UC Santa Cruz professor Michael Loik tests how plants respond to climate extremes
Acute drought is parching Santa Cruz. For the past four years, the coastal prairie of Younger Lagoon Reserve, on the west end of town, has received just over half the rain that normally falls. The situation is so dire it’s likely to happen no more than once a century.
The extreme dry spell makes Michael Loik smile in satisfaction. A professor of environmental studies at UC Santa Cruz, Loik is the mastermind behind this record dry spell. The fact that reserve soils are more arid than usual means his experiment—part of a global effort to study the effects of drought on biodiversity and plant growth—is going gangbusters.
“In light of climate change, we have a lot of evidence from models that California's weather patterns are likely to get a lot more variable. We may have wetter wet years, and drier dry years,” Loik says. “So the effects of drought on ecosystems is of primary importance to understand. We want to know how much ecosystems can help buffer those effects by taking carbon out of the atmosphere and putting it into the soil.”
The carbon-scrubbing powers of plants
In theory, plants could apply some brakes to the global warming juggernaut. Green things pull carbon dioxide from air to build their own tissues. Higher CO2 levels ease that process. Therefore global warming should boost plant productivity.
This scenario ignores one key fact: plants need water to grow. And since water is forecast to be scarce in the future, plants might not be that effective at slowing global warming.
Knowing exactly how sensitive plants in different ecosystems are to drought would be useful on many fronts. The results should help project drought impacts at regional and continental scales.
A global drought experiment
To test how a drier climate will affect plant growth, Loik and colleagues around the world have launched the International Drought Experiment, or IDE. The IDE simulates one-in-a-hundred- year droughts in different ecosystems around the world.
“What are the commonalities in the way ecosystems such as grasslands, deserts, and shrublands compare in their response to drought?” Loik asks.
The setup for each IDE plot is relatively simple. Posts at each corner of a square plot are connected by crossbeams a few feet above the ground. Translucent plastic troughs that work like rain gutters to funnel water away prevent a carefully calculated proportion of rainfall from reaching the plot. At Younger Lagoon, these rain-out shelters exclude 60 percent of natural precipitation. It’s an amount equivalent to local once-a-century drought levels. Plastic sheeting forms an underground barrier preventing water from moving sideways within soils and roots from gathering moisture outside plot borders. Sensors measure rainfall, temperature, humidity, sunlight, and soil moisture at regular intervals.
Loik has installed a second set of IDE plots at the UC Santa Cruz Arboretum and a third set in the Santa Cruz Mountains, enabling him to observe potential differences across this modest elevation gradient.
Keeping the project accessible
The rain-out structures are designed to be “as inclusive and accessible as possible,” says Loik, who sits on the steering committee of DroughtNet, the network of IDE participants. “The standard design for the shelter is fairly small in order to try to make this accessible to those who may not have the financial capacity to build out an elaborate experiment.”
Their carefully thought out approach has caught on. Worldwide, about 35 IDE sites have been built to date, including at the NRS’s Sedgwick Reserve east of Santa Barbara and the McLaughlin Reserve north of the Bay Area.
The value of comparisons
“Being able to make comparisons across sites is really important. The kinds of impacts or outcomes you find at one location may not be the same at other locations because they have different weather or climate patterns, and different soil types. You gain so much you can't understand otherwise from a single site,” Loik says.
As someone who studies plant responses on a large scale, Loik is grateful to have access to the wide variety of ecosystems protected within the NRS. “The NRS reserves provide infrastructure, they provide data, a certain degree of security for research infrastructure, great people, networking capacity. The NRS is ideally suited for things like this, and we're lucky we have it in California.”
“We've been monitoring what's survived, and how much vegetation each has grown each year” since the first shelters were installed in fall of 2015, Loik says.
At the end of each growing season, once the rains have ceased, Loik and his students record the species of plants occurring beneath each shelter. Then, in sections of each droughted and control plot, they snip all the vegetation down to the ground, oven dry the harvest, and record its mass. All IDE experiments are supposed to run for at least five years, so they’ll conduct a major analysis of the data in 2020.
Loik has already observed some intriguing results. “During the really wet winter of2017, plants grew more under the rainout shelters than in the open plots. If the soils can get really wet, the chemistry of the soils changes, and the roots aren’t able to respire,” Loik says. “We would not have anticipated that. It's one example of how field work can result in surprising outcomes.”
Implications for native plants
Loik’s graduate student, Justin Luong, is running a parallel experiment investigating the response of native vegetation to drought. Luong planted native species under rain-out shelters and control plots and compared their growth to that of the introduced species that now dominate California grasslands.
According to this pilot study, in drought conditions “it appears the native species do better than the non-native weedy species, though non-natives are not disappearing,” Loik says.
The finding is more than just good news for native ecosystem fans. During droughts, this tendency “could help replenish seedbanks of native species—every little bit of an edge helps.” Luong is now scaling up the study to examine seedlings at more coastal prairie sites statewide.
Luong’s project, Loik says, is “finding that some species have certain traits, like leaf thickness or number of veins in each leaf, that might make them more tolerant to drought.” That knowledge could help restoration experts select the right palette of species for regions forecast to become far more arid.
Snow subsidy, snow shortage
In eastern California, Loik had the genius to take advantage of an experiment inadvertently established by CalTrans. Working out of the NRS’s Valentine Eastern Sierra Reserve in Mammoth Lakes, he had been trying to study how future changes in snow melt water would affect the growth of local plants. He had gone as far as enlisting students to move more snow on some plots, and remove it from others, using shovels and a snow blower. But the manipulations proved exhausting and not so effective.
“It’s hard to take snow far where it won’t melt and come back to the plot,” Loik says.
Then one day, Loik realized that the snow fences along Highway 395 were piled high with drifts, while areas just downwind had been robbed of that moisture. A lightbulb went on in his head.
“I realized the fences were creating a snow depth treatment for us for free, and had been doing it since the 1950s. It was a fortuitous and long-term experiment,” he says—exactly what he had been trying to do by hand.
More than 60 years of altered snowfall have left ecological footprints around the fences. “You can see the effect in some of the tree rings. They grow slightly more if they’re located close to the fences” and get more water via snow, Loik says.
Whether snowfall will be heavier or lighter remains an open question. But one thing’s for sure: weather as usual will be a thing of the past. And Loik’s efforts will provide a better sense of what to expect from plant communities, and how to protect the biodiversity of California, in the strange years ahead.