Posts Tagged: forest health
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.
"Trees are poems that the earth writes upon the sky,” wrote Kahlil Gibran. But trees falling into power lines have sparked catastrophic fires and falling trees have injured nature lovers.
To prevent power outages, PG&E looks for trees near power lines that need to be trimmed or removed. To prevent power outages and other mishaps caused by failing trees, Matteo Garbelotto, UC Cooperative Extension forest pathology specialist at UC Berkeley, has incorporated science into a mobile application that can be used to determine whether a tree presents a hazard and should be removed.
“PG&E was doing tree surveys with pencil and paper,” said Garbelotto, who saw the manual process as fraught with opportunities for error. A paper record needs to be sent to a central collection site where it is transcribed. In the transcription process, mistakes can be made. And there's no way of verifying if a person actually examined the tree to fill out the form.
“Why don't you do a digital survey?” he asked a PG&E tree surveyor. “Using a tablet or phone, the data could be shipped directly, in real time, to the San Francisco office. Using a phone or GPS device, you will know the precise location of the tree and know the worker did the job. If there's a fire, you have proof.”
PG&E Corporation Foundation, the philanthropic arm of the utility, gave Garbelotto a $70,000 grant to develop the app he envisioned for determining which trees are hazards.
“Developed by dedicated UC Berkeley researchers, the tool will provide benefits for other utilities and the forestry industry as they work to create safe and healthy forests. The easy-to-use mobile platform collects data in real time and creates a record that the survey was completed including relevant details like “when,” “where” and “who,” said Stephanie Isaacson, director of community relations for PG&E.
The UC Cooperative Extension tree disease expert created a list of questions that help evaluate tree health. For example, in addition to asking if the tree leaning toward a power line, surveyors are asked, Are there obvious signs of internal decay? Is there a large wound on the tree?
“If a tree has a wound of 5 inches or more, there is a good chance there is significant decay behind the wound,” Garbelotto said. “If there is a mushroom or conk growing on the tree, that portion of the tree is dead and the branch or whole tree may fall down.”
The app, which Garbelotto has dubbed “Evalutree,” can be used for more than powerline safety.
UC Berkeley Ph.D. student Michael Johnson has been using the app to evaluate different species of trees.
“We have just started our third field season using the app on a project for the Department of Defense that quantifies the health and economic value of the oak woodlands on the 100,000-acre Vandenberg Air Force Base,” said Johnson. “We started with coast live oak the first summer, added tanoak the second summer, and have expanded to bishop pine this summer.”
The mobile app has simplified data collection for Johnson, who is in the Forest Pathology and Mycology Lab at UC Berkeley.
“I used pencil and paper studying postfire aspen regeneration on Forest Service land in Northern Arizona in 2012-2013, where I also did my master's work on ponderosa pine decay in 2013-2015,” Johnson said.
He described his undergraduate work collecting data with pencil and paper carried in a tatum, a 8.5-inch by 12-inch metal case with a clipboard, compared with working with the Evalutree phone app.
“Each day would start with making sure that we had all of our data sheets packed in our bulky field tatums,” Johnson said, “making sure our GPS points were preloaded in a separate, expensive GPS device, making sure that our camera had batteries and that we had dry erase markers for our small white board so that we could indicate which plot each photograph belonged to.
“After the fieldwork was complete, we would spend weeks doing data entry, trying to make out the scrawled numbers and notes – smeared with charcoal and raindrops – and sorting and compiling the data, photos and GPS points. It was time-consuming and painstaking, to say the least.”
For his graduate research, Johnson was able to enter data directly into a spreadsheet on a field computer. “At the end of the field work, I would just have to compile the data from the computer, photos from the camera, and GPS points from the Garmin to make a report,” he said.
“Evalutree has changed all of that. Instead of field tatums and multiple bulky devices, I walk out into the field with a lab cell phone. The app has preloaded survey questions, the ability to connect photographs to specific plots, and drops GPS points at each plot and tree that I survey.”
Working in the U.S. Defense Department's sprawling, undeveloped landscapes, Johnson said, “We are often in the field all day without internet or phone connectivity. The app is prepared to meet this challenge and relies on our phone's internal storage and pre-existing GPS functionality to order and store our data with precision accuracy. At the end of the day – when we have returned to civilization and technology – we simply upload all of our surveys for the day and I immediately have my data and reports in multiple formats, including pdf, xls and kml files, at my fingertips.
“Within minutes, I can update my maps to show the exact location of all of the day's surveys, start crunching data in Excel, or print out a report with the photographs from each plot for my boss,” Johnson said.
Garbelotto, the UC Cooperative Extension specialist, would like to make the technology available to cities and companies that manage trees.
“The app can be used by any agency or government that owns or manages a significant number of trees and needs to run surveys on a regular basis to ensure these trees are not at risk of failing, causing property damage or, worse, casualties or injuries to people,” Garbelotto said.
“The surveys can be easily customized for different projects,” he said. “It can be used for campgrounds or parks to calculate the likelihood of a tree failing and likelihood of causing damage. You could have an answer within minutes of submitting the survey.”
For more information about Evalutree, contact Garbelotto.
This story was updated July 21 to add a quote from PG&E.
Central Valley residents from Visalia to Sacramento look forward every year to the beginning of strawberry season in early April, when roadside strawberry stands operated by Hmong and Mien farmers open to the public.
These farms grow strawberry varieties such as Chandler and Camarosa that haven't traded flavor for shelf life – they don't ship or store well, but they are far sweeter than varieties usually sold in stores, and they reach their peak ripeness and flavor in the fields next to the strawberry stands.
As strawberry season opens this year, farmers are hoping that customers will still stop by the stands to pick up their fresh, seasonal strawberries, and also that they will observe 6-foot social distancing and other guidelines to reduce the spread of COVID-19. UC Cooperative Extension agricultural assistant Michael Yang and I were interviewed on a local news station to encourage Fresno residents to practice these guidelines while supporting local farmers.
To assist Fresno strawberry farmers, the UCCE small farms team in Fresno County developed, printed, and distributed signs for roadside strawberry stands reminding customers to observe social distancing and other safety practices, as well as guidelines for farm stands to reduce the spread of COVID-19. Versions of the signs were also developed for strawberry stands in Merced and Sacramento, as well as a general sign for local produce at any farm stand.
Signs and safety guidelines were printed with funding from the Western Extension Risk Management Education Center, and Michael Yang distributed large printed versions of the signs to all strawberry stands on the Fresno County Fruit Trail map in Fresno County. These materials have also been shared with UCCE small farms and food systems advisors as well as nonprofit and agency partners and county Agricultural Commissioner's offices, and they are available for printing on the UCCE Fresno strawberry website.
Even as Californians shelter in place to contain the novel coronavirus that causes COVID-19, nutritious food remains vital to the health and well-being of our communities.
“Eating fruits and vegetables is known to benefit our overall health and help our immune system,” said Lorrene Ritchie, director of the UC Nutrition Policy Institute. “At a time when we need to be especially vigilant about staying healthy, eating healthy is essential.”
Farms, farm stands and farmers markets are listed as “essential businesses” in the state shelter-in-place order because they are important parts of the food supply. Urban farms are included in this category. As large produce distributors struggle to switch from selling large quantities to restaurants, schools and institutions to supplying supermarkets, these small businesses may offer a better selection of fresh foods, and may be closer to homes and less crowded.
To help minimize exposure and risk of spreading of the virus, urban farms need to follow some key guidelines from the CDC , said Jennifer Sowerwine, UC Cooperative Extension metropolitan agriculture and food systems specialist in the Department of Environment, Science, Policy and Management at UC Berkeley.
UC Cooperative Extension has compiled a list of resources for farmers, community gardeners and other people working in the food system to ensure that they can continue supplying fresh, healthy and affordable food to Californians.
“Social distancing, heightened health and hygiene practices and cleaning and disinfecting reduce the risk,” said Sowerwine.
Although eating a nutritious diet can boost our immunity, the Los Angeles Times reported produce sales plummeted by 90% or more at Southern California produce markets after the statewide shelter-in-place rules went into effect.
“It's worrisome to see that sales of fruits and vegetables are dropping so sharply, but not surprising,” said Rachel Surls, UC Cooperative Extension sustainable food systems advisor for Los Angeles County. “As people shop during the crisis, they may be prioritizing groceries that can be stored for a longer time in the fridge or pantry. And they may be on a very limited food budget, even more so than usual, so they are likely prioritizing essentials like bread and rice and baby formula.”
To support farmers in California, the UC Sustainable Agriculture Research and Education Program created a directory at http://www.calagtour.org for consumers to find local farms to purchase produce directly.
For families who have lost jobs and income, the risk of food insecurity increases. Some families could supplement their food from gardens and urban agriculture during this crisis.
Consumers must practice safety, too, when visiting farmers markets and farm stands. UC Cooperative Extension small farm advisor Ruth Dahlquist-Willard explained, "Things like keeping the minimum six-foot distance from customers, not touching any produce that you're not planning to buy, leaving as soon as you've made a purchase and washing the produce when you get home would be some good guidelines."
The virus is thought to be spread mainly from person to person, however there is evidence that COVID-19 can last for days on hard surfaces, thus the need to ramp up good health and hygiene practices, social distancing and cleaning and sanitizing of surfaces.
University of California research and extension faculty have compiled a list of helpful fact sheets and resources for farmers, community gardeners and other food system workers to ensure fresh, healthy and affordable food for communities across the state:
- Food-related resources for consumers and members of the food industry for COVID-19
- on the UC Davis Food Safety website.
- Sowerwine's PowerPoint presentation Safe Handling Practices for Fresh Produce in a Time of Coronavirus Disease 2019 (COVID-19) for urban farmers.
- A set of policies and procedures for safe food handling at the farm during COVID-19 provides step-by-step instructions for applying new food and health precautions on the farm including checklists, standard operating procedures and signage posting guidelines for preventing the spread of infection.
- COVID-19 safety guidelines for farm stands.
- Handouts for safe food-handling at home that can be distributed to customers receiving food from the farm.
All of these resources are posted on the UC Urban Agriculture website at https://ucanr.edu/sites/UrbanAg.
“During this challenging time, I am heartened by the quick and thoughtful responses by many extension, grassroots and institutional efforts, including Community Alliance with Family Farm's COVID-19 Responses and Resources for California Family Farms, Mutual Aid organizations where groups of young, healthy and lower-risk people are bringing food and services to vulnerable people who shouldn't be in public at all, and Bayareafood.info that seeks to support local restaurants, farmers, and food systems workers as they weather this latest storm,” said Sowerwine. “Crisis can spawn innovation, and I am hopeful that through this, we will come out the other end with a more compassionate and resilient food system.”
Road side stands selling fresh strawberries and vegetables are opening up around the San Joaquin Valley, and are a excellent option for safe shopping, reported Dale Yurong on ABC 30 News in Fresno.
In keeping with social distancing guidelines, Yurong conducted remote interviews with UC Cooperative Extension advisor Ruth Dahlquist-Willard and agricultural assistant Michael Yang, who work closely with small-scale farmers in Fresno and Tulare counties.
Dahlquist-Willard suggested customers maintain a six-foot space from other shoppers at farm stands and follow other common sense precautions when purchasing the healthful fresh food by, "not touching any produce that you're not planning to buy, leaving as soon as you've made a purchase and washing the produce when you get home . . . . Similar to what we're seeing at farmers markets right now."
Some valley farmers have been selling their produce at farmers markets out of town and have noticed fewer people are out shopping, Yurong said. They hope more people will stop by the local farm stands, away from the crowded grocery stores, and pick up something straight out of the field.
"My farmers that go to farmers markets, even though the farmers market is still open, they only allow a few people at a time. You don't have a lot of customers walk by just like before," Yang said.
San Joaquin Valley strawberry stands were all expected to be open by April 10, Yurong said.