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Moisture Gradient (moisture + gradient)
Selected AbstractsAnt Activity along Moisture Gradients in a Neotropical Forest,BIOTROPICA, Issue 4a 2000Michael Kaspari ABSTRACT Insect activity often tracks moisture gradients. We studied ant activity, size, and diversity along three moisture gradients in a Panamanian rain forest. Ant activity at baits increased by 25 percent from the dry to the wet season, and > 200 percent on a topographical gradient from a ravine to an exposed plateau. Activity varied little from day to night. Three microhabitats,tree trunk, shrub, and litter,showed different responses to these three gradients. The size distribution of the species pool (N= 63) was right skewed, but the average size of ants at a bait was strongly bimodal. Ants active in moister times and places were not significantly smaller. We suggest that gradients of desiccation risk and food availability were the two most likely causes of these patterns. Two temporal niche axes (daily and seasonal) showed little species specialization, but half of the common species could be categorized as litter or plant microhabitat specialists. RESUMEN Nosotros estudiamos actividad de hormiga, tamaño, y diversidad en 4 microhabitats a lo largo de tres gradientes de humedad en un bosque Panameño. La actividad de hormiga aumentada por 25 percent desde la seca a la temporada mojada, y > 200 percent sobre un gradiente topográfico desde un barranco a una meseta expuesta. La actividad varió poco desde el día a la noche. Tres microhabitats,tronco de árbol, arbusto, y la hojarasca-mostró respuestas diferentes a estos tres de gradientes. El tamaño la distribución de las especies combina (N= 63) tuvo razón skewed, pero el tamaño promedio de hormigas a una carnada era fuertemente bimodal. Las hormigas activas en los lugares y veces más húmedas no eran significativamente menores. Nosotros sugerimos que los gradientes de desecamiento arriesgan y la disponibilidad alimentaria son los dos muy probables ocasiona de estos modelos. Dos temporal los nichos (diarios y estacionales) mostraron poca especialización de especies. La mitad de las especies comunes podría categorizarse como hojarasca o plantada microhabitat especialistas. [source] Patterns of abundance of fire ants and native ants in a native ecosystemECOLOGICAL ENTOMOLOGY, Issue 4 2009KATHARINE L. STUBLE Abstract 1.,This correlational study examines the relationship between the red imported fire ant (Solenopsis invicta) and native ants in a longleaf pine savanna. Fire ants are frequently associated with a decline in native ants throughout the invaded range, but fire ant invasion is often coupled with habitat disturbance. Invasion of fire ants into the longleaf pine savanna provides an opportunity to examine the structure of the ant community in the absence of habitat disturbance. 2.,Pitfall trapping was conducted within the longleaf pine savanna as well as across a naturally occurring soil moisture gradient, in plots that had been artificially watered. 3.,Species richness did not vary as a function of fire ant density. There was an inverse relationship between native ant density and fire ant density, but this abundance pattern does not necessarily imply a causal link between fire ant invasion and native ant decline. For individual species, fire ant densities were negatively correlated with the densities of only two native ant species, including Solenopsis carolinensis, a native species that potentially limits the invasion of fire ants. Additionally, fire ants and native ants respond differently to soil moisture, with native ants favouring drier conditions than fire ants. 4.,The possible exclusion of fire ants by some native ants, as well as differences in habitat preferences, provide alternative explanations for the frequently observed negative correlation between fire ants and native ants. [source] Canopy structure in savannas along a moisture gradient on Kalahari sandsGLOBAL CHANGE BIOLOGY, Issue 3 2004Robert J. Scholes Abstract Measurements of tree canopy architecture were made at six savanna sites on deep, sandy soils, along a gradient of increasing aridity. There was substantial variation in the leaf area estimated within each site, using the same sample frame, but different measurement techniques. The trends in canopy properties in relation to the aridity gradient were consistent, regardless of the technique used for estimating the properties. The effective plant area index for the tree canopy (the sum of the stem area index and the leaf area index (LAI)) declined from around 2 to around 0.8 m2 m,2 over a gradient of mean annual rainfall from 1000 to 350 mm. Stems contributed 2,5% of the tree canopy plant area index. Since the tree canopy cover decreased from 50% to 20% over this aridity range, the leaf area index within the area covered by tree canopies remained fairly constant at 3,4 m2 m,2. Tree leaves tended from a horizontal orientation to a more random orientation as the aridity increased. On the same gradient, the leaf minor axis dimension decreased from around 30 mm to around 3 mm, and the mean specific leaf area decreased from 14 to 5 m2 kgha,1. There was good agreement between LAI observed in the field using a line ceptometer and the LAI inferred by the MODIS sensor on the Terra satellite platform, 2 months later in the same season. [source] Positive and negative effects of livestock grazing on plant diversity of Mongolian nomadic pasturelands along a slope with soil moisture gradientGRASSLAND SCIENCE, Issue 3 2009Noboru Fujita Abstract To examine different effects of herbivorous large mammals' grazing pressure on plant diversity along a slope in a Mongolian nomadic pasture, we compared species richness, Simpson's index of diversity, and the total plant coverage of plants between protected pasture from livestock grazing and grazed pasture on the near ridge, upper slope, lower slope, foot slope and valley bottom. The species richness and Simpson's index of diversity decreased and the total coverage increased downwardly with increase in pasture soil moisture along the slope. The species richness of the protected pasture decreased, changed little, and increased on the near ridge and the upper slope, the lower slope and the foot slope, and the valley bottom, respectively. Simpson's index of diversity of the protected pasture decreased compared with the grazed pasture only on the valley bottom. The total coverage became lower in the grazed pasture. As the reason for our results, we discuss positive and negative effects of livestock grazing on the species diversity of plants. The positive effect is shown on the valley bottom, where soil moisture and plant growth becomes high with the total coverage over 100%, due to relaxing indirectly the competitive exclusion among plants due to the grazing of dominant plants. The negative effect is obtained on the near ridge and the upper slope, where the soil moisture and the plant growth are low, because of elimination of some plants from the pasture by direct grazing damage. [source] Climatic limits for the present distribution of beech (Fagus L.) species in the worldJOURNAL OF BIOGEOGRAPHY, Issue 10 2006Jingyun Fang Abstract Aim, Beech (Fagus L., Fagaceae) species are representative trees of temperate deciduous broadleaf forests in the Northern Hemisphere. We focus on the distributional limits of beech species, in particular on identifying climatic factors associated with their present range limits. Location, Beech species occur in East Asia, Europe and West Asia, and North America. We collated information on both the southern and northern range limits and the lower and upper elevational limits for beech species in each region. Methods, In total, 292 lower/southern limit and 310 upper/northern limit sites with available climatic data for all 11 extant beech species were collected by reviewing the literature, and 13 climatic variables were estimated for each site from climate normals at nearby stations. We used principal components analysis (PCA) to detect climatic variables most strongly associated with the distribution of beech species and to compare the climatic spaces for the different beech species. Results, Statistics for thermal and moisture climatic conditions at the lower/southern and upper/northern limits of all world beech species are presented. The first two PCA components accounted for 70% and 68% of the overall variance in lower/southern and upper/northern range limits, respectively. The first PCA axis represented a thermal gradient, and the second a moisture gradient associated with the world-wide distribution pattern of beech species. Among thermal variables, growing season warmth was most important for beech distribution, but winter low temperature (coldness and mean temperature for the coldest month) and climatic continentality were also coupled with beech occurrence. The moisture gradient, indicated by precipitation and moisture indices, showed regional differences. American beech had the widest thermal range, Japanese beeches the most narrow; European beeches occurred in the driest climate, Japanese beeches the most humid. Climatic spaces for Chinese beech species were between those of American and European species. Main conclusions, The distributional limits of beech species were primarily associated with thermal factors, but moisture regime also played a role. There were some regional differences in the climatic correlates of distribution. The growing season temperature regime was most important in explaining distribution of Chinese beeches, whilst their northward distribution was mainly limited by shortage of precipitation. In Japan, distribution limits of beech species were correlated with summer temperature, but the local dominance of beech was likely to be dependent on snowfall and winter low temperature. High summer temperature was probably a limiting factor for southward extension of American beech, while growing season warmth seemed critical for its northward distribution. Although the present distribution of beech species corresponded well to the contemporary climate in most areas, climatic factors could not account for some distributions, e. g., that of F. mexicana compared to its close relative F. grandifolia. It is likely that historical factors play a secondary role in determining the present distribution of beech species. The lack of F. grandifolia on the island of Newfoundland, Canada, may be due to inadequate growing season warmth. Similarly, the northerly distribution of beech in Britain has not reached its potential limit, perhaps due to insufficient time since deglaciation to expand its range. [source] Spatial and temporal analysis of vegetation mosaics for conservation: poor fen communities in a Cornish valley mireJOURNAL OF BIOGEOGRAPHY, Issue 9 2003E. J. Southall Abstract Aim Biogeographers increasingly realize the importance of seeing plant communities as spatial mosaics and understanding the spatial and temporal heterogeneity of a site is often a key to successful conservation. The aim of this paper is to examine the approaches to the description and analysis of spatial and temporal variation in sub-communities within patch mosaics of vegetation in order to inform conservation management. The activities of the tin streaming industry in Cornwall over the last century have created a highly varied mosaic of poor fen vegetation on Goss Moor National Nature Reserve (NNR). The wetland mosaics comprise dry hummocks and different sized wet pools. The size and depth of the pools determines the rate and type of vegetation that develops, as does the nature of boundary or edge. The ergodic hypothesis is used to describe the various plant sub-communities and their boundaries to identify pathways of hydroseral succession. A further aim was to test the use of Ellenberg Indicator (EI) values as a tool for the rapid description of spatial and temporal environmental change on wetland sites with a view to their management. Location Goss Moor National Nature Reserve, Cornwall, UK. Methods An extensive survey of the whole wetland complex was undertaken to identify patches of poor fen vegetation containing Potentilla palustris (L.) Scop. and Menyanthes trifoliata L. At each patch, species abundance data were collected as well as associated environmental information such as depth of the organic layer and standing water depth, patch location, patch size and boundary type. The plant sub-communities present were defined using techniques of numerical classification [two-way indicator species analysis (twinspan)] and ordination [detrended correspondence analysis (DCA)] and these were ordered using the ergodic hypothesis in order to characterize the stages of the hydrosere. Floristic and environmental relationships were examined using canonical correspondence analysis (CCA). Further environmental differences between the poor fen sub-community types were characterized by weighted EI values for acidity (R), moisture (F), nitrogen (N) and light (L). Results and conclusions Twelve poor fen sub-community types were described and found to be distributed along a primary environmental gradient of organic matter depth, surface water height and bare substrate. Separation of the poor fen communities by a moisture gradient was considered as spatial evidence for hydroseral succession, which begins with the colonization of open-water pools created by tin excavations. High water levels were associated with the swamp communities, increased organic depth was associated with poor fen, and the type of boundary was shown to affect the resulting community composition. Weighted Community Ellenberg Indicator values for nitrogen, light, reaction and moisture are recommended as an effective tool for indicating differences between plant (sub-)communities. The importance of examining sub-community mosaics in the study of hydroseral development is stressed and the manner in which both sets of information may be used to underpin the conservation management of the site is demonstrated. [source] Modern Sphagnum,13C signatures follow a surface moisture gradient in two boreal peat bogs, James Bay lowlands, Québec,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2009Julie Loisel Abstract Carbon isotopic composition of Sphagnum macrofossils can potentially be used as a palaeohydrological tool for peat-based climatic studies since a relationship between Sphagnum ,13C values and peatland surface moisture has been presented in previous studies. In order to verify this hypothesis, modern Sphagnum,13C values were measured along a moisture (microtopographic) gradient in two boreal peat bogs. Isotopic measurements were performed on bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis of variance. A significant positive correlation (P,<,0.0001) was found between Sphagnum,13C values and their position along the surface moisture gradient. Results show that 13C-depleted values are related to low water table depths (WTD), while 13C-enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not well understood, we demonstrate that water resistance to CO2 diffusion is an important fractionation process that is observed in bulk Sphagnum,13C measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright © 2008 John Wiley & Sons, Ltd. [source] Quantifying patterns and controls of mire vegetation succession in a southern boreal bog in Finland using partial ordinationsJOURNAL OF VEGETATION SCIENCE, Issue 6 2007E.-S. Tuittila Abstract Question: How do we distinguish between concurrent allogenic and autogenic forcings behind changing patterns in plant community structures during mire development? Location: Lakkasuo raised bog, southern Finland. Methods: Two radiometrically dated peat profiles were studied using high resolution plant macrofossil analysis. A combination of partial direct and indirect gradient analyses (CCA and DCA) was applied to quantify the role of different drivers of vegetation changes. Results: Autogenic hydroseral succession explained 16% of the compositional variation in the vegetation. Disturbance successions initiated by fire explained 15% of the variation in the hummock, but only 9% in the wetter lawn. The early post-disturbance successional stages were characterized by Eriophorum vaginatum. After partialling out the effects of peat depth and time since fire, a moisture gradient explained 29% of variation in the hummock core and 26% in the lawn. The analyses also indicated alternation between species with a similar niche. This interaction gradient explained 26% and 31% of the compositional variation in the hummock and lawn, respectively. The similar order of species replacement from both cores supported the existence of general directional succession in mire vegetation, both during the mire development and after fire events. The autogenic succession was slow and gradual while the disturbance successions were episodic and fast. Conclusion: Our results support the paradigm of the complex nature of mire vegetation dynamics where several interlinked agents have simultaneous effects. The approach of combining partial ordinations developed here appeared to be a useful tool to assess the role of different environmental factors in controlling the vegetation succession. [source] Thermal characterisation of active layer across a soil moisture gradient in the McMurdo Dry Valleys, AntarcticaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2009Scott J. Ikard Abstract Heat transport into active layer soils is important to understanding potential responses to changes in surface energy balance, particularly in the context of changing climate. Here we present results of a study to characterise soil thermal properties along a soil moisture gradient adjacent to Lake Fryxell in Taylor Valley, Antarctica. Our goals were to characterise the thermal characteristics of these relatively wet soils (compared to the rest of the McMurdo Dry Valleys landscape), and to assess the response of the active layer to possible increases in soil moisture. We measured subsurface temperatures at depths from 3 to 50,cm at four locations along a natural gradient of wet to dry soils adjacent to Lake Fryxell from January 2006 to January 2007. We used a numerical model to estimate apparent thermal diffusivity (ATD) and simulate observed temperature time series. Calculations of ATD at discrete locations yielded values ranging from 1.0,×,10,9 , 2.4,×,10,5,m2,s,1, and the corresponding range of bulk (i.e. depth averaged at a single surface location) ATD was 2.9,×,10,9,1.2,×,10,7,m2,s,1. Thawed soils had a range of bulk ATD during warming of 2.9,×,10,9,3.8,×,10,8,m2,s,1, and during cooling of 2.9,×,10,9,4.8,×,10,8,m2,s,1. When soils were frozen, however, the range of bulk ATD was 7.6,×,10,9,1.2,×,10,7,m2,s,1 during warming, and 7.8,×,10,9,1.1,×,10,7,m2,s,1 during cooling. Estimated bulk ATD values were consistently greater in locations of enhanced soil moisture, so lakeside soils were more likely to conduct energy into the subsurface. Increased soil moisture across the landscape would likely increase ATD, allowing for greater heat exchange between the atmosphere and the subsurface. Copyright © 2009 John Wiley & Sons, Ltd. [source] Diagnostic study of generalized moist potential vorticity in a non-uniformly saturated atmosphere with heavy precipitationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 650 2010Zhaoming Liang Abstract A Meiyu front accompanied by a band of heavy precipitation in East Asia is typically characterized by a much larger moisture gradient than temperature gradient. Many previous studies have suggested use of equivalent potential temperature as a thermodynamic variable under this circumstance. However, dynamic variables coupled with such a thermodynamic variable, e.g. a derived moist potential vorticity (MPV) based on equivalent potential temperature, does not provide useful dynamic insight into these systems. In this study, generalized moist potential vorticity (GMPV) is derived based on a generalized form of potential temperature. Diagnoses of numerical simulations for three typical Meiyu rainfall events show that GMPV provides remarkably accurate tracking of rainfall location, suggesting its potential use as a dynamic tracer for heavy rainfall events such as Meiyu rain bands. Copyright © 2010 Royal Meteorological Society [source] Survival and growth responses of eight Everglades tree species along an experimental hydrological gradient on two tree island typesAPPLIED VEGETATION SCIENCE, Issue 4 2010Susana L. Stoffella Abstract Questions: How are the early survival and growth of seedlings of Everglades tree species planted in an experimental setting on artificial tree islands affected by hydrology and substrate type? What are the implications of these responses for broader tree island restoration efforts? Location: Loxahatchee Impoundment Landscape Assessment (LILA), Boynton Beach, Florida, USA. Methods: An experiment was designed to test hydrological and substrate effects on seedling growth and survivorship. Two islands , a peat and a limestone-core island representing two major types found in the Everglades , were constructed in four macrocosms. A mixture of eight tree species was planted on each island in March of 2006 and 2007. Survival and height growth of seedlings planted in 2006 were assessed periodically during the next two and a half years. Results: Survival and growth improved with increasing elevation on both tree island substrate types. Seedlings' survival and growth responses along a moisture gradient matched species distributions along natural hydrological gradients in the Everglades. The effect of substrate on seedling performance showed higher survival of most species on the limestone tree islands, and faster growth on their peat-based counterparts. Conclusions: The present results could have profound implications for restoration of forests on existing landforms and artificial creation of tree islands. Knowledge of species tolerance to flooding and responses to different edaphic conditions present in wetlands is important in selecting suitable species to plant on restored tree islands [source] Short-term fitness benefits of physiological integration in the clonal herb Hydrocotyle peduncularisAUSTRAL ECOLOGY, Issue 6 2002Andrew G. Peterson Abstract We test whether physiological integration enhances the short-term fitness of the clonal herb Hydrocotyle peduncularis (Apiaceae, R. Brown ex A. Richards) subjected to spatial variation in water availability. Our measures of fitness and costs and benefits are based on the relative growth rate of fragmented genets. Physiological integration over a gradient in soil moisture resulted in a highly significant net benefit to genet growth of 0.015 g g,1 day,1. This net benefit represents a significant enhancement of the average fitness of fragmented genets spanning the moisture gradient relative to the average of those growing in homogeneous moist or dry conditions. Sections of genet fragments growing in dry conditions in spatially heterogeneous treatments had significantly higher growth than the sections they were connected to that were growing in moist conditions. Within fragments, older (parent) sections growing in moist conditions experienced significant costs from connection to younger (offspring) sections growing in dry conditions. In contrast, offspring sections with ample water did not experience any costs when connected to parent sections growing in dry conditions. However, the net benefit of physiological integration was similar for parent and offspring sections, suggesting that parent and offspring sections contributed equally to the net benefit of physiological integration to genet growth and short-term fitness. [source] Implications of Climatic Warming for Conservation of Native Trees and Shrubs in FloridaCONSERVATION BIOLOGY, Issue 4 2001David W. Crumpacker Climatic-envelope models are useful for simultaneous investigation of many plant species whose range-limiting mechanisms are poorly known. They are most effectively applied in regions with strong temperature and moisture gradients and low relief. Their required databases are often relatively easy to obtain. We provide an example involving the effect of six annual warming scenarios, ranging from +1° C to +2° C and from +10% to ,20% annual precipitation (some have greater warming in winter than in summer), on 117 native woody species in Florida (U.S.A.). Tree species at their southern range boundaries in several parts of Florida are likely to be negatively affected by as little as 1° C warming if it is greater in winter than in summer or is accompanied by a 20% decrease in annual precipitation. Potential species responses to an identical type of 1° C warming may be different for some conservation areas in the same region of Florida. Potentially extensive disruption of some major woody ecosystems is predicted under certain types of 1° C annual warming and under all types of 2° C annual warming that were investigated. Additional consideration of nonclimatic factors suggests that many potential effects on species and ecosystems are not underestimates of actual effects over a 100-year period of warming. We recommend monitoring for decreased fertility and viability of ecologically important, temperate woody species near their southern range limits in Florida. Early detection of such changes in fitness might then provide time for mitigations designed to alleviate more serious subsequent effects on biodiversity. Control of invasive, non-native plant species and prevention of their additional introduction, human-assisted translocation of native subtropical plant species into previously temperate parts of Florida, and restoration of more natural hydrological regimes are examples of potentially useful mitigations if climatic warming continues. Resumen: Los modelos de procesos ecológicos y los modelos empíricos han sido usados para relacionar predicciones de cambio climático con los efectos en especies de plantas y vegetación. Los modelos climáticos son útiles para la investigación simultánea de muchas especies de plantas cuyos mecanismos limitantes de rango son poco conocidos. Estos modelos son más eficientemente aplicados en regiones con gradientes de temperatura y humedad fuertes y con relieve bajo. Las bases de datos requeridas son a menudo relativamente fáciles de adquirir. Proveemos un ejemplo que involucra el efecto de seis escenarios anuales de calentamiento con un rango de +1° C a +2° C y de +10% a ,20% de precipitación anual (algunos con rangos de calentamiento mayores en el invierno que en el verano), en 117 especies leñosas nativas de Florida ( E.U.A.). Las especies de árboles en sus límites de rango al sur en diversas partes de Florida son más factibles de ser negativamente afectadas por tan poco como 1° C de calentamiento, si este es mayor en el invierno que en el verano o si es acompañado por una disminución de un 20% de precipitación anual. Las respuestas potenciales de las especies a un tipo idéntico de calentamiento de 1° C puede ser diferente para algunas áreas de conservación en la misma región de Florida. Se predicen perturbaciones potencialmente extensivas en algunos ecosistemas leñosos principales investigados bajo ciertos tipos de calentamiento anual de 1° C y bajo todos los tipos de calentamiento anual de 2° C. Las consideraciones adicionales de factores no climáticos sugieren que muchos efectos potenciales sobre las especies y ecosistemas no son subestimaciones de los efectos actuales sobre un período de calentamiento de 100 años. Se recomienda el monitoreo de la disminución de la fertilidad y viabilidad de especies leñosas templadas ecológicamente importantes cerca de los límites sureños de sus rangos en la Florida. La detección temprana de estos cambios en adaptabilidad pueden proveer tiempo para mitigaciones diseñadas para aliviar efectos posteriores más serios en la biodiversidad. Algunos ejemplos de mitigaciones potencialmente útiles en caso de que el calentamiento global continúe incluyen el control de especies de plantas invasoras no nativas y la prevención de su introducción adicional, la translocación asistida por humanos de plantas nativas subtropicales en partes previamente templadas de Florida y la restauración de regimenes hidrológicos más naturales. [source] Ant Activity along Moisture Gradients in a Neotropical Forest,BIOTROPICA, Issue 4a 2000Michael Kaspari ABSTRACT Insect activity often tracks moisture gradients. We studied ant activity, size, and diversity along three moisture gradients in a Panamanian rain forest. Ant activity at baits increased by 25 percent from the dry to the wet season, and > 200 percent on a topographical gradient from a ravine to an exposed plateau. Activity varied little from day to night. Three microhabitats,tree trunk, shrub, and litter,showed different responses to these three gradients. The size distribution of the species pool (N= 63) was right skewed, but the average size of ants at a bait was strongly bimodal. Ants active in moister times and places were not significantly smaller. We suggest that gradients of desiccation risk and food availability were the two most likely causes of these patterns. Two temporal niche axes (daily and seasonal) showed little species specialization, but half of the common species could be categorized as litter or plant microhabitat specialists. RESUMEN Nosotros estudiamos actividad de hormiga, tamaño, y diversidad en 4 microhabitats a lo largo de tres gradientes de humedad en un bosque Panameño. La actividad de hormiga aumentada por 25 percent desde la seca a la temporada mojada, y > 200 percent sobre un gradiente topográfico desde un barranco a una meseta expuesta. La actividad varió poco desde el día a la noche. Tres microhabitats,tronco de árbol, arbusto, y la hojarasca-mostró respuestas diferentes a estos tres de gradientes. El tamaño la distribución de las especies combina (N= 63) tuvo razón skewed, pero el tamaño promedio de hormigas a una carnada era fuertemente bimodal. Las hormigas activas en los lugares y veces más húmedas no eran significativamente menores. Nosotros sugerimos que los gradientes de desecamiento arriesgan y la disponibilidad alimentaria son los dos muy probables ocasiona de estos modelos. Dos temporal los nichos (diarios y estacionales) mostraron poca especialización de especies. La mitad de las especies comunes podría categorizarse como hojarasca o plantada microhabitat especialistas. [source] Anthropogenic and climatic impacts on surface pollen assemblages along a precipitation gradient in north-eastern ChinaGLOBAL ECOLOGY, Issue 5 2010Yun Zhang ABSTRACT Aim, To understand the scenarios of ,anthropogenic biomes' that integrate human and ecological systems, we need to explore the impacts of climate and human disturbance on vegetation in the past and present. Interactions among surface pollen, modern vegetation and human activities along climate and land-use gradients are tested to evaluate the natural and anthropogenic forces shaping the modern vegetation, and hence to aid the reconstruction of vegetation and climate in the past. This in turn will help with future predictions. Location, The North-east China Transect (NECT) in north-eastern China. Methods, We analysed 33 surface pollen samples and 213 quadrats across four vegetation zones along the moisture/land-use gradients of the NECT. Detrended correspondence analysis (DCA) and redundancy analysis (RDA) of 52 pollen taxa and three environmental variables were used to distinguish anthropogenic and climatic factors that affect surface pollen assemblages along the NECT. Results, The 33 surface samples are divided into four pollen zones (forest, meadow steppe, typical steppe and desert steppe) corresponding to major vegetation types in the NECT. Variations in pollen ratios of fern/herb (F/H), Artemisia/Chenopodiaceae (A/C) and arboreal pollen/non-arboreal pollen (AP/NAP) represent the vegetation and precipitation gradient along the NECT. DCA and RDA analyses suggest that surface pollen assemblages are significantly influenced by the precipitation gradient. Changes in the abundance of Chenopodiaceae pollen are related to both human activities and precipitation. Main conclusions, Surface pollen assemblages, fossil pollen records, archaeological evidence and historical documents in northern China show that a large increase of Chenopodiaceae pollen indicates human-caused vegetation degradation in sandy habitats. The A/C ratio is a good indicator of climatic aridity, but should be used in conjunction with multiple proxies of human activities and climate change in the pollen-based reconstruction of anthropogenic biomes. [source] | |||||||||||||||||||||||||