Posts Tagged: Plant Sciences

Can vines speed urban cooling?

Study explores cooling benefits of fast-growing vines as trees take their time

Once perceived as a problem, conservation grazing by cattle a boon to vernal pools

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.

“We found that after 40 years of rest from grazing, reintroducing conservation grazing had – across the board – positive impacts on vernal pool plant diversity,” said Julia Michaels, a visiting professor at Reed College who led a three-year study in a Sacramento-area reserve during her time as a UC Davis Ph.D. student.

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.

“It's estimated that more than 90% of the original vernal pools in California have been destroyed due to agriculture and urban development, so management of those remaining – including those that have been re-created – is of high concern,” said Valerie Eviner, a UC Davis plant sciences professor and UC Agriculture and Natural Resources affiliate. Eviner is a co-author of the study, along with UC Davis colleague Kenneth Tate, UC Cooperative Extension specialist.

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.

In their study within the Sacramento Valley, the researchers focused on transition zones – the “battlegrounds” between vernal pool native species and the encroaching invasive grasses, where they are able to detect most readily the effects of disturbances such as grazing.

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.

Although the researchers were concerned about a loss of biodiversity, excessive nutrients in the ponds due to defecation and harmful compaction of “fluffy” soil, none of their worries materialized on the test sites where grazing was reintroduced.

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.

High Society--with Bad Breath?

It was right where it belonged--by the UC Davis Department of Plant Sciences. As I returned from a meeting in the building today, something green...

A praying mantis hanging out in the society garlic next to the UC Davis Department of Plant Sciences building. (Photo by Kathy Keatley Garvey)

A praying mantis hanging out in the society garlic next to the UC Davis Department of Plant Sciences building. (Photo by Kathy Keatley Garvey)

Find the praying mantis. Amid all the green, there's a green predator in the society garlic. (Photo by Kathy Keatley Garvey)

Find the praying mantis. Amid all the green, there's a green predator in the society garlic. (Photo by Kathy Keatley Garvey)

Connecting wildfires to climate change and drought

Longer summers, less moisture and warmer climates are predicted for California's Sierra Nevada mountains. These changing patterns bring frequent droughts and extended wildfire seasons — as seen from the current extreme drought. The question no longer is whether wildfires will be more common or more intense — they already are — but how forest managers want these fires to burn.

Jens Stevens, a postdoctoral researcher in disturbance ecology at the University of California, Davis, has tracked how forests thinned for wildfire react to high-intensity burns. The answers he found touch on growing concerns over how the state can protect its forests.

Under the context of climate change, Stevens studies how understory plants recover from wildfires, measuring the effects fuel treatments — such as the thinning of small trees — have on the way these forests burn.

Historically Sierra forests had gaps and openings, which prevented the spread of fires. More than a century ago land management agencies began a campaign of extinguishing all wildfires. Today's forest floors are blanketed with litter — fallen branches, leaves and shrubs — and many of the fire-tolerant pines have been replaced by firs, which handle shade well but act as fuel sources.

Stevens' research showed fuel treatments encourage resilience to wildfires, giving forests a greater ability to withstand a burn. Under really hot, dry summer conditions this makes a powerful difference.

“If you get warmer temperatures you're going to dry out the fuels,” says Stevens. “If we want to retain forest-dominated landscapes, we don't have the choice of doing nothing, because eventually these stands are going to burn."

To preserve forests, Stevens looked to native plant diversity under each management strategy. After a high severity fire, the tree canopy is non-existent. This new high-light environment favors other species, such as shrubs and flowering plants, which crowd out young trees.

In treating a stand before a fire, land managers are already encouraging plant diversity and when the stand burns, diversity increases even more, Stevens discovered.

While the treatments do protect the forest and encourage plant diversity, they are expensive and lead to uncertainty over how sensitive wildlife species are affected. Yet these areas will burn eventually, Stevens argues. The choice is either a more open forest or no forest at all.

He points out research by UC Davis ecologist Malcolm North, which shows the current pace of treatments can't keep up with the extent of Sierra forests that have been fire suppressed. The US Forest Service can treat up to 40 percent of a forest before managers must start over for follow-up treatments. The other 60 percent doesn't get touched.

“So the only real way to address that is to let the fire do the work for you,” says Stevens.

The proposal North and his colleagues arrived at relies on “firesheds.” These fire-prone areas would have boundaries that allow officials to efficiently manage the fires. If a burn begins after a treatment, they don't put it out. Allowing the fire to burn fuels they would otherwise be removing frees up resources to treat other areas.

“So if it's going to burn,” says Stevens, “you need to figure out ways the fire's going to give you your desired outcome.”

Watch Stevens explain more in his seminar.

This post was adapted from a longer piece by the UC Davis Department of Plant Sciences.
 

A report from the war on weeds

Over the last three millennia, the practice of growing rice has evolved and spread throughout much of the globe. From China, through India, to Greece and parts of the Mediterranean and from Europe to the Americas, rice has demonstrated its versatility in desert regions and wetland deltas alike. Abundant in carbohydrates, it is today one of the world’s most widely eaten foods.

While University of California researchers develop rice varieties more tolerant to the modern challenges of climate change — flooding, heat stress, drought — California rice farmers each year discover more new threats in the form of non-native and herbicide-resistant weeds. So well adapted are these weeds that if left unmanaged, they cause rice yields in some places to plummet to nearly nothing.

The introduction of rice to California in 1912 was fraught with weed challenges from the start. The traditional dry-seeding method allowed barnyard grass to quickly overrun fields. While a new water-seeding technique suppressed the weed, it led to a whole other set of problems. In continuously flooded fields — still the most widely used practice in California today — an imported weed, late watergrass, flourished. Aquatic weeds took advantage of the new environment while others gradually became more flood tolerant. For many years, advanced herbicides allowed farmers to gain ground over these weeds.

Then, beginning in the early 1990s, several weed species, including late watergrass, were found to be evolving resistance against the most powerful herbicides. A metabolic resistance to one herbicide, researchers discovered, could lead to resistance for another.

Weeds also found new ways to outcompete rice. One invasive weed, Ludwigia, grows fast and tall — as high as 10 feet. Shadowing the rice plants, it spawns tiny seeds that travel well in water. Other weeds, meanwhile, are small and run along the ground to avoid combines and some emerge earlier in the season than rice, dominating resources.

In the Department of Plant Sciences at UC Davis, professor Albert Fischer’s laboratory is battling rice weeds on a variety of fronts: by researching the evolution and mechanisms of herbicide resistance, finding traits that make rice varieties more competitive, developing resistance techniques through field testing at the industry-supported Rice Experiment Station in Biggs, Calif., and by encouraging farmers to diversify management methods.

“Use as many little hammers as you can on your weeds,” advises Whitney Brim-DeForest, a doctoral student at the University of California, Davis, in reference to the established ecology text “Many Little Hammers.” She instructs growers and is currently running Fischer’s field trials. “Don’t use just one tool year in, year out,” she says, “because you’re applying evolutionary pressures to the weeds.”

One system Fischer encourages is the stale seedbed technique, which allows weeds to emerge first from a reserve of seeds in the soil. Once that flush is up, farmers use a general herbicide to kill the weeds. At least one local farmer with a bad weed problem has controlled late watergrass this way. By replacing herbicides with shallow tilling, organic farmers can use this method.

With each management system is a different combination of growing techniques and herbicides, depending on weather, soil moisture and soil temperature, among other factors. Fischer’s team at the experiment station spends much of its time testing these herbicides on new weeds.

UC Cooperative Extension farm advisors encourage growers to also sanitize equipment, rotate crops, scout for surviving weeds and apply herbicide only when necessary, easing selection pressure on weeds while reducing environmental impact. Along that line, Fischer’s team is discovering how switching growing techniques and irrigation systems may be helping farmers meet higher environmental standards, addressing a trend of steeper water prices in California. Other researchers see this as an opportunity to reduce greenhouse gases released from decaying rice stalks post-harvest.

For each strategy, researchers weigh costs over benefits to select the right weapons for arming farmers entangled in this ongoing war with weeds.

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