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Saplings
Kinds of Saplings Terms modified by Saplings Selected AbstractsUV-B radiation constrains the photosynthesis of Quercus robur through impacts on the abundance of Microsphaera alphitoidesFOREST PATHOLOGY, Issue 5 2000By K. K. Newsham Summary Quercus robur saplings were exposed at an outdoor facility in the UK to supplemental levels of UV-B radiation (280,315 nm) under arrays of cellulose diacetate-filtered fluorescent lamps which also produced UV-A radiation (315,400 nm). Saplings were also exposed to supplemental UV-A radiation under arrays of polyester-filtered lamps and to ambient levels of solar radiation under arrays of unenergized lamps. The UV-B treatment was modulated to maintain a 30% elevation above the ambient level of erythemally weighted UV-B radiation. Naturally occurring infections by oak powdery mildew (Microsphaera alphitoides) were more abundant, and developed more rapidly, on lammas leaves of saplings which were exposed to treatment levels of UV-B radiation than on leaves of saplings exposed to supplemental UV-A or to ambient levels of solar radiation over 12 weeks in summer and autumn 1996. An analysis of leaf photosynthetic capacities revealed that M. alphitoides infection reduced the quantum efficiency of photosystem (PS) II by 14% at moderate irradiance. Although there was no direct effect of UV-B radiation on PSII photochemistry, exposure of saplings to supplemental UV-A radiation under polyester-filtered lamps resulted in a 17.5% decrease in PSII quantum efficiency, compared with saplings exposed to ambient solar radiation. The results from our study suggest that photosynthesis of Q. robur may be constrained by exposure to UV-B radiation in the natural environment through impacts on the abundance of M. alphitoides. [source] UV-B effect on Quercus robur leaf litter decomposition persists over four yearsGLOBAL CHANGE BIOLOGY, Issue 4 2001K. K. Newsham Summary The effects of elevated UV-B (280,315 nm) radiation on the long-term decomposition of Quercus robur leaf litter were assessed at an outdoor facility in the UK by exposing saplings to elevated UV-B radiation (corresponding to a 30% increase above the ambient level of erythemally weighted UV-B, equivalent to that resulting from a c. 18% reduction in ozone column) under arrays of cellulose diacetate-filtered fluorescent UV-B lamps that also produced UV-A radiation (315,400 nm). Saplings were also exposed to elevated UV-A radiation alone under arrays of polyester-filtered fluorescent lamps and to ambient solar radiation under arrays of nonenergized lamps. After 8 months of irradiation, abscised leaves were placed into litter bags and allowed to decompose in the litter layer of a mixed deciduous woodland for 4.08 years. The dry weight loss of leaf litter from saplings irradiated with elevated UV-B and UV-A radiation during growth was 17% greater than that of leaf litter irradiated with elevated UV-A radiation alone. Annual fractional weight loss of litter (k), and the estimated time taken for 95% of material to decay (3/k) were respectively increased and decreased by 27% for leaf litter exposed during growth to elevated UV-B and UV-A radiation, relative to that exposed to UV-A alone. The present data corroborate those from a previous study indicating that UV-B radiation applied during growth accelerates the subsequent decomposition of Q. robur leaf litter in soil, but indicate that this effect persists for over four years after abscission. [source] Facilitation of tree saplings by nurse plants: Microhabitat amelioration or protection against herbivores?JOURNAL OF VEGETATION SCIENCE, Issue 2 2008Lorena Gómez-Aparicio Abstract Question: Positive interactions are predicted to be common in communities developing under high physical stress or high herbivory pressure due to neighbour amelioration of limiting physical and consumer stresses, respectively. However, when both stress sources meet in the same community, the relative importance of the two facilitation mechanisms is poorly understood. We ask: What is the relative importance of abiotic vs. biotic mechanisms of facilitation of tree saplings by shrubs in Mediterranean mountain forests? Location: Sierra Nevada, SE Spain (1800,1850 m a.s.l.) Methods: Saplings of four tree taxa (Acer opalus ssp. grana-tense, Quercus ilex, Pinus nigra ssp. salzmanii and P. sylvestris var. nevadensis) were planted following a 2 × 2 factorial design: two levels of herbivory (control and ungulate exclusion) and two microhabitats (under shrubs and in open areas). Sapling survival and growth were monitored for five years. Results: Shrubs had positive effects on sapling survival both in control and ungulate excluded plots. This effect was species-specific, with shrubs increasing the survival of Acer opalus and Quercus ilex three and twofold, respectively, but having a minor effect on the Pinus species. Herbivory damage was also species-specific, being much higher for Acer opalus than for any other species. Shrubs did not protect saplings of any species against ungulates. Thus, all Acer saplings (the most damaged species) suffered herbivory outside the exclosures, which largely reduced sapling height. Conclusions: Protection from abiotic stress (summer drought and winter frost) was much more relevant than protection from biotic stress (herbivory). However, we propose that the final balance between the two mechanisms can be expected to vary strongly between sites, depending on the relative magnitude of the different sources of stress and the intrinsic traits (e.g. palatability) of the species interacting. [source] Spatial patterns and associations in a Quercus-Betula forest in northern ChinaJOURNAL OF VEGETATION SCIENCE, Issue 3 2004J.H. Hou Abstract: Question: Are species-specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest? Location: Dongling Mountains, North China, 1300 m a.s.l. Methods: Ripley's K -function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling). Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m). Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long-term dynamics of the forest. [source] Interactive effects of increased temperature and CO2 on the growth of Quercus myrsinaefolia saplingsPLANT CELL & ENVIRONMENT, Issue 10 2001T. Usami Abstract The interactive effects of increased temperature and CO2 enrichment on the growth of 2-year-old saplings of Quercus myrsinaefolia, an evergreen broad-leaved oak, were studied throughout an entire year in the vicinity of their northernmost distribution. Saplings were grown under different conditions in two chambers: (1) a temperature gradient chamber at ambient temperature, 3 and 5 °C warmer conditions with an ambient CO2 concentration, and (2) in a CO2 temperature gradient chamber at 3 °C warmer conditions with 1·5 times the normal CO2 concentration, and 5 °C warmer conditions with doubled CO2 concentration. The 3 and 5 °C warmer conditions enhanced the relative growth rate during almost the entire year, producing 53 and 47% increases in annual biomass production, 27 and 44% enhancement of root growth during shoot dormancy and 3 and 5 week prolongation of the shoot growing period, respectively. However, a daily mean air temperature exceeding 30 °C under the 5 °C warmer condition caused a marked reduction in net assimilation rate (NAR) from July to September. The CO2 enrichment further enhanced the positive effects of warming in spring and the resulting increases in NAR almost completely compensated for the negative effect of warming during summer. From autumn to winter, attenuation of the effects of CO2 was compensated by the increased sink strength produced by the warming. The annual biomass production was more than doubled by the combination of temperature elevation and CO2 enrichment. [source] The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscapeECOGRAPHY, Issue 2 2006Anne M. Bartuszevige Although invasive plants are recognized as a major ecological problem, little is known of the relative importance of plant community characteristics versus landscape context in determining invasibility of communities. We determined the relative importance of community and landscape features of 30 woodlots in influencing the invasion of Lonicera maackii. We sampled woodlots using the point-quarter method and calculated canopy openness and basal areas and densities of shrub, sapling and tree species, as well as woody species richness. We used aerial photos and ArcView GIS to calculate landscape parameters from the same woodlots using a buffer distance of 1500,m. We used logistic and linear regression analyses to determine the community and landscape factors that best explain L. maackii presence and density. We also tested whether woodlot invasion by L. maackii begins at woodlot edges. Presence of L. maackii was significantly explained only by distance from the nearest town (logistic regression, p=0.017); woodlots nearer town were more likely to be invaded. Among invaded woodlots, density of L. maackii was positively related to the amount of edge in the landscape (partial R2=0.592) and negatively related to total tree basal area (partial R2=0.134), number of native woody species (partial R2=0.054), and sapling shade tolerance index (partial R2=0.054). Lonicera maackii in woodlot interiors were not younger than those on the perimeters, leading us to reject the edge-first colonization model of invasion. Our findings reveal that landscape structure is of primary importance and community features of secondary importance in the invasion of L. maackii. This shrub is invading from multiple foci (towns) rather than an advancing front. Connectivity in the landscape (i.e. the number of corridors) did not promote invasion. However, edge habitat was important for invasion, probably due to increased propagule pressure. The community features associated with L. maackii invasion may be indicators of past disturbance. [source] Natural regeneration and population dynamics of the tree Afzelia quanzensis in woodlands in Southern AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Karin Gerhardt Abstract The logging of tree species of high commercial value is increasing throughout the African continent, yet the ecology of these species is generally poorly known. We studied the regeneration pattern and size class distribution of Afzelia quanzensis populations in northern South Africa over a 5-year period. Recruitment was low as the annual seedling mortality was >65%. Seedlings were located under the canopy and were affected by drought and browsing. The adults were scattered or were in a clump-dispersed pattern, which would result in higher recruitment of offspring near parents. Individuals of 0,10 cm diameter at breast height (DBH) were few, while there were 32 trees ha,1 at >10 cm DBH with an annual mortality of 0.8%. Annual diameter increments varied between 0.06 and 0.28 cm. It appears that the transition from the sapling into the juvenile stage could be a bottleneck in the regeneration of the species. A longer study, including more rainfall cycles, may reveal other patterns as dry and wet years have different impacts on dynamics. Résumé La coupe d'espèces d'arbres de grande valeur commerciale augmente dans tout le continent africain, pourtant l'écologie de ces espèces est généralement mal connue. Nous avons étudié le schéma de régénération et la distribution des classes d'âge des populations d'Afzelia quanzensis dans le nord de l'Afrique du Sud pendant cinq ans. Le recrutement était faible car la mortalité annuelle des jeunes plants était de plus de 65%. Les jeunes plans se trouvaient sous la canopée et étaient affectés par la sécheresse et par le broutage des animaux. Les adultes étaient dispersés ou se trouvaient en un schéma en bosquet, qui résulte en un plus fort recrutement de la progéniture près des parents. Les individus de 0,10 cm DBH étaient rares, alors qu'il y avait32 arbres ha,1à >10 cm DBH, avec une mortalité annuelle de 0,8%. L'incrément annuel du diamètre variait entre 0,06 et 0,28 cm. Il semble que la transition entre le stade de jeune arbre et celui de juvénile pourrait bien constituer un étranglement dans la régénération de l'espèce. Une étude plus longue, comprenant plus de cycles de pluies, pourrait révéler un autre schéma étant donné que les années sèches et humides ont des impacts différents sur cette dynamique. [source] Spatial patterns and associations in a Quercus-Betula forest in northern ChinaJOURNAL OF VEGETATION SCIENCE, Issue 3 2004J.H. Hou Abstract: Question: Are species-specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest? Location: Dongling Mountains, North China, 1300 m a.s.l. Methods: Ripley's K -function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling). Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m). Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long-term dynamics of the forest. [source] Chimpanzees prey on army ants with specialized tool setAMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2010Crickette M. Sanz Abstract Several populations of chimpanzees have been reported to prey upon Dorylus army ants. The most common tool-using technique to gather these ants is with "dipping" probes, which vary in length with regard to aggressiveness and lifestyle of the prey species. We report the use of a tool set in army ant predation by chimpanzees in the Goualougo Triangle, Republic of Congo. We recovered 1,060 tools used in this context and collected 25 video recordings of chimpanzee tool-using behavior at ant nests. Two different types of tools were distinguished based on their form and function. The chimpanzees use a woody sapling to perforate the ant nest, and then a herb stem as a dipping tool to harvest the ants. All of the species of ants preyed upon in Goualougo are present and consumed by chimpanzees at other sites, but there are no other reports of such a regular or widespread use of more than one type of tool to prey upon Dorylus ants. Furthermore, this tool set differs from other types of tool combinations used by chimpanzees at this site for preying upon termites or gathering honey. Therefore, we conclude that these chimpanzees have developed a specialized method for preying upon army ants, which involves the use of an additional tool for opening nests. Further research is needed to determine which specific ecological and social factors may have shaped the emergence and maintenance of this technology. Am. J. Primatol. 72:17,24, 2010. © 2009 Wiley-Liss, Inc. [source] Contrasting Population Dynamics of the Endemic New Caledonian Conifer Araucaria laubenfelsii in Maquis and Rain ForestBIOTROPICA, Issue 4 2010Lesley S. Rigg ABSTRACT This study compares demographic parameters and population dynamics for high disturbance (maquis) and low disturbance (rain forest) environments of the montane conifer, Araucaria laubenfelsii, in New Caledonia. The establishment, growth, survival and reproduction of ca 2500 individuals were followed in permanent plots over 10 yr. Growth and survival rates for A. laubenfelsii show that it is a long-lived, slow growing tree, with evidence of suppression in the sapling size classes in mature rain forest. Growth rates for all size classes are generally faster in maquis than rain forest. Transition matrix analyses estimated positive rates of population increase (, values>1), with populations expanding in maquis, and stable in mature forest. Araucaria laubenfelsii is able to regenerate continuously in maquis and early successional rain forest, but recruitment is limited in older stands. Life table response experiment analyses showed that reproduction, and transitions from sapling to mature tree stage, contributed positively to , in maquis, but negatively in forest. Araucaria laubenfelsii on Mont Do can be considered a long-lived pioneer, with early maquis colonizers helping to drive succession from maquis to forest. While opportunities for recruitment decline with time as rain forest sites develop a closed canopy, occasional gap phase recruitment, combined with disturbance by cyclones, landslides and fire, provide opportunities to ensure species persistence. Understanding contrasting population dynamics of A. laubenfelsii in maquis and rain forest will better facilitate conservation management of this species, particularly given current high rates of land conversion and degradation in New Caledonia. Abstract in French is available at http://www.blackwell-synergy.com/loi/btp [source] Interspecific and Inter-site Variation in Wood Specific Gravity of Tropical TreesBIOTROPICA, Issue 1 2004Article first published online: 15 MAR 200, Helene C. Muller-Landau ABSTRACT Variation in climate and soils results in inter-site differences in the assemblages of tree life history strategies within a community, which has important implications for ecosystem structure and dynamics. I investigated interspecific and inter-site variation in wood specific gravity,an easily measured indicator of tree life history strategy,in four Neotropical forests and analyzed its correlates. Mean wood specific gravity (oven-dry weight divided by fresh volume, sometimes also referred to as wood density in the literature) differed significantly among sites, varying inversely with soil fertility and independently of rainfall, seasonality, and temperature. Mean wood specific gravity values were much higher at Kilometer 41, Manaus, Brazil, where soils are extremely poor, than at Cocha Cashu, Peru, Barro Colorado Island, Panama, or La Selva, Costa Rica, where soils are better and mortality rates of trees are higher. Within sites, wood specific gravity varied widely among species. On Barro Colorado Island, among-species variation was significantly, albeit weakly, negatively correlated with sapling and tree mortality and relative growth rates. Altogether, the results suggest that the distribution of tree life history strategies in a community varies substantially among sites, with important consequences for community and ecosystem properties such as aboveground carbon stores. RESUMEN La variación climática y edáfica da lugar a diferencias entre sitios con respecto a los ensambles de las estrategias de historia de vida de los árboles de una comunidad, lo cual tiene consecuencias importantes para la estructura y la dinámica del ecosistema. Investigué la variación interespecífica y espacial en la gravedad específica de la Madera,un indicador de fácil medición de la estrategia de historia de vida de los árboles,en cuatro bosques neotropicales y analizé sus factores asociados. La gravedad especifica media de la madera (el peso seco dividido por el volumen fresco, frecuentemente llamado "densidad de la madera" en la literatura ecológica) fue significativamente diferente entre sitios, variando inversamente con la fertilidad del suelo, e independientemence de la precipitación, la estacionalidad, y la temperatura. La gravedad especifica media de la madera fue mucho más alta en Kilómetro 41, Manaus, Brasil, donde los suelos son extremadamente pobres, en comparación con Cocha Cashu, Perú, Barro Colorado, Panamá, o La Selva, Costa Rica, donde los suelos son mejores y las tasas de mortalidad de los árboles son más altas. Dentro de los sitios, la gravedad especifica de la madera varió extensamente entre especies. En Barro Colorado, la variación entre especies estuvo correlacionada negativamente, aunque sólo débilmente, con las tasas de mortalidad y de crecimiento relativo de los árboles juveniles y adultos. En conjunto, los resultados sugieren que la distribución de las estrategias de historia de vida de los árboles en una comunidad varía sustancialmente entre sitios, con consecuencias importantes para características comunitarias y del ecosistema tales como las reservas de carbono. [source] Prescribed Burning to Restore Mixed-Oak Communities in Southern Ohio: Effects on Breeding- Bird PopulationsCONSERVATION BIOLOGY, Issue 5 2001Vanessa L. Artman We studied the effects of repeated burning (1,4 years of annual burning) and recovery (1 year after burning,) on the breeding bird community. Burning resulted in incremental but temporary reductions in the availability of leaf litter, shrubs, and saplings, but it did not affect trees, snags, or understory vegetation cover. Of 30 bird species monitored, 4 were affected negatively and 2 were affected positively by burning. Population densities of Ovenbirds ( Seiurus aurocapillus), Worm-eating Warblers ( Helmitheros vermivorus), and Hooded Warblers ( Wilsonia citrina) declined incrementally in response to repeated burning and did not recover within 1 year after burning, suggesting a lag time in response to the changes in habitat conditions. Densities of Northern Cardinals ( Cardinalis cardinalis) fluctuated among years in the control units, but remained low in the burned units. Densities of American Robins ( Turdus migratorius) and Eastern Wood-Pewees ( Contopus virens) increased in response to burning, but these increases were apparent only after several years of repeated burning. In general, burning resulted in short-term reductions in the suitability of habitat for ground- and low-shrub-nesting birds, but it improved habitat for ground- and aerial-foraging birds. Overall, there were no changes in the composition of the breeding-bird community. Total breeding bird population levels were also unaffected by burning. Our results suggest that prescribed burning applied on a long-term basis or across large spatial scales is likely to have adverse effects on ground- and low-shrub-nesting bird species, but other changes in the composition of the breeding-bird community are likely to be minimal as long as the closed-canopy forest structure is maintained within the context of prescribed burning. Resumen: Se está reintroduciendo fuego artificialmente en los bosque del sur de Ohio para determinar su efectividad para restaurar y mantener comunidades de bosques mixtos de encino ( Quercus spp.). Estudiamos los efectos de quemas repetidas (1,4 años de quema anual,) y de recuperación (1 año después de la quema) sobre la comunidad de aves reproductivas. La quema resultó en reducciones temporales en la disponibilidad de hojarasca, arbustos y renuevos, pero no afectó a los árboles, tocones o la cubierta vegetal del sotobosque. De 30 especies de aves monitoredas, 4 fueron afectadas negativamente por la quema y 2 fueron afectadas positivamente. Las densidades de población de Seiurus aurocapillus, de Helmitheros vermivorus y de Wilsonia citrina declinaron incrementalmente en respuesta a quemas repetidas y no se recuperaron en un año después de la quema, sugiriendo un retraso en el tiempo de respuesta a los cambios en las condiciones del hábitat. Las densidades de Cardinalis cardinalis fluctuaron entre años en las unidades control, pero permanecieron bajas en las unidades quemadas. Las densidades de Turdus migratorius y de Contopus virens aumentaron en respuesta a la quema, pero estos incrementos fueron evidentes sólo hasta varios años después de quemas repetidas. En general, en el corto plazo la quema resultó en reducciones en la calidad del hábitat para aves que anidan sobre el suelo y en arbustos bajos, pero mejoró el hábitat para aves que forrajean en el suelo y el aire. En general, no hubo cambios en la composición de la comunidad de aves reproductivas. Los niveles totales de poblaciones de aves reproductivas tampoco fueron afectados por la quema. Nuestros resultados sugieren la posibilidad de que la quema prescrita aplicada a largo plazo o en escalas espaciales grandes tenga efectos adversos sobre especies de aves que anidan sobre el suelo y en arbustos bajos, pero la posibilidad de cambios en la composición de la comunidad de aves reproductivas es mínima. [source] Effects of Acer platanoides invasion on understory plant communities and tree regeneration in the northern Rocky MountainsECOGRAPHY, Issue 5 2005Kurt O. Reinhart Quantitative studies are necessary to determine whether invasive plant species displace natives and reduce local biodiversity, or if they increase local biodiversity. Here we describe the effects of invasion by Norway maple Acer platanoides on riparian plant communities and tree regeneration at two different scales (individual tree vs stand scales) in western Montana, USA, using both descriptive and experimental approaches. The three stands differed in community composition with the stand most dominated by A. platanoides invasion being more compositionally homogenous, and less species rich (,67%), species even (,40%), and diverse (,75%) than the two other stands. This sharp decrease in community richness and diversity of the highly invaded stand, relative to the other stands, corresponded with a 28-fold increase in A. platanoides seedlings and saplings. The dramatic difference between stand 1 vs 2 and 3 suggests that A. platanoides invasion is associated with a dramatic change in community composition and local loss of species diversity; however, other unaccounted for differences between stands may be the cause. These whole-stand correlations were corroborated by community patterns under individual A. platanoides trees in a stand with intermediate levels of patchy invasion. At the scale of individual A. platanoides canopies within a matrix of native trees, diversity and richness of species beneath solitary A. platanoides trees declined as the size of the trees increased. These decreases in native community properties corresponded with an increase in the density of A. platanoides seedlings. The effect of A. platanoides at the stand scale was more dramatic than at the individual canopy scale; however, at this smaller scale we only collected data from the stand with intermediate levels of invasion and not from the stand with high levels of invasion. Transplant experiments with tree seedlings demonstrated that A. platanoides seedlings performed better when grown beneath conspecific canopies than under natives, but Populus and Pinus seedlings performed better when grown beneath Populus canopies, the dominant native. Our results indicate that A. platanoides trees suppress most native species, including the regeneration of the natural canopy dominants, but facilitate conspecifics in their understories. [source] Interannual changes in folivory and bird insectivory along a natural productivity gradient in northern Patagonian forestsECOGRAPHY, Issue 1 2004C. Noemi Mazía Trophic regulation models suggest that the magnitude of herbivory and predation (top-down forces) should vary predictably with habitat productivity. Theory also indicates that temporal abiotic variation and within-trophic level heterogeneity both affect trophic dynamics, but few studies addressed how these factors interact over broad-scale environmental gradients. Here we document herbivory from leaf-feeding insects along a natural rainfall/productivity gradient in Nothofagus pumilio forests of northern Patagonia, Argentina, and evaluate the impact of insectivorous birds on foliar damage experienced by tree saplings at each end of the gradient. The study ran over three years (1997,2000) comprising a severe drought (1998,1999), which allowed us to test how climatic events alter top-down forces. Foliar damage tended to increase towards the xeric, least productive forests. However, we found a predictable change of insect guild prevalence across the forest gradient. Leaf miners accounted for the greater damage recorded in xeric sites, whereas leaf chewers dominated in the more humid and productive forests. Interannual folivory patterns depended strongly on the feeding guild and forest site. Whereas leaf-miner damage decreased during the drought in xeric sites, chewer damage increased after the drought in the wettest site. Excluding birds did not affect leaf damage from miners, but generally increased chewer herbivory on hydric and xeric forest saplings. Indirect effects elicited by bird exclusion became most significant after the drought, when total folivory levels were higher. Thus, interannual abiotic heterogeneity markedly influenced the amount of folivory and strength of top-down control observed across the forest gradient. Moreover, our results suggest that spatial turnovers between major feeding guilds may need be considered to predict the dynamics of insect herbivory along environmental gradients. [source] Wolves, trophic cascades, and rivers in the Olympic National Park, USAECOHYDROLOGY, Issue 2 2008Robert L. Beschta Abstract Gray wolves (Canis lupus) were extirpated in the early 1900s from the Olympic Peninsula of northwestern Washington. Thus, we studied potential cascading effects of wolf removal by undertaking a retrospective study of Roosevelt elk (Cervus elaphus) populations, riparian forests, and river channel morphology. For three riparian sites within the western portion of Olympic National Park, the age structure of black cottonwood and bigleaf maple indicated a pattern of significantly decreased recruitment (growth of seedlings/sprouts into tall saplings and trees) associated with intensive elk browsing in the decades following the loss of wolves. At a riparian site outside the park, which represented a refugium from elk browsing, cottonwood recruitment has been ongoing during the 20th century, indicating that climate and flow regimes, in the absence of intensive herbivory, have not limited the establishment and growth of this deciduous woody species. Using 1994 orthophotos, we also measured channel dimensions and planform morphology of 8-km-long river reaches at each vegetation sampling site and an additional reach outside the park. Channels inside the park versus those outside the park had greater percent braiding (37 vs 2%) and larger ratios of active channel width/wetted width (3·0 vs 1·5 m/m). Results for western Olympic National Park were consistent with a truncated trophic cascade hypothesis whereby ungulate browsing following the extirpation of wolves caused significant long-term impacts to riparian plant communities which, in turn, allowed increased riverbank erosion and channel widening to occur. Copyright © 2008 John Wiley & Sons, Ltd. [source] Resilience of tropical rain forests: tree community reassembly in secondary forestsECOLOGY LETTERS, Issue 5 2009Natalia Norden Abstract Understanding the recovery dynamics of ecosystems presents a major challenge in the human-impacted tropics. We tested whether secondary forests follow equilibrium or non-equilibrium dynamics by evaluating community reassembly over time, across different successional stages, and among multiple life stages. Based on long-term and static data from six 1-ha plots in NE Costa Rica, we show that secondary forests are undergoing reassembly of canopy tree and palm species composition through the successful recruitment of seedlings, saplings, and young trees of mature forest species. Such patterns were observed over time within sites and across successional stages. Floristic reassembly in secondary forests showed a clear convergence with mature forest community composition, supporting an equilibrium model. This resilience stems from three key factors co-occurring locally: high abundance of generalist species in the regional flora, high levels of seed dispersal, and local presence of old-growth forest remnants. [source] Willow genotype, but not drought treatment, affects foliar phenolic concentrations and leaf-beetle resistanceENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2004Carolyn Glynn Abstract In a greenhouse experiment we examined the effect of willow genotype and irrigation regime (moderate drought and well-watered) on plant growth parameters, foliar nitrogen, and phenolic concentrations, as well as on the preference and performance of the blue leaf beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae). The 10 vegetatively propagated willow genotypes in the experiments were F2 full-sibling hybrids, originated from a cross between Salix viminalis (L.) (Salicaceae) (high in condensed tannins) and Salix dasyclados (L.) (Salicaceae) (rich in phenolic glycosides). Insect bioassays were conducted on detached leaves in Petri dishes as well as with free-living insects on intact potted plants. The 10-week long irrigation treatments caused statistically significant phenotypic differences in the potted willow saplings. Total biomass was somewhat higher in the well-watered treatment. The root to total biomass ratio was higher in the drought-treatment plants. There was significant genotypic variation in foliar nitrogen concentrations, and they were higher in the drought-treatment plants. There was also a strong genotypic variation in each of the phenolic substances analyzed. Condensed tannins, which accounted for the greatest proportion of total phenolic mass, were higher in the well-watered treatment. There was, however, no difference in levels of the other phenolics (salicylates, cinnamic acid, flavonoids, and chlorogenic acid) between irrigation treatments. The sum of these phenolics was higher in the well-watered treatment. There was a strong variation in P. vulgatissima larval development on different willow genotypes, and larval performance was negatively correlated with levels of salicylates and cinnamic acid. There was, however, no effect of irrigation treatment on larval performance. Phratora vulgatissima preferred to feed on well-watered plants, and we found a preference for oviposition there, but neither feeding nor oviposition site preference was affected by willow genotype. Adult feeding and oviposition preferences were not correlated with larval performance. [source] UNEXPLAINED SPLIT SEX RATIOS IN THE NEOTROPICAL PLANT-ANT, ALLOMERUS OCTOARTICULATUS VAR. DEMERARAE (MYRMICINAE): A TEST OF HYPOTHESESEVOLUTION, Issue 1 2010Gabriel D. G. Debout We investigated sex allocation in the Neotropical ant Allomerus octoarticulatus var. demerarae. Because Allomerus is a plant symbiont, we could make geographically extensive collections of complete colonies and of foundresses in saplings, allowing us to estimate not only population- and colony-level sex allocation but also colony resource levels and the relatednesses of competing ant foundresses. This species exhibits a strongly split sex ratio, with 80% of mature colonies producing ,90% of one sex or the other. Our genetic analyses (DNA microsatellites) reveal that Allomerus has a breeding system characterized by almost complete monogyny and a low frequency of polyandry. Contrary to theoretical explanations, we find no difference in worker relatedness asymmetries between female- and male-specialist colonies. Furthermore, no clear link was found between colony sex allocation and life history traits such as the number of mates per queen, or colony size, resource level, or fecundity. We also failed to find significant support for male production by workers, infection by Wolbachia, local resource competition, or local mate competition. We are left with the possibility that Allomerus exhibits split sex ratios because of the evolution of alternative biasing strategies in queens or workers, as recently proposed in the literature. [source] Sirococcus shoot blight on Picea spinulosa in BhutanFOREST PATHOLOGY, Issue 1 2007T. Kirisits Summary During a recent survey of forest tree diseases in Western and Central Bhutan, Sirococcus shoot blight and an associated Sirococcus sp. were found on saplings and mature trees of Eastern Himalayan spruce (Picea spinulosa). Based on morphological characteristics and DNA sequence comparisons of the ITS region of the rDNA operon, representative isolates from Bhutan were unequivocally identified as Sirococcus conigenus. The DNA sequence data also showed that these isolates belong to the P group of S. conigenus. To our best knowledge, this is the first report of Sirococcus shoot blight from the Himalayas or any other part of Asia. Sirococcus conigenus does not appear to cause dramatic damage at the moment, but this fungus has the potential to cause severe disease problems on P. spinulosa in Bhutan. [source] Biomass, nutrient and pigment content of beech (Fagus sylvatica) saplings infected with Phytophthora citricola, P. cambivora, P. pseudosyringae and P. undulataFOREST PATHOLOGY, Issue 2 2004F. Fleischmann Summary Fagus sylvatica saplings were infected with Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae and Phytophthora undulata to study the influence of these root pathogens on total belowground and aboveground biomass, on the nutrient distribution within plants, on the concentration of plastid pigments, including tocopherol and on components of the xanthophyll cycle. Phytophthora citricola and P. cambivora infection significantly reduced total biomass of beech when compared with control plants and finally most of these plants died at the end of the experiment. However, beech invaded by the other two Phytophthora spp. did not differ from control plants and none of them was killed. Fine root length as well as the number of root tips of all infected beeches were reduced between 30 and 50%. The excellent growth of beech infected with P. pseudosyringae and P. undulata when compared with control plants was correlated with a strong increase of important root efficiency parameters. Phytophthora citricola and P. cambivora caused a significant reduction in nitrogen concentration of leaves in comparison with control and other infected plants, whereas this nutrient was slightly increased in fine and coarse roots. Furthermore, the phosphorus and potassium concentrations in leaves were impaired after infection with P. citricola. However, foliar concentrations of Ca and Mg were not affected by the different Phytophthora spp., whereas fine and coarse roots were significantly enriched with Ca in beech infected with P. citricola or P. cambivora. The concentrations of , -tocopherol and xanthophyll cycle pigments were increased in plants infected by P. citricola and P. cambivora, indicating that several reactive oxygen species might be formed in leaves during infection. Résumé Des plants de Fagus sylvatica ont été infectés par Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae et Phytophthora undulata pour étudier l'effet de ces pathogènes racinaires sur la biomasse totale aérienne et racinaire, la distribution des éléments minéraux dans les plantes et la concentration en pigments des plastes, tocophérol et composants du cycle des xanthophylles. L'infection par P. citricola et P. cambivora a entraîné une réduction significative de la biomasse totale par rapport aux plantes témoins et la plupart des plants infectés sont morts au cours de l'expérience. Par contre, les hêtres infectés par les deux autres espèces de Phytophthora ne différent pas des témoins et aucune mortalité n'a été observée. Chez tous les hêtres infectés, une réduction de 30 à 50% de la longueur de racines fines et du nombre d'extrémités racinaires a été observée. La très bonne croissance des plants infectés par P. pseudosyringae et P. undulata par rapport aux témoins est associée à une forte augmentation de paramètres importants d'efficience racinaire. P. citricola et P. cambivora ont causé une réduction significative de la concentration foliaire en azote par rapport aux plantes témoins et aux autres plantes infectées, alors que la concentration était légèrement augmentée dans les fines et grosses racines. De plus, la concentration foliaire en phosphore et potassium a été altérée après infection par P. citricola. Les concentrations foliaires en Ca et Mg n'ont pas été affectées par les différentes espèces de Phytophthora, les fines et grosses racines étant significativement enrichies en Ca chez les plants infectés par P. citricola ou P. cambivora. La concentration en , -tocophérol et pigments du cycle des xanthophylles a augmenté dans les plants infectés par P. citricola et P. cambivora, suggérant la formation de plusieurs espèces actives de l'oxygène dans les feuilles pendant l'infection. Zusammenfassung Buchensämlinge wurden mit Phytophthora citricola, Phytophthora cambivora, Phytophthora pseudosyringae und mit Phytophthora undulata infiziert, um den Einfluss dieser Wurzelpathogene auf die oberirdische und unterirdische Biomasse, auf die Nährstoffverteilung innerhalb verschiedener Pflanzenorgane, sowie auf die Gehalte unterschiedlicher Photosynthesepigmente und Komponenten des Xanthophyll- Zyklus studieren zu können. Die Infektion mit P. citricola und P. cambivora führte zu einer deutlich reduzierten Gesamtbiomasse und am Versuchsende waren die meisten Pflanzen abgestorben. Dagegen überlebten alle mit P. pseudosyringae oder P. undulata infizierten Buchen und sie zeigten keine Unterschiede in ihren Biomassen verglichen mit Kontrollpflanzen bzw. übertrafen diese sogar. Die Feinwurzellänge und die Anzahl ihrer Wurzelspitzen war bei allen Phytophthora infizierten Pflanzen zwischen 30 und 50% im Vergleich zu denen der Kontrollen reduziert. Das ausgezeichnete Wachstum der P. pseudosyringae und P. undulata infizierten Pflanzen ging mit stark gesteigerten Wurzeleffizienzparametern einher. Die P. citricola und P. cambivora Infektion führte zu reduzierten Stickstoffgehalten in den Blättern. Die Gehalte in den Wurzeln waren jedoch leicht erhöht. Zudem wurden reduzierte Gehalte an Phosphor und Kalium in den Blättern gemessen. Die Calcium und Magnesium- Konzentrationen der Blätter unterschieden sich nicht von denen der Kontrollen. Allerdings wurde eine Calcium-Anreicherung in den Fein- und Grobwurzeln infizierter Pflanzen gemessen. Weiterhin zeigten wir, dass die Konzentrationen von , -Tocopherol und Pigmenten des Xanthophyll-Zyklus in Blättern P. citricola und P. cambivora infizierter Pflanzen erhöht waren, was möglicherweise auf die Bildung reaktiver Sauerstoffspezies hindeutet. [source] Anisogramma virgultorum on saplings of Betula pendula and Betula pubescens in a district of northern SwedenFOREST PATHOLOGY, Issue 4-5 2002J. WITZELL Summary During the autumn of 1999, the occurrence of the ascomycete Anisogramma virgultorum on saplings of Betula pubescens and Betula pendula was studied in two stands of B. pubescens, two stands of B. pendula and two mixed (B. pubescens and Pinus sylvestris) stands (age approximately 10 years, mean height 2,4 m, d.b.h. 10,20 mm) in a district in the vicinity of Umeå, northern Sweden. Stem and branch cankers associated with A. virgultorum were found on 54.8% of the investigated saplings, without significant difference between B. pendula and B. pubescens. Cankers were observed on 16.0% of stems and on branches of 54.2% of the saplings. Stem cankers appeared on the current year's shoot, as well as at the base of the trees. The mean diameter of the damaged saplings was significantly greater than the mean diameter of undamaged saplings. All samples of cankers with stromata examined in the laboratory showed perithecia with asci. Résumé Anisogramma virgultorum sur jeunes plants de Betula pendula et Betula pubescens dans un district du nord de la Suède Pendant l'été 1999, le développement de l'ascomycète Anisogramma virgultorum a étéétudié sur de jeunes plants de Betula pendula et Betula pubescens dans deux peuplements de B. pubescens, deux peuplements de B. pendula et deux peuplements mélangés (B. pubescens et Pinus sylvestris) (âge: environ 10 ans, hauteur moyenne: 2 à 4 m, dbh: 10 à 20 mm), dans un district près d'Umeå au nord de la Suède. Des chancres de tige et de branches associés àA. virgultorum ont été trouvés sur 54,8% des plants, sans différences significative entre B. pendula et B. pubescens. Les chancres de tige étaient présents sur 16% des plants, et les chancres de branches sur 54,2%. Les chancres de tige étaient situés sur les pousses de l'année en cours aussi bien qu'à la base des arbres. La diamètre moyen des plants attaqués était significativement plus grand que celui des arbres sains. Tous les chancres avec stromas examinés au laboratoire présentaient des périthèces avec des asques. Zusammenfassung Anisogramma virgultorum an Sämlingen von Betula pendula und Betula pubescens in einem Distrikt in Nordschweden Im Herbst 1999 wurde das Vorkommen des Ascomyceten Anisogramma virgultorum an Betula pubescens und Betula pendula in jeweils zwei Reinbeständen dieser Baumarten sowie in zwei Mischbeständen (B. pubescens und Pinus sylvestris) in einem Distrikt in der Nähe von Umeå, Nordschweden, untersucht (Alter ca. 10 Jahre, mittlere Baumhöhe 2,4 m, DBH 10,20 mm). Bei 54,8 % der untersuchten Bäumchen wurden an Stamm und Zweigen Krebse gefunden, die für A.virgultorum typisch sind. Zwischen B. pendula und B. pubescens gab es keine signifikanten Unterschiede. Bei 16 % der Pflanzen wurden Krebse an den Stämmen, bei 54,2 % an den Zweigen beobachtet. Die Stammkrebse traten sowohl am diesjährigen Gipfeltrieb auf als auch an der Stammbasis. Der mittlere Durchmesser geschädigter Pflanzen war signifikant grösser als derjenige von ungeschädigten Pflanzen. Alle Proben von Krebsen mit Stromata, die im Labor untersucht wurden, enthielten Perithecien mit Asci. [source] Co-occurrence of the ascomycete Lophodermium piceae and the rust fungus Chrysomyxa abietis in Norway spruce needlesFOREST PATHOLOGY, Issue 1 2001A. Lehtijärvi The frequency of needles and the proportion of needle segments infected by Lophodermium piceae were compared in symptomless and Chrysomyxa abietis- infected, 1-year-old needles of Picea abies. In late spring, symptomless needles from both rust-infected and healthy saplings were sampled. In addition, rust-infected, totally chlorotic needles and needles with chlorosis along about half their length from the diseased trees were examined. In all three stands, the proportion of segments infected by L. piceae was larger in the rust-infected half of the needle than in the symptomless half; but the difference was statistically significant in only one of the stands. The proportion of L. piceae -infected segments among the nonrust-infected needles was the same as that found for the uninfected half of rust-infected needles (after correction for size differences). No differences in the proportion of L. piceae -infected segments were found between the totally chlorotic, rust-infected needles and the green needles of diseased or healthy trees. [source] UV-B radiation constrains the photosynthesis of Quercus robur through impacts on the abundance of Microsphaera alphitoidesFOREST PATHOLOGY, Issue 5 2000By K. K. Newsham Summary Quercus robur saplings were exposed at an outdoor facility in the UK to supplemental levels of UV-B radiation (280,315 nm) under arrays of cellulose diacetate-filtered fluorescent lamps which also produced UV-A radiation (315,400 nm). Saplings were also exposed to supplemental UV-A radiation under arrays of polyester-filtered lamps and to ambient levels of solar radiation under arrays of unenergized lamps. The UV-B treatment was modulated to maintain a 30% elevation above the ambient level of erythemally weighted UV-B radiation. Naturally occurring infections by oak powdery mildew (Microsphaera alphitoides) were more abundant, and developed more rapidly, on lammas leaves of saplings which were exposed to treatment levels of UV-B radiation than on leaves of saplings exposed to supplemental UV-A or to ambient levels of solar radiation over 12 weeks in summer and autumn 1996. An analysis of leaf photosynthetic capacities revealed that M. alphitoides infection reduced the quantum efficiency of photosystem (PS) II by 14% at moderate irradiance. Although there was no direct effect of UV-B radiation on PSII photochemistry, exposure of saplings to supplemental UV-A radiation under polyester-filtered lamps resulted in a 17.5% decrease in PSII quantum efficiency, compared with saplings exposed to ambient solar radiation. The results from our study suggest that photosynthesis of Q. robur may be constrained by exposure to UV-B radiation in the natural environment through impacts on the abundance of M. alphitoides. [source] Spring 2007 warmth and frost: phenology, damage and refoliation in a temperate deciduous forestFUNCTIONAL ECOLOGY, Issue 6 2009Carol K. Augspurger Summary 1.,Climate change is predicted to bring earlier bud break and perhaps a greater risk of frost damage to developing leaves and flowers. Given the rarity and unpredictability of major frost events and limited community-level phenological observations, comparisons among deciduous forest species experiencing frost damage and refoliation are rare. 2.,This study used phenological observations ongoing at the time of a hard freeze to compare leaf and flower development, frost damage and leaf refoliation of 20 deciduous woody species in Trelease Woods, Champaign Co., IL, USA. Freezing temperatures from 5 to 9 April 2007 followed 22 days after very warm temperatures began in March. 3.,Bud break was the earliest in 17 years. Frost caused damage to leaf buds, developing shoots and/or expanding leaves of canopy trees of six species and saplings of two species. Undamaged species were inactive, or in bud break or shoot expansion. Among damaged species, 11,100% of individuals exhibited some frost damage. Mean damage level per individual ranged from 20% to 100% among species. 4.,Refoliation from dormant buds led to mean final canopy fullness that ranged from 46% to 99% among damaged species, but time of full leaf expansion was extended by 16,34 days for refoliating species. 5.,Frost damaged flowers, but not flower buds or developing fruit, of five of eight species that flowered during the frost period. 6.,The extent of frost damage in 2007 was unusual; damage was greater than any of the other 4 years with frost damage from 1993 to 2009 because record-breaking March temperatures in 2007 caused more species to be at later vulnerable stages with the advent of subfreezing temperatures in April. 7.,Differences among individuals and species in frost damage and ability to refoliate caused strong selection on individuals and differences in carbon gain that could, in the long-term, affect species' abundances. The frost also reduced fruit/seed abundance for insects and mammals. [source] Allocation of above-ground growth is related to light in temperate deciduous saplingsFUNCTIONAL ECOLOGY, Issue 4 2003D. A. King Summary 1Allocational shifts in response to light may be an important factor in allowing plants to survive in shade, while increasing their extension rates and competitive ability in sun. To investigate this response, the allocation of above-ground growth between leaves, branches and stems was studied in saplings of Acer pensylvanicum L. and Castenea dentata (Marsh.) Borkh. in the Appalachian mountains of western Virginia, USA. Measurements of current leaf biomass, current and past year leaf numbers and the growth ring widths of branches and stem were used to estimate biomass partitioning for saplings growing in locations ranging from forest understorey to large openings. 2Both species showed higher leaf area per unit leaf biomass (SLA) and higher allocation of above-ground growth to leaves in shade than in sun. 3There were no differences between species in the slopes of the relationships of allocation and SLA vs estimated irradiance, but SLA was significantly greater in A. pensylvanicum than in C. dentata at a given light level. Hence, somewhat lower production per unit leaf area is required to maintain the canopy in A. pensylvanicum, consistent with foresters' ratings of greater shade tolerance for this species. 4Greater foliar allocation in shade than sun has also been observed in broad-leaved evergreen saplings, but generally not in seedlings. This difference is probably related to differences in size and age between seedlings and saplings. Young seedlings typically show exponential growth with no immediate foliar losses, while shaded saplings lie closer to the steady state where new leaves replace old ones with little additional stem growth. 5Thus trees shift their allocation patterns in an acclimatory fashion, depending on their size and light environment, with the costs of replacing senesced leaves becoming of consequence as juveniles age. [source] The effect of tree height and light availability on photosynthetic leaf traits of four neotropical species differing in shade toleranceFUNCTIONAL ECOLOGY, Issue 1 2000T. Rijkers Abstract 1.,Light-saturated rate of photosynthesis (Amax), nitrogen (N), chlorophyll (Chl) content and leaf mass per unit area (LMA) were measured in leaves of trees of different heights along a natural light gradient in a French Guiana rain forest. The following four species, arranged in order from most shade-tolerant to pioneer, were studied: Duguetia surinamensis, Vouacapoua americana, Dicorynia guianensis and Goupia glabra. Light availability of trees was estimated using hemispherical photography. 2.,The pioneer species Goupia had the lowest LMA and leaf N on both an area and mass basis, whereas Duguetia had the highest values. In general, leaf variables of Vouacapoua and Dicorynia tended to be intermediates. Because Amax/area was similar among species, Goupia showed both a much higher light-saturated photosynthetic nitrogen-use efficiency (PNUEmax) and Amax/mass. Leaves of Vouacapoua demonstrated the greatest plasticity in Amax/area, particularly in small saplings. 3.,A distinction could be made between the effect of tree height and light availability on the structural, i.e. LMA, and photosynthetic leaf characteristics of all four species. The direction and magnitude of the variation in variables were similar among species. 4.,LMA was the key variable that mainly determined variation in the other leaf variables along tree height and light availability gradients, with the exception of changes in chlorophyll concentration. Amax/area, N/area, LMA and stomatal conductance to water vapour (gs) increased, whereas Chl/mass decreased, with both increasing tree height and canopy openness. Amax/mass, PNUEmax and Amax/Chl increased with increasing openness only. N/mass and Chl/area were independent of tree height and openness, except for small saplings of Goupia which had a much lower Chl/area. [source] Erosion and Nutrient Loss on Sloping Land under Intense Cultivation in Southern VietnamGEOGRAPHICAL RESEARCH, Issue 1 2008NGUYEN VAN DE Abstract To help improve the well-being of the local people, a joint Vietnamese-UK team set out to establish a way of estimating soil and nutrient losses under different land management scenarios, using field data extrapolated through remote sensing and GIS, to obtain catchment-wide estimates of the impact of land cover change. Immigration from remote provinces to the Dong Phu District of Binh Phuóc Province, about 120 km north of Ho Chi Minh City, has led to disruption of soil surface stability on easily eroded clayey sandstones, creating rapid nutrient depletion that affects crop yields and siltation in the channel of the Rach Rat river downstream. The poor farmers of the areas see crop yields drop dramatically after two or three years of cultivation due to the fertility decline. Soil loss varies dramatically between wet season and dry season and with ground cover. Erosion bridge measurements showed a mean loss of 85.2 t ha,1 y,1 under cassava saplings with cashew nuts, 43.3 t ha,1 y,1 on uncultivated land and 41.7 t ha,1 y,1 under mature cassava. The rates of erosion were higher than those reported in many other parts of Vietnam, reflecting the high erodibility of the friable sandy soils on the steep side-slopes of the Rach Rat catchment. However, although the actual measurements provide better soil loss data than estimates based on the parameters of soil loss equations, a large number of measurement sites is needed to provide adequate coverage of the crop and slope combinations in this dissected terrain for good prediction using GIS and remote sensing. [source] Patterns of rhizosphere carbon flux in sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) saplingsGLOBAL CHANGE BIOLOGY, Issue 6 2005Richard P. Phillips Abstract Despite its importance in the terrestrial C cycle rhizosphere carbon flux (RCF) has rarely been measured for intact root,soil systems. We measured RCF for 8-year-old saplings of sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) collected from the Hubbard Brook Experimental Forest (HBEF), NH and transplanted into pots with native soil horizons intact. Five saplings of each species were pulse labeled with 13CO2 at ambient CO2 concentrations for 4,6 h, and the 13C label was chased through rhizosphere and bulk soil pools in organic and mineral horizons for 7 days. We hypothesized yellow birch roots would supply more labile C to the rhizosphere than sugar maple roots based on the presumed greater C requirements of ectomycorrhizal roots. We observed appearance of the label in rhizosphere soil of both species within the first 24 h, and a striking difference between species in the timing of 13C release to soil. In sugar maple, peak concentration of the label appeared 1 day after labeling and declined over time whereas in birch the label increased in concentration over the 7-day chase period. The sum of root and rhizomicrobial respiration in the pots was 19% and 26% of total soil respiration in sugar maple and yellow birch, respectively. Our estimate of the total amount of RCF released by roots was 6.9,7.1% of assimilated C in sugar maple and 11.2,13.0% of assimilated C in yellow birch. These fluxes extrapolate to 55,57 and 90,104 g C m,2 yr,1 from sugar maple and yellow birch roots, respectively. These results suggest RCF from both arbuscular mycorrhizal and ectomycorrhizal roots represents a substantial flux of C to soil in northern hardwood forests with important implications for soil microbial activity, nutrient availability and C storage. [source] The importance of low atmospheric CO2 and fire in promoting the spread of grasslands and savannasGLOBAL CHANGE BIOLOGY, Issue 7 2003W. J. BOND Abstract The distribution and abundance of trees can be strongly affected by disturbance such as fire. In mixed tree/grass ecosystems, recurrent grass-fuelled fires can strongly suppress tree saplings and therefore control tree dominance. We propose that changes in atmospheric [CO2] could influence tree cover in such metastable ecosystems by altering their postburn recovery rates relative to flammable herbaceous growth forms such as grasses. Slow sapling recovery rates at low [CO2] would favour the spread of grasses and a reduction of tree cover. To test the possible importance of [CO2]/fire interactions, we first used a Dynamic Global Vegetation Model (DGVM) to simulate biomass in grassy ecosystems in South Africa with and without fire. The results indicate that fire has a major effect under higher rainfall conditions suggesting an important role for fire/[CO2] interactions. We then used a demographic model of the effects of fire on mesic savanna trees to test the importance of grass/tree differences in postburn recovery rates. We adjusted grass and tree growth in the model according to the DGVM output of net primary production at different [CO2] relative to current conditions. The simulations predicted elimination of trees at [CO2] typical of the last glacial period (180 ppm) because tree growth rate is too slow (15 years) to grow to a fire-proof size of ca. 3 m. Simulated grass growth would produce an adequate fuel load for a burn in only 2 years. Simulations of preindustrial [CO2] (270 ppm) predict occurrence of trees but at low densities. The greatest increase in trees occurs from preindustrial to current [CO2] (360 ppm). The simulations are consistent with palaeo-records which indicate that trees disappeared from sites that are currently savannas in South Africa in the last glacial. Savanna trees reappeared in the Holocene. There has also been a large increase in trees over the last 50,100 years. We suggest that slow tree recovery after fire, rather than differential photosynthetic efficiencies in C3 and C4 plants, might have been the significant factor in the Late Tertiary spread of flammable grasslands under low [CO2] because open, high light environments would have been a prerequisite for the spread of C4 grasses. Our simulations suggest further that low [CO2] could have been a significant factor in the reduction of trees during glacial times, because of their slower regrowth after disturbance, with fire favouring the spread of grasses. [source] UV-B effect on Quercus robur leaf litter decomposition persists over four yearsGLOBAL CHANGE BIOLOGY, Issue 4 2001K. K. Newsham Summary The effects of elevated UV-B (280,315 nm) radiation on the long-term decomposition of Quercus robur leaf litter were assessed at an outdoor facility in the UK by exposing saplings to elevated UV-B radiation (corresponding to a 30% increase above the ambient level of erythemally weighted UV-B, equivalent to that resulting from a c. 18% reduction in ozone column) under arrays of cellulose diacetate-filtered fluorescent UV-B lamps that also produced UV-A radiation (315,400 nm). Saplings were also exposed to elevated UV-A radiation alone under arrays of polyester-filtered fluorescent lamps and to ambient solar radiation under arrays of nonenergized lamps. After 8 months of irradiation, abscised leaves were placed into litter bags and allowed to decompose in the litter layer of a mixed deciduous woodland for 4.08 years. The dry weight loss of leaf litter from saplings irradiated with elevated UV-B and UV-A radiation during growth was 17% greater than that of leaf litter irradiated with elevated UV-A radiation alone. Annual fractional weight loss of litter (k), and the estimated time taken for 95% of material to decay (3/k) were respectively increased and decreased by 27% for leaf litter exposed during growth to elevated UV-B and UV-A radiation, relative to that exposed to UV-A alone. The present data corroborate those from a previous study indicating that UV-B radiation applied during growth accelerates the subsequent decomposition of Q. robur leaf litter in soil, but indicate that this effect persists for over four years after abscission. [source] | |||||||||||||||||||||||||||||||