impact of climate change on na forests fire courtesy of tom swetnam, u of arizona, ltrr
TRANSCRIPT
Impact of Climate Change on NA Forests
Fire
Courtesy of Tom Swetnam, U of Arizona, LTRR
Fires and Ecosystem Health
Fire is a natural part most western forest ecosystems
It plays an important role in maintaining the health of forest ecosystems
In fact, many forest types are dependent upon a particular frequency and intensity of fire for survival Ponderosa Pine forests are an example of a
fire-dependent ecosystem
Fire regime of Ponderosa Pine Forests
Under “natural” conditions, ponderosa pine forests burn every 2-12 years
These frequent, low-intensity fires (surface fires) serve to: Clean out understory thus reducing
fuel load Enhance nutrient cycling Promote germination of ponderosa
pine seeds Maintained open forest structure Maintained mountain meadows
Courtesy of Tom Swetnam, U of Arizona, LTRR
Fire regime of ponderosa pine
How do we know the natural fire frequency for Ponderosa Pine? Dendrochronology (study of tree-rings!)
Sugar pine with fire scars labeled. © A.C. Caprio
Causes of Fire in Ponderosa Pine Forests
The cause of natural fires in Ponderosa Pine is usually lightning strikes
However, many of the frequent periodic fires are also thought to be human-caused
Native American Fire Management
Almost every Native American tribe has engaged in active fire management of forests
The purpose of these fires was to enhance their quality of life within the environment Based on personal or secondary accounts of Native
American fire management, fires were burned to Establish or keep diverse habitats such as meadows
interspersed with forests The forests productivity is greatest at the interface of
meadows and forests
Native American Fire Management
Purposeful fires set by Native Americans differ from natural fires by the seasonality of burning
Fires were set in early spring or summer, or in the fall after the hunt and berry picking season was over
Never in mid-summer when the forest was most vulnerable to catastrophic wildfires
frequency of burning certain areas Selected areas were burned every year, every other
year or as long as a five years the intensity of pattern and overall ignition patterns
Frequent fires ensured low-intensity fires which served to maintain the health and biodiversity of forests
Post-European Fire Management Practices
The effects of forest management in the past 100 years have placed western dry forests at risk of large, high-intensity fires.
Multiple interrelated factors are: Logging large trees Fire suppression Livestock grazing
Effects of logging
Effects of logging Logging operations have historically
removed the largest, most fire resistant trees
The young trees that replace the cut trees are highly susceptible to fires and serve as fire ladders leading to crown fires
Effects of fire suppression
Fire suppression has led to High density fires with high fuel loads Infrequent, high intensity fires
High temperature fires are destructive to forest ecosystems Leads to crown fires which kill mature trees Causes soil sterilization which kills all seeds
and organisms so that forest regeneration takes decades
Effects of grazing
Livestock grazing on public lands has severely reduced the amount of grasses
This leads to More severe fires since they are only able
to burn with a significant build-up of woody debris
Climate Change and Fire
The following have been observed and predicted:
Increased wildfire frequency and intensity Drier soils Tree mortality due to global warming type
drought and/insect infestation will increase fire severity
Longer fire season due to longer growing season
Climate-fire linkages
Synchronous large fires in the Southwest over three centuries have been associated with the high-SO phase (dry phase) and deficient spring precipitation
This implies that seasonal climate, and not just fire weather, determines burning of vegetation on a subcontinental scale.
With a drier, warmer climate forecasted for the SW, this means more frequent large fires
Climate-fire linkages
Conversely, Large-scale severe
fires can accelerate global warming since carbon is released into the atmosphere
Especially if tree mortality is due to fire since stored carbon is released
Courtesy of MODIS Rapid Response Project at NASA/gsfc
Forest Restoration
What can be done? Reintroduce fire as a natural component of the
ecosystem through controlled burns Reduce the number of small trees
This will decrease risk of severe fires Decrease competition with mature trees increasing
drought-related stress and mortality Small trees comprise ~90% of trees in the southwest. Larger trees are relatively rare after 100 years of
logging in forests Stop or reduce grazing in our forests Enhancing habitat for imperiled or endangered
species