Juniperus Scopulorum Sarg Research Articles

Westward Expansion by Juniperus virginiana of the Eastern United States and Intersection with Western Juniperus Species in a Novel Assemblage

Eastern redcedar (Juniperus virginiana L.) is increasing in density in the eastern United States and expanding in range to the west, while western Juniperus species also are increasing and expanding, creating the potential for a novel assemblage. I estimated range expansion and intersection by comparing recent USDA Forest Service Forest Inventory and Analysis surveys (mean year = 2009) to the oldest available surveys (mean year = 1981), with adjustments for sampling changes, and predicted climate envelopes during the following year ranges: 1500–1599, 1800–1849, 1850–1899, 1900–1949, and 1960–1989. During approximately 28 years, eastern redcedar range expanded by about 54 million ha (based on ≥0.5% of total stems ≥12.7 cm in diameter in ecological subsections). Combined range of western species of juniper did not expand. Range intersection of eastern redcedar and western Juniperus species totaled 200,000 km2 and increased by 31,600 km2 over time, representing a novel assemblage of eastern and western species. Predicted ranges during the other time intervals were 94% to 98% of predicted area during 1960–1989, suggesting major climate conditions have been suitable for centuries. The southern western Juniperus species and Rocky Mountain juniper (Juniperus scopulorum Sarg.) have the greatest potential for intersection with eastern redcedar, whereas eastern redcedar may have concluded westward expansion.

2,500 Years of Hydroclimate Variability in New Mexico, USA

AbstractWe provide a 2,508‐year reconstruction (492 BCE–2015 CE) of hydroclimate variability for west‐central New Mexico using the long‐lived conifer Rocky Mountain juniper (Juniperus scopulorum Sarg.). The reconstruction model explains 53% of the instrumental soil moisture variance and all validation statistics indicate a skillful record. More hydroclimate flips (extreme wet‐dry, vice versa) occur during the 20th–21st century than any other century in the past 2,500 years. Yet, drought and pluvial events captured during the instrumental period (since ca. 1900) do not represent the full range and variability of historical conditions. Since ca. 500 BCE, over 50 drought events have surpassed the severity of recent 21st century conditions, including the first documentation of a prolonged and severe drought during the second to third century BCE (Pre‐Ancestral Puebloan). Continued extreme hydroclimate variability (e.g., flips) in the 21st century could create infrastructure challenges for regional water planning authorities in this arid region.

Development of woody plants phenotyping sys tem with the help of machine vision and spectral analysis algorithms

Phenotyping is a modern technology that allows registering and analyzing data about living systems phenotypes in automatic mode. In recent years a high-efficiency higher plants phenotyping with the aim of deep study of the physiological and biochemical bases of their functioning, as well as selection of new high-yielding and stress-resistant varieties has acquired significant development. It is based on adaptation and introduction of modern information approaches such as algorithms of «computer vision» and allows receiving detailed information about plants phenomes at various organization levels. One of the unreached research sections in this field is tree plant cuttings phenotyping, which represents a great practical interest. In this work the system of phenotyping of green stem cuttings of woody plants Thuja occidentalis L. (Smaragd), Juniperus scopulorum Sarg. (Blue Arrow), Picea Abies L., H. Karst. was developed using machine vision algorithms and spectral analysis. A modular phenomics complex was created. It consist of phenomics box, plant cultivation system, lighting and watering systems, as well as system of registration and processing of RGB-images, including software. This complex has been tested in the laboratory and in field conditions. The initial testing of the phenomics complex was carried out. It showed that the data of changes in the pixel distribution of RGB-images by wavelengths can be the basis for estimating the size and physiological state of stem cuttings of woody plants. It was shown that the shift of the spectral curve of the reflected light into the long-wave area under the influence of water deficit allows to non-invasive and statistically reliably register the death of some cells. At the same time, statistically reliable distinctions have not been revealed at testing of influence of phytohormones (auxins and brassinosteroids) on rooting of stem cuttings of coniferous species. The obtained results have a fundamental practical significance and can be used in the research of physiological processes in higher plants, ornamental crop production and forestry.

Historical (1860) forest structure in ponderosa pine forests of the northern Front Range, Colorado

Management of many dry conifer forests in western North America is focused on promoting resilience to future wildfires, climate change, and land use impacts through restoration of historical patterns of forest structure and disturbance processes. Historical structural data provide models for past resilient conditions that inform the design of silvicultural treatments and help to assess the success of treatments at achieving desired conditions. We used dendrochronological data to reconstruct nonspatial and spatial forest structure at 1860 in fourteen 0.5 ha plots in lower elevation (∼1900–2100 m) ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) forests across two study areas in northern Colorado. Fires recorded by trees in two or more plots from 1667 to 1859 occurred, on average, every 8–15 years depending on scale of analysis. The last fire recorded in two or more plots occurred in 1859. Reconstructed 1860 stand structures were very diverse, with tree densities ranging from 0 to 320 trees·ha−1, basal areas ranging from 0.0 to 17.1 m2·ha−1, and quadratic mean diameters ranging from 0.0 to 57.5 cm. All trees in 1860 were ponderosa pine. Trees were significantly aggregated in 62% of plots in which spatial patterns could be estimated, with 10% to 90% of trees mainly occurring in groups of two to eight (maximum, 26). Current stands based on living trees with a diameter at breast height of ≥4 cm are more dense (range, 175–1010 trees·ha−1) with generally increased basal areas (4.4 to 23.1 m2·ha−1) and smaller trees (quadratic mean diameters ranging from 15.7 to 28.2 cm) and contain greater proportions of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and Rocky Mountain juniper (Juniperus scopulorum Sarg.). This is the first study to provide detailed quantitative metrics to guide restoration prescription development, implementation, and evaluation in these and similar ponderosa pine forests in northern Colorado.

Study of cytotoxic activity, podophyllotoxin, and deoxypodophyllotoxin content in selected Juniperus species cultivated in Poland

Context: The demand for podophyllotoxin and deoxypodophyllotoxin is still increasing and commercially exploitable sources are few and one of them, Podophyllum hexandrum Royle (Berberidaceae), is a “critically endangered” species.Objective: The first aim was to quantify the amount of podophyllotoxin and deoxypodophyllotoxin in 61 Juniperus (Cupressaceae) samples. Cytotoxic activity of podophyllotoxin and ethanolic leaf extracts of Juniperus scopulorum Sarg. “Blue Pacific” and Juniperus communis L. “Depressa Aurea” was examined against different leukemia cell lines.Materials and methods: Ultra-performance liquid chromatography (UPLC) analysis was performed with the use of a Waters ACQUITY UPLCTM system (Waters Corp., Milford, MA). The peaks of podophyllotoxin and deoxypodophyllotoxin were assigned on the basis of their retention data and mass-to-charge ratio (m/z). Trypan blue assay was performed to obtain IC50 cytotoxicity values against selected leukemia cell lines.Results: Juniperus scopulorum was characterized with the highest level of podophyllotoxin (486.7 mg/100 g DW) while Juniperus davurica Pall. contained the highest amount of deoxypodophyllotoxin (726.8 mg/100 g DW). Podophyllotoxin IC50 cytotoxicity values against J45.01 and CEM/C1 leukemia cell lines were 0.0040 and 0.0286 µg/mL, respectively. Juniperus scopulorum extract examined against J45.01 and HL-60/MX2 leukemia cell lines gave the respective IC50 values: 0.369–9.225 µg/mL. Juniperus communis extract was characterized with the following IC50 cytotoxity values against J45.01 and U-266B1 cell lines: 3.310–24.825 µg/mL.Conclusions: Juniperus sp. can be considered as an alternative source of podophyllotoxin and deoxypodophyllotoxin. Cytotoxic activity of podophyllotoxin and selected leaf extracts of Juniperus sp. against a set of leukemia cell lines was demonstrated.

Seasonal Resource Selection and Distributional Response by Elk to Development of a Natural Gas Field

Global energy demand is predicted to increase dramatically, suggesting the need to understand the role of disturbance from energy development better and to develop more efficient conservation strategies for affected wildlife populations. We evaluated elk (Cervus elaphus) response to disturbance associated with natural gas development in summer and winter, including shifts in resource selection and concomitant distribution. We collected elk locations prior to (1992–1995) and during (2008–2010) coal bed natural gas (CBNG) development in the ∼ 498-km2 Fortification Creek Area (FCA) of northeastern Wyoming, USA, where approximately 700 CBNG wells and 542 km of collector, local, and resource roads were developed from 2000 through 2010. We developed resource selection functions for summer and winter using coordinate data from VHF-collared female elk prior to CBNG development and similar location data from GPS-collared female elk during CBNG development to assess spatial selection shifts. By pooling across all locations we created population level models for each time period (e.g., pre- and during development) and incorporated individual variation through bootstrapping standard errors for parameter estimates. Comparison of elk resource selection prior to and during natural gas development demonstrated behavioral and distributional shifts whereby during development, elk demonstrated a higher propensity to use distance and escape cover to minimize exposure to roads. Specifically, during-development elk selected areas with greater Rocky Mountain juniper (Juniperus scopulorum Sarg.) cover, increased terrain ruggedness, and farther from CBNG roads than prior to development. Elk distributional changes resulting from avoidance behavior led to a loss of high-use areas by 43.1% and 50.2% in summer and winter, respectively. We suggest reducing traffic, protecting woody escape cover, and maintaining refugia within the energy-development footprint to promote persistence of elk within energy fields.

Climate-growth relationships for Rocky Mountain juniper (Juniperus scopulorum Sarg.) on the volcanic badlands of western New Mexico, USA

We sampled Rocky Mountain junipers (RMJ) to produce a multi-century tree-ring chronology from a relict lava flow, the Paxton Springs Malpais (PAX), in the Zuni Mountains of western New Mexico. Our objective was to assess crossdating potential for RMJ growing on the volcanic badlands of the region, investigate potential relationships between climate and RMJ growth, and investigate temporal variability in relationships identified between climate and RMJ growing at our site. We hypothesized that, similar to other drought stressed-conifers growing on the lava flows, RMJ responds to climate factors that influence and indicate moisture availability. We found a high average mean sensitivity value (0.53), which indicated the PAX chronology exhibited enough annual variability to capture fluctuations in environmental conditions. The average interseries correlation (0.74) indicated confident crossdating and a significant association of annual growth among trees within the stand. The positive correlation between the PAX chronology and total precipitation for the local water year was significant (r=0.53; P<0.001). Significant positive correlations also were identified between monthly PDSI, monthly total precipitation, and RMJ radial growth. Analyses of temporal stability indicated that the positive relationship between RMJ growth at the PAX site and monthly PDSI was the most stable relationship during the period of analysis (1895–2007). More importantly, we identified a unique inverse relationship between radial growth and monthly mean temperature during periods of the preceding year and current growing year, the first such finding of a strong temperature response for a low-mid elevation tree species in the American Southwest. Our results confirm that RMJ samples collected on the Paxton Springs Malpais are sensitive to climate factors that affect moisture availability, further suggesting that RMJ may be suitable for use in dendroclimatic research at additional locations across the broad distribution of the species.

Year-round Variations in Essential Oil Content and Composition of Male and Female Juniper

Rocky Mountain juniper (Juniperus scopulorum Sarg.) is an evergreen dioecious tree (produces male and female plants). The pleasant aroma and the medicinal value of this species are the result of the essential oil. The hypothesis of this study was that the essential oil content and composition may be different in male and in female trees and also may be affected with seasonal changes throughout the year. The objective was to evaluate year-round variations in essential oil composition of Rocky Mountain juniper within single male and female trees. The concentration of essential oil in fresh leaves varied from 0.335% to 0.799%, and at most sampling points, the oil content in the biomass of the male tree was greater than that in the biomass of the female tree. There was a trend toward increased essential oil content in male juniper in 220 to 342 days after the first sampling (DAFS), compared with the one in 35 to 184 DAFS. The concentrations of the oil constituents alpha-pinene, alpha-terpinene, gamma-terpinene, terpinolene, pregeijerene B, elemol, beta-eudesmol/alpha-eudesmol, and 8-alpha-acetoxyelemol were greater in the oil of the female tree than in the oil of the male tree. Conversely, the concentrations of alpha thujene, sabinene, myrcene, limonene, and delta-cadinene were greater in the oil of the male tree than in the oil of the female tree. However, the concentration gradient trends for both female and male trees were similar for myrcene and sabinene, for alpha-terpinene and terpinolene, for pereijerene B and elemol, and for beta-eudesmol/alpha-eudesmol and 8-alpha-acetoxyelemol. Overall, lower concentrations in the oils at 101 to 132 or 163 DAFS were found for myrcene and alpha-pinene sabinene, whereas the concentrations of gamma-terpinene, elemol (female tree), beta-eudesmol/alpha-eudesmol (female tree), and 8-alpha-acetoxyelemol (female tree) were greater during this period. This study demonstrated that the content and composition of the essential oil from Rocky Mountain juniper are subject to seasonal changes and also depend on the sex of the tree.

Propagation protocol for Rocky Mountain juniper (Juniperus scopulorum Sarg.)

We present our techniques for producing Rocky Mountain juniper ( Juniperus scopulorum Sarg. [Cupressaceae]) from seeds in a container nursery in Idaho. Our combination of warm, moist treatment and long stratification along with our use of germinants rather than direct sowing yields a reliable, uniform annual crop of seedlings that are 10 to 12 in (25 to 30 cm) tall with 3 to 6 mm RCD.

Effects of seed source and pre-planting treatment on emergence of Juniperus scopulorum Sarg. in a Great Plains nursery

Reliable propagation of Rocky Mountain juniper (<i>Juniperus scopulorum</i> Sarg. [Cupressaceae]) for use as an evergreen shelterbelt species in the southern Great Plains is hindered by inconsistent seedling emergence and establishment. We evaluated a series of pre-planting treatments as well as 2 planting depths for both fall and spring planting dates using a single seed source. We then tested 6 seed sources using the 3 best treatments. The best treatment was 13 wk at 22 °C (72 °F) followed by 13 wk at 4 °C (39 °F; 23% emergence for fall and spring planting combined). Fall planting resulted in greater success for differing pre-planting treatments. Planting depth did not affect emergence. Only one of 6 seed sources produced seedlings in response to cold-only treatment while combining warm and cold treatments was generally successful for all seed sources.

Fire history of pinyon–juniper woodlands at upper ecotones with ponderosa pine forests in Arizona and New Mexico

We used maps of fire evidence, fire scar dendrochronology, forest age-structure analysis, and landscape analysis to investigate fire history at pinyon pine ( Pinus edulis Engelm.) – juniper ( Juniperus osteosperma (Torr.) Little, Juniperus scopulorum Sarg.) woodland – ponderosa pine ( Pinus ponderosa P. &amp; C. Lawson) forest ecotones in Arizona (Tusayan) and in New Mexico (Canjilon). Results showed that charred trees were not evenly distributed across vegetative communities but were significantly (p &lt; 0.001) more abundant than expected in ponderosa pine communities. Composite fire scar analysis indicated that surface fires occurred in ponderosa pine stands at both sites and burned at intervals of 7.2–11.1 years (WMPI; Weibull median probability interval). At Tusayan, landscape structure was fine grained, and maximum pinyon age was &gt;200 years across 80% of the site. At Canjilon, landscape pattern was relatively coarse, and most pinyon patches were 200–300 years old. Cumulative standing age distributions suggested pinyon–juniper fire rotations of 340 and 290 years at Tusayan and Canjilon, respectively. We concluded the following: (i) surface fires in ponderosa pine stands did not spread through pinyon–juniper communities at either site, (ii) fire evidence was prevalent across both sites, but old pinyon trees indicated that no widespread lethal fires had occurred in the last 300–400 years, and (iii) structurally heterogeneous landscapes suggested that historical pinyon–juniper fires were of limited extent but lethal in patches.

Assessment of Juniper Encroachment With The Use of Satellite Imagery and Geospatial Data

Juniper encroachment into otherwise treeless shrub lands and grasslands is one of the most pronounced environmental changes observed in rangelands of western North America in recent decades. Most studies on juniper change are conducted over small areas, although encroachment is occurring throughout regions. Whether changes in juniper cover can be assessed over large areas with the use of long-term satellite data is an important methodological question. A fundamental challenge in using satellite imagery to determine tree abundance in rangelands is that a mix of trees, sagebrush, and herbaceous cover types can occur within a given image pixel. Our objective was to determine if spectral mixture analysis could be used to estimate changes in Rocky Mountain juniper (Juniperus scopulorum Sarg) and Utah juniper (Juniperus osteosperma [Torr.] Little) cover over 20 yr and 20 000 ha in southeast Idaho with the use of Landsat imagery. We also examined the spatial patterns and variation of encroachment within our study area using Geographic Information Systems–based data sets of grazing use, land-cover types, and topography. Juniper cover determined from 15-cm-resolution digital aerial orthophotography was used to train and validate juniper presence/absence classification in 1985 and 2005 Landsat images. The two classified images were then compared to detect changes in juniper cover. The estimated rate of juniper encroachment over our study area was 22–30% between 1985 and 2005, consistent with previous ground-based studies. Moran’s I analysis indicated that juniper encroachment pattern was spatially random rather than clustered or uniform. Juniper encroachment was significantly greater in grazed areas (P 5 0.02), and in particular in grazed shrub land cover type (P 5 0.06), compared to ungrazed areas. Juniper encroachment was also greater on intermediate slopes (10–35% slopes) compared to steeper or flatter terrain, and encroachment was somewhat less on north-facing (P 5 0.03) and more on west-facing (P 5 0.02) slopes compared to other aspects.

The influence of fertilization regime and mycorrhizal inoculum on outplanting success: a field trial of containerized seedlings in Oregon

Mycorrhizal inoculum is marketed as a means of increasing seedling survival, growth, and drought resistance, among other benefits. The production of plant materials colonized by arbuscular mycorrhizal fungi, however, has proved to be problematic due to the lack of integration between biotechnical firms that produce mycorrhizal inoculum and cultural procedures at commercial nurseries. Our research demonstrates that inoculum-compatible fertilization regimes can have significant effects on mycorrhizal colonization rates and plant performance following outplanting. Mycorrhizal inoculum was applied to 5 species ( Ribes aureum Pursh [Grossulariaceae], Prunus pumila L. var. besseyi (L.H. Bailey) Gleason [Rosaceae], Dasiphora fruticosa (L.) Rydb. [Rosaceae], Amorpha canescens Pursh [Fabaceae], Juniperus scopulorum Sarg. [Cupressaceae]) grown under a traditional fertigation regime and under an alternative regime consisting of a mix of low phosphorus, slow-release fertilizer. The percentage of seedlings exhibiting mycorrhizal structures ranged from 0 to 20% for the traditional fertigation regime compared with a range of 16 to 92% for the alternative slow-release regime. Following outplanting, seedling survival ranged from 20 to 60% for traditional fertigation regime compared with 65 to 95% for the alternative slow-release regime. This study emphasizes the need to consider greenhouse fertilization strategies in order to effectively produce colonized plant material and to achieve the potential benefits of mycorrhiza under field conditions. Meikle TW, Amaranthus M. 2008. The influence of fertilization regime and mycorrhizal inoculum on outplanting success: a field trial of containerized seedlings in Oregon. Native Plants Journal 9(2):107–116.

Rocky Mountain Juniper Seed Source Test in Western Kansas, U.S.

Twenty-six sources of Rocky Mountain juniper (Juniperus scopulorum Sarg.) were established as a provenance test near Colby, Kansas, U.S. in 1980. Height, diameter, survival, number of stems, crown density, branch angle, and vigor were evaluated with analysis of variance, cluster analysis, simple correlation, and regression analysis techniques. Source differences were found. Total height at 23 years ranged from 3.6 to 5.4 m (11.9 to 17.8 ft), diameter breast height (dbh) ranged from 5.6 to 10.4 cm (2.2 to 4.2 in), and survival from 10% to 100%. Height growth was weakly related to geographic variables, but dbh was related to latitude, longitude, and elevation. Selection of fast-growing sources may begin at 5 years after field planting.

Rocky Mountain Juniper Seed Collecting, Processing and Germinating

Abstract Propagating Rocky Mountain juniper (Juniperus scopulorum Sarg. [Cupressaceae]) from seeds is difficult, but proper collection, cleaning, storage, and dormancy treatment can improve success. Our best results are achieved by: 1) avoiding collection of immature and insect damaged cones; 2) minimizing cone storage or storing surface-dried cones under well-ventilated conditions at 1 to 3 °C (34 to 37 °F) and 80% to 90% humidity; 3) macerating cones in hand-cleaner-amended water; 4) separating light or unfilled seeds from viable seeds with flotation; and 5) treating seeds with a 120-d warm moist stratification in peat moss mix followed by a 150-d cold moist chilling. Establishment and management of cultivated orchards improves seed yield and quality.

Fire History of the Rochelle Hills Thunder Basin National Grasslands

A fire scar chronology was constructed from ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and Rocky Mountain juniper (Juniperus scopulorum Sarg.) trees within the 70 km 2 R o c h e l l e Hills Area of the Thunder Basin National Grasslands, in north east Wyoming. A total of 65 fire scars occurred in 48 crossdated samples, and a master fire chronology was constructed for the period 1565 to 1988. No trees recorded more than 3 fires and most (26 of 42) recorded only one. For this reason, fire frequency intervals were considered as fire-free intervals in the Rochelle Hills Area. The Weibull Median Probability Interval (WMPI) for the entire period of record was 7.4; 7.9 for the non suppression period (1565 to 1939); and 6.7 for the suppression period (1940 to 1988). Infrequent occurrence of multiple scars, rough topography, and low potential substrates suggest that understory fuel loads were limited in amount and spatial consistency during most fire years. Position of scars within annual growth rings suggests that most fires (80%) occurred during the latter stages of the growing season or during the dormant period.

The use of RAPD markers to distinguish among juniper and cedar cultivars

Two species of Chamaecyparis and six cultivars each of Juniperus chinensis L. and Juniperus scopulorum Sarg. (Cupressaceae) were subjected to random amplified polymorphic DNA (RAPD) analysis using seven primers. Unweighted pair group method with averages (UPGMA) and principal component analyses of genetic distances between cultivars showed that 42 polymorphic RAPD bands could distinguish among all cultivars and properly group them by species and genera. Where the origin of a specific juniper cultivar is uncertain, analysis of genetic distance can pinpoint close relatives. For example, we were unable to trace the origin of J. chinensis 'Alps', and we initially thought it was a mislabeled J. chinensis 'Blue Alps'. However, we found 'Alps' to be closer to J. chinensis 'Fairview' and 'Mountbatten' than to 'Blue Alps'. Similarly, 'Wichita Blue' has an unknown origin, but it had the highest genetic similarity with 'Medora'.Key words: juniper, cedar, RAPD, cultivars, phylogenetics.

Fire history of the Rochelle Hills Thunder Basin National Grasslands

A fire scar chronology was constructed from ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and Rocky Mountain juniper (Juniperus scopulorum Sarg.) trees within the 70 km2 Rochelle Hills Area of the Thunder Basin National Grasslands, in north-east Wyoming. A total of 65 fire scars occurred in 48 crossdated samples, and a master fire chronology was constructed for the period 1565 to 1988. No trees recorded more than 3 fires and most (26 of 42) recorded only one. For this reason, fire frequency intervals were considered as fire-free intervals in the Rochelle Hills Area. The Weibull Median Probability Interval (WMPI) for the entire period of record was 7.4; 7.9 for the non-suppression period (1565 to 1939); and 6.7 for the suppression period (1940 to 1988). Infrequent occurrence of multiple scars, rough topography, and low potential substrates suggest that understory fuel loads were limited in amount and spatial consistency during most fire years. Position of scars within annual growth rings suggests that most fires (80%) occurred during the latter stages of the growing season or during the dormant period.

The use of RAPD markers to distinguish among juniper and cedar cultivars

Two species of Chamaecyparis and six cultivars each of Juniperus chinensis L. and Juniperus scopulorum Sarg. (Cupressaceae) were subjected to random amplified polymorphic DNA (RAPD) analysis using seven primers. Unweighted pair group method with averages (UPGMA) and principal component analyses of genetic distances between cultivars showed that 42 polymorphic RAPD bands could distinguish among all cultivars and properly group them by species and genera. Where the origin of a specific juniper cultivar is uncertain, analysis of genetic distance can pinpoint close relatives. For example, we were unable to trace the origin of J. chinensis 'Alps', and we initially thought it was a mislabeled J. chinensis 'Blue Alps'. However, we found 'Alps' to be closer to J. chinensis 'Fairview' and 'Mountbatten' than to 'Blue Alps'. Similarly, 'Wichita Blue' has an unknown origin, but it had the highest genetic similarity with 'Medora'.Key words: juniper, cedar, RAPD, cultivars, phylogenetics.

Xylem Embolism in Response to Freeze-Thaw Cycles and Water Stress in Ring-Porous, Diffuse-Porous, and Conifer Species

Vulnerability to xylem embolism by freeze-thaw cycles and water stress was quantified in ring-porous (Quercus gambelii Nutt.), diffuse-porous (Populus tremuloides Michx., Betula occidentalis Hook.), and conifer species (Abies lasiocarpa Nutt., Juniperus scopulorum Sarg.). Embolism was measured by its reduction of xylem hydraulic conductivity; it was induced by xylem tension (water-stress response) and by a tension plus a freeze-thaw cycle (freeze response). Conifers showed little (Juniperus) or no (Abies) freeze response even to repeated cycles. In contrast, Quercus embolized more than 90% by freezing at tensions below 0.2 MPa, whereas similar embolism without freezing required tensions above 4.5 MPa. Diffuse-porous trees (Betula, Populus) showed an intermediate freeze response. The magnitude of the freeze response was correlated with conduit volume but occurred at higher tensions than predicted from theory. Large early-wood vessels (2.8 x 10(-9) m(3)) in oak were most vulnerable to embolism by freezing, small vessels in Populus and Betula were intermediate (approximately 7 x 10(-11) m(3)), and tracheids in conifers (about 3 x 10(-13) m(3)) were most resistant. The same trend was found within a stem: embolism by freeze-thawing occurred preferentially in wider conduits. The water-stress response was not correlated with conduit volume; previous work indicates it is a function of interconduit pit membrane structure. Native embolism levels during winter corroborated laboratory results on freezing: Quercus embolized 95% with the first fall freeze, Populus and Betula showed gradual increases to more than 90% embolism by winter's end, and Abies remained below 30%.