[Response of radial growth of different timberline species to climate change in Yading Nature Reserve, Sichuan, China]. / å››å·äºšä¸è‡ªç„¶ä¿æŠ¤åŒºä¸åŒæž—çº¿æ ‘ç§å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

The radial growth of trees in alpine timberline is particularly sensitive to climate change. We sampled and disposed tree-ring cores of three coniferous tree species including Juniperus saltuaria, Abies forrestii, and Larix potaninii at alpine timberline in Yading Nature Reserve. The standard tree-ring chronology was used to explore the response of radial growth of different timberline species to climate change. The results showed that radial growth of L. potaninii increased after 2000, while that of A. forrestii declined after 2002, and J. saltuaria showed a significant decreasing growth trend in the past 10 years. Such results indicated divergent growth responses to climate factors among the three tree species at alpine timberline. The radial growth of J. saltuaria was sensitive to temperature, and was positively correlated with the minimum temperature from previous October to current August, the mean tempera-ture from previous November to current April and from current July to October, but was negatively associated with the relative humidity from current July to October. The radial growth of A. forrestii showed negative correlation with mean temperature and the maximum temperature from May to June in the current year, while it exhibited positive association with the relative humidity and the Palmer drought severity index from May to June in the current year. L. potaninii radial growth was positively associated with mean temperature and the maximum temperature of November-December in the previous year, the maximum temperature of current March and mean temperature of current August. The temporal stability of climate-growth relationship varied among different timberline species. The positive correlation between radial growth of A. forrestii and J. saltuaria and temperature gradually decreased, while the posi-tive relationship of L. potaninii radial growth and temperature gradually increased. Under the background of climate warming, rapid rise in surface air temperatures may promote the radial growth of L. potaninii, while inhibit that of J. saltuaria and A. forrestii, which may change the position of regional timberline.

The impact of NPK fertilizer on growth and nutrient accumulation in juniper (Juniperus procera) trees grown on fire-damaged and intact soils.

Wildfires significantly alter soil properties and result in vegetation shifts; therefore, rapid reforestation activities are needed in the forests affected by wildfires. The decreased nutrient in the soil is the obvious effect of wildfires; however, little is known about the reforestation of Juniper (Juniperus procera) forests with application of NPK fertilizers. Juniper forests are common in Asir and Taif regions of Saudi Arabia and vulnerable to wildfires; thus, reforestation is needed after the onset of fires. This study assessed the impact of different doses of organic NPK fertilizer (0, 5 and 10 g/L) on growth and nutrient accumulation of Juniper trees grown on fire-damaged and intact soils. Data relating to tree height, number of leaves per plant, fresh and dry biomass accumulation in shoot and root, chlorophyll contents and uptake of N, P, K, and Na were recorded. Individual and interactive effects of soil types and fertilizer doses significantly altered all measured traits with minor exceptions. Overall, higher values of the measured traits were recorded for intact soil and 10 g/L fertilize dose. The increasing fertilizer doses improved the growth and nutrient acquisition and application of 10 g/L fertilizer on intact soil recorded the highest values of growth traits. Juniper trees grown on fire-damaged soil accumulated higher amount of nitrogen than intact soil. Similarly, the trees grown on intact soil accumulated lower amount of Na and maintained comparable K/Na ratio to intact soil. It is concluded that supplying 10 g/L fertilizer could improve the establishment of Juniper trees on fire-damaged soil. Therefore, organic fertilizer can be used to improve the reforestation of wildfire-affected Juniper forests in the Asir province.

Foliar respiration is related to photosynthetic, growth and carbohydrate response to experimental drought and elevated temperature.

Short-term plant respiration (R) increases exponentially with rising temperature, but drought could reduce respiration by reducing growth and metabolism. Acclimation may alter these responses. We examined if species with different drought responses would differ in foliar R response to +4.8°C temperature and -45% precipitation in a field experiment with mature piñon and juniper trees, and if any differences between species were related to differences in photosynthesis rates, shoot growth and nonstructural carbohydrates (NSCs). Short-term foliar R had a Q10 of 1.6 for piñon and 2.6 for juniper. Piñon foliar R did not respond to the +4.8°C temperatures, but R increased 1.4× for juniper. Across treatments, piñon foliage had higher growth, lower NSC content, 29% lower photosynthesis rates, and 44% lower R than juniper. Removing 45% precipitation had little impact on R for either species. Species differences in the response of R under elevated temperature were related to substrate availability and stomatal response to leaf water potential. Despite not acclimating to the higher temperature and having higher R than piñon, greater substrate availability in juniper suggests it could supply respiratory demand for much longer than piñon. Species responses will be critical in ecosystem response to a warmer climate.

Longevity and germination of Juniperus communis L. pollen after storage.

Pollen storage belongs among the most important activities associated with pollen handling. It overcomes the differences in pollen shedding and ovule receptivity during controlled pollination experiments. It is especially important for species like common juniper (Juniperus communis L.) with an extremely low quality of seeds due to pollination failure. Additionally, it is a substantial part of germplasm preservation programmes in pollen banks. In the present paper, the effect of short-term storage of pollen was studied using pollen samples from five shrubs in an in vitro germination test. Two temperature regimes were tested. The pollen viability of freshly collected pollen varied considerably between individual shrubs, exhibiting 67.3-88.6% germination rate and 248.0-367.3 µm of pollen tubes. Storage at + 4 °C for four months was accompanied by a profound decline in pollen viability. The germination percentage was reduced to 49.2-75.2% and the pollen tube length to 32.5-69.0%, depending on individual shrubs. The corresponding decline in pollen viability characteristics during storage at - 20 °C was only negligible in two of the tested shrubs. In the remaining three shrub samples, an increase in germination percentage was observed. Pollen tube growth responded more sensitively to freezing, but, on average, the decrease in length was lower than that at + 4 °C. The rate of reduction in pollen tube length varied between 11.5 and 45.4%. Cytological events accompanying in vitro germination of freezer-stored pollen exhibited some delay in releasing the exine from pollen grains during the early stages of germination as compared with freshly collected pollen. In conclusion, short-term storage of the common juniper pollen in a freezer is better for the preservation of its viability than storage at + 4 °C.

Cavitation fatigue in conifers: a study on eight European species.

After drought-induced embolism and repair, tree xylem may be weakened against future drought events (cavitation fatigue). As there are few data on cavitation fatigue in conifers available, we quantified vulnerability curves (VCs) after embolism/repair cycles on eight European conifer species. We induced 50% and 100% loss of conductivity (LC) with a cavitron, and analyzed VCs. Embolism repair was obtained by vacuum infiltration. All species demonstrated complete embolism repair and a lack of any cavitation fatigue after 50% LC . After 100% LC, European larch (Larix decidua), stone pine (Pinus cembra), Norway spruce (Picea abies), and silver fir (Abies alba) remained unaffected, while mountain pine (Pinus mugo), yew (Taxus baccata), and common juniper (Juniperus communis) exhibited 0.4-0.9 MPa higher vulnerability to embolism. A small cavitation fatigue observed in Scots pine (Pinus sylvestris) was probably biased by incomplete embolism repair, as indicated by a correlation of vulnerability shifts and conductivity restoration. Our data demonstrate that cavitation fatigue in conifers is species-specific and depends on the intensity of preceding LC. The lack of fatigue effects after moderate LC, and relevant effects in only three species after high LC, indicate that conifers are relatively resistant against cavitation fatigue. This is remarkable considering the complex and delicate conifer pit architecture and may be important considering climate change projections.

Mass propagation of Juniperus procera Hoechst. Ex Endl. From seedling and screening of bioactive compounds in shoot and callus extract.

BACKGROUND: Juniperus procera Hoechst. ex Endl. is a medicinal tree in Saudi Arabia, primarily in the Enemas region, but it is locally threatened due to die-back disease and difficulties regarding seed reproduction (seed dormancy and underdeveloped embryonic anatomy, and germination rate < 40%). Hence, the alternative methods for reproduction of Juniperus procera are really needed for conservation and getting mass propagation for pharmaceutical uses. RESULTS: In this manuscript, we articulated the successful in vitro shoot multiplication and callus induction of J. procera by using young seedling as explants and detected an important antibacterial and antitumor product. Explants were grown on different types of media with the supplement of different combinations of Plant Growth Regulators (PGRs) at different concentrations. The best media for shoot multiplication was Woody Plant Media (WPM) supplemented with PGRs (0.5 µM of IAA and 0.5 µM BAP or 0.5 µM IBA and 0.5 µM BAP). Whereas for callus induction and formation Woody Plant Media (WPM) with the addition of PGRs (0.5 µM 2,4-D and 0.5 µM BAP) was better than the Chu Basal Salt Mixture (N6), Gamborg's B-5 Basal Medium (B5), and Murashige and Skoog media. The possibility of multiplication of J. procera in vitro creates significant advantages to overcome the difficulties of seeds dormancy for the reproduction of plants, conservation of trees, and getting mass propagation material for pharmaceutical studies. The shoot and callus extract of J. procera was detected using gas chromatography-mass spectrometry analysis and revealed more than 20 compounds related to secondary metabolites, which contained antibacterial and antitumor agents, such as ferruginol, Retinol, and Quinolone as well as confirmed by Direct Analysis in Real Time, Time of Flight Mass Spectrometry (DART-ToF-MS). Podophyllotoxin (PTOX) was detected in callus material by HPLC with sigma standard and confirmed by DART-ToF-MS and UV spectra. CONCLUSION: We successfully conducted in vitro shoot multiplication and callus induction from J. procera seedlings using WPM and a different combination of PGRs and, detected an important antibacterial and antitumor product such as ferruginol and podophyllotoxin. According to our findings, J. procera has become a new natural source of novel bioactive compounds.

Behavior-specific occurrence patterns of Pinyon Jays (Gymnorhinus cyanocephalus) in three Great Basin study areas and significance for pinyon-juniper woodland management.

The Pinyon Jay is a highly social, year-round inhabitant of pinyon-juniper and other coniferous woodlands in the western United States. Range-wide, Pinyon Jays have declined ~ 3-4% per year for at least the last half-century. Occurrence patterns and habitat use of Pinyon Jays have not been well characterized across much of the species' range, and obtaining this information is necessary for better understanding the causes of ongoing declines and determining useful conservation strategies. Additionally, it is important to better understand if and how targeted removal of pinyon-juniper woodland, a common and widespread vegetation management practice, affects Pinyon Jays. The goal of this study was to identify the characteristics of areas used by Pinyon Jays for several critical life history components in the Great Basin, which is home to nearly half of the species' global population, and to thereby facilitate the inclusion of Pinyon Jay conservation measures in the design of vegetation management projects. To accomplish this, we studied Pinyon Jays in three widely separated study areas using radio telemetry and direct observation and measured key attributes of their locations and a separate set of randomly-selected control sites using the U. S. Forest Service's Forest Inventory Analysis protocol. Data visualizations, principle components analysis, and logistic regressions of the resulting data indicated that Pinyon Jays used a distinct subset of available pinyon-juniper woodland habitat, and further suggested that Pinyon Jays used different but overlapping habitats for seed caching, foraging, and nesting. Caching was concentrated in low-elevation, relatively flat areas with low tree cover; foraging occurred at slightly higher elevations with generally moderate but variable tree cover; and nesting was concentrated in slightly higher areas with high tree and vegetation cover. All three of these Pinyon Jay behavior types were highly concentrated within the lower-elevation band of pinyon-juniper woodland close to the woodland-shrubland ecotone. Woodland removal projects in the Great Basin are often concentrated in these same areas, so it is potentially important to incorporate conservation measures informed by Pinyon Jay occurrence patterns into existing woodland management paradigms, protocols, and practices.

Shade is the most important factor limiting growth of a woody range expander.

The expansion of woody plants into grasslands and old fields is often ascribed to fire suppression and heavy grazing, especially by domestic livestock. However, it is also recognized that nutrient availability and interspecific competition with grasses and other woody plants play a role in certain habitats. I examined potential factors causing range- and niche expansion by the eastern redcedar Juniperus virginiana, the most widespread conifer in the eastern United States, in multifactorial experiments in a greenhouse. Historical records suggest that the eastern redcedar is a pioneer forest species, and may be replaced as the forest increases in tree density due to shading. Another possible factor that affects its distribution may be nutrient availability, which is higher in old fields and other disturbed lands than in undisturbed habitats. In its historic range, eastern redcedars are particularly abundant on limestone outcrops, often termed 'cedar barrens'. However, the higher abundance on limestone could be due to reduced interspecific competition rather than a preference for high pH substrates. I manipulated shade, fertilization, lime, and interspecific competition with a common dominant tree, the post oak Quercus stellata. In a separate experiment, I manipulated fire and grass competition. I measured growth rates (height and diameter) and above- and belowground biomass at the end of both experiments. I also measured total non-structural carbohydrates and nitrogen in these plants. Shade was the most important factor limiting the growth rates and biomass of eastern redcedars. I also found that there were significant declines in nitrogen and non-structural carbohydrates when shaded. These results are consistent with the notion that the eastern redcedar is a pioneer forest species, and that shade is the reason that these redcedars are replaced by other tree species. In the second experiment, I found that a single fire had a negative effect on young trees. There was no significant effect of competition with grass, perhaps because the competitive effect was shading by grasses and not nutrient depletion. Overall, the effects of shade were far more apparent than the effects of fire.

Sexual Dimorphism in the Chemical Composition of Male and Female in the Dioecious Tree, Juniperus communis L., Growing under Different Nutritional Conditions.

We hypothesized that female and male individuals of the dioecious tree species, Juniperus communis, exhibit different strategies of resource allocation when growing under stress conditions. To test this hypothesis, we performed a two-year pot experiment on plants exposed to different levels of nutrient availability. Analysis of the plants revealed a higher concentration of carbohydrates, carbon, and phenolic compounds in needles of female plants, indicating that females allocate more resources to storage and defense than males. This difference was independent of nutrient availability. Differences in carbohydrates levels between the sexes were most often significant in June, during the most intensive phase of vegetative growth in both sexes, but could also be attributed to female resources investment in cone development. A higher level of nitrogen and other macroelements was observed in males than in females, which may have been connected to the accumulation of resources (nitrogen) for pollen grain production in males or greater allocation of these elements to seeds and cones in females. The interaction between sex and soil fertilization for the C:N ratio may also indicate sex-specific patterns of resource allocation and utilization, which is impacted by their availability during specific periods of J. communis annual life cycle.

Variations in leaf traits of Juniperus przewalskii from an extremely arid and cold environment.

How leaf traits vary with environmental and climatic variables in cold and arid environments is an essential issue in environmental ecology. Here, we analyzed the variations in leaf nitrogen (N) and phosphorus (P) stoichiometry and leaf dry matter content (LDMC) in Qilian juniper (Juniperus przewalskii Kom.) growing in 14 environmentally different plots on the northeastern Tibetan Plateau. The results showed that the N and P concentrations, N:P ratio and LDMC of Qilian juniper were 10.89 mg.g-1, 1.04 mg.g-1, 10.80 and 483.06 mg.g-1, respectively. The spatial coefficients of the variations in leaf N and P stoichiometry were significantly higher than the seasonal ones, and the correlations of leaf N and P concentrations with spatial variables were stronger than their correlations with the season. During the growing season, only the leaf N concentration and N:P ratio significantly increased. Soil nutrients were highly positively significantly correlated with leaf P concentrations but negatively correlated with the N:P ratio and LDMC. However, leaf N concentrations showed no significant correlations with soil nutrients. We suggest that the effects of temperature on the N concentration and LDMC were stronger than the effects of drought, while those on the P concentration and N:P ratio were weaker. Drought reduced leaf N and P concentrations and increased the N:P ratio and LDMC. In the arid region, with an increasing mean annual temperature (MAT), leaf N concentration significantly decreased, and LDMC significantly increased. In the semi-arid region, as MAT increased, leaf N and P concentrations significantly increased and LDMC and the N:P ratio significantly decreased. These opposite results supported the growth rate hypothesis that plant N and P concentrations increase while the N:P ratio and LDMC decrease as the growth rate increases.

Winter precipitation - not summer temperature - is still the main driver for Alpine shrub growth.

High latitude and altitude environments are universally recognized as particularly sensitive to environmental changes and the current climate warming is inducing remarkable transformations on vegetation assemblage in these temperature-limited regions. However, next to the wealth of studies describing the effect of rising growing season temperature on trees, much less is known about the concurrent effects of precipitation and snowpack dynamics on the other key component of alpine vegetation represented by prostrate life forms. Selecting the most widespread shrub species in the North Hemisphere, we assembled a monospecific (Juniperus communis L.) network of 7 sites overarching the European Alps, measured the annual growth on >330 individuals and assessed the climate-growth associations for the last century (1910-2010) adopting a new model estimating the solid fraction of precipitation from unique highly-resolved daily climate records. Despite the high space-time variability of the yearly precipitation amount and distribution across the region, our analysis found a prominent, consistent and negative role of winter precipitation for shrub growth. Moreover, this crucial role of snow is maintained even in recent years, despite the persistent and significant warming trend. The presence of this underrated key factor for Alpine long-lived vegetation will require a thorough consideration. For the prostrate life form, not only temperature but also the solid fraction of winter precipitation should be considered to improve the projections of future growth trajectories.

Tree resilience to drought increases in the Tibetan Plateau.

Forests in the Tibetan Plateau are thought to be vulnerable to climate extremes, yet they also tend to exhibit resilience contributing to the maintenance of ecosystem services in and beyond the plateau. So far the spatiotemporal pattern in tree resilience in the Tibetan Plateau remains largely unquantified and the influence of specific factors on the resilience is poorly understood. Here, we study ring-width data from 849 trees at 28 sites in the Tibetan Plateau with the aim to quantify tree resilience and determine their diving forces. Three extreme drought events in years 1969, 1979, and 1995 are detected from metrological records. Regional tree resistance to the three extreme droughts shows a decreasing trend with the proportion of trees having high resistance ranging from 71.9%, 55.2%, to 39.7%. Regional tree recovery is increasing with the proportion of trees having high recovery ranging from 28.3%, 52.2%, to 64.2%. The area with high resistance is contracting and that of high recovery is expanding. The spatiotemporal resistance and recovery are associated with moisture availability and diurnal temperature range, respectively. In addition, they are both associated with forest internal factor represented by growth consistence among trees. We conclude that juniper trees in the Tibetan Plateau have increased resilience to extreme droughts in the study period. We highlight pervasive resilience in juniper trees. The results have implications for predicting tree resilience and identifying areas vulnerable to future climate extremes.

Phenolic profile and in vitro bioactive potential of Saharan Juniperus phoenicea L. and Cotula cinerea (Del) growing in Algeria.

The aim of this study was to characterize the individual phenolic profile and antioxidant, anti-inflammatory, cytotoxic, and antimicrobial activities of hydroethanolic and infusion extracts prepared from Algerian Saharan Juniperus phoenicea L. and Cotula cinerea (Del). The phenolic profile was determined using a liquid chromatograph coupled to a diode array detector and an electrospray ionization mass spectrometer (LC-DAD-ESI/MS). A total of thirteen and nine individual phenolic compounds were identified in J. phoenicea and C. cinerea, respectively. 3-p-Coumaroylquinic acid, quercetin- and myricetin-O-pentoside were the major compounds present in J. phoenicea; on the other hand, C. cinerea presented luteolin-7-O-glucoside, luteolin-O-malonylhexoside, and 5-O-caffeoylquinic acid as the main molecules. In general, all samples exhibited interesting antioxidant activity when compared to the standard Trolox, but J. phoenicea extracts presented the highest bioactivity. Likewise, all the samples exhibited anti-inflammatory activity; thus J. phoenicea hydroethanolic extracts showed the highest potential (88 ± 8 µg mL-1). In addition, their cytotoxicity was evaluated towards a panel of four selected cell lines (HeLa, NCI-H460, MCF-7 and HepG2), and all the extracts showed cytotoxic effects, with J. phoenicea extracts being the most effective. The in vitro antimicrobial activity of the plant extracts was moderate, Gram-positive bacteria thus being more sensitive than the Gram-negative strains (MIC values between 5 and 20 mg mL-1). The present work suggests that J. phoenicea and C. cinerea are sources of bioactive ingredients with potential use in the food and pharmaceutical industries.

Stem radial growth and water storage responses to heat and drought vary between conifers with differing hydraulic strategies.

We investigated stem radial growth and water storage dynamics of 2 conifer species differing in hydraulic carbon strategies, Juniperus monosperma and Pinus edulis, under conditions of ambient, drought (∼45% reduction in precipitation), heat (∼4.8 °C temperature increase), and the combination of drought + heat, in 2013 and 2014. Juniper maintained low growth across all treatments. Overall, the relatively isohydric piñon pine showed significantly greater growth and water storage recharge than the relatively anisohydric juniper across all treatments in the average climate year (2014) but no differences in the regionally dry year (2013). Piñon pine ceased growth at a constant predawn water potential across all treatments and at a less negative water potential threshold than juniper. Heat has a greater negative impact on piñon pines' growth and water storage than drought, whereas juniper was, in contrast, unaffected by heat but strongly impacted by drought. The whole-plant hydraulic carbon strategies, in this case captured using the isohydric/anisohydric concept, translate into alternative growth and water storage strategies under drought and heat conditions.

Juniperus chinensis Fruits Attenuate Oxazolone- and 2,4-Dinitrochlorobenzene-Induced Atopic Dermatitis Symptoms in Mice.

Juniperus chinensis, commonly Chinese juniper, has been used for treating inflammatory diseases. This study aimed to investigate anti-atopic dermatitis (AD) effects of standardized J. chinensis fruits extract on murine oxazolone- and 2,4-dinitrochlorobenzene (DNCB)-induced models of AD. Ear swelling, epidermis thickening, and eosinophils infiltration in the oxazolone-mediated dermatitis of BALB/c mice were significantly reduced upon topical application of J. chinensis fruits 95% EtOH extract (JCE). Besides, transdermal administration of JCE to SKH-1 hairless mice inhibited the development of DNCB-induced AD-like skin lesions by suppressing transepidermal water loss and improving skin hydration. Decreased total serum immunoglobulin E (IgE) and interleukin (IL)-4 levels could be observed in atopic dorsal skin samples of JCE-treated group. According to the phytochemical analysis, JCE was found to contain isoscutellarein-7-O-ß-D-xyloside, cupressuflavone, and amentoflavone as main compounds. Therapeutic attempts with the J. chinensis fruits might be useful in the treatment of AD and related skin inflammatory diseases.

Cambial phenology in Juniperus przewalskii along different altitudinal gradients in a cold and arid region.

Knowing more precisely the cambial phenology and wood formation dynamics of trees can lead to a better understanding on how trees react to short-term changes in environmental conditions. Such an understanding could also shed light on the physiological foundation of climate-growth interactions at a regional scale. Although it has been documented that temperature is an important factor determining the cambial phenology in cold and humid climates, there is less agreement on the driver(s) that trigger the onset and end of wood formation in cold and arid climates. Here, the phenological traits of cambial activity and xylem formation were analyzed biweekly along an altitudinal transect ranging from 3580 to 3980 m above sea level, a transect that covers the distribution of Qilian juniper (Juniperus przewalskii Kom.) along a slope of the Tibetan Plateau. Cambial phenology and the duration and rate of wood formation were assessed from anatomical observations during the growing season of the developing xylem obtained from microcores collected from the stem of 10 trees total in 2012 (five at two altitudes each) and 25 trees (five at five altitudes each) in 2013. We found that the onset of wood formation was significantly correlated with altitude in 2013, with onset beginning 8.2 days earlier with every 100 m decrease in elevation. The change in onset with elevation corresponds to a change of 14.1 days °C-1 when adjusted for the monitored altitudinal lapse rate of -0.58 °C per 100 m. The duration of wood formation lasted from mid-May to mid-August, with the length of the 2013 growing season decreasing from 97 to 65 days from low to high elevation. Although the end of growing season appeared minimally related to altitude during both growing seasons, differences in end of wood production and wood formation between the two growing seasons were significant. It appears that summer drought conditions constricted the end of growing season across all elevations along our transect in 2013. Sensitivity analysis found xylem growth was positively correlated with rate and duration of wood production, with the former explaining most variability in growth. Our findings provide new data on the timing and duration of wood formation and help quantify the potential impacts of global warming on tree growth and productivity in cold and arid regions.

Critical temperature and precipitation thresholds for the onset of xylogenesis of Juniperus przewalskii in a semi-arid area of the north-eastern Tibetan Plateau.

Background and Aims: The onset of xylogenesis plays an important role in tree growth and carbon sequestration, and it is thus a key variable in modelling the responses of forest ecosystems to climate change. Temperature regulates the resumption of cambial activity, but little is known about the effect of water availability on the onset of xylogenesis in cold but semi-arid regions. Methods: The onset of xylogenesis during 2009-2014 was monitored by weekly microcoring Juniperus przewalskii trees at upper and lower treelines on the north-eastern Tibetan Plateau. A logistic regression was used to calculate the probability of xylogenic activity at a given temperature and a two-dimensional reverse Gaussian model to fit the differences between the observed and estimated days of xylogenesis onset at given temperatures and precipitation within a certain time window. Key Results: The thermal thresholds at the beginning of the growing season were highly variable, suggesting that temperature was not the only factor initiating xylem growth under cold and dry climatic conditions. The onset of xylogenesis was well predicted for climatic thresholds characterized by a cumulative precipitation of 17.0 ± 5.6 mm and an average minimum temperature of 1.5 ± 1.4 °C for a period of 12 d. Conclusions: Xylogenesis in semi-arid regions with dry winters and springs can start when both critical temperature and precipitation thresholds are reached. Such findings contribute to our knowledge of the environmental drivers of growth resumption that previously had been investigated largely in cold regions without water shortages during early growing seasons. Models of the onset of xylogenesis should include water availability to improve predictions of xylem phenology in dry areas. A mismatch between the thresholds of temperature and moisture for the onset of xylogenesis may increase forest vulnerability in semi-arid areas under forecasted warmer and drier conditions.

Multi-century tree-ring precipitation record reveals increasing frequency of extreme dry events in the upper Blue Nile River catchment.

Climate-related environmental and humanitarian crisis are important challenges in the Great Horn of Africa (GHA). In the absence of long-term past climate records in the region, tree-rings are valuable climate proxies, reflecting past climate variations and complementing climate records prior to the instrumental era. We established annually resolved multi-century tree-ring chronology from Juniperus procera trees in northern Ethiopia, the longest series yet for the GHA. The chronology correlates significantly with wet-season (r = .64, p < .01) and annual (r = .68, p < .01) regional rainfall. Reconstructed rainfall since A.D. 1811 revealed significant interannual variations between 2.2 and 3.8 year periodicity, with significant decadal and multidecadal variations during 1855-1900 and 1960-1990. The duration of negative and positive rainfall anomalies varied between 1-7 years and 1-8 years. Approximately 78.4% (95%) of reconstructed dry (extreme dry) and 85.4% (95%) of wet (extreme wet) events lasted for 1 year only and corresponded to historical records of famine and flooding, suggesting that future climate change studies should be both trend and extreme event focused. The average return periods for dry (extreme dry) and wet (extreme wet) events were 4.1 (8.8) years and 4.1 (9.5) years. Extreme-dry conditions during the 19th century were concurrent with drought episodes in equatorial eastern Africa that occurred at the end of the Little Ice Age. El Niño and La Niña events matched with 38.5% and 50% of extreme-dry and extreme-wet events. Equivalent matches for positive and negative Indian Ocean Dipole events were weaker, reaching 23.1 and 25%, respectively. Spatial correlations revealed that reconstructed rainfall represents wet-season rainfall variations over northern Ethiopia and large parts of the Sahel belt. The data presented are useful for backcasting climate and hydrological models and for developing regional strategic plans to manage scarce and contested water resources. Historical perspectives on long-term regional rainfall variability improve the interpretation of recent climate trends.

Sex determines xylem anatomy in a dioecious conifer: hydraulic consequences in a drier world.

Increased drought frequency and severity may reshape tree species distribution in arid environments. Dioecious tree species may be more sensitive to climate warming if sex-related vulnerability to drought occurs, since lower performance of one sex may drive differential stress tolerance, sex-related mortality rates and biased sex ratios. We explored the effect of sex and environment on branch hydraulic (hydraulic conductivity and vulnerability to embolism) and trunk anatomical traits in both sexes of the dioecious conifer Juniperus thurifera L. at two sites with contrasting water availability. Additionally, we tested for a trade-off between hydraulic safety (vulnerability to embolism) and efficiency (hydraulic conductivity). Vulnerability to embolism and hydraulic conductivity were unaffected by sex or site at branch level. In contrast, sex played a significant role in xylem anatomy. We found a trade-off between hydraulic safety and efficiency, with larger conductivities related to higher vulnerabilities to embolism. At the anatomical level, females' trunk showed xylem anatomical traits related to greater hydraulic efficiency (higher theoretical hydraulic conductivity) over safety (thinner tracheid walls, lower Mork's Index), whereas males' trunk anatomy followed a more conservative strategy, especially in the drier site. Reconciling the discrepancy between branch hydraulic function and trunk xylem anatomy would require a thorough and integrated understanding of the tree structure-function relationship at the whole-plant level. Nevertheless, lower construction costs and higher efficiency in females' xylem anatomy at trunk level might explain the previously observed higher growth rates in mesic habitats. However, prioritizing efficiency over safety in trunk construction might make females more sensitive to drought, endangering the species' persistence in a drier world.

Responses of a Federally Endangered Songbird to Understory Thinning in Oak-Juniper Woodlands.

Wildlife conservation and management on military lands must be accomplished in the context of military readiness, which often includes ground-based training that is perceived to conflict with wildlife needs and environmental regulations. From 2008‒2012, we examined territory density, pairing success, and fledging success of the federally endangered golden-cheeked warbler (Setophaga chrysoparia; hereafter warbler) in relation to removal of small-diameter trees from the understory of mature oak-juniper (Quercus-Juniperus) woodland at the 87,890 ha Fort Hood Military Reservation in central Texas. Understory thinning created troop maneuver lanes, but left canopy vegetation intact. Warbler density, pairing success, and fledging success were similar across thinned and control sites. We found that warbler pairing and fledging success were best predicted by Ecological site (hereafter Ecosite), an indicator of hardwood tree species composition. Warbler pairing and fledging success were about 1.5 and 1.6 times higher, respectively, for territories dominated by the Low Stony Hill Ecosite than territories dominated by the Redlands Ecosite. Our results indicate that understory thinning for military training purposes did not have a negative effect on warblers at Fort Hood in the manner tested, and suggest that removal of smaller trees from the understory in a way that replicates historic conditions may elicit neutral responses from this forest-dependent songbird. Quantifying wildlife responses to military activities provides the Department of Defense and US Fish and Wildlife Service with data to guide conservation of threatened and endangered species on Department of Defense facilities while maintaining the military mission, and supports wildlife management efforts on other public and private lands.