Posts Tagged: water yield
Wildfire management vs. fire suppression benefits forest and watershed
Reposted from UC Berkeley News
An unprecedented 40-year experiment in a 40,000-acre valley of Yosemite National Park strongly supports the idea that managing fire, rather than suppressing it, makes wilderness areas more resilient to fire, with the added benefit of increased water availability and resistance to drought.
After a three-year, on-the-ground assessment of the park's Illilouette Creek basin, UC Berkeley researchers concluded that a strategy dating to 1973 of managing wildfires with minimal suppression and almost no preemptive, so-called prescribed burns has created a landscape more resistant to catastrophic fire, with more diverse vegetation and forest structure and increased water storage, mostly in the form of meadows in areas cleared by fires.
“When fire is not suppressed, you get all these benefits: increased stream flow, increased downstream water availability, increased soil moisture, which improves habitat for the plants within the watershed. And it increases the drought resistance of the remaining trees and also increases the fire resilience because you have created these natural firebreaks,” said Gabrielle Boisramé, a graduate student in UC Berkeley's Department of Civil and Environmental Engineering and first author of the study.
Boisramé and co-author Sally Thompson, a UC Berkeley ecohydrologist and assistant professor of civil and environmental engineering, found that even in the drought years covered by the study, the basin retained more water than similar areas outside the park. That translated into more runoff into the Upper Merced River, which flows through Yosemite Valley, at a time when other rivers in the surrounding areas without a restored fire regime showed the same or decreased flow.
“We know that forests are deep-rooted and that they have a large leaf area, which means they are both thirsty and able to get to water resources,” Thompson said. “So if fire removes 20 percent of that demand from the landscape, that frees up some of the water to do different things, from recharging groundwater resources to supporting different kinds of vegetation, and it could start to move into the surface water supplies as stream flow.”
The study is published in the current issue of the journal Ecosystems.
If the results are confirmed from other studies, including the UC Berkeley team's new project analyzing the Sugarloaf Creek Basin in Sequoia and Kings Canyon national parks, they could alter the way the federal government as well as water districts deal with fire, benefiting not only the forest environment but potentially also agriculture and cities because of more runoff into streams and reservoirs.
“I think it has the potential to change the conversation about wildfire management,” said co-author Scott Stephens, a fire expert and UC Berkeley professor of environmental science, policy and management who has studied the Illilouette basin since 2002.
This “wildfire management” strategy is counter to the federal government's 110-year-old Smokey Bear policy, which is followed throughout the West and emphasizes suppressing fires wherever they occur for fear they will get out of control. With persistent drought and a warming climate, the U.S. Forest Service budget is increasingly going to firefighting. On most federal land, only forest thinning and human-initiated prescribed burns are allowed as a way to manage the trees and underbrush.
Stephens noted, however, that these agencies have recognized the folly of total suppression — thanks in part to his own studies throughout the Sierra Nevada over several decades — and current draft wildland management policies for three of the state's national forests allow active wildfire management in up to 60 percent of the forests.
The value of forest clearings
Wildfire management, as opposed to suppression, comes with major changes in the way the forest looks, Stephens and Thompson said. Unlike the dense stands of pine and fir most people associate with Yosemite and similar mid-elevation Sierra Nevada and Rocky Mountain forests, the Illilouette Creek basin has thinner forests and more clearings with dead trees.
“There is much more dramatic structural change in this forest than most people would probably feel comfortable with,” he said. “You are talking about low-density forests and gaps of 4 or 5 acres, up to maybe 100 acres. These are the result of major fires about every decade or so, large enough to cause tree scarring and affecting as much as one-quarter of the basin.”
These fire-caused clearings, however, act as natural fire breaks and make the area resistant to catastrophic fires such as the 2013 Rim Fire in the western part of the park, which burned 250,000 acres and left patches up to 20,000 acres in which not a single conifer tree survived. These areas could take a century to recover, Stephens said.
“In the Illilouette basin we lost about 20 percent of the forest cover, but there was a 200 percent increase in wetland vegetation: meadows starting to reemerge from forests that have probably encroached on historical locations,” Thompson said. “That sets us up to think that this new regime should be leakier as far as water goes — leaky in the way that suits us as a society.”
Even if these wildfire management techniques don't produce more runoff, Thompson added, “I think it is a fabulous result in terms of forest management if you end up with a healthier forest with some better intact aquatic habitat, even if you don't see a drop of water further downstream. It is still the right thing to do from an ecological point of view.
“Bottom line, this strategy might be a triple win-win-win for water, forest structure and fire risk,” she said.
The ‘jewel' of Yosemite National Park
The findings are the culmination of a 14-year study led by Stephens and his UC Berkeley colleagues to learn how monitoring natural, lightning-caused fires with a bias toward letting them burn affects the landscape, the vegetation and the groundwater. Only four areas in the western U.S., including two in California — the Illilouette Creek basin and the Sugarloaf Creek basin — have allowed lightning fires to burn in large areas for decades.
Most studies of different ways to manage wildland fires have been limited to a few hundred acres, and it's hard to extrapolate from such limited experiments to an entire forest. Luckily, Yosemite National Park started its experiment in 1973 — spurred by a 1963 report authored by the late UC Berkeley forester Starker Leopold — to let nature take its course in the Illilouette Creek watershed, stepping in only when fires in the basin threatened to get out of control or sent too much smoke into Yosemite Valley two miles to the northwest.
“This is the first study that looks at fire regime restoration on a watershed scale with empirical data,” he said. “Others do smaller areas or modeling, but this is 40,000 acres — a big place — over many years.”
One reason the basin was chosen was that it was surrounded by granite walls, which naturally prevented fires from spreading outside the basin. It had not been burned by the indigenous tribes of the region, which often set fires to increase acorn production, and had no history of prescribed burns. In fact, it saw only natural, lightning-caused fires except for an interval of nearly a century — 1875 to 1972 — when the park suppressed all fires.
While Stephens and his many students documented the changes in fire over the past 400 years, Boisramé and Thompson analyzed aerial photos to document vegetation change. Then, with the help of installed sensors and more than 3,000 soil moisture measurements throughout the basin, the team was able to estimate the amount of water in the landscape today versus in the past. They found similar or marginally drier conditions where forests had been replaced with shrubs, but these were balanced by much wetter conditions in small areas where meadows expanded.
They observed more snow reaching the ground because of the clearings, and more snow remaining during the spring, delaying runoff. And in recent drought years, when surrounding basins saw more trees die, there was almost no tree mortality in the Illilouette basin.
“In order to really understand whether this approach should be part of our management toolkit, I would recommend that we give it a crack in a few other places,” Thompson said. “This appears to be a promising management strategy without significant harm and with several very strongly quantifiable benefits and several very suggestive outcomes.”
Boisramé, who spent the past four summers sampling and camping in the Illilouette Creek basin, emphasized that this is not a strategy that would work everywhere. But in wilderness areas where wildfire management is being considered because of its safety benefits — to reduce underbrush and eliminate fuel for out-of-control and catastrophic fires that risk lives and property — the ecological and hydrological benefits are a big bonus. Areas with similar elevation and climatic conditions to the Illilouette basin, and thus perhaps suitable for managed wildfire, comprise about 18 percent of the Sierra Nevada, though the strategy may work at lower elevations as well.
“The whole ecosystem will be better off if we let the natural fire process back in,” she said.
The research was supported by a grant from the federal Joint Fire Science Program.
Forest scientsist bid on the trifecta SWEEP in the Sierra Nevada
September 21, 2012
Forest scientists bet on the trifecta SWEEP in the Sierra Nevada
Article reviewed: Forests and water in the Sierra Nevada: Sierra Nevada Watershed Ecosystem Enhancement Project (SWEEP)
By R.C. Bales, J.J. Battles, Y. Chen, M.H. Conklin, E. Holst, K.L. O’Hara, P. Saksa, and W. Stewart
The plot line: [Note that this is a “white paper” (self-published), so I am straying from my typical format of reviewing only peer reviewed articles. Given the relevance for management and the quality of this particular paper, it seems worth making an exception]. This group of forest scientists quite aggressively makes the argument that forests in the Sierra Nevada can be managed for improving both the quantity and quality of water to benefit the commonwealth of California, and that there should be monetary incentives for the landowners who do such management. Their case is built upon the notion that water is of very high value and that several studies done in other similar forests clearly document that lower density forests (i.e. recently harvested) do increase water yield and potentially increase snow pack persistence. They make the case for large-scale studies that can be used in the future to help foresters and landowners meet the triad objectives of water, fire severity reduction, and species restoration (the trifecta SWEEP).
Relevant quote: “The perspective that forest management for water supply is not worth the trouble is ingrained in both upstream and downstream resource managers. The SWEEP team contends that forest management for water supply is worth the trouble…”
Relevance to landowners and stakeholders:
Forest landowners pay attention any time a scientist or economist suggests that they should be paid more for the “ecosystem services” that they provide to society. Forests support wildlife, clean air, and natural beauty that people from the city enjoy. So why shouldn’t the folks that own these forests get paid for it? There is of course a way in which landowners can be paid for protecting their forests. That is, through a conservation easement. But what these scientists are suggesting is something quite different than a conservation easement. Instead of a forest landowner getting paid to do nothing with an easement, they are suggesting that they get paid to do something! Doesn’t that sound more feasible as an economic model?
We are of course a ways away from this actually happening, but this team of scientists is trying to conduct research that will help such a system to develop. Rigorous experiments will have to be done in order to measure with accuracy how much more water can actually come from a forest managed for water quantity and quality (when I say quality, I am referring mainly to the timing of snow melt- if snow melts later in the spring/summer, then it is of higher quality in terms of value).
You can find the arguments for why forest management could be managed for water in any forest ecology text book. A simplified version of it is this:
- All plants have leaves.
- Leaves do photosynthesis, which pulls water from the soil and transpires some of it into the air
- Leaves intercept snow and rain, some of which evaporates directly back into the atmosphere
- The fewer leaves that are present, the less water will be sent into the air, and the more water will leave the site and go into reservoirs or hydro-electric facilities.
Relevance to managers:
I think the relevant quote above says it all for managers. These authors are right- water can no longer be ignored. I have personally heard other scientists and mangers state that forest management simply cannot make a significant difference when it comes to water yield or the timing of runoff. But the large amount of evidence presented in this paper suggests the contrary. And it is no secret that water is becoming a more valuable resource every year, so even small increases in yield can be meaningful. It is only a matter of time before markets force us managers to more explicitly manage forests with water as the objective. If the research these and other scientists propose comes to fruition, then we’ll be more ready for the challenge.
The UC Center for Forestry has been managing for what we call a “water efficient forest” for the past decade. It is at a slightly lower elevation than what these authors say will be optimal for increasing water yield and runoff timing, but they also provide some logic in this paper that suggests these lower elevations could increase yield as well. The easy part was thinning the forest down to a level where one could reasonably expect an increase in throughfall and runoff. In this particular case, we have harvested to a density at about 50% of the maximum that we observe on nearby stands. The density then fluctuates between about 50 and 75% of maximum over time in between harvests. Based on the estimates from this paper, this level of density reduction might result in somewhere between a 9 and 18% increase in water yield and it should mean snow persisting for a little while longer (although for low elevation forests, it is likely more about water yield than the timing of snow melt).
In my experience, the easy part in managing for water has been conducting the commercial thins. After all, it is a productive forest so we can generate revenue from the thins by harvesting commercial sized trees. We have been able to, concurrently or immediately following harvests, reduce the small tree cover and surface fuels to make the forest resistant to high severity fires. According to this paper, this action has resulted in what should be a structure that yields more water (somewhere between 9 and 18% increase). The challenge over time has been in managing the understory vegetation in order to prevent it from developing a significant amount of leaf area that would defeat the purpose of increasing water yield. It is challenging because this means conducting treatments that are not paid for with a commercial harvest. Theoretically, one could save the revenue from the commercial thin and apply it to understory treatments in between thins. This is indeed what we have done in this particular case (in the form of mastication and broadcast burn treatments), but without a financial incentive to do these treatments, I can see the situation occurring where these follow-up treatments simply aren’t done. So the authors make a good point in this paper that a water efficient forest needs to be maintained over time. It is not a one-and-done situation.
Critique (I always have one, no matter how good the article is):
They say that many of the upper watershed forests are zoned as wilderness areas, the implication being that these areas cannot be managed for increased water yield. I would argue that these areas can also be managed for water quality with fire being the mechanism for maintaining low density. Without fire in these areas, they will burn with higher severity fire that could input massive amounts of sediment into downstream watercourses, thus countering any positive effect of water quantity and quality treatments that are done in non-wilderness areas.
They make an excellent point that, if runoff is delayed because of forest management activity, then hydro-electric energy production can occur later in the summer, when demands are high. I think they missed out on a point to make about the further potential for these treatments to benefit energy production during the summer. If the treatments are done in the summer and involves a biomass harvest of small trees and tops/limbs, then this would also potentially result in energy production during a time when it is most needed. Perhaps this is too speculative, but it is interesting to think about the potential for biomass harvests to by synergistic with water yield treatments from an energy production perspective.
They focus on forests between 5,000 and 12,000 feet elevation as having the most potential for increasing water yield and runoff timing, because they are productive and warm (above freezing). 12,000 feet… really? Any time I’ve been at 12,000 feet in the Sierra Nevada, I have not noticed many trees. At 12,000 feet, I’m catching my breath and enjoying the view because there aren’t many trees, if any at all. And lots of the winter period is cold at this elevation. Given their logic, it seems like this elevation should be shifted downward, perhaps between 4000 and 9000 feet. 4000-5000 foot elevation forests may not be dominated by snow, so the potential to delay runoff timing is less. But based on their logic and points scattered throughout the paper, forests in this elevation could increase yield substantially. The paper could use some clarity in reconciling all of the different factors of water yield and runoff timing in order to justify the 5 to 12,000 foot elevation target.
They report an average basal area in one of their targeted study areas of 400ft2/acre, with an average canopy cover of only 51% and an average canopy height of only 60 feet in a forest dominated by 100 year old trees. These numbers are not adding up in my head. That basal area seems very high for a forest that does not appear to be highly productive (trees growing 60 feet in 100 years). On the other hand, the LAI they report is also exceptionally high. A high LAI is the only way that I can visualize a forest like this having such a high basal area, so perhaps the numbers are good. But their statement about this forest being typical of much of the northern Sierra Nevada is a stretch- especially considering the 5000 to 12000 foot elevation range that they are talking about.