- Author: Jaquelyn Lugg
Reposted from the UCANR Green Blog
To effectively reduce these adverse effects of harvest, foresters first need to know the precise causes of sediment increases. Historically, researchers investigating the effects of timber harvest on the land have considered two primary drivers: hydrologic changes following timber harvest or fuel reduction that drive sediment transport, and increased sediment supply from ground disturbances and/or mass movements that result from those harvest or fuel reduction activities.
While these causes are tightly linked, little is understood about the relative role each plays in transporting sediment from the watersheds. In other words, which is dominant in increasing sediment delivery and transport: increased streamflow due to greater water availability that can sweep up and transport sediment, or a greater supply of sediment entering the waterway in the first place?
A new analytical approach developed by Safeeq Khan, UC Cooperative Extension specialist in water and watershed sciences at UC Merced, and collaborators now provides valuable insights into this issue, and ways to target effective mitigation strategies.
Published in the Journal of Hydrology last fall, the team's study analyzed long-term (1952-2017) streamflow and sediment data from two adjacent paired watersheds in the H. J. Andrews Experimental Forest in the western Cascades Range of Oregon. One of the watersheds was harvested and replanted in the 1960s, while the second was not disturbed and used as a control.
“The data is from Oregon, but highly relevant for our work in the Sierra Nevada,” said Khan, lead author of the study. “We have tried to quantify the effect of hydrologic changes and increased sediment supply from logging activities on total sediment yield.”
To isolate the relative contributions of streamflow changes and increased sediment supply on sediment transport, Khan and colleagues developed a statistical reconstruction technique to account for the hydrologic changes following harvest.
“This approach allows us to analyze and estimate background sediment production in the treated watershed during the post-treatment period as if the harvest had not occurred, which is remarkable,” said Khan.
The new approach demonstrated that sharp increases in sediment following harvests can be confidently attributed to ground disturbances associated with timber harvest or thinning operations to reduce fuel. Changes in sediment supply overwhelmingly dominate streamflow in terms of contributions to increased sediment in the watershed. Streamflow increases alone led to modest increases in sediment, less than 10%, with the watershed transporting about twice as much total sediment than it would have had the area been left unharvested. This effect diminishes more or less exponentially over time, especially with respect to suspended sediment, as bare areas revegetate, which reduces hillslope sediment supply, and as streamflow returns to pre-treatment levels.
“Once we know the background sediment production, we can easily attribute how much of the increase is due to what mechanisms” said Gordon Grant, a hydrologist with the U.S. Forest Service Pacific Northwest Research Station and co-author on the study.
“Determining that increased sediment in watersheds after harvests is primarily driven by ground disturbance is crucial in targeting mitigation efforts,” explained Khan. “Now, we know that strategies that limit ground disruption – like suspending logs while transporting instead of dragging them, avoiding heavy machinery when and where possible, and mastication and mulching – are likely to be highly effective in reducing sediment yields.”
These changes are most pronounced in the first few years following harvest, but the treated watershed did not return to pre-harvest levels of sediment for two decades, underscoring the long-term effects of harvest on a forest's hydrologic and geomorphic systems.
While clearcutting is no longer practiced on U.S. federal land, it is still the primary timber harvest method used across the globe. Additionally, many other types of forest disturbances such as wildfires, mass tree die-offs, and salvage logging create hydrogeomorphic conditions not too different from clearcutting.
"Our findings provide insights that can help land managers and foresters better target land management and restoration in the future,” said Khan. “We're hopeful that these results will lead to strategies that minimize the long-term impacts and legacies of intense land-use disturbances.”
The full study, titled “Disentangling effects of forest harvest on long-term hydrologic and sediment dynamics, western Cascades, Oregon" is available online in the Journal of Hydrology at https://www.sciencedirect.com/science/article/pii/S0022169419309941?via%3Dihub.
- Author: Faith Kearns
Reposted from the Confluence - Blog of the California Institute for Water Resources
Don Hankins is a professor of geography and planning at Chico State and a Miwkoʔ (Plains Miwok) traditional cultural practitioner. He has spent his academic career working on water and fire issues in California, with a focus on applied traditional Indigenous stewardship.
You've done work on the use of Indigenous traditional knowledge related to fire and water. A major result of your research and practice has been to reveal a disconnect between current environmental management and Indigenous approaches to working with the environment. Can you say more about what you have found?
Tribal knowledge and experience are often marginalized or devalued in environmental management, and relationships between managers and Tribes are often non-reciprocal. For example, when it comes to fire, there can be a sense that Indigenous knowledge is a relic of the past. This is not the case – Indigenous fire practice is alive and well. It brought us through the major climate events of the past and is absolutely relevant to the challenges we face today.
Integrating Indigenous knowledge and people into ongoing management efforts can preserve traditional ways and invigorate agency approaches, but my own research has shown it can also subjugate Indigenous perspectives. For example, there is a great deal of resistance regarding how traditional cultural burning can be carried out in partnership with agency-based programs. Rather than recognize the knowledge and preparation that traditional cultural practitioners have, agencies see their standards-based approach as the only path to putting fire on the ground. This in turn risks traditional knowledge of fire and related cultural practices. Burning is a traditional sovereign right, but in many places, including the U.S. and Australia, legal systems work to regulate fire out of the land.
These kinds of challenges also exist with water. For example, my ancestral homelands of the Delta are now used as a major water conveyance, compromising ecosystems and Indigenous cultural properties. Despite our deep understanding of the area, Indigenous perspectives are really not considered in its management.
I also think about what nature has provided in terms of water storage within the landscape and the fact that we still see interest in building dams rather than restoring natural basins and sinks. Luckily, some headway is being made in recognizing that natural landscape features contribute a great deal to recharge and storage.
What about your work on fire and water in California do you find most challenging?
I wish I had more time to devote to research, publications, and outreach. A lot of my current work is unfunded or has limited support, despite the applicability to current issues. Some projects have started out of me seeing a research need, starting a pilot project, and getting students or community members engaged to help out in the field. I really strive to be in the field because that's where I can do what I'm most interested in: applying Indigenous approaches to management and using scientific methods to assess the results. This work provides me opportunities to advance science, but also to keep a cultural lens on the landscape to assess the condition of, and changes to, traditional resources and interspecies relationships in the places I work.
Every day I see news about new research or political initiatives, and I feel overwhelmed. Getting word out, particularly to decision makers, is challenging, likely because they are overwhelmed too. We have a lot of misinformation on major decisions. I'm thinking of the Governor declaring a drought, or referencing year round fire as the “new normal.” If we teach people to read the land, they will know it is a drought, and when good fire can be used, instead of being vulnerable to what nature will provide otherwise. If we are to succeed in living in this land, we must consider what it is telling us and not force unrealistic solutions on it.
What do you see as some ways forward to better align Indigenous perspectives and current management efforts?
- Author: Gabrielle Boisramé
Reposted from the California Water Blog
Now that summer is over and rain has returned to California, it appears that the dramatic 2017 fire season is finally behind us. The effects of fire season can linger, however, with the possibilities of erosion and polluted runoff from burned areas. Napa County has even issued suggestions for how to protect waterways in burned landscapes.
Not all news is bad when it comes to the interactions between fire and water, however. These two seemingly opposite elements can actually work in tandem under the right circumstances, to the benefit of people as well as the environment.
While the North Bay fires were filling the headlines in October, another fire 200 miles away was quietly entering its third month of burning in the Sierra Nevada wilderness. This other fire, known as the Empire Fire, was ignited by lightning. By allowing this fire to slowly burn, the park service allowed natural processes to remove fuels that could otherwise build up and lead to more dangerous fires in the future.
The Empire fire burned through an area in Yosemite where fires have been allowed to burn for over 40 years, the longest period managed with such a strategy anywhere in California. Research in Yosemite and other areas shows that allowing these wilderness fires to burn can increase the amount of water stored in the soil or flowing downstream. In the winter, forest clearings opened up by fires often store deeper snow that melts later than in densely forested areas, meaning more water is released slowly in the spring and summer rather than all rushing out as floods in the winter.
Fires can also open up meadow areas that have been overgrown by forest. Although wet meadows cover only a small percentage of California's landscape, they provide important benefits to the water supply. Meadows reduce the size of floods by storing water during high runoff periods. They also help to store water for the dry summer months by holding that water like sponges and slowly releasing it.
The biggest news about fire and water, unfortunately, is usually about how burned landscapes contribute to erosion, which then pollutes streams and clogs reservoirs. When fires burn homes, pollution risks can be especially high due to the presence of hazardous chemicals. Fires can also lead to larger floods since there is less vegetation to slow water's path from rainfall to stream runoff.
These negative effects, however, usually happen because a large portion of a watershed has been completely stripped of vegetation, and plants have not been able to re-grow in time to stabilize the soil. These kinds of fires are usually caused by a combination of dense fuels and extreme weather. When fires burn under less extreme conditions (lower fuel loads, high humidity, low temperatures, and/or low wind speeds), they can clear out dead fuels and remove a small number of trees while leaving most large trees intact. After the fire, the remaining trees (as well as new growth of understory plants) often enjoy wetter soils and less competition. This increases the ability of plants to survive drought conditions.
Wildfire has always been a part of California – especially northern California and the Sierra Nevada – for as long as it has had lush vegetation and dry summers. Native Californian plants have adapted to this process. Some species, like redwoods, even depend on fire for regeneration. Native Californian people historically used fire as a tool to promote the growth of desired plants.
In the early 1900s, however, those in charge came to what seemed to be a very logical decision: to protect our homes and forests from fire, we should put out all fires as quickly as possible. Although this policy was initially very successful, a century later we have flammable forests with heavy fuel loads, as well as densely packed trees that send large amounts of water into the air through their leaves rather than allowing it to flow downstream or remain underground to be used during droughts.
Large public land managers such as the National Park Service and U.S. Forest Service have lately been shifting away from the strategy of suppressing every single fire. Instead, lightning-ignited fires that are burning under acceptable conditions (not too windy, not too close to infrastructure, etc.) are allowed to burn and perform their natural functions of clearing fuels and thinning forests to sustainable tree densities. Prescribed fires and mechanical thinning are also used in situations where greater control is required to reduce risk.
In this way, letting some fires burn today can prevent catastrophic fires from burning through dense fuel in the future. Preventing such catastrophic fires removes their threat to the water supply – as well as the potentially devastating human losses, as we saw from the Atlas, Tubbs, Nuns, and other fires this year. Increased streamflow, snowpack, and drought resistance in burned watersheds all add to this increased water security. The water benefits of more natural forests are receiving increased attention lately, with some companies even working to set up markets for downstream water users to pay for upstream forest care.
We cannot prevent all wildfires in California. However, by understanding their role in our natural systems and incorporating them into our land management, we can benefit from them.
Gabrielle Boisramé has a PhD in environmental engineering from U.C. Berkeley, where she studied the effects of wildfire on water balance in the Sierra Nevada with Prof. Sally Thompson. She continued this work as a post-doctoral scholar with Prof. Scott Stephens, also at U.C. Berkeley.
Boisramé, Gabrielle, S. Thompson, B. Collins, and S. Stephens. “Managed wildfire effects on forest resilience and water in the Sierra Nevada.”
Lundquist, J. D., S. E. Dickerson-Lange, J. A. Lutz, and N. C. Cristea. Lower forest density enhances snow retention in regions with warmer winters: A global framework developed from plot-scale observations and modeling.
Neary, D., K. C. Ryan, and L. F. DeBano. Wildland fire in ecosystems: Effects of fire on soil and water.
van Wagtendonk, J. W. The history and evolution of wildland fire use.