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Lowland Sites (lowland + site)
Selected AbstractsEFFECTS OF TOPOGRAPHY AND SOIL PROPERTIES ON RECHARGE AT TWO SITES IN AN AGRICULTURAL FIELD,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2000Geoffrey N. Delin ABSTRACT: Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7-hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site-specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the lowland site (annual average of all methods of 29 cm) exceeded those at the upland site (annual average of 18 cm). On an annual basis, estimates by the individual methods ranged from 12 to 44 percent of precipitation at the upland site and from 21 to 83 percent at the lowland site. The difference in recharge rates between the sites is primarily attributed to depression focusing of surface water runon at the lowland site. However, two other factors were also important: the presence of thin lamellae at the upland site, and coarser textured soils below a depth of 1.5 m at the lowland site. [source] Subtle topographical differences along a floodplain promote different plant strategies among Paspalum dilatatum subspecies and populationsAUSTRAL ECOLOGY, Issue 2 2010FEDERICO P. O. MOLLARD Abstract It was hypothesised that subtle topographical differences might cause the existence of ecotypes along a floodplain. The apomict grass Paspalum dilatatum subspecies dilatatum inhabits flood-prone lowlands as well as nearby uplands in the floodplains of Argentina, while the sexual P. dilatatum subspecies flavescens almost exclusively inhabits the uplands. The aim of the present study was to identify the different traits that allow these P. dilatatum populations to inhabit different habitats. Plants of P. dilatatum were reciprocally transplanted between uplands and lowlands. Morphophysiological traits related to flooding tolerance were measured during a flood. Subspecies dilatatum from the uplands and subspecies flavescens showed a high physiological performance in the uplands but a considerable decrease in stomatal conductance, net photosynthesis rates and tiller number in the flooded lowlands. In contrast, the subspecies dilatatum from the lowlands showed relatively lower and stable stomatal conductance, photosynthesis rates and leaf water potential at both sites. Subspecies dilatatum from the lowlands outperformed upland populations at the lowland site with respect to tillering. Leaves of subspecies dilatatum from the lowlands that had grown at the lowland habitat had a lower blade/sheath proportion than leaves of plants transplanted to the uplands. This behavior did not occur in both upland populations. Results suggest that dilatatum Lowland plants have the typical strategy of stress-tolerant genotypes and that the upland populations are adapted to habitats where competitive species are selected. In conclusion, habitats with subtle differences in topographic level can favour both ecotypic differentiations within an apomict subspecies but also the maintenance of morphophysiological similitudes between coexisting upland populations belonging to different subspecies. [source] Elevation and forest clearing effects on foraging differ between surface , and subterranean , foraging army ants (Formicidae: Ecitoninae)JOURNAL OF ANIMAL ECOLOGY, Issue 1 2009Anjali Kumar Summary 1Forest fragmentation often results in a matrix of open areas mixed with patches of forest. Both biotic and abiotic factors can affect consumer species' ability to utilize the altered habitat, especially for species that range over large areas searching for prey. 2Army ants (Formicidae: Ecitoninae) are highly mobile top predators in terrestrial Neotropical ecosystems. Army ant foraging behaviour is influenced by forest clearing at lowland sites, and clearing can reduce army ant population persistence. 3Because high temperatures are implicated in hindering above-ground army ant foraging, we predicted that forest clearing effects on army ant foraging would be reduced at higher (cooler) elevations in montane forest. We also predicted that subterranean foraging, employed by some army ant species, would buffer them from the negative effects of forest clearing. 4We quantified the foraging rates of above-ground and underground foraging army ants at eight sites along an elevational gradient from 1090 to 1540 m a.s.l. We asked whether these two foraging strategies cause a difference in the ability of army ants to forage in open matrix areas relative to elevationally matched forested habitats, and whether elevation predicts open area vs. forest foraging rate differences. 5As predicted, army ants that forage above-ground had lower foraging rates in open areas, but the open area vs. forest difference declined with elevation. In contrast, underground foragers were not affected by habitat type, and underground foraging rates increased with elevation. Ground surface temperatures were higher in open areas than forested areas. Temperatures declined with elevation, and temperature differences between open and forested areas decreased with elevation. 6We conclude that army ants that forage above-ground may be restricted to forested areas due to a thermal tolerance threshold, but that they are released from this limitation at higher elevations. We further suggest that underground foraging permits some army ants to persist within modified landscapes. Our findings have implications for the effects of habitat modification and climate change on these top predators. [source] A comparative analysis of restoration measures and their effects on hydromorphology and benthic invertebrates in 26 central and southern European riversJOURNAL OF APPLIED ECOLOGY, Issue 3 2010Sonja C. Jähnig Summary 1.,Hydromorphological river restoration usually leads to habitat diversification, but the effects on benthic invertebrates, which are frequently used to assess river ecological status, are minor. We compared the effects of river restoration on morphology and benthic invertebrates by investigating 26 pairs of non-restored and restored sections of rivers in Austria, Czech Republic, Germany, Italy and the Netherlands. 2.,Sites were grouped according to (1) region: central Europe vs. southern Europe; (2) river type: mountain vs. lowland rivers; (3) restoration approach: active vs. passive restoration and (4) a combination of these parameters. All sites were sampled according to the same field protocol comprising hydromorphological surveys of river and floodplain mesohabitats, microhabitats at the river bottom and habitat-specific sampling of benthic invertebrates. Restoration effects were compared using Shannon,Wiener Indices (SWIs) of mesohabitats, microhabitats and invertebrate communities. Differences in metric values between non-restored and restored sites were compared for 16 metrics that evaluated hydromorphology and the benthic invertebrate community. 3.,Mean SWIs differed for both mesohabitats (1·1 non-restored, 1·7 restored) and microhabitats (1·0 non-restored, 1·3 restored), while SWIs for invertebrate communities were not significantly different (2·4 non-restored, 2·3 restored). Meso- and microhabitat metrics in the restored sections were usually higher compared with the non-restored sections, but the effects on invertebrate metrics were negligible. 4.,Measures in southern Europe and mountainous regions yielded larger differences between non-restored and restored sections of rivers. Differences in the meso- and microhabitat metrics were largest for actively restored sections of central European mountain rivers and rivers from southern Europe, followed by passively restored mountain rivers in central Europe. The smallest differences were observed for lowland sites. There was no significant restoration effect on invertebrate metrics in any categories. 5.,Synthesis and applications. Restoration measures addressing relatively short river sections (several hundred metres) are successful in terms of improving habitat diversity of the river and its floodplain. Active restoration measures are suitable if short-term changes in hydromorphology are desired. To realize changes in benthic invertebrate community composition, habitat restoration within a small stretch is generally not sufficient. We conclude that restoring habitat on a larger scale, using more comprehensive measures and tackling catchment-wide problems (e.g. water quality, source populations) are required for a recovery of the invertebrate community. [source] Does biogeographical history matter?AUSTRAL ECOLOGY, Issue 1 2005Diversity, distribution of lotic midges (Diptera: Chironomidae) in the Australian Wet Tropics Abstract We examined broad scale patterns of diversity and distribution of lotic Chironomidae (Diptera) within the Wet Tropics bioregion of northern Queensland, Australia. Field surveys across broad latitudinal and altitudinal gradients within the Wet Tropics revealed a fauna of 87 species-level taxa in 49 genera comprising three main elements: a small genuinely tropical fraction, and larger cosmopolitan and Gondwanan components. The latter group originated when Australia, as part of the ancient Gondwana supercontinent, was situated over Antarctic latitudes with a cooler, wetter climate than today. In the Wet Tropics, cool Gondwanan taxa occurred predominantly in upland and shaded lowland sites, but no species appeared narrowly temperature restricted, and there was no faunal zonation with altitude. Most chironomid species occurred at all latitudes within the Wet Tropics, with no evidence for an enduring effect of the historical rainforest contractions on current-day distribution patterns. These findings contrast with those for aquatic faunas elsewhere in the world and for the terrestrial Wet Tropics fauna. We relate this to the generally broad environmental tolerances of Australian chironomids, and comment on why the latitudinal diversity gradient does not apply to the Australian chironomid fauna. [source] Does biogeographical history matter?AUSTRAL ECOLOGY, Issue 1 2005Diversity, distribution of lotic midges (Diptera: Chironomidae) in the Australian Wet Tropics Abstract We examined broad scale patterns of diversity and distribution of lotic Chironomidae (Diptera) within the Wet Tropics bioregion of northern Queensland, Australia. Field surveys across broad latitudinal and altitudinal gradients within the Wet Tropics revealed a fauna of 87 species-level taxa in 49 genera comprising three main elements: a small genuinely tropical fraction, and larger cosmopolitan and Gondwanan components. The latter group originated when Australia, as part of the ancient Gondwana supercontinent, was situated over Antarctic latitudes with a cooler, wetter climate than today. In the Wet Tropics, cool Gondwanan taxa occurred predominantly in upland and shaded lowland sites, but no species appeared narrowly temperature restricted, and there was no faunal zonation with altitude. Most chironomid species occurred at all latitudes within the Wet Tropics, with no evidence for an enduring effect of the historical rainforest contractions on current-day distribution patterns. These findings contrast with those for aquatic faunas elsewhere in the world and for the terrestrial Wet Tropics fauna. We relate this to the generally broad environmental tolerances of Australian chironomids, and comment on why the latitudinal diversity gradient does not apply to the Australian chironomid fauna. [source] Soil Charcoal in Old-Growth Rain Forests from Sea Level to the Continental DivideBIOTROPICA, Issue 6 2007Beyhan Titiz ABSTRACT Soil charcoal is an indicator of Holocene fires as well as a palaeoecological signature of pre-Colombian land use in Neotropical rain forests. To document rain forest fire history, we examined soil charcoal patterns in continuous old-growth forests along an elevational transect from sea level to the continental divide on the Atlantic slope of Costa Rica. At 10 elevations we sampled 1-ha plots, using 16 cores/ha to collect 1.5-m deep soil samples. We found charcoal in soils at every elevation, with total dry mass ranging from 3.18 g/m2 at 2000-m elevation to as much as 102.7 g/m2 at 300 m. Soil charcoal is most abundant at the wettest lowland sites (60,500 m) and less at montane elevations (> 1000 m) where there is less rainfall. Between 30- and 90-cm soil depth, soil charcoal is present consistently and every 1-ha plot has charcoal evidence for multiple fire events. Radiocarbon dates range from 23,240 YBP at 1750-m elevation to 140 YBP at 2600 m. Interestingly, none of the charcoal samples from 2600 m are older than 170 yr, which suggests that forests near the continental divide are relatively young replacement stands that have re-established since the most recent localized volcanic eruption on Volcán Barva. We propose that these old-growth forests have been disturbed infrequently but multiple times as a consequence of anthropogenic and natural fires. RESUMEN El carbón es un indicador de los fuegos Holocenos así como una huella paleoecológica del uso de las tierras precolombinas en bosques neotropicales. Para documentar la historia de fuegos en los bosques, examinamos modelos de carbón en la tierra en bosques primarios continuos a lo largo de un transecto en altitud en zonas de vida forestal desde el nivel del mar hasta la División Continental en la vertiente atlántica de Costa Rica. En diez elevaciones tomamos muestras de parcelas de una hectárea, donde se usaron dieciséis cilíndricas de acero por hectárea para recoger muestras de suelo a 1.5 metros de profundidad. Descubrimos carbón en suelos en cada elevación, con un rango de masa seca total desde los 3.18 g/m2 a 2000 metros de altura hasta un máximo de 102.7 g/m2 a 300 metros de altura. El carbón abunda más en las zonas más lluviosas (60,500 metros) y menos en elevaciones montañosas (>1000 metros) donde hay menos precipitación. Entre los 30 a los 90 centímetros de profundidad en la tierra, el carbón está presente consistentemente y cada parcela de una hectárea tiene evidencia de carbón de incendios múltiples. Fechas de 14C van desde los 23,240 años a.P. a 1750 metros de elevación hasta los 140 años a.P. a 2600 metros. De modo interesante, ninguna de las muestras de carbón a partir de los 2600 metros de altura tiene más de 170 años, lo que sugiere que los bosques cerca de la División Continental son árboles relativamente jóvenes que se han reestablecido después de las erupciones volcánicas confinadas del Volcán Barva. Pensamos que estos bosques primarios han sido disturbados en muchas ocasiones pero en un largo periodo de tiempo como consecuencia de fuegos antropogénicos y naturales. [source] | ||||||||||