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Rainfall Gradient (rainfall + gradient)
Selected AbstractsRegional-scale spatial patterns of fire in relation to rainfall gradients in sub-tropical mountains, NW ArgentinaGLOBAL ECOLOGY, Issue 2 2001Héctor Ricardo Grau Abstract 1Spatial patterns of burns are described using Landsat TM images from the sub-tropical mountains of north-west Argentina, over a span of 6 degrees of latitude, and a precipitation range from 250 to 1300 mm/yr. Burns were discriminated easily from unburnt vegetation, mainly by using infrared spectral bands from images taken at the end of the fire season of 1986. 2Nineteen sampling units were defined on the basis of geographical proximity and relatively homogeneous rainfall as inferred from topography, and they were characterized in terms of percentage of burnt area and burn size distribution during one fire season. Regression and Correspondence Analysis were used to assess the relationship between rainfall and spatial descriptors of fire regime. 3Burnt size area was log-normally distributed with most fires in the small-size classes. Of a total of 643 burns, the five largest (more than 2000 hectares each) represented about 30% of the total burnt area. 4Percentage of burnt area, density of burns per unit area, and skewness of the burn-size frequency distribution showed a unimodal pattern along the rainfall gradient, peaking between 700 and 900 mm/yr. Mean and maximum burn size showed a negative but weak correlation with rainfall. The first axis of a Correspondence Analysis ordination of sampling units, on the basis of different descriptors of spatial patterns of fire, was significantly correlated with the rainfall of the sampling unit. 5The results suggest that climate is an important factor controlling fuel conditions and therefore fire regime at the spatial scale of this study, which includes different mountain ranges spanning , 700 km. [source] Spatial variation in the duration of the rainy season in monsoonal AustraliaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2001Garry D. Cook Abstract Climatological research in the tropics of northern Australia has focused particularly on the Australian summer monsoon. However, the timing of many ecologically important processes is determined not by the monsoon but by extra-monsoonal rainfall events. These events produce a temporal pattern of wet and dry spells that is at least as important ecologically as the amount of rain. We defined the rainy season as that period when the probability of 10-day dry spells was less than 0.5, and the wet season as that period within the rainy season when the probability of dry spells was less than 0.1. We applied these criteria to seven stations along a strong north,south rainfall gradient spanning more than 12° of latitude in tropical north Australia. The duration of the rainy and wet seasons in northern Australia decreases with increasing latitude. The timing and duration of these seasons were also affected by the El Niño,Southern Oscillation (ENSO). The relative contribution of temporally isolated rainfall events to both the duration of the rainy season and the amount of rainfall increases with latitude. The geographic variation in these seasons corresponds to many patterns occurring in natural ecosystems. We argue that understanding the extra-monsoon rainfall events is critical to understanding how climate variation affects natural ecosystems. Copyright © 2001 Royal Meteorological Society [source] Effects of climate and local aridity on the latitudinal and habitat distribution of Arvicanthis niloticus and Arvicanthis ansorgei (Rodentia, Murinae) in MaliJOURNAL OF BIOGEOGRAPHY, Issue 1 2004B. Sicard Abstract Introduction, The genus Arvicanthis (Lesson 1842) (Rodentia: Murinae), usually referred to as the unstriped grass rat, is mainly distributed in savanna and grassland habitats of Sub-Saharan Africa. Among the four chromosomal forms of Arvicanthis recently differentiated in Western and Central Africa, the one with a diploid chromosomal number (2n) of 62 and an autosomal fundamental number (NFa) of 62 or 64 is ascribed to Arvicanthis niloticus (Demarest 1822), while the one with 2n = 62 and a NFa between 74 and 76 is referred to A. ansorgei (Thomas 1910). Despite the broad area of sympatry recently uncovered along the inner delta of the Niger river in Mali [details in Volobouev et al. (2002) Cytogenetics and Genome Research, 96, 250,260], the distribution of the two species is largely parapatric and follows the latitudinal patterns of the West-African biogeographical domains, which are related to the latitudinal patterns of annual rainfall in this region. Here, we analyse the suggestion that the two species show specific adaptations to differences in climate aridity. Methods, Karyologically screened animals were sampled in 19 localities in seasonally flooded regions located along the ,Niger' river in Mali and extending from 1100 to 200 mm of mean annual rainfall. The analysis of trapping success (TS) data allowed us to investigate the respective effects of climate (i.e. annual rainfall) and local (i.e. duration of the green herbaceous vegetation) aridity on the latitudinal and habitat distribution of the two species. Conclusions, The broad zone of sympatry was found to correspond to a northward expansion of the recognized distribution area of A. ansorgei. TS values indicated that the two species responded very differently to climatic and local conditions of aridity. Arvicanthis ansorgei decreased in TS as regional conditions became more arid; a similar trend was also observed within regions where habitat occupancy decreased with local aridity. The higher TS observed in the most humid habitat relative to the others persisted throughout the latitudinal rainfall gradient. In contrast, TS of A. niloticus increased with latitudinal aridity. This species was present in more arid habitats than A. ansorgei from 1000 mm down to 400 mm of mean annual rainfall where a shift to the most humid habitat occurred. These opposite trends in TS distribution between species suggest that A. ansorgei is less adapted than A. niloticus to arid environments at both a regional and habitat level; thus, A. ansorgei would be able to invade dry regions only along the extensive floodplains bordering the inner delta of the ,Niger' river. Several biological traits that may be involved in limiting the southward distribution of A. niloticus are discussed. [source] Palaeohydrology of Laguna de Tagua Tagua (34° 30, S) and moisture fluctuations in Central Chile for the last 46,000,yr,JOURNAL OF QUATERNARY SCIENCE, Issue 7-8 2005Blas L. Valero-Garcés Abstract Central Chile (32,35° S) lies at the northern border of the strong influence of the westerly circulation belt and thus exhibits a steep rainfall gradient. A new core from Laguna de Tagua Tagua (34° 30, S) provides a sedimentologic, geochemical and palynological record of regional hydrologic balance for the last 46,000,cal.,yr,BP. According to our age model, relatively humid conditions occurred during glacial times before 43,500,cal.,yr,BP and from 40,000 to 21,500,cal.,yr,BP. Reduced moisture conditions and likely lower temperatures occurred from 42,400,40,100,cal.,yr,BP. Higher lake levels, and pollen assemblages with Valdivian rainforest taxa, imply much higher precipitation during glacial times (40,100,21,000,cal.,yr,BP) compared to today and, therefore, enhanced westerly activity in northern Central Chile. Afterwards, the general decrease in moisture was punctuated by two abrupt arid periods at 21,000,19,500,cal.,yr,BP and 17,000,15,000,cal.,yr,BP, and two more humid intervals: 19,500,17,000 (almost coincident with the global Last Glacial Maximum, LGM) and 13,500,11,500,cal.,yr,BP. The early and mid-Holocene were the most arid periods in Central Chile for the studied time interval. Millennial-scale palaeohydrological reconstructions from Tagua Tagua are consistent with regional climatic records. Copyright © 2005 John Wiley & Sons, Ltd. [source] The effect of soil on the growth performance of tropical species with contrasting distributionsOIKOS, Issue 10 2008Tania Brenes-Arguedas Within the tropics, a marked gradient in rainfall between dry and wet forests correlates with a well documented turnover of plant species. While water availability along these gradients is an important determinant of species distributions, other abiotic and biotic factors correlate with rainfall and may also contribute to limit species distribution. One of these is soil fertility, which is often lower in the wetter forests. To test its possible role in species distribution along a rainfall gradient, we performed a screen-house experiment where we measured the growth performance of seedlings of 23 species with contrasting distributions across the Isthmus of Panama. We grew seedlings in soils collected from the drier Pacific side and the wetter Atlantic side. Differences in soil fertility across the Isthmus were large enough to significantly influence the growth performance of the seedlings. However, we found no evidence of home-soil advantage among species with contrasting distributions. Dry-distribution species grew on average slower than wet-distribution species suggesting a cost to drought adaptations. The response to soil differences correlated with the growth rate of the species, such that fast-growing species responded more to changes in soil quality. We hypothesize that inherently slow growth rates of some dry-distribution tropical species may be a more important factor limiting their colonization of wetter sites along the rainfall gradient. [source] Relations of sugar composition and ,13C in phloem sap to growth and physiological performance of Eucalyptus globulus (Labill)PLANT CELL & ENVIRONMENT, Issue 8 2010ANDREW MERCHANT ABSTRACT We characterized differences in carbon isotopic content (,13C) and sugar concentrations in phloem exudates from Eucalyptus globulus (Labill) plantations across a rainfall gradient in south-western Australia. Phloem sap ,13C and sugar concentrations varied with season and annual rainfall. Annual bole growth was negatively related to phloem sap ,13C during summer, suggesting a water limitation, yet was positively related in winter. We conclude that when water is abundant, variations in carboxylation rates become significant to overall growth. Concentrations of sucrose in phloem sap varied across sites by up to 600 mm, and raffinose by 300 mm. These compounds play significant roles in maintaining osmotic balance and facilitating carbon movement into the phloem, and their relative abundances contribute strongly to overall ,13C of phloem sap. Taken together, the ,13C and concentrations of specific sugars in phloem sap provide significant insights to functions supporting growth at the tree, site and landscape scale. [source] Decadal dynamics of tree cover in an Australian tropical savannaAUSTRAL ECOLOGY, Issue 6 2009CAROLINE E. R. LEHMANN Abstract Spatio-temporal variation in tropical savanna tree cover remains poorly understood. We aimed to quantify the drivers of tree cover in tropical mesic savannas in Kakadu National Park by relating changes in tree cover over 40 years to: mean annual rainfall, fire activity, initial tree cover and prior changes in tree cover. Aerial photography, acquired in 1964, 1984 and 2004, was obtained for fifty sites in Kakadu that spanned a rainfall gradient from approximately 1200 to 1600 mm. The remotely sensed estimates of tree cover were validated via field survey. Linear mixed effects modelling and multi-model inference were used to assess the strength and form of the relationships between tree cover and predictor variables. Over the 40 years, tree cover across these savannas increased on average by 4.94 ± 0.88%, but was spatio-temporally variable. Tree cover showed a positive albeit weak trend across the rainfall gradient. The strength of this positive relationship varied over the three measurement times, and this suggests that other factors are important in controlling tree cover. Tree cover was positively related to prior tree cover, and negatively correlated with fire activity. Over 20 years tree cover was more likely to increase if (i) tree cover was initially low or (ii) had decreased in the previous 20-year interval or (iii) there had been fewer fires. Across the examined rainfall gradient, the greater variability in fire activity and inherently higher average tree cover at the wetter latitudes resulted in greater dynamism of tree cover compared with the drier latitudes. This is consistent with savanna tree cover being determined by interactions between mean annual rainfall, tree competition and frequent fire in these tropical mesic savannas. [source] Incidence of leaf mining in different vegetation types across rainfall, canopy cover and latitudinal gradientsAUSTRAL ECOLOGY, Issue 3 2008ROBYN J. SINCLAIR Abstract Leaf miners are insects whose larval stages live between layers of leaf epidermis, feeding on mesophyll and lower epidermis to create mine-like cavities. Little is known about the ecology or distribution of leaf miners in Australia. We investigated the incidence of leaf miners in relation to aridity, vegetation types, host plant taxonomy, leaf traits, canopy cover and latitude. We surveyed leaf miners at 15 sites in NSW, eastern Australia, situated along a rainfall gradient from 300 to 1700 mm per annum and a latitudinal gradient of 28°S to 33°S, within four vegetation types (mallee, heath, woodland and rainforest). Leaf mining was recorded from 36 plant species, 89% of which had no previous record of mining. The proportion of mined plant species at each site varied, but there was no significant difference between vegetation types. Leaf mining presence was positively correlated with both total leaf length and leaf thickness. No significant correlations were found between the proportion of mined species at a site and rainfall, latitude or foliar projected cover. We conclude that leaf mining is a widespread type of insect herbivory whose distribution patterns are more likely to be influenced by biotic than abiotic factors. [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] Regional-scale spatial patterns of fire in relation to rainfall gradients in sub-tropical mountains, NW ArgentinaGLOBAL ECOLOGY, Issue 2 2001Héctor Ricardo Grau Abstract 1Spatial patterns of burns are described using Landsat TM images from the sub-tropical mountains of north-west Argentina, over a span of 6 degrees of latitude, and a precipitation range from 250 to 1300 mm/yr. Burns were discriminated easily from unburnt vegetation, mainly by using infrared spectral bands from images taken at the end of the fire season of 1986. 2Nineteen sampling units were defined on the basis of geographical proximity and relatively homogeneous rainfall as inferred from topography, and they were characterized in terms of percentage of burnt area and burn size distribution during one fire season. Regression and Correspondence Analysis were used to assess the relationship between rainfall and spatial descriptors of fire regime. 3Burnt size area was log-normally distributed with most fires in the small-size classes. Of a total of 643 burns, the five largest (more than 2000 hectares each) represented about 30% of the total burnt area. 4Percentage of burnt area, density of burns per unit area, and skewness of the burn-size frequency distribution showed a unimodal pattern along the rainfall gradient, peaking between 700 and 900 mm/yr. Mean and maximum burn size showed a negative but weak correlation with rainfall. The first axis of a Correspondence Analysis ordination of sampling units, on the basis of different descriptors of spatial patterns of fire, was significantly correlated with the rainfall of the sampling unit. 5The results suggest that climate is an important factor controlling fuel conditions and therefore fire regime at the spatial scale of this study, which includes different mountain ranges spanning , 700 km. [source] Temporal and spatial variation of annual rainfall on the island of Crete, GreeceHYDROLOGICAL PROCESSES, Issue 10 2003S. Naoum Abstract Annual rainfall records from the island of Crete in Greece were used with the aid of a geographical information system (GIS) to study the temporal and spatial rainfall characteristics. The GIS was used to produce a digital elevation model, delineate watersheds and estimate the areal rainfall from a network of raingauges by using different interpolation schemes. The rainfall,elevation correlation was significant, suggesting an orographic type of precipitation for the island. The rainfall records for the majority of the stations were found to fit the normal distribution. Deviation from normal for the rest of the records was attributed to the wettest year of 1977,1978. The year 1989,1990 was the driest, and most rainfall records showed a decrease in rainfall over 30 years with higher negative rainfall gradients at the higher elevations. Frequency analysis of the rainfall records was used to estimate areal rainfall for the island of Crete and its main watersheds for return periods of 2, 5 and 10 years. Copyright © 2003 John Wiley & Sons, Ltd. [source] Seed Dispersal Distances and Plant Migration Potential in Tropical East AsiaBIOTROPICA, Issue 5 2009Article first published online: 9 MAR 200, Richard T. Corlett ABSTRACT Most predictions of vegetation responses to anthropogenic climate change over the next 100 yr are based on plant physiological tolerances and do not account for the ability of plant species to migrate over the distances required in the time available, or the impact of habitat fragmentation on this ability. This review assesses the maximum routine dispersal distances achievable in tropical East Asia and their vulnerability to human impacts. Estimates for various plant,vector combinations range from < 10 m, for species dispersed by ants or mechanical means, to > 10 km for some species dispersed by wind (tiny seeds), water, fruit pigeons, large fruit bats (tiny seeds), elephants, rhinoceroses, and people. Most plant species probably have maximum dispersal distances in the 100,1000 m range, but the widespread, canopy-dominant Dipterocarpaceae and Fagaceae are normally dispersed < 100 m. Large fruit bats and fruit pigeons are particularly important for long-distance dispersal in fragmented landscapes and should be protected from hunting. The maximum seed dispersal distances estimated in this study are potentially sufficient for many plant species to track temperature changes in steep topography, but are far too small for a significant role in mitigating climate change impacts in the lowlands, where temperature and rainfall gradients are much more shallow. [source] | |||||||||||||