Initiation Date (initiation + date)

Distribution by Scientific Domains

Selected Abstracts

Estimation of the carbon sequestration by a heterogeneous forest: night flux corrections, heterogeneity of the site and inter-annual variability

Abstract Continuous measurements of the net CO2 flux exchanged in a mixed forest with the atmosphere were performed over 5 years at the Vielsalm experimental site. The carbon sequestration at the site was deduced by a summation of the measurements. Problems associated with this summation procedure were discussed. The carbon sequestration in the ecosystem was presented and its interannual variability was discussed. An estimation of the night flux correction was given. The correction was applied by replacing measurements made during quiet nights by a parameterization. The impact of the correction was shown to vary between 10 and 20% of the uncorrected flux, according to the year. The need to include the storage flux during turbulent periods was emphasized: its neglect leads to an error which will be greater than the one it tries to correct. It was also shown that the heterogeneity of the site made it necessary to split the data into separate series corresponding to the different vegetation patches and to fill the data gaps by using an algorithm that takes account of the weather conditions. Two series were defined, one corresponding to a beech subplot, the other to a conifer subplot. The uncertainty owing to the data split and the data gap-filling was about 15,20% annually. The carbon sequestration was then analysed in both the subplots. The length of the growing season was about 210 days in the beech and 240 days in the conifer. The carbon sequestration over 5 years was 2.28 kg C m2,2 in the beech and 3.58 kg C m2,2 in the conifer. The main difference between the species appeared in spring, between March and May, when the beeches were leafless. Significant interannual variations were observed in both the subplots. They appeared mainly in summer and were primarily because of the variations in the radiation and air humidity regimes. In addition, an impact of the interannual variation of the vegetation area index (VAI) and of the leaf initiation date was observed in the beech. Finally, a decline of the carbon sequestration efficiency of the ecosystem during the season was observed in both the subplots. It was because of neither the variation in any climatic variables nor VAI variation. [source]

Individual quality mediates trade-offs between reproductive effort and immune function in tree swallows

Summary 1Individual variation in the trade-off between self-maintenance and offspring quality was assessed in tree swallows, Tachycineta bicolor, by manipulating reproductive effort while simultaneously immunochallenging breeding females. 2An experimental manipulation of parental effort was conducted by creating broods of, on average, three, five and eight nestlings. Breeding females were immunochallenged to mount a humoral immune response to sheep red blood cells (SRBC) and a cell-mediated response to phytohaemagglutinin (PHA). The consequences of adult decisions on offspring quality were assessed through immune responses to PHA, growth rates and residual body mass of nestlings. 3Clutch initiation date, a strong measure of individual quality in tree swallows, was linked with immune responses, with earlier-nesting, presumably higher quality, females mounting stronger immune responses than did later-nesting birds. Increased reproductive effort led to decreased parental immune responses. There was a significant interaction between individual quality and reproductive effort treatment, with lower-quality individuals showing greater depression of humoral immune response to SRBC while raising enlarged broods, suggesting individual-level variation in trade-offs. 4Breeding females raising enlarged broods tended to raise offspring of similar quality to control females, with only growth rate decreasing with increasing brood size, but not residual nestling body mass or nestling immunocompetence. This suggests that females are maintaining offspring quality at the cost of their own immune system maintenance. [source]

A record of Late Pleistocene and Holocene carbon accumulation and climate change from an equatorial peat bog (Kalimantan, Indonesia): implications for past, present and future carbon dynamics

S. E. Page
Abstract A 9.5,m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26,000,cal.,yr,BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation in SE Asia. The core shows clear evidence for differential rates of peat formation and carbon storage. A short period of initial accumulation is followed by a slow rate during the LGM, with fastest accumulation during the Holocene. Between ,13,000 and 8000,cal.,yr,BP, >,450,cm of peat were deposited, with highest rates of peat (>,2,mm,yr,1) and carbon (>,90,g,C,m,2,yr,1) accumulation between 9530 and 8590,cal.,yr,BP. These data suggest that Kalimantan peatlands acted as a large sink of atmospheric CO2 at this time. Slower rates of peat (0.15,0.38,mm,yr,1) and carbon (7.4,24.0,g,C,m,2,yr,1) accumulation between ,8000 and 500,cal.,yr,BP coincide with rapid peat formation in coastal locations elsewhere in SE Asia. The average LORCA (long-term apparent carbon accumulation rate) for the 9.5,m core is 56,g,C,m,2,yr,1. These data suggest that studies of global carbon sources, sinks and their dynamics need to include information on the past and present sizeable peat deposits of the tropics. Copyright © 2004 John Wiley & Sons, Ltd. [source]

A saltwater flotation technique to identify unincubated eggs

Carol A. Devney
ABSTRACT Field studies on nesting birds sometimes involve questions related to nest initiation dates, length of the incubation period, or changes in parental incubation behavior during various stages of incubation. Some of this information can be best assessed when a nest is discovered before the eggs have undergone any incubation, and this has traditionally been assessed by floating eggs in freshwater. However, because the freshwater method is not particularly accurate in identifying unincubated eggs, we developed a more reliable saltwater flotation method. The saltwater method involves diluting a saturated saltwater solution with freshwater until a salt concentration is reached where unincubated eggs sink to the bottom and incubated eggs float to the surface. For Laughing Gulls (Leucophaeus atricilla), floating eggs in freshwater failed to identify 39.0% (N= 251) of eggs that were subsequently found by candling to have undergone incubation prior to collection. By contrast, in a separate collection of gull eggs, no eggs that passed the saltwater test (N= 225) were found by a later candling to have been incubated prior to collection. For Double-crested Cormorants (Phalacrocorax auritus), floating eggs in freshwater failed to identify 15.6% (N= 250) of eggs that had undergone incubation prior to collection, whereas in a separate collection, none of the eggs that passed the saltwater test (N= 85) were found by a later candling to have been incubated prior to collection. Immersion of eggs in saltwater did not affect embryo survival. Although use of the saltwater method is likely limited to colonial species and requires calibrating a saltwater solution, it is a faster and more accurate method of identifying unincubated eggs than the traditional method of floating eggs in freshwater. RESUMEN Los estudios de campo sobre la nidificación a veces involucran preguntas relacionadas a las fechas de iniciación de la nidificación, la duración del periodo de incubación o cambios en el comportamiento de incubación de los padres durante varias etapas del periodo de incubación. Parte de esta información se puede evaluar mejor cuando un nido es descubierto antes de que los huevos han sido incubados y esto se ha tradicionalmente evaluado mediante la flotación de los huevos en agua dulce. Sin embargo, por la razón que este método no es particularmente preciso en la identificación de huevos que no han sido incubados, hemos desarrollado un método de flotación en agua salada más fiable. El método de agua salada involucra la dilución de una solución saturada de agua salada con agua dulce hasta llegar a una concentración en la cual los huevos no-incubados se hunden hasta el fondo y los huevos incubados flotan. Para huevos de Leucophaeus atricilla, la flotación de huevos en agua dulce no pudo identificar el 39.0% (N= 251) de los huevos que fueron subsecuentemente identificados mediante el uso de luz de vela de haber sido incubados antes que fueron colectados. En contraste, un una colección separada de huevos de esta especie, ninguno de los huevos que pasaron la prueba de agua salada (N= 225) fueron identificados subsecuentemente mediante el método de luz de vela como incubados. Para los huevos de Phalacrocorax auritus, la flotación de huevos en agua dulce no pudo identificar el 15.6% (N= 250) de los huevos que fueron incubados antes de ser colectados, mientras que en una colección separada, ninguno de los huevos que pasaron la prueba de agua salada (N= 85) fueron identificados en una prueba posterior usando luz de vela como incubados antes de ser colectados. La inmersión de huevos en agua salada no afectó la supervivencia del embrión. Aunque el uso del método de agua salada es probablemente limitado a especies que nidifican en colonias y requiere de calibrar una solución de agua salada, es un método más rápido y fiable para identificar los huevos no-incubados en comparación al método tradicional de flotar los huevos en agua dulce. [source]