Stand Reconstruction and 200 Years of Forest Development on Selected Sites in the Upper South Umpqua Watershed
Dubrasich, Mike. 2010. Stand Reconstruction and 200 Years of Forest Development on Selected Sites in the Upper South Umpqua Watershed. W.I.S.E. White Paper 2010-5. Western Institute for Study of the Environment.
Full text [here]
Selected excerpts:
Abstract
Stand development of ten structurally complex forest stands in the Upper South Umpqua Watershed was studied by backdating (reconstructing) stand conditions circa 1825. Mixed conifer and conifer/hardwood stands across a selected range of “Areas of Special Interest” sites were sampled for tree ages, tree characteristics, and fire history. Logistic regression analysis was used to create age/diameter models and the stands were backdated using increment core data and tree positions to create stand statistics for 185 years prior to measurement. The changes in number of trees and basal area over the last 185 years were calculated by species for each stand. Density of trees greater than 8 inches DBH increased from an average of 20 trees per acre to 90 (from 10 to 35 trees per acre to 60 to 115 trees per acre). Basal area increased 5-fold on average, from 65 square feet per acre to 225 (from 25 to 150 sqft/ac to 150 to 300 sqft/ac). In 1825 the ten stands were open and park-like with widely spaced trees. By 2010 the ten stands had accumulated from 10 to 20 times the tree biomass they had held 185 years earlier. In 1825 pines and oaks were dominant in stands below 3,800 feet in elevation. Today those same stands are dominated by Douglas-fir, grand fir, and incense-cedar, especially in younger age classes. In higher elevation stands the most abundant species has changed from Shasta red fir to Pacific silver fir.
Several lines of evidence suggest that the prairies, savannas, and open forests have been persistent vegetation types in the Upper South Umpqua Watershed for the last few thousand years, at least. Precontact forest development pathways were mediated by frequent, purposeful, anthropogenic fires deliberately set by skilled practitioners, informed by long cultural experience and traditional ecological knowledge in order to achieve specific land management objectives. At a landscape scale the result was maintenance of an (ancient) anthropogenic mosaic of agro-ecological patches. In the absence, over the last 150 years, of purposeful anthropogenic fires, the anthropogenic mosaic has been invaded and obscured by (principally) Douglas-fir. As a result, the Upper South Umpqua Watershed is now at risk from a-historical, catastrophic stand-replacing fires. …
Conclusions
1. In 1825 vegetation types in the Upper South Umpqua watershed consisted of prairie, oak savanna, sugar and ponderosa pine open woodlands, and high elevation shrublands.
2. Since 1825 the changes in stand structures have been dramatic. Density of trees greater than 8 inches DBH increased an average of 450 percent and basal area increased 5-fold. By 2010 the ten stands had accumulated from 10 to 20 times the tree biomass they had held 185 years earlier. In most of the stands the species relative proportions also changed significantly. In 1825 pines and oaks were dominant in stands below 3,800 feet in elevation. Today those same stands are dominated by Douglas-fir, grand fir, and incense-cedar, especially in younger age classes.
3. By implication the forest development pathways have changed since 1825. Tree recruitment and biomass accumulation rates have increased, and tree species relative proportions have changed (from dominance by pine and oak to dominance by Douglas-fir).
4. Human-set fire has played an important role in the development of these stands. Frequent anthropogenic fires maintained uneven-aged, sparsely stocked, open and park-like stands for thousands of years. The elimination of anthropogenic fire over the last 150 years is the key factor that has altered development pathways and forest structure and composition.
5. The anthropogenic fire regime was typified by frequent, low-severity fires of limited individual extent, which cumulatively burned over the entire watershed every 1 to 10 years. At a landscape scale the result was maintenance of an (ancient) anthropogenic mosaic of agro-ecological patches. In the absence of the purposeful fires set by skilled practitioners, the anthropogenic mosaic has been invaded and obscured by (principally) Douglas-fir. Infrequent, a-historical, catastrophic stand-replacing wildfires have replaced low severity fires due to the massive build-up of biomass (fuels).
These findings should be useful in:
* Advancing understanding of forest dynamics, historical human influences, and historical landscape geography,
* Informing the maintenance and preservation of historic cultural landscape features — the anthropogenic landscape patterns are cultural legacies by themselves (Lake 2005),
* Evaluating and mitigating catastrophic fire hazards and risks, and
* Informing restoration efforts, where restoration means active management to recover historical cultural landscapes, historical forest development pathways, and traditional ecological stewardship to achieve resiliency to fire and insects, provide sustainable resource products and services, and to preclude and prevent a-historical catastrophic fires that degrade and destroy myriad resource values (Charnley et al. 2008, Dubrasich 2010b). …
The Evils of Pinyon and Juniper
Charles E. Kay. 2010. The Evils of Pinyon and Juniper. Mule Deer Foundation Magazine Vol 10(5): 6-13
Dr. Charles E. Kay, Ph.D. Wildlife Ecology, Utah State University, is the author/editor of Wilderness and Political Ecology: Aboriginal Influences and the Original State of Nature [here], author of Are Lightning Fires Unnatural? A Comparison of Aboriginal and Lightning Ignition Rates in the United States [here], co-author of Native American influences on the development of forest ecosystems [here], and numerous other scientific papers.
Full text with photos (click on photos for larger images):
PINYON PINES and upright junipers are found throughout the West. Ash and red berry juniper occur in Texas, while western juniper is most abundant in the interior Pacific Northwest. One-seeded and Utah juniper are widespread in Nevada, Utah, and on the Colorado Plateau, whereas Rocky Mountain juniper can be found in Idaho, Montana, and Wyoming. All junipers have small, scale-like leaves and are often called cedars due to their aromatic wood. In fact, the most widely occurring juniper in the East is known as eastern red cedar. In addition to the tall, or upright junipers, there are a few, low-growing species of which horizontal and common are the mostly likely to be encountered.
Pinyons, on the other hand, are represented by only two species. Single-leaf pinyon has only one needle per fascicle, while two-needle pinyon has two needles per fascicle or bundle. Pinyons are abundant in Nevada, Utah, Colorado, Arizona, and New Mexico. Pinyons and junipers are the most drought tolerant of all western conifers. In addition, pinyons and junipers are chemically defended by terpenes and other compounds that inhibit ruminant microbial digestion. Livestock will generally not consume pinyon or juniper and mule deer will generally browse juniper only if the animals are starving. Pinyons and most junipers are also extremely invasive.
Prior to European settlement, it has been estimated that pinyon and juniper covered 7.5 million acres in the West, while today P-J has infested over 75,000,000 acres, a ten-fold increase. Moreover, the number of trees per acre has increased 10 to 100 fold. I have compiled 1,879 repeat photosets in southern Utah and of that total, 1,007 photo pairs depict pinyon and/or juniper. In 96% of those cases, P-J increased, often dramatically. As pinyon and juniper have expanded their range and thickened, the production of shrubs, forbs, and grasses has declined precipitously. In many stands, understory forage production is near zero, and as understory species decrease, soil erosion increases, even on ungrazed sites. In New Mexico’s Bandelier National Monument, for instance, as pinyon and juniper have thickened, understory species have been eliminated, which has lead to a drastic increase in soil erosion threatening the park’s archaeological sites.
Closed-canopy stands of pinyon-juniper are rare in early historical photographs. Instead, most stands once consisted of a few widely-spaced pinyon and/or juniper with abundant grasses, shrubs, and forbs in what could be characterized as a savanna. With time, however, those stands have infilled until today many pinyon-juniper sites have a closed canopy. Pinyon and juniper have also extended their range by invading grasslands, sagebrush, and other plant communities. Historically, old-growth pinyon-juniper was restricted to rocky outcroppings, areas with poor soils, and other fire refugia. Crown-fire behavior in pinyon-juniper is increasingly common in the West today, but there is no evidence that was the norm prior to European settlement and the expansion and infilling of pinyon-juniper woodlands. Only 3 or 1,007 historical photos taken in southern Utah show any evidence of stand-replacing fire in pinyon-juniper until modern times. The same is true in other areas.
Climate Changes and their Effects on Northwest Forests
Schlichte, Ken. 2010. Climate Changes and their Effects on Northwest Forests. Northwest Woodlands, Spring 2010.
Ken Schlichte is a retired Washington State Department of Natural Resources forest soil scientist. Northwest Woodlands Magazine [here] is a quarterly publication produced in cooperation with woodland owner groups in Oregon, Washington, Idaho and Montana.
Full text [here]
Selected excerpts:
Climate changes are always occurring, for a variety of reasons. Climate changes were responsible for the melting and retreat of the Vashon Glacier back north into Canada at the beginning of the postglacial Holocene Epoch around 11,000 years ago. Climate changes were also responsible for the warmer temperatures of the Holocene Maximum from around 10,000 to 5,000 years ago, the warmer temperatures of the Medieval Warm Period around 1,000 years ago and the coldest temperatures of the Little Ice Age during the Maunder Minimum around 300 years ago. These climate changes, the reasons for them and their effects on our Northwest forests are discussed below.
Forests soon became established on the glacial soil deposits left by the retreat of the Vashon Glacier, but some of these forests were later replaced by prairies and oak savannahs as temperatures increased during the Holocene Maximum. …
Forests began advancing into the South Puget Sound area prairies and replacing them as temperatures began decreasing following the Holocene Maximum. Native Americans began burning these prairies in order to maintain them against the advancing forests for their camas-gathering and game-hunting activities. Forest replacement of these and other Northwest prairies has proceeded rapidly since the late-1800s in the absence of these burning activities. …
The warmer temperatures and increased solar activity of the Medieval Warm Period were followed by a period of cooler temperatures and reduced solar activity known as the Little Ice Age. The coldest temperatures and lowest solar activity of the Little Ice Age both occurred during the Maunder Minimum from 1645 to 1715… The Dalton Minimum was a period of lower solar activity and colder temperatures from 1790 to 1820. Mount Rainier’s Nisqually Glacier reached a maximum extent in the last 10,000 years during the colder temperatures of the Maunder Minimum and the Dalton Minimum and then began retreating as Northwest temperatures warmed following the mid-1820s and the Dalton Minimum. Beginning in 1950 and continuing through the early 1980s the Nisqually Glacier and other major Mount Rainer glaciers advanced in response to the relatively cooler temperatures and higher snowfalls of the mid-century, according to the National Park Service. …
The Fictional Ecosystem and the Pseudo-science of Ecosystem Management
Travis Cork III. 2010. The Fictional Ecosystem and the Pseudo-science of Ecosystem Management. W.I.S.E. White Paper No. 2010-3, Western Institute for Study of the Environment.
Full text [here]
Selected excerpts:
LAND USE CONTROL has long been the goal of the statist element in our society. Zoning was the first major attempt at land use control. Wetland regulation and the Endangered Species Act have extended some control, but nothing has yet brought about a general policy of land use control. Ecosystem management is an attempt to achieve that end.
The fictional ecosystem
In The Use and Abuse of Vegetational Concepts and Terms, A. G. Tansley coined the term “ecosystem.” Tansley rejected the “conception of the biotic community” and application of the “terms ‘organism’ or ‘complex organism’” to vegetation. “Though the organism may claim our primary interest, when we are trying to think fundamentally we cannot separate them from their special environment, with which they form one physical system. It is the systems so formed which, from the point of view of the ecologist, are the basic units of nature on the face of the earth. … These ecosystems, as we may call them, are of the most various kinds and sizes… which range from the universe as a whole down to the atom” 1/
Tansley further writes “[e]cosystems are extremely vulnerable, both on account of their own unstable components and because they are very liable to invasion by the components of other systems. … This relative instability of the ecosystem, due to the imperfections of its equilibrium, is of all degrees of magnitude. … Many systems (represented by vegetative climaxes) which appear to be stable during the period for which they have been under accurate observation may in reality have been slowly changing all the time, because the changes effected have been too slight to be noticed by observers.” 2/
Lackey confirms writing “[t]here is no ‘natural’ state in nature; it is a relative concept. The only thing natural is change, some-times somewhat predictable, oftentimes random, or at least unpredictable. It would be nice if it were otherwise, but it is not.” 3/
The ecosystem may be the basic unit of nature to the ecologist, that is—man, but it is not the basic unit to nature. Its proponents confirm that it is a man-made construct.
We are told in Creating a Forestry for the 21st Century: The Science of Ecosystem Management that “ecosystems, in contrast to forest stands, typically have been more conceptual than real physical entities.” 4/
The Report of the Ecological Society of America Committee on the Scientific Basis for Ecosystem Management tells us “[n]ature has not provided us with a natural system of ecosystem classification or rigid guidelines for boundary demarcation. Ecological systems vary continuously along complex gradients in space and are constantly changing through time.” 5/
“People designate ecosystem boundaries to address specific problems, and therefore an ecosystem can be as small as the surface of a leaf or as large as the entire planet and beyond.” 6/
“Defining ecosystem boundaries in a dynamic world is at best an inexact art,” says the U.S. Forest Service (USFS) in its 1995 publication, Integrating Social Science and Ecosystem Management: A National Challenge.
“Among ecologists willing to draw any lines between ecosystems, no two are likely to draw the same ones. Even if two agree, they would recognize the artificiality of their effort…” 7/ …
Defining, Identifying, and Protecting Old-Growth Trees
Mike Dubrasich. 2010. Defining, Identifying, and Protecting Old-Growth Trees. W.I.S.E. White Paper 2010-1. Western Institute for Study of the Environment.
Full text [here]
Selected excerpts [here]
IN ORDER TO SOLVE our current forest crisis and protect our old-growth, it is useful to understand what old-growth trees are and how to identify them in the field.
At first blush this may seem to be a simple problem, but it is not, and much confusion and debate abounds over the issue. Old-growth trees are “old,” but how old does a tree have to be to qualify as “old-growth”? And what is the difference between an individual old-growth tree and an old-growth stand of trees? Why does it matter?
Some rather sophisticated understanding of forest development is required to get at the root of these questions. …
Reduced Fire Frequency Changes Species Composition of a Ponderosa Pine Stand
Alan Dickman. 1978. Reduced Fire Frequency Changes Species Composition of a Ponderosa Pine Stand. Journal of Forestry, January 1978.
Full text [here]
Selected excerpts:
Abstract
In the Umpqua National Forest, Oregon, a 35-acre ponderosa pine (Pinus ponderosa Laws.) stand situated in the midst of a Douglas-fir (Pseudotsuga menziesii [Mirb.]Franco) forests is being invaded by Douglas-fir seedlings as a result of reduced fire frequency within the last 50 years. In earlier times frequent ground fires kept Douglas-fir at a minimum.
Pine Bench, an area on the Umpqua National Forest, Oregon, is undergoing a drastic change in species composition. The understory, which according to an early settler, Jessie Wright (personal communication, 1975), was open and grassy until a half-century ago, now contains thickets of Douglas-fir that are shading out seedlings of the overstory ponderosa pines. A study was made to determine the cause and extent of this shift. …
Results
The size-class distribution (fig .1) shows that among the large trees there are far more ponderosa pines than Douglas-firs, while among the small trees there are far more Douglas-firs than ponderosa pines. The age class distribution (fig. 2) shows that the change occurred rather suddenly. …
The linear regressions show that Douglas-fir grows faster than ponderosa pine on Pine Bench; Douglas-fir appearing in the same size-class is actually younger. Therefore, the difference in the large number of old ponderosa pine and the small number of old Douglas-fir is actually even greater than the size-class distribution indicates.
The shift in, species composition began, then, when the middle-aged trees were seedlings. The number of Douglas-fir germinating and surviving was relatively small and stable until 1925, but thereafter increased steadily up to the present.
Discussion
The change seems too quick and drastic to be a result of natural succession. Grazing does not seem responsible, either. According to Jessie Wright (personal communication) cattle were driven through Pine Bench from 1917 to 1952 on their way between summer and winter grazing areas. The cattle were never on the bench long, however, and their impact was slight. Furthermore, Mrs. Wright told me that they grazed fir in preference to pine.
Reduced fire frequency seems the most likely cause of the invasion. …
Two factors may have combined to reduce the frequency of fires on Pine Bench in this century. First is the absence of Indian or settler-caused fires, although as early as 1840 the number of Indians in the North Umpqua Valley was very small (Bakken 1970). An equally likely cause is the suppression of fires by the U.S. Forest Service.
By 1920, a Forest Service fire lookout was established on Illahee Rock, only four miles from Pine Bench, although it was not until the introduction of aerial fire-fighting techniques that control became highly effective. Douglas-firs living through the 1920s and 1930s would have almost been assured of survival once the more effective fire suppression of later decades began.
Prescribed burning has been proven valuable and workable in maintaining ponderosa pine stands (Weaver 1964, 1965) and should be considered for Pine Bench.
Using a spatially explicit ecological model to test scenarios of fire use by Native Americans: An example from the Harlem Plains, New York, NY
William T. Bean and Eric W. Sanderson. 2007. Using a spatially explicit ecological model to test scenarios of fire use by Native Americans: An example from the Harlem Plains, New York, NY. Ecological Modelling 211 (2008) pp. 301–308.
Full text [here]
Selected excerpts:
Abstract
It is unclear to what extent Native Americans in the pre-European forests of northeast North America used fire to manipulate their landscape. Conflicting historical and archaeological evidence has led authors to differing conclusions regarding the importance of fire. Ecological models provide a way to test different scenarios of historical landscape change.We applied FARSITE, a spatially explicit fire model, and linked tree mortality and successional models, to predict the landscape structure of the Harlem Plains in pre-European times under different scenarios of Native American fire use. We found that annual burning sufficed to convert the landscape to a fire-maintained grassland ecosystem, burning less often would have produced a mosaic of forest and grasslands, and even less frequent burning (on the order of once every 20 years) would not have had significant landscape level effects. These results suggest that if the Harlem Plains had been grasslands in the 16th century, they must have been intentionally created through Native American use of fire.
Introduction
The use of fire by Native Americans in northeast North America has been the subject of much debate shared among a broad group of ecologists, archaeologists and environmental historians. Some like Day (1953), Cronon (1983) and Krech (1999) believe that Native Americans used fire often to manipulate their landscape, and that these manipulations may have taken place over broad extents in the pre-European forests.
Skeptics admit that the rate of forest fires around a village might have been elevated over a background rate because Northeast Indians were using fire for cooking and pottery. However, they find little evidence that fires were widespread or intentionally set (Russell, 1983). Early settlers rarely offer first-hand accounts of fires and fewer still tell of intentional burning. These, Russell says, might be attributed to escaped fires.
Intentional burning has many potential benefits for hunting and gathering peoples: frequent fires can clear tangled vegetation, making it easier to travel through and to clear for horticulture (Lewis, 1993); fire can create vegetation mosaics that are attractive to deer and other game species, and make hunting easier (Williams, 1997); sometimes people set fires just for fun (Putz, 2003).
Of course different fire regimes have different effects on the ecology of Northeast forests. A frequent fire regime would favor a grassland with lingering oaks, a fire-tolerant genus (Swan, 1970; Abrams, 1992, 2000). Less frequent fire would lead to regenerating forests (Abrams, 1992). Understanding Native American use of fire is important for understanding the structure and function of pre-European forests.
The Forest Health Crisis: How Did We Get In This Mess?
Charles E. Kay. 2009. The Forest Health Crisis: How Did We Get In This Mess? Mule Deer Foundation Magazine No.26:14-21.
Dr. Charles E. Kay, Ph.D. Wildlife Ecology, Utah State University, is the author/editor of Wilderness and Political Ecology: Aboriginal Influences and the Original State of Nature [here], author of Are Lightning Fires Unnatural? A Comparison of Aboriginal and Lightning Ignition Rates in the United States [here], co-author of Native American influences on the development of forest ecosystems [here], and numerous other scientific papers.
Full text with photos (click on photos for larger images):
THE WEST is ablaze! Every summer large-scale, high-intensity crown fires tear through our public lands at ever increasing and unheard of rates. Our forests are also under attack by insects and disease. According to the national media and environmental groups, climate change is the villain in the present Forest Health Crisis and increasing temperatures, lack of moisture, and abnormally high winds are to blame. Unfortunately, nothing could be further from the truth.
The Sahara Desert, for instance, is hot, dry, and the wind blows, but the Sahara does not burn. Why? Because there are no fuels. Without fuel there is no fire. Period, end of story, and without thick forests there are no high-intensity crown fires. Might not the real problem then be that we have too many trees and too much fuel in our forests? The Canadians, for instance, have forest problems similar to ours but they do not call it a “Forest Health Crisis,” instead they call it a Forest Ingrowth Problem. The Canadians have correctly identified the issue, while we in the States have not. That is to say, the problem is too many trees and gross mismanagement by land management agencies, as well as outdated views of what is natural.
When Europeans first arrived in the West, ponderosa pine forests were open and park-like. You could ride everywhere on horseback or even in a horse and buggy, the forests were so open. On average there were only between 10 and 40 trees per acre with an understory of grasses, forbs, and shrubs. Extensive meadows were also common. In short, ideal mule dear habitat.
Photo 1 — A 1905 photograph of a ponderosa pine forest on the Kaibab in northern Arizona. It is amazing how parklike our pine forests once were. The forests were so open that you could travel virtually anywhere in a horse and buggy. Understory grasses, forbs, and shrubs were abundant. U.S. Geological Survey photo.
Photo 2 — A 1903 photograph of a ponderosa pine forest on the Coconino in northern Arizona. Note the park-like conditions and the men for scale, as well as the abundance of understory forage. Due to the openness of the forest, historically, crown fires never occurred, unlike conditions today. U.S. Forest Service photo.
Today, however, those same forests contain anywhere from 500 to 2,000 mostly smaller trees per acre. Travel on horseback is out of the question, and access by foot is even difficult. Many former meadows are now overgrown with trees. Understory forage production is approaching zero and our pine forests are becoming increasingly worthless as mule deer habitat.
Fire Gods and Federal Policy
Thomas M. Bonnicksen, Ph.D. 1989. Fire Gods and Federal Policy. American Forests 95(7 & 8): 14-16, 66-68.
Full text:
THE ISSUE I am presenting is based on a summary of both the letter I sent to the Interagency Fire Management Policy Review Team and testimony I presented to a joint committee of Congress in January of 1989 on the Yellowstone wildfire problem. The issue is how to restore naturalness to park and wilderness areas while preventing such wildfires from occurring again. I will concentrate on the “let nature takes its course” philosophy that led to the Yellowstone fires. I will also provide a scientifically sound and responsible approach to resource management. My purpose is to encourage the use of scientific management in national park and wilderness areas.
I was critical of the Park Service fire management program when it started. I was a ranger-naturalist at Kings Canyon National Park where the program began. At that time, I wrote a white paper that pointed out the flaws in the fire management program and the entire ranger-naturalist staff agreed with my conclusions and signed the paper. This was the first documented internal Park Service critique of the fire management program. The points that we made so many years ago are still true today, only now the problem has grown worse and it has taken on a more ominous dimension with the Yellowstone wildfires.
I have been conducting research, publishing and speaking on fire management and restoration ecology in national park and wilderness areas for twenty years. Most of my research addressed the management of giant sequoia-mixed conifer forests in the Sierra Nevada. I also investigated the effects of the Yellowstone wildfires for members of Congress. After giving so much thought to this issue over so many years, I am convinced that the real problem is the lack of clear objectives for the management of national park and wilderness areas.
The wildfires that swept through Yellowstone and surrounding wilderness areas during the summer of 1988 were not a natural event. Unlike the eruption of Mount St. Helens (which could not be controlled) the number, size and destructiveness of the Yellowstone wildfires could have been substantially reduced. The changes that took place in the vegetation mosaic and fuels in Yellowstone during nearly a century of fire suppression were preventable and reversible. The Park Service was aware of the risks of letting lightning fires burn, especially during a drought. Mr. Howard T. Nichols, a Park Service Environmental Specialist sent to help in the command center during the Yellowstone wildfires, stated in an internal memo that members of the Yellowstone staff knew “that 1988 was a very dry year” yet they “were determined to maintain the Park’s natural fire regime.” Thus the Yellowstone wildfires were caused by a combination of decades of neglect and incredibly poor judgment.
Dr. James K. Brown, a Forest Service scientist, stated in a paper he delivered to the American Association for the Advancement of Science in January of 1989 that, assuming a prescribed burning program was initiated in 1972, “threats to villages may have been prevented or greatly reduced.” Dr. Brown also stated “a program of manager ignited prescribed burning in subalpine forests such as lodgepole pine” is “feasible.” In an earlier paper presented at the Wilderness Fire Symposium in Missoula, Montana, in 1983, Dr. Brown also said that “To manage for a natural role of fire, planned ignitions, in my view, are necessary to deal with fuels and topography that have high potential for fire to escape established boundaries.” Thus, it is likely that the wildfires would not have reached the mammoth size of 1.4 million acres if only a fraction of the hundreds of millions of dollars used to fight the Yellowstone wildfires had been spent on scientific management that utilized prescribed burning, especially if vigorous suppression efforts had been undertaken by the Park Service when each fire began.
Causes of Post-Fire Runoff and Erosion: Water Repellency, Cover, or Soil Sealing?
Isaac J. Larsen, Lee H. MacDonald, Ethan Brown, Daniella Rough, Matthew J. Welsh, Joseph H. Pietraszek, Zamir Libohova, Juan de Dios Benavides-Solorio, Keelin Schaffrath. 2009. Causes of Post-Fire Runoff and Erosion: Water Repellency, Cover, or Soil Sealing? Soil Sci. Soc. Am. J. 73:1393-1407
Full text [here, 2.1MB]
Selected excerpts:
Abstract
Few studies have attempted to isolate the various factors that may cause the observed increases in peak flows and erosion after high-severity wildfires. This study evaluated the effects of burning by: (i) comparing soil water repellency, surface cover, and sediment yields from severely burned hillslopes, unburned hillslopes, and hillslopes where the surface cover was removed by raking; and (ii) conducting rainfall simulations to compare runoff , erosion, and surface sealing from two soils with varying ash cover. The fire-enhanced soil water repellency was only stronger on the burned hillslopes than the unburned hillslopes in the first summer after burning. For the first 5 yr after burning, the mean sediment yield from the burned hillslopes was 32 Mg ha-1, whereas the unburned hillslopes generated almost no sediment. Sediment yields from the raked and burned hillslopes were indistinguishable when they had comparable surface cover, rainfall erosivity, and soil water repellency values. The rainfall simulations on ash-covered plots generated only 21 to 49% as much runoff and 42 to 67% as much sediment as the plots with no ash cover. Soil thin sections showed that the bare plots rapidly developed a structural soil seal. Successive simulations quickly eroded the ash cover and increased runoff and sediment yields to the levels observed from the bare plots. The results indicate that: (i) post-fire sediment yields were primarily due to the loss of surface cover rather than fire-enhanced soil water repellency; (ii) surface cover is important because it inhibits soil sealing; and (iii) ash temporarily prevents soil sealing and reduces post-fire runoff and sediment yields.
Introduction
Wildfires increase hillslope- and watershed-scale runoff and sediment yields by several orders of magnitude (e.g., Prosser and Williams, 1998; Robichaud and Brown, 1999; Moody and Martin, 2001; Benavides-Solorio and MacDonald, 2005; Malmon et al., 2007). Land use and climate change have increased, or are projected to increase, the size and frequency of fires in many wildland environments (e.g., Mouillot et al., 2002; Hennessy et al., 2005; Westerling et al., 2006). The increase in fire risk is generating considerable concern about the potential adverse effects on water quality, aquatic habitat, and water supply systems (Rinne, 1996; Robichaud et al., 2000; Moody and Martin, 2001; Burton, 2005).
The large increases in runoff and sediment yields after high-severity fires have been attributed to several factors, including: (i) soil water repellency (DeBano, 2000; Doerr et al., 2000); (ii) loss of surface cover ( Johansen et al., 2001; Pannkuk and Robichaud, 2003); (iii) soil sealing by sediment particles (Lowdermilk, 1930; Neary et al., 1999); and (iv) soil sealing by ash particles (Mallik et al., 1984; Etiégni and Campbell, 1991). The problem is that the relative contribution of each factor to the observed increases in post-fire runoff and sediment yields is largely unknown (Shakesby et al., 2000; Letey, 2001). This lack of understanding hampers our ability to predict post-fire sediment yields and design effective post-fire rehabilitation treatments.
