Response of the mean global vegetation distribution to interannual climate variability   总被引：1，自引：0，他引：1  

Michael Notaro 《Climate Dynamics》2008,30(7-8):845-854

The impact of interannual variability in temperature and precipitation on global terrestrial ecosystems is investigated using a dynamic global vegetation model driven by gridded climate observations for the twentieth century. Contrasting simulations are driven either by repeated mean climatology or raw climate data with interannual variability included. Interannual climate variability reduces net global vegetation cover, particularly over semi-arid regions, and favors the expansion of grass cover at the expense of tree cover, due to differences in growth rates, fire impacts, and interception. The area burnt by global fires is substantially enhanced by interannual precipitation variability. The current position of the central United States’ ecotone, with forests to the east and grasslands to the west, is largely attributed to climate variability. Among woody vegetation, climate variability supports expanded deciduous forest growth and diminished evergreen forest growth, due to difference in bioclimatic limits, leaf longevity, interception rates, and rooting depth. These results offer insight into future ecosystem distributions since climate models generally predict an increase in climate variability and extremes. CCR Contribution # 941  相似文献   

Comparing fire-history interpretations based on area, number and estimated volume of macroscopic charcoal in lake sediments     

Adam A. Ali  Philip E. Higuera  Yves Bergeron  Christopher Carcaillet   《Quaternary Research》2009,72(3):462-468

Sedimentary charcoal particles from lakes are commonly used to investigate fire history. Fire-history reconstructions are based on measuring the surface area or counting the number of charcoal fragments in adjacent samples. Recently, the volume of charcoal particles was advised as a more accurate method for quantifying past charcoal production. Large charcoal datasets, used to synthesize global fire history, include these different types of charcoal measurements and implicitly assume that they provide comparable fire-history information. However, no study has demonstrated that this assumption is valid. Here we compare fire-frequency reconstructions based on measurements of charcoal area and number, and estimates of charcoal volume from two lake sediment records from the eastern Canadian boreal forest. Results indicate that the three proxies provide comparable fire-history interpretations when using a locally defined threshold to identify fire events.  相似文献   

Performance of geosynthetic reinforced soil bridge abutments with modular block facing under fire scenarios     

《Computers and Geotechnics》2017

This paper investigates the effect of fire on the performance of geosynthetic reinforced soil bridge abutments using experimental tests and finite element analyses. Experimental programs were comprised of a series of tensile strength tests at elevated temperatures and fire resistance tests, which were performed on a physical model. Findings revealed the adverse effect of fire on geosynthetic reinforced soil bridge abutments when fire duration exceeded 60 min. Results show that the depth within the backfill affected by the fire is approximately 50 cm.  相似文献   

火试金富集-重量法测定铜精矿中金银含量   总被引：2，自引：0，他引：2       下载免费PDF全文

赵伟  尤雅婷  徐松  封亚辉  郑建明  李建军 《江苏地质》2010,34(1):89-91

研究了新型试金炉和灰吹炉在铜精矿中金银含量重量法检测中的应用,大大提高了铜精矿中金银含量的检出效率,满足了大批量铜精矿样品的快速测定。该方法具有简单、快速、准确度高的特点。  相似文献   

1200 years of fire impact on biogeochemistry as inferred from high resolution diatom analysis in a kettle lake from the Picea mariana-moss domain (Quebec, Canada)     

A. Philibert  Y.T. Prairie  C. Carcaillet 《Journal of Paleolimnology》2003,30(2):167-181

The consequences of fire on water chemistry are important considering that major changes in the frequency and intensity of forest fires are anticipated as a result of global warming. Due to the important differences in succesionnal vegetative trends after fire between mixed-wood and coniferous-dominated forests in Quebec (Canada), we undertook a long-term paleoecological study of the impact of fires on the biogeochemistry of Lac à la Pessière, a small lake located in a conifer-dominated boreal forest ecoregion (Picea mariana-moss domain). The paleolimnological study was carried out using diatom assemblages (class:Bacillariophyceae) to reconstruct changes in environmental variables of limnological interest [pH, total phosphorus (TP), total nitrogen (TN), dissolved organic carbon (DOC) and, epilimnetic carbon dioxide (CO₂)] potentially associated with fire over the last 1200 calendar years. Diatom composition and related reconstructed limnological variables were compared before and after fire events. No significant changes were systematically observed in lake chemistry associated with fire events. However, diatom-inferred epilimnetic CO₂showed a clear decreasing trend over the last 400 cal. yrs BP. The results suggest that fire-induced changes in lake chemistry are limited in catchments dominated by black spruce (Picea mariana). We hypothesize that this fact result of excess moisture associated to the thick humus layer, which likely limits the mobilization of nutrients and major ions even during a fire event.  相似文献   

Postglacial vegetation, climate, and fire history along the east side of the Andes (lat 41-42.5°S), Argentina     

Cathy Whitlock  Maria Martha Bianchi  Vera Markgraf  Megan Walsh 《Quaternary Research》2006,66(2):187-201

The history of the low-elevation forest and forest-steppe ecotone on the east side of the Andes is revealed in pollen and charcoal records obtained from mid-latitude lakes. Prior to 15,000 cal yr BP, the vegetation was characterized by steppe vegetation with isolated stands of Nothofagus. The climate was generally dry, and the sparse vegetation apparently lacked sufficient fuels to burn extensively. After 15,000 cal yr BP, a mixture of Nothofagus forest and shrubland/steppe developed. Fire activity increased between 13,250 and 11,400 cal yr BP, contemporaneous with a regionally defined cold dry period (Huelmo/Mascardi Cold Reversal). The early-Holocene period was characterized by an open Nothofagus forest/shrubland mosaic, and fire frequency was high in dry sites and low in wet sites; the data suggest a sharp decrease in moisture eastward from the Andes. A shift to a surface-fire regime occurred at 7500 cal yr BP at the wet site and at 4400 cal yr BP at the dry site, preceding the expansion of Austrocedrus by 1000-1500 yr. The spread of Austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late Holocene. The change to a surface-fire regime is consistent with increased interannual climate variability and the onset or strengthening of ENSO. The present-day mixed forest dominated by Nothofagus and Austrocedrus was established in the last few millennia.  相似文献   

我们需要保护自然资源吗？     

Bambang Hero Saharjo  Basuki Wasis 《地球科学进展》2006,21(2):178-182

正常而言，在印度尼西亚的苏门答腊和加里曼丹岛，即使在非厄尔尼诺年，每年6月或7月的旱季会出现烟雾问题。研究发现，近年来烟雾问题并不仅仅出现在旱季，雨季也有发生。进一步的观测和野外调研表明，这些烟雾来源于用火烧的方式进行油棕榈及其它林木种植前的土地整理，然而这种方式早已被完全禁止。结果，这两个省的绝大多数的水灾灾区位于这些植被被焚毁的地区。  相似文献   

Holocene Vegetation Dynamics, Fire History, Lake Level and Climate Change in the Kootenay Valley, Southeastern British Columbia, Canada     

Douglas J. Hallett  Leonard V. Hills 《Journal of Paleolimnology》2006,35(2):351-371

The environmental history of the Kootenay Valley in the southern Canadian Rockies was reconstructed using lake sediment from Dog Lake, British Columbia, and compared to other paleoenvironmental studies in the region to understand how vegetation dynamics and fire regimes responded to climate change during the Holocene. A pollen-based vegetation reconstruction indicates five periods of vegetation change. At 10,300 cal yr B.P. Pinus-Juniperus parkland colonized the valley and by 7600 cal yr B.P. was replaced by mixed stands of Pinus, Picea and Pseudotsuga/Larix. Fire frequencies increased to their Holocene maximums during the 8200–4000 cal yr B.P. period. From 5500–4500 cal yr B.P. Pseudotsuga/Larix reached its maximum extent in the Kootenay Valley under a more frequent fire regime. At 5000 cal yr B.P. Picea and Abies began to expand in the area and by 4500 cal yr B.P. the forest shifted to a closed montane spruce forest type with dramatically reduced fire frequency. The shift to less frequent forest fires after 4500 cal yr B.P., along with a moisterPicea – dominated closed forest, corresponds to Neoglacial advances in the Canadian Rockies and Coast Mountains. Fire intervals after 4000 cal yr B.P. are significantly longer than the shorter fire intervals of the early to mid Holocene. A return to drier, more open forest condition occurs between 2400–1200 cal yr B.P. with a slight increase in fire activity and summer drought events. Lower lake levels inferred by charophyte accumulation rates during the 2400–1200 cal yr B.P. interval support this moisture regime shift. An abrupt shift toPicea dominated forest occurred from 1200–1000 cal yr B.P. and a final period of wet-closed forest cover reaches its maximum extent from 700–150 cal yr B.P. that appears to be a response to Little Ice Age cooling. Present forests are within their natural range of variability but are predicted to shift again to a drier more open structure with increased Pseudotsuga/Larix cover. More frequent stand replacing fires and increased area burned likely will accompany this change due to continued global warming.  相似文献   

Predicting gully rejuvenation after wildfire using remotely sensed burn severity data     

Kevin Hyde  Scott W. Woods  Jack Donahue 《Geomorphology》2007,86(3-4):496-511

The loss of surface vegetation and reduced infiltration caused by wildfires can trigger gully rejuvenation, resulting in damage to downstream aquatic resources and risk to human life and property. We developed a spatially explicit metric of burn severity — the Burn Severity Distribution Index (BSDI) — and tested its ability to predict post-fire gully rejuvenation in 1st and 2nd order basins burned in the 2000 Valley Complex fires in the Sapphire Mountains of western Montana. The BSDI was derived from burn severity data interpreted from Landsat 7 satellite imagery using the Normalized Burn Ratio (NBR) method, and ranged from 0.0 for completely unburned basins to 4.0 for basins burned entirely at high severity. In July 2001 rainstorms with peak 30-minute intensities of up to 17 mm h^− 1 triggered gully rejuvenation in 66 of the 171 basins examined. The frequency of gully rejuvenation was higher in basins with higher BSDI values, increasing from zero for basins with a BSDI less than 1.3 to 67% for basins with a BSDI greater than 3.0. Binary logistic regression indicated that BSDI was a more significant predictor of gully rejuvenation than basin morphometric variables. The absence of gully rejuvenation in several basins with a high BSDI was attributed to low gradient, dense riparian vegetation, or concentration of high burn severity at lower elevations in the basin. The presence of gully rejuvenation in several basins with a low BSDI was associated with false negative NBR classification errors in northwest aspects, and concentration of severe burn impacts in the drainage headslopes. BSDI is a useful metric for predicting gully rejuvenation after wildfire. The use of the BSDI in Burned Area Emergency Response team assessments could improve the planning, implementation, and monitoring of burned area recovery treatments.  相似文献   

The Response of Aboriginal Burning Practices to Population Levels and El Niño–Southern Oscillation Events during the mid- to late-Holocene: a case study from the Sydney Basin using charcoal and pollen analysis     

Manu P. Black 《The Australian geographer》2007,38(1):37-52

Pollen and macroscopic charcoal have been analysed from a sedimentary sequence representing approximately 6100 years from a site within Wollemi National Park. This is located to the north-west of Sydney and forms a part of the Greater Blue Mountains World Heritage Area. The overall aim of the work was to examine the prehistoric interrelationships between vegetation, fire and human activity. There were relatively minor changes in the vegetation over the last ～6000 years, perhaps reflecting the climate- and fire-resilient nature of the sclerophyllous vegetation found on Hawkesbury Sandstone throughout the Sydney Basin. Casuarinaceae declined in the late Holocene, a trend that has been detected in numerous palaeoecological studies throughout south-eastern Australia. This decline was unrelated to fire, which has been a persistent feature at the site over the entire analysed sequence. The fire regime at the site changed from 5.7 ka, which is interpreted as reflecting the onset of increased climatic variability associated with El Niño-Southern Oscillation (ENSO) events. Another dramatic change in the fire regime occurred at 3 ka, which was coeval with archaeological changes in the region. It is possible that the change in fire activity from 3 ka represented an alteration to Aboriginal management strategies associated with an increasing population and/or the increased risk of conflagrations in an ENSO-dominated climate.  相似文献