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Climate change is shifting forest tree species distributions across elevational and latitudinal gradients, and these changes are often pronounced at ecotones where species meet their climatic bounds and are replaced by other species. Using an extensive ecotone composed of lower‐montane white fir (Abies concolor var. lowiana) and upper‐montane red fir (Abies magnifica var. magnifica) in the central Sierra Nevada range of California, USA, we (1) examined how the demographics of the ecotone have responded to recent climate using a field observational study and a historical dataset, (2) quantified climate drivers across species life stages using contemporary demographic data, and (3) tested the potential impacts of future climate on species‐specific seedling survival and growth in a fully factorial growth chamber experiment that varied temperature, growing season length, and water availability. A re‐examination of the ecotone midpoint after 35 yr suggested a reduction in A. concolor sapling and tree densities and a rise in A. magnifica proportional dominance between surveys. Seedling abundances across the ecotone indicated that A. magnifica tends to dominate the regeneration layer and currently forms an important component of the seedling community at elevations below those where A. magnifica saplings or trees begin to co‐dominate stands. Observational and experimental assessments suggest that temperature and precipitation serve as important drivers, differentiating A. concolor vs. A. magnifica distributions, and are primary stressors at the seedling stage. Seedlings of both species were adversely affected by experimental climate treatments, although A. concolor exhibited greater survival and a more conservative growth strategy under extreme climatic stress than A. magnifica. Projections indicate that historical climate conditions will rise by an amount greater than the ecotone's current elevational extent by the end of the 21st century. Differential drivers of species abundances suggest that the projected climate will expand conditions that promote A. concolor abundance and impede A. magnifica abundance across the ecotone; however, disturbance activity and microclimatic conditions will also influence regeneration and overstory tree dynamics. Our study demonstrates the importance of quantifying species‐specific responses to climate and indicates that widespread regeneration failure may be one possible consequence in which species exhibit strong sensitivity to projected climate conditions. [ABSTRACT FROM AUTHOR]

Twentieth-century land management has altered the structure and composition of mixed-conifer forests and decreased their resilience to fire, drought, and insects in many parts of the Interior West. These forests occur across a wide range of environmental settings and historical disturbance regimes, so their response to land management is likely to vary across landscapes and among ecoregions. However, this variation has not been well characterized and hampers the development of appropriate management and restoration plans. We identified mixed-conifer types in central Oregon based on historical structure and composition, and successional trajectories following recent changes in land use, and evaluated how these types were distributed across environmental gradients. We used field data from 171 sites sampled across a range of environmental settings in two subregions: the eastern Cascades and the Ochoco Mountains. We identified four forest types in the eastern Cascades and four analogous types with lower densities in the Ochoco Mountains. All types historically contained ponderosa pine, but differed in the historical and modern proportions of shade-tolerant vs. shade-intolerant tree species. The Persistent Ponderosa Pine and Recent Douglas-fir types occupied relatively hot- dry environments compared to Recent Grand Fir and Persistent Shade Tolerant sites, which occupied warm-moist and cold-wet environments, respectively. Twentieth-century selective harvesting halved the density of large trees, with some variation among forest types. In contrast, the density of small trees doubled or tripled early in the 20th century, probably due to land-use change and a relatively cool, wet climate. Contrary to the common perception that dry ponderosa pine forests are the most highly departed from historical conditions, we found a greater departure in the modern composition of small trees in warm-moist environments than in either hot-dry or cold-wet environments. Furthermore, shade-tolerant trees began infilling earlier in cold-wet than in hot-dry environments and also in topographically shaded sites in the Ochoco Mountains. Our new classification could be used to prioritize management that seeks to restore structure and composition or create resilience in mixed-conifer forests of the region. [ABSTRACT FROM AUTHOR]

In the spring of 2008, Dothistroma septosporum, a damaging quarantine pathogen of pine foliage, was documented in Järvselja (southeastern Estonia), apparently for the first time, on white fir ( Abies concolor). Thus, a new host species and genus for the fungus were recorded. Infection of white fir by D. 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 fir ( Abies alba). It is not clear why this fungus with a worldwide distribution appeared on this new host genus definitely in northern Europe. [ABSTRACT FROM AUTHOR]

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

Understanding tree growth as a function of tree size is important for a multitude of ecological and management applications. Determining what limits growth is of central interest, and forest inventory permanent plots are an abundant source of long-term information but are highly complex. Observation error and multiple sources of shared variation (spatial plot effects, temporal repeated measures, and a mosaic of sampling intervals) make these data challenging to use for growth estimation. We account for these complexities and incorporate potential limiting factors (tree size, competition, and resource supply) into a hierarchical state-space model. We estimate the diameter growth of white fir (Abies concolor) in the Sierra Nevada of California from forest inventory data, showing that estimating such a model is feasible in a Bayesian framework using readily available modeling tools. In this forest, white fir growth depends strongly on tree size, total plot basal area, and unexplained variation between individual trees. Plot-level resource supply variables (representing light, water, and nutrient availability) do not have a strong impact on inventory-size trees. This approach can be applied to other networks of permanent forest plots, leading to greater ecological insights on tree growth. [ABSTRACT FROM AUTHOR]

In managed forests dominated by true fir ( Abies) species, stands are often restocked using understory trees retained during timber harvest, making the effects of dwarf mistletoe ( Arceuthobium spp.) infestation on small true fir a concern. This study examined the response of small red ( A. magnifica) and white ( A. concolor) fir and their dwarf mistletoes ( A. abietinum f.sp. magnificae and A. abietinum f.sp. concoloris, respectively) to precommercial thinning treatments in fir-dominated stands in the Sierra Nevada Mountains of California. Tree diameters and dwarf mistletoe ratings were monitored from 1981 to 2001, and mortality was observed from 1981 to 2006. Red and white fir survival and radial growth decreased significantly with greater mistletoe ratings and increased with larger diameters and live crown ratios. Thinning significantly increased survival and growth of white, but not red fir. Over the course of the study, mistletoe ratings for both fir species did not change significantly in unthinned stands, but increased in thinned stands. However, while statistically significant, increases in mistletoe ratings in thinned stands were gradual and mistletoe ratings did not statistically differ between treatments 20 years post-thinning. Additionally, thinning did not significantly influence mistletoe spread to uninfected trees, indicating that precommercial thinning in lightly infested red and white fir stands will not likely result in substantial increases in dwarf mistletoe abundance over typical harvesting intervals. Overall, while severe dwarf mistletoe infection ratings reduced tree survival and growth, because ratings remained low, actual losses resulting from mistletoes during this study were minor and will not likely result in substantial economic losses over normal harvesting intervals. This finding indicates that precommercial thinning treatments designed specifically to compensate for mistletoe-associated losses may not be necessary when managing red and white fir for timber production. [ABSTRACT FROM AUTHOR]

For many species of long-lived organisms, such as trees, survival appears to be the most critical vital rate affecting population persistence. However, methods commonly used to quantify tree death, such as relating tree mortality risk solely to diameter growth, almost certainly do not account for important spatial processes. Our goal in this study was to detect and, if present, to quantify the relevance of such processes. For this purpose, we examined purely spatial aspects of mortality for four species, Abies concolor, Abies magnifica, Calocedrus decurrens, and Pinus lambertiana, in an old-growth conifer forest in the Sierra Nevada of California, USA. The analysis was performed using data from nine fully mapped long-term monitoring plots. In three cases, the results unequivocally supported the inclusion of spatial information in models used to predict mortality. For Abies concolor, our results suggested that growth rate may not always adequately capture increased mortality risk due to competition. We also found evidence of a facilitative effect for this species, with mortality risk decreasing with proximity to conspecific neighbors. For Pinus lambertiana, mortality risk increased with density of conspecific neighbors, in keeping with a mechanism of increased pathogen or insect pressure (i.e., a Janzen-Connell type effect). Finally, we found that models estimating risk of being crushed were strongly improved by the inclusion of a simple index of spatial proximity. Not only did spatial indices improve models, those improvements were relevant for mortality prediction. For P. lambertiana, spatial factors were important for estimation of mortality risk regardless of growth rate. For A. concolor, although most of the population fell within spatial conditions in which mortality risk was well described by growth, trees that died occurred outside those conditions in a disproportionate fashion: Furthermore,.as stands of A. concolor,become increasingly dense, such spatial factors are likely to become increasingly important. In general, models that fail to account for spatial pattern are at risk of failure as conditions change. [ABSTRACT FROM AUTHOR]

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

Abstract Aim This study appraises historical fire regimes for Californian mixed-conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed-conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire. Location The SSPM is a north–south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California. Methods We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time-series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1-ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non-conifer trees and shrubs. Twenty-four stands were sampled on-the-ground by a point-centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover. Results Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25–45% cover and 65–145 trees per ha. Sapling densities were two to three times that of overstory trees. Size-age distributions of trees ≥ 4 cm dbh indicate multi-age stands with steady-state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration. Main conclusions Our spatially-based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4–20 years proposed from California fire-scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole-size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build-up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site-based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests. [ABSTRACT FROM AUTHOR]

The article presents abstracts of plant diseases. They include "Incidence of Wounding and Echinodontium Tinctorium Infection in Advanced White Fir Regeneration," "Georgia Pecan Trees With Crown Gall Yielded Mainly Agrocin Sensitive Biovar I Strains of Agrobacterium Tumefaciens," and "An Improved Defined Medium for Growth of Endothia Parasitica."

Wetwood in whit fir (Abies concolor) occupies the central cylinder of heartwood and is also associated with branch gaps, wounds, insect scars, and root and butt decay. In two experiments, a bacterium associated with wetwood did not cause wetwood, and wetwood formed while external water was excluded. Wetwood formation resulted from large wounds, treatment with HgCl2, and inoculation with Heterobasidion annosum. Wetwood formed in seedlings which survived inoculation with H. annosum but not in those which were killed by the fungus or which received control inoculations. Large variation was observed among trees in quantity or quality of wetwood formed in response to various treatments. Observations of natural columns and circumstantial evidence from inoculations indicate that wetwood may be inhibitory to H. annosum. Results suggest that wetwood is a host response to parenchyma death rather than a baterial disease or accumulation of external water. [ABSTRACT FROM AUTHOR]

The behaviour of amitrole (3-amino-l,2,4-triazole) in 3-year old seedlings of Pinuti ponderosa (ponderosa pine) and Abies concolor (white fir) is described. Visual symptoms of amitrole action appeared as a chlorosis of young needles, the extent of which varied with time and species. Maximum chlorosis was obtained when the application was made during the stage when no visible growth occurred. The greater susceptibility of ponderosa pine seedlings could be accounted for by the lower resistance to uptake of the herbicide into the needles and not by any difference between the conifer species in the metabolism of amitrole. The translocation and metabolism of amitrole in the two conifer species are discussed. In both of the conifer species amitrole was converted into three metabolic products two of which were found to be identical with the previously described Unknown I and 11. Two types of treatment, on exposed phloem and on the needles, provided the possibility for a direct study of the site of amitrole metabolism. This site appeared to be in the stem. Amitrole was the mobile, toxic compound in both species and was translocated in both sympolast and apoplast. A circulation of the herbicide in the plant was observed. From the phloem amitrole diffused relatively slowly into the xylem, and during this lateral translocation part of the amitrole was metabolized. The rate of this detoxification process seemed to be dependent upon how fast amitrole moved from phloem to xylem and vice versa. This rate seemed to show a positive correlation with the intensity of the cambial activity. The translocation of amitrole lo the roots was greatest when no visible growth could be detected. [ABSTRACT FROM AUTHOR]