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1.
Quantitative Evidence for Increasing Forest Fire Severity in the Sierra Nevada and Southern Cascade Mountains, California and Nevada, USA 总被引:2,自引:0,他引:2
Recent research has concluded that forest wildfires in the western United States are becoming larger and more frequent. A
more significant question may be whether the ecosystem impacts of wildfire are also increasing. We show that a large area
(approximately 120000 km2) of California and western Nevada experienced a notable increase in the extent of forest stand-replacing (“high severity”)
fire between 1984 and 2006. High severity forest fire is closely linked to forest fragmentation, wildlife habitat availability,
erosion rates and sedimentation, post-fire seedling recruitment, carbon sequestration, and various other ecosystem properties
and processes. Mean and maximum fire size, and the area burned annually have also all risen substantially since the beginning
of the 1980s, and are now at or above values from the decades preceding the 1940s, when fire suppression became national policy.
These trends are occurring in concert with a regional rise in temperature and a long-term increase in annual precipitation.
A close examination of the climate–fire relationship and other evidence suggests that forest fuels are no longer limiting
fire occurrence and behavior across much of the study region. We conclude that current trends in forest fire severity necessitate
a re-examination of the implications of all-out fire suppression and its ecological impacts.
Author Contributions: Jay Miller designed the study, performed research, analyzed data, and wrote the article. Hugh Safford performed research,
analyzed data, and wrote the article. Michael Crimmins performed research and analyzed data. Andi Thode designed the study
and performed research. 相似文献
2.
Natural disturbances are an important source of environmental heterogeneity that have been linked to species diversity in
ecosystems. However, spatial and temporal patterns of disturbances are often evaluated separately. Consequently, rates and
scales of existing disturbance processes and their effects on biodiversity are often uncertain. We have studied both spatial
and temporal patterns of contemporary fires in the Sierra Nevada Mountains, California, USA. Patterns of fire severity were
analyzed for conifer forests in the three largest fires since 1999. These fires account for most cumulative area that has
burned in recent years. They burned relatively remote areas where there was little timber management. To better characterize
high-severity fire, we analyzed its effect on the survival of pines. We evaluated temporal patterns of fire since 1950 in
the larger landscapes in which the three fires occurred. Finally, we evaluated the utility of a metric for the effects of
fire suppression. Known as Condition Class it is now being used throughout the United States to predict where fire will be
uncharacteristically severe. Contrary to the assumptions of fire management, we found that high-severity fire was uncommon.
Moreover, pines were remarkably tolerant of it. The wildfires helped to restore landscape structure and heterogeneity, as
well as producing fire effects associated with natural diversity. However, even with large recent fires, rates of burning
are relatively low due to modern fire management. Condition Class was not able to predict patterns of high-severity fire.
Our findings underscore the need to conduct more comprehensive assessments of existing disturbance regimes and to determine
whether natural disturbances are occurring at rates and scales compatible with the maintenance of biodiversity. 相似文献
3.
In our previous article (Odion and Hanson, Ecosystems 9:1177–89, 2006), we reported that fire severity in the conifer forests of the Sierra Nevada mountains of California, contrary
to prevailing assumptions, did not burn with predominately stand-replacing, high severity fire. The reply by Safford and others
(Ecosystems, this issue) using a new mapping approach also found this pattern. Their methods identify more high severity fire; however,
as we illustrate here, this may be attributed to the different mapping approaches used. We previously also found that condition
class based upon fire return interval departure (FRID) was not an effective predictor of fire severity. Safford and others
(this issue) concluded that there was a strong correlation between FRID-based condition class and fire severity based upon
data from the McNally fire of 2002. The difference between these findings about McNally fire reflects the fact that they combined
FRID categories whereas we kept the categories separate. Here, using their fire severity data to evaluate all three fires,
we found that severity was not predicted by FRID. Developing a consensus definition of fire severity within the scientific
community might help alleviate future contradictions regarding fire effects. 相似文献
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Fire ecology and Aboriginal land management in central Arnhem Land, northern Australia: a tradition of ecosystem management 总被引:9,自引:0,他引:9
D. Yibarbuk P. J. Whitehead J. Russell-Smith D. Jackson C. Godjuwa A. Fisher P. Cooke D. Choquenot & D. M. J. S. Bowman 《Journal of Biogeography》2001,28(3):325-343
8.
Worldwide, savanna remnants are losing acreage due to species replacement with shade-tolerant midstory forest species as a response to decades of fire suppression. Because canopy closes grasses and other easily ignitable fuels decline, therefore, fire, when reintroduced after years of absence, is not always effective at restoring the open structure original to these communities. Our study sought to determine if managed grazing is an alternative tool for reducing shrub densities and restoring savanna structure without the impacts on soils and native vegetation observed with unmanaged grazing. We compared effects of fire and managed grazing on shrub and herb composition within degraded oak savanna and tallgrass prairie of the U.S. Upper Midwest using a randomized complete block design. The vegetation response to treatments differed by species and by vegetation type. Total shrub stem densities declined 44% in grazed and 68% in burned paddocks within savanna and by 33% for both treatments within prairie. Within savanna, cattle reduced stem densities of Rubus spp. 97%, whereas fire reduced Ribes missouriense stems 96%. Both fire and grazing were effective at reducing stem numbers for several other shrub species but not to the same degree. Native forbs were suppressed in grazed savanna paddocks, as were native grasses in grazed prairie paddocks along with a minor increase of exotic forbs. We did not observe changes in soil bulk density. We conclude that managed grazing can serve as a valuable supplement but not as a replacement to fire for controlling shrubs in these systems. 相似文献