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California’s high density, fire-excluded forests experienced an extreme drought accompanied by warmer than normal temperatures from 2012 to 2015, resulting in the deaths of millions of trees. We examined tree mortality and growth of mixed-conifer stands that had been experimentally treated between 2011 and 2013 with two different thinning treatments, one with more structural variability (HighV) and one with less structural variability (LowV), applied alone or in combination with prescribed burning. Tree mortality between 2014 and 2018 varied by species ranging from 42% of white fir (Abies concolor) to 18% of sugar pine (Pinus lambertiana), 12% of incense cedar (Calocedrus decurrens) and 10% of yellow pine (P. ponderosa and P. jeffreyi). Lower overall tree mortality rates at this location relative to drier locations in the southern Sierra Nevada suggested that drought effects may have been ameliorated by lower water deficits due to our site’s more northerly location and deep, productive soils in combination with reductions in tree competition following thinning and burning. Averaged across burn treatments, thinning reduced the overall mortality rate between 2014 and 2018 from 34% to 11%. A total of 23% of the basal area was lost in the unthinned control treatments during this time period, while basal area was unchanged in the thinned treatments, with growth offsetting mortality. There was no significant difference in mortality or basal area change between LowV and HighV, suggesting that leaving trees at variable spacing may not compromise growth or resilience of the stand during a drought. Overall tree mortality was greater in the prescribed burn treatments, most pronounced in the smaller tree size classes, and varied by species, with burning having a significant effect on incense cedar and all pines, but not white fir. Trees with greater competition (Hegyi index) were more likely to die, particularly when also burned. Burning, however, consumed surface fuels and lowered fire hazard. With predictions of warmer droughts and greater weather variability, reducing forest density (basal area) and keeping surface fuel loads low will be important for building greater resilience to future drought stress and wildfire.

Tree mortality associated with drought and concurrent bark beetle outbreaks is expected to increase with further climate change. When these two types of disturbance occur in concert it complicates our ability to accurately predict future forest mortality. The recent extreme California USA drought and bark beetle outbreaks resulted in extensive tree mortality and provides a unique opportunity to examine questions of why some trees die while others survive these co-occurring disturbances. We use plot-level data combined with a three-proxy tree-level approach using radial growth, carbon isotopes, and resin duct metrics to evaluate 1) whether variability in stand structure, tree growth or size, carbon isotope discrimination, or defenses precede mortality, 2) how relationships between these proxies differ for surviving and now-dead trees, and 3) whether generalizable risk factors for tree mortality exist across pinyon pine (Pinus monophylla), ponderosa pine (P. ponderosa), white fir (Abies concolor), and incense cedar (Calocedrus decurrens) affected by the combination of drought and beetle outbreaks. We find that risk factors associated with mortality differ between species, and that few generalizable patterns exist when bark beetle outbreaks occur in concert with a particularly long, hot drought. We see evidence that both long-term differences in physiology and shorter-term beetle-related selection and variability in defenses influence mortality susceptibility for ponderosa pine, whereas beetle dynamics may play a more prominent role in mortality patterns for white fir and pinyon pine. In contrast, incense cedar mortality appears to be attributable to long-term effects of growth suppression. Risk factors that predispose some trees to drought and beetle-related mortality likely reflect species-specific strategies for dealing with these particular disturbance types. The combined influence of beetles and drought necessitates the consideration of multiple, species-specific risk factors to more accurately model forest mortality in the face of similar extreme events more likely under future climates.

Understanding impacts of drought on tree growth and forest health is of major concern given projected climate change. Droughts may become more common in the Southwest due to extreme temperatures that will drive increased evapotranspiration and lower soil moisture, in combination with uncertain precipitation changes. Utilizing ~1.3 million tree-ring widths from the International Tree Ring Data Bank representing 10 species (eight conifers, two oaks) in the Southwest, we evaluated the effects of drought on tree growth. We categorized ring widths by formation year in relation to drought (pre-drought, drought year, and post-drought), and we used a mixed-effects model to estimate the effects of current and antecedent precipitation and temperature on tree growth during the post-drought recovery period. This allowed us to assess changes in sensitivity of tree growth to precipitation and temperature at multiple timescales following multiple droughts, and to evaluate drought resistance and recovery in these species. The effects of precipitation and temperature on ring widths following drought varied among species and time since drought. Across species, 16% of the climate effects (i.e., “sensitivities”) were significantly different from their pre-drought values. Species differed, with some showing increased sensitivities to precipitation and temperature following drought, and others showing decreased sensitivities. Furthermore, some species (e.g., Abies concolor and Pinus ponderosa) showed low resistance and slow recovery, with changes in growth sensitivities persisting up to 5 yr; others (e.g., Juniper spp.) showed high resistance, such that their climatic sensitivities did not change. Among species, the importance of different antecedent climate variables changed with time since drought. Though a majority of species responded positively to same-year precipitation pre-drought, all 10 species were positively affected by same-year precipitation the second year after drought. Our results demonstrate tree growth sensitivities vary among species and with time since drought, raising questions about physiological mechanisms and implications for forest health under future drought.

The William Hawk Cabin is considered one of the oldest pioneer structures in Salt Lake City, Utah. Tradition suggests that it was originally constructed in 1848 inside the “Old Fort” established by Mormon settlers in 1847, and then moved to its current location between 1850 and 1852. We examined tree rings from 23 Douglas-fir (Pseudotsuga menziesii var. glauca) and eight white fir (Abies concolor) timbers in the cabin to (1) evaluate and refine the suggested range of construction dates of 1848–1852, (2) verify or refute the suggestion that the cabin was originally constructed within the Old Fort, (3) identify any evidence of use of deadwood, timber re-use, stockpiling, or renovation, and (4) determine the provenance of the timbers. We built a 209-year floating chronology from 36 cores crossdated visually and verified statistically with COFECHA. Statistically significant (p < 0.0001) comparisons with established regional chronologies indicated that the Hawk Cabin chronology extends from 1651–1859....

The mid-elevation forest of California's Sierra Nevada poses a bioclimatic paradox. Mid-elevation trees experience a montane Mediterranean climate, with near-freezing winter days and rain-free summers. The asynchrony between warmth and water input suggests low primary production, limited by photosynthetic dormancy in winter cold, and again in summer and early autumn with drought, yet this forest is characterized by tall trees and high biomass. We used eddy covariance in a mid-elevation Sierra stand to understand how winter cold and summer drought limit canopy photosynthesis and production. The trees exhibited canopy photosynthesis year-round. Trees avoided winter dormancy, and daytime CO2uptake continued despite a deep snowpack and near-freezing temperatures. Photosynthesis on sunny days continued at half of maximum rates when air temperature was 0 °C. Likewise, the vegetation avoided summer drought dormancy, and high rates of daytime CO2uptake and transpiration continued despite a 5-month period with only negligible water input. We attribute this drought avoidance to deep rooting and availability of deep soil water. Year-round photosynthesis helps explain the large biomass observed in the Sierra Nevada, and implies adaptive strategies that may contribute to the resiliency or vulnerability of Sierran vegetation to climate change.

We studied bark thickness in the mixed-conifer forest type throughout California. Sampling included eight conifer species and covered latitude and elevation gradients. The thickness of tree bark at 1.37 m correlated with diameter at breast height (DBH) and varied among species. Trees exhibiting more rapid growth had slightly thinner bark for a given DBH. Variability in bark thickness obscured differences between sample locations. Model predictions for 50 cm DBH trees of each species indicated that bark thickness was ranked Calocedrus decurrens > Pinus jeffreyi > Pinus lambertiana > Abies concolor > Pseudotsuga menziesii > Abies magnifica > Pinus monticola > Pinus contorta. We failed to find reasonable agreement between our bark thickness data and existing bark thickness regressions used in models predicting fire-induced mortality in the mixed-conifer forest type in California. The fire effects software systems generally underpredicted bark thickness for most species, which could lead to an overprediction in fire-caused tree mortality in California. A model for conifers in Oregon predicted that bark was 49% thinner in Abies concolor and 37% thicker in Pseudotsuga menziesii than our samples from across California, suggesting that more data are needed to validate and refine bark thickness equations within existing fire effects models.

Paleoecological records detailing fire and vegetation histories during previous interglacials are extremely rare. We present a unique, high-resolution, 10-m long record of fire from a high elevation conifer-dominated site – the Snowmastodon (Ziegler Reservoir) site – in the southern Rocky Mountains, USA, for the period spanning MIS 6 to MIS 4. The charcoal particle influx (CHAR) over the entire Snowmastodon record documents that fire was a significant process on this high elevation landscape during MIS 5e-MIS 5a, just as it is today, but during a period without human influence. Both vegetation and precession cycles influence fire occurrence, with warm stages (MIS 5e, 5c, 5a) exhibiting higher CHAR than cool stages (MIS 6, 5d, 5b, 4). CHAR abruptly increases at the MIS 6-MIS 5e boundary, contemporaneously with a rapid increase in arboreal pollen. A strong positive correlation during MIS 5e between CHAR and Pinus pollen strongly suggests control of charcoal production and deposition through burning of Pinus forests within the region. Subsequently, elevated CHAR is correlated to abundant Abies concolor in MIS 5c, and Picea in MIS 5a, while minimal CHAR occurs during MIS 5b when local vegetation was sagebrush steppe. Comparison of the Termination II (TII) Snowmastodon record with Termination I (TI) from several nearby published sites shows mostly similar patterns of developing forest preceding increased burning, with a lag of several hundred years. This may signify the development of a new fire regime tied specifically to the new vegetation type, as climate warmed and fine fuels accumulated in a forested community.

The persistence and distribution of species under changing climates can be affected by both direct effects of the environment and indirect effects via biotic interactions. However, the relative importance of direct and indirect climate effects on recruitment stages is poorly understood. We conducted a manipulative experiment to test the multiway interaction of direct and competition-mediated effects of climate change on vegetation dynamics. Following stand-replacing fire in California mixed-conifer forest, we seeded two conifer species, Pinus ponderosa and Abies concolor, in two consecutive years, one relatively normal and the other with an unusually wet and snowy winter followed by a hot summer. We additionally manipulated snow amount and competitive environment for both years. We found the effects of the snowpack treatment were contingent upon other abiotic factors (year of seeding) and biotic factors (shrub competition). Under ambient snowpack, shrubs reduced recruitment of P. ponderosa seedlings, but this negative effect disappeared with reduced snowpack. Additionally, the effects of shrubs on seedlings differed between cohorts and by life stage. In a warmer future, decreased snowpack may increase seedling emergence, but hotter and drier summers will decrease seedling survival; the effects of shrubs on conifers may become less negative as temperatures increase.

Extreme drought stress and associated bark beetle population growth contributed to an extensive tree mortality event in California, USA, resulting in more than 129 million trees dying between 2012 and 2016. Although drought is an important driver of this mortality event, past and ongoing fire suppression and the consequent densification of forests may have contributed. In some areas, land management agencies have worked to reduce stand density through mechanical treatments and prescribed fire to restore forests to less dense, more open conditions that are presumably more resilient to disturbance and changing climate. Here, we evaluate if stand structural conditions associated with treated (e.g., thinned and prescribed burned) forests in the Sierra Nevada of California conferred more resistance to the bark beetle epidemic and drought event of 2012-2016. We found that, compared to untreated units, treated units had lower stand densities, larger average tree diameters, and greater dominance of pines (Pinus), the historically dominant trees. For all tree species studied, mortality was substantially greater in climatically drier areas (i.e., lower elevations and latitudes). Both pine species studied (ponderosa pine [Pinus ponderosa] and sugar pine [Pinus lambertiana]) had greater mortality in areas where their diameters were larger, suggesting a size preference for their insect mortality agents. For ponderosa pine, the tree species experiencing greatest mortality, individual-tree mortality probability (for a given tree diameter) was significantly lower in treated stands. Ponderosa pine mortality was also positively related to density of medium- to large-sized conspecific trees, especially in areas with lower precipitation, suggesting that abundance of nearby host trees for insect mortality agents was an important determinant of pine mortality. Mortality of incense cedar (Calocedrus decurrens) and white fir (Abies concolor) was positively associated with basal area, suggesting sensitivity to competition during drought, but overall mortality was lower, likely because the most prevalent and effective mortality agents (the bark beetles Dendroctonus brevicomis and D. ponderosae) are associated specifically with pine species within our study region. Our findings suggest that forest thinning treatments are effective in reducing drought-related tree mortality in forests, and they underscore the important interaction between water and forest density in mediating bark beetle-caused mortality.

The study analysed the causes of the annual variation of tree−ring widths of silver fir and white fir. The partial populations of both fir species has been growing for over 100 years in Rzepin (western Poland) in a fresh broadleaved forest site. We assumed that the year−to−year changes of the size of radial increment presents sensitivity of trees to local climate factor. The period from 1931 to 2015 was analysed. We found that the silver and white firs had high homogeneity of radial growth responses and sensitivity to year−to−year changes of weather conditions. Warm November of the previous year, short winter and high air temperature in August had positive influence on the size of their radial increment. Moreover, precipitation in February, April and July of the year of tree−ring formation contributed to wider tree−ring. The white fir was highly resistant to winter frost in contrast to the silver fir. In addition, this fir species preferred cold springs. Furthermore, the silver fir suffered from overabundant precipitation in August. The climate conditions of western lowland part of Poland were not a limiting factor for growth of both species because the studied populations achieved the highest site index class., Sylwan 162 (3): 220-230

In February 2018, Abies concolor (white fir) trees with shoot dieback were detected in an arboretum located in southeast Finland. Closer examination of the diseased firs revealed bleeding stems, branch cankers and necrotic shoots with …

Understanding temporal forest change across spatial biophysical gradients is fundamental to managing dynamic forests across variable landscapes. This is especially true for identifying how biophysical variation mediates forest development through multi-century changes in climate and eras of forest manipulation by humans. We examined 155 years of forest change across a 13,000-ha mixed conifer landscape in the Spring Mountains, Nevada, USA. We reconstructed forest composition at 31 sites in 1855 (pre-Euro-American settlement, and near the end of the Little Ice Age), 1881 (logging era), 1900 (before establishment of government forest reserve), 1950 (mid-century fire exclusion), and 2009 (present forest). Differing from many other western conifer landscapes, density of large trees (>50 cm in diameter) increased through time. Aside from large trees and one measure of species compositional change, five other measures of forest change (e.g., percent difference in tree density) were spatially variable across the landscape and not well represented by ‘average’ change in the study area. Forest composition in 1855 minimally influenced the next 155 years of forest change. In contrast, the amount, timing, and direction of forest change were linked with topographic gradients. Forests on warm slope aspects incurred the least amount of change, which also was delayed in time, whereas forests on cooler aspects already appreciably changed by 1900. Warm aspects were the only ones to lose trees during the most recent 60-year period (1950–2009), with a decline in median tree density of 13%, compared to continued gains on moister sites. Management applications of this spatio-temporal variation include anchoring fuel treatments around areas of open, little-changed forest to increase effective size of treatments.

Homoploid hybridization has increasingly been recognized as an important source of genetic variation to support adaptation to changing environmental conditions, the invasion of novel ecological niches and, ultimately, speciation. Although ecological selection pressures have been theorized to play a key role in the stabilization of homoploid hybrid lineages, surprisingly few detailed quantitative studies compare the realized ecological niches of hybrids and their progenitors. In this study, we compare twenty bioclimatic variables (Worldclim) at representative occurrence sites of Abies grandis, Abies concolor, and two classes of their natural hybrids, which are variably intergradient between their progenitors, to assess the potential role of ecological selection in the evolution of the observed morphological patterns of introgression. We find that both hybrid classes occupy distinct habitats that are variably intermediate between those associated with A. grandis and A. concolor for a majority of environmental variables, but with lower precipitation in the summertime in the southern Cascade, Siskiyou, and Sierra Nevada Mountains than associated with either progenitor. We hypothesize that moisture stress and high levels of solar insolation in the summertime associated with hybrid populations have played an important role in the observed patterns of introgression of key traits: leaf angle, specific leaf area, and abundance of adaxial stomates. Phenotypic plasticity in two of these traits may allow hybrids to adapt to an environment with a higher degree of variability in moisture stress. Moreover, in the context of moisture stress associated with predicted climate change, hybrids may have an adaptive advantage over A. grandis.

We investigated the forest health of red fir (Abies magnifica) and how it compared with commonly-associated species Jeffrey pine (Pinus jeffreyi), lodgepole pine (Pinus contorta) and white fir (Abies concolor) in the upper montane forests of California. We evaluated tree mortality rates, changes in the density of recently-dead trees and the amount of insect and disease damage on live trees from comprehensive forest inventories. The annual mortality rate for red fir was 1.8%, while the rates for Jeffrey pine, lodgepole pine and white fir were 1.9, 1.1 and 3.0%, respectively. The proportion of recently-dead red fir trees increased over time, suggesting an increase in mortality; however, stage-transition models suggested the current population structure of red fir is stable. Dwarf mistletoe and drought-stressed sites were significant predictors of red fir mortality. Trees with substantial damage had a higher probability of experiencing mortality in five years. Our results are consistent with others, but the timeframe is too short to make conclusions about long-term declines. Our results suggest that the most significant of multiple biotic factors involved in red fir mortality processes is dwarf mistletoe, while tree age and the proportion of forest in old-growth may also influence mortality rates.

Trees in urban areas are important for their ecological functions in addition to their esthetic characteristics. Trees provide positive effects on urban microclimate by canopy, reflection, and transpiration activities; therefore, they help to decline formation of heat island. The objective of this study was to determine thermal effects of 15 different tree types: 4 coniferous and 11 deciduous species commonly found in the city of Erzurum located at the northeastern part of Turkey. The relationships between sky view factor and surface temperature regarding the differences in leaf density and tree species. In August 2016, the surface temperature of trees was measured using a thermal camera at 10:00 am and 4:00 pm hours. Sky view factor (SVF) was obtained by fisheye photos and physiologically characteristics of trees were determined. In all trees while the surface temperature was 20.1 degrees C at 10:00 am. it was 23.4 degrees C at 4:00 pm. Among the deciduous tree species, Betula verrucosa Ehrh. and Robinia pseudoacacia "Umbracuifera" had the lowest surface temperature; however, Abies concolor (Gord. & Glen.) had the lowest surface temperature among the coniferous tree species. The results indicated that the surface temperatures of different tree species varied considerably, and the SW value had a significant effect on tree surface temperatures. However, it was obtained that the leaf types had no statistically significant effect on tree surface temperature.

Dry mixed-conifer forests in the Southwest occupy an important ecological and hydrological role in upper watersheds. In the absence of reoccurring fire and silvicultural treatments over the last 50 years, we quantified forest structure and composition on prevailing north and south aspects of a dry mixed-conifer forest in southcentral New Mexico using mixed models and ordination analysis in preparation for an experiment in ecological restoration. Results indicated overstory and midstory were dominated by Douglas-fir (Pseudotsuga menziesii) and shade tolerant/fire intolerant white fir (Abies concolor) with interspersed mature aspen on north aspects, and Douglas-fir and Southwestern white pine (Pinus strobiformis) on south aspects. Ponderosa pine (Pinus ponderosa), which was historically co-dominant with Douglas-fir on north and south aspects, was subdominant on south aspects and almost entirely absent on north aspects. Regeneration was dominated by white fir saplings and seedlings on north aspects while ponderosa pine was completely absent. South aspect saplings and seedlings were characterized by Douglas-fir and Southwestern white pine, but almost no ponderosa pine. Ordination analysis characterized the effect of aspect on species composition. Understanding contemporary forest structure and composition is important when planning for desired future conditions that are to be achieved through ecological restoration using silvicultural techniques designed to foster resilience.

Tree mortality because of beetle outbreaks has become substantial and widespread in conifer forests in western North America. A number of environmental and physiological factors influence patterns of mortality. Tree diversity may reduce the severity and extent of insect damage to host trees by providing associational resistance, but the existence and importance of associational resistance varies by forest type and by tree and insect species. We assessed whether plot-level tree diversity contributed to survival of Engelmann spruce (Picea engelmannii Parry ex Engelm.) following a spruce beetle (Dendroctonus rufipennis Kirby) epidemic. Our study plots comprised 2 to 5 tree species including Engelmann spruce, subalpine fir (Abies lasiocarpa (Hook) Nutt.), Douglas-fir (Pseudostuga menziesii (Mirb.) Franco), quaking aspen (Populus tremuloides Michx.), and white fir (Abies concolor (Gordon & Glend.) Hildebr.). We used a model-selection analysis to compare the importance of tree diversity with other known factors that influence spruce survival. We found lower rates of spruce survival in stands where spruce was the dominant tree species (by percent of stand density index) and higher survival in stands where nonspruce conifers (Douglas-fir, subalpine, and white fir) were dominant. We also found that tree diversity (Shannon index) did not show a positive correlation to spruce survival and that there was no additional benefit derived from the presence of aspen, which has higher phylogenetic distance from Engelmann spruce than the other trees in this study. The relationship between diversity and survival is complicated by factors that naturally co-vary with diversity, such as elevation, aspect, and stand density of spruce. Our results best support an explanation that if associational resistance does increase spruce survival during a beetle epidemic, it is due to host or resource dilution, which may be an indirect effect of higher stand diversity.

Ninety plant macrofossil taxa from the Ziegler Reservoir fossil site near Snowmass Village, Colorado, record environmental changes at high elevation (2705 m asl) in the Rocky Mountains during the Last Interglacial Period. Present-day vegetation is aspen forest (Populus tremuloides) intermixed with species of higher (Picea,Abies) and lower (Artemisia,Quercus) elevations. Stratigraphic units 4–13 contain montane forest taxa found near the site today and several species that today generally live at lower elevations within (Abies concolor,Lycopus americanus) and outside Colorado (Najas flexilis). These data suggest near-modern climatic conditions, with slightly warmer summer and winter temperatures. This montane forest period was succeeded by a shorter treeless interval (Unit 14) representing colder and/or drier conditions. In units 15–16, conifer trees reoccur but deciduous and herb taxa are lacking, suggesting a return to warmer conditions, although cooler than during the earlier forest period. Comparison of these inferred paleoclimatic changes with the site's geochronologic framework indicates that the lower interval of sustained warmth correlates with late MIS 6–early 5b (~138–94 ka), the cold interval with MIS 5b (~94–87 ka), and the uppermost cool assemblages with MIS 5a (~87–77 ka).

Pleistocene biogeography of conifer species is poorly known in much of western North America. We conducted morphological studies on 201 conifer cones and cone fragments recovered from Pleistocene sediments at the Ziegler Reservoir fossil site (2705 m) near Snowmass Village, Colorado. The basin, formed ~155–130 ka, contains fossil-bearing lacustrine, palustrine, and colluvial sediments spanning approximately 85 ka. Using a suite of morphological characters, particularly cone-scale bracts, we differentiated species ofAbies,Picea, andPseudotsuga. All fossilAbiesspecimens were assignable based on bract morphology toAbies concolor, which is currently absent from central Colorado (nearest populations are 160 km southwest of the site).A.concoloroccurs only in sediments of MIS 5d and 5c.Pseudotsuga menziesiiandPicea engelmanniicones occurred in sediments corresponding to MIS 5e, 5d, 5c, and 5a. A fourth conifer species, occurring in sediments of MIS 5e, 5d, 5c, and 5a, is difficult to assign to any extant species. Bract morphology is similar toPicea pungens, which grows near the site today, but scale morphology is unlikeP.pungens. These fossils may represent ancestralP.pungens, an extinct variant, or an extinct sister species.

Woody biomass has the potential to be utilized at an alternative fuel source through its pyrolytic conversion. Here, fast pyrolysis bio-oils derived from several western USA woody species are characterized by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to determine molecular-level composition. The composition and properties (pH, electrical conductivity, and elemental analyses) of the biochar byproduct were also determined. The bio-oils are comprised mainly of Ox species. Oak (Quercus garryana Douglas ex Hook), mixed conifer (Pseudotsuga menziesii Mirb. Franco, Tsuga heterophylla (Raf.) Sarg, Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.), and scotch broom (Cytisus scoparius (L.) Link) bio-oils contain lower Ox (O1-O7) species that exhibit bimodal distributions whereas mixed conifer feedstock from a fire salvage harvest contains a larger range of Ox species (O2-O13) that exhibit a mainly monomodal distribution. Boron-containing species in the pyrolysis oils were also identified for the first time by FT-ICR MS. Biochar analysis revealed that all biochars had similar pH values (~7-8); however, the electrical conductivity and elemental analyses varied across the samples. Understanding the composition of pyrolysis byproducts will help direct their uses to the most appropriate locations.

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 comb...

Impacts of drought on tree mortality in high-elevation mixed-conifer forests of southwestern U.S. are poorly understood. A recent extended and severe drought in the region provided an opportunity to investigate the patterns and factors associated with tree mortality in this forest type. Specifically, we quantified mortality that occurred between 1995 and 2008 of four tree species, white fir (Abies concolor), limber pine (Pinus flexilis), trembling aspen (Populus tremuloides), and Douglas-fir (Pseudotsuga menziesii), in mixed-conifer forests over three sites in northern Arizona within 84, 0.02 ha plots. We found: (1) varied but substantial tree mortality (4–56% by basal area) in most species between 1996 and 2006 in association with recent severe and prolonged drought; (2) tree mortality differed among sites and species with aspen and white fir having the most mortality (>30% by basal area); (3) relationships between tree mortality and most climatic factors (e.g. temperature, precipitation, Palmer Drought Severity Index) were lagged 1–4 yr; (4) bark beetle attack and intraspecific tree basal area were consistently and positively related to tree mortality for most species and sites, whereas topographic and other stand characteristics were less consistently related to mortality. Results show that aspen, Douglas-fir, and white fir were more vulnerable to recent drought-associated mortality than limber pine. Associations between tree mortality and intraspecific basal area support further evaluation of treatments that reduce intraspecific competition within stands to lower risks of tree mortality in southwestern mixed conifer forests.

The correlation of the distribution of five subalpine and montane tree species with precipitation and temperature were modeled using GIS. The results were compared with data presented by Thompson et al. (2000). Distributions of subalpine fir (Abies concolor), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta), limber pine (Pinus flexilis) and bristlecone pine (Pinus aristata) were compared to estimated precipitation and temperature fields that had been constructed from the Parameter-elevation Regressions on Independent Slopes Model (PRISM), National Climatic Data Center (NCDC) station data, and Snowpack Telemetry (SNOTEL) system data. Plant distribution maps from Little (1971) and CoGAP (2001) were used to determine the temperature and precipitation associated with the selected tree species. The estimates from this study were compared to those of Thompson, Anderson & Bartlein (2000). In many cases precipitation and temperatures values were higher than those of Thompson, Anderson & Bartlein (2000). Suggestions are made to improve the predictive power of GIS analysis for mapping climate and plant variability.

Mosaics of tree clumps and openings are characteristic of forests dominated by frequent, low- and moderate-severity fires. When restoring these fire-suppressed forests, managers often try to reproduce these structures to increase ecosystem resilience. We examined unburned and burned forest structures for 1937 0.81 ha sample areas in Yosemite National Park, USA. We estimated severity for fires from 1984 to 2010 using the Landsat-derived Relativized differenced Normalized Burn Ratio (RdNBR) and measured openings and canopy clumps in five height strata using airborne LiDAR data. Because our study area lacked concurrent field data, we identified methods to allow structural analysis using LiDAR data alone. We found three spatial structures, canopy-gap, clump-open, and open, that differed in spatial arrangement and proportion of canopy and openings. As fire severity increased, the total area in canopy decreased while the number of clumps increased, creating a patchwork of openings and multistory tree clumps. The presence of openings > 0.3 ha, an approximate minimum gap size needed to favor shade-intolerant pine regeneration, increased rapidly with loss of canopy area. The range and variation of structures for a given fire severity were specific to each forest type. Low- to moderate-severity fires best replicated the historic clump-opening patterns that were common in forests with frequent fire regimes. Our results suggest that managers consider the following goals for their forest restoration: 1) reduce total canopy cover by breaking up large contiguous areas into variable-sized tree clumps and scattered large individual trees; 2) create a range of opening sizes and shapes, including ~ 50% of the open area in gaps > 0.3 ha; 3) create multistory clumps in addition to single story clumps; 4) retain historic densities of large trees; and 5) vary treatments to include canopy-gap, clump-open, and open mosaics across project areas to mimic the range of patterns found for each forest type in our study.

Leucothoe davisiae Torr. ex A. Gray (Ericaceae), Sierra laurel, is an endemic shrub of the Sierra Nevada, Klamath Mountains, and Warner Mountains. We compared the woody plant community and allometry of Leucothoe with one widespread wetland shrub, red osier dogwood (Cornus sericea L. (Cornaceae)), and one widespread upland shrub, bush chinquapin (Chrysolepis sempervirens (Kellogg) Hjelmq. (Fagaceae)), in an Abies concolor – Pinus lambertiana forest. We examined 2282 mapped shrub patches and 34 392 trees in the Yosemite Forest Dynamics Plot (25.6 ha), Yosemite National Park, California, USA. We dissected 40–41 stems of each shrub species and determined foliage, bark, wood, and total biomass as a function of stem diameter. Community compositions determined from plants within a 5 m buffer of Leucothoe were different from those reported for Leucothoe communities in the Siskiyou National Forest and the Central Klamath. Leucothoe allometry based on basal diameter was more variable (total biomass R2 = 0.64; P < 0.001) than that of Cornus (R2 = 0.93; P < 0.001) or Chrysolepis (R2 = 0.95; P < 0.001), reflecting greater canopy variation. Allometry based on diameter at 1.37 m along the main stem offered equivalent explanatory power for Cornus (R2 = 0.89; P < 0.001) and Chrysolepis (R2 = 0.84; P < 0.001), but Leucothoe rarely reached that stature. These allometric equations that we report can improve species-specific modeling of carbon dynamics, fuel loading, and fire behavior.

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 ...

Summary In the spring of 2008, Dothistroma septosporum, a damaging quarantine pathogen of pine foliage, was documented in J€ (southeastern Estonia), apparently for the first time, on white fi r( Abies concolor). Thus, a new host species and genus for the fungus were recorded. Infection of white fi rb yD. septosporum, and also of some other fir species, was monitored annually on a transect proceeding from southeastern Estonia to northern Latvia. As a result, D. septosporum was detected also on silver fi r( Abies alba). It is not clear why this fungus with a worldwide distribution appeared on this new host genus definitely in northern Europe.

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, ...

a b s t r a c t We used dendroarchaeological techniques to determine the year of construction of two historic structures in the Valles Caldera National Preserve of New Mexico, USA. Historical documents date some structures in the headquarters area of the Preserve, but the Commissary Cabin and Salt Barn were lacking conclusive construction dates. Both structures were originally thought to have been built by the Otero family who bought the property in 1899. We found that the structures were built from two tree species, white fir (Abies concolor (Gordon) Lindl. ex Hildebr.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), surprising given that ponderosa pines are also found in great numbers in the adjacent forest. Tree rings from 20 logs were confidently crossdated both graphically and statistically and provided cutting dates of trees in both structures of 1940 and 1941 when compared against the Fenton Lake reference chronology (Commissary Cabin: r = 0.69, t = 15.54, p < 0.0001, n = 263 years; Salt Barn: r = 0.77, t = 11.7, p < 0.0001, n = 232 years). By combining the cutting date years and terminal ring attributes, we suggest that both structures were built in the spring or early summer of 1941 using freshly cut logs and logs that had been cut the previous spring (1940, before or during the growing season) and stockpiled. The cutting dates of 1940 and 1941 indicate that these buildings were constructed during the Franklin Bond (1939-1945) era and associated with the transition from sheep ranching to more modern cattle grazing. These new dates provide a more distinct understanding of the cultural resources at the Valles Caldera National Preserve and provide interpretative staff with more accurate information that can be given to the public. © 2014 Elsevier GmbH. All rights reserved.

Mechanical thinning and the application of prescribed fire are commonly used to restore fire-adapted forest ecosystems in the Western United States. During a 10-year period, we monitored the effects of fuel-reduction and forest-restoration treatments on levels of tree mortality in an interior ponderosa pine, Pinus ponderosa Dougl. ex Laws., forest in California. Twelve experimental plots, ranging in size from 77–144 ha, were established to create two distinct forest structural types: mid-seral stage (low structural diversity; LoD) and late-seral stage (high structural diversity; HiD). Following harvesting, half of each plot was treated with prescribed fire (B). A total of 16,473 trees (8.7% of all trees) died during the 10-year period. Mortality was primarily attributed to bark beetles (Coleoptera: Curculionidae, Scolytinae) (10,655 trees), specifically fir engraver, Scolytus ventralis LeConte, mountain pine beetle, Dendroctonus ponderosae Hopkins, western pine beetle, D. brevicomis LeConte, pine engraver, Ips pini (Say), and, to a much lesser extent, Jeffrey pine beetle, D. jeffreyi Hopkins. Trees of all ages and size classes were killed, but mortality was concentrated in the smaller-diameter classes (19–29.2 and 29.3–39.3 cm at 1.37 m in height). Most mortality occurred three to five years following prescribed burns. Higher levels of bark beetle-caused tree mortality were observed on LoD + B (8.7%) than LoD (4.2%). The application of these and other results to the management of interior P. ponderosa forests are discussed, with an emphasis on the maintenance of large trees.

Mountain conifers in the Great Basin of North America have provided some of the longest, continuous, and annually resolved paleoclimate records. Climate-growth relationships at the cellular level, which help understand wood formation processes that underlie dendroclimatic reconstructions, are at present largely unexplored in the Great Basin. We analyzed 42 trees located in the Snake Range (eastern Nevada, USA) at three sites along an elevation gradient. Sampled species included white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii), limber pine (Pinus flexilis), bristlecone pine (Pinus longaeva), and Engelmann spruce (Picea engelmannii). Wood anatomical features were quantified for two consecutive years, 2011 and 2012. Lumen area, cell wall thickness, lumen diameter, and wall-to-cell ratio were measured for the total ring as well as for earlywood and latewood. Mean standardized tracheidograms highlighted differences between 2011 and 2012, in particular concerning lumen area and wall-to-cell ratio. Most annual variation was due to earlywood, rather than latewood. Anatomical parameters of limber pine, the only species that could be tested at both the montane and subalpine sites, varied with elevation. Principal component analysis showed that the main axis of variability was related to dimensional parameters (e.g. lumen area), which reflected differences in water availability.

The increase in compounding disturbances, such as “hotter droughts” coupled with insect outbreaks, has significant impacts on the integrity of forested ecosystems and their subsequent management for important ecosystem services and multiple-use objectives. In the Southern Sierra Nevada, years of severe drought have resulted in unprecedented tree mortality across this mountainous landscape. Additionally, past land management practices, including fire suppression, have led to overly stocked, homogenous forest stand structures, dominated by small diameter, shade-tolerant and fire-intolerant tree species. Thus, the current condition of the landscape has further increased the susceptibility of forest trees to multiple stressors. We sought to determine the effects of extreme drought and insect outbreaks on tree mortality and their influence on forest stand structure and composition. To characterize mortality patterns, we monitored the condition of mature forest trees (>25.4 cm diameter at breast height) across 255 monitoring plots with four repeated measurements from 2015 through 2017. Tree mortality varied by species and through time. Reductions in pine species (Pinus lambertiana Douglas and P. ponderosa Lawson & C. Lawson) occurred earlier in the study period than Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr. or Calocedrus decurrens (Torr.) Florin. Across species, larger tree size, most often associated with tree height, was consistently related to increased survival in mature, overstory trees. As expected, sites with greater pine stocking and subsequently more bark beetle (Curculionidae: Scolytinae) host availability had increased pine mortality, especially for P. ponderosa. For Abies concolor, lower overstory basal area increased tree survival for this species. This study highlights the importance of effective forest monitoring, especially during a period of unprecedented ecological change as the compounding disturbance had a disproportional effect on pine species in smaller diameter classes. Proactive forest management may be necessary to maintain and promote these ecologically important species in heterogeneous mixtures across the landscape.

Post-fire tree mortality models are vital tools used by forest land managers to predict fire effects, estimate delayed mortality and develop management prescriptions. We evaluated the performance of mortality models within the First Order Fire Effects Model (FOFEM) software, and compared their performance to locally-parameterised models based on five different forms. We evaluated all models at the individual tree and stand levels with a dataset comprising 34174 trees from a mixed-conifer forest in the Sierra Nevada, California that burned in the 2013 Rim Fire. We compared stand-level accuracy across a range of spatial scales, and we used point pattern analysis to test the accuracy with which mortality models predict post-fire tree spatial pattern. FOFEM under-predicted mortality for the three conifers, possibly because of the timing of the Rim Fire during a severe multi-year drought. Locally-parameterised models based on crown scorch were most accurate in predicting individual tree mortality, but tree diameter-based models were more accurate at the stand level for Abies concolor and large-diameter Pinus lambertiana, the most abundant trees in this forest. Stand-level accuracy was reduced by spatially correlated error at small spatial scales, but stabilised at scales ≥1ha. The predictive error of FOFEM generated inaccurate predictions of post-fire spatial pattern at small scales, and this error could be reduced by improving FOFEM model accuracy for small trees.

[1] Tree ring data are analyzed for a multicentury record of drought history in the Sierra San Pedro Martir (SSPM) of Baja California, Mexico. Climatic variation in the study area is of particular interest because the SSPM is a rich biotic environment at the southern limit of the California floristic province and the southern limit of the planetary jet stream. Future shifts in the jet stream would be expected to have amplified effect on this marginal environment. The study applies linear regression to tree ring indices of earlywood-width of Abies concolor to estimate a 353 year (1658–2010 C.E.) record of cool-season (October–April) precipitation, P, in SSPM. Time-nested regression models account for more than half the variance of grid point P in calibration periods of length 50–65 years. Cross-spectral analysis indicates strong tracking of observed P by the reconstruction over a broad range of frequencies. Robustness of the reconstruction is supported by synchrony of reconstructed P with tree ring variations in other tree species from SSPM. The reconstruction emphasizes the severity of the 1950s drought in a long-term context and the single-year intensity of droughts in the last decade: 2007 stands out as the driest reconstructed year, with a high percentage of missing rings in A. concolor. The reconstruction identifies the early twentieth century pluvial as the wettest epoch in the last 353 years in the SSPM. High-elevation tree species in SSPM may be especially well-suited to sensing snowpack-related moisture variations associated with a southerly branched jet stream and the types of weather systems active in the pluvial.

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 bioma...

Variation in consumption of forest floor fuels in temperate coniferous forests have been linked to variation in fire effects, including mineral soil heating, tree mortality, and erosion. Moisture content of forest floor fuels influences consumption and therefore is a primary predictor of fire behavior and effects. To better understand spatial and temporal variability in forest floor moisture, we collected fuels from each forest floor horizon, cones, and woody fuels in four long-unburned Jeffrey pine (Pinus jeffreyi) – white fir (Abies concolor) stands within the Lake Tahoe Basin, USA. To isolate the effects of spatial position within a stand, fuel moisture was measured at the base of trees, beneath the crown drip line, and beyond the crown in open gaps across a fire season. We compared spatial moisture dynamics at the m2, ha, and Basin scales and temporal dynamics at the day (one 24-h sampling period), month, and year scales (one site was measured in 2009 and 2010). Duff moisture varied spatially within stands, whereas moisture in litter, cones, and woody fuels did not. Forest floor moisture differed between years while woody fuel moisture did not. The variability in field results underscore the importance of measuring duff moisture content, as well as 10-h woody fuel moisture. A better understanding of the complexity of forest fuels will help land managers manage fire in Tahoe Basin forests and inform the understanding of fuels dynamics in other temperate coniferous forests.

We assessed tree mortality caused by bark beetles in a mixed-conifer forest in the central Sierra Nevada in response to fire and mechanical treatments. The treatments were: (1) no treatment, (2) prescribed fire, (3) mechanical (crown thinning-from-below followed by rotary mastication), and (4) mechanical followed by prescribed fire. Ponderosa pine (Pinus ponderosa Laws) mortality caused by the western pine beetle (Dendroctonus brevicomis LeConte), sugar pine (Pinus lambertiana Dougl.) mortality caused by mountain pine beetle (D. ponderosae Hopkins), and white fir (Abies concolor Gord. and Glend) mortality caused by the fir engraver beetle (Scolytus ventralis LeConte) was assessed pre-treatments, one-year post-treatments, and three years post-treatments. For the duration of the study, bark beetle caused mortality across all treatments for each tree species was less than 7%. Bark beetle-caused mortality of small and medium white firs increased in treatments that included fire, and bark beetle-caused mortality of medium size sugar pines was elevated in the fire only treatment compared with other treatments. Our results indicate that mechanical treatments cause little risk of mortality to residual trees from bark beetles in the short term. The higher secondary mortality in the small and medium size white firs in both fire treatments can be considered a benefit in overly dense mixed conifer forests where the understory is dominated by shade-tolerant white firs.

Understanding the habitat relationships of rare species is critical to conserving populations and habitats of those species. Nesting habitat is suspected to limit distribution of the threatened Mexican spotted owl (Strix occidentalis lucida), and may vary among geographic regions. We studied selection of nesting habitat by Mexican spotted owls within their home ranges in the Sacramento Mountains, New Mexico. We comparedcharacteristics ofowl nesttreesandnestsites tocharacteristics ofrandomlylocatedtrees andsitesat 2 spatial scales: the general nest vicinity and within activity centers used by spotted owls. Owls nested primarily in mixed-conifer forest (92%), and most nested in cavities in trees or snags (48%), or in dwarf mistletoe (Arceuthobium spp.) witches' brooms (36%). Owl nest trees had greater levels of dwarf mistletoe infection and were larger in diameter than random trees at both of the evaluated spatial scales. Nest trees also were more likely than random trees to be in white fir (Abies concolor) or Douglas-fir (Pseudotsuga menziesii), and in trees or snags with broken tops. Differences between owl nest sites and random sites differed with the scale at which we selected random sites, but at both scales examined, owl nest sites had greater canopy cover and more basal area contributed by large trees and white fir than random sites. In addition, most nest sites occurred in drainage bottoms or on the lower 2 thirds of north- or east-facing slopes. Conservation of owl nesting habitat in this area will require retaining forest patches with high canopy cover and large trees containing cavities or large dwarf mistletoe witches' brooms. Locating forest management treatments on ridgetops or the upper third of slopes and/or on south- or west-facing slopes may reduce impacts to owl nesting habitat while simultaneously targeting the drier forest types most in need of restoration. 2013 The Wildlife Society.

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 rockcre...

Few studies have examined temperatures inside bark roosts of tree-roosting bats. We measured temperatures beneath plates of exfoliating bark of six species of dead trees used for roosting by long-legged myotis (Myotis volans) from June to July 2003–2006 in Idaho and Oregon, USA, and compared these across tree species and with ambient temperature (TA). Temperature profiles beneath bark oscillated within the range of TA, demonstrating the ability of bark cavities on dead trees to insulate against daily extremes in maximum and minimum TA. Slope position affected the difference in bark cavity temperature from TA during daytime periods, with bark cavities on dead trees in upper slope positions being cooler than TA compared to bark cavities on dead trees in lower slope positions. Differences in bark cavity temperatures from TA varied among dead tree species during nighttime periods, with white fir (Abies concolor) and ponderosa pine (Pinusponderosa) warmer than TA compared to other dead tree species. Mean daily...

A full factorial design crossing overstory (O) and understory (U) thinning and prescribed burning (B) was started at Teakettle Experimental Forest, California, in 2001 with the aim of achieving shifts in species composition to favor fire-resistant pines over fir. The goal of the present study was to evaluate the use of metabolic changes as early indicators for predicting the effects of these treatments on species-specific growth and long-term productivity of Pinus jeffreyi, Pinus lambertiana, and Abies concolor. Foliar polyamines, amino acids, soluble proteins and chlorophyll were quantified and related with foliar and soil chemistry. Most changes in soil chemistry occurred only with combined treatments (BU or BO). Changes in foliar metabolism were not driven by soil chemistry. In general, the pines were more sensitive to water stress as compared to fir as indicated by proline content. Understory thinning had no effect on any species. Both O and BO had species-specific effects on foliar amino acids, chlorophyll, soluble proteins, and inorganic ions. In addition, both O and BO were the most extreme thinning treatments for pines as they greatly increase the time needed to replenish carbon stocks. With the exception of some amino acids, B by itself had no major effects on foliar inorganic ions, chlorophyll content, and polyamines for any of the three species while BU caused a decrease in chlorophyll in white fir, suggesting a decline in photosynthetic capacity. These data point to BU as the best management option to specifically decrease the growth of fire-sensitive white fir without a major impact on pines.