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91.
Grant James Williamson Guy S. Boggs David M. J. S. Bowman 《Regional Environmental Change》2011,11(1):19-27
In Kakadu National Park, a World Heritage property in the Australian monsoon tropics 250 km to the east of Darwin, a number
of recent studies have shown that woody encroachment (expansion of woody communities) and densification (increased biomass
in woody communities) has occurred in the last 40 years. The cause of this increase in woody biomass is poorly understood,
but possibly associated with the control of invasive Asian water buffalo, trend to higher rainfall, and increased frequency
of fires. Mangroves provide an important context to understand these landscape changes, given that they are unaffected by
fire or feral water buffalo. We examine change in mangrove distribution in a series of coastal tropical swamps fringing Darwin,
Northern Territory, Australia over a 30-year period using a series of 7 aerial photographs spanning 23 years from 1974 and
a 2004 high-resolution satellite image. In late 1974, Darwin was impacted by an intense tropical cyclone. Vegetation at 3,000
randomly placed points was manually classified, and a multinomial logistic model was used to asses the impact of landscape
position (coastal, intertidal, and upper-tidal) and swamp on mangrove change between 1974 and 2004. Over the study period,
there was instability and slight mangrove loss at the coast, stability in the intertidal zone, and mangrove gain in the upper-tidal
zone, with an overall increase in mangrove presence of 16.2% above the pre-cyclone distribution. A swamp that was impacted
by drainage works for mosquito control and the construction of a sewage treatment plant showed a greater mangrove increase
than the two unmodified swamps. The mangrove expansion is consistent with woody encroachment observed in nearby but ecologically
distinct systems. Plausible causes for this change include changed local hydrology, changes in sea level, and elevated atmospheric
CO2 concentrations. 相似文献
92.
INTRODUCTION: Compared to younger age groups, older people are more likely to be seriously injured or to die as a result of a traffic crash. METHOD: The aim of the study is to examine the impact of environmental, vehicle, crash, and driver characteristics on injury severity in older drivers involved in traffic crashes by using recently linked police crash records and hospitalization data from New South Wales, Australia. The severity of injury resulting from traffic crashes was measured using the International Classification of Diseases, 10th revision (ICD-10) Injury Severity Score (ICISS). RESULTS: Multivariate analysis identified rurality, presence of complex intersections, road speed limit, driver error, speeding, and seat belt use as independent predictors of injury severity in older people. The type of intersection configuration explained over half of the observed variations in injury severity. IMPACT ON INDUSTRY: Environmental modification such as intersection treatments might contribute to a decrease in the severity of injury in older people involved in road crashes. 相似文献
93.
This study documents the annual reproductive cycle of the Temnopleurid echinoid Holopneustes purpurascens near Sydney. H. purpurascens reached sexual maturity between 11 and 26 mm diameter and was gonochoristic. The sequence of oogenesis was similar to previously described echinoids. However, the proportion of eggs at each stage showed no temporal pattern in abundance, suggesting that vitellogenesis is continuous throughout the year. Spermatogenesis was also similar to other echinoids and showed a significant increase in the proportion of partially spawned testes in spring, followed by a similar increase in the proportion of partially spawned testes in late spring and summer. Gonad indices showed a peak in weight from late winter to mid-spring (9.10ǃ.47 for females; 6.28ǂ.43 for males; mean-SE), then a decline for both sexes. Although spawning was variable over time, there was a peak in the proportion of spawning from late winter to early summer that correlated with the observed peaks in gonad indices and gametogenic cycles. The demographic implications of this reproductive pattern are that new recruits can enter the population through synchronous spawning during the breeding period, and smaller haphazard spawning events at other times of the year. 相似文献
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What resources should be committed to the control of invasive species? This study is based on a survey of nature conservation and forestry authorities, wildlife trusts and private landowners which investigated the extent of the ecological and economic impacts of the invasive non-native plant Rhododendron ponticum in the British Isles. There are data on 52,000 ha of land affected by R. ponticum, more than 30,000 ha of it in nature reserves. For nearly all nature reserves, displacement of native species and habitat changes were both reported. In 2001, respondents controlled 1275 ha of R. ponticum at a cost of pound 670,924. To test the optimality of this, we apply a model of social expenditure. The external costs of R. ponticum control are estimated from the probability that it will spread to contiguous sites and the damage done on invaded sites. These are then used to calculate the socially optimal level of expenditure on R. ponticum control, and the funding gap it identified by comparing the result with current levels of expenditure. The results suggest that a socially optimal level of control effort requires a significant increase in social funding for R. ponticum control, although the size of the increase varies between landholders. 相似文献
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