- Author: Kat Kerlin, UC Davis
Study finds resilient, frequent-fire forests have far fewer trees
What does a “resilient” forest look like in California's Sierra Nevada? A lot fewer trees than we're used to, according to a study of frequent-fire forests from the University of California, Davis.
More than a century ago, Sierra Nevada forests faced almost no competition from neighboring trees for resources. The tree densities of the late 1800s would astonish most Californians today. Because of fire suppression, trees in current forests live alongside six to seven times as many trees as their ancestors did — competing for less water amid drier and hotter conditions.
The study, published in the journal Forest Ecology and Management, suggests that low-density stands that largely eliminate tree competition are key to creating forests resilient to the multiple stressors of severe wildfire, drought, bark beetles and climate change.
This approach would be a significant departure from current management strategies, which use competition among trees to direct forest development.
Defining ‘resilience'
But first, the study asks: Just what does “resilience” even mean? Increasingly appearing in management plans, the term has been vague and difficult to quantify. The authors developed this working definition: “Resilience is a measure of the forest's adaptability to a range of stresses and reflects the functional integrity of the ecosystem.”
They also found that a common forestry tool — the Stand Density Index, or SDI — is effective for assessing a forest's resilience.
“Resilient forests respond to a range of stressors, not just one,” said lead author Malcolm North, an affiliate professor of forest ecology with the UC Davis Department of Plant Sciences and a research ecologist with the U.S. Forest Service, Pacific Southwest Research Station. “‘Resistance' is about surviving a particular stress, like fire — but there's a lot more going on in these forests, particularly with the strain of climate change.”
Competitive nature
For fire-adapted forests in the Sierra, managing for resilience requires drastically reducing densities — as much as 80% of trees, in some cases.
“Treatments for restoring resilience in today's forests will need to be much more intensive then the current focus on fuels reduction,” said Scott Stephens of UC Berkeley, a co-author on the paper.
The study compared large-scale historical and contemporary datasets and forest conditions in the southern and central Sierra Nevada, from Sequoia National Forest to the Stanislaus National Forest. It found that between 1911 and 2011, tree densities increased six- to seven-fold while average tree size was reduced by half.
A century ago, both stand densities and competition were low. More than three-quarters of forest stands had low or no competition to slow a tree's growth and reduce its vigor. In contrast, nearly all — 82%-95% — of modern frequent-fire forests are considered in “full competition.”
The study indicates that forests with very low tree densities can be more resilient to compounded threats of fire, drought and other climate stressors while maintaining healthy water quality, wildlife habitat and other natural benefits. Forests burned by high-severity fires or killed by drought lose such ecosystem services.
Wake-up call
The authors say the 2012-2016 drought, in which nearly 150 million trees died from drought-induced bark beetle infestations, served as a wake-up call to the forestry community that different approaches are required to help forests confront multiple threats, not only severe wildfires.
A shift away from managing for competitive forests and toward eliminating competition could allow the few to thrive and be more resilient.
“People have grown accustomed to the high-density forest we live in,” North said. “Most people would be surprised to see what these forests once looked like when frequent surface fires kept them at very low densities. But taking out smaller trees and leaving trees able to get through fire and drought leaves a pretty impressive forest. It does mean creating very open conditions with little inter-tree competition. But there's a lot of historical data that supports this.”
“We think resilient forests can be created, but it requires drastically reducing tree density until there's little to no competition,” said Brandon Collins of UC Berkeley, another co-author on the paper. “Doing this will allow these forests to adapt to future climate.”
Additional co-authors include Ryan Tompkins of UC Cooperative Extension, and Alexis Bernal and Robert York of UC Berkeley.
The study was funded by the National Park Service Pacific West Region, U.S. Forest Service Pacific Southwest Research Station, U.S. Joint Fire Sciences Program, and the UC Agriculture and Natural Resources Division.
/h3>/h3>/h3>/h2>- Author: Kathy Keatley Garvey
Egerer will speak on "Entomological Investigations in Urban Gardens," focusing on wild bees and natural enemies in urban gardens in Germany, at a virtual seminar hosted by the UC Davis Department of Entomology and Nematology on Wednesday, Nov. 24.
Her seminar begins at 4:10 p.m., Pacific Time. The Zoom link is here.
More than 60 percent of our world's population will live in cities in the next decades, Egerer says in her abstract. "Urban agriculture has great potential to support arthropod biodiversity and thereby potentially enhance ecosystem services such as pollination and pest predation for more sustainable food production. In this talk, I discuss interdisciplinary research on wild bees and natural enemies in urban community gardens in Berlin and Munich, Germany. Specifically, I examine how urban garden management can play an important role in supporting species diversity and the provision of insect-mediated services. Furthermore, I discuss citizen science initiatives that our group uses to engage the public in scientific research on urban biodiversity and ecosystem services."
Egerer, whose research and teaching interests include ecology, biodiversity, agroecology, urban ecology, insect ecology, climate change, and food systems, holds a bachelor's degree in biology (2013) from Kalamazoo College, Mich., and then received her master's degree (2017) and her doctorate (2019) in environmental studies from UC Santa Cruz, studying with major professor Stacy Philpott.
After research work in Australia, Egerer joined the Institute of Ecology at the Technical University of Berlin in 2019 as an International Postdoc Initiative (IPODI) postdoctoral fellow. In 2020, she was appointed to the professorship for Urban Productive Ecosystems in the TUM School of Life Sciences.
- Egerer M and Kowarik I. (2020) Confronting the modern Gordian Knot of urban beekeeping, Trends in Ecology and Evolution 1-4.
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Philpott SM, Egerer M, Bichier P, Cohen H, Cohen R, Liere H, Jha S, Lin BB. (2020) Gardener demographics, experience, and motivations drive differences in plant species richness and composition in urban gardens, Ecology and Society
- Buchholz S and Egerer M. (2020) Functional ecology of wild bees in cities: what we know about trait-urbanization relationships, Biodiversity and Conservation 1-23.
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Philpott SM, Lucatero A, Bichier P, Egerer M, Jha S, Lin BB, Liere H. (2020) Changes in natural enemy-herbivore networks along local and landscape gradients in urban agroecosystems, Ecological Applications 0: 1-13.
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Egerer M, Lin B, Diekmann L. (2020) Nature connection, experience and policy encourage and maintain adaptation to drought in urban agriculture, Environmental Research Communications 2: 1-12.
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Egerer M, Liere H, Lucatero A, Philpott SM. (2020) Plant damage in urban agroecosystems varies with local and landscape factors, Ecosphere 11(3): 1-19.
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Egerer M, Fouch N, Anderson EC, and Clarke M. (2020) Socio-ecological connectivity differs in magnitude and direction across urban landscapes, Scientific Reports 10: 1-16.
- Egerer M, Wagner B, Lin BB, Kendal D and Zhu K. (2020) New methods of spatial analysis in urban gardens inform future vegetation surveying, Landscape Ecology 1: 1-18.
- Egerer M, Cecala JM and Cohen H. (2020) Wild bee conservation within urban gardens and nurseries: effects of local and landscape management, Sustainability 12: 1-10.
The Department of Entomology and Nematology seminars are coordinated by nematologist and assistant professor Shahid Siddique, who may be reached at ssiddique@ucdavis.edu for any technical issues.
![Urban garden management can play an important role in supporting species diversity and the provision of insect-mediated services, says ecologist Monika Egerer, an assistant professor at Technical University of Munich (TUM), Germany. Urban garden management can play an important role in supporting species diversity and the provision of insect-mediated services, says ecologist Monika Egerer, an assistant professor at Technical University of Munich (TUM), Germany.](/blogs/blogcore/blogfiles/87359.jpg)
- Author: Kathy Keatley Garvey
Murray, who anticipates receiving her bachelor of science degree in evolution, ecology and biodiversity in June 2021, is one of 396 students selected from a national pool of 5000 sophomores and juniors to receive a scholarship from the Barry Goldwater Scholarship and Excellence in Education Foundation, a federally endowed agency honoring the late senator and “designed to foster and encourage outstanding students” who are pursuing research careers in natural sciences, engineering and mathematics.
The honor includes a monetary prize of $7500. “Goldwater Scholars have impressive academic and research credentials that have garnered the attention of prestigious post-graduate fellowship programs,” according to a foundation spokesperson. Goldwater Scholars have received 93 Rhodes scholarships, 146 Marshall scholarships, 170 Churchill scholarships, 109 Hertz fellowships, and numerous other distinguished awards, including National Science Foundation Graduate Research Fellowships.
Murray, who joined the Karban lab in 2018, is a member of the campuswide Research Scholars Program in Insect Biology (RSPIB), founded and directed by three UC Davis Department of Entomology and Nematology faculty members (Jay Rosenheim, distinguished professor; Joanna Chiu, vice chair and associate professor; and Louie Yang, associate professor) to provide "academically strong and highly motivated undergraduates" with multi-year experience in biological research. The program pairs students with faculty mentors.
In the Karban lab, Murray designs and conducts independent research on plant development, flowering, and communication. She generates questions, creates protocols, collects and analyzes data.
In addition, Naomi works with UC Davis Professor Jay Stachowicz at the Bodega Marine Laboratory, where she does independent research on seagrass disease ecology, specifically herbivore-plant-pathogen interaction. She formerly worked as a full-time undergraduate researcher on seagrass ecology in the Stachowicz lab.
Native of San Diego
Naomi was born and raised in San Diego and is the first scientist in her family. Her father holds a bachelor of science degree in engineering and works as a home inspector and her mother is a newly retired lawyer.
“My interest in ecology started in high school, when I interned at the San Diego Zoo,” Naomi related. “Before the internship, I knew I loved animals and the environment, but I had no idea how I could turn those passions into a career--I thought if I liked animals, my only options were to be a zookeeper or a vet. The internship exposed me to a lot of other professionals and researchers working to protect nature, which was really my first glimpse into ecology and conservation."
"When I selected ecology, evolution, and biodiversity as my major, I intended to be primarily animal-focused, but that changed when I went to the Botanical Conservatory on UC Davis Biodiversity Museum Day my freshman year. I absolutely fell in love with it, and I interned there that spring. It turned into employment and since then, my love for plants has really grown; they're the main subject of my research now!”
Naomi is one of two Goldwater Scholars from UC Davis; the other is Jayashri Viswanathan, who seeks a doctorate in neuroscience and plans to teach biological sciences at the college level. They are among 32 recipients statewide.
Career in Forest Ecology
Naomi is leaning toward a research career in forest ecology, studying how trees affect community function and resilience “with the goal of minimizing the impacts of climate change.” She worked three weeks as a field technician on a project monitoring tree mortality in the forests of Yosemite Valley, where she tent-camped without running water or electricity, and collected data for 10 hours a day.
She acknowledged that after a few days there, she didn't know if she could meet the challenges. “But as the days passed, I realized that even when I was at my most uncomfortable, I was asking questions about the system, proposing new hypotheses for old phenomena, and marveling at the beauty of the forest,” she wrote in her essay, part of the Goldwater Scholarship application.
“As the world changes and becomes increasingly interconnected, we are in desperate need of critical thinkers, synthesizers, and people able to approach complex problems with broad, interdisciplinary perspectives,” Murray wrote. “I am working to become one of these pioneers and intend on pursuing a career in research to monitor, track, and minimize the impacts of climate change. Specifically, I plan to focus on forest ecology and how patterns of resource allocation and carbon storage among trees affect community function and ecosystem resilience.”
After receiving her bachelor's degree, Naomi plans to pursue a doctorate in ecology. “My current major prepares me with a strong foundation in basic science, and I have taken it upon myself to seek out diverse research experiences in both field and lab settings to develop a multi-dimensional perspective on critical issues in ecology,” she noted. “My time as a field technician has prepared me for ecological field work. Living as a full-time undergraduate researcher gave me a glimpse into conducting research as a career and made me familiar with work beyond the field. Additionally, participation in the Research Scholars Program in Insect Biology, a long-term pairing of undergraduates with faculty mentors to conduct research, has fostered connections instrumental in my path towards a successful research career. Perhaps most importantly, my independent design and execution of three experiments has taught me how to ask and test scientific questions.”
Murray earlier received a UC Davis Provost's Undergraduate Fellowship of $1200, a Regents Scholarship of $30,000, and a Bodega Marine Lab Undergraduate Research Fellowship of $5000, among other honors and awards.
Active in SEEDS
The Goldwater Scholar is active in Strategies for Ecology Education, Diversity, and Sustainability (SEEDS), an offshoot of the Ecological Society of America, and serves as an officer of the Davis SEEDS Chapter. The group seeks to make ecology more accessible to underrepresented groups of students. The club fosters science exploration and guidance through career panels and research facility tours.
“When I attended the 2018 SEEDS National Field Trip, the student group was mainly women of color,” Murray related in her essay. “I listened to them speak about the racism that structures this nation and its higher institutions, creating foundational issues of access to opportunity, mentorship, and funding. It was a wake-up call, making me aware of my privilege and inspiring me to deconstruct the walls that exist in my academic sphere.”
“I became an officer for the UC Davis SEEDS chapter. Through the club, I work to organize graduate student and career panels, amplifying underrepresented stories and connecting students with mentors who have similar backgrounds. I plan field trips and study sessions, and promote campus opportunities. And I help apply for funding to make all our activities equal access. Moving forward in my career I will continue this work, grateful that SEEDS has pushed me to become an active participant in scientific advancement through social justice.”
![Naomi Murray, a third-year student at UC Davis, shown here doing field work in Davis, anticipates receiving her bachelor of science degree in evolution, ecology and biodiversity in June 2021. (Photo by Alicia Bird) Naomi Murray, a third-year student at UC Davis, shown here doing field work in Davis, anticipates receiving her bachelor of science degree in evolution, ecology and biodiversity in June 2021. (Photo by Alicia Bird)](/blogs/blogcore/blogfiles/71655.jpg)
![Naomi Murray with eelgrass at Tomales Bay. (Photo by Katie DuBois) Naomi Murray with eelgrass at Tomales Bay. (Photo by Katie DuBois)](/blogs/blogcore/blogfiles/71656.jpg)
- Author: Ben Faber
This is a cross-post from the "Topics in Subtropics" blog.
Join us on alternate Tuesdays in May and June, 3:00 pm to 4:00 pm, for this opportunity designed for middle and high school students. Treemendous Tuesdays is a collaboration of U.S. Forest Service, Los Angeles Center for Urban Natural Resources, California Project Learning Tree, California 4-H, and University of California Agriculture and Natural Resources.
Five webinars will be hosted every other week starting May 5 and ending June 30. These events are free and registration is required. Flyer is attached. Dates, topics, and link to registration are below.
Please share this online opportunity with organizations, community members, teachers, parents, and students. We look forward to giving students a glimpse of the wonders and benefits that trees offer!
- May 5: Invasive Species (invasive shot hole borers)
- May 19: Invasive Plants & Trees
- June 2: Benefits of the Urban Forest
- June 16: iTree
- June 30: Living with Fire
Register https://ucanr.edu/survey/survey.cfm?surveynumber=29846
- Author: Annemiek Schilder
In this weekly blog, Dr. Annemiek Schilder, Director, UCCE Ventura County and Hansen Agricultural Research and Extension Center, shares her observations about the natural world across the seasons. As she says:
"Gently observing your surroundings with curiosity will teach you some amazing things. There are so many fascinating things happening under our noses, only wanting for an observant eye."
As I was poking around my garden and looking at flowers, my eye suddenly fell on an odd-looking green spider carrying a honey bee on the spadix of a calla lily. My first thought was “poor bee”, working so hard to pollinate flowers and then getting caught by a spider – life is not fair!
A spider and a bee: eat or be eaten. Photo: Annemiek Schilder
Of course I was fascinated by the little scene and was wondering what was going on, what kind of spider was that? It was green with a large patterned abdomen and looked like one of those spiders that hang out in flowers. The spider hung on to the bee for a while, walking this way and that, it almost seemed too big for it to handle. The next day, I saw the dead bee lying at the bottom of the flower and no sign of the spider. I wondered if it had given up on the bee. As I looked into it, I discovered a much more sinister thing had taken place…
The spider turned out to be a flower crab spider (genus Misumena). These spiders are harmless to humans and often take on the color of the flower background to camouflage themselves. They have long “arms” like crabs to capture their prey and can walk forwards, backwards and sideways.
According to the Missouri Department of Conservation: “Crab spiders don't use webs to capture their prey; instead, they hide in flowers and wait for insects to come to them. Crab spiders often look like part of the flowers they inhabit. Unlike spiders that spin webs, crab spiders have good vision. When a bee, fly, or other prey lands on the flower seeking nectar, the crab spider attacks, injects venom into the prey, then holds it while drinking its juices.”
Flower crab spider feeding on honey bee blood, like a vampire! Do you notice another insect in the picture? This is an ant looking for nectar. Photo: Annemiek Schilder
So there we have the answer! The crab spider obviously sucked out the hemolymph (insect blood) and then discarded the bee corpse after dinner.
The next day it looked like the tables were turned: to my surprise, I saw a motionless brown spider being dragged by a blue-black insect into a hole in the ground. Before long, the same insect was walking nervously, zigzagging and fluttering its wings, over the ground. It was difficult to photograph since as soon as I approached, it would fly away.
However, I got a closer look at it by zooming in on the photograph: it turned out to be a spider wasp in the family Pompilidae, which often have a bluish-black body with a metallic sheen. They have long spiny legs and curved antennae. Spider wasps are solitary and the adults feed on flower nectar. The female wasps hunt spiders which they sting and paralyze, then drag to their burrows in the ground. Next, the female wasp lays a single egg in the spider and as the larva grows, it eats the insides of the still-living spider. How's that for a horror story to keep you up at night?
Spider wasp looking for a spider to attack among wood chips and leaves. Photo: Annemiek Schilder
I then remembered seeing a giant wasp over 2 inches long in Costa Rica. That wasp was a Tarantula hawk, which hunts and lays eggs in tarantulas. They are not aggressive towards humans but can give one of the most painful insect stings in the world when handled!
Did you know that Dr. Justin Schmidt, an entomologist (someone who studies insects) from Arizona, devised a scale known as the Schmidt Sting Pain Index? To develop this scale, he allowed himself to be stung by a variety of wasps, bees and ants. He rated the Tarantula hawk's sting as a “4” on a 0-4 scale and described it as "blinding, fierce, and shockingly electric. A running hair dryer has been dropped into your bubble bath. A bolt out of the heavens. Lie down and scream."
So look, but don't touch, is the best strategy!