- Author: Emily Dooley
- Posted by: Gale Perez
Non-native species can wait decades or centuries before spreading
Invasive plants can stay dormant for decades or even centuries after they have been introduced into an environment before rapidly expanding and wreaking ecological havoc, according to a new study led by the University of California, Davis.
The research, published in Nature Ecology and Evolution, looked at more than 5,700 species of invasive plants in nine regions around the globe. It represents the most comprehensive analysis of plant invasions conducted to date, said senior author Mohsen Mesgaran, an assistant professor in the Department of Plant Sciences at UC Davis.
“The longer it is dormant, we're more likely to ignore it,” Mesgaran said. “This latency allows them to be overlooked, contributing to their eventual emergence as a serious invasive threat. They're like invasive time bombs.”
Long periods of dormancy
The international team found that nearly one-third of the invasive plants they analyzed exhibited lag periods between introduction and rapid expansion, with the average time being 40 years. The longest dormant period – sycamore maples in the United Kingdom — was 320 years.
Consider the common lawn weed Plantago lanceolata, commonly known as ribwort or buckhorn plantain, which has the longest dormancy in the United States, according to the report. Noxious to livestock and native plants, the plant was introduced into the United States in 1822 and is found widely here. Velvetleaf, which was introduced as a possible fiber crop, can be dormant for 50 years before it expands, threatening corn, soybean and other crops as it sucks up water and nutrients.
Nonnative species are generally introduced in two ways: by accident or through intentional importation for medicinal, ornamental, agricultural and other purposes. In California, about 65 percent of invasive plants were knowingly introduced.
“This lag phase may have played a role,” Mesgaran said. “They didn't know. With an increase in trade and transportation and tourism, we're going to have more problems.”
Longest lag times per region
Region | Dormancy (in years) |
Australia | 221 |
Great Britain (excluding Ireland) | 320 |
Ireland | 130 |
Japan | 80 |
New Zealand, North Island | 48 |
New Zealand, South Island | 60 |
Madagascar | 121 |
South Africa | 114 |
United States of America | 177 |
Global herbaria
The researchers generated a list of invasive plants in Australia, Great Britain, Ireland, Japan, New Zealand, Madagascar, South Africa, Japan and the United States. They used herbaria records, which are digitized and accessible online, to obtain global data on the location and time of species observations.
They then looked at trends to determine whether species exhibited dormant phases and, if so, for how long. A time series analysis was applied to detect lag periods, followed by a second analysis that compared climate during dormant and expansion phases.
In some of the species that invaded different regions, dormancy periods varied by location. In 90% of cases, climate conditions were different during times when the species spread, suggesting the plants waited for the right conditions or adapted to survive to an environment that was once unsuitable, Mesgaran said.
Planning for the future
Knowing that problems could loom in the future is key to managing pests and preventing widespread invasion and economic losses down the road. That means growers, policymakers and others should consider dormancy periods.
“The problem is most of the models that we have for risk assessment to see if the species are going to be invasive and a pest problem in the future don't account for this lag phase or this dormant phase,” Mesgaran said. “It's not that they're not going to be a problem, it's just the calm before the storm.”
The next steps in the research will be to examine the native climate of invasive species relative to conditions in these newer locations.
Scientists from Charles University and the Institute of Botany in Czech Republic, Stellenbosch University in South Africa, Taizhou University in China, University of Gottingen and University of Konstanz in Germany, University of Melbourne in Australia and the University of Vienna in Austria contributed to the research.
Grants from the German Research Foundation, Czech Science Foundation, Czech Academy of Sciences, Belmont Forum and European Biodiversity Partnership supported the research.
Media Resources
- Mohsen Mesgaran, UC Davis Department of Plant Sciences, (530) 752-0852, mbmesgaran@ucdavis.edu
- Emily C. Dooley, College of Agricultural and Environmental Sciences, (530) 650-6807, ecdooley@ucdavis.edu
Original source: UCD Plant Sciences NEWS website
/h3>/h3>/h3>/h3>/h3>/h3>- Author: Mathew Burciaga, UC Berkeley Rausser College
A new book edited by UC Berkeley Rausser College researchers centers equity and justice while delving into the complex elements that support or constrain biodiversity in cities.
Research continues to show that development has created environmental hazards like factories, freeways, or power plants that are often disproportionately placed in low-income areas or communities of color, and that remaining natural resources in urban areas, like trees and parks, are concentrated in wealthier neighborhoods. With renewed attention placed on the role of conservation, researchers are exploring new ways to make cities and their inhabitants active partners in preserving biodiversity and mitigating climate change.
A new book edited by Rausser College researchers delves into the complex elements that support or constrain biodiversity in cities — including human-wildlife interactions, climate fluctuations, landscape diversity, and environmental racism. Edited by Environmental Science, Policy and Management professor Christopher Schell and former postdoctoral researcher Max Lambert, Urban Biodiversity and Equity: Justice-Centered Conservation in Cities offers scientists, decision-makers and practitioners a new model to develop solutions for managing urban biodiversity while centering social justice, environmental justice, and civil rights.
Rausser College spoke to Schell and Lambert about their book ahead of its Dec. 19 release in the United States.
This conversation has been edited for length and clarity.
What inspired you to create this book?
Max Lambert: We were invited to put together a book on urban ecology and biodiversity. We knew there were other books out there, but we knew we wanted to write a book through a different lens: specifically, we're building off a Science paper led by Chris that centers equity and justice as the primary axis for conservation work. That was our guiding principle for taking this from journal publications to something that people can hold.
Christopher Schell: This is something that Max and I have been discussing since 2018. After our Science paper came out in 2020, Max contacted me to discuss what it would look like to expand that paper as a larger volume. We connected with folks who reached out about the paper and others whose work spans the urban-ecological spectrum to coalesce their contributions into a book that integrates equity throughout.
We didn't want to fall into the trap of thinking that academic institutions somehow have a hold on all this knowledge. Max led our efforts in trying to convey how applied this field is and emphasize the field's interconnectedness. We were excited to get folks who could span what it looks like to think of these theoretical applications in biodiversity science in relation to a city.
Lambert: And because urban ecology has blossomed so much as a field during the past 20 years, we spent a lot of time determining what topics we knew we wanted to emphasize in this book and what we would put on the back burner. We also wanted to bring in people from different backgrounds, walks of life, career stages, or parts of the world who can tie the threads of equity and justice together with this science.
How would you say the field of urban ecology has evolved over time?
Lambert: There have been pockets of people studying urban ecology from the 60s onwards, but their research never became part of the dominant mantra. By the 90s, we had the National Science Foundation (NSF) support two Long Term Ecological Research stations in Baltimore and Phoenix, which helped blossom and lead this area of research. But in my experience, even when I started my doctoral work a decade ago, urban conservation wasn't really a thing—there were still tons of folks saying we needed to protect nature from the city.
Schell: For us, the question is, when do we recognize that urban ecology has entered the public consciousness to the point that folks outside the academic sphere are thinking about it? We're certainly getting there in the Bay Area, as well as in a handful of cities across the country and globe. Folks in these communities are thinking more and more about their relationships with wildlife, biodiversity and nature inside these urban spaces. But sometimes folks look at us like we're crazy when we talk about the critically endangered species that are encased in a metropolitan area, or when we tell them about the large carnivores that roam their backyard. Some people have not yet fully understood that cities are hubs of nature that we created on top of existing biodiversity hotspots.
How does this approach differ from traditional models of conservation research?
Schell: We're leveraging a past research framework called the ecology in, of, and for cities to propose something called conservation in, of, for and with cities. We're still thinking about the many ways in which we maintain biodiversity across different axes; incorporate biological, social, and built elements of cities to manage ecosystem processes; and implement justice-centered approaches as we build sustainable practices. But all that felt unidirectional, where scientists or practitioners are doing things for the people who live in the city.
Conservation in, of, for and with cities is the new atom. It's explicitly calling out co-production, how we have equitable resource distribution, and how we fold in the other paradigms. We're emphasizing that if we don't have conservation with cities, none of the other components are going to work. In our minds, this is the linchpin to all those other pieces. We're not the only knowledge holders in this conversation, and by no means do you need to be of a certain age, race, class or ethnicity to participate in it. We're all in this together and have something to add to the conversation.
Lambert: You can't do conservation work without cities. You can't grey out urban areas and focus conservation work elsewhere. It's all part of the mix. Conservation with cities means engaging in conservation work at any scale — from state to national to international. You can't set goals just for remote places; you have to bring them into urban areas as well. All this goes back to our fundamental principle of centering equity and justice in all conservation. It is heavily pronounced in urban areas, but it's central to conservation work anywhere in the world.
Ecology and evolutionary biology are fundamental fields of biology, but they don't exist in a vacuum. Our Science paper showed that we need to be mindful of how society, culture, and politics influence life on Earth. We're doing the same thing here with conservation.
Can you think of any people, cities or organizations that are taking the principles you describe in your book and using them to improve urban biodiversity?
Schell: Max and I often riff off of Singapore being the mecca of urban ecology because of how that city is designed and embedded inside of nature, but we're starting to make improvements on the West Coast, too. One of the local organizations that has been pushing urban ecology forward is the California Academy of Sciences. Their Reimagining SF initiative brings together researchers and practitioners from across the Bay Area to think about San Francisco not as an urban environment with nature sprinkled in, but as a city inside of nature — one built in collaboration with ecosystem processes. It's a clear departure from the ways in which cities have thought about urban ecosystems in the past, which was strictly concerned about providing municipal services to its people.
Lambert: I went to Canberra, the capital of Australia, in 2016. It's a highly built place, but they've embedded trails and green spaces throughout the city; there are kangaroos, wallabies, and all kinds of parrots everywhere. It's very clearly designed, as Chris said, in collaboration with nature. The Presidio of San Francisco has also been an interesting nexus of urban conservation work. The Presidio Trust, which manages the park with the National Park Service, has done tremendous work with communities nearby. They've replaced non-native plants that have overgrown the area, cleaned up a bunch of pollution in the pond, and reintroduced endangered plants within the Presidio.
I also work closely with the City of Tacoma in Washington. Maintenance workers — the folks who take care of the concrete, asphalt, and sewers—are not the type of people you traditionally think of as doing conservation work, but in Tacoma, they are so impassioned to make sure biodiversity can thrive, and people can experience it everywhere they live.
Have you found engaging with policymakers or community members difficult while conducting your research?
Schell: The flagship species that my lab studies is coyotes, a species that garners a lot of interest in the Bay Area. In SF, a good chunk of folks have a real love-hate relationship with them. They think that their cats have some agency to stay outdoors indefinitely or that their dog can stay off-leash in an on-leash area, which often results in conflicts with coyotes. And as we start doing more of this work, it seems as if everybody has a story about a coyote — or a bobcat, raccoon or a fox — doing something they adore or disdain.
These fine-scale human-animal interactions bring everybody to the table. They want to hear more about how these are connected to the larger universe of stories around urban biodiversity, environmental justice, equity and resilience because it impacts them at this individual level.
Lambert: Maps will become essential to these conversations and are what entice people to join. For so long, the image of conservation was just David Attenborough in the middle of the world somewhere, in a place we can't necessarily relate to. But now, I can set up a map on iNaturalist that everyone can contribute to and access for free. Whether it's a map of all the trees in their city or observations of turtles, frogs or hawks, people will be able to put themselves in the context of their city. They can actually paint that picture of the landscape — they can see the asphalt, they can see trees — and place their community in the broader grand scheme of the universe.
Schell: One of our flagship projects deploys camera traps across urban to wildland spaces. We put up placards that give out our contact information if people are interested in the project; we've had over a dozen people in the last year reach out to us who are interested in learning more about the camera traps, including city officials. A figure from our Science paper created by co-author Dr. Simone de Roches was recently republished in the New York Times, and after reading that, some folks from the City of Piedmont's Recreation Department reached out. This small example highlights how far-reaching and continually helpful the work has been in creating collaborations across the Bay.
Lambert: I think that's the power of urban areas for conservation and getting people engaged. They know where they fit into much more easily than if you were to ask, “How do we protect tigers inMumbai?” It matters in the grand scheme — people generally care about tigers — but they have no context for it. People have context for their backyard coyote: almost everyone has a story about something in their urban area; they're just looking for someone to tell it to.
Do you think it's possible to create policies that improve urban biodiversity without first addressing the inequities like redlining?
Lambert: There are two panels to the figure that was just republished in the New York Times. The panel on the right shows conservation embedded in a cycle of social justice, environmental justice, and civil rights: that's the foundation for which successful conservation efforts will ever be possible. You can try to chip away at it in small ways, but you will always fight an uphill battle unless you center equity and justice because the things that cause injustice and inequities also degrade the natural world. These things are inherently intertwined.
Schell: If we can't figure ourselves out and figure out how we got to this point while centering equity and justice —which is something we said in the Science paper and at the beginning and end of this book, and also urged all of our co-authors to talk about it — then we will never get to our goals. This book was something that we wanted to get out into the world because this is not something we're alone in; there are other folks who are also interested in this, who also feel the same way, and who have been beating this drum in their communities. It's been a good journey to be able to put this into words and have folks understand how important it is to be able to restore ourselves as a means of then going on to continue to restore the natural world.
- Author: Sonia Fernandez, UC Santa Barbara
Naturally fire-prone ecosystems tend to have more species of birds and mammals, new study reveals
Wildfires. Many see them as purely destructive forces, disasters that blaze through a landscape, charring everything in their paths. But a study published in the journal Ecology Letters reminds us that wildfires are also generative forces, spurring biodiversity in their wakes.
“There's a fair amount of biodiversity research on fire and plants,” said Max Moritz, a UC Cooperative Extension wildfire specialist who is based at UC Santa Barbara's Bren School of Environmental Science & Management and the study's lead author. Research has shown that in ecosystems where fire is a natural and regular occurrence, there can be more species of plants — a greater “species richness” — due to a variety of factors, including fire-related adaptations. But, he said, there hasn't been nearly as much research in the way of animal biodiversity and fire.
If fire regularly consumes some of the base of an ecosystem's food chain, how does that ripple up to affect the biodiversity at higher levels?
That was the question Moritz investigated during a project supported by UC Santa Barbara's National Center for Ecological Analysis & Synthesis; he later recruited collaborators Enric Batllori from Universitat de Barcelona and Benjamin M. Bolker from McMaster University in Canada. For several years they combed through global datasets on various factors such as plant biomass, fire observations and species richness patterns.
While it might be natural to assume that plant biomass regularly consumed by fire would in turn lead to lower animal biodiversity, they found that for birds and mammals, fire is associated with increased diversity. In fact, they say, the effect of fire on biodiversity in the case of birds rivals that of the ecosystem's productivity. And in the case of mammals, fire's influence was even stronger than that of productivity.
“It's counterintuitive,” Moritz said. In the short term, fire's consumption of plant material (also known as “net primary productivity”) could result in less food for the animals that consume plants and make it more difficult to survive and reproduce. But in the longer term, he said, there may be evolutionary effects that unleash adaptations and formations of new species.
The researchers also looked at the effect of fire on amphibian species, however, the connection between fire and biodiversity in their case was difficult to make, possibly because amphibians live in wetter environments where fires may not be a regular occurrence.
So what accounts for the net positive effects of fire on mammal and bird diversity? The study is a correlative one, Moritz said, so more granular examinations have to be made to find out for sure. But it's likely that fire selects for species that can adapt to and quickly recover from a burn, and fire often creates environmentally complex habitats that meet different species' requirements.
“We know that fire creates a lot of heterogeneity and opens up all these niches,” Moritz said, and this resource availability might create favorable environments for some organisms to flourish alongside or over others. For example, animals that have strategies to survive fires or reproduce faster might do better in a fire-prone environment, as could those that make use of different habitats that emerge in the wake of a blaze.
Despite the connection between fire and species richness, the authors are careful to point out it does not mean fire is good for all ecosystems. In places where fire is not a natural occurrence, its presence “is more of a modern threat than an important process to maintain,” they said. And for places where fire is a natural part of the ecosystem, climate change-driven and intentional deforestation fires “may be quite different from natural fire regimes.”
Nevertheless, they say, these findings indicate that fire plays an underappreciated role in the generation of animal species richness and biodiversity conservation. Furthermore, the study adds nuance to the Latitudinal Biodiversity Gradient, a global pattern of terrestrial biodiversity in which the world's most biodiverse areas are located nearest to the equator, with levels of biodiversity generally decreasing toward the poles.
“This is a pattern that people have known for decades and have argued quite a bit about in terms of what drives it,” Moritz said. “And it turns out, it's hard to figure out. And it looks like fire plays a far more important role than we've ever really understood.”
/h2>/h2>- Author: Adina M Merenlender
When Al Murphy first took the reins at the UC Hopland Research and Extension Center (HREC) back in the 1950s, he had the joy of listening to California red-legged frogs living in a couple of perennial ponds. Maybe it was the frog chorus or just the rarity of year-round water that made Al and his staff decide to keep the sheep out and declare the ponds a biological area. Despite the designation as a biological area, the ponds have lost a good deal of biodiversity since Al's time.
The native frogs took a beating thanks to bullfrogs and exotic fish such as large-mouth bass that were introduced for sport fishing and by the time Kevin Lunde did his Ph.D. on chorus frogs at HREC in 2011, there were no native frogs to be found in the ponds. Also, by removing grazing and the use of fire to manage the rangelands surrounding the ponds, tule reeds dominate the pond's edge and invasive plants such as vetch spread across the higher ground.
The recent periods of drought are devastating for most of California's ecosystems, but were good news for the ponds. They went completely dry for the first time in recorded history, and the largemouth bass died off. The long, dry period also puts us at an advantage for bullfrog eradication while the habitat for the species is limited. As part of the restoration efforts, HREC staff removed some of the bullrush and community volunteers along with members from the California Conservation Corps spent the day translocating spike rush plants from nearby locations to the recently cleared areas along the edge of the pond to provide additional warm, shallow sunning areas for native amphibians.
Only time will tell if the spike rush takes hold and, in the meantime, we hope volunteers will return to help get rid of some bullfrogs. If we can keep the bass out and the bullfrogs under control, we can look forward to a time when red-legged frogs can safely return to HREC.
Thanks, HREC staff and GrizzlyCorps member Mona Latil-Quinn, for your help.
- Author: Mike Hsu
Giving 1,200-pound cows access to one of California's most fragile and biologically rich ecosystems seems a strange way to protect its threatened and endangered species.
But a recently published study suggests that reintroducing low to moderate levels of cattle grazing around vernal pools – under certain conditions – leads to a greater number and greater variety of native plants.
Ecologists consider vernal pools – ephemeral ponds that form seasonally – “islands of native habitat” amid California's grasslands that are dominated by exotic grasses. These biodiversity hotspots harbor about 200 native species of animals and plants, such as the coyote thistle, which germinates under water and forms a snorkel-like straw to deliver oxygen to its roots – and then “fills in” its stem as the pool dries.
Specially adapted to survive in those stages of wet and dry, many of these species are found only in vernal pools scattered across California – making those pools an urgent priority for conservationists.
During the 1970s and 1980s, vernal pools were fenced off in parts of the state, in the hopes of protecting the flora and fauna from grazing cattle. In the early 2000s, however, UC Davis researcher Jaymee Marty found that grazing was actually crucial to vernal pool biodiversity: once livestock were removed from areas that had been grazed historically, the diversity of plants plummeted.
“Her research was critical to rethinking the best ways to protect the diversity in California's vernal pool ecosystems,” Eviner said.
The Michaels-led study, published in the Journal of Applied Biology, builds on Marty's work, by looking at scenarios where cattle had been blocked from vernal pools for decades, and then observes the rate at which biodiversity returns after reintroduction of the animals. Michaels said she wanted to provide some initial answers to the practical questions that ranchers and land managers have in potentially reintroducing cattle.
“A lot of them had these areas that had been fenced off from grazing for the last 20–30 years, and they were very concerned about what happens if we let cattle back onto these vernal pool grasslands – are there going to be negative impacts because that land had been at rest for a few decades?” Michaels explained.
They discovered that, after reintroducing cattle to areas that had been fenced off since the 1970s, there was a greater abundance of native flora (species like the vernal pool buttercup, bractless hedge-hyssop and bristled downingia), as well as increased diversity among the plants (both in number of species and in how evenly distributed they were).
“Encouragingly, diversity is rapidly restored,” Eviner said, “providing conservationists with strong data to show that rapid action can enhance plant diversity.”
And as for potential worries about cattle making a snack of vernal pool plants, Michaels and her colleagues observed that the cattle appear to be more interested in munching on grasses.
“Anecdotally, we saw very few signs of herbivory on the vernal pool species because the timing is such that [the plants] are underwater for a good part of the late winter and early spring, and then by the time they're blooming, there's plenty of good forage around for the cattle,” Michaels said.
In fact, the cattle seem to be performing a function filled for millennia by native grazers (namely, the once-abundant tule elk), helping to knock down vernal pool species' chief competitor in those transition zones: the grasses.
Instead, microdepressions created by the cattle appeared to encourage the proliferation of native plants. Each hoofprint became a miniature basin – “a vernal pool within a vernal pool.”
“Right in those transition zones, where they could be hosting either the vernal pool species or the upland grasses, just a couple centimeters of soil topography can make a big difference,” Michaels explained. “If a cow comes and steps in that transition zone, and that lowers the soil surface so it stays inundated a little longer, you end up seeing these pockets of vernal pool species that are able to persist.”
Michaels is currently conducting a follow-up study on the hoofprints to pinpoint their role in boosting native plant abundance and biodiversity. Because the prints can last for several years, they might be able to deliver some enduring benefits – and land managers might not have to bring cattle in to graze the pools as often.
“If it's really the hoofprints making the big difference, maybe we don't need to graze every year – only during certain times of year when we know the hoofprints will form well and harden, and then we're good for a few years,” Michaels said.