Elevation modulates how Arctic arthropod communities are structured along local environmental gradients

We exploited the natural climate gradient in the northern hardwood forest at the Hubbard Brook Experimental Forest (HBEF) to evaluate the effects of climate variation similar to what is predicted to occur with global warming over the next 50–100 years for northeastern North America on soil carbon (C) and nitrogen (N) cycle processes. Our objectives were to (1) characterize differences in soil temperature, moisture and frost associated with elevation at the HBEF and (2) evaluate variation in total soil (TSR) and microbial respiration, N mineralization, nitrification, denitrification, nitrous oxide (N2O) flux, and methane (CH4) uptake along this gradient. Low elevation sites were consistently warmer (1.5–2.5°C) and drier than high elevation sites. Despite higher temperatures, low elevation plots had less snow and more soil frost than high elevation plots. Net N mineralization and nitrification were slower in warmer, low elevation plots, in both summer and winter. In summer, this pattern was driven by lower soil moisture in warmer soils and in winter the pattern was linked to less snow and more soil freezing in warmer soils. These data suggest that N cycling and supply to plants in northern hardwood ecosystems will be reduced in a warmer climate due to changes in both winter and summer conditions. TSR was consistently faster in the warmer, low elevation plots. N cycling processes appeared to be more sensitive to variation in soil moisture induced by climate variation, whereas C cycling processes appeared to be more strongly influenced by temperature.

Although there is considerable evidence that large mammalian herbivores influence ecosystem‐level processes, studies have reported such widely varying results that generalizations have remained elusive. Here, we use an 18‐year‐old exclosure experiment—stratified across a landscape heterogeneous with respect to soil texture, moisture and herbivore activity—to understand the variable effects of tule elk (Cervus canadensis nannodes), a native reintroduced herbivore, on soil properties along the coast of northern California. Elk significantly increased soil bulk density and created a compacted layer at shallow soil depth, while decreasing infiltration rate and pH. The effects of elk on bulk density, penetration resistance, and pH varied with soil type, being least pronounced in coarse, sandy loams, and greatest in loose sand. The effects of elk on nutrient availability varied along gradients of soil texture and moisture. In coarser soils, elk decreased ammonium availability, but increased it in finer soils. Elk also decreased soil moisture content, in part through their positive effect on bulk density, and this effect was most pronounced in coarser soils. Through decreasing soil moisture content, elk also decreased nitrate availability in coarser soils. At greater levels of elk activity (as measured by dung deposition), the elk effect on bulk density was amplified, and this had a corresponding negative effect on nitrate and phosphate availability. Our study has demonstrated that a better understanding of spatial variation in the effects of herbivores on ecosystems can emerge by evaluating their influences across gradients of soil texture, soil moisture, and herbivore activity. These data enabled us to evaluate several frameworks that have been developed to understand the variable effects of herbivores on ecosystems, which is a significant step in reconciling the many competing ideas put forth to explain the context‐dependent effects of large herbivores on grazed ecosystems.

Trees growing at the margins of their species' distributional ranges are considered to be the most sensitive to environmental factors. In tree species distributed across wide elevational gradients and playing vital roles in local ecosystems,altitudinal variation in growth conditions may be of great importance for sustainable forest management. The importance of altitudinal gradients is thus often emphasized. To investigate climate-growth relationships at different elevations,tree-ring width chronologies of Larix olgensis and Pinus koraiensis were developed from four and six sampling sites,respectively,at different elevations of a north-facing slope in the Changbai Mountains of northeastern China. Ten final residual chronologies were produced. Mean sensitivity( MS) and standard deviation( SD) were used to describe interannual variability in ring width as a proportion of local mean ring width. The signal-to-noise ratio( SNR) served as an expression of the strength of the observed common signal among trees. All chronologies had relatively high MS,SD,and SNR values, which reflected the sensitivities of trees to environmental conditions. There were no consistent trends in statistical characteristics of tree-ring chronologies along the elevational gradient. For L. olgensis,all values decreased with increasing elevation,reaching a minimum at the mid-elevation site; increases in these values were then observed above the midelevation site,which suggested that trees in the mid-elevation site had a complacent growth pattern. For P. koraiensis,all values increased with increasing elevation,reaching a maximum at the mid-elevation site,and then decreasing. Hierarchicalclustering analysis was used to highlight differences in radial growth among sites and to determine radial growth associations. For L. olgensis,chronologies were classified into two groups—low and high elevation—,while P. koraiensis chronologies at large were categorized into three groups—low,intermediate,and high elevation. Correlation and response functions were analyzed to determine primary climatic influences on growth. The bootstrap method was used to test significance. Monthly mean temperature and monthly total precipitation were used for the analysis. Our results suggest that along the elevational gradient,both species may respond in different ways to local climate change. March and June temperatures and previous November temperatures appeared to be the primary limitations to L. olgensis growth under either high or low elevation chronologies. Our data demonstrate that temperature is the dominant factor limiting growth at high elevations. At low elevations,no significant correlations with the current year' s climatic conditions were discerned. The previous year' s October temperatures and June precipitation affected P. koraiensis at high elevations. This lag in response suggests that a relatively warm autumn may favor the following year's growth. Precipitation in the previous year,temperature of the current year,and current spring temperatures had the greatest contributions to P. koraiensis growth at either intermediate or low elevations. In both species,lag effects were observed in growth responses to climate forces. Comparing the two species,L. olgensis is cold-tolerant,whereas P. koraiensis is warm-loving. The elevational differences in responses of L. olgensis and P. koraiensis to climate that were uncovered in this study should assist future regional dendroclimatological studies.

QuestionsAre communities structured on a hydrological (soil moisture) gradient? Is there spatial segregation into hydrological niches? What is the shape of the hydrological niches of individual species? Controlling for spatial autocorrelation, how much of the spatial structure in the community is due to variation in hydrology? Do annuals and perennials behave alike with respect to the above questions?LocationsLa Mina in Moscosa Farm, Salamanca, western Spain (dehesa community) and Laguna Larga in the Urbión Peaks, Soria, central‐northern Spain (alpine grassland).MethodsThe presence of plant species was sampled in two contrasting field sites, for which we also built hydrological models. First, we reduced the dimensionality of the plant distribution data (non‐metric multidimensional scaling) and measured the correlation between the resulting ordination and the hydrological gradient. Then we defined hydrological niches and tested niche segregation of plant species against null models (Pianka metrics). Finally, we characterized the hydrological niche of each species using generalised additive mixed models and partitioned the species distribution variance into (1) a hydrological component, (2) a linear trend component and (3) and a spatial component, defined through sets of spatial variables (Moran's eigenvector maps).ResultsBoth plant communities were primarily structured along hydrological gradients, and spatial segregation into hydrological niches occurred among perennial species, although not among annuals in the dehesa community. Dehesa annuals were spatially aggregated in the driest niches. Hydrological variation shaped the responses of 60% of the annual and about 70% of the perennial species in both the dehesa meadow and the alpine community. Most responses were either monotonic or hump‐shaped. Finally, spatially structured hydrological variation proved to be the main driver of spatially structured species composition in all cases.ConclusionsLinearly (gradient of slope) and topographically (at a fine scale) structured variation in hydrology is the main driver of spatially structured species composition in both communities. Our results support the ecological hypothesis that spatial niche segregation on soil moisture gradients is an important mechanism of co‐existence for perennials in both test communities, although not for the species‐rich sub‐community of annuals in the dehesa meadow.

From years ago, climate change effects are happening in different areas of the world, including Rwanda. Potato as one of main commodities grown mainly in the cooler and wetter highlands of Rwanda, its production could be facing the global warming. The purpose of this study is to carry out weather (temperature and rainfall) change dynamics in the potato growing zones of Rwanda over the last thirty years. Weather daily data from 1987 to 2016 were collected from three weather stations, at Kawangire for low elevation, at Gikongoro mid elevation, and at Kora high elevation, respectively. Farmers were interviewed to know their perceptions on weather conditions during past thirty years. Weather data were analyzed by ombrothermic diagram, Nickolson Index and graphing with generated trend equation methods. Interview data were analyzed with Chi-square test at P =.05. Results have shown as dry June, July and August months in low elevation; June, July and August in medium elevation and June and July in high elevation depending on decade. Rainfall was increasing in low and medium elevations, while it was decreasing in high elevation. Temperature was decreasing in low elevation area and it was increasing in medium and high elevation areas. All interviewed farmers confirmed long term-shift in temperature and precipitations. A total of 95%, 54% and 43% of farmers from respectively low, medium and high elevations reported that weather was becoming wetter during last years. As conclusion, potato growing cooler and wetter conditions of high elevation are shifting to low elevation in Rwanda. For climate change mitigation, Rwanda needs to promote potato in its Eastern part, the low elevation region, in order to increase the crop production in the future.

Growth response of subalpine fir (Abies lasiocarpa) to climate was studied across its local geographical and elevation range in the Olympic Mountains, Washington. A dendroecological analysis of subalpine fir across a range of elevations (1350‐1850 m) and annual precipitation (125‐350 cm y−1), was used to compare environmental factors affecting growth. Climate‐growth relationships were explored using Pearson product‐moment correlation coefficients; partial correlation analysis was used to assess relationships among site chronologies and climatic variables. Radial growth is negatively correlated with winter precipitation at high elevation and wet sites, but not at low and middle elevation dry sites. Growth is positively correlated with current growing season temperature at all sites; however, growth is negatively correlated with previous year August temperature, indicating that climate affects growth in subsequent years. Positive correlations between growth and summer precipitation during the growing season at low and middle elevation dry sites suggest that soil moisture is partially limiting to growth on these sites. If the climate of the Pacific Northwest becomes warmer and drier, then subalpine fir growth may increase at high elevation and wet sites, but may decrease at lower elevation dry sites in the Olympic Mountains. However, the growth response of subalpine fir to potentially rapid climate change will not be uniform because subalpine fir grows over a wide range of topographic features, habitats, and local climates at different geographical scales. A comparison of growth response to current growing season temperature suggests that the temperature‐related growth response of subalpine fir is not adequately described by the parabolic curve used in JABOWA‐based models.

Aim To examine patterns in anuran species richness along an elevation gradient and identify factors that govern anuran species richness on a tropical elevational gradient.Location Sampling for anurans was carried out in Kalakad Mundanthurai Tiger Reserve (KMTR) in the southern Western Ghats, India.Methods Night‐time sampling for anuran species richness was carried out from 20 November 2004 to 20 April 2005, during the north‐east monsoon and dry seasons, using transects (50 × 2 m) and visual encounter surveys along the streams. The entire gradient was classified into thirteen 100‐m elevation zones. Sampling at the alpha (single drainage basin) level was carried out in the Chinnapul River drainage basin (40–1260 m a.s.l.) and at the gamma (landscape) level in four drainage basins. Additionally, published records were used to arrive at an empirical species richness (S) for the entire landscape. Mid‐Domain Null software was used to test for the possible influence of geometric constraints on anuran species at both the alpha and gamma levels. The influence of area under each elevation zone on empirical S was tested. The pattern in anuran species richness along the elevational gradient was investigated using: (1) species boundaries in each elevation zone and their habitat correlates, (2) abiotic factors as predictor variables, (3) mean snout vent lengths of anurans, and (4) correlation between the matrices of distance in the elevation zones based on microhabitat parameters and species composition. Cluster analysis on species presence–absence in the elevation zones was used to categorize the entire gradient into high, middle and low elevations. In these three elevation categories, pattern in composition of species was examined for endemism in Western Ghats–Sri Lanka biodiversity hotspot, uniqueness to an elevation zone, adaptations of adults and modes of breeding.Results Species richness at the alpha level increased linearly with elevation, while at the gamma level there were three peaks. Maximum species richness was observed at the highest elevation (1200 m) at both the alpha and the gamma levels. The observed patterns differed significantly from mid‐domain null predictions. The multi‐modal pattern in species richness was a consequence of overlapping species range boundaries. Soil temperature was the best single measure in explaining the majority of variation in species richness at the alpha level (r2 = 0.846, P < 0.01). However, soil moisture was the best predictor when both the alpha and the gamma sites were pooled (r2 = 0.774, P < 0.01). Anuran body size decreased with an increase in elevation. The highest proportions of endemic and unique species were found at high elevations (> 700 m). The proportion of arboreal anurans increased from low to high elevation. Anurans exhibiting direct development were predominantly found at high elevations.Main conclusions Geometric constraints did not influence anuran species richness along the elevational gradient. Overlapping range boundaries influenced species richness at the gamma level. Abiotic factors such as soil temperature and moisture influenced anuran species richness in the mountain range. The ‘Massenerhebung effect’ could be responsible for range restriction and endemism of anurans, differences in guilds and mode of reproduction. These findings highlight the importance of cloud forests for endemic anurans.

The Nevada Rural Ozone Initiative (NVROI): Insights to understanding air pollution in complex terrain

The technology of using spaceborne SAR systems for soil moisture estimation has been refined over the last few years. In order to reduce the confounding effects of surface roughness on soil moisture inversion, multifrequency SAR systems have shown promise. The Shuttle Imaging Radar (SIR-C) has an onboard SAR system operating at L-, C-, and X-bands for high resolution imaging of the Earth's surface. Over the early part of October 1994, the SIR-C SAR collected radar reflectance data from two sites near Concord, New Hampshire. SIR-C data were collected on four consecutive days and concurrent ground truth measurements were also made of the actual soil moisture distribution at the test sites. The objective of the study was to evaluate the radar system's ability not only to estimate soil moisture, but also to characterize its spatial variability. The University of Nebraska has developed inversion algorithms to estimate soil moisture from SIR-C data. The spatial statistics of the in-situ measurements were used to refine the soil moisture inversion algorithm. The SIR-C derived and the in-situ soil moisture estimates compared well not only for the mean soil moisture of each pixel, but also for the spatial statistical parameters, such as correlation lengths and the gradients of soil moisture.

Wetland drying indirectly influences plant community and seed bank diversity through soil pH

<sec><st>Aims</st> Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants. Here, we aimed to address whether three major woody invaders of low-mountain areas are constrained to lower altitudes due to climatic restrictions or just by low propagule pressure. We hypothesize that the increasing climatic harshness towards higher altitudes restricts seedling establishment and survival of these woody invaders and thus their potential for altitudinal expansion. </sec> <sec><st>Methods</st> The study was carried out in the Sierras Grandes Mountains, C<a><ac>o</ac><ac>´</ac></a>rdoba, central Argentina (32º50′S, 64º90′W). We addressed the hypothesis with an experimental approach, dissociating the effect of the environmental gradient from that of propagule pressure, by discarding the influence of seed sources. We translocated seeds of <it>Gleditsia triacanthos</it> L.<it>, Ligustrum lucidum</it> W.T. Aiton. and <it>Pyracantha angustifolia</it> (Franch.) C.K.Schneid. along the altitudinal gradient (from 900 to 2700 m asl). Seven sites were selected along the altitudinal gradient, spaced every 200–400 m. Three plots (4×4 m) were selected within each altitudinal site and excluded from livestock; 100 seeds of each species were sown within each plot (6300 seeds in total). Seedling emergence and survival was monitored during two growing seasons and soil temperature and moisture was recorded as well. The field experiment was complemented with lab assays. </sec> <sec><st>Important Findings</st> Climate along this altitudinal gradient might be least restrictive at mid elevations, as a result of the intersection between opposite soil temperature and moisture gradients. Sown seeds germinated along the whole altitudinal gradient and seedlings successfully established and over-wintered well above their current altitudinal distribution (up to 2200 m for <it>Ligustrum</it> and 2400 m for <it>Gleditsia</it> and <it>Pyracantha</it>). Additional lab assays confirmed field patterns and gave some insights into contrasting regeneration strategies between these invaders that might help to overcome stochastic environmental constraints in the germination stage. Overall, seedlings of three major woody invaders of low-mountain woodlands can establish and survive at higher elevations than their current distribution. In contrast to natives, they seem to be broad climate tolerators, rather than specialized stress tolerators, capable of germinating and growing across a wide elevational range. While long-term experiments might be necessary to fully address the potentials for altitudinal expansion, out results on early lifecycle stage suggest that the invaders studied here would have mostly a dispersal barrier rather than a climate barrier to establish in the upper belt of the Sierras Grandes. </sec>

By utilizing the data observed at Dunhuang during August and September 2000 in the “Field Experiment on Interaction between Land and Atmosphere in the Arid Region of Northwest China (FEILARNC)”, the characteristics of the soil moisture, temperature, and atmospheric humidity are analyzed. It is found that the thickness of the soil temperature active layer is about 5 cm and much thinner than is typical, that not only the atmospheric humidity gradient is often inverted but also the soil moisture gradient in the shallow layer in the Gobi near oasis, that the diurnal variation of soil moisture can be divided into the four stages that are called the wet stage, the losing-water stage, the dry stage, and the attaining-water stage. It is shown that in soil moisture profiles, the depth of the soil moisture active layer is about 10 cm and soil moisture inversion is the main feature in the shallow layer during the wet stage. Such a feature as soil moisture inversion indicates that soil in the shallow layer can inhale moisture from the air through condensation in the nighttime and exhale moisture to the air through evaporation in the daytime. The condensation and evaporation constitute together the full respiration process of moisture on the ground. The formation of soil moisture inversion is related with the state of soil temperature and moisture, the intensity of atmospheric humidity inversion, and the atmospheric thermodynamic stability.

Urbanization has profound effects on ecological interactions and the composition of various taxa, including arthropod communities. Recent research has endeavoured to examine arthropod community responses along urban-rural gradients and found that some of the most important characteristics driving the changes were body size, dispersal ability, and nesting requirements. Parasites are particularly important in anthropogenic environments, affecting host population dynamics and potentially acting as vectors of diseases. Arthropod communities in nestboxes specific for small birds offer an interesting system to study how urbanization affects trophic interactions in general, and host-parasite interactions in particular. This thesis investigates the complex interactions between urbanization and arthropod communities associated with bird nests, specifically focusing on nests of the great tit (Parus major) and the blue tit (Cyanistes caeruleus). We collected data from Flanders, Belgium, a highly urbanized region in a strict sampling design allowing us to disentangle effects of urbanization at different spatial scales and land-use variables. The research sheds light over various aspects of nest arthropod ecology, such as community build-up and diversity, host-parasite dynamics and parasite dispersal. First, this study sought to investigate how urbanization and land-use variables influenced the diversity and species composition of nest-associated arthropods. This endeavour revealed that while urban settings do not significantly diminish overall arthropod community diversity or richness, idiosyncratic responses at the arthropod group level were observed. Then, the dynamics of nest-arthropod communities at three points during the nesting cycle were studied, demonstrating notable shifts in abundances and trophic structure, showing that for many groups the peak in abundances was seen during the nestling stage. Focus was then shifted to the distribution and ecological requirements of parasitic Dermanyssus mites, highlighting species-specific responses to urbanization and habitat features. Finally, the population genetics of the parasitic mite Dermanyssus carpathicus was explored, revealing moderate genetic diversity and significant population structuring potentially influenced by urbanization and host ecology. Overall, this study shows how arthropod diversity is maintained in urban communities and highlight the intricate relationships between urban landscapes, host species and their parasites and commensals, contributing valuable insights into host-parasite dynamics in human-altered ecosystems.

Understanding drivers and controls on Mesoscale Convective Systems (MCSs) is critical for predicting rainfall extremes and its impacts across time scales, from nowcasting to climate change. For MCSs over land, heterogeneity in surface fluxes across length scales presents a primary influence on storms. In West Africa, for example, MCS initiation is enhanced by ~20km scale gradients in soil moisture [1]; mature MCS cores are favoured over ~200km scale dry soil anomalies [2]; and the regional circulation responds to ~2000km scale soil moisture gradients [3], with this response explaining an observed intensification in MCSs over the last 30 years [4].To better understand how MCSs respond to this spectrum of surface flux gradients, here we present a novel sensitivity experiment framework in which a convection-permitting Control simulation is reinitialised daily from a soil moisture field where we have modified the spectrum of surface variability using wavelet filtering. We conduct two scale experiments: one in which all sub-1000km scale soil moisture variability is suppressed; and one in which we return sub-mesoscale variability. The Control simulation is run at 1.5km over West Africa for 40 days using the Met Office Unified Model and features realistic land-surface and radiation schemes and a full suite of moisture tracers. Combining results from this simulation and outputs from 2-day long sensitivity experiments gives 200 days of CP data, enabling investigation of the impact of land-surface heterogeneity on MCSs in unprecedented detail.We hereby elucidate the chain of mechanisms through which variability in mesoscale soil moisture anomalies propagates through surface fluxes to planetary boundary layer (PBL) fields and the regional circulation, and crucially, the effect on MCS lifecycles and intensities. We find a substantial reduction in MCSs when all sub-1000km soil moisture variability is suppressed, with numbers recovering when

Coastal forests in the Mid-Atlantic region are threatened by sea level rise through chronic and episodic salinization and hydrologic alterations, leading to inland marsh migration and the occurrence of ghost forests. This study uses dendrochronology to explore the impact of rising sea level on the annual growth of Juniperus virginiana (the Eastern red cedar) at the St. Jones component of the Delaware National Estuarine Research Reserve in Dover, DE. Chronologies from low and high elevations were developed, and a difference chronology (high–low) was generated. A rapid field assessment of tree stress indicated greater stress in low elevation trees, and low elevation soil tests showed higher soil moisture and salt content compared to samples from high elevation. Ring width indices were analyzed in relation to water level, precipitation, the Standardized Precipitation Evapotranspiration Index, and temperature, with Pearson’s correlation analysis. Trees growing at low elevation showed greater climate sensitivity and responded favorably to cool, wet summers. Over time, correlations between growth and climate variables decreased, while negative correlations with tidal water level increased—a pattern that presented nearly a decade earlier in the low elevation system. Given the widespread distribution of the Eastern red cedar and its sensitivity to changes in sea level, this species may be particularly useful as a sentinel of change in coastal landscapes as sea levels rise.