- Author: Jules Bernstein, UC Riverside
Disappearing native is like an environmental Swiss Army knife
Though it is disappearing, California's official state grass has the ability to live for 100 years or more. New research demonstrates that sheep and cattle can help it achieve that longevity.
Purple needlegrass once dominated the state's grasslands, serving as food for Native Americans and for more than 330 terrestrial creatures. Today, California has lost most of its grasslands, and the needlegrass occupies only one tenth of what remains.
It is drought resistant, promotes the health of native wildflowers by attracting beneficial root fungi, burns more slowly than non-native grasses and speeds the postfire recovery of burned lands. For these and other reasons, many who work toward habitat restoration hope to preserve the needlegrass.
“Where it grows, these tall, slender bunches become focal points, beautiful as well as environmentally beneficial,” said Loralee Larios, a UC Riverside plant ecologist affiliated with UC Agriculture and Natural Resources. “However, identifying successful management strategies for a species that can live for a couple hundred years is challenging.”
To meet that challenge, Larios teamed up with University of Oregon plant ecologist Lauren Hallett and Northern California's East Bay Regional Park District. They tracked the health of nearly 5,000 individual needlegrass clumps over six years, including an El Niño rain year as well as historic drought.
The researchers took measurements of plant health including growth and seed production. They placed small bags over many of the grass clumps to capture the seeds and quantify the number of seeds they produced.
Their findings, now published in the Journal of Applied Ecology, were that purple needlegrass did better in places where sheep were allowed to graze. The positive effects of the grazing were amplified in times of wetter weather.
Previously, the park district spent a decade trying to assess the success of its grassland maintenance techniques. However, the district's method of applying a strategy like grazing, and then measuring the percentage of needlegrass clumps in a given area resulted in data that didn't follow a discernable pattern from year to year.
“By tracking each plant over time, rather than scanning broadly across an area, we gained much more clarity about how the grass responds to the grazing,” Larios explained. “Perhaps counterintuitively, we saw that the needlegrass generally died back when sheep weren't allowed to graze on it.”
When sheep were removed from the study sites, the needlegrass in all but two of the sites became less healthy. The researchers would like to learn whether the two sites that remained healthy have needlegrasses that are genetically distinct.
Grazing is a controversial strategy for grassland restoration. Some conservationists believe sheep eating the target grass, particularly during already stressful drought years, does not enhance their survival. As far back as the 1800s, some researchers hypothesized that the combination of grazing and drought resulted in the loss of perennial grasses.
Though drought was not beneficial for any of the plants in this study, the researchers believe grazing helped needlegrass survive in at least two ways. One, by trampling on leaf litter and other organic debris, sheep created space for new needlegrass to grow.
“Sometimes you get litter that's as deep as a pencil — so much dead, non-native grass piles up. It's hard for a little seed to get enough light through all of that,” Larios said.
Secondly, sheep eat non-native grasses that generate growth-suppressing debris and compete with purple needlegrass for resources.
When the Spanish colonized California, they brought forage grasses like wild oats that they thought would benefit cattle. Those introduced grasses spread, and now dominate the state's grasslands.
“Our grasslands are known as one of the world's biggest biological invasions,” Larios said.
California has as many as 25 million acres of grasslands, equivalent to the combined areas of Massachusetts, Connecticut, and Rhode Island. Though Larios does not believe it is possible to rid the state of all non-native grasses, she said it is possible to maintain or even increase the amount of purple needlegrass.
“It's great for carbon storage, which mitigates climate change, it doesn't serve as wildfire fuel, and cultivates a space for wildflowers that pollinators are then able to use,” Larios said. “We want to keep all those benefits.”
/h3>- Contributor: Biao Zhu
Impacts of soil warming and plant roots on organic matter decomposition in a Mediterranean grassland
Accurate understanding of soil carbon cycling is critical for predicting future climate. Decomposition of root litter and its transformation into soil organic matter are critical processes of soil carbon cycling. Thanks to support from the U.S. Department of Energy's Terrestrial Ecosystem Science program, a team led by Dr. Margaret Torn from Lawrence Berkeley National Laboratory have been studying the impacts of soil warming and plant rhizosphere on decomposition of 13C-labeled roots buried at two soil depths using a field lysimeter facility at Hopland Research and Extension Center, California.
The lysimeters contain soil columns of 38-cm diameter and 48-cm depth and annual grasses dominated by wild oats (Avena barbata). The experiment has three treatments (planted-ambient, planted-warming by 4°C, and unplanted-ambient). 13C-labeled Avena fatua roots were added to two depths (8-12 and 38-42 cm). The team will quantify the fate of added root litter in CO2 efflux from soil surface, dissolved organic carbon (DOC) leached from the bottom drain, and organic carbon remaining in bulk soil and different physical fractions for two growing seasons.
First season results show strong role of soil moisture in controlling soil carbon cycling in this Mediterranean ecosystem. Soil warming enhanced plant growth and ecosystem respiration in the early growing season with high soil moisture, while it suppressed plant growth and ecosystem respiration in the late growing season when soil moisture was limited. The team will continue measurements on CO2 flux, DOC loss, and organic carbon recovery in soil fractions, as well as collaborate with microbial ecologists and ecosystem modelers to better understand the underlying processes and to improve the models used for prediction of our future climate.