Middle Elevations Research Articles

Plant-microbe specificity varies as a function of elevation.

Specialized associations between interacting species fundamentally determine the diversity and distribution of both partners. How the specialization of guilds of organisms varies along environmental gradients underpins popular theories of biogeography and macroecology, whereas the degree of specialization of a species is typically considered fixed. However, the extent to which environmental context impacts specialization dynamics is seldom examined empirically. In this study, we examine how specialization within a bipartite network consisting of three co-occurring plant species and their foliar fungal endophyte symbionts changes along a 1000-meter elevation gradient where host species were held constant. The gradient, along the slope of Mauna Loa shield volcano, represents almost the entire elevational range of two of the three plants. Network and plant specialization values displayed a parabolic relationship with elevation, and were highest at middle elevations, whereas bipartite associations were least specific at low and high elevations. Shannon's diversity of fungal endophytes correlated negatively with specificity, and was highest at the ends of the transects. Although plant host was a strong determinant of fungal community composition within sites, fungal species turnover was high among sites. There was no evidence of spatial or elevational patterning in fungal community compositon. Our work demonstrates that specificity can be a plastic trait, which is influenced by the environment and centrality of the host within its natural range.

Soil charcoal elucidates the role of humans in the development of landscape of extreme biodiversity

AbstractThe south‐western White Carpathians (Czech Republic, Slovakia) are one of the few places in low‐elevation Central Europe where a diverse landscape, including extremely species rich meadows, scattered oak trees, and mixed oak woodlands, has escaped modern transformation. We studied C14‐dated and taxonomically identified macroscopic soil charcoal record to elucidate the genesis of this landscape. Thirteen soil profiles were sampled in grasslands along a gradient of elevation and history of human settlement. We identified clear pattern in the taxonomic composition of woody soil charcoal and anthracomass along this gradient, which we ascribe to different pathways of landscape development. Charcoal assemblages of chernozem‐like soils in the promontories of the mountain range have a low anthracomass and are dominated by heliophilous and semishade species (Quercus, Pinus), with the oldest charcoals dated to pre‐Neolithic times. Soils of the middle elevations have a high anthracomass and often show pronounced differences in charcoal composition at different soil depths; the oldest charcoal samples date back between the Neolithic and Early Middle Ages, and heliophilous species increase towards the topsoil. The soil of the summit area shows a medium anthracomass and charcoal assemblage dominated by shade‐tolerant trees; the charcoal dates from the Middle Ages. Our results suggest continuity of an open to semiopen landscape in lower elevations of the White Carpathians, whereas middle and higher elevations experienced a forested period. Humans and fire played an important role in landscape development, as indicated by both soil charcoal and available palaeoecological and archaeological evidence. Local meadows with extremely high biodiversity thus appear to be a continuation of an ancient forest‐steppe‐like ecosystem.

Effects of extractive use on forest birds in Western Himalayas: Role of local and landscape factors

Rural populations in developing countries depend on forests for fuelwood, fodder and other non-timber forest products. Such dependence has significant effects on faunal diversity and composition, primarily due to alteration of vegetation structure. While earlier studies have assessed the consequences of extractive activities for forest fauna, very few simultaneously acknowledge the role of landscape context, which includes agricultural land-uses and managed forests. This study was carried out in oak-dominated forests located in the middle elevations of the Western Himalayas to investigate effects of extractive activities on avifaunal communities, taking into account the role of landscape composition. Birds were sampled at 74 sites, six times each, over two seasons using fixed-radius point counts. We analysed avian species richness, abundance, composition and guild abundances (based on foraging and habitat preference) as a function of vegetation structure and proportion of dense oak forest around each site. Our results suggest that extractive activities in forests can result in reduced species richness, abundance and altered composition of forest avifauna, brought about by changes in vegetation structure. We also find that these effects may be intensified by the loss of dense oak forests in the landscape. Insectivorous birds and forest specialists were most sensitive to extractive activities and landscape composition. Decreasing canopy cover and proportion of oak forest in the landscape had strong negative effects on insectivorous and forest specialist species. Other local factors such as vertical stratification and understory density also had effects on these avian guilds. Our study indicates that in order to conserve bird species in an increasingly human-dominated landscape of the Western Himalayas, it may be necessary to control extractive activities that affect forest structure as well as retain protected forest stands within a continuum of harvested forest and agricultural landscapes.

Effects of solar UV-B radiation exclusion on physiology, growth and yields of taro (Colocasia esculenta (L.)) at different altitudes in tropical environments of Southern Ethiopia

Plants are sessile by nature, they have to be able to cope with exposure to many biotic and abiotic stress factors, including solar UV-B radiation. The degree of stresses varies with geographic locations. The impact of solar UV radiation on growth, physiology and yield of taro (Colocasia esculenta (L.)) at different altitudes under tropical environments was evaluated in Southern Ethiopia at 1500 m, 1800 m and 2200 m a.s.l. The experiment was conducted under open field conditions, and was compared to the yield of taro under UV-B blocking plastic film at every location. Four taro cultivars (‘Black’, ‘Boloso-1’, ‘Purple’ and ‘White’) were used as planting materials. Each treatment was planted using RCB design with three replications. The result indicates that leaf number, shoot number, leaf area and leaf area index under UV-B exclusion were found to be higher at higher elevation than either lower or middle elevation for ‘Boloso-1’ and ‘Black’ cultivars. Exclusion of UV-B spectrum from solar radiation improved the number of leaves and the leaf area index, for two cultivars: ‘Black’ and ‘Boloso-1’. Blocking UV-B radiation also significantly enhanced stomata conductance, photosynthesis rate stomata opening area, stomata number and dry matter in ‘Boloso-1’, compared to other cultivars. However, physiologically ‘Purple’ cultivar did not respond to solar UV-B irradiation. Among all the cultivars, ‘Boloso-1’ was found to be a good candidate for maximum corm size, marketable and maximum total yield production in all test locations irrespective of solar UV-B irradiation. In conclusion, vegetative growth of taro cultivars responded better to altitudinal variation than variability of UV-B irradiation. Whereas, physiological parameters like stomata number, stomata opening area, stomata conductance and photosynthesis of different taro cultivars responded stronger to the level of UV-B irradiation than the altitude.

Variability of soil surface characteristics in a mountainous watershed in Valle del Cauca, Colombia: Implications for runoff, erosion, and conservation

Understanding catchment sediment or solute transport frequently relies on understanding of soil nutrient conditions and physical properties. This study investigates hydropedological patterns in a tropical catchment by understanding soil nutrient and soil surface changes. Soil nutrient concentrations and hydraulic properties were measured from the La Vega micro watershed in the southwestern Colombian Andes at 16 distributed locations in four elevation ranges (between 1450 and 1700 m a.s.l.). The site is a part of a conservation partnerships which implements programs and monitor impacts. Soil samples were analyzed for total nitrogen (TN), Bray II-available phosphorus, exchangeable cations, pH, organic matter, and texture. Soil hydraulic conductivities at two depths (0–5 cm and 5–10 cm) were determined in conservation implementation areas (enclosures and natural regrowth). In the upper elevation range, regrowth of natural vegetation was found on deep soils (∼3 m) with moderate infiltration (26 cm hr−1), the lowest bulk density (0.92 g cm−3), and the highest TN (0.4%). The lowest elevation (mixed land use of grazing and riparian forests with deep profiles) had the lowest infiltration (4 cm hr−1), highest bulk density (1.02 g cm−3), and the lowest TN (0.26%). In the middle elevation ranges, conserved tropical forest vegetation were located on shallow soil depths with high organic matter (∼6%) and high infiltration (86 cm hr−1). The lowest infiltration rate average (2.3 cm hr−1) exceeded the estimated erosive regional precipitation intensity (∼2.5 cm hr−1) about 60% of the time, while the median infiltration rate (10 cm hr−1) exceeded rainfall intensities 94% of the time, indicating that infiltration excess and saturation excess runoff mechanisms are both present. Coupling data with sediment concentration and solute concentration patterns can help discern correlations between scales and will help to monitor effectiveness of conservation programs aimed at sustaining ecosystem services.

Phosphorus mediates soil prokaryote distribution pattern along a small-scale elevation gradient in Noijin Kangsang Peak, Tibetan Plateau.

Environmental factors that are important in shaping microbe community structure are less explored along elevation in the alpine grassland ecosystem of Tibet Plateau, which is generally phosphorus limited. Here, we examined soil prokaryote communities at three elevations to explore soil prokaryote community distribution and mediation factors in Noijin Kangsang Peak, Tibetan Plateau. Results showed prokaryote community compositions differed significantly by elevations. Topsoil or subsoil prokaryote richness and Shannon diversity were significantly lower at the middle than other elevations, while significantly higher aboveground biomass (AGB) and available P (AP) were found at the middle elevation. The importance of P for both soil layers was discovered by variation partitioning analysis based on redundancy analysis, finding that soil AP and total phosphorus, interacted with pH, explained 43% the variance in topsoil prokaryote community compositions, while soil AP, as well as AGB, explained 44% in subsoil. Consistently, structural equation model also revealed that AP was a mediating factor for prokaryote community diversity. Other than plant beta diversity, soil prokaryote beta diversity positively correlated with AP difference significantly. Taken together, the distribution patterns of soil prokaryote community were distinct along elevations even in a small scale in Noijin Kangsang Peak and was likely mediated predominantly by soil AP in both topsoil and subsoil.

Late Holocene hydroclimate variability in Costa Rica: Signature of the terminal classic drought and the Medieval Climate Anomaly in the northern tropical Americas

In the northern tropical Americas (Neotropics), notable hydrological variability has been documented in multi-proxy paleoclimate records between ∼600 and 1200 CE. This interval generally overlaps with the Maya Terminal Classic Drought (TCD: ∼770–1100 CE) and the Medieval Climate Anomaly (MCA: ∼950–1250 CE). There is, however, limited paleoclimate data that provide reliable estimates of terrestrial thermal variability in southern Central America during this time. In this study, we present chironomid-based temperature reconstructions, developed from sediment cores from two lakes: (1) Lago Morrenas 3C, a high-elevation glacial lake located on the crest of the Atlantic slope of the Cordillera Talamanca, Costa Rica, and (2) Laguna Zoncho, a mid-elevation lake located on the Pacific slope in southern Costa Rica. Distinctive shifts in the chironomid assemblages occurred at both sites between ∼610 and 1230 CE. These changes are inferred to reflect an ∼600-year interval characterized by depressed mean annual temperatures at Lago Morrenas 3C and dry conditions and lake level decline at Laguna Zoncho. Taken together, the multi-proxy paleoclimate records from these two lakes, including stable carbon isotope (δ13C) and charcoal data, suggest that middle elevations on the Pacific slope and high elevations on the Atlantic slope of Costa Rica experienced sustained drought, and possible cooling coeval with the TCD-MCA interval. The timing of hydroclimate variability in these records provides support for the hypothesis that cooling and drought in the northern tropical Americas during the TCD and early MCA were linked to thermal changes in the tropical North Atlantic.

Genetic variability and heritability of some morphological and physiological traits in Fagus orientalis Lipsky along an elevation gradient in Hyrcanian forests

Abstract The purpose of the present study was to evaluate the genetic variability and heritability of some morphological and physiological traits in Fagus orientalis Lipsky along an elevation gradient in northern forests of Iran. Beech leaves were sampled from southern and northern crown parts of healthy mature trees along an elevation gradient comprising sites situated at 700 m, 1,200 m and 1,700 m above the sea level. Our statistical analysis showed that the investigated traits differed significantly between the populations. The results indicated the lowest and the highest coefficients of variation for the high (1,700 m) and middle elevation populations (1,200 m) for leaf length, petiole length, leaf area, specific leaf area, dry weight, specific dry weight, leaf index and petiole index traits. With increasing elevation, mean leaf width, distance from leaf base to the leaf maximum width, dry weight and petiole index increased. The plasticity of leaf length, specific leaf area, specific dry weight, petiole index and petiole length peaked at middle elevation, and with increasing elevation, the plasticity of these traits declined. The distance from leaf base to the leaf maximum width had the highest coefficient of genetic (75.5%) and phenotypic (75.5%) variation. The heritability results showed that there were differences in all traits, and that the highest heritability was recorded for the distance from the leaf base to the leaf maximum width (99.95 %). The results suggest that the studied beech populations responded to the environmental changes by changing their leaf traits in different ways at different altitudes.

Contributions of day length, temperature and individual variability on the rate and timing of leaf senescence in the common lilac Syringa vulgaris.

Deciduous trees prepare for winter by breaking up chlorophyll and other nitrogen-rich compounds, which are resorbed for storage. Timing is important as senescence too early will waste growing season, while senescence too late risks the loss of the leaf resources to frost. While plants of temperate and boreal regions use decreasing day length as a cue of approaching winter, we show that decreasing temperature may also play a role in the variability of leaf senescence. We investigated the timing of autumnal decrease in photosynthetic efficiency and the concentration of chlorophyll and total carotenoids in nine common lilac (Syringa vulgaris L.) trees over two consecutive years. Day length explained a greater proportion of photosynthetic efficiency, but temperature had a significant additional role, which seems to be related to individual differences. Precipitation and cloudiness did not explain photosynthetic efficiency. Photosynthetic efficiency was higher outside the canopy and at high and middle elevations than inside and low elevations of the canopy. Late onset of senescence led to a steeper decline in photosynthetic efficiency than early senescence. The onset of decline in photosynthetic efficiency differed between years, but there was no difference in the steepest rate of change in photosynthetic efficiency with respect to sampling year or location. Contributions of day-length vs temperature to leaf senescence have important consequences for the adaptability and invasibility of deciduous trees in a changing climate, especially at the edge of species distributions.

Postglacial vegetation dynamics at high elevation from Fairy Lake in the northern Greater Yellowstone Ecosystem, Montana, USA

AbstractThe postglacial vegetation and fire history of the Greater Yellowstone Ecosystem is known from low and middle elevations, but little is known about high elevations. Paleoecologic data from Fairy Lake in the Bridger Range, southwestern Montana, provide a new high-elevation record that spans the last 15,000 yr. The records suggest a period of tundra-steppe vegetation prior to ca. 13,700 cal yr BP was followed by openPiceaforest at ca. 11,200 cal yr BP.Pinus-Pseudotsugaparkland was present after ca. 9200 cal yr BP, when conditions were warmer/drier than present. It was replaced by mixed-conifer parkland at ca. 5000 cal yr BP. Present-day subalpine forest established at ca. 2800 cal yr BP. Increased avalanche or mass-wasting activity during the early late-glacial period, the Younger Dryas chronozone, and Neoglaciation suggest cool, wet periods. Sites at different elevations in the region show (1) synchronous vegetation responses to late-glacial warming; (2) widespread xerothermic forests and frequent fires in the early-to-middle Holocene; and (3) a trend to forest closure during late-Holocene cooling. Conditions in the Bridger Range were, however, wetter than other areas during the early Holocene. Across the Northern Rockies, postglacial warming progressed from west to east, reflecting range-specific responses to insolation-driven changes in climate.

The structure of forest stands in the Tatra National Park: The results of 2016–2017 inventory

Abstract The composition and structure of forest stands in the Tatra National Park were examined using data gathered in 2016 and 2017 from 617 circular sample plots (0.05 ha each). The diameter at breast height of all living trees, standing dead trees, snags, and wind throws was measured along with diameters and lengths of fallen logs within the plot boundaries. Tree height was measured for all living trees within the core (0.01 ha) of the sample plots. Using the obtained data, height-diameter curves were calculated for all major tree species and in the case of spruce, the height-diameter relationships were also calculated separately for each of the three elevation zones (up to 1200 m, between 1200 and 1400 m, above 1400 m). For each elevation zone and park protection zone, we also determined the volumes of live and dead trees. The volume of living trees in the Tatra National Park amounted to 259 m3/ha, which was higher than the volume of dead trees (176 m3/ha). Snags constituted the largest part of the dead wood whilst over 97% of the standing dead trees were spruce Picea abies. Among living trees, the share of spruce ranged from 81% in the low elevation zone to 98% in the middle zone. Other significant species in the lower zone were Abies alba (11%) and Fagus sylvatica (4.5%), while in the middle and upper elevation zones only Sorbus aucuparia occurred in significant numbers. Furthermore, in the lower elevation zone, Fagus sylvatica was the only species displaying significantly higher volumes in the ‘strict protection’ zone compared to the other park areas. In the ‘landscape protection’ zone, Picea abies was the most dominant species and the share of other species in the lowest elevation zones calculated based on tree density was smaller than calculated based on tree volume, indicating problems with stand conversion from spruce monoculture to mixed forest.

Forest structure and pattern vary by climate and landform across active-fire landscapes in the montane Sierra Nevada

Restoration of fire-dependent forests is often guided by reference conditions from forests with an active fire regime, thought to be resilient to current and future disturbances and stresses. Reference conditions are usually based on historical data or reconstruction, which greatly limits the scale and completeness of data that can be collected. In the Sierra Nevada of California, large areas with reintroduced active fire regimes coupled with extensive lidar data coverage provide the unique opportunity to develop a contemporary regional reference condition dataset across a wide gradient of biophysical conditions. We developed this dataset with a focus on three questions: (1) What is the geographic and environmental distribution of restored active-fire forest areas in the Sierra Nevada mixed-conifer zone? (2) What are the ranges of variation in forest structure and spatial patterns across reference areas? And (3) How do stand density, tree clumping, and canopy opening patterns vary by topography and climate in reference areas? We analyzed fire history and environmental conditions over 10.8 million ha, including 3.9 million ha in the Sierra Nevada mixed-conifer zone, and found 30,377 ha of restored active-fire areas. Although reference areas were distributed throughout the Sierra Nevada they were more abundant on National Park lands (81% of reference areas) than National Forest lands and were associated with higher lightning strike density. Lidar-measured ranges of variation in reference condition structure were broad, with tree densities of 6–320 trees ha−1 (median 107 trees ha−1), basal area of 0.01–113 m2 ha−1 (median 21 m2 ha−1), average size of closely associated clumps of trees from >1 to 207 trees (median 3.1 trees), and average percent of stand area >6 m from the nearest canopy ranging from 0% to 100% (median 5.1%). These ranges correspond well with past studies reporting density and spatial patterns of contemporary and historical active-fire reference stands in the Sierra Nevada, except this study observed greater total variation due to the much greater spatial extent of sampling. Within the montane forest zone, reference areas at middle elevations had lower density (86 vs. 121 trees ha−1), basal area, (13.7 vs. 31 m2 ha−1), and mean clump size (2.7 vs. 4.0 trees) compared to lower- and higher-elevation reference areas, while ridgetops had lower density (101 vs. 115 trees ha−1), basal area (19.6 vs. 24.1 m2 ha−1), and mean clump size (3.0 vs. 3.3 trees) and more open space (7.4% vs. 5.1%) than other landforms. Many of the relationships between physiography and reference structure were context-dependent, suggesting that management practices should create heterogeneous forest structure congruent with local climatic and topographic factors influencing stand conditions.

Quantitative attribution analysis of soil erosion in different geomorphological types in karst areas: Based on the geodetector method

The formation mechanism and influencing factors identification of soil erosion are the core and frontier issues of current research. However, studies on the multi-factor synthesis are still relatively lacked. In this study, the simulation of soil erosion and its quantitative attribution analysis have been conducted in different geomorphological types in a typical karst basin based on the RUSLE model and the geodetector method. The influencing factors, such as land use type, slope, rainfall, elevation, lithology and vegetation cover, have been taken into consideration. Results show that the strength of association between the six influencing factors and soil erosion was notably different in diverse geomorphological types. Land use type and slope were the dominant factors of soil erosion in the Sancha River Basin, especially for land use type whose power of determinant (q value) for soil erosion was much higher than other factors. The q value of slope declined with the increase of relief in mountainous areas, namely it was ranked as follows: middle elevation hill> small relief mountain> middle relief mountain. Multi-factors interactions were proven to significantly strengthen soil erosion, particularly for the combination of land use type with slope, which can explain 70% of soil erosion distribution. It can be found that soil erosion in the same land use type with different slopes (such as dry land with slopes of 5° and above 25°) or in the diverse land use types with the same slope (such as dry land and forest with a slope of 5°), varied much. These indicate that prohibiting steep slope cultivation and Grain for Green Project are reasonable measures to control soil erosion in karst areas. Based on statistics of soil erosion difference between diverse stratifications of each influencing factor, results of risk detector suggest that the amount of stratification combinations with significant difference accounted for 55% at least in small relief mountain and middle relief mountainous areas. Therefore, the spatial heterogeneity of soil erosion and its influencing factors in different geomorphological types should be investigated to control karst soil loss more effectively.

Vegetation–environment relationship in Pinus wallichiana forests of the Swat Hindukush range of Pakistan

Understanding the influence of environmental variables on the spatial distribution of ecological communities is essential to predict the response of vegetation to various environmental drivers. Ecological theory suggests that multiple environmental factors shape local species assemblages and should influence the various components of community structure and composition in different ways. This study aimed to classify Pinus wallichiana dominated forests in the Swat Hindukush range mountains to understand the relative influence of multiple environmental filters on its composition and structure. These forests represent the most typical of the species distribution in northern Pakistan and were not subjected to any phytosociological study. For this purpose, thirty forest stands, spanning a wide range of physical habitats were sampled using 10 × 10 m plots and the importance value index was calculated. The floristic and environmental data were subjected to Ward’s agglomerative cluster analysis for objective classification and ordinated with NMS ordination for pattern description and testing the vegetation–environmental relationships. Three floristically and ecologically distinct communities were recognized along the topographic gradient (elevation, r = 0.377; slope, r = 0.5548) coupled with soil physical (clay, r = 0.2782; silt, r = 0.3225) and chemical properties (pH, r = 0.4975; lime, r = 3982). An elevation gradient of 100 m separated the low (Pinus wallichiana–Quercus dilatata community) and middle elevations forest stands (P. wallichiana pure population) from the highland population type (Pinus wallichiana–Cedrus deodara community). The floristics and structure of these forest types respond directly or indirectly to topographic and soil variables which were evidenced from the floristic composition, species richness, and community physiognomy. These characteristics of the communities changed from heterogenous, dense stands to sparsely dispersed conifers, broadleaved-evergreen, and deciduous vegetation types along the environmental gradients. We concluded that several factors explained the spatial pattern. Thus, we predict that elevation coupled with soil physical and chemical properties could be considered if the ultimate goal is the restoration and conservation of these forests. We also recommend broad-scale phytosociological study on P. wallichiana forests including multiple sampling from diverse locations to define the floristic diversity and to better understand its ecological requirements.

Warming hiatus and evergreen conifers in Altay-Sayan Region, Siberia

“Warming hiatus” occurred in the Altay-Sayan Mountain Region, Siberia in c. 1997–2014. We analyzed evergreen conifer (EGC) stands area (satellite data) and trees (Siberian pine, Pinus sibirica Du Tour, Siberian fir, Abies sibirica Ledeb.) growth increment (dendrochronology data) response to climate variables before and during the hiatus. During the hiatus, EGC area increased in the highlands (>1000 m) (+30%), whereas at low and middle elevations (<1000 m. a.s.l.) the EGC area decreased (-7%). The EGC area increase was observed on the rain-ward northwest slopes mainly. In highlands, EGC area increase mainly correlated with summer air temperature, whereas at low and middle elevations EGC area decrease correlated with drought index SPEI and vapor pressure deficit (VPD). EGC mortality (fir and Siberian pine) in lowland was caused by the synergy of water stress (inciting factor) and barkbeetle attacks (contributing factor). Tree growth increment (GI) dynamics differs with respect to elevation. At high elevation (1700 m) GI permanently increased since warming onset, whereas at the middle (900 m) and low elevations (450 m) GI increased until c. 1983 yr. with followed depression. That GI “breakpoint” occurred about a decade before hiatus onset. In spite of growth depression, during hiatus GI was higher than that in pre-warming period. At high elevation, GI positively responded to elevated June temperatures and negatively to moisture increase (precipitation, root zone moisture content, VPD, and SPEI). At low elevation GI negatively responded to June temperatures and positively to moisture increase. For both, low and high elevation, these patterns persisted throughout the study period (1967–2014). On the contrary, at middle elevations GI dependence on climate variables switch after breakpoint year (1983). Before breakpoint, June air temperature (positive correlation) and moisture (negative correlations) controlled GI. Further temperature increase leads GI depression and switched correlation signs to opposite (from positive to negative with temperature, and from negative to positive with moisture variables).

Insect-flower interaction networks vary among endemic pollinator taxa over an elevation gradient.

Interaction networks are sensitive to elevation gradients through changes in local distribution of interacting partners. Here, we use plant-pollinator interaction network metrics to assess the effect of elevation on flowers and flower-visiting insect assemblages on a sentinel mountain used for monitoring climate change in the flower- and insect-rich Cape Floristic Region. We also use these interaction metrics to explain the effect of environmental factors on the interaction networks. We did this over four vegetation zones <1640m asl, as determined by former botanical studies. Overall, bees were the dominant flower visitors, followed by monkey beetles, and far behind were wasps and flies. The middle elevation zone (650–744 m a.s.l), which is also an ecotone between two distinct botanical zones, had the highest species richness and abundance of interacting plants and insects. Interaction frequency and size of network were also greatest in the middle zone, as were network diversity, generality, and linkage density, while lowest in the peak zone. In sum, there was distinct elevation zoning of flower-visiting insects. The greatest zonal change was between species at the middle compared with peak zone. Large-sized monkey beetles, bees and flies characterized the unique assemblage in the peak zone (1576–1640 m a.s.l.). The insect zonation tracked that of plant assemblages, with air temperature (lapse rate) being the primary driver of bee distribution, with lowest levels in the peak zone. In contrast, beetle distribution was driven mostly by flower assemblages as well as air temperature. In turn, wasp and fly interaction networks were not affected by any of the measured environmental variables. We conclude that increased elevation stress from reduced temperatures, changing abiotic weather conditions (e.g. strong winds at high elevations),and decline in flowering plant composition causes breakdown of interaction networks involving bees and beetles but not that of flies and wasps.

The importance of productivity and seasonality for structuring small rodent diversity across a tropical elevation gradient.

Photosynthetic productivity is a key determinant of the abundance and distribution of biodiversity around the world. The effect of this productivity on the distribution patterns of mammals is frequently invoked; however, it is seldom measured directly. In this study, we used Sherman live traps set in dry and rainy seasons across a 2300-m elevation gradient in southwestern Mexico to assess small rodent species distributions, and to relate these patterns to habitat structure, climate, and a well-accepted measure of photosynthetic productivity: the normalized difference vegetation index (NDVI). While habitat structure and climate helped explain some of the patterns observed, NDVI proved to be the most important contributing variable for most of the distribution models. We also found that partitioning the gradient-distribution model by trapping season revealed strong differences in terms of the effect of NDVI and the other explanatory variables. For example, lower elevations were associated with seasonal and year-round reductions in rodent diversity and were composed almost exclusively of granivore-based species assemblages. By contrast, the middle and upper elevations were more species rich, less affected by seasonality, and characterized by omnivorous species. Our results suggest that the positive productivity-diversity relationship found may be due, at least in part, to increased food resources and niche opportunities at more productive elevations. Increased diversity at the higher elevations may also be partially due to reductions in competition that result from productivity increases, as well as from the broader spectrum of feeding guild representation that it and the lack of seasonality allow.

Structure of local adaptation across the landscape: flowering time and fitness in Mexican maize (Zea mays L. subsp. mays) landraces

In crop centers of origin and diversity, often biotic and abiotic conditions vary across the landscape creating the possibility for local adaptation of crops, whereby local landraces perform better than non-local ones under local conditions. By studying patterns of local adaptation we can better understand the degree of adaptation of landraces, phenotypic mechanisms driving that adaptation, and the plastic responses of adapted populations to environmental change. Studying these basic processes in crop centers of origin and diversity improves basic understanding of adaptive evolution and provides insight for existing farming systems encountering climate change. Using maize landraces collected and reciprocally transplanted in the field in two years along an elevational gradient in Chiapas, Mexico, we aimed to understand their degree of local adaptation, the distribution of adaptive diversity within elevations, and how landraces compared to improved varieties in their responses to environmental variation. We found some patterns consistent with local adaptation among the landraces, although the degree of adaptation differed across measures of fitness components and years. Flowering time variables showed more variability within elevations than total fitness estimates or fitness components did. Improved varieties, like low elevation landraces, were not well-adapted to conditions at higher elevations, although they did possess some beneficial traits. These data reaffirmed experimentally the local adaptation of landraces and their difficulty in reproducing under novel conditions, and indicated the importance of landraces for high productivity (especially in middle and high elevation systems).

Fagus sylvatica seedlings show provenance differentiation rather than adaptation to soil in a transplant experiment

BackgroundUnderstanding and predicting the response of tree populations to climate change requires understanding the pattern and scale of their adaptation. Climate is often considered the major driver of local adaptation but, although biotic factors such as soil pathogens or mutualists could be as important, their role has typically been neglected. Biotic drivers might also interact with climate to affect performance and mycorrhizae, in particular, are likely to play a key role in determining drought resistance, which is important in the context of adaptation to future environmental change. To address these questions, we performed a fully reciprocal soil–plant transplant experiment using Fagus sylvatica seedlings and soils from three regions in Germany. To separate the biotic and abiotic effects of inoculation, half of the plants were inoculated with natural soil from the different origins, while the rest were grown on sterilized substrate. We also imposed a drought stress treatment to test for interactions between soil biota and climate. After 1 year of growth, we measured aboveground biomass of all seedlings, and quantified mycorrhizal colonization for a subset of the seedlings, which included all soil–plant combinations, to disentangle the effect of mycorrhiza from other agents.ResultsWe found that plant origin had the strongest effect on plant performance, but this interacted with soil origin. In general, trees showed a slight tendency to produce less aboveground biomass on local soils, suggesting soil antagonists could be causing trees to be maladapted to their local soils. Consistently, we found lower mycorrhizal colonization rate under local soil conditions. Across all soils, seedlings from low elevations produced more annual biomass than middle (+ 290%) and high (+ 97%) elevations. Interestingly, mycorrhizal colonization increased with drought in the two provenances that showed higher drought tolerance, which supports previous results showing that mycorrhizae can increase drought resistance.ConclusionsOur findings suggest that soil communities play a role in affecting early performance of temperate trees, although this role may be smaller than that of seed origin. Also, other effects, such as the positive response to generalists or negative interactions with soil biota may be as important as the highly specialized mycorrhizal associations.

Persistently Elevated Microvascular Resistance Postrecanalization.

Background and Purpose- Impaired microvascular reperfusion despite complete recanalization (no-reflow) represents a potential therapeutic target to improve outcomes after recanalization therapies. Although well documented in animal models, this phenomenon has not been demonstrated clinically. We investigated whether transcranial Doppler can detect acute microvascular changes postrecanalization as a biomarker of the no-reflow phenomenon in stroke patients. Methods- Consecutive patients with recanalized (Thrombolysis in Cerebral Infarction grade IIb/III) acute middle cerebral artery occlusion by thrombectomy at a Comprehensive Stroke Centre with a high-volume neurovascular laboratory were retrospectively identified. Sonographic measures of middle cerebral artery territory microvascular resistance (pulsatility index and resistive index) on days 1 to 3 follow-up transcranial Doppler were compared between patients and age/gender-matched controls. Results- In 53 patients, middle cerebral artery pulsatility index was significantly more likely to be asymmetrically increased on interside comparison (27.9% versus 4.9%; P=0.007) and abnormally elevated beyond normal reference ranges (46.7% versus 22.0%; P=0.016) in the symptomatic hemisphere. Middle cerebral artery pulsatility index elevation was associated with less hemorrhagic infarction (9.5% versus 45.8%; P=0.009) but worse functional outcome irrespective of infarct volume as assessed on 90-day modified Rankin Scale (score of ≤1, 18.2% versus 58.1%; P=0.035). Conclusions- Elevated microvascular resistance within the ischemic territory is commonly present after successful recanalization as measured by pulsatility index on transcranial Doppler and may be a readily available and clinically relevant biomarker of the no-reflow phenomenon.