Cumulative Effects of Wildfire Adversely Affect Greater Sage-Grouse in the Great Basin plus 1 more

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Title: USGS Newsroom

Cumulative Effects of Wildfire Adversely Affect Greater Sage-Grouse in the Great Basin plus 1 more

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Cumulative Effects of Wildfire Adversely Affect Greater Sage-Grouse in the Great Basin

Posted: 10 Sep 2015 11:30 AM PDT

Summary: Slowing fire-related population declines in greater sage-grouse in the Great Basin over the next 30 years may depend on the intensity of fire suppression efforts in core breeding areas and long-term patterns of precipitation, according to a just-published USGS-led study

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Contact Information:

Catherine Puckett ( Phone: 352-377-2469 ); Carol  Schuler ( Phone: 541-750-1031 );

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Slowing fire-related population declines in greater sage-grouse in the Great Basin over the next 30 years may depend on the intensity of fire suppression efforts in core breeding areas and long-term patterns of precipitation, according to a just-published USGS-led study.

The authors conducted an extensive analysis of wildfire and climatic effects on greater sage-grouse population growth derived from 30 years (1984-2013) of breeding area-count data, along with wildfire and precipitation patterns. They constructed a model that also simulated different post-fire recovery times for sagebrush habitats based on soil attributes -- soil moisture and temperature maps -- that strongly influence resilience to wildfire and resistance to invasive grass species.

This research links multi-decadal patterns of wildfire across the Great Basin with multi-decadal data on greater sage-grouse population dynamics and climate.

If the current trend in wildfire continues unabated, model results predicted steady and substantial declines of greater sage-grouse populations across the Great Basin, with an average of about half of current population numbers being lost by the mid-2040s.

The researchers also found that greater sage-grouse populations increased following periods of above-average precipitation; however the long-lasting effects of wildfire in greater sage-grouse breeding areas negated the positive effects associated with precipitation.

Forecasted climate change may result in less precipitation and warmer, drier soils in sagebrush ecosystems, leaving greater sage-grouse habitat vulnerable to increasingly frequent wildfires. Fire is a natural process in sagebrush ecosystems, but burn size and frequency in the Great Basin have increased over the past few decades in response to the increasing expansion of invasive grasses, primarily cheatgrass.

Wildfires kill nearly all native species of sagebrush, which can transform the habitat into landscapes dominated by invasive grasses when soils are warm and dry. In turn, the presence of invasive grasses can prevent sagebrush from returning and, by serving as tinder, result in a positive feedback loop that promotes more wildfires in future years.

“Greater sage-grouse population persistence may be compromised as sagebrush ecosystems and sage-grouse habitat become more impacted by fire and a changing climate,” said Peter Coates, a research scientist with the USGS Western Ecological Research Center. “Our research shows that targeted fire suppression in core sage-grouse areas is vital to help conserve large blocks of the best habitat for sage-grouse in the Great Basin,”

Scientists also examined different management scenarios that could help offset adverse wildfire effects on greater sage-grouse populations, especially when focused on areas with the best sage-grouse habitat and the greatest number of breeding sage-grouse.

For example, reducing the trend in annual cumulative burned area near leks sites within 3.1 miles (5 km) by 25 percent in identified greater sage-grouse core areas is predicted to do little to prevent population declines over the next 30 years, but reducing it by 75 percent in the same period would substantially slow the decline even under below-average precipitation conditions, stabilize it under normal conditions and result in population growth under above-average conditions.

Coates noted that further long-term research can help identify populations that are most at risk from wildfire or changing climate and lead to more effective targeting of management resources for conservation of sagebrush and greater sage-grouse populations.

This peer-reviewed research, Long-term effects of wildfire on sage-grouse populations: an integration of population and ecosystem ecology for management in the Great Basin, was authored by Peter Coates, USGS; M.A. Ricca, USGS; B.G. Prochazka, USGS; , K.E. Doherty, USFWS; M.L. Brooks, USGS; and M.L. Casazza, USGS.

About Greater Sage-Grouse and the Great Basin

The Great Basin comprises more than 72.7 million hectares (more than 179 million acres) across five states: Nevada, Utah, Idaho, Oregon and California. Wildfire has been identified as a primary disturbance in the Great Basin.

 Greater sage-grouse occur in parts of 11 U.S. states and 2 Canadian provinces in western North America.  The U.S. Fish and Wildlife Service is formally reviewing the status of greater sage-grouse to determine if the species is warranted for listing under the Endangered Species Act.

Megathrust Quake Faults Weaker and Less Stressed than Thought

Posted: 10 Sep 2015 11:00 AM PDT

Summary: Some of the inner workings of Earth’s subduction zones and their “megathrust” faults are revealed in a paper published today in the journal “Science.&rdquo

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Contact Information:

Leslie  Gordon ( Phone: 650-329-4006 ); Susan  Garcia ( Phone: 650-346-0998 
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MENLO PARK, Calif. — Some of the inner workings of Earth’s subduction zones and their “megathrust” faults are revealed in a paper published today in the journal “Science.” U.S. Geological Survey scientist Jeanne Hardebeck calculated the frictional strength of subduction zone faults worldwide, and the stresses they are under. Stresses in subduction zones are found to be low, although the smaller amount of stress can still lead to a great earthquake.

Subduction zone megathrust faults produce most of the world’s largest earthquakes. The stresses are the forces acting on the subduction zone fault system, and are the forces that drive the earthquakes. Understanding these forces will allow scientists to better model the physical processes of subduction zones, and the results of these physical models may give us more insight into earthquake hazards.

“Even a ‘weak’ fault, meaning a fault with low frictional strength, can accumulate enough stress to produce a large earthquake. It may even be easier for a weak fault to produce a large earthquake, because once an earthquake starts, there aren't as many strongly stuck patches of the fault that could stop the rupture,” explained lead author and USGS geophysicist Hardebeck. 

Although the physical properties of these faults are difficult to observe and measure directly, their frictional strength can be estimated indirectly by calculating the directions and relative magnitudes of the stresses that act on them. The frictional strength of a fault determines how much stress it can take before it slips, creating an earthquake.

Evaluating the orientations of thousands of smaller earthquakes surrounding the megathrust fault, Hardebeck calculated the orientation of stress, and from that inferred that all of the faults comprising the subduction zone system have similar strength.  Together with prior evidence showing that some subduction zone faults are “weak”, this implies that all of the faults are “weak”, and that subduction zones are “low-stress” environments.

A “strong” fault has the frictional strength equivalent to an artificial fault cut in a rock sample in the laboratory. However, the stress released in earthquakes is only about one tenth of the stress that a “strong” fault should be able to withstand. A “weak” fault, in contrast, has only the strength to hold about one earthquake's worth of stress.  A large earthquake on a “weak” fault releases most of the stress, and before the next large earthquake the stress is reloaded due to motion of the Earth’s tectonic plates.