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Grasslands Make a Comeback in Limestone Canyon

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An ongoing native grassland restoration project aims to rehabilitate this endangered habitat and reduce wildfire risk.

As summer months turn green hills to gold, the extremely dry grassy hillsides begin to pose a significant fire risk. Non-native and invasive annual grasses dry up and die, becoming fuel waiting for a spark. Many of these grasses are left behind from former ranching days, and replacing them with native grasslands is one critical step in restoring valuable habitat and reducing wildfire risk. 

An ongoing native grasslands restoration project in the West Loma and Bee Flat areas of OC Parks’ Limestone Canyon Nature Preserve aims to restore former cattle grazing fields to the native grasslands and oak savannas that once thrived there. Land managers are already seeing the fruits of their labor, and at over 50 acres, this is the largest grasslands restoration project within the Irvine Ranch Natural Landmarks to date. For many years, grassland habitats in California have been on the decline, since non-native annual grasses can very quickly take over a habitat and choke out the native grasses.


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Looking at the local hillsides, it’s easy to tell native grasslands from non-native – the native grasslands are still green and are mostly dominated by purple needlegrass (Stipa pulchra). Many native grassland plant species bloom later in the summer than invasive plants and can live for years. Certain pollinators need these perennial plants to thrive. Palmer’s goldenbush (Ericameria palmeri), coastal goldenbush (Isocoma menziesii) and gum plant (Grindelia camporum) are all native to California grasslands and provide late spring and summer food for the pollinators that help keep local habitats healthy.

Monarch butterflies feed exclusively on native grassland milkweeds such as narrow-leaved milkweed (Asclepias fascicularis) and California milkweed (Asclepias californica). Other butterflies, like skippers and California ringlets, breed in grassland areas, and in turn act as active summer pollinators as they feed. Native bees love to feed on splendid mariposa lilies (Calochortus splendens) that grow in grasslands, and help provide both nectar and pollen to them.

The grassy annual weeds that can take over habitat and push out native grassland species often look very similar to the native grasses, but are different in several key ways. One important difference is that native grassland plants tend to stay greener for a much longer period each year. Non-native annuals die off every year and leave behind dry thatch that is much more flammable, posing a threat to surrounding habitats.

“Large amounts of light fuels like these weeds are dangerous because when ignited they can spread fire much more rapidly,” said Kevin McArthur, Fire Watch Coordinator for Irvine Ranch Conservancy. “The drought has turned these non-native plants into a real threat to our local canyons.”

The spacing and growing patterns of native versus non-native grasses can also make an impact on wildfire risk. Native grasses grow less contiguously, or carpet-like, than do many invasive, non-native plants, making the non-natives much more likely to spread fire faster and farther.

As the restoration project moves forward, Conservancy ecologists will continue to closely monitor the health and success of planted grasslands, especially in the early stages of growth. By keeping invasive weeds from being able to take root, Conservancy ecologists can give the grasses a much better chance to reestablish and thrive, and can facilitate the build-up and spread of healthy native habitat.

“If we walked away from this project now,” said Lars Higdon, Irvine Ranch Conservancy Restoration Project Manager, “in a few years the invasive, non-natives plants, like the ubiquitous mustard, would take over once again.”

The restoration team will also be working to add some species diversity to the grasslands, by adding native annual and perennial flowers like chia (Salvia columbariae), winecup Clarkia (Clarkia purpurea), purple owl’s clover (Castilleja exserta) and cobweb thistle (Cirsium occidentale) to the restoration sites. This will make those areas more attractive to wildlife and bring back the pollinators that will help ensure continued success.

To find out how to volunteer to support habitat restoration efforts, visit www.LetsGoOutside.org/activities and select Stewardship from the Categories menu.