat is a significant factor in determining success or failure in rehabilitation efforts after disturbance.  相似文献   

17.
Root growth in seedling transplants of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), Pacific silver fir (Abies amabilis(Dougl.) Forbes), noble fir (Abies procera Rehd.), lodgepole pine (Pinus contorta Dougl. ex Loud.) and ponderosa pine (Pines ponderosa Doug. ex Laws.) began when soil temperature exceeded 5 °C. Root growth increased rapidly after 10 °C and attained maximum values at 20 °C. At 30 °C, no root growth occurred in the firs; in the pines, root growth was 30 to 39% of maximum. Maximum shoot growth also occurred at 20 °C. In ponderosa pine, height growth of seedlings from a high-elevation source was unaffected by cold soil, but in low-elevation seedlings it was reduced. Budburst in Douglas-fir and the pines was delayed up to 11 days by cold soil, whereas in silver fir and noble fir, it was only slightly delayed. Prior to new root growth in ponderosa pine, xylem pressure potentials and stomatal conductances during the afternoon indicated reduced stomatal opening at all soil temperatures, whereas 23 days later, stomata were open to a greater degree when temperatures exceeded 10 °C.  相似文献   

18.
Five conifer species grown in the Great Lakes region of North America were examined for their susceptibility to Fusarium circinatum, (syns. Fusarium subglutinans f. sp. pini and F. moniliforme var. subglutinans), the causal agent of pitch canker. Three‐year‐old (3‐0) seedlings of red (Pinus resinosa), jack (P. banksiana) eastern white (P. strobus), Scots (P. sylvestris) and Austrian (P. nigra) pine were planted in 4 l pots in a greenhouse at Auburn University in November 1998. In April and June 1999, seedlings were inoculated by removing a needle fascicle approximately 5 cm from the terminal bud and placing a drop containing F. circinatum conidia on the wound. Resin production, canker length and seedling mortality were recorded 12 weeks later. Jack, Scots and eastern white pine were the most susceptible with Austrian and red pine more resistant to the fungus. F. circinatum was re‐isolated from 37% to 96% of inoculated seedlings. The susceptibility of jack, Scots and eastern white pine indicates a potential risk to these important species of the region if F. circinatum were to be introduced into the area.  相似文献   

19.
The abundance of eastern white pine (Pinus strobus L.) has been significantly reduced across its distribution range over the past few centuries. The species’ regeneration dynamics is well documented in the centre of its range, but is poorly understood at the northern limit of continuous distribution. To address this knowledge gap, we quantified natural white pine regeneration in unmanaged mature stands, identified the most important variables influencing it, and evaluated the impact of damaging agents, namely white pine blister rust (Cronartium ribicola J.C. Fisch.), white pine weevil (Pissodes strobi Peck), and herbivory. We also quantified the influence of remnant stands and residual trees on the spatial distribution of regeneration in logged sites. The results reveal continuous but low recruitment in mature stands. The basal area of balsam fir (Abies balsamea (L.) Miller) had a strong negative effect on white pine regeneration. Regeneration was more abundant than expected on moister substrates, including moss, decaying wood and organic matter. White pine regeneration was noted in recently logged areas, where distance from remnant stands had a significant effect on the abundance of white pine regeneration. The northern limit of continuous distribution holds potential for white pine restoration, for example by preserving remnant white pine stands that can provide seed sources for natural regeneration in a shelterwood cut system, or in adjacent clearcut areas. This study illustrates that different management strategies should be used near northern range limits, where effects of site conditions and disturbance agents are different than in the center of a species’ range.  相似文献   

20.
The Warner Mountains of northeastern California on the Modoc National Forest experienced a high incidence of tree mortality (2001–2007) that was associated with drought and bark beetle (Coleoptera: Curculionidae, Scolytinae) attack. Various silvicultural thinning treatments were implemented prior to this period of tree mortality to reduce stand density and increase residual tree growth and vigor. Our study: (1) compared bark beetle-caused conifer mortality in forested areas thinned from 1985 to 1998 to similar, non-thinned areas and (2) identified site, stand and individual tree characteristics associated with conifer mortality. We sampled ponderosa pine (Pinus ponderosa var ponderosa Dougl. ex Laws.) and Jeffrey pine (Pinus jeffreyi Grev. and Balf.) trees in pre-commercially thinned and non-thinned plantations and ponderosa pine and white fir (Abies concolor var lowiana Gordon) in mixed conifer forests that were commercially thinned, salvage-thinned, and non-thinned. Clusters of five plots (1/50th ha) and four transects (20.1 × 100.6 m) were sampled to estimate stand, site and tree mortality characteristics. A total of 20 pre-commercially thinned and 13 non-thinned plantation plot clusters as well as 20 commercially thinned, 20 salvage-thinned and 20 non-thinned mixed conifer plot clusters were established. Plantation and mixed conifer data were analyzed separately. In ponderosa pine plantations, mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB) caused greater density of mortality (trees ha−1 killed) in non-thinned (median 16.1 trees ha−1) compared to the pre-commercially thinned (1.2 trees ha−1) stands. Percent mortality (trees ha−1 killed/trees ha−1 host available) was less in the pre-commercially thinned (median 0.5%) compared to the non-thinned (5.0%) plantation stands. In mixed conifer areas, fir engraver beetles (Scolytus ventralis LeConte) (FEN) caused greater density of white fir mortality in non-thinned (least square mean 44.5 trees ha−1) compared to the commercially thinned (23.8 trees ha−1) and salvage-thinned stands (16.4 trees ha−1). Percent mortality did not differ between commercially thinned (least square mean 12.6%), salvage-thinned (11.0%), and non-thinned (13.1%) mixed conifer stands. Thus, FEN-caused mortality occurred in direct proportion to the density of available white fir. In plantations, density of MPB-caused mortality was associated with treatment and tree density of all species. In mixed conifer areas, density of FEN-caused mortality had a positive association with white fir density and a curvilinear association with elevation.  相似文献   

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