East-facing Slopes Research Articles

New insights into debris-flow hazards from an extraordinary event in the Colorado Front Range

Rainfall on 9–13 September 2013 triggered at least 1,138 debris flows in a 3430 km area of the Colorado Front Range. The historical record reveals that the occurrence of these flows over such a large area in the interior of North America is highly unusual. Rainfall that triggered the debris flows began after ~75 mm of antecedent rain had fallen, a relatively low amount compared to other parts of the United States. Most flows were triggered in response to two intense rainfall periods, one 12.5-hour-long period on 11–12 September, and one 8-hour-long period on 12 September. The maximum 10 min. intensities during these periods were 67 and 39 mm/hr. Ninety-five percent of flows initiated in canyons and on hogbacks at elevations lower than a widespread erosion surface of low slope and relief ( 25°), predominantly southand east-facing slopes with upslope contributing areas 3300 m. Areal concentrations of debris flows revealed that colluvial soils formed on sedimentary rocks were more susceptible to flows than soils on crystalline rocks. This event should serve as an alert to government authorities, emergency responders, and residents in the Front Range and other interior continental areas with steep slopes. Widespread debris flows in these areas occur infrequently but may pose a greater risk than in areas with shorter return periods, because the public is typically unprepared for them.

설악산 양사면 하천에서의 고도차에 따른 저서성 대형무척추동물 군집의 공간 분포

There are marked differences in climate condition between east-facing slopes and west-facing slopes in Mt. Seorak (1,708 m). This study was conducted to find out the differences of benthic macroinvertebrate communities between both slopes of Mt. Seorak. Quantitative (Surber net; <TEX>$30cm{\times}30cm$</TEX>, mesh: 1mm) and qualitative (Hand net; mesh: 1mm) samplings ware carried out seasonally in each site which had 100-meter-high difference from November 2010 to November 2011. Most of the survey sites showed sound environmental conditions because they were located in the protection area of the national park. The benthic macroinvertebrates collected from all survey sites were composed of 158 species, 62 families, 17 orders, 7 classes and 5 phyla. DCA (Detrended Correspondence Analysis) ordination based on the abundance of benthic mactoinvertebrates showed that altitude was a major factor governing the structure of benthic macroinvertebrate community. There was no significant difference of the communities between both slopes.

Passive restoration augments active restoration in deforested landscapes: The role of root suckering adjacent to planted stands of Acacia koa

Active forest restoration in Hawaii’s Hakalau Forest National Wildlife Refuge has produced a network of Acacia koa tree corridors and islands in deforested grasslands. Passive restoration by root suckering has potential to expand tree cover and close gaps between planted stands. This study documents rates of encroachment into grassland, clonal stand structure, and tree architecture. Data were collected from random replicate strip transects that started inside 23-year-old koa plantations and ended either in open grassland or in adjacent planted stands. For the former, sucker densities increased from near zero inside planted stands to a maximum of 5–38 stemsm−2 5–14m away from the edge of the plantation canopy, and then decreased to zero–a typical pattern for trees invading grassland. No suckers occurred more than 28m from the canopy edge on east-facing slopes, or more than 18m on south-facing slopes. Rates of expansion into grassland ranged from 0.8 to 1.5myr−1; suckers had already filled gaps between closely spaced plantation stands located on north-facing slopes. Continued suckering should result in the eventual re-establishment of tree cover on deforested areas between planted tree islands and corridors, and without additional active restoration.

تعیین معیارهای ارزیابی اراضی بهمنظور شناسایی اراضی مناسب کشت محصولات دیم منطقه روئین، خراسان شمالی

Classification and utilization of lands based on their capability are necessary for sustainable land use management. The purpose of this study was to identify and grade the effective qualities on the rainfed farming in the Roin area, North Khorasan province, during the year of 2011. Based on field observations and literature review the land qualities including climate, rooting conditions, moisture availability, field workability and land degradation hazard were distinguished and rated as the most effective factors on the rainfed land suitability. To evaluate the land degradation hazard, the variations of soil organic carbon content in north-, south-, west- and east-facing slopes as a result of land use change was measured. In seven sites, 84 soil samples were taken from 0-15 cm soil depth of Back Slope with aspect of north- south- west- and east-facing slopes of rangeland, wheat dry farming and alfalfa dry farming. In addition, 21 soil samples were taken from nearly flat areas (Toe slopes and back slopes) of studied land uses. The results indicated that all aspects except the south-face slopes the amount of soil organic carbon suitable for semiarid regions. In the study area, the climate and qualities related to soil, have no limitations for dry farming. Only field workability and land degradation hazard qualities which are affected by slope and slope aspect are main limitation factors. Based on results the slopes more than 20% and the southern slopes were identified non-suitable for dry farming but the southern slopes were partly suitable for alfalfa dry farming. Considering the mentioned limitations, the areas under dry farming cultivation will be decreased from 1186 to 942 ha. More investigation for new land utilization types is necessary to compensate the negative economic consequences of cultivation land reduction.

QUANTATAIVE ANALYSIS OF RELATIONSHIP BETWEEN ALOS PALSAR BACKSCATTER AND FOREST STAND VOLUME

To estimate forest stand volume, topographic effects should be considered in Synthetic Aperture Radar (SAR) data processing, because most forests are located on mountainous areas in Korea. This paper shows how the effects on the ALOS Phased-Array L-Band SAR (PALSAR) backscatter in Kwangneung Experiment Forest can be reduced by gamma-nought γ^0.Regardless of coniferous and deciduous forests, the gamma-nought γ^0 values are always lower compared to the sigma-nought σ^0 values at HH and HV polarization for 58 standwise tree volume of the fore-slope (here, the west-facing slope) and are always higher in case of far-slope (here, east-facing slope).Comparison of the fore-slope with the far-slope, relating to the stand volume of the γ^0 and σ^0 values, demonstrates that the σ^0 values are significantly remarkable, while the γ^0 values are not. This means that the topographic normalized backscattering coefficient γ^0 can be used to estimate tree volume, independent of fore-slope and far-slope.Though the aforementioned two backscattering coefficients of γ^0 and σ^0 indicate L-band HH and HV saturations with tree volume observed at around 310 m^3ha^(-1), they increase with increasing trend with forest stand volume.These results show that stand volume retrieval of mountain forests can be improved by using topographic normalized backscattering coefficient of ALOS PALSAR data.

Habitat correlates of the red panda in the temperate forests of Bhutan.

Anthropogenic activities and associated global climate change are threatening the biodiversity in the Himalayas against a backdrop of poor knowledge of the region's threatened species. The red panda (Ailurus fulgens) is a threatened mammal confined to the eastern Himalayas, and because of Bhutan's central location in the distributional range of red pandas, its forests are integral to the long-term viability of wild populations. Detailed habitat requirements of the red panda are largely speculative, and there is virtually no ecological information available on this species in Bhutan. Between 2007 and 2009, we established 615 presence/absence plots in a systematic sampling of resident habitat types within Jigme Dorji and Thrumshingla National Parks, Bhutan, to investigate broad and fine-scale red panda habitat associations. Additional locality records of red pandas were obtained from interviewing 664 park residents. Red pandas were generally confined to cool broadleaf and conifer forests from 2,110–4,389 m above sea level (asl), with the majority of records between 2,400–3,700 m asl on south and east-facing slopes. At a finer scale, multivariate analysis revealed that red pandas were strongly associated with old growth Bhutan Fir (Abies densa) forest dominated by a dense cover of Yushania and Arundanaria bamboo with a high density of fallen logs and tree stumps at ground level; a high density of trees, dead snags, and rhododendron shrubs in the mid-storey; and locations that were close to water. Because Bhutan's temperate forests that encompass prime red panda habitat are also integral to human subsistence and socio-economic development, there exists an inadvertent conflict between the needs of people and red pandas. As such, careful sustainable management of Bhutan's temperate forests is necessary if a balance is to be met between the socioeconomic needs of people and the conservation goals for red pandas.

Little change in the fir tree‐line position on the southeastern Tibetan Plateau after 200 years of warming

• As one of the world's highest natural tree lines, the Smith fir (Abies georgei var. smithii) tree line on the southeastern Tibetan Plateau is expected to vary as a function of climate warming. However, the spatial patterns and dynamics of the Smith fir tree line are not yet well understood. • Three rectangular plots (30 m × 150 m) were established in the natural alpine tree-line ecotone on two north-facing (Plot N1, 4390 m asl; Plot N2, 4380 m asl) and one east-facing (Plot E1, 4360 m asl) slope. Dendroecological methods were used to monitor the tree-line patterns and dynamics over a 50-yr interval. • The three study plots showed a similar pattern of regeneration dynamics, characterized by increased recruitment after the 1950s and an abrupt increase in the 1970s. Smith fir recruitment was significantly positively correlated with both summer and winter temperatures. However, Smith fir tree lines do not show a significant upward movement, despite warming on the Tibetan Plateau. • The warming in the past 200 yr is already having a significant impact on the population density of the trees, but not on the position of the Smith fir tree line.

Mapping herbage biomass and nitrogen status in an Italian ryegrass (&lt;italic&gt;Lolium multiflorum&lt;/italic&gt; L.) field using a digital video camera with balloon system

Improving current precision nutrient management requires practical tools to aid the collection of site specific data. Recent technological developments in commercial digital video cameras and the miniaturization of systems on board low-altitude platforms offer cost effective, real time applications for efficient nutrient management. We tested the potential use of commercial digital video camera imagery acquired by a balloon system for mapping herbage biomass (BM), nitrogen (N) concentration, and herbage mass of N (Nmass) in an Italian ryegrass (Lolium multiflorum L.) meadow. The field measurements were made at the Setouchi Field Science Center, Hiroshima University, Japan on June 5 and 6, 2009. The field consists of two 1.0 ha Italian ryegrass meadows, which are located in an east-facing slope area (230 to 240 m above sea level). Plant samples were obtained at 20 sites in the field. A captive balloon was used for obtaining digital video data from a height of approximately 50 m (approximately 15 cm spatial resolution). We tested several statistical methods, including simple and multivariate regressions, using forage parameters (BM, N, and Nmass) and three visible color bands or color indices based on ratio vegetation index and normalized difference vegetation index. Of the various investigations, a multiple linear regression (MLR) model showed the best cross validated coefficients of determination (R2) and minimum root-mean-squared error (RMSECV) values between observed and predicted herbage BM (R2 = 0.56, RMSECV = 51.54), Nmass (R2 = 0.65, RMSECV = 0.93), and N concentration (R2 = 0.33, RMSECV = 0.24). Applying these MLR models on mosaic images, the spatial distributions of the herbage BM and N status within the Italian ryegrass field were successfully displayed at a high resolution. Such fine-scale maps showed higher values of BM and N status at the bottom area of the slope, with lower values at the top of the slope.

Modeling all-sky global solar radiation using MODIS atmospheric products: A case study in Qinghai-Tibet Plateau

The surface solar radiation (SSR) is of great importance to bio-chemical cycle and life activities. However, it is impossible to observe SSR directly over large areas especially for rugged surfaces such as the Qinghai-Tibet Plateau. This paper presented an improved parameterized model for predicting all-sky global solar radiation on rugged surfaces using Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric products and Digital Elevation Model (DEM). The global solar radiation was validated using 11 observations within the plateau. The correlation coefficients of daily data vary between 0.67-0.86, while those of the averages of 10-day data are between 0.79-0.97. The model indicates that the attenuation of SSR is mainly caused by cloud under cloudy sky, and terrain is an important factor influencing SSR over rugged surfaces under clear sky. A positive relationship can also be inferred between the SSR and slope. Compared with horizontal surfaces, the south-facing slope receives more radiation, followed by the west- and east-facing slopes with less SSR, and the SSR of the north-facing slope is the least.

Spatial Distributions of Mule Deer and North American Elk: Resource Partitioning in a Sage-Steppe Environment

We examined spatial distributions and resource partitioning among female mule deer (Odocoileus hemionus) and female North American elk (Cervus elaphus) during summer and winter in southeastern Idaho, USA. Our objective was to understand differences in distributions and habitat selection by these two species of large herbivores in a sagebrush-steppe ecosystem. We used multi-response permutation procedures to examine seasonal distributions of mule deer and elk. We compared animal locations with random locations on a GIS-based habitat map to examine habitat selection and importance. Both species were more widely distributed during summer than winter, when distributions of both species were more restricted. During winter, habitat selection differed among mule deer and elk in use of aspect; east facing slopes were selected by elk and west-facing slopes by mule deer. Mule deer also were located closer to roads than random locations, which may have resulted from avoidance of elk. We observed no differences in habitat selection between mule deer and elk during summer, although these large herbivores showed resource separation by strongly partitioning use of habitats. Conversely, both species used the shrub-steppe ecosystem during winter, but partitioned habitat mostly via use of aspect and distance to roads. Our research provides insights into niche partitioning between these large mammals.

Assessing the Change in Cover of Non-Indigenous Dwarf-Pine Using Aerial Photographs, a Case Study from the Hrubý Jeseník Mts., the Sudetes

Assessing the Change in Cover of Non-Indigenous Dwarf-Pine Using Aerial Photographs, a Case Study from the Hrubý Jeseník Mts., the SudetesIn addition to ongoing climate change, alpine ecosystems are also threatened by the expansion of non-indigenous species. Expansion of dwarf pine (Pinus mugoTurra) in the Hrubý Jeseník Mts. is an excellent example of the interactions between a planted alpine shrub and alpine ecosystems dominated by grassland species. Based on a comparison of aerial photographs taken in two different periods (1971/73 and 2003) we analyzed spatial changes in the dwarf pine cover. We focused on an evaluation of the current proportion of dwarf pine stands above the upper forest limit, as well as on the effects of stand texture and environmental variables on dwarf pine expansion over this 30 year period. During this time, dwarf pine stands increased their extent by 63%. Small forest-free areas above the upper forest limit in the northern part of the Hrubý Jeseník ridge are currently covered by dwarf pine on more than 30% of their surface. Expansion of dwarf pine was fastest in open, fine-grained stands, often situated in lower altitudes and on north- to east-facing slopes. The dwarf pine expansion was more intense than predicted by simple model of vegetative growth, especially within open stands with short polycormon margins in low altitudes. This might be explained by more intensive growth in less extreme environment and/or by higher generative reproduction on these sites. Finally, we suggest that expanding dwarf pine shrubs and recessing grassland patches negatively affects the abundance of heliophilous alpine plants and insects. We believe that the results of this study could be relevant to ongoing discussions on the management of summit forest-free areas in the Hrubý Jeseník Mts.

Avalanches keep habitats open and species-rich in the montane and subalpine belt

From a conservation point of view, avalanches are a natural ecological process. However, they can also endanger people and cause serious damage to buildings and infrastructure. From an anthropocentric point of view, protective measures in the form of avalanche barriers are necessary. Avalanche barriers in the starting zone of avalanches can prevent avalanche events. Hence there is a conflict between nature conservation and protection against natural hazards. This study aimed primarily at assessing the conservation value of active avalanche tracks. To this end we examined 16 plant stands on three different avalanche tracks in the Gesäuse National Park (Styria, Austria) and recorded butterfly species at the same time. On the investigated avalanche tracks, the soils are very shallow, stony, periodically dry, nutrient-poor, base-rich rendzinas developed over limestone debris. The sites are scree-covered, steep and mainly east-facing slopes located in the montane belt. The plant stands investigated belong mainly to the Origano-Calamagrostietum variae community. This study of biodiversity concludes that under these conditions the vegetation in active avalanche tracks is characterized by a high richness of vascular plant species. On average, a plot size of 20 m² contains 71 vascular plant species and 5 bryophyte species. The species-rich plant stands, colourful when in bloom, are dominated by herbs, resulting in a high aesthetic value and an increased diversity of butterflies. The avalanche tracks investigated have a high conservation value because natural ecological processes continue to happen, leading to near-natural and species-rich disclimax communities.

Glaciation in the surroundings of Prášilské Lake (Bohemian Forest, Czech Republic)

Comprehensive geomorphological and sedimentological analyses confirmed three phases of Würm glaciation in the surroundings of Prášilské Lake and Stará Jímka, in the Bohemian Forest (Šumava Mountains). Glaciations were affected by a steep east-facing slope, by plateaus on the adjacent ridges and by local geological conditions. A small valley glacier (about 2km long and 50m thick) occurred during the first phase. In the second phase, a glacier–rock glacier developed, probably based on remnants of the valley glacier. During the last phase glacial activity was divided into Stará Jímka and the stepped cirque of Prášilské Lake. A further shallow (∼3m deep) lake in Stará Jímka was dammed by slope movements after deglaciation (∼14cal.kaBP) and survived until ∼4cal.kaBP. The Late Pleistocene chronology of the Bohemian Forest seems to be related more closely to the Alps than to northern Europe. In the mid-mountains of central Europe, Pleistocene glaciation decreases significantly eastward, because of increasing continentality. The presence of plateaus (deflation areas), around 1300m altitude, across the approach of westerly winds was important for the development of glaciers in the Bohemian Forest. The termination of glaciation before the Younger Dryas is specific to the Bohemian Forest in comparison with the Vosges and Krkonoše Mountains.

Influence of slope orientation on sex ratio and size distribution in a dioecious plant Bursera fagaroides var. purpusii (Brandeg.) McVaugh and Rzed. (Burseraceae)

It has been hypothesized that environmental variability can influence the sex ratio of a plant population, and it has been observed that in stressful environments, male plants are more abundant than females. However, it is unknown whether this is due to differential mortality rates between males and females. In this study, we analyzed sex ratio, mortality, and size distribution in a population of the neotropical tree/bush Bursera fagaroides in two different environments (east- and west-oriented slopes) over a 10-year period. We determined that the sex ratio favored males in the more stressful environment (east-facing slope) and that females were significantly larger in the less stressful environment (west-facing slope). Despite a significant difference in size between sexes by slope aspect, the difference in sex ratio cannot be explained by slope or by mortality during the 10 years of observation.

Darkling beetle communities in two geologically contrasting biotopes: testing biodiversity patterns by microsite comparisons

Studies at a microsite scale, where most of the environmental variation can be reduced to a few factors, may help to identify the actual contribution of a particular environmental factor to community organization. Climate is known to be an important factor for regulating animal diversity. However, for soil-dwelling animals, the role of soil characteristics can hardly be extracted out because of the inter-relationships between climate and soil. The community structure of soil-dwelling darkling beetles inhabiting the two geologically highly contrasting west- and east-facing slopes (WFS and EFS, respectively) of the Mediterranean island of Santorini (Greece) was investigated in a case study aiming to assess the separate influence of soil characteristics and climate. Eroded pumice soils of EFS allowed a higher abundance of darkling beetle individuals and biomass, hosting more productive vegetation and being more penetrable to fossorial larvae. Moreover, the two slopes differed significantly with respect to the abundance of certain species that are characterized by a peculiar morphological adaptation to different soil characteristics. Thus, local geological sharp divergence led to darkling beetle interslope community differences as a result of local selection towards certain species. However, the two communities are similar in terms of darkling beetle diversity, evenness, and species niche-breadth. This demonstrates that sites sharing the same climatic conditions tend to have similarly structured darkling beetle communities, even if there are marked differences in soil characteristics that promote differences in species composition, thus suggesting that climate is the major factor for regulating species diversity.

Habitat Selection by Cerulean Warblers in Eastern Kentucky

Abstract We examined habitat characteristics associated with Cerulean Warblers (Dendroica cerulea) in breeding areas on the Cumberland Plateau in eastern Kentucky. Cerulean Warbler distribution was examined in 2004 within a large forest stand and no differences were found between occupied and unoccupied areas. We examined differences between preferred song perches and random points in 2005, and identified three potentially important predictors of Cerulean Warbler habitat: large diameter trees, east-facing aspect, and high shrub cover. Cerulean Warbler habitat selection on the Cumberland Plateau appears to be similar to other well-studied portions of the breeding range. Conservation and management efforts directed toward establishing and protecting large tracts of mature forest, especially those on east-facing slopes, should be a reasonable approach to managing Cerulean Warbler populations in this area.

Intra- and interspecific variation in wood density and fine-scale spatial distribution of stand-level wood density in a northern Thai tropical montane forest

Abstract:Tropical tree wood density is often related to other species-specific functional traits, e.g. size, growth rate and mortality. We would therefore expect significant associations within tropical forests between the spatial distributions of stand-level wood density and micro-environments when interspecific variation in wood density is larger than intraspecific variation and when habitat-based species assembly is important in the forest. In this study, we used wood cores collected from 515 trees of 72 species in a 15-ha plot in northern Thailand to analyse intra- and interspecific variation in wood density and the spatial association of stand-level wood density. Intraspecific variation was lower than interspecific variation (20% vs. 80% of the total variation), indicating that species-specific differences in wood density, rather than phenotypic plasticity, are the major source of variation in wood density at the study site. Wood density of individual species was significantly negatively related to maximum diameter, growth rate of sapling diameter and mortality of saplings. Stand-level mean wood density was significantly negatively related to elevation, slope convexity, sapling growth rate and sapling mortality, and positively related to slope inclination. East-facing slopes had significantly lower stand-level mean wood densities than west-facing slopes. We hypothesized that ridges and east-facing slopes in the study forest experience strong and frequent wind disturbance, and that this severe impact may lead to faster stand turnover, creating conditions that favour fast-growing species with low wood density.

Biogeography of Mindoro mosses

The moss flora of Mindoro Island was updated based on the 2004–2006 expeditions conducted by the author. The island’s moss flora now consists of 282 species in 128 genera and 39 families, which is higher than Palawan but far less than those of Luzon and Mindanao. Generally, the flora is most abundant in the eastern rainy part of the island, especially along mid-elevations on the east-facing slope of the central mountain range in the transition zone between montane and mossy forests. Moss diversity is also greater in riverine forests than in inland forests at low elevations. Only three moss taxa, Rhaccocarpus alpinus, Dicranoloma daymannianum and Distichophyllum noguchianum, have their Philippine range restricted to the island. Distichophyllum noguchianum is a Philippine endemic. Floristically, the Mindoro moss flora is identified more with Luzon within the Philippine archipelago, while its sharing of other widespread Malesian taxa reinforced its role as an integral component of the Malesian flora. Reports of taxa with Australasian affinity show growing evidence for a Gondwanan influence on the island moss flora, although a tenuous one. Likewise, the presence of moss taxa such as Acroporium johanneswinkleri, Cryptogonium phyllogonioides and Glyptothecium sciuroides in Mindoro, reinforce the important role of Palawan as link in the exchange of biota between Mindoro, Borneo and Peninsular Malaysia during the Pleistocene. Finally, the importance of the island in enriching the Philippine flora and the necessity to protect its remaining forests are discussed.

Statistic-empirical modelling of mountain permafrost distribution in the Abisko region, sub-Arctic northern Sweden

The mountain permafrost distribution in the Abisko region in northern Sweden has been assessed using a combination of empirical and statistical analysis. The empirical data was obtained using the bottom temperature of snow cover (BTS) method, supported by continuous ground temperature measurements. The statistical analysis was based on 148 data points in total and used logistic regression to model the probability of permafrost occurrence. Further, Geographically Weighted Regression (GWR) was introduced as an exploratory tool for detecting non-stationarity in the relationships between permafrost and the independent variables models and showed to be a useful tool in the statistical analysis. As a result of the GWR analysis the region was divided into two subregions. The models show probabilities >0.8 for permafrost at elevations above 1300 m a.s.l. in the western part of the region. In the eastern part, the probabilities are likely to be influenced by the potential incoming shortwave summer radiation, indicating a probability >0.8 above 850 m a.s.l. on the north-east and east-facing slopes, above 1000 m on the west-facing slopes and above 1100 m a.s.l. on the south-facing slopes. Permafrost conditions throughout the region were found to be marginal and sensitive to current warming trends.

Cold-Trapping of Persistent Organic Pollutants in the Mountain Soils of Western Sichuan, China

In the Chinese province of Sichuan steep mountains rise from the very densely populated and intensely cultivated Chengdu basin more than 4000 elevational meters to the Tibetan Plateau. This steep physical gradient is exceptionally well suited to investigate the transport of persistent pesticides and other organic contaminants from low to high elevations. In spring and autumn 2006, 25 soil samples were taken at five elevations ranging from 2636 to 4479 m along the East-facing slope of Balang Mountain in Wolong Nature Reserve. Analysis of soil extracts was done by gas chromatography-high resolution mass spectrometry. Whereas hexachlorobenzene (HCB), hexachlorocyclohexanes (HCH), and dichlorodibenzotrichloroethane and its degradation products (DDTs) were present at levels of a few ng/g, only two light PCB congeners were detected at levels below 1 ng/g in soil. Soil concentration for all analytes increased significantly and exponentially with altitude. The rate of concentration increase, expressed quantitatively through the slope of the linear regression between the logarithm of the concentrations and altitude, increases along the sequence HCB < PCB < HCH < or = DDT. This trend is consistent with, and therefore lends additional observational support to, a mountain cold-trapping mechanism based on the temperature dependence of precipitation scavenging.