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Low Elevations (low + elevation)
Selected AbstractsSpatial patterns of simulated transpiration response to climate variability in a snow dominated mountain ecosystemHYDROLOGICAL PROCESSES, Issue 18 2008Lindsey Christensen Abstract Transpiration is an important component of soil water storage and stream-flow and is linked with ecosystem productivity, species distribution, and ecosystem health. In mountain environments, complex topography creates heterogeneity in key controls on transpiration as well as logistical challenges for collecting representative measurements. In these settings, ecosystem models can be used to account for variation in space and time of the dominant controls on transpiration and provide estimates of transpiration patterns and their sensitivity to climate variability and change. The Regional Hydro-Ecological Simulation System (RHESSys) model was used to assess elevational differences in sensitivity of transpiration rates to the spatiotemporal variability of climate variables across the Upper Merced River watershed, Yosemite Valley, California, USA. At the basin scale, predicted annual transpiration was lowest in driest and wettest years, and greatest in moderate precipitation years (R2 = 0·32 and 0·29, based on polynomial regression of maximum snow depth and annual precipitation, respectively). At finer spatial scales, responsiveness of transpiration rates to climate differed along an elevational gradient. Low elevations (1200,1800 m) showed little interannual variation in transpiration due to topographically controlled high soil moistures along the river corridor. Annual conifer stand transpiration at intermediate elevations (1800,2150 m) responded more strongly to precipitation, resulting in a unimodal relationship between transpiration and precipitation where highest transpiration occurred during moderate precipitation levels, regardless of annual air temperatures. Higher elevations (2150,2600 m) maintained this trend, but air temperature sensitivities were greater. At these elevations, snowfall provides enough moisture for growth, and increased temperatures influenced transpiration. Transpiration at the highest elevations (2600,4000 m) showed strong sensitivity to air temperature, little sensitivity to precipitation. Model results suggest elevational differences in vegetation water use and sensitivity to climate were significant and will likely play a key role in controlling responses and vulnerability of Sierra Nevada ecosystems to climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] Effects of the Little Ice Age on avalanche boulder tongues in the French Alps (Massif des Ecrins)EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2004Vincent Jomelli Abstract Lichens of the subspecies Rhizocarpon geographicum s.l were measured on 25 avalanche boulder tongues in the Massif des Ecrins to elucidate the Little Ice Age history of avalanche activity. Results show: (1) an increase of lichen size from the median to the distal zone of deposits, and a decrease from the edges to the centre; (2) three types of lichen settlement. From the uppermost to the median zone, lichens are absent, because avalanche activity is very active. Down-slope, lichens occur in two different zones: the median zone is colonized by 5,20 mm size lichens on sides of blocks protected from the abrasional action of avalanches, while in the distal zone lichen diameters are largest (>30 mm) and occur on all sides of the blocks. The spatial distribution of the lichens and their size according to elevation make it possible to distinguish different phases during which avalanche activity has increased. At high elevation, the avalanche activity was at a maximum before ad 1650 and between ad 1730 and 1830. During these two periods avalanches had suf,cient magnitude to reach the basal zone of the deposits. At low elevation since ad 1650 the magnitude and frequency of avalanches have declined. Copyright © 2004 John Wiley & Sons, Ltd. [source] The importance of interspecific interactions for breeding-site selection: peregrine falcons seek proximity to raven nestsECOGRAPHY, Issue 6 2004Fabrizio Sergio The advent of GIS is initiating a rapid increase in the utilization of wildlife-habitat models as tools for species and habitat management. However, such models rarely include estimates of interspecific interactions among explanatory variables. We tested the importance of such variables by using the peregrine falcon Falco peregrinus, a medium-sized raptor frequently reported to be affected by heterospecifics, as a model species. In an Alpine population, compared to random locations, peregrines selected breeding sites farther from conspecifics, on taller cliffs, with higher availability of farmland and closer to raven Corvus corax nests. Within suitable habitat, peregrines selected sites near ravens and far from elevations associated with golden eagle Aquila chrysaetos nests. Productivity increased with cliff size, farmland availability (rich in the local main prey) and with proximity to ravens, suggesting that the observed choices were adaptive. Finally, at the regional level, peregrine density peaked at low elevation and was positively associated with raven density. The results suggested an active breeding association of peregrines with ravens, which may provide early-warning cues against predators and safe alternative nest-sites. They also confirmed the importance of including estimates of interspecific interactions among explanatory variables, which may: 1) make models more realistic; 2) increase their predictive power by lowering unexplained variance due to unmeasured factors; 3) provide unexpected results such as the cryptic, large-scale breeding association of our study; and 4) stimulate further hypothesis formulation and testing, ultimately leading to deeper ecological knowledge of the study system. [source] Costs and benefits of breeding in human-altered landscapes for the Eagle Owl Bubo buboIBIS, Issue 4 2002Luigi Marchesi We studied a population of 23,25 Eagle Owl Bubo bubo pairs between 1994 and 2000 in a 1330-km2 study plot in the central-eastern Italian Alps. Compared to random sites, territories were located at lower elevation and closer to intensively cultivated-urbanized valley floors. Early laying was associated with low elevation and negatively affected productivity. Diet was dominated by rats, hedgehogs and dormice (n = 978 prey items), all of them typical of low-elevation habitats. Higher productivity was associated with a higher proportion of rats in the diet of individual pairs. Low availability of rats resulted in a more diverse diet, in turn associated with low productivity. Territories were occupied every year in a non-random fashion, and those most occupied were characterized by higher productivity and higher occurrence of the favoured prey types in the diet, suggesting they were of superior quality. Eagle Owls also paid a cost associated with nesting near human-altered habitats: the main cause of mortality reported to local authorities was electrocution. This is an increasing cause of death for many European populations and may be a cause for conservation concern. Human persecution is also an important cause of mortality in some parts of the European range. Apart from such costs, the study population appeared to have adapted well to the proximity of humans: estimates of density and productivity were comparable to those recorded elsewhere in Europe. The pattern found in our population also held at higher spatial scales: data from 17 European populations showed density to be highest in low-elevation, human-altered landscapes. [source] Breeding in high-elevation habitat results in shift to slower life-history strategy within a single speciesJOURNAL OF ANIMAL ECOLOGY, Issue 2 2009H. Bears Summary 1Elevational gradients create environmental variation that is hypothesized to promote variation in life-history strategies. We tested whether differences in life-history strategies were associated with elevation in a songbird, the dark-eyed junco (Junco hyemalis; Aves; A.O.U. 1998). 2We monitored birds in four replicated sites per elevation, at 2000 m a.s.l. (high elevation) and 1000 m a.s.l. (low elevation), in the Rocky Mountains of Canada. 3Over 5 years, we measured the following traits and vital rates: egg-laying schedules, morphological indicators of reproductive stage, seasonal reproductive success, indicators of competitive class (age, size, arrival time), and survival rates. 4We found two main patterns: with an increase in breeding elevation, dark-eyed juncos delayed the development of structures necessary for reproduction (e.g. cloacal protuberance in males) and reduced the duration of their reproductive period to less than half of the time used by low-elevation birds; and 5Juncos at high-elevation sites had 55,61% lower annual reproductive success and 15 to 20% higher survival rates. While adult juncos at high elevations produced fewer offspring, those offspring were in better condition. Proportions of age and size classes in high- compared to low-elevation populations were similar, suggesting that a life-history trade-off is present, rather than competition forcing inferior competitors to breed in a peripheral habitat. The apparent trade-off between reproduction and survival corresponded to a shorter period of favourable weather and available food in high- compared to low-elevation habitats. 6Thus, elevation had a strong influence on life-history characteristics of a single species over a short spatial distance, suggesting a shift in life history from a high reproductive strategy at lower elevations to a high survivor strategy at high elevations. 7This is the first paper to show a shift in avian life-history strategies along an elevational gradient (in both genders, of multiple age classes) when region (latitude) and phylogenetic histories are controlled for. [source] Being high is better: effects of elevation and habitat on arctic ground squirrel demographyOIKOS, Issue 2 2005Elizabeth A. Gillis We investigated the effect of local environment on the demography and population dynamics of arctic ground squirrels (Spermophilus parryii plesius) by comparing reproduction, survival, and population trends of squirrels living in low elevation boreal forest and high elevation alpine tundra sites in southwestern Yukon Territory, Canada. Contrary to the trend for most birds and mammals, reproduction was significantly lower at the lower elevation and females living at higher elevation did not delay the age at which they first reproduced. Even though survival in the boreal forest was lower in summer than in the alpine, it was higher over winter so annual adult female survival was similar between sites. Sensitivity analysis of model parameters revealed that in the forest, population growth rate (,) was most sensitive to small changes in adult active season survival whereas for the alpine population, , was most sensitive to changes in juvenile winter survival. In their respective habitats, these parameters also showed high year to year variation and thus contributed greatly to the population trends observed. Even though ground squirrels persisted in the boreal forest, the measured demographic rates indicate the forest was sink habitat (,<1) and may have relied on nearby grassy meadows for immigrants. In contrast, the alpine habitat maintained a ground squirrel population in the absence of immigration (,=1). The variation in demographic rates between ground squirrels living at high and low elevation may arise from phenotypic responses of squirrels to different habitat structure. Arctic ground squirrels rely on sight to detect predators from a safe distance, and the boreal forest, with its lower visibility and higher predator density, appears to be suboptimal habitat. [source] Fruit load and elevation affect ethylene biosynthesis and action in apple fruit (Malus domestica L. Borkh) during development, maturation and ripeningPLANT CELL & ENVIRONMENT, Issue 11 2007VALERIANO DAL CIN ABSTRACT The influence of internal and external factors such as tree fruit load and elevation on ethylene biosynthesis and action was assessed during apple fruit development and ripening. Ethylene biosynthesis, as well as transcript accumulation of the hormone biosynthetic enzymes (MdACS1 and MdACO1), receptors (MdETR1 and MdERS1) and an element of the transduction pathway (MdCTR1), were evaluated in apples borne by trees with high (HL) and low (LL) fruit load. Orchards were located in two localities differing in elevation and season day degree sum. These parameters significantly affected the date of bloom and commercial harvest, and the length of the fruit developmental cycle. Trees from the low elevation (LE) bloomed and the fruit ripened earlier than those from the high elevation (HE), displaying also a shortened fruit developmental cycle. Dynamics of ethylene evolution was apparently not affected by elevation. The onset of ethylene evolution started 130 days after bloom (DAB) at both elevations. During early ripening, fruits from LL trees produced significantly more ethylene than those from HL trees. Expression analysis of MdACS1, MdACO1 and MdERS1 indicated that the transcript accumulation well correlated with ethylene evolution. MdCTR1 was expressed at constant level throughout fruit growth and development up to 130 DAB, thereafter, the transcript accumulation decreased up to commercial harvest, concurrently with the onset of ethylene evolution. [source] Diversity of insect-induced galls along a temperature, rainfall gradient in the tropical savannah region of the Northern Territory, AustraliaAUSTRAL ECOLOGY, Issue 4 2000K. R. Blanche Abstract Evidence regarding the effect of temperature and rainfall on gall-inducing insects is contradictory: some studies indicate that species richness of gall-inducing insects increases as environments become hotter and drier, while others suggest that these factors have no effect. The role of plant species richness in determining species richness of gall-inducing insects is also controversial. These apparent inconsistencies may prove to be due to the influence of soil fertility and the uneven distribution of gall-inducing insect species among plant taxa. The current study tested hypotheses about determinants of gall-inducing insect species richness in a way different to previous studies. The number of gall-inducing insect species, and the proportion of species with completely enclosed galls (more likely to give protection against heat stress and desiccation), were measured in replicate plots at five locations along a 500-km N-S transect in the seasonal tropics of the Northern Territory, Australia. There is a strong temperature,rainfall gradient along this transect during the wet season. Plant species lists had already been compiled for each collection plot. All plots were at low elevation in eucalypt savannah growing on infertile soils. There was no evidence to suggest that hot, dry environments in Australia have more gall-inducing insect species than cooler, wetter environments, or that degree of enclosure of galls is related to protecting insects from heat stress and desiccation. The variable number of gall-inducing insect species on galled plant species meant that plant species richness did not influence gall species richness. Confirmation is still required that low soil fertility does not mask temperature,rainfall effects and that galls in the study region are occupied predominantly in the wet season, when the temperature,rainfall gradient is most marked. [source] Interpretation of observed fluid potential patterns in a deep sedimentary basin under tectonic compression: Hungarian Great Plain, Pannonian BasinGEOFLUIDS (ELECTRONIC), Issue 1 2001J. Tóth Abstract The , 40 000 km2 Hungarian Great Plain portion of the Pannonian Basin consists of a basin fill of 100 m to more than 7000 m thick semi- to unconsolidated marine, deltaic, lacustrine and fluviatile clastic sediments of Neogene age, resting on a strongly tectonized Pre-Neogene basement of horst-and-graben topography of a relief in excess of 5000 m. The basement is built of a great variety of brittle rocks, including flysch, carbonates and metamorphics. The relatively continuous Endr,d Aquitard, with a permeability of less than 1 md (10,15 m2) and a depth varying between 500 and 5000 m, divides the basin's rock framework into upper and lower sequences of highly permeable rock units, whose permeabilities range from a few tens to several thousands of millidarcy. Subsurface fluid potential and flow fields were inferred from 16 192 water level and pore pressure measurements using three methods of representation: pressure,elevation profiles; hydraulic head maps; and hydraulic cross-sections. Pressure,elevation profiles were constructed for eight areas. Typically, they start from the surface with a straight-line segment of a hydrostatic gradient (,st = 9.8067 MPa km,1) and extend to depths of 1400,2500 m. At high surface elevations, the gradient is slightly smaller than hydrostatic, while at low elevations it is slightly greater. At greater depths, both the pressures and their vertical gradients are uniformly superhydrostatic. The transition to the overpressured depths may be gradual, with a gradient of ,dyn = 10,15 MPa km,1 over a vertical distance of 400,1000 m, or abrupt, with a pressure jump of up to 10 MPa km,1 over less than 100 m and a gradient of ,dyn > 20 MPa km,1. According to the hydraulic head maps for 13 100,500 m thick horizontal slices of the rock framework, the fluid potential in the near-surface domains declines with depth beneath positive topographic features, but it increases beneath depressions. The approximate boundary between these hydraulically contrasting regions is the 100 m elevation contour line in the Duna,Tisza interfluve, and the 100,110 m contours in the Nyírség uplands. Below depths of ,,600 m, islets of superhydrostatic heads develop which grow in number, areal extent and height as the depth increases; hydraulic heads may exceed 3000 m locally. A hydraulic head ,escarpment' appears gradually in the elevation range of ,,1000 to ,,2800 m along an arcuate line which tracks a major regional fault zone striking NE,SW: heads drop stepwise by several hundred metres, at places 2000 m, from its north and west sides to the south and east. The escarpment forms a ,fluid potential bank' between a ,fluid potential highland' (500,2500 m) to the north and west, and a ,fluid potential basin' (100,500 m) to the south and east. A ,potential island' rises 1000 m high above this basin further south. According to four vertical hydraulic sections, groundwater flow is controlled by the topography in the upper 200,1700 m of the basin; the driving force is orientated downwards beneath the highlands and upwards beneath the lowlands. However, it is directed uniformly upwards at greater depths. The transition between the two regimes may be gradual or abrupt, as indicated by wide or dense spacing of the hydraulic head contours, respectively. Pressure ,plumes' or ,ridges' may protrude to shallow depths along faults originating in the basement. The basement horsts appear to be overpressured relative to the intervening grabens. The principal thesis of this paper is that the two main driving forces of fluid flow in the basin are gravitation, due to elevation differences of the topographic relief, and tectonic compression. The flow field is unconfined in the gravitational regime, whereas it is confined in the compressional regime. The nature and geometry of the fluid potential field between the two regimes are controlled by the sedimentary and structural features of the rock units in that domain, characterized by highly permeable and localized sedimentary windows, conductive faults and fracture zones. The transition between the two potential fields can be gradual or abrupt in the vertical, and island-like or ridge-like in plan view. The depth of the boundary zone can vary between 400 and 2000 m. Recharge to the gravitational regime is inferred to occur from infiltrating precipitation water, whereas that to the confined regime is from pore volume reduction due to the basement's tectonic compression. [source] Global patterns of genetic variation in plant species along vertical and horizontal gradients on mountainsGLOBAL ECOLOGY, Issue 2 2008Takafumi Ohsawa ABSTRACT Aim To understand global patterns of genetic variation in plant species on mountains and to consider the significance of mountains for the genetic structure and evolution of plant species. Location Global. Methods We review published studies. Results Genetic diversity within populations can vary along altitudinal gradients in one of four patterns. Eleven of 42 cited studies (26% of the total) found that populations at intermediate altitudes have greater diversity than populations at lower and higher altitudes. This is because the geographically central populations are under optimal environmental conditions, whereas the peripheral populations are in suboptimal situations. The second pattern, indicating that higher populations have less diversity than lower populations, was found in eight studies (19%). The third pattern, indicating that lower populations have lower diversity than higher populations, was found in 10 studies (24%). In 12 studies (29%), the intrapopulation genetic variation was found to be unaffected by altitude. Evidence of altitudinal differentiation was found in more than half of these studies, based on measurements of a range of variables including genome size, number of chromosomes or a range of loci using molecular markers. Furthermore, great variation has been found in phenotypes among populations at different altitudes in situ and in common garden experiments, even in cases where there was no associated variation in molecular composition. Mountains can be genetic barriers for species that are distributed at low elevations, but they can also provide pathways for species that occupy high-elevation habitats. [Correction added after publication 9 October 2007: ,less diversity' changed to ,greater diversity' in the second sentence of the Results section of the Abstract] Main conclusions Genetic diversity within populations can vary along altitudinal gradients as a result of several factors. The results highlight the importance of phenotypic examinations in detecting altitudinal differences. The influence of mountain ridges on genetic differentiation varies depending, inter alia, on the elevation at which the species occurs. Based on these findings, zoning by altitudes or ridges would be helpful for the conservation of tree populations with the onset of global warming. [source] Combined effects of climate and biotic interactions on the elevational range of a phytophagous insectJOURNAL OF ANIMAL ECOLOGY, Issue 1 2008Richard M. Merrill Summary 1The ranges of many species have expanded in cool regions but contracted at warm margins in response to recent climate warming, but the mechanisms behind such changes remain unclear. Particular debate concerns the roles of direct climatic limitation vs. the effects of interacting species in explaining the location of low latitude or low elevation range margins. 2The mountains of the Sierra de Guadarrama (central Spain) include both cool and warm range margins for the black-veined white butterfly, Aporia crataegi, which has disappeared from low elevations since the 1970s without colonizing the highest elevations. 3We found that the current upper elevation limit to A. crataegi's distribution coincided closely with that of its host plants, but that the species was absent from elevations below 900 m, even where host plants were present. The density of A. crataegi per host plant increased with elevation, but overall abundance of the species declined at high elevations where host plants were rare. 4The flight period of A. crataegi was later at higher elevations, meaning that butterflies in higher populations flew at hotter times of year; nevertheless, daytime temperatures for the month of peak flight decreased by 6·2 °C per 1 km increase in elevation. 5At higher elevations A. crataegi eggs were laid on the south side of host plants (expected to correspond to hotter microclimates), whereas at lower sites the (cooler) north side of plants was selected. Field transplant experiments showed that egg survival increased with elevation. 6Climatic limitation is the most likely explanation for the low elevation range margin of A. crataegi, whereas the absence of host plants from high elevations sets the upper limit. This contrasts with the frequent assumption that biotic interactions typically determine warm range margins, and thermal limitation cool margins. 7Studies that have modelled distribution changes in response to climate change may have underestimated declines for many specialist species, because range contractions will be exacerbated by mismatch between the future distribution of suitable climate space and the availability of resources such as host plants. [source] Relationships between expanding pinyon,juniper cover and topography in the central Great Basin, NevadaJOURNAL OF BIOGEOGRAPHY, Issue 5 2008Bethany A. Bradley Abstract Aim, Increasing geographical range and density of conifers is a major form of land-cover change in the western United States, affecting fire frequency, biogeochemistry and possibly biodiversity. However, the extent and magnitude of the change are uncertain. This study aimed to quantify the relationship between changing conifer cover and topography. Location, The central Great Basin in the state of Nevada, USA. Methods, We used a series of Landsat Thematic Mapper satellite images from 1986, 1995 and 2005 to map change in pinyon,juniper woodlands (Pinus monophylla, Juniperus spp.) in the montane central Great Basin of Nevada. We derived fractional greenness for each year using spectral mixture analysis and identified all areas with an above average increase in greenness from 1986 to 1995 and 1995 to 2005. Results, Areas with high fractional greenness in 2005 were most likely to occur at elevations between 2200 and 2600 m a.s.l. Increases in fractional greenness between 1986 and 2005 were most likely to occur at elevations below 2000 m a.s.l. and on south-facing slopes. However, relationships between elevation and increasing greenness for individual mountain ranges varied considerably from the average trend. Fractional greenness values measured by Landsat suggest that the majority of pinyon,juniper woodlands have not reached their maximum potential tree cover. Main conclusions, Expansion of pinyon,juniper at low elevations and on south-facing slopes probably reflects increasing precipitation in the 20th century, higher water use efficiency caused by increasing atmospheric CO2 in the late 20th century and livestock grazing at the interface between shrubland and woodland. Identification of the spatial relationships between changing fractional greenness of pinyon,juniper woodland and topography can inform regional land management and improve projections of long-term ecosystem change. [source] Patterns in diversity of anurans along an elevational gradient in the Western Ghats, South IndiaJOURNAL OF BIOGEOGRAPHY, Issue 5 2007Rohit Naniwadekar Abstract 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. [source] Post-fire tree establishment patterns at the alpine treeline ecotone: Mount Rainier National Park, Washington, USAJOURNAL OF VEGETATION SCIENCE, Issue 1 2009Kirk M. Stueve Abstract Questions: Does tree establishment: (1) occur at a treeline depressed by fire, (2) cause the forest line to ascend upslope, and/or (3) alter landscape heterogeneity? (4) What abiotic and biotic local site conditions are most important in structuring establishment patterns? (5) Does the abiotic setting become more important with increasing upslope distance from the forest line? Location: Western slopes of Mount Rainier, USA. Methods: We performed classification analysis of 1970 satellite imagery and 2003 aerial photography to delineate establishment. Local site conditions were calculated from a LIDAR-based DEM, ancillary climate data, and 1970 tree locations in a GIS. We used logistic regression on a spatially weighted landscape matrix to rank variables. Results: Considerable establishment after 1970 caused forest line elevation to increase over 150 m in specific locations. Landscape heterogeneity increased with distance from the 1970 forest line. At a broad spatial context, we found establishment was most common near existing trees (0-50 m) and at low elevations (1250-1350 m). Slope aspect (W, NW, N, NE, and E), slope angle (40-60°), and other abiotic factors emerged as important predictors of establishment with increasing upslope distance from the forest line to restricted spatial extents. Conclusions: Favorable climatic conditions likely triggered widespread tree establishment. Readily available seed probably enhanced establishment rates near sexually mature trees, particularly in the less stressful environment at low elevations. The mass effect of nearly ubiquitous establishment in these areas may have obscured the importance of the abiotic setting to restricted spatial extents. Topographic variability apparently produced favorable sites that facilitated opportunistic establishment with increasing upslope distance from the forest line, thereby enabling additional trees to invade the alpine tundra. [source] Natural avalanche disturbance shapes plant diversity and species composition in subalpine forest beltJOURNAL OF VEGETATION SCIENCE, Issue 5 2007Christian Rixen Abstract Background: Disturbances by avalanches have created unique habitats for animals and plants in subalpine ecosystems worldwide, but at the same time avalanches can pose a major threat to humans. Thus, avalanches are suppressed by means of avalanche barriers to protect settlements and infrastructures in populated areas of the European Alps. As a consequence, the disturbance regime in avalanche tracks has fundamentally changed. Methods: In the present study we address ecological consequences of avalanche suppression on plant diversity. We analysed plant diversity and species composition in recent and old avalanche tracks with and without avalanche suppression and in undisturbed adjacent forests at high and low elevations. Results: The number of species was higher in both active and inactive avalanche tracks as compared to undisturbed subalpine forest. The species composition indicated a wider range of ecological niches in active than in inactive avalanche tracks. The vegetation from active tracks showed lower indicator values for temperature and nitrogen availability. The proportion of alpine species was lower in formerly active tracks. Conclusions: The conditions that exist in active avalanche tracks increase plant diversity in relation to undisturbed forest. In the few decades following avalanche suppression, species composition changes in tracks from which avalanches have been excluded. Continued suppression of avalanche disturbance may lead to a decline in plant and habitat diversity. Avalanche disturbance can exert an important influence on the biodiversity of subalpine forests and provide important habitats. Anthropogenic changes in the natural regime of avalanche disturbance are likely to contribute significantly to future landscape changes in subalpine forests. [source] Rice versus fish revisited: On the integrated management of floodplain resources in BangladeshNATURAL RESOURCES FORUM, Issue 2 2004Bhavani Shankar Abstract Disproportionately little attention has been paid to the dry season trade-off between rice and (inland capture) fish production on the floodplains of Bangladesh, compared to the same trade-off during the flood season. As the rural economy grows increasingly dominated by dry-season irrigated rice production, and floodplain land and water come under ever-increasing pressure during the dry winter months, there is an urgent need to focus attention on these dry months that are so critical to the survival and propagation of the floodplain resident fish, and to the poor people that depend on these fish for their livelihood. This article examines three important dry-season natural resource constraints to floodplain livelihoods in Bangladesh, and finds a common factor at the heart of all three: rice cultivation on lands at low and very low elevations. The article articulates the system interlinkages that bind these constraints and the long-run trend towards irrigated rice cropping on lower-lying lands, and suggests a management approach based on locally tailored strategies to arrest this trend. Apart from its direct relevance to the floodplains of Bangladesh, which support more than 100 million people, these lessons have relevance for river floodplain systems elsewhere in the developing world, notably the Mekong Delta. [source] Small-scale variation in growing season length affects size structure of scarlet monkeyflowerOIKOS, Issue 1 2004Jennifer L. Williams Growing season length can control plant size over altitudinal and biogeographic scales, but its effect at the scale of meters is largely unexplored. Within the riparian zone of a northern California river, scarlet monkeyflower, Mimulus cardinalis, grows significantly larger at sites high in the channel as compared to sites low in the channel, and even larger where tributaries meet the main stem of the river. We explored the hypothesis that markedly different growing season length controls this size variation. Due to the very gradual retreat of the water level following winter flooding, emergence time is three months longer for plants growing at tributary confluences than for plants growing at low elevations in the channel. Consistent with the growing season length hypothesis, we found no difference in transplant growth between river and tributary confluence sites in an experiment where we equalized growing season length at these locations. Moreover, a second experiment showed that individuals planted earlier in the year gain a distinct size advantage over those planted later, even though growing conditions are less ideal. These results suggest that emergence time may be a key determinant of plant size structure along rivers, an important result considering forecasted variation in water flows with climate change. [source] Effect of Hydrologic Restoration and Lonicera maackii Removal on Herbaceous Understory Vegetation in a Bottomland Hardwood ForestRESTORATION ECOLOGY, Issue 3 2008Rebecca M. Swab Abstract Amur honeysuckle (Lonicera maackii (Rupr.) Herder), a large deciduous shrub from China, has invaded many forests in eastern/central United States. The species was removed by cutting and herbicide application from a recently hydrologically restored section of a bottomland hardwood forest in central Ohio, and the response of understory plants, especially herbaceous species, was measured. Plots were established in uncleared and cleared sections, and percent cover of each herbaceous understory species was estimated monthly. One season after several years of Lonicera removal efforts, no significant association was discovered between percentage of Lonicera cover and total understory species abundance. There was, however, a direct correlation between elevation and honeysuckle abundance; L. maackii abundance was negatively associated with low elevations, likely due to hydrologic factors. Plant species diversity (H) and richness (s) increased with elevation but were not significantly different on plots with honeysuckle removal (H = 0.86 ± 0.08 vs. 0.78 ± 0.09 and s = 4.4 ± 0.19 vs. 4.2 ± 0.2 species/m2, respectively) despite the fact that understory light levels measured by densiometer were significantly higher (,= 0.003) in cleared versus uncleared sections. Native and invasive species were found in similar proportions in the two sections, and significant sprouting and regrowth of L. maackii were observed throughout the cleared section. Although the removal of L. maackii altered the characteristics of the plant species assemblage, the value of this management remains questionable in the years immediately following treatment. [source] | |||||||||||||