Spring Rainfall (spring + rainfall)

Distribution by Scientific Domains

Selected Abstracts

Long-term carbon exchange in a sparse, seasonally dry tussock grassland

John E. Hunt
Abstract Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m,2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was <0.2 by early summer. The maximum daily net CO2 uptake rate was only 1.5 g C m,2 day,1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m,2 was lost to the atmosphere. During the wet year, 41 g C m,2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall. The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m,3) to the driest value obtained (0.04 m3 m,3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term. [source]

Changes in clutch size, brood size and numbers of nesting Squacco Herons Ardeola ralloides over a 32-year period in the Camargue, southern France

IBIS, Issue 1 2001
Changes in numbers of nesting pairs, clutch size, and brood size of Squacco Herons Ardeola ralloides in the Camargue, southern France were analysed over a 32-year period. The annual numbers of breeding pairs [average 84 pairs pL 30 sd, n = 32 years) exhibited a possible increasing trend, but with considerable variability. This variability is associated with local spring rainfall, which may influence the available surface area of their preferred freshwater habitats. In contrast to population size, clutch size decreased substantially in recent years. Our data do not provide a causal explanation for this change in clutch size, although the reduction temporally corresponds with increasing rice cultivation and with a dramatic increase in the number of Cattle Egrets Bubulcus ibis in the Camargue. [source]

Climate change may account for the decline in British ring ouzels Turdus torquatus

Summary 1Climate change is already affecting biodiversity, but the number of species for which reliable models relate weather and climate to demographic parameters is low. 2We modelled the effect of temperature and rainfall on the breeding success and territory occupancy of ring ouzels Turdus torquatus (L.) in northern Britain, using data from a range of study areas, including one where there was a long-term decline in ring ouzel abundance. 3Timing of breeding was significantly related to meteorological variables affecting birds in the early spring, though there was no evidence that laying dates had advanced. Breeding success was not significantly related to weather variables; instead, over 90% of annual variation in this parameter could be explained by density dependence. 4Annual change in territory occupancy was linked to rainfall and temperature the preceding summer, after the main breeding season and to rainfall in the wintering grounds 24 months previously, coincident with the period of juniper Juniperus sp. (L.) flowering. High temperature in late summer, intermediate levels of late summer rainfall, and high spring rainfall in Morocco 24 months previously all had negative impacts on territory occupancy the following year. 5All three weather variables have changed over recent decades, with a significant increase in summer temperature, a significant decrease in summer rainfall, and a nonsignificant decline in Moroccan spring rainfall. A model based on these trends alone predicted an annual decline in occupancy of 36% (compared with an observed decline of 12%), and suggested that increased summer temperatures may underlie declines in the British ring ouzel population. 6Changes in summer temperature after the main breeding period could affect the survival rates of adult and/or juvenile birds. An improved understanding of the post-breeding ecology of ring ouzels is required to elucidate the mechanisms and causes of this relationship. Such knowledge might allow management aimed at buffering the impacts of climate change on ring ouzels. [source]

Dynamics of common wasps in New Zealand beech forests: a model with density dependence and weather

N. D. Barlow
Summary 1Nest densities of the common wasp ( Vespula vulgaris (L.)) were monitored at six sites for 13 years in the honeydew-rich southern beech ( Nothofagus spp.) forests of New Zealand's South Island. 2Densities of wasp nests were among the highest in the world, up to 30 ha ,1 , and at any one site varied approximately twofold over the study period. 3Strong but not overcompensating density dependence was identified, together with a negative effect of spring rainfall. 4The density dependence appeared to act from the number of autumn queens produced during one year to the number of mature (autumn) nests the next year, rather than through variations in queen production per nest. The same stage was also responsible for most of the variability in autumn nest numbers from year to year, with queen production per nest contributing less. 5Yearly changes in nest density could be summarized by a simple Ricker model including both density dependence and weather, thereby incorporating both previous hypotheses for the determination of wasp abundance. [source]

Dynamic social system in Nubian ibex: can a second mating season develop in response to arid climate?

A. Massolo
Abstract We studied a population of Nubian ibex Capra ibex nubiana in the eastern extreme of its range, the hyper-arid central desert of the Sultanate of Oman. Long-term data were collected from January 1983 to December 1997 by direct observation, as well as VHF telemetry on 12 animals (eight from 1987 to 1990; four from 1994 to 1996). We recorded 884 sightings: 40.4% of single animals and 59.6% of groups. Although no significant monthly variation of group size (Jarman's Typical Group Size) was found, there were distinct peaks in March (4.0 ind. group,1) and September (5.1 ind. group,1). Groups of males and females formed especially in March and November, and female,kid groups in February and July,August. Our data may suggest two mating periods: the first one in autumn (similar to the rut of ibex in temperate mountain areas), with kids born in spring/early summer, after winter,spring rainfall, and the second one in spring, with kids born in late summer/autumn, before winter,spring rainfalls. We suggest that the second rutting period may have evolved as a micro-evolutionary process, with the local population adapting to hyper-arid environment constraints. The spring mating season may favour only females in prime conditions, who can afford a pregnancy in the local severe summers and will deliver kids when plant greening begins, in the autumn, whereas the autumn (original) mating season may be afforded by any female, but kids will be born in an unfavourable period, before the summer drought. [source]