Mountain Site Research Articles

Spatial and temporal variability of ozone along the Colorado Front Range occurring over 2 days with contrasting wind flow

Transport of pollution into pristine wilderness areas is of concern for both federal and state agencies. Assessing such transport in complex terrain is a challenge when relying solely on data from standard federal or state air quality monitoring networks because of the sparsity of network monitors beyond urban areas. During the Front Range air quality study, conducted in the summer of 2008 in the vicinity of Denver, CO, research-grade surface air quality data, vertical wind profiles and mixing heights obtained by radar wind profilers, and ozone profile data obtained by an airborne ozone differential absorption lidar augmented the local regulatory monitoring networks. Measurements from this study were taken on 2 successive days at the end of July 2008. On the first day, the prevailing winds were downslope westerly, advecting pollution to the east of the Front Range metropolitan areas. On this day, chemistry measurements at the mountain and foothills surface stations showed seasonal background ozone levels of approximately 55–68 ppbv (nmol mol–1 by volume). The next day, upslope winds prevailed, advecting pollution from the Plains into the Rocky Mountains and across the Continental Divide. Mountain stations measured ozone values greater than 90 ppbv, comparable to, or greater than, nearby urban measurements. The measurements show the progression of the ozone-enriched air into the mountains and tie the westward intrusion into high-elevation mountain sites to the growth of the afternoon boundary layer. Thus, under deep upslope flow conditions, ozone-enriched air can be advected into wilderness areas of the Rocky Mountains. Our findings highlight a process that is likely to be an important ozone transport mechanism in mountainous terrain adjacent to ozone source areas when the right circumstances come together, namely a deep layer of light winds toward a mountain barrier coincident with a deep regional boundary layer.

Spatiotemporal Heterogeneity of Ecological Policy Compromises Human Well-Being and Giant Panda Habitat Conservation in Giant Panda National Park

Identifying how policy, socioeconomic factors, and environmental factors influence changes in human well-being (HWB) and conservation efficiency is important for ecological management and sustainable development, especially in the Giant Panda National Park (GPNP). In this study, we systematically analyzed the differences in the conservation status of the giant panda habitat and changes in HWB over 15 years in the GPNP, which includes six mountain sites, Minshan (MS), Qionglai (QLS), Xiaoxiangling (XXL), Liangshan (LS), Qinling (QL), and Daxiangling (DXL). Redundancy analyses were used to determine the factors contributing (policy, socioeconomic factors, and environmental factors) to HWB and giant panda habitat conservation (HC). In addition, using a structural equation model (SEM), we investigated the relationship between the aforementioned three factors and their direct and indirect effects on HWB and HC. The results indicated that there was spatiotemporal heterogeneity of HWB and HC in our study area. There was an increasing number of plant species as well as an increased number of giant panda in GPNP. Generally, HWB in 2015 showed an increasing trend compared with that in 2000. Socioeconomic factors (23.6%) have the biggest influence on HWB and HC, followed by policy (23.2%) and environmental factors (19.4%). Conservation policy had a significantly positive influence on HWB (0.52), while it negatively influenced HC (−0.15). Socioeconomic factors significantly negatively influenced HWB (−0.38). The formulation and implementation of policies to promote economic development will contribute to the protection of giant pandas and their habitat. Our results provide insight on the conservation status of the giant panda habitat, HWB, and factors influencing them in different mountain sites in the GPNP, as well as having implications for the future management of the GPNP.

Estimation of the Productivity Potential of Mountain Sites (Mixed Beech-Coniferous Stands) in the Romanian Carpathians

Research Highlights: This study highlighted the possibility of estimating the productivity of mountain sites (mixed beech-coniferous stands) based on tree and stand dendrometric characteristics. Background and Objectives: The mountainous region of Romania offers suitable conditions for the formation and development of mixed beech-coniferous stands with complex, multi-aged structures. Based on the dendrometric characteristics of the trees, established indicators were used to estimate the productivity of the sites, with other quantitative indicators being proposed to better capture the particularities of mixed multi-aged stands. Materials and Methods: To evaluate the productive potential of the sites, a combined in situ mapping method was applied. Laboratory analyses of soils, and information provided indirectly by indicator plant and tree overstories, led to the characterization of soil types and the identification of forest sites for study. The productivity of the sites was estimated using quantitative indicators established based on the dendrometric characteristics of the trees and stands. Results: Indicators based on stand production and growth are relevant for multi-aged stands of mixed beech-coniferous formation. The ratio between tree volume and the basal area is the result of basal area and height increments, both of which are variable and depend on the quality of the site. Thus, a form height stand can be used as an indicator to characterize the productivity of the site in mixed multi-aged stands. Conclusions: Knowing the ecological specificity of sites in the formation of mixed beech-coniferous forests is a first condition necessary to achieving stable stands that are able to continuously fulfill multiple functions. The favorability of forest sites for a certain assortment of species is a fundamental character of the sites, which is essential for the management of these forest formations.

The San Andreas Fault Paleoseismic Record at Elizabeth Lake: Why are There Fewer Surface-Rupturing Earthquakes on the Mojave Section?

ABSTRACTThe structural complexity of active faults and the stress release history along the fault system may exert control on the locus and extent of individual earthquake ruptures. Fault bends, in particular, are often invoked as a possible mechanism for terminating earthquake ruptures. However, there are few records available to examine how these factors may influence the along-fault recurrence of earthquakes. We present a new paleoearthquake chronology for the southern San Andreas fault at Elizabeth Lake and integrate this record with existing paleoearthquake records to examine how the timing and frequency of earthquakes vary through a major restraining bend. This restraining bend features a mature, throughgoing right-lateral strike-slip fault, two major fault intersections, proposed subsurface fault dip changes, and a >200 km long section of fault misaligned with the regional plate motion. The Frazier Mountain, Elizabeth Lake, Pallett Creek, Wrightwood, and Pitman Canyon paleoseismic sites are located on this relatively linear surface trace of the San Andreas fault between fault bends. Our paleoseismic investigations at Elizabeth Lake document 4–5 earthquakes, since ∼1100 C.E., similar to the number of earthquakes recorded at Pallett Creek. In contrast, the Frazier Mountain and Wrightwood sites each record 8–9 earthquakes during this same time period. Differences in earthquake frequency demonstrate that fewer earthquakes rupture the central portion of the restraining bend than occur near the fault bends and intersections. Furthermore, the similarity of earthquake records from the Bidart Fan paleoseismic site northwest of the restraining bend and the Frazier Mountain paleoseismic site suggests that the broad, 30° curve of the Big Bend section of the San Andreas fault exerts less influence on fault rupture behavior than the 3D geometry of the Mojave sections of the fault.

STATE OF AGRO-DIVERSITY IN A MOUNTAIN ECOSYSTEM: CASE OF THE OLIVE TREE (OLEA EUROPEA L.) IN THE MOUNTAINS OF BENI-SNOUS: (TLEMCEN-ALGERIA)

Fruit growing in the Tlemcen region is carried out in a more or less traditional way, and this is largely the result of a lack of knowledge of areas favorable to a particular fruit species, but also of a lack of training and initiatives. Many fruit species are considered as a local product because they occupy mountainous areas with rugged relief. The latter have organoleptic qualities specific to the ecosystem in which they live. Hence the name of niche product. The most significant example is the Sigoise olive or Olive of the Tlemcen mountains. Thus the present study aims to enhance and preserve some experiences of upkeep and preservation of olive trees in mountainous ecological sites with very difficult relief. This aspect has made it possible to generate varieties of olives with by-products of highly appreciated qualitative value.

Ectomycorrhizal fungal communities associated with Larix gemelinii Rupr. in the Great Khingan Mountains, China.

Larix gemelinii is an important tree species in the Great Khingan Mountains in Northeast China with a high economic and ecological value for its role in carbon sequestration and as a source of lumber and nuts. However, the ectomycorrhizal (EM) fungal diversity and community composition of this tree remain largely undefined. We examined EM fungal communities associated with L. gemelinii from three sites in the Great Khingan Mountains using Illumina Miseq to sequence the rDNA ITS2 region and evaluated the impact of spatial, soil, and climatic variables on the EM fungal community. A total of 122 EM fungal operational taxonomic units (OTUs) were identified from 21 pooled-root samples, and the dominant EM fungal lineages were /tricholoma, /tomentella-thelephora, /suillus-rhizopogon, and /piloderma. A high proportion of unique EM fungal OTUs were present; some abundant OTUs largely restricted to specific sites. EM fungal richness and community assembly were significantly correlated with spatial distance and climatic and soil variables, with mean annual temperature being the most important predictor for fungal richness and geographic distance as the largest determinant for community turnover. Our findings indicate that L. gemelinii has a rich and distinctive EM fungal community contributing to our understanding of the montane EM fungal community structure from the perspective of a single host plant that has not been previously reported.

Conversion of forest to rangelands suppress soil fauna and flora densities during long-term in mountain ecosystems

The effect of vegetation types at mountainous sites on the relationships between soil biota and environmental variables applicable for the evaluation of soil quality and functions are barely studied and remain almost unknown. In the present study, the effect of forest degradation and vegetation types changes [i.e. natural forest with dominant species of Zelkova carpinifolia (Pall.) K. Koch. and three rangelands with dominant species of Festuca ovina L. Dactylis glomerata L. and Stachys byzantina K. Koch.] on the dynamics of soil properties and density of soil organisms in northern Iran has been considered. For each studied vegetation types, three different sites (at a distance of 4–6 km) with 1 ha area were selected. In summer (August), litter or O-horizon (i.e. L, F, and H) and soil (0–10 cm) layers were collected in an area of 30 × 30 cm. Also, in order to study the dynamics of soil properties, in addition to summer, soil samples were collected in the spring (May) and autumn (November) in each of the habitats. The study area is commonly covered with snow from late December to early April every year and therefore soil sampling was not considered in the winter season. A total of 48 litters (12 samples for each of those studied vegetation types), in the summer, and a total of 144 soil [(4 vegetation types × 3 seasons × 12 samples)] samples were collected and transferred to the laboratory. According to our findings, with higher values in the autumn season, the highest density of the soil earthworm (epigeic, anecic and endogeic), microarthropods (Acarina and collembola), nematode, and protozoa were detected in the Zelkova vegetation soils. Also, the highest density of bacterial and soil fungal communities were observed, especially in summer, under the tree cover of forest habitat. Based on our data, forest degradation and vegetation type changes suppressed the density of soil biota ranked in Zelkova > Festuca > Dactylis > Stachys due to low quality of litter, soil climate, and fertility condition. Although each vegetation type plays a prominent ecological role, forest covers are worthwhile because of their capacity to create hotspots identified by soil fauna and flora densities, which play a key role in the nutrient cycle and ecosystem services, in mountain habitats.

Influence of sensory experiences on tourists' emotions, destination memories, and loyalty

We examined the influence of tourists' sensory experiences on their destination loyalty, and the mediating effects of tourists' emotions and memories of their experience. Data were collected using a self-report survey from 304 tourists visiting Wuyi Mountain, a natural and cultural World Heritage Site in China. We found positive impacts of sensory experiences on emotions, memories, and loyalty; of emotions on memories and loyalty; and of experience memories on loyalty. Further, sensory experiences increased tourists' loyalty by positively influencing their memories, and sensory experiences positively affected tourists' memories by arousing their emotions, thereby affecting their loyalty. Our findings provide a deeper understanding of the internal mechanism of stimulating sensory experiences for enhancing tourist loyalty. Avenues for engaging tourists should address the effect of sensory experiences on emotions and destination memories.

Path Planning for a Solar-Powered UAV Inspecting Mountain Sites for Safety and Rescue

This paper focuses on the application using a solar-powered unmanned aerial vehicle (UAV) to inspect mountain sites for the purpose of safety and rescue. An inspection path planning problem is formulated, which looks for the path for an UAV to visit a set of sites where people may appear while avoiding collisions with mountains and maintaining positive residual energy. A rapidly exploring random tree (RRT)-based planning method is proposed. This method firstly finds a feasible path that satisfies the residual energy requirement and then shortens the path if there is some abundant residual energy at the end. Computer simulations are conducted to demonstrate the performance of the proposed method.

Microtektites and glassy cosmic spherules from new sites in the Transantarctic Mountains, Antarctica

AbstractWe report on the geochemical analyses of glassy spherules from sediments at three Transantarctic Mountain locations and the discovery of Australasian microtektites at two of these sites. Australasian microtektites are present at Mt. Raymond (RY) in the Grosvenor Mountains and Meteorite Moraine (MM) at Walcott Névé, in the Beardmore Glacier region of Antarctica. The microtektites were identified based on their pale yellow appearance, the high concentrations of silica (SiO2 = 60 ± 7 wt%) and alumina (Al2O3 = 23 ± 4 wt%), and a K2O/Na2O > 1, which are all characteristics of microtektites and distinct from spherules of meteoritic origin. Additionally, trace element patterns for these microtektites match the upper continental crust compositions with enrichments in refractory elements and depletions in volatile elements, most likely as a result of melting and vaporization of source material. The presence of Australasian microtektites in RY sediment confirms the recent Australasian strewn field extension to Antarctica and the presence of highly volatile depleted microtektites. In addition to microtektites, thousands of chondritic spherules and a few unique differentiated cosmic spherules were identified in RY, MM, and Jacobs Nunatak sediments. Two unique spherules were calculated to have Fe/Mn ratios similar to micrometeorites assumed to be derived from Vesta (Fe/Mn 33.2 ± 0.5 atom%) and two other unique spherules are extremely rich in refractory components (Al2O3 ~ 30% and TiO2 = ~2%). The three sites examined are evidently successful cosmic dust and impact debris collectors, and thus are useful traps for recording and examining the nature of influx events.

New Particle Formation and Growth to Climate‐Relevant Aerosols at a Background Remote Site in the Western Himalaya

AbstractNew particle formation (NPF) can influence the Earth's radiative budget when the newly formed particles grow to climate‐relevant sizes. Here, we present analysis of 21 months of continuous aerosol size distribution measurements at a background remote site in the western Himalaya and provide observational evidence that newly formed particles grow to cloud condensation nuclei (CCN)‐active sizes (i.e., >20–100 nm in diameter). Out of total 55 NPF events, 38 (66%) events occurred in the pre‐monsoon season (March–May). NPF events were classified into those with and without pollution influence as polluted and cleaner, respectively, using black carbon data. The analysis of air mass age, based on the ratio of number concentration of Aitken to accumulation mode aerosols, indicated that NPF occurred in the relatively cleaner air masses reaching to the site. The median formation rate of 10 nm particles and particle growth rates for cleaner events were three‐fold and two‐fold, respectively, higher than polluted events. We present the first estimates of the survival probability of newly formed particles to 50 and 100 nm size, which was not attempted in an Indian environment previously. The survival probability to 50 nm particles ranged from 44% to 98%, with a mean and standard deviation of 82 ± 18%. On average, ∼60% of the particles surviving to 50 nm survived to 100 nm, making the overall survival probability of 100 nm to 53 ± 31%. This indicates that the probability of nucleated particles growing to CCN‐active sizes under a large source of condensing vapor (transported from nearby lower‐altitude regions) and low pre‐existing particle concentrations (background mountain site) is high compared to the previous studies. These findings highlight the importance of the efficiency of nucleation events for producing CCN, which is a critical basis of aerosol indirect effects.

Unexpected seasonal variations and high levels of ozone observed at the summit of Nanling Mountains: Impact of Asian monsoon on southern China

Five-year continuous O3 measurements were conducted for the first time at the summit of Nanling Mountains (112.88° E, 24.68° N, 1690 m a.s.l), southern China in 2013–2017. Unlike most mountains over the world with O3 maximum in spring or summer, Nanling showed O3 maximum in mid-autumn (October; 62.8 ± 0.7 ppbv, ± 95% confidence intervals) and minimum in summer (July; 46.6 ± 0.7 ppbv). This distinct seasonal cycle of O3 at Nanling was mainly caused by the special impact of Asian monsoon in southern China, which brought clean maritime background air and fresh emissions of the Pearl River Delta (PRD) region in spring/summer, and polluted northern continental air masses in autumn/winter, respectively. Further comparisons found that O3 of Nanling in four seasons were all higher than other similar mountainous background sites, making the annual mean of O3 (55.0 ± 0.2 ppbv) at Nanling the second highest that ever reported in the mountainous sites worldwide. Moreover, the diurnal variation showed the higher impact of regional transport during nighttime from the free troposphere (FT) and presented the potential air exchange between the FT and local atmosphere in the plenary boundary layer on the summit of Nanling. Both the seasonal variation and high O3 level indicated a strong impact of anthropogenic emissions from alternatively PRD/northern China on O3 pollution in this mountainous background region. This study diversifies the seasonal variations among mountains over the world, and also illustrates the complicated impact of anthropogenic emissions on the mountainous atmosphere in southern China.

The effect of community‐wide phytochemical diversity on herbivory reverses from low to high elevation

Abstract Theory predicts that a large fraction of phytochemical diversity—the richness of individual chemical compounds produced by plants—governs the complexity of interactions between plants and their herbivores. While the effect of specific classes of chemical compounds on plant resistance against herbivores has been largely documented, the effect of community‐level variation in phytochemical diversity on plant–herbivore interactions has so far received minimal consideration. We hypothesized that plant communities bearing on average higher levels of phytochemical diversity should sustain lower herbivory rates, overall. Yet, the magnitude of this effect could vary across different environmental conditions, potentially because of climate‐mediated effects on phytochemical production and changes in herbivore community richness and composition. To address these hypotheses, we used previous knowledge of species‐level phytochemical make‐up for more than 400 plant species of the Swiss Alps. Using common garden experiments, we estimated season‐wide herbivore damage on low (average 3,500 unique molecules) and high (average 4,500 unique molecules) phytochemical diversity plant communities that were planted in the colline, mountain and alpine vegetation sites along two elevation transects in the Alps. We found that high phytochemical diversity plant communities showed reduced levels of herbivore damage in the colline (low elevation) sites, but this pattern reversed in the alpine (high elevation) sites. Our results suggest that the outcome of phytochemical diversity on plant–herbivore interactions depends on the characteristics of the local herbivore communities, together with trade‐offs between chemical defences and other plant traits (i.e. physical defences and plant palatability). Synthesis. Phytochemical diversity is a key component of functional diversity, influencing community composition and dynamics. We show that the effect of phytochemical diversity on herbivory is environmental‐dependent, generating ecological switches when moving from low to high elevation. Through upward movement of plants under climate change, phytochemical community structure will be likely modified, ultimately disrupting local community assembly processes.

Seasonal variations in the highly time-resolved aerosol composition, sources and chemical processes of background submicron particles in the North China Plain

Abstract. For the first time in the North China Plain (NCP) region, we investigated the seasonal variations in submicron particles (NR-PM1) and their chemical composition at a background mountainous site of Xinglong using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer. The average concentration of NR-PM1 was highest in autumn (15.1 µg m−3) and lowest in summer (12.4 µg m−3), with a greater abundance of nitrate in spring (34 %), winter (31 %) and autumn (34 %) and elevated organics (40 %) and sulfate (38 %) in summer. PM1 in Xinglong showed higher acidity in summer and moderate acidity in spring, autumn and winter, with average pH values of 2.7±0.6, 4.2±0.7, 3.5±0.5 and 3.7±0.6, respectively, which is higher than those estimated in the United States and Europe. The size distribution of all PM1 species showed a consistent accumulation mode peaking at approximately 600–800 nm (dva), indicating a highly aged and internally mixed nature of the background aerosols, which was further supported by the source appointment results using positive matrix factorization and multilinear engine analysis. Significant contributions of aged secondary organic aerosol (SOA) in organic aerosol (OA) were resolved in all seasons (>77 %), especially in summer. The oxidation state and the process of evolution of OAs in the four seasons were further investigated, and an enhanced carbon oxidation state (−0.45–0.10) and O/C (0.54–0.75) and OM/OC (1.86–2.13) ratios – compared with urban studies – were observed, with the highest oxidation state appearing in summer, likely because of the relatively stronger photochemical processing that dominated the formation processes of both less oxidized OA (LO-OOA) and more oxidized OA (MO-OOA). Aqueous-phase processing also contributed to the SOA formation and prevailed in winter, with the share to MO-OOA being more important than that to LO-OOA. In addition, regional transport also played an important role in the variations in SOA. Especially in summer, continuous increases in SOA concentration as a function of odd oxygen (Ox=O3+NO2) were found to be associated with the increases in wind speed. Furthermore, backward trajectory analysis showed that higher concentrations of submicron particles were associated with air masses transported short distances from the southern regions in all four seasons, while long-range transport from Inner Mongolia (western and northern regions) also contributed to summertime particulate pollution in the background areas of the NCP. Our results illustrate that the background particles in the NCP are influenced significantly by aging processes and regional transport, and the increased contribution of aerosol nitrate highlights how regional reductions in nitrogen oxide emissions are critical for remedying occurrence of nitrate-dominated haze events over the NCP.

Seasonal Abundance and Source Attribution of Carbonaceous Aerosols at Different Altitude of Mountainous Locations in Uttarakhand Himalaya

The present study reports on carbonaceous aerosol concentrations determined in total suspended particles (TSP) from three mountainous sites Devasthal (2450 m asl), Manora Peak (1940 m asl), and Bhimtal (1413 m asl) in Kumaun province of Uttarakhand Himalaya, India. The concentrations of organic carbon (OC) and elemental carbon (EC) were measured using IMPROVE_thermal optical reflectance protocol. Results showed that TSP and carbonaceous species varied significantly and decreased with increasing altitudes. Seasonal/(diurnal) analysis indicated that TSP and carbonaceous species were significantly higher during summer than winter, while day-night-time variation was not statistically significant. Correlation analysis was performed between carbonaceous species and meteorological factors which showed significant positive correlations with planetary boundary layer, temperature, and solar radiation. OC and EC were noted to be strongly correlated (correlation coefficient > 0.8), implying similar emission sources and atmospheric processes. The ratios of OC/EC varied from 2.4 to 9.3 (Devasthal), 2.1 to 8.6 (Manora Peak) and 1.9 to 4.3 (Bhimtal), which suggested mixed sources of biomass burning, coal combustion and vehicular emissions. The large variations in OC/EC ratios suggested the presence of secondary organic carbon (SOC) and it contributed higher during winter (~ 40–45%) to total OC than summer (~ 26–35%) at all sites could be attributed to higher condensation of secondary species, low temperature and large emissions of VOC precursors during winter.

Seasonal patterns of atmospheric mercury in tropical South America as inferred by a continuous total gaseous mercury record at Chacaltaya station (5240 m) in Bolivia

Abstract. High-quality atmospheric mercury (Hg) data are rare for South America, especially for its tropical region. As a consequence, mercury dynamics are still highly uncertain in this region. This is a significant deficiency, as South America appears to play a major role in the global budget of this toxic pollutant. To address this issue, we performed nearly 2 years (July 2014–February 2016) of continuous high-resolution total gaseous mercury (TGM) measurements at the Chacaltaya (CHC) mountain site in the Bolivian Andes, which is subject to a diverse mix of air masses coming predominantly from the Altiplano and the Amazon rainforest. For the first 11 months of measurements, we obtained a mean TGM concentration of 0.89±0.01 ng m−3, which is in good agreement with the sparse amount of data available from the continent. For the remaining 9 months, we obtained a significantly higher TGM concentration of 1.34±0.01 ng m−3, a difference which we tentatively attribute to the strong El Niño event of 2015–2016. Based on HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) back trajectories and clustering techniques, we show that lower mean TGM concentrations were linked to either westerly Altiplanic air masses or those originating from the lowlands to the southeast of CHC. Elevated TGM concentrations were related to northerly air masses of Amazonian or southerly air masses of Altiplanic origin, with the former possibly linked to artisanal and small-scale gold mining (ASGM), whereas the latter might be explained by volcanic activity. We observed a marked seasonal pattern, with low TGM concentrations in the dry season (austral winter), rising concentrations during the biomass burning (BB) season, and the highest concentrations at the beginning of the wet season (austral summer). With the help of simultaneously sampled equivalent black carbon (eBC) and carbon monoxide (CO) data, we use the clearly BB-influenced signal during the BB season (August to October) to derive a mean TGM / CO emission ratio of (2.3±0.6)×10-7 ppbvTGM ppbvCO-1, which could be used to constrain South American BB emissions. Through the link with CO2 measured in situ and remotely sensed solar-induced fluorescence (SIF) as proxies for vegetation activity, we detect signs of a vegetation sink effect in Amazonian air masses and derive a “best guess” TGM / CO2 uptake ratio of 0.058 ±0.017 (ng m−3)TGM ppmCO2-1. Finally, significantly higher Hg concentrations in western Altiplanic air masses during the wet season compared with the dry season point towards the modulation of atmospheric Hg by the eastern Pacific Ocean.

Early Performance of Tree Species in a Mountain Reforestation Experiment

Climate change requires forest managers to explore new concepts in reforestation. High-elevation sites are posing challenges because the range of tree species that can cope with present and future conditions is small and limited experience with candidate species is available. Methods: We selected a mountain site with nutrient-poor silicatic soils. The previous Norway spruce (Picea abies) stand performed poorly. We established a reforestation experiment with 27 tree species that were planted in different combinations in order to evaluate silvicultural options. Site preparation activities and planting techniques reflected the locally applied regular procedures. After planting, we monitored height growth and phenological characteristics of needle/leaf development in spring. The presently dominant Norway spruce was genetically characterized. Results: Tree seedlings planted at high elevation are highly vulnerable. The temporal course of needle/leaf sprouting varies widely. Early developers are vulnerable to frost, impairing tree development. Biotic stressors such as high population densities of weevils or mice can cause high mortality. Conclusion: we suggest a conservative approach to tree species selection because present site conditions in mountain areas may impair the development of many tree species that could be viable options in a considerably warmer climate.

Drought variation recorded by growth rings of the shrub Sabina vulgaris in the middle Qilian Mountains, northwest China

The evergreen coniferous creeping shrub, Sabina vulgaris, is widely distributed in China, from high and cold mountain sites to low-elevation arid desert areas. This paper performed dendroclimatological analysis of the samples of S. vulgaris from three sampling sites (2700–2900 m a.s.l.) at sites in the northern border of the middle Qilian Mountains, Northwest China. We found that the radial growth of S. vulgaris was mainly limited by rainfall during the growing season, especially in May and June, but was also limited by low temperatures in the late growing season. It presents the regional differention of the climate response of the shrub radial growth from the other distributed areas, such as the sandland and mountains. We constructed a 274-year drought record by calibrating growth-ring data and relating this data to the regional monthly Palmer Drought Severity Index (PDSI56), which represents regional moisture conditions. The PDSI56 reconstruction accounted for 35.5 % of the variation of the actual May to June PDSI56 during the period for which meteorological data was available (1950–2014). The most severe drought occurred during the 1920s, followed by the 1950s, 1740s, and the period from the 1870s to the 1880s; the wettest years were during the 1980s, followed by the 2010s, 1770s, and 1750. The changes between drought, normal, and wet periods were consistent with the reconstructed results from previous conifer ring series for Sabina przewalskii and Picea crassifolia in the study area. Our results demonstrate the value of S. vulgaris in dendrochronology.

Optical and hygroscopic properties of black carbon influenced by particle microphysics at the top of the anthropogenically polluted boundary layer

Abstract. Aerosols at the top of the planetary boundary layer (PBL) could modify its atmospheric dynamics by redistributing the solar radiation and start to be activated to form low-level cloud at this layer. Black carbon (BC), as an aerosol component efficiently absorbing solar radiation, can introduce heating and positive radiative effects at this sensitive layer, especially in the polluted PBL over the continent. This study presents continuous measurements of detailed BC properties at a mountain site located at the top of the polluted PBL over the North China Plain, during seasons (3 and 4 weeks of data during winter and summer, respectively) with contrasting emission structure and meteorology. The pollution level was persistently influenced by local surface anthropogenic emission on a daily basis through daytime convective mixing, but the concentration was also enhanced or diluted depending on air mass direction, defined as a neutral, polluted and diluted PBL, respectively. Winter was observed to have a higher BC mass fraction (4 %–8 %) than summer (2 %–7 %). By resolving the detailed particle size-resolved mixing state of BC in optical and hygroscopic models, we found an enhanced BC mass absorption cross section (MACBC) for the polluted PBL (up to 13 m2 g−1 at λ = 550 nm), which was 5 % higher during summer than winter due to a smaller BC core size. The higher BC mass fraction in winter corresponded to a lower single-scattering albedo by 0.03–0.09 than summer, especially the lowest for the diluted winter PBL (0.86 ± 0.02). The water supersaturation (SS) required to activate half the number of BC decreased from 0.21 % ± 0.08 % to 0.1 % ± 0.03 % for the winter diluted and polluted PBL and from 0.22 % ± 0.06 % to 0.17 % ± 0.05 % for summer. Notably, at the top of the anthropogenically polluted PBL in both seasons, the enlarged BC with enhanced absorption capacity could also be efficiently droplet activated; e.g. winter (summer) BC with an MAC of 9.84 ± 1.2 (10.7 ± 1) m2 g−1 could be half activated at SS = 0.13 % ± 0.06 % (0.18 % ± 0.05 %). This BC at the top of the PBL can more directly interact with the free troposphere and be transported to a wider region, exerting important direct and indirect radiative impacts.

Sensitivity of Snowfall Characteristics to Meteorological Conditions in the Yeongdong Region of Korea

This study investigates the characteristics of cold clouds and snowfall in both the Yeongdong coastal and mountainous regions under different meteorological conditions based on the integration of numerical modeling and three-hourly rawinsonde observations with snow crystal photographs for a snowfall event that occurred on 29−30 January 2016. We found that rimed particles predominantly observed turned into dendrite particles in the latter period of the episode when the 850 hPa temperature decreased at the coastal site, whereas the snow crystal habits at the mountainous site were largely needle or rimed needle. Rawinsonde soundings showed a well-defined, two-layered cloud structure along with distinctive wind-directional shear, and an inversion in the equivalent potential temperature above the low-level cloud layer. The first experiment with a decrease in lower-layer temperature showed that the low-level cloud thickness was reduced to less than 1.5 km, and the accumulated precipitation was decreased by 87% compared with the control experiment. The difference in precipitation amount between the single-layered experiment and control experiment (two-layered) was not so significant to attribute it to the effect of the seeder−feeder mechanism. The precipitation in the last experiment by weakening wind-directional shear was increased by 1.4 times greater than the control experiment specifically at the coastal site, with graupel particles accounting for the highest proportion (~62%). The current results would improve snowfall forecasts in complicated geographical environments such as Yeongdong in terms of snow crystal habit as well as snowfall amount in both time and space domains.