Search

During drought, the tree subpopulations (such as size or vigour classes) that suffer disproportionate mortality can be conceptually arrayed along a continuum defined by the actions of biotic agents, particularly insects. At one extreme, stress dominates: insects are absent or simply kill the most physiologically stressed trees. At the opposite extreme, host selection dominates: outbreaking insects kill trees independently of their stress, instead selecting trees based on size or other traits. Intermediate responses are also possible. Yet for mixed‐species forests, we lack a broad understanding of the relative importance of insects in determining exactly which subpopulations of trees suffer disproportionate mortality during drought, and whether these subpopulations differ among co‐occurring tree species. During an extreme drought, we documented the roles of native bark beetles in the mortality of five tree species in California’s Sierra Nevada. We analysed the patterns and agents of tree mortality in 12 permanent plots and the patterns of mortality in 89 temporary plots. Most tree mortality was associated with bark beetles. However, the growth rates (an indicator of chronic stress) and sizes of trees that suffered greatest bark beetle‐related mortality differed sharply among tree taxa, variously conforming with domination by stress (Abies concolor), domination by host selection (Pinus lambertiana and P. ponderosa) or a mix of the two (Calocedrus decurrens). Quercus kelloggii mortality remained relatively low. Thus, even during extreme drought substantial proportions of stressed trees survived because they were of sizes that mostly avoided fatal insect attack. Conversely, substantial proportions of comparatively unstressed trees died because they were of sizes that were selectively killed by outbreaking insects. Synthesis. Native bark beetles were primarily responsible for determining which subpopulations of trees suffered greatest mortality during drought. However, idiosyncratic host‐tree selection by the different bark beetle taxa meant that the tree subpopulations suffering greatest mortality differed strikingly among tree taxa—for example, high mortality of small trees of one species, but of large trees of another. If idiosyncratic host‐tree selection by biotic mortality agents proves to be a generally common phenomenon, it could help explain weak broadscale correlations between tree traits and tree mortality during drought.

Rising temperatures and more frequent and severe droughts are driving increases in tree mortality in forests around the globe. However, in many cases, the likely trajectories of forest recovery following drought-related mortality are poorly understood. In many fire-suppressed western U.S. forests, management is applied to reverse densification and restore natural forest structure and species composition, but it is unclear how such management affects post-mortality recovery. We addressed these uncertainties by examining forest stands that experienced mortality during the severe drought of 2012-2016 in California, USA. We surveyed post-drought vegetation along a gradient of overstory mortality severity in paired treated (mechanically thinned or prescribed-burned) and untreated areas in the Sierra Nevada. Treatment substantially reduced tree density, particularly in smaller tree size classes, and these effects persisted through severe drought-related overstory mortality. However, even in treated areas with severe mortality (>67% basal area mortality), the combined density of residual (surviving) trees (mean 44 trees/ha) and saplings (mean 189 saplings/ha) frequently (86% of plots) fell within or exceeded the natural range of variation (NRV) of tree density, suggesting little need for reforestation intervention to increase density. Residual tree densities in untreated high-mortality plots were significantly higher (mean 192 trees/ha and 506 saplings/ha), and 96% of these plots met or exceeded the NRV. Treatment disproportionately removed shade-tolerant conifer species, while mortality in the drought event was concentrated in pines (Pinus ponderosa and P. lambertiana); as a consequence, the residual trees, saplings, and seedlings in treated areas, particularly those that had experienced moderate or high drought-related mortality, were more heavily dominated by broadleaf ("hardwood") trees (particularly Quercus kelloggii and Q. chrysolepis). In contrast, residual trees and regeneration in untreated stands were heavily dominated by shade-tolerant conifer species (Abies concolor and Calocedrus decurrens), suggesting a need for future treatment. Because increased dominance of hardwoods brings benefits for plant and animal diversity and stand resilience, the ecological advantages of mechanical thinning and prescribed fire treatments may, depending on the management perspective, extend even to stands that ultimately experience high drought-related mortality following treatment.

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.

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.

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.

Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ13C and δ18O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one-seed juniper (Juniperous monosperma), pinon pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ13C or δ18O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ13C (up to 0.4‰) and δ18O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (Ophiostoma) on the δ13C and δ18O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ13C for ponderosa, pinon and juniper yielded slopes of ~1, while the relationship between δ18O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States.

Bark beetles (Coleoptera: Curculionidae, Scolytinae) are commonly recognized as important tree mortality agents in coniferous forests of the western U.S.A. 2 High stand density is consistently associated with bark beetle infestations in western coniferous forests, and therefore thinning has long been advocated as a preventive measure to alleviate or reduce the amount of bark beetle-caused tree mortality. 3 The present study aimed to determine the effectiveness of thinning to reduce stand susceptibility to bark beetle infestations over a 10-year period in Pinus jeffreyi forests on the Tahoe National Forest, California, U.S.A. Four treatments were replicated three times within 1-ha square experimental plots. Treatments included thinning from below (i.e. initiating in the smallest diameter classes) to a residual target basal area (cross-sectional area of trees at 1.37 m in height) of: (i) 18.4 m 2 /ha (low density thin); (ii) 27.6 m 2 /ha (medium density thin); (iii) 41.3 m 2 /ha (high density thin); and (iv) no stand manipulation (untreated control). 4 Throughout the present study, 107 trees died as a result of bark beetle attacks. Of these, 71% (75 trees) were Abies concolor killed by Scolytus ventralis; 20.6% (22 trees) were Pinus ponderosa killed by Dendroctonus ponderosae; 4.7% (five trees) were P. jeffreyi killed by Dendroctonus jeffreyi ; 1.8% (two trees) were P. jeffreyi killed by Ips pini ; 0.9% (one tree) were P. jeffreyi killed by Orthotomicus (= Ips) latidens; 0.9% (one tree) were P. ponderosa killed by both Dendroctonus brevicomis and D. ponderosae; and 0.9% (one tree) were P. jeffreyi killed by unknown causes. 5 In the low density thin, no pines were killed by bark beetles during the 10-year period. Significantly fewer trees (per ha/year) were killed in the low density thin than the high density thin or untreated control. No significant treatment effect was observed for the percentage of trees (per year) killed by bark beetles.

Questions: Do large, old Sequoiadondron giganteum trees respond to the creation of adjacent canopy gaps? Do other co-occurring tree species and younger S. giganteum adjacent to gaps also respond? What are the likely factors affecting growth responses? Location: Mixed-conifer forests of the southern Sierra Nevada, California, USA. Methods: We measured the growth response of large, old S. giganteum trees (mean DBH 5 164 cm; ages estimated 41000 yr) to gap creation by coring trees and comparing growth after gap creation to growth before gap creation. We also measured young Abies concolor, Pinus lambertiana, and young S. giganteum. Gap-adjacent trees were compared with non-adjacent reference trees. Tree rings were analysed for carbon isotope discrimination and for longer-term growth trend correlations with climate. Results: Following gap creation gap-adjacent old S. giganteum grew more than reference trees. Abies concolor trees also exhibited a growth response to gap creation. No response was detected for young S. giganteum or P. lambertiana, although detection power was lower for these groups. There was no difference in carbon isotope discrimination response to gap creation between gap-adjacent and reference trees for old S. giganteum and radial growth was positively correlated with winter precipitation, but not growing season temperature. Conclusion: It is unclear what caused the growth release in old S. giganteum trees, although liberation of below-ground resources following removal of competing vegetation appears to be a significant contributor. Sequoiadondron giganteum, the thirdlongest lived and the largest of all species, remains sensitive to local environmental changes even after canopy emergence. Management activities that reduce vegetation surrounding individual specimen trees can be expected to result in increased vigor of even these very old and large trees.

Question: How does competition between quaking aspen (Populus tremuloides) and white fir (Abies concolor) affect growth and spatial pattern of each species? Location: The northern Sierra Nevada, California, USA. Methods: In paired plots in mixed aspen- (n 5 3) or white fir-dominated (n 5 2) stands, we mapped trees and saplings and recorded DBH, height, species, and condition and took increment cores. We tallied seedlings by species. Tree ring widths were used as a measure of basal area change over the last decade, and canopy openness was identified using hemispherical photographs. Linear mixed models were used to relate neighborhood indices of competition, stand, and tree-level variables to diameter increment. Spatial patterns of stems were identified using the Neighborhood Density Function. Results: White fir radial growth was higher in aspenthan white fir-dominated plots. Individual-level variables were more important for white fir than for aspen growth, while variables representing competitive neighborhood were important only for aspen. The forest canopy was more open in aspen- than white fir-dominated stands, but ample aspen seedlings were observed in all stands. Canopy stems of aspen and white fir were randomly distributed, but saplings and small trees were clumped. Aspen saplings were repelled by canopy aspen stems. Conclusions: Variation in canopy openness explained more stand–stand variation in white fir than aspen growth, but high light levels were correlated with recruitment of aspen seedlings to the sapling class. Radial growth of aspen was predicted by indices of neighborhood competition but not radial growth of white fir, indicating that spacing and stem arrangement was more important for aspen than white fir growth. Fire suppression has removed a major disturbance mechanism that promoted aspen persistence and reduced competition from encroaching conifers, and current forests favor species that regenerate best by advance regeneration (white fir).

We studied breeding populations of 2 coexisting ground-nesting birds, the red-faced warbler (Cardellina rubrifrons) and yellow-eyed junco (Junco phaeonotus), in high-elevation (.2,000 m) forested drainages of the Santa Catalina Mountains, Arizona, USA. From 2004 to 2005, we 1) estimated density and nesting success of breeding populations of red-faced warblers and yellow-eyed juncos, 2) identified nest-site characteristics for each species (i.e., used sites vs. random plots), 3) compared nest-site characteristics between the 2 species, and 4) examined effects of a recent (2003) wildfire on distribution of nests of both species. In addition, we estimated the areal extent of montane riparian forest (the preferred breeding habitat of both species) within high-elevation forests of the Santa Catalina Mountains. We found that red-faced warblers and yellow-eyed juncos were the 2 most common ground-nesting birds within our study area with an average density of 2.4 and 1.4 singing males/ha, respectively, along drainage bottoms. Compared to random plots, most red-faced warbler and yellow-eyed junco nests were located close ( M m) to drainage bottoms within a strip of montane riparian forest characterized by abundant brush, small woody debris, ferns, and forbs (both species), high number and diversity of saplings and small trees (red-faced warblers), and abundant shrubs and downed logs and less canopy cover (yellow-eyed juncos). Although both species nested in close proximity within montane riparian forest, nest-site characteristics differed between the 2 species, especially at finer spatial scales. For example, most yellow-eyed juncos nested adjacent to grass (principally Muhlenbergia spp.), whereas red-faced warblers nested adjacent to a variety of plant species, including grass, bigtooth maple (Acer grandidentatum), white fir (Abies concolor), and Douglas-fir (Pseudotsuga menziesii). Both red-faced warblers and yellow-eyed juncos avoided nesting in areas burned during a recent wildfire. In addition, nesting success was low for red-faced warblers (13%) and yellow-eyed juncos (19%) following the wildfire, suggesting an indirect negative effect of fire on breeding populations in the short-term. Montane riparian forest appears to provide important breeding habitat for red-faced warblers and yellow-eyed juncos. However, little research or conservation planning has been directed toward montane riparian forest in the region, even though this forest type is limited in its areal extent (,11% of high-elevation forest in the Santa Catalina Mountains) and increasingly threatened by disturbance. Results from our study can be used to facilitate the management and conservation of breeding populations of red-faced warblers and yellow-eyed juncos in high-elevation forests of the southwestern United States.

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.

We linked radiotelemetry data from California spotted owls (Strix occidentalis occidentalis) with forest inventory data from mixed coniferous forests managed primarily via partial timber harvest practices. We estimated a discrete-choice resource selection function (RSF) based upon 21 choice sets from the forest inventories and nocturnal telemetry locations of radiotagged adult spotted owls occupying 17 home ranges. Nocturnal foraging was strongly associated with forests close to nests and small streams. The combined basal areas of Douglas-fir (Pseudotsuga menziesii), white fir (Abies concolor), and red fir (Abies magnifica) and basal area of hardwoods ≥20 cm diameter at breast height were positively and unimodally correlated to foraging habitat selection by owls, whereas the relative probability of selection decreased with increasing basal area of ponderosa pine (Pinus ponderosa). Opportunistically collected diurnal data indicated that owls roosted in forest stands that contained greater tree den...

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

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

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

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

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

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

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

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

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

The fire disturbance regime and forest structure prior to Euro-American settlement (AD 1883) of a southwestern ponderosa pine (Pinus ponderosa) landscape were quantified in order to establish reference conditions as a baseline for ecosystem management. The mean presettlement fire interval between 1637 and 1883 was 3.7 yr for all fires and 6.5 yr for widespread fires, but fire has been excluded from the study area since 1883. Forest density increased under fire exclusion from an average of 148 trees/ha in 1883 (65 pines, 80 oaks, three other species), an open forest dominated by relatively large ponderosa pines, to 1265 trees/ha in 1994/1995 (720 pines, 471 oaks, 74 others), a dense forest characterized by relatively small and young trees. Species composition has shifted toward greater dominance by Gambel oak (Quercus gambelii) and conifers less adapted to frequent fires: white fir (Abies concolor) and Douglas-fir (Pseudotsuga menziesii). The reference presettlement conditions can be applied to management of this ecosystem in two ways. First, reference conditions are a benchmark against which to evaluate contemporary conditions and future alternatives. The comparison shows that the contemporary forest is well above the range of presettlement variability in forest density, and both live and dead fuel structures have developed that can support high-intensity wildfire. Second, reference conditions can serve as a goal for ecological restoration treatments.

Anthropogenic influences on recent tree mortality in mid-montane mixed conifer forests of southern California, USA, and northern Baja California, Mexico, were investi- gated. The Pinus jeffreyi-Abies concolor phase of the mixed- conifer montane community was sampled at three sites, char- acterized by: (1) low levels of air pollution and long-term fire suppression (Holcomb Valley in the San Berardino Moun- tains, California); (2) chronic, severe air pollution and long- term fire suppression (Barton Flats in the San Bernardino Mountains, California); and (3) little air pollution and no fire suppression (La Corona Arriba in the Sierra San Pedro Martir in Baja California, Mexico). Similar percentages of dead standing trees, around 14 %, were found at both San Bernardino sites, but a comparatively low level, 4 %, was found in the Mexican forest. Anthropogenic effects, in particular fire sup- pression, may play an important role in enhancing the impact of natural stresses on the dynamics of mixed conifer forests.

Tree ring chronologies from 24 mixed—conifer stands were used to reconstruct the long—term history of western spruce budworm (Choristoneura occidentalis) in northern New Mexico. Temporal and spatial patterns of budworm infestations (within—stand occurrences) and outbreaks (more—or—less synchronous infestations across many stands) were investigated to identify local—scale to regional—scale forest disturbance patterns. Nine regional—scale outbreaks were identified from 1690 to 1989. One ancient stand of Douglas—fir trees (Pseudotsuga menziesii) exceeding 700 yr in age revealed that budworms and overstory trees can coexist for extraordinary lengths of time. Using spectral analysis we found that the regional outbreak record contained important cyclical components with periods varying from ≈20 to 33 yr. The statistically significant (P < .05) but variable periodicity of regional outbreaks suggests the forest—budworm dynamic is pseudoperiodic (i.e., a stable limit cycle or damped oscillator perturbed by noise). Duration of infestations within stands was ≈11 yr and has not obviously changed in the 20th century; however, infestations tended to be more synchronous among stands in this century than during earlier centuries. Regional budworm activity was low from the mid—1920s to late 1930s and mid—1960s to late 1970s, and the most recent outbreak, beginning in the late 1970s, was unusually severe. These results, and contrasting infestation patterns in mountain ranges with different land use histories, generally support a hypothesis that human—induced changes in Southwestern forests have led to more widespread and intense budworm outbreaks in the late 20th century. Despite human—induced changes in the 20th century, climate variation also appears to have been important to budworm regimes in this century as well as in earlier times. Regional outbreaks in the 20th century tended to occur during years of increased spring precipitation, and decreased budworm activity coincided with decreased spring precipitation. No clear association with temperature was identified. Comparisons of regional outbreak history since AD 1600 with a reconstruction of spring precipitation from limber pine (Pinus flexilis) ring width chronologies also shows that periods of increased and decreased budworm activity coincided with wetter and drier periods, respectively. This finding contrasts with results from shorter time—scale studies conducted in northwestern U.S. and Canada (western spruce budworm) and eastern Canada (spruce budworm C. fumiferana), where low precipitation and/or warmer temperatures were generally associated with outbreaks. Different patterns of budworm population response to changing moisture regimes might be due to differences in regional forest—budworm systems, or to differences in the spatial and temporal scales of observation. We conclude that changes in forest structure in the southwestern U.S. may have shifted the spatial and temporal pattern of budworm outbreaks. The dynamic behavior and statistically significant association between multicentury, regional budworm and climate time series also suggest that complex budworm dynamics are driven by a combination of internal and external factors.

Abies magnifica (Red fir) forests in the Cascade Range and Sierra Nevada of California are composed of groups, or patches, of even-sized individuals that form structurally complex stands. Patches may be even-aged, resulting from synchronous post-disturbance establishment, or multi-aged, reflecting continuous recruitment of seedlings moderately tolerant of shade. We analyze the population structure (i.e. age, size, and spatial patterning) of A. magnifica, and associated A. concolor, White fir, and reconstruct the disturbance history of two mature to old-growth A. magnifica forests in order to determine the relationship between disturbance and forest structure. Within both stands examined, the distributions of A. magnifica seedlings, saplings, and small understory trees were clumped, with clump sizes corresponding to the area of canopy gaps. Gaps were created by frequent wildfire (mean fire return interval of 41 yr) and by windstorms. Severe fire initiated mass establishment of Abies magnifica, whereas gaps created by windthrow released already established individuals. Low inten- sity fire stimulated little recruitment, but Red fir established continuously during fire-free intervals. Thus, the complex age and structures of Red fir forests reflect both episodic and continuous recruitment, as determined by the type and severity of natural disturbance.

We hypothesized that differential seedling establishment was responsible for the transition from white fir- to red fir-dominated forest. Nearly 2,000 seeds of each species were sown within six fenced gardens that spanned the ecotone (1,902-2,073 m). Germination and seedling mortality were monitored through the first growing season. Red fir germination percentage exceeded that of white fir in all gardens in sites dominated by red fir saplings and overstory trees, and a similar pattern was true for white fir. Survival at the end of the first growing season was low and statistically similar for both species, as was the average length of life for seedlings and the causes of mortality. Relative demographic performances (an integrated measure of germination and survivorship over time) suggest that: 1) open/xeric microhabitats within the ecotone favor white fir over red fir; 2) both open/mesic and shaded/xeric microhabitats favor red fir over white fir; and 3) shaded/mesic microhabitats are equally favorable for both species. Seedlings of red and white fir were grown for 6 mo in a growth chamber that imitated early summer temperature and soil moisture conditions. Red fir seedlings were consistently heavier than white fir seedlings, in part a result of the 2.5 x greater caloric content of red fir seed. Relative growth rates were similar for both. Allocation of photosynthate to roots was greater for red fir than white fir, a result contrary to the expected pattern, given that white fir occurs at more xeric, lower elevations than red fir. No consistent differences between the species occurred in root growth or morphology.

Seedling and transplant mortality from charcoal root rot was a power function of the sclerotial density of M. phaseolina in nursery soil while height and weight of surviving seedlings were negatively correlated with the inoculum density. Abies concolor was most susceptible to mortality followed by Pseudotsuga menziesii, Abies magnifica, Pinus lambertiana, Pinus jeffreyi and Libocedrus decurrens

A forest succession simulator, SILVA, has been developed for the mixed-conifer forest (seven major species) of the Sierra Nevada, California, to simulate the effects of fire on forest dynamics. SILVA is an extensive modification of a simulator for forests of the northeastern United States. The simulation includes the time development of the growth in tree diameter, tree height, and leaf-area index. Recruitment and mortality are modeled stochastically. Modifications include fire ecology, temporal seed-crop patterns, and seedling-survival factors unique to Sierra Nevada forests. The prob- ability of mortality from fire is determined by the height of crown scorch (a function of fire intensity, diameter at breast height, and bark thickness). The model simulates the dynamic and structural responses of communities to many factors. For 500-yr simulations from an initial clear-cut condition, the time-averaged basal-area ratios of Pinus ponderosa to Abies concolor were 5.2:1 and 1:16 for elevations of 1524 m and 1829 m, respectively. At 1524 m, the ratio of P. ponderosa to A. concolor decreased 59% when fire suppression was intro- duced. Fire provides P. ponderosa with a strong competitive advantage. Its growth form and growth rate are significant factors in its ability to evade fire. Rank correlations of species were compared with data for stands of ponderosa pine and white fir. Correlations were significant at 1% and 10% levels, respectively.

Morphological variation in color of female cones in white fir, Abies concolor, is postulated to have adaptive value. The purple variant is only found in one part of the range of white fir where it grows at high elevations. In addition, the frequency of purple cones increases with increasing elevation, suggesting a thermoregulatory function for the purple variant in the cold habitats found at high elevations. Temperature measurements support this hypothesis: purple cones attain higher internal temperatures than do green cones of comparable size. Cone diameter may, in fact, be correlated with cone color but definitive evidence is lacking. Alternative hypotheses are offered which may also be important in maintaining the presence of the purple variant at high elevations. It is suggested that other characters associated with purple cones may place them at a competitive disadvantage at lower elevations. ADAPTIVE COLORATION in animals has received serious consideration by several au

Epicuticular waxes of five cultivated varieties of Picea pungens and six other species of conifers were examined directly with a scanning electron microprobe. The quality, quantity, and distribution patterns of surface wax deposits varied between species, within species, within plants, and within individual leaves. Two basic types of wax were observed, structural and amorphous. Structural wax is associated with glaucousness and the blue foliage color in Picea pungens and other species. The degree of occlusion of the stomatal pore by surface waxes also varied from heavily occluded to completely free of wax. Wax in the epistomatal chamber may be another resistance barrier to gas exchange by ccnifer needles. NUMEROUS FUNCTIONS or adaptive roles have been suggested for the surface waxes of plant leaves. These include modification of the rate of moisture and other gaseous exchange with the atmosphere, protection against mechanical and pest damage, and protection against ultraviolet radiation and air pollutants. Despite the potential significance of these and other postulated physiological functions of the surface waxes, experimental evidence for specific functions is lacking. An understanding of the physical and chemical properties and patterns of natural variation of leaf surface waxes is basic to a determination of function for these materials. Several investigators have examined certain physical characteristics of the wax deposits on the foliage of xerophytic coniferous species with which we are mainly concerned. Mueller, Carr, and Loomis (1954) used a double replica technique to make indirect observations of Picea pungens var. glauca needles with the electron microscope. They showed a net-like pattern of wax deposition which was altered by aging and weathering. Leyton and Juniper (1963) found two morphological types of wax on Scotch pine. The portion of the needles enclosed by the basal sheath lacked the waxy projections which occur on the exposed surface of the needle. Eglinton and Hamilton (1967) reviewed the chemical properties of plant surface waxes which are complex mixtures of long chain alkanes, alcohols, ketones, aldehydes, acetals, esters, and acids. Considerable chemical variation exists between species suggesting their usefulness for taxonomic purposes. ' Received for publication 22 February 1971. Journal article No. 5388, Michigan Agricultural Experiment Station. This research was supported in part by Grant No. AP Al 00736 from the United States Public Health Service (JWH) and by McIntire-Stennis Cooperative Forest Tree Research Funds. Little is known about either chemical or physical variation patterns for epicuticular waxes within a species. However, Barber (1955) has reported that the variation patterns in visible glaucousness of Tasmanian Eucalypts are genetically controlled and are related to the environment in the native habitat, especially to frost conditions. Our study of the surface waxes focuses on their physical characteristics with particular reference to their patterns of distribution and associations with stomates and degree of needle glaucousness. MATERIALS AND METHODS-One-year-old needles were removed with forceps from three trees of each of the following 3-year-old grafted varieties of blue spruce; Picea pungens var. glauca Thomsen c.v. Hoopsii, c.v. Kosteri, c.v. Moerheimi and c.v. Pendula. The plants were grown in the greenhouse to obtain needles on which the epicuticular waxes were relatively undisturbed by weathering. Second and third year needles were sampled from var. Thomsen to observe the effects of weathering on the waxes. Seven other conifers 8-10 years old, grown under field conditions, were sampled in a similar manner. These were Picea pun,sens, Picea glauca, Abies concolor, Pinus strobus, Pinus nigra, Pinus sylvestris, and Pseudotsuga menziesii. The needles were affixed to polished carbon discs with rubber cement, coated with a gold-palladium alloy (60:40) about 200 A thick, and examined directly under vacuum with an Applied Science Laboratory EMX-SM scanning electron microprobe operated at 15 KV and 2.0 nanoamps. The beam diam for the instrument was 2000 A. Replicate needles of each tree and species were examined at levels of magnification ranging from 100 X to 5000 X to verify consistency of surface wax

IN NOVEMBER, 1941, Cornell University received fromii Norwich, New York, the basal end of the trunk of a white fir tree (Abies concolor L.) that had fallen "in a mysterious manner." The tree, an ornamental specimen grown in a cemetery, was about 40 years old, 25 feet tall, and 12 inches in diamiieter at the base. It was found fallen, separated cleanly from the stump just below the ground level. The break was nearly transverse and remarkably smooth (fig. 1, 3), suggesting to local people that it hlad been sawed down or that some animal had gnawed it down. It seemed probable that the fall was the result of a break in tissues along a line of incomplete graft union and members of the staffs of the Departments of Forestry and Botany went to Norwich and dug up the stump for further evidence of the cause of the fall. When the basal section of the trunk is fitted to the stump, a transverse furrow is evident in the bark along the line of break (fig. 2) and the trunk just above the line of break is seen to be slightly greater in diameter than the stump. The undulate surfaces of separation show, on opposite sides of the pith, a projecting hump and a concavity (fig. 1, 7). Both of these facts supported the view that the fall was the result of graft-union failure. Aniatomical study of the region of the break confirmiied this view and demonstrated the presence of a possibly new type of failure of anatomical union of stock and scion. Slight color differences of the inner bark indicated the probability that a different species was used as stock but these could not be used in identification, and wood characters also proved of no value. Bailey (1935) states that varieties and forms of firs are grafted on seedlings of the particular species, if these are available; if not, on those of .4bies balsamea (L.) AMill., A. concolor Lindl. and Gord., and A. alba Mill. (= A. Picea Lindl.; A. pectinata DC.). Though foliage forms of white fir are grafted on seedlings of the same species, it seemiis unlikely that the stock in this tree was of that species because of the differences in bark color, rate of growth, and a probable incompatibility. It is unlikely that the balsam fir was used because of the lack of vigor of growth of this species. That the European white fir was used is possible since at the time this tree was planted-about 1900-much grafted fir nursery stock probably came from Holland. Detailed anatomical study disclosed the story of the method of grafting used and the progress of growth to the fall of the tree. Perfectly preserved in the heart of the tree is the region of grafting, with the cut surfaces of stock and scion, the thread which held stock and scion together, and the callus 1 Received for publication February 26, 1945. tissue which closed the wound areas (fig. 8). The surfaces of rupture and the furrow in the bark show the position of the cambium layers of both stock and scion (fig. 7, 14-16) and the structural basis for the extraordinary break in the tree. The grafting method used was that known as "lateral," in which the scion was applied to the side of the stock. In preparation of the stock for grafting the cut was made extremely deep, well bevond the pith (fig. 10) so that less than half of the stem remained at that point. The position of the pith (fig. 8) determines the depth of the cut, as does also the absence of the pith in a transverse cut higher up (fig. 9). This doubtless accidental condition may have been in part the cause of the graft-union failure. The-scion, applied obliquely to the cut, was tied in by a linen thread (about 0.3 mm. in diam.) (fig. 11) which is preserved in position, overgrown by the later-formed xylem of stock and scion (fig. 8, 12). The lower part of the cut-surface of the stock, resin-coated, is clearly seen in the dissection (fig. 8), as is also the short oblique cut by which the top of the stock seedling was later removed (fig. 8, 12). Overgrowth by callus and xylem and phloem took place rapidly on these surfaces, both inward from the sides and downward over the top (fig. 8, 9, 12, 13). Some bark remains on this overgrowth adjacent to the scion (fig. 8). Overgrowth was so extensive and continued so long-three to six years-that it is clear that there was no close contact of the upper cut-surfaces of stock and scion; the tying-in of the scion was defective above, and the two plant-tops apparently stood apart, held together tightly only at the base of the union (fig. 11, 12). Callus development rapidly covered most of the wound surface of the stock, leaving contact with only the very base of the scion. Similarly most of the cut surface of the scion became callused. From the beginning, therefore, there was contact of vascular tissues over only a small part of the possible surface, and the cambium margins failed to unite. The failure of cambium union was probably due to incompatibility of stock and scion but may have been in part because of the early establishment on both stock and scion of callus that almost completely enclosed each wound area independently. The margins of the cambium cylinders lay close together but remained unfused. The position of the ends of the cylinders is evident from the form of the annual rings (fig. 16). The in-turned ends of the cambia formed tracheids which, similarly, were bent inward at right angles or lay horizontallv in the tree (fig. 4, 5). Thus there was no interlocking of the cells of the stock and scion, and horizontally lying vascular cells separated the stump of the tree from the trunk (fig. 4, 5, 14, 15). Contact between

The behaviour of amitrole (3-amino-l,2,4-triazole) in 3-year old seedlings of Pinus 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 II. 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 symplast 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 to the roots was greatest when no visible growth could be detected.

which the fully formed telescoped shoot remains in a state of suspended growth; the first growth phase, during which the telescoped shoot elongates rapidly and gives rise to numerous cataphylls; and, the second growth phase, during which shoot elongation is completed and a new unelongated axis bearing many needle primordia is formed. The shoot tip of Abies consists of 4 clearly definable cytohistological zones; the apical initials, the sub-terminal mother cells, the peripheral zone, and the

Vegetation of the southwest slope of the Santa Catalina Mountains of southeastern Arizona was sampled and transects prepared for 1,000—ft (305 m) elevation belts on granite and gneiss soils from the summit forests (2,440—2,750 m) to the base of the mountains (900 m). Transects also represented subalpine forests above 2,750 m in the Pinaleno Mts. and vegetation of the valley plain or bajada below the mountains, and samples were taken from volcanic soils below 900 m in the Tucson Mts. Principal community—types from high elevations to low are: subalpine forest (Picca engelmanni in the Pinaleno Mts. and Abies lasiocarpa), montane fir forest (Abies concolor, Pseudotsuga menziesii), pine forests (Pinus ponderosa, P. strobiformis), pine—oak forests (P. ponderosa, Quercus hypoleucoides), pine—oak woodlands (P. ponderosa, P. chihuahuana, Q. hypoleucoides, Q. arizonica), pygmy conifer—oak scrub (Pinus cembroides, Juniperus deppeana, Q. arizonica, Q. emoryi, Arctostaphylos pringlei, A. pungens, monocot shrubs), open...

Cylindrocarpon cylindroides var. tenue as a pathogen of Abies concolor and some Abies hybrids. By artificial inoculations it was proved that Cylindrocarpon cylindroides Wollenw. var. tenue Wollenw. is the cause of a disease of Abies concolor and the progenies of the species-combinations A. concolor×A. procera and A. concolor×A. nordmanniana. The disease finally can cause the death of the trees.

Six plant communities occurring within the ponderosa pine (Pinus ponderosa) and white fir (Abies concolor) zones were identified east of the Cascade Mountains in south—central Oregon. These units, listed in order of increasing effective moisture and increasing elevation, are as follows: (1) Pinus ponderosa/Purshia tridentata, (2) Pinus ponderosa/Purshia tridentat/Festuca idahoensis, (3) Pinus ponderosa/Purshia tridentata—Arctostaphylos parryana var. pinetorum, (4) Pinus ponderosa/Ceanothus velutinus—Purshia tridentata, (5) Pinus ponderosa/Ceanothus velutinus, and (6) Abies concolor/Ceanothus velutinus. The Pinus/Purshia/Festuca association is restricted to areas of Shanahan coarse study loam, while the remaining five units all occur on Lapine loamy coarse sand. Both series are Regosols developed on aeolian pumice deposits. Lapine profile characteristics influencing plant root distribution, such as thickness of the gravelly C1 horizon and amount of mixing of C2 material with the buried soil, showed some ap...