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Southern South America (southern + south_america)
Selected AbstractsUsing Phylogenetic Diversity Measures to Set Priorities in Conservation: an Example from Southern South AmericaCONSERVATION BIOLOGY, Issue 5 2001Paula Posadas The goal of these ranks for conservation is to consider as many factors as possible that provide additional taxic information, such as taxa richness, taxa distributional patterns, area endemicity, and complementarity between areas. At present there are many measures that consider phylogenetic information, including node-based, genetic-distance, and feature-based measures. We devised a modified phylogenetic node-based index that we call "taxonomic endemicity standardized weight," which considers not only the taxonomic distinctness of the taxa that inhabit a given area but their endemicity as well. Once the standardized weight of the taxonomic endemicity identifies the area of highest priority, complementarity can be used to identify the second area and so on. We used this node-based index to rank priority areas for conservation in southern South America, and we compared the results of our rankings to results based on other node-based indexes. Our index identified Santiago district, in Central Chile province, as the highest priority area for conservation, followed by Maule, Malvinas, and districts of Subantarctic province. Malvinas exhibits greater complementarity relative to Santiago than Maule does, however, so Malvinas is ranked second in priority. Indexes based on phylogenetic information measure the evolutionary component of biodiversity and allow one to identify areas that will ensure the preservation of evolutionary potential and phylogenetically rare taxa. The modified index we propose is sensitive to taxic distinctness and endemicity as well and allows information from diverse taxa to be combined (i.e., different cladograms). The use of complementarity allows for preservation of the maximum quantity of taxa in a minimal number of protected areas. Resumen: Las medidas de diversidad filogenética jerarquiza a las áreas para prioridades de conservación de biodiversidad con base en información codificada en filogenias (cladogramas), La meta de estas categorías de conservación requiere tomar en consideración tantos factores que proporcionan información adicional (riqueza de taxones, patrones de distribución de los taxones, endemicidad del área y complementariedad entre áreas) como sea posible. Actualmente hay muchas medidas que consideran información filogenética (basadas en nodos, distancia genética y basadas en características). Diseñamos un índice filogenético modificado basado en nodos que denominamos "peso estandarizado de endemicidad taxonómica", el cual considera no solo la peculiaridad genética de los taxa que habitan una región determinada sino también su endemicidad. Una vez que el peso estandarizado de endemicidad identifica el área de mayor prioridad, la complementariedad se puede usar para identificar la segunda área y así sucesivamente. Utilizamos este índice basado en nodos para jerarquizar áreas prioritarias para conservación en el sur de América del Sur, y comparamos los resultados de nuestras jerarquizaciones con resultados obtenidos con otros índices basados en nodos. Nuestro índice identificó al distrito de Santiago, en la provincia de Chile Central, como el área de mayor prioridad para conservación, seguido por Maule, Malvinas y distritos de la provincia Subantártica. Sin embargo, Malvinas presenta mayor complementariedad en relación con Santiago que el Maule y, por tanto, Malvinas ocupa la segunda prioridad. Los índices basados en información filogenética miden el componente evolutivo de la biodiversidad y permiten la identificación de áreas que aseguran la preservación de taxones con potencial evolutivo y filogenéticamente peculiares. El índice modificado que proponemos es sensible tanto a la peculiaridad de los taxones como a la endemicidad y permite combinar información de diversos taxones (i.e. cladogramas diferentes). El uso de la complementariedad permite la preservación de la mayor cantidad de taxones en un número mínimo de áreas protegidas. [source] Diagnostic osteology and analysis of the Mid- to Late Holocene dynamics of shags and cormorants in Tierra del FuegoINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 2 2007D. Causey Abstract We present here illustrated characteristics and anatomical descriptions of features that can be used to discriminate between four common skeletal elements (i.e. humerus, coracoid, femur, tarsometatarsus) of the five species of shags and cormorants known to occur in southern South America. We also present a detailed study of their distribution and abundance from about 6000 years before present to historical times as revealed by identification of faunal material excavated earlier and by re-analysis of material published previously. Our results present a high-resolution examination of the avian resource base used by early human hunters, and provide a foundation for future studies on the palaeoavifauna of Tierra del Fuego during the Mid- to Late Holocene. On the broadest scales, species diversity of the Phalacrocoracidae is qualitatively stable over space and time, a pattern that is also reflected in the larger marine bird community. On a finer scale, however, our results indicate that the abundance and distribution of cormorants and shags in Mid- and Late Holocene zooarchaeological deposits varied in a complex manner through time. These patterns do not appear to be related to proximity effects of hunters to colonies, but to other factors possibly associated with environmental change. Copyright © 2006 John Wiley & Sons, Ltd. [source] Out of the Palaeotropics?JOURNAL OF BIOGEOGRAPHY, Issue 4 2009Historical biogeography, diversification of the cosmopolitan ectomycorrhizal mushroom family Inocybaceae Abstract Aim, The ectomycorrhizal (ECM) mushroom family Inocybaceae is widespread in north temperate regions, but more than 150 species are encountered in the tropics and the Southern Hemisphere. The relative roles of recent and ancient biogeographical processes, relationships with plant hosts, and the timing of divergences that have shaped the current geographic distribution of the family are investigated. Location, Africa, Australia, Neotropics, New Zealand, north temperate zone, Palaeotropics, Southeast Asia, South America, south temperate zone. Methods, We reconstruct a phylogeny of the Inocybaceae with a geological timeline using a relaxed molecular clock. Divergence dates of lineages are estimated statistically to test vicariance-based hypotheses concerning relatedness of disjunct ECM taxa. A series of internal maximum time constraints is used to evaluate two different calibrations. Ancestral state reconstruction is used to infer ancestral areas and ancestral plant partners of the family. Results, The Palaeotropics are unique in containing representatives of all major clades of Inocybaceae. Six of the seven major clades diversified initially during the Cretaceous, with subsequent radiations probably during the early Palaeogene. Vicariance patterns cannot be rejected that involve area relationships for Africa,Australia, Africa,India and southern South America,Australia. Northern and southern South America, Australia and New Zealand are primarily the recipients of immigrant taxa during the Palaeogene or later. Angiosperms were the earliest hosts of Inocybaceae. Transitions to conifers probably occurred no earlier than 65 Ma. Main conclusions, The Inocybaceae initially diversified no later than the Cretaceous in Palaeotropical settings, in association with angiosperms. Diversification within major clades of the family accelerated during the Palaeogene in north and south temperate regions, whereas several relictual lineages persisted in the tropics. Both vicariance and dispersal patterns are detected. Species from Neotropical and south temperate regions are largely derived from immigrant ancestors from north temperate or Palaeotropical regions. Transitions to conifer hosts occurred later, probably during the Palaeogene. [source] Panbiogeographical analysis of the genus Bomarea (Alstroemeriaceae)JOURNAL OF BIOGEOGRAPHY, Issue 7 2008Fernando Alzate Abstract Aim, A panbiogeographical analysis of the genus Bomarea was undertaken in order to determine generalized tracks and biogeographical nodes, and to evaluate the current distribution of the genus based on the available tectonic information and the biogeographical regionalization of Latin America. Location, The Neotropical region from northern Mexico to northern Argentina, and the Nearctic and Andean regions. Method, A total of 2205 records of 101 species were analysed, representing 95% of the species assigned to Bomarea. Localities were represented on maps and their individual tracks were drawn. Based on their comparison, generalized tracks were detected and mapped. Nodes were identified in the areas where different generalized tracks were superimposed. Results, Five generalized tracks were recovered. One is located in the Eastern Central America and Western Panamanian Isthmus provinces (Caribbean subregion, Neotropical region), which was supported by three species of Central American distribution. The four remaining generalized tracks were located in South America, in the North Andean Paramo, Cauca and Puna biogeographical provinces. These tracks were supported by species of Bomarea with an Andean distribution. Biogeographical nodes were established in the Central Andean region of Colombia, central Ecuador and central Peru. Main conclusions, The nodes obtained for Bomarea support a hybrid origin for the Andean region, which presents diverse components from both northern and southern South America. Likewise, the track recovered between Colombia and Ecuador includes Andean and Neotropical areas, providing further support for this hypothesis. The nodes obtained are coherent with vicariant elements evident for Bomarea. Species of three clades proposed for Bomarea are distributed in specific generalized tracks. [source] Panbiogeography of Nothofagus (Nothofagaceae): analysis of the main species massingsJOURNAL OF BIOGEOGRAPHY, Issue 6 2006Michael Heads Abstract Aim, The aim of this paper is to analyse the biogeography of Nothofagus and its subgenera in the light of molecular phylogenies and revisions of fossil taxa. Location, Cooler parts of the South Pacific: Australia, Tasmania, New Zealand, montane New Guinea and New Caledonia, and southern South America. Methods, Panbiogeographical analysis is used. This involves comparative study of the geographic distributions of the Nothofagus taxa and other organisms in the region, and correlation of the main patterns with historical geology. Results, The four subgenera of Nothofagus have their main massings of extant species in the same localities as the main massings of all (fossil plus extant) species. These main massings are vicariant, with subgen. Lophozonia most diverse in southern South America (north of Chiloé I.), subgen. Fuscospora in New Zealand, subgen. Nothofagus in southern South America (south of Valdivia), and subgen. Brassospora in New Guinea and New Caledonia. The main massings of subgen. Brassospora and of the clade subgen. Brassospora/subgen. Nothofagus (New Guinea,New Caledonia,southern South America) conform to standard biogeographical patterns. Main conclusions, The vicariant main massings of the four subgenera are compatible with largely allopatric differentiation and no substantial dispersal since at least the Upper Cretaceous (Upper Campanian), by which time the fossil record shows that the four subgenera had evolved. The New Guinea,New Caledonia distribution of subgenus Brassospora is equivalent to its total main massing through geological time and is explained by different respective relationships of different component terranes of the two countries. Global vicariance at family level suggests that Nothofagaceae/Nothofagus evolved largely as the South Pacific/Antarctic vicariant in the breakup of a world-wide Fagales ancestor. [source] The biogeography of Gunnera L.: vicariance and dispersalJOURNAL OF BIOGEOGRAPHY, Issue 7 2003Livia Wanntorp Abstract Aim The genus Gunnera is distributed in South America, Africa and the Australasian region, a few species reaching Hawaii and southern Mexico in the North. A cladogram was used to (1) discuss the biogeography of Gunnera and (2) subsequently compare this biogeographical pattern with the geological history of continents and the patterns reported for other Southern Hemisphere organisms. Location Africa, northern South America, southern South America, Tasmania, New Zealand, New Guinea/Malaya, Hawaii, North America, Antarctica. Methods A phylogenetic analysis of twenty-six species of Gunnera combining morphological characters and new as well as published sequences of the ITS region, rbcL and the rps16 intron, was used to interpret the biogeographical patterns in Gunnera. Vicariance was applied in the first place and dispersal was only assumed as a second best explanation. Results The Uruguayan/Brazilian Gunnera herteri Osten (subgenus Ostenigunnera Mattfeld) is sister to the rest of the genus, followed sequentially upwards by the African G. perpensa L. (subgenus Gunnera), in turn sister to all other, American and Australasian, species. These are divided into two clades, one containing American/Hawaiian species, the other containing all Australasian species. Within the Australasian clade, G. macrophylla Blume (subgenus Pseudogunnera Schindler), occurring in New Guinea and Malaya, is sister to a clade including the species from New Zealand and Tasmania (subgenus Milligania Schindler). The southern South American subgenus Misandra Schindler is sister to a clade containing the remaining American, as well as the Hawaiian species (subgenus Panke Schindler). Within subgenus Panke, G. mexicana Brandegee, the only North American species in the genus, is sister to a clade wherein the Hawaiian species are basal to all south and central American taxa. Main conclusions According to the cladogram, South America appears in two places, suggesting an historical explanation for northern South America to be separate from southern South America. Following a well-known biogeographical pattern of vicariance, Africa is the sister area to the combined southern South America/Australasian clade. Within the Australasian clade, New Zealand is more closely related to New Guinea/Malaya than to southern South America, a pattern found in other plant cladograms, contradictory to some of the patterns supported by animal clades and by the geological hypothesis, respectively. The position of the Tasmanian G. cordifolia, nested within the New Zealand clade indicates dispersal of this species to Tasmania. The position of G. mexicana, the only North American species, as sister to the remaining species of subgenus Panke together with the subsequent sister relation between Hawaii and southern South America, may reflect a North American origin of Panke and a recolonization of South America from the north. This is in agreement with the early North American fossil record of Gunnera and the apparent young age of the South American clade. [source] Do introduced North American beavers Castor canadensis engineer differently in southern South America?MAMMAL REVIEW, Issue 1 2009An overview with implications for restoration ABSTRACT 1Twenty-five pairs of North American beavers Castor canadensis Kuhl were introduced to Tierra del Fuego Island in 1946. The population has expanded across the archipelago, arriving at the Chilean mainland by the mid-1990s. Densities range principally between 0.5,2.05 colonies/km. They have an impact on between 30,50% of stream length and occupy 2,15% of landscape area with impoundments and meadows. Beaver impacts constitute the largest landscape-level alteration in subantarctic forests since the last ice age. 2The colonization pattern, colony densities and impacted area indicate that habitat in the austral archipelago is optimal for beaver invasion, due to low predator pressure and suitable food resources. Nothofagus pumilio forests are particularly appropriate habitat, but a more recent invasion is occurring in adjacent steppe ecosystems. Nonetheless, Nothofagus reproductive strategies are not well adapted to sustain high beaver population levels. 3Our assessment shows that at the patch-scale in stream and riparian ecosystems, the direction and magnitude of exotic beaver impacts are predictable from expectations derived from North American studies, relating ecosystem engineering with underlying ecological mechanisms such as the relationships of habitat heterogeneity and productivity on species richness and ecosystem function. 4Based on data from the species' native and exotic range, our ability to predict the effects of beavers is based on: (i) understanding the ecological relationships of its engineering effects on habitat, trophic dynamics and disturbance regimes, and (ii) having an adequate comprehension of the landscape context and natural history of the ecosystem being engineered. 5We conclude that beaver eradication strategies and subsequent ecosystem restoration efforts, currently being considered in southern Chile and Argentina, should focus on the ecology of native ecosystems rather than the biology of this invasive species per se. Furthermore, given the nature of the subantarctic landscape, streams will probably respond to restoration efforts more quickly than riparian ecosystems. [source] Synoptic features associated with critical water level rises in the Río de la PlataMETEOROLOGICAL APPLICATIONS, Issue 2 2005A. P. Alessandro This study aims to describe the synoptic features that caused the water level in the Río de la Plata estuary to rise above critical levels between December 1989 and December 1998. Floods in the estuary can seriously affect the land beside the river from Punta Indio (35.22°S,57.17°W) to the Paraná delta, including the lowlands of Buenos Aires City. Surface pressure patterns associated with floods in the Río de la Plata estuary were obtained by using Quartimax rotated T-mode Principal Component Analysis (PCA) of 1000 hPa geopotential heights. The PCA patterns and 1000 hPa composite and anomaly fields show two main causes for overflows in the Río de la Plata estuary. First, the presence of a surface anticyclone, located south of Buenos Aires province and over northern Patagonia; and, second, cyclogenesis over northeastern Argentina or over Uruguay. The two synoptic features are often present simultaneously. Two representative points were selected in the area under study: one over the continent at the Aeroparque meteorological station (34.34°S,58.25°W) and another over the ocean between 36°S,56°W and 36°S,50°W. Predominant 1000 hPa wind directions associated with overflows were SE at the former location and SSW at the latter. Based on the analysis of the obtained fields, the relationship between the estuary overflow and blocking situations and/or positive pressure anomalies over southern South America and adjacent seas was studied. The zonal circulation index (I), used to detect blocking actions, was found to be useful for identifying synoptic situations related to the estuary swelling. The probability of water level rises in the Río de la Plata with a blocking or I > 0 at 70°W is 0.48, 0.72, 0.78 and 0.73, for summer, autumn, winter and spring, respectively. When I > 0 is observed over the Atlantic at 40°W the probability of flooding is 0.16 for the whole year, but it decreases to 0.028 in autumn, winter and spring. These results and weather charts from different numerical prediction models show that alerts of possible Río de la Plata estuary overflow can be released five days in advance. Copyright © 2005 Royal Meteorological Society [source] Reproductive interactions mediated by flowering overlap in a temperate hummingbird,plant assemblageOIKOS, Issue 4 2010Marcelo A. Aizen Pollinator-mediated competition through shared pollinators can lead to segregated flowering phenologies, but empirical evidence for the process responsible for this flowering pattern is sparse. During two flowering seasons, we examined whether increasing overlap in flowering phenology decreased conspecific pollination, increased heterospecific pollination, and depressed seed output in the seven species composing a hummingbird,plant assemblage from the temperate forest of southern South America. Overall trends were summarized using meta-analysis. Despite prevailing negative associations, relations between phenological overlap and conspecific pollen receipt varied extensively among species and between years. Heterospecific pollen receipt was low and presumably of limited biological significance. However, our results supported the hypothesis that concurrent flowering promotes interspecific pollen transfer, after accounting for changes in the abundance of conspecific flowers. Seed output was consistently reduced during maximum phenological overlap during the first flowering season because of limited fruit set. Responses varied more during the second year, despite an overall negative trend among species. Relations between estimated effects of phenological overlap on pollination and seed output, however, provided mixed evidence that conspecific pollen loss during pollinator visits to foreign flowers increases pollen limitation. By flowering together, different plant species might benefit each other's pollination by increasing hummingbird recruitment at the landscape level. Nevertheless, our results are mostly consistent with the hypothesis of pollinator-mediated competition shaping the segregated flowering pattern reported previously for this temperate plant assemblage. The mechanisms likely involve effects on male function, whereby pollen-transport loss during heterospecific flower visits limit pollen export, and more variable effects on female function through pollen limitation. [source] Spatial patterns and evolutionary processes in southern South America: A study of dental morphometric variationAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Valeria Bernal Abstract The purpose of this article is to examine the patterns of evolutionary relationships between human populations from the later Late Holocene (1,500,100 years BP) of southern South America on the basis of dental morphometric data. We tested the hypotheses that the variation observed in this region would be explained by the existence of populations with different phylogenetic origin or differential action of gene flow and genetic drift. In this study, we analyzed permanent teeth from 17 samples of male and female adult individuals from throughout southern South America. We measured mesiodistal and buccolingual diameters at the base of the crown, along the cement,enamel junction. The results of multiple regression analysis and a mantel correlogram indicate the existence of spatial structure in dental shape variation, as the D2 Mahalanobis distance between samples increases with increasing geographical distance between them. In addition, the correlation test results show a trend toward reduction of the internal variation of samples with increasing latitude. The detected pattern of dental variation agrees with the one expected as an outcome of founder serial effects related to an expansion of range during the initial occupation of southern South America. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Southern hemisphere winter ozone fluctuationsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 572 2001P. K. Vigliarolo Abstract In this paper the relationship between ozone and atmospheric variability is explored over the southern hemisphere during the austral winter season, with special emphasis on synoptic transient fluctuations. The analysis of ozone tracks (or high-frequency ozone variability) shows that they have a significant correspondence with storm tracks at middle and high latitudes. Moreover, ozone tracks maximize over the Indian Ocean slightly downstream of the storm-track maximum, while over the Pacific region both ozone and storm tracks show decreased amplitudes. In particular, over southern South America (a region of climatological winter ozone minima and moderate to high ozone variability) the leading winter synoptic-scale variability mode was identified through a rotated extended empirical orthogonal function analysis applied to the meridional-wind perturbation at 300 hPa. The resulting mode is characterized by a baroclinic wave travelling eastward along subpolar latitudes, which maximizes near the tropopause level. Composite ozone fields based on this mode confirm, from a statistical point of view, the classical relationship between ridges (troughs) and minimum (maximum) ozone content. Furthermore, it is shown that dynamical processes in the upper troposphere and lower stratosphere associated with subpolar waves are responsible for the observed ozone distribution. This happens due to the barotropic equivalent vertical structure of the wave, together with the fact that ozone partial pressure maximizes near the level where the waves attain maximum amplitudes. [source] Non-symbiotic nitrogen fixation during leaf litter decomposition in an old-growth temperate rain forest of Chiloé Island, southern Chile: Effects of single versus mixed species litterAUSTRAL ECOLOGY, Issue 2 2010CECILIA A. PÉREZ Abstract Heterotrophic nitrogen fixation is a key ecosystem process in unpolluted, temperate old-growth forests of southern South America as a source of new nitrogen to ecosystems. Decomposing leaf litter is an energy-rich substrate that favours the occurrence of this energy demanding process. Following the niche ,complementarity hypothesis', we expected that decomposing leaf litter of a single tree species would support lower rates of non-symbiotic N fixation than mixed species litter taken from the forest floor. To test this hypothesis we measured acetylene reduction activity in the decomposing monospecific litter of three evergreen tree species (litter C/N ratios, 50,79) in an old-growth rain forest of Chiloé Island, southern Chile. Results showed a significant effect of species and month (anova, Tukey's test, P < 0.05) on decomposition and acetylene reduction rates (ARR), and a species effect on C/N ratios and initial % N of decomposing leaf litter. The lowest litter quality was that of Nothofagus nitida (C/N ratio = 78.7, lignin % = 59.27 ± 4.09), which resulted in higher rates of acetylene reduction activity (mean = 34.09 ± SE = 10.34 nmol h,1 g,1) and a higher decomposition rate (k = 0.47) than Podocarpus nubigena (C/N = 54.4, lignin % = 40.31 ± 6.86, Mean ARR = 4.11 ± 0.71 nmol h,1 g,1, k = 0.29), and Drimys winteri (C/N = 50.6, lignin % = 45.49 ± 6.28, ARR = 10.2 ± 4.01 nmol h,1 g,1, k = 0.29), and mixed species litter (C/N = 60.7, ARR = 8.89 ± 2.13 nmol h,1g,1). We interpret these results as follows: in N-poor litter and high lignin content of leaves (e.g. N. nitida) free-living N fixers would be at competitive advantage over non-fixers, thereby becoming more active. Lower ARR in mixed litter can be a consequence of a lower litter C/N ratio compared with single species litter. We also found a strong coupling between in situ acetylene reduction and net N mineralization in surface soils, suggesting that as soon N is fixed by diazotroph bacteria it may be immediately incorporated into mineral soil by N mineralizers, thus reducing N immobilization. [source] Patterns of species turnover in plant-pollinator communities along a precipitation gradient in Patagonia (Argentina)AUSTRAL ECOLOGY, Issue 8 2009MARIANO DEVOTO Abstract Recent studies have assessed the influence of different types of gradients (e.g. altitudinal, latitudinal and temporal, among others) on the structure and function of community-level plant-pollinator webs. Although the importance of humidity as a major driver of species-richness gradients worldwide has been stressed by recent reviews, no studies have been specifically designed to address the influence of precipitation gradients on pollination webs. In the present paper we describe for the first time the turnover of species of plants and their associated flower visitors between eight communities located along a steep precipitation gradient in north-west Patagonia, Argentina. Our results show that: (i) there is a high spatial turnover of plant communities and their associated pollinators; (ii) this turnover is strongly related to precipitation changes across the region; and (iii) the turnover rate is similar for plants and pollinators. Our results support the view that the precipitation gradient is a significant factor associated with the regional turnover of plants and their pollinators in the temperate forests of southern South America. [source] A long-term record of Nothofagus dominance in the southern Andes, ChileAUSTRAL ECOLOGY, Issue 1 2005William Pollmann Abstract The general model of regeneration dynamics in Nothofagus forests of southern South America could have value in community ecology if predictive relationships between disturbance history, functional traits and site attributes could be identified. Examined here is the proposal that on favourable sites shade-intolerant Nothofagus are likely not to survive in competition with shade-tolerant, broad-leaved evergreen taxa of temperate rain forests, and persistence, thus, is dependent on periodic coarse-scale disturbance. Comparison of stand dynamics of three old-growth Nothofagus forests at different elevations in the southern Andes, Chile where deciduous Nothofagus alpina dominates the upper canopy, and examination of the life history trade-offs of this variation were made. Stem density of all stems ,5.0 cm d.b.h. was 233,303 stems per hectare, and basal area was 123.9,171.0 m2ha,1. Maximum lifespan of N. alpina was found to be greater than ca 640 years, exceeding all previously reported ages for this species in the region. Forests had a stable canopy composition for this long-term, but some appeared to lack effective regeneration of N. alpina in recent years. Regeneration of N. alpina was generally greater in disturbed stands and higher elevation than in undisturbed stands and at lower elevation. Recruitment emerged to be strongly affected by competitive over- and understorey associates. There was a gradient of increasing dependence of N. alpina on disturbance towards the more productive end of the environment gradients, and hence less dependence of N. alpina on disturbance for its regeneration towards higher elevation. The study confirms that changes in forest composition may be explained by processes occurring in accordance with the predictions of the existing model of Nothofagus regeneration dynamics, providing stronger evidence specifically directed at mid-tolerant N. alpina, and by factoring out regeneration dynamics on favourable sites. Thus, for N. alpina, trait differences probably contribute to the competitive advantage over its associates in productive habitats, and may be linked to small-to-intermediate-sized disturbances which inevitably occur as older trees die, enabling N. alpina to persist in forests and therefore maintain species coexistence for the long-term. [source] Litterfall dynamics and nitrogen use efficiency in two evergreen temperate rainforests of southern ChileAUSTRAL ECOLOGY, Issue 6 2003CECILIA A. PEREZ Abstract In unpolluted regions, where inorganic nitrogen (N) inputs from the atmosphere are minimal, such as remote locations in southern South America, litterfall dynamics and N use efficiency of tree species should be coupled to the internal N cycle of forest ecosystems. This hypothesis was examined in two evergreen temperate forests in southern Chile (42°30'S), a mixed broad-leaved forest (MBF) and a conifer forest (CF). Although these forests grow under the same climate and on the same parental material, they differ greatly in floristic structure and canopy dynamics (slower in the CF). In both forests, biomass, N flux, and C/N ratios of fine litterfall were measured monthly from May 1995 to March 1999. There was a continuous litter flux over the annual cycle in both forests, with a peak during autumn in the CF. In the MBF, litterfall decreased during spring. In both forests, the C/N ratios of litterfall varied over the annual cycle with a maximum in autumn. Annual litterfall biomass flux (Mean ± SD = 3.3 ± 0.5 vs 2.0 ± 0.5 Mg ha -1) and N return (34.8 ± 16 vs 9.1 ± 2.8 kg N ha -1) were higher in the MBF than in the CF. At the ecosystem level, litterfall C/N was lower in the MBF (mean C/N ratio = 60.1 ± 15, n= 3 years) suggesting decreased N use efficiency compared with CF (mean C/N ratio = 103 ± 19.6, n= 3 years). At the species level, subordinated (subcanopy) tree species in the MBF had significantly lower C/N ratios (<50) of litterfall than the dominant trees in the CF and MBF (>85). The litterfall C/N ratio and percentage N retranslocated were significantly correlated and were lower in the MBF. The higher net N mineralization in soils of the MBF is related to a lower N use efficiency at the ecosystem and species level. [source] | |||||||||||||