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Stem growth responses to soil and atmospheric drought are critical to forecasting the tree carbon sink strength. Yet, responses of drought-prone forests remain uncertain despite global aridification trends. Stem diameter variations at an hourly resolution were monitored in five Mediterranean tree species from a mesic and a xeric site for 6 and 12 years. Stem growth and dehydration responses to soil (REW) and atmospheric (VPD) drought were explored at different timescales. Annually, growth was determined by the number of growing days and hours. Seasonally, growth was bimodal (autumn growth ≈ 8%-18% of annual growth), varying among species and sites across the hydrometeorological space, while dehydration consistently responded to REW. Sub-daily, substantial growth occurred during daytime, with nighttime-to-daytime ratios ranging between 1.2 and 3.5 (Arbutus unedo ≈ Quercus faginea < Quercus ilex < Pinus halepensis in the mesic site, and Juniperus thurifera < P. halepensis in the xeric site). Overall, time windows favourable for growth were limited by soil (rather than atmospheric) drought, modulating annual and seasonal growth in Mediterranean species, and stems maintained non-negligible growth during daytime. These patterns contrast with observations from wetter or cooler biomes, demonstrating the growth plasticity of drought-prone species to more arid climate conditions., (© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Climate warming is altering snowpack permanence in alpine tundra, modifying shrub growth and distribution. Plant acclimation to snowpack changes depends on the capability to guarantee growth and carbon storage, suggesting that the content of non-structural carbohydrates (NSC) in plant organs can be a key trait to depict the plant response under different snow regimes. To test this hypothesis, we designed a 3-years long manipulative experiment aimed at evaluating the effect of snow melt timing (i.e., early, control, and late) on NSC content in needles, bark and wood of Juniperus communis L. growing at high elevation in the Alps. Starch evidenced a general decrease from late spring to summer in control and early melting, while starch was low but stable in plants subjected to a late snow melt. Leaves, bark and wood have different level of soluble NSC changing during growing season: in bark, sugars content decreased significantly in late summer, while there was no seasonal effect in needles and wood. Soluble NSC and starch were differently related with the plant growth, when considering different tissues and snow treatment. In leaf and bark we observed a starch depletion in control and early melting plants, consistently to a higher growth (i.e., twig elongation), while in late snow melt, we did not find any significant relationship between growth and NSC concentration. Our findings confirmed that snowpack duration affects the onset of the growing season promoting a change in carbon allocation in plant organs and, between bark and wood in twigs. Finally, our results suggest that plants, at this elevation, could take advantage from an early snow melt caused by climate warming, most likely due to photosynthetic activity by maintaining the level of reserves and enhancing the carbon investment for growth., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024. Published by Elsevier B.V.)

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.

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., Competing Interests: The authors have declared that no competing interests exist.

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 Q 10 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., (© 2021 John Wiley & Sons Ltd.)

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., (© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

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.

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.

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., Competing Interests: The authors have declared that no competing interests exist.

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., Competing Interests: The author declares that no competing interests exist.

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.

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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

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., (© 2018 The Authors Global Change Biology Published by John Wiley & Sons Ltd.)

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.

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., (© 2018 John Wiley & Sons Ltd.)

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.

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.

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-β-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.

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., (© 2017 John Wiley & Sons Ltd.)

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., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Tree-ring width standard chronologies were created from juniperus przewalskii Kom data collected in the Lancang River Headwaters region. Statistical analysis results showed high correlation (r = 0.69) between the composite tree-ring chronology and instrumental streamflow records at the Xiangda Hydrological Station during the annual September-August interval. Streamflow of the Zaqu River in the Lancang river source region was reconstructed for the past 419 years. The model was stable and revealed 14 extremely dry years and 6 extremely wet years. The results showed relatively low streamflow periods occurred during 602-1614, 1633-1656, 1684-1697, 1712-1722, 1735-1753, 1817-1829, 1847-1861, 1874-1884, 1946-1959, 1961-1977, and 1990-2000. Relatively high streamflow periods occurred during 1615-1630, 1657-1678, 1698-1711, 1754-1783, 1803-1813, 1830-1840, 1862-1873, 1892-1909, and 1932-1945. Comparison with tree-ring based streamflow reconstructions and chronologies from surrounding areas provided a high degree of confidence in our reconstruction. The empirical mode decomposition analysis suggests the existence of significant periods with intervals of 2-4, 5-9, 11-16, and 26-50 years. Regional comparison indicated that our reconstruction was associated with large-scale atmospheric-oceanic variability, such as the El Niño-Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO) index, Pacific Decadal Oscillation (PDO) index, and East Asian monsoon variation. This research provides a useful foundation for water resource planning and management guidance in the Three-River Headwaters Region.

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.

Plant tissue cultures are a potential source of secondary metabolites. However, their production, when compared with intact plants, is usually lower. Phenylalanine, a biogenetic precursor of podophyllotoxin, was used to stimulate podophyllotoxin production in callus and suspension cultures of Juniperus virginiana L. The best phenylalanine effect on podophyllotoxin production was manifested in three-years-old callus cultures after a 21-days application of a 10 mmol/L concentration. A podophyllotoxin content of 0.15 mg/g DW was determined, which was about 400% higher in comparison with the control. The maximum content (0.48 mg/g DW) in newly derived suspension cultures (the 4' passage) was induced by 14-days application of a I mmol/L concentration; this was about 243% higher than the control. In one-year-old suspension cultures the highest podophyllotoxin content (0.56 mg/g DW) was recorded also after 14-days application of a I mmol/L concentration; this was about 211% higher than in the control cultures.

Knowledge about the spatiotemporal tree growth variability and its associations with climate provides key insights into forest dynamics under future scenarios of climate change. We synthesized 17 tree-ring width chronologies from four tree species at the high-elevation sites in the southeast Tibetan Plateau (SETP) to study the regional tree growth variability and climate-growth relationships. Despite of diverse habitats and different physiological characteristics of these species, these tree-ring chronologies shared a significant common variance in SETP. An unprecedented increase in the shared variance is found along the latter half of the 20th century, coinciding with the enhancement of the frequency of extreme rings among chronologies. It is found that minimum winter temperature tends to be the dominant climate for trees in this region. The site-specific responses in cold (1965-1980) and warm (1990-2005) intervals by means of Fuzzy Cmeans (FCM) clustering reveal that the remarkable enhancement of growth synchrony among trees mainly occur in warm conditions. This is different from previous findings indicating that increased consistence among temperature sensitive tree rings in cold periods. This may be related to the reduced temperature sensitivity of regional tree growth as winter minimum temperature is lower than a certain threshold, which is in agreement with the "principle of ecological amplitude". In addition, it is worth noting that precipitation in June have started to restrain the tree growth since the beginning of the 1980s, which is possibly an important contributor for synchronized growth among trees in SETP.

Forecasted warmer and drier conditions will probably lead to reduced growth rates and decreased carbon fixation in long-term woody pools in drought-prone areas. We therefore need a better understanding of how climate stressors such as drought constrain wood formation and drive changes in wood anatomy. Drying trends could lead to reduced growth if they are more intense in spring, when radial growth rates of conifers in continental Mediterranean climates peak. Since tree species from the aforementioned areas have to endure dry summers and also cold winters, we chose two coexisting species: Aleppo pine (Pinus halepensisMill., Pinaceae) and Spanish juniper (Juniperus thuriferaL., Cupressaceae) (10 randomly selected trees per species), to analyze how growth (tree-ring width) and wood-anatomical traits (lumen transversal area, cell-wall thickness, presence of intra-annual density fluctuations-IADFs-in the latewood) responded to climatic variables (minimum and maximum temperatures, precipitation, soil moisture deficit) calculated for different time intervals. Tree-ring width and mean lumen area showed similar year-to-year variability, which indicates that they encoded similar climatic signals. Wet and cool late-winter to early-spring conditions increased lumen area expansion, particularly in pine. In juniper, cell-wall thickness increased when early summer conditions became drier and the frequency of latewood IADFs increased in parallel with late-summer to early-autumn wet conditions. Thus, latewood IADFs of the juniper capture increased water availability during the late growing season, which is reflected in larger tracheid lumens. Soil water availability was one of the main drivers of wood formation and radial growth for the two species. These analyses allow long-term (several decades) growth and wood-anatomical responses to climate to be inferred at intra-annual scales, which agree with the growing patterns already described by xylogenesis approaches for the same species. A plastic bimodal growth behavior, driven by dry summer conditions, is coherent with the presented wood-anatomical data. The different wood-anatomical responses to drought stress are observed as IADFs with contrasting characteristics and responses to climate. These different responses suggest distinct capacities to access soil water between the two conifer species., (© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Rainfall partitioning and redistribution by canopies are important ecohydrological processes underlying ecosystem dynamics. We quantified and contrasted spatial and temporal variations of rainfall redistribution for a juniper (Juniperus virginiana, redcedar) woodland and a tallgrass prairie in the south-central Great Plains, USA. Our results showed that redcedar trees had high canopy storage capacity (S) ranging from 2.14 mm for open stands to 3.44 mm for closed stands. The canopy funneling ratios (F) of redcedar trees varied substantially among stand type and tree size. The open stands and smaller trees usually had higher F values and were more efficient in partitioning rainfall into stemflow. Larger trees were more effective in partitioning rainfall into throughfall and no significant changes in the total interception ratios among canopy types and tree size were found. The S values were highly variable for tallgrass prairie, ranging from 0.27 mm at early growing season to 3.86 mm at senescence. As a result, the rainfall interception by tallgrass prairie was characterized by high temporal instability. On an annual basis, our results showed no significant difference in total rainfall loss to canopy interception between redcedar trees and tallgrass prairie. Increasing structural complexity associated with redcedar encroachment into tallgrass prairie changes the rainfall redistribution and partitioning pattern at both the temporal and spatial scales, but does not change the overall canopy interception ratios compared with unburned and ungrazed tallgrass prairie. Our findings support the idea of convergence in interception ratio for different canopy structures under the same precipitation regime. The temporal change in rainfall interception loss from redcedar encroachment is important to understand how juniper encroachment will interact with changing rainfall regime and potentially alter regional streamflow under climate change.

Recent droughts in southwestern USA have led to large-scale mortality of piñon (Pinus edulis) in piñon-juniper woodlands. Piñon mortality alters soil moisture, nutrient and carbon availability, which could affect the root-associated fungal (RAF) communities and therefore the fitness of the remaining plants. We collected fine root samples at a piñon-juniper woodland and a juniper savannah site in central New Mexico. Roots were collected from piñon and juniper (Juniperus monosperma) trees whose nearest neighbors were live piñon, live juniper or dead piñon. RAF communities were analyzed by 454 pyrosequencing of the universal fungal ITS region. The most common taxa were Hypocreales and Chaetothyriales. More than 10% of ITS sequences could not be assigned taxonomy at the phylum level. Two of the unclassified OTUs significantly differed between savanna and woodland, had few like sequences in GenBank and formed new fungal clades with other unclassified RAF from arid plants, highlighting how little study has been done on the RAF of arid ecosystems. Plant host or neighbor did not affect RAF community composition. However, there was a significant difference between RAF communities from woodland vs. savanna, indicating that abiotic factors such as temperature and aridity might be more important in structuring these RAF communities than biotic factors such as plant host or neighbor identity. Ectomycorrhizal fungi (EM) were present in juniper as well as piñon in the woodland site, in contrast with previous research, but did not occur in juniper savanna, suggesting a potential shared EM network with juniper. RAF richness was lower in hosts that were neighbors of the opposite host. This may indicate competitive exclusion between fungi from different hosts. Characterizing these communities and their responses to environment and plant neighborhood is a step toward understanding the effects of drought on a biome that spans 19,000,000 ha of southwestern USA., (© 2015 by The Mycological Society of America.)

Higher temperatures associated with climate change are anticipated to trigger an earlier start to the growing season, which could increase the terrestrial C sink strength. Greater variability in the amount and timing of precipitation is also expected with higher temperatures, bringing increased drought stress to many ecosystems. We experimentally assessed the effects of higher temperature and drought on the foliar phenology and shoot growth of mature trees of two semiarid conifer species. We exposed field-grown trees to a ~45% reduction in precipitation with a rain-out structure ('drought'), a ~4.8 °C temperature increase with open-top chambers ('heat'), and a combination of both simultaneously ('drought + heat'). Over the 2013 growing season, drought, heat, and drought + heat treatments reduced shoot and needle growth in piñon pine (Pinus edulis) by ≥39%, while juniper (Juniperus monosperma) had low growth and little response to these treatments. Needle emergence on primary axis branches of piñon pine was delayed in heat, drought, and drought + heat treatments by 19-57 days, while secondary axis branches were less likely to produce needles in the heat treatment, and produced no needles at all in the drought + heat treatment. Growth of shoots and needles, and the timing of needle emergence correlated inversely with xylem water tension and positively with nonstructural carbohydrate concentrations. Our findings demonstrate the potential for delayed phenological development and reduced growth with higher temperatures and drought in tree species that are vulnerable to drought and reveal potential mechanistic links to physiological stress responses. Climate change projections of an earlier and longer growing season with higher temperatures, and consequent increases in terrestrial C sink strength, may be incorrect for regions where plants will face increased drought stress with climate change., (© 2015 John Wiley & Sons Ltd.)

Optimal allocation of resources is crucial to maximize plant success. Plants modify their economic strategies by adjusting functional traits in response to shifts in environmental conditions. Facilitation has been recognized as a major biotic filter of trait distribution in communities, although the effect of facilitation on intraspecific variability has been scarcely explored. We evaluated intraspecific shifts in leaf functional traits of a perennial forb (Helleborus foetidus) in relation to the presence of a nurse plant (Juniperus sabina) in two sites with contrasting abiotic stress levels. The effects of abiotic (site) and biotic (juniper presence, microsite) environments on specific leaf area (SLA), leaf area (LA), lamina/petiole length ratio (LPR), intrinsic water use efficiency (iWUE) and leaf nutrient content (N, P and N:P) per mass were evaluated. Alleviation of drought stress associated with nurse plant presence was reflected in SLA, LA, LPR and iWUE at the high-stress site. Individuals growing in open areas showed more resource-conservative traits, supporting the argument that this strategy is advantageous in environments that limit opportunities for rapid carbon gain. Leaf nutrients were unrelated to other traits. The large amount of intraspecific variation in leaf functional traits related to facilitative processes highlights the importance of facilitation as a major source of plant trait variation. Both positive and negative biotic interactions, as well as intraspecific trait variability, should be considered in mechanistic models of plant communities' functional responses to environmental changes.

Western juniper (Juniperus occidentalis subsp. occidentalis) range expansion into sagebrush steppe ecosystems has affected both native wildlife and economic livelihoods across western North America. The potential listing of the greater sage-grouse (Centrocercus urophasianus) under the U.S. Endangered Species Act has spurred a decade of juniper removal efforts, yet limited research has evaluated program effectiveness. We used a multi-objective spatially explicit model to identify optimal juniper removal sites in Northeastern California across weighted goals for ecological (sage-grouse habitat) and economic (cattle forage production) benefits. We also extended the analysis through alternative case scenarios that tested the effects of coordination among federal agencies, budgetary constraints, and the use of fire as a juniper treatment method. We found that sage-grouse conservation and forage production goals are somewhat complementary, but the extent of complementary benefits strongly depends on spatial factors and management approaches. Certain management actions substantially increase achievable benefits, including agency coordination and the use of prescribed burns to remove juniper. Critically, our results indicate that juniper management strategies designed to increase cattle forage do not necessarily achieve measurable sage-grouse benefits, underscoring the need for program evaluation and monitoring.

Background and Aims: A series of studies have shown that temperature triggers the onset of xylogenesis of trees after winter dormancy. However, little is known about whether and how moisture availability influences xylogenesis in spring in drought-prone areas., Methods: Xylogenesis was monitored in five mature Qilian junipers (Juniperus przewalskii) by microcore sampling from 2009 to 2011 in a semi-arid area of the north-eastern Tibetan Plateau. A simple physical model of xylem cell production was developed and its sensitivity was analysed. The relationship between climate and growth was then evaluated, using weekly wood production data and climatic data from the study site., Key Results: Delayed onset of xylogenesis in 2010 corresponded to a negative standardized precipitation evapotranspiration index (SPEI) value and a continuous period without rainfall in early May. The main period of wood formation was in June and July, and drier conditions from May to July led to a smaller number of xylem cells. Dry conditions in July could cause early cessation of xylem differentiation. The final number of xylem cells was mainly determined by the average production rate rather than the duration of new cell production. Xylem growth showed a positive and significant response to precipitation, but not to temperature., Conclusions: Precipitation in late spring and summer can play a critical role in the onset of xylogenesis and xylem cell production. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure. These findings could thus demonstrate an evolutionary adaptation of Qilian juniper to the extremely dry conditions of the north-eastern Tibetan Plateau., (© The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Ongoing changes in global climate are altering ecological conditions for many species. The consequences of such changes are typically most evident at the edge of the geographical distribution of a species, where range expansions or contractions may occur. Current demographical status at geographical range limits can help us to predict population trends and their implications for the future distribution of the species. Thus, understanding the comparability of demographical patterns occurring along both altitudinal and latitudinal gradients would be highly informative. In this study, we analyse the differences in the demography of two woody species through altitudinal gradients at their southernmost distribution limit and the consistency of demographical patterns at the treeline across a latitudinal gradient covering the complete distribution range. We focus on Pinus sylvestris and Juniperus communis, assessing their demographical structure (density, age and mortality rate), growth, reproduction investment and damage from herbivory on 53 populations covering the upper, central and lower altitudes as well as the treeline at central latitude and northernmost and southernmost latitudinal distribution limits. For both species, populations at the lowermost altitude presented older age structure, higher mortality, decreased growth and lower reproduction when compared to the upper limit, indicating higher fitness at the treeline. This trend at the treeline was generally maintained through the latitudinal gradient, but with a decreased growth at the northern edge for both species and lower reproduction for P. sylvestris. However, altitudinal and latitudinal transects are not directly comparable as factors other than climate, including herbivore pressure or human management, must be taken into account if we are to understand how to infer latitudinal processes from altitudinal data., (© 2014 John Wiley & Sons Ltd.)

Climate change, along with exotic species, disturbances, and land use change, will likely have major impacts on sagebrush steppe ecosystems in the western U.S. over the next century. To effectively manage sagebrush steppe landscapes for long-term goals, managers need information about the interacting impacts of climate change, disturbances and land management on vegetation condition. Using a climate-informed state-and-transition model, we evaluated the potential impacts of climate change on rangeland condition in central Oregon and the effectiveness of multiple management strategies. Under three scenarios of climate change, we projected widespread shifts in potential vegetation types over the twenty-first century, with declining sagebrush steppe and expanding salt desert shrub likely by the end of the century. Many extreme fire years occurred under all climate change scenarios, triggering rapid vegetation shifts. Increasing wildfire under climate change resulted in expansion of exotic grasses but also decreased juniper encroachment relative to projections without climate change. Restoration treatments in warm-dry sagebrush steppe were ineffective in containing exotic grass, but juniper treatments in cool-moist sagebrush steppe substantially reduced the rate of juniper encroachment, particularly when prioritized early in the century. Overall, climate-related shifts dominated future vegetation patterns, making management for improved rangeland condition more difficult. Our approach allows researchers and managers to examine long-term trends and uncertainty in rangeland vegetation condition and test the effectiveness of alternative management actions under projected climate change.

Understanding community dynamics during early life stages of trees is critical for the prediction of future species composition. In Mediterranean forests drought is a major constraint for regeneration, but likely not the only factor determining the observed spatial patterns. We carried out a sowing experiment aimed at identifying main filters during seed-seedling transition. Specifically, we studied seed fate (predation, fungi infection, emergence) and subsequent seedling performance (mortality during the first summer and overall recruitment after 2 years) of four co-occurring Mediterranean tree species (Quercus ilex, Quercus faginea, Juniperus thurifera, Pinus nigra). We related these processes to the dominant species composition, microhabitat heterogeneity, herb cover and seed mass. The identity of the dominant species in the forest canopy was more important for recruitment than the forest canopy being dominated by conspecific vs. heterospecific species. The patterns we found suggest that biotic interactions such as facilitation (lower mortality under the canopies) and herb competition (during emergence of J. thurifera) are relevant during recruitment. Moreover, our results pointed to ontogenetic conflicts regarding the seed mass of Q. faginea and to density-dependent seed mortality for Q. ilex, rarely described in Mediterranean ecosystems. We propose that our study species experience population growth in forests dominated by heterospecifics where the recruitment success depends on habitat heterogeneity and on moderated biotic and abiotic stresses created by each species. Our results reveal patterns and mechanisms involved in recruitment constraints that add complexity to the well-known drought-related processes in Mediterranean ecosystems.

Mediterranean plants cope with cold wet winters and dry hot summers, with a drought gradient from northwest to southeast. Limiting climatic conditions have become more pronounced in the last decades due to the warming trend and rainfall decrease. Juniperus thurifera L., a long-lived conifer tree endemic to the western Mediterranean region, has a disjunct distribution in Europe and Africa, making it a suitable species to study sensitivity to climate in both sides of the Mediterranean Basin. Tree-ring width chronologies were built for three J. thurifera stands at Spain (Europe) and three in Morocco (Africa) and correlated with monthly temperature and precipitation. The temporal stability of climate-growth relationships was assessed using moving correlations; the drought effect on growth was calculated using the monthly standardized precipitation-evapotranspiration index (SPEI) at different temporal scales. In the wettest stands, increasing spring temperature and summer precipitation enhanced growth, while in the driest stands, growth was enhanced by higher spring precipitation and lower summer temperature. The climate-growth correlations shifted during the twentieth century, especially since the 1970s. Particularly noticeable is the recent negative correlation with previous autumn and winter precipitation in the wettest stands of J. thurifera, probably related with an effect of cloud cover or flooding on carbon storage depletion for next year growth. The driest stands were affected by drought at long time scales, while the wettest stands respond to drought at short time scales. This reveals a different strategy to cope with drought conditions, with populations from drier sites able to cope with short periods of water deficit.

In order to understand the impact of drought and intrinsic water-use efficiency (iWUE) on tree growth, we evaluated the relative importance of direct and indirect effects of water availability on secondary growth and xylem anatomy of Juniperus thurifera, a Mediterranean anisohydric conifer. Dendrochronological techniques, quantitative xylem anatomy, and (13)C/(12)C isotopic ratio were combined to develop standardized chronologies for iWUE, BAI (basal area increment), and anatomical variables on a 40-year-long annually resolved series for 20 trees. We tested the relationship between iWUE and secondary growth at short-term (annual) and long-term (decadal) temporal scales to evaluate whether gains in iWUE may lead to increases in secondary growth. We obtained a positive long-term correlation between iWUE and BAI, simultaneously with a negative short-term correlation between them. Furthermore, BAI and iWUE were correlated with anatomical traits related to carbon sink or storage (tracheid wall thickness and ray parenchyma amount), but no significant correlation with conductive traits (tracheid lumen) was found. Water availability during the growing season significantly modulated tree growth at the xylem level, where growth rates and wood anatomical traits were affected by June precipitation. Our results are consistent with a drought-induced limitation of tree growth response to rising CO2, despite the trend of rising iWUE being maintained. We also remark the usefulness of exploring this relationship at different temporal scales to fully understand the actual links between iWUE and secondary growth dynamics.

Western juniper (Juniperus occidentalis ssp. occidentalis Hook) encroachment into mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) steppe has reduced livestock forage production, increased erosion risk, and degraded sagebrush-associated wildlife habitat. Western juniper has been successfully controlled with partial cutting followed by prescribed burning the next fall, but the herbaceous understory and sagebrush may be slow to recover. We evaluated the effectiveness of seeding perennial herbaceous vegetation and sagebrush at five sites where juniper was controlled by partially cutting and prescribed burning. Treatments tested at each site included an unseeded control, herbaceous seed mix (aerially seeded), and the herbaceous seed mix plus sagebrush seed. In the third year post-treatment, perennial grass cover and density were twice as high in plots receiving the herbaceous seed mix compared to the control plots. Sagebrush cover and density in the sagebrush seeded plots were between 74- and 290-fold and 62- and 155-fold greater than the other treatments. By the third year after treatment, sagebrush cover was as high as 12 % in the sagebrush seeded plots and between 0 % and 0.4 % where it was not seeded. These results indicate that aerial seeding perennial herbaceous vegetation can accelerate the recovery of perennial grasses which likely stabilize the site. Our results also suggest that seeding mountain big sagebrush after prescribed burning encroaching juniper can rapidly recover sagebrush cover and density. In areas where sagebrush habitat is limited, seeding sagebrush after juniper control may increase sagebrush habitat and decrease the risks to sagebrush-associated species.

Mechanical and prescribed fire treatments are commonly used to reduce fuel loads and maintain or restore sagebrush steppe rangelands across the Great Basin where pinyon (Pinus) and juniper (Juniperus) trees are encroaching and infilling. Geospatial technologies, particularly remote sensing, could potentially be used in these ecosystems to (1) evaluate the longevity of fuel reduction treatments, (2) provide data for planning and designing future fuel-reduction treatments, and (3) assess the spatial distribution of horizontal fuel structure following fuel-reduction treatments. High-spatial resolution color-infrared imagery (0.06-m pixels) was acquired for pinyon and juniper woodland plots where fuels were reduced by either prescribed fire, tree cutting, or mastication at five sites in Oregon, California, Nevada, and Utah. Imagery was taken with a Vexcel UltraCam X digital camera in June 2009. Within each treatment plot, ground cover was measured as part of the Sagebrush Steppe Treatment Evaluation Project. Trimble eCognition Developer was used to classify land cover classes using object-based image analysis (OBIA) techniques. Differences between cover estimates using OBIA and ground-measurements were not consistently higher or lower for any land cover class and when evaluated for individual sites, were within ±5 % of each other. The overall accuracy and the K hat statistic for classified thematic maps for each treatment were: prescribed burn 85 % and 0.81; cut and fell 82 % and 0.77, and mastication 84 % and 0.80. Although cover assessments from OBIA differed somewhat from ground measurements, they are sufficiently accurate to evaluate treatment success and for supporting a broad range of management concerns.

Background and Aims: Environmental change is increasingly impacting ecosystems worldwide. However, our knowledge about the interacting effects of various drivers of global change on sexual reproduction of plants, one of their key mechanisms to cope with change, is limited. This study examines populations of poorly regenerating and threatened common juniper (Juniperus communis) to determine the influence of four drivers of global change (rising temperatures, nitrogen deposition, potentially acidifying deposition and altering precipitation patterns) on two key developmental phases during sexual reproduction, gametogenesis and fertilization (seed phase two, SP2) and embryo development (seed phase three, SP3), and on the ripening time of seeds., Methods: In 42 populations throughout the distribution range of common juniper in Europe, 11,943 seeds of two developmental phases were sampled. Seed viability was determined using seed dissection and related to accumulated temperature (expressed as growing degree-days), nitrogen and potentially acidifying deposition (nitrogen plus sulfur), and precipitation data., Key Results: Precipitation had no influence on the viability of the seeds or on the ripening time. Increasing temperatures had a negative impact on the viability of SP2 and SP3 seeds and decreased the ripening time. Potentially acidifying depositions negatively influenced SP3 seed viability, while enhanced nitrogen deposition led to lower ripening times., Conclusions: Higher temperatures and atmospheric deposition affected SP3 seeds more than SP2 seeds. However, this is possibly a delayed effect as juniper seeds develop practically independently, due to the absence of vascular communication with the parent plant from shortly after fertilization. It is proposed that the failure of natural regeneration in many European juniper populations might be attributed to climate warming as well as enhanced atmospheric deposition of nitrogen and sulfur.

Forest dynamics will depend upon the physiological performance of individual tree species under more stressful conditions caused by climate change. In order to compare the idiosyncratic responses of Mediterranean tree species (Quercus faginea, Pinus nigra, Juniperus thurifera) coexisting in forests of central Spain, we evaluated the temporal changes in secondary growth (basal area increment; BAI) and intrinsic water-use efficiency (iWUE) during the last four decades, determined how coexisting species are responding to increases in atmospheric CO2 concentrations (C(a)) and drought stress, and assessed the relationship among iWUE and growth during climatically contrasting years. All species increased their iWUE (ca. +15 to +21%) between the 1970s and the 2000s. This increase was positively related to C(a) for J. thurifera and to higher C(a) and drought for Q. faginea and P. nigra. During climatically favourable years the study species either increased or maintained their growth at rising iWUE, suggesting a higher CO2 uptake. However, during unfavourable climatic years Q. faginea and especially P. nigra showed sharp declines in growth at enhanced iWUE, likely caused by a reduced stomatal conductance to save water under stressful dry conditions. In contrast, J. thurifera showed enhanced growth also during unfavourable years at increased iWUE, denoting a beneficial effect of C(a) even under climatically harsh conditions. Our results reveal significant inter-specific differences in growth driven by alternative physiological responses to increasing drought stress. Thus, forest composition in the Mediterranean region might be altered due to contrasting capacities of coexisting tree species to withstand increasingly stressful conditions.

There is controversy regarding the limiting climatic factor for tree radial growth at the alpine treeline on the northeastern Tibetan Plateau. In this study, we collected 594 increment cores from 331 trees, grouped within four altitude belts spanning the range 3550 to 4020 m.a.s.l. on a single hillside. We have developed four equivalent ring-width chronologies and shown that there are no significant differences in their growth-climate responses during 1956 to 2011 or in their longer-term growth patterns during the period AD 1110-2011. The main climate influence on radial growth is shown to be precipitation variability. Missing ring analysis shows that tree radial growth at the uppermost treeline location is more sensitive to climate variation than that at other elevations, and poor tree radial growth is particularly linked to the occurrence of serious drought events. Hence water limitation, rather than temperature stress, plays the pivotal role in controlling the radial growth of Sabina przewalskii Kom. at the treeline in this region. This finding contradicts any generalisation that tree-ring chronologies from high-elevation treeline environments are mostly indicators of temperature changes.

Spatio-temporal variability in fruit production (masting) has been regarded as a key mechanism to increase plant fitness by reducing seed predation. However, considerably more effort has been devoted into understanding the consequences of temporal rather than spatial variations in fruit crop for plant fitness. In order to simultaneously evaluate both components, we quantify fruit production and pre-dispersal damage by three arthropod species (mites, chalcid wasps and moths) in the Spanish juniper (Juniperus thurifera) during 3 years in a spatially explicit context. Our aims were to assess (1) the interaction between fruit production and pre-dispersal fruit damage by arthropods, (2) the potential interference or competition between arthropods, and (3) the form of the phenotypic selection exerted by arthropods on fruit traits considering the spatial context. Arthropods damaged a substantial fraction of fruits produced by Spanish juniper with levels of damage showing sharp inter-annual variations. Fruit damage by mites was negatively related to yearly fruit crop and positively correlated at individual trees fruiting in consecutive years. Increased interspecific interference was an additional consequence of reduced fruit availability during small crop years. During a masting year, fruit damage by less mobile species such as mites was negatively affected by tree crop size, and no spatial structure was observed for mite damage. The incidence of chalcid wasps was low, so the spatial pattern of seed predation was unclear, and no preferences for fruit or seed traits were detected. Conversely, moths selected larger fruits and their incidence on trees was spatially aggregated up to 20 m, with predation levels being negatively affected by fruit abundance at the patch level, suggesting a positive density-dependent effect of neighbors on fruit output. These results highlight the importance of including the spatial component to understand complex species interactions at local scales.

Summary: Model-data comparisons of plant physiological processes provide an understanding of mechanisms underlying vegetation responses to climate. We simulated the physiology of a piñon pine-juniper woodland (Pinus edulis-Juniperus monosperma) that experienced mortality during a 5 yr precipitation-reduction experiment, allowing a framework with which to examine our knowledge of drought-induced tree mortality. We used six models designed for scales ranging from individual plants to a global level, all containing state-of-the-art representations of the internal hydraulic and carbohydrate dynamics of woody plants. Despite the large range of model structures, tuning, and parameterization employed, all simulations predicted hydraulic failure and carbon starvation processes co-occurring in dying trees of both species, with the time spent with severe hydraulic failure and carbon starvation, rather than absolute thresholds per se, being a better predictor of impending mortality. Model and empirical data suggest that limited carbon and water exchanges at stomatal, phloem, and below-ground interfaces were associated with mortality of both species. The model-data comparison suggests that the introduction of a mechanistic process into physiology-based models provides equal or improved predictive power over traditional process-model or empirical thresholds. Both biophysical and empirical modeling approaches are useful in understanding processes, particularly when the models fail, because they reveal mechanisms that are likely to underlie mortality. We suggest that for some ecosystems, integration of mechanistic pathogen models into current vegetation models, and evaluation against observations, could result in a breakthrough capability to simulate vegetation dynamics., (No claim to original US goverment works. New Phytologist © 2013 New Phytologist Trust.)

Widespread piñon (Pinus edulis) mortality occurred across the southwestern USA during 2002-2003 in response to drought and bark beetle infestations. Given the recent mortality and changes in regional climate over the past several decades, there is a keen interest in post-mortality regeneration dynamics in piñon-juniper woodlands. Here, we examined piñon and Utah juniper (Juniperus osteosperma) recruitment at 30 sites across southwestern Colorado, USA that spanned a gradient of adult piñon mortality levels (10-100%) to understand current regeneration dynamics. Piñon and juniper recruitment was greater at sites with more tree and shrub cover. Piñon recruitment was more strongly facilitated than juniper recruitment by trees and shrubs. New (post-mortality) piñon recruitment was negatively affected by recent mortality. However, mortality had no effect on piñon advanced regeneration (juveniles established pre-mortality) and did not shift juvenile piñon dominance. Our results highlight the importance of shrubs and juniper trees for the facilitation of piñon establishment and survival. Regardless of adult piñon mortality levels, areas with low tree and shrub cover may become increasingly juniper dominated as a result of the few suitable microsites for piñon establishment and survival. In areas with high piñon mortality and high tree and shrub cover, our results suggest that piñon is regenerating via advanced regeneration., (© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.)

Using dendroisotopic techniques, we show the recovery of Juniperus virginiana L. (eastern red cedar) trees in the Central Appalachian Mountains from decades of acidic pollution. Acid deposition over much of the 20th century reduced stomatal conductance of leaves, thereby increasing intrinsic water-use efficiency of the Juniperus trees. These data indicate that the stomata of Juniperus may be more sensitive to acid deposition than to increasing atmospheric CO2. A breakpoint in the 100-y δ(13)C tree ring chronology occurred around 1980, as the legacy of sulfur dioxide emissions declined following the enactment of the Clean Air Act in 1970, indicating a gradual increase in stomatal conductance (despite rising levels of atmospheric CO2) and a concurrent increase in photosynthesis related to decreasing acid deposition and increasing atmospheric CO2. Tree ring δ(34)S shows a synchronous change in the sources of sulfur used at the whole-tree level that indicates a reduced anthropogenic influence. The increase in growth and the δ(13)C and δ(34)S trends in the tree ring chronology of these Juniperus trees provide evidence for a distinct physiological response to changes in atmospheric SO2 emissions since ∼1980 and signify the positive impacts of landmark environmental legislation to facilitate recovery of forest ecosystems from acid deposition.

The expansion of piñon-juniper woodlands the past 100 years in the western United States has resulted in large scale efforts to kill trees and recover sagebrush steppe rangelands. It is important to evaluate vegetation recovery following woodland control to develop best management practices. In this study, we compared two fuel reduction treatments and a cut-and-leave (CUT) treatment used to control western juniper (Juniperus occidentalis spp. occidentalis Hook.) of the northwestern United States. Treatments were; CUT, cut-and-broadcast burn (BURN), and cut-pile-and-burn the pile (PILE). A randomized complete block design was used with five replicates of each treatment located in a curl leaf mahogany (Cercocarpus ledifolius Nutt. ex Torr. & A. Gray)/mountain big sagebrush (Artemisia tridentata Nutt. spp. vaseyana (Rydb.) Beetle)/Idaho fescue (Festuca idahoensis Elmer) association. In 2010, 4 years after tree control the cover of perennial grasses (PG) [Sandberg's bluegrass (Poa secunda J. Pres) and large bunchgrasses] were about 4 and 5 % less, respectively, in the BURN (7.1 ± 0.6 %) than the PILE (11.4 ± 2.3 %) and CUT (12.4 ± 1.7 %) treatments (P < 0.0015). In 2010, cover of invasive cheatgrass (Bromus tectorum L.) was greater in the BURN (6.3 ± 1.0 %) and was 50 and 100 % greater than PILE and CUT treatments, respectively. However, the increase in perennial bunchgrass density and cover, despite cheatgrass in the BURN treatment, mean it unlikely that cheatgrass will persist as a major understory component. In the CUT treatment mahogany cover increased 12.5 % and density increased in from 172 ± 25 to 404 ± 123 trees/ha. Burning, killed most or all of the adult mahogany, and mahogany recovery consisted of 100 and 67 % seedlings in the PILE and BURN treatments, respectively. After treatment, juniper presence from untreated small trees (<1 m tall; PILE and CUT treatments) and seedling emergence (all treatments) represented 25-33 % of pre-treatment tree density. To maintain recovery of herbaceous, shrub, and mahogany species additional control of reestablished juniper will be necessary.

It is generally hypothesized that tree growth at the upper treeline is normally controlled by temperature while that at the lower treeline is precipitation limited. However, uniform patterns of inter-annual ring-width variations along altitudinal gradients are also observed in some situations. How changing elevation influences tree growth in the cold and arid Qilian Mountains, on the northeastern Tibetan Plateau, is of considerable interest because of the sensitivity of the region's local climate to different atmospheric circulation patterns. Here, a network of four Qilian juniper (Sabina przewalskii Kom.) ring-width chronologies was developed from trees distributed on a typical mountain slope at elevations ranging from 3000 to 3520 m above sea level (a.s.l.). The statistical characteristics of the four tree-ring chronologies show no significant correlation with increasing elevation. All the sampled tree growth was controlled by a common climatic signal (local precipitation) across the investigated altitudinal gradient (520 m). During the common reliable period, covering the past 450 years, the four chronologies have exhibited coherent growth patterns in both the high- and low-frequency domains. These results contradict the notion of contrasting climate growth controls at higher and lower elevations, and specifically the assumption that inter-annual tree-growth variability is controlled by temperature at the upper treeline. It should be stressed that these results relate to the relatively arid conditions at the sampling sites in the Qilian Mountains.