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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Nov 14


Posted on November 14, 2014 at 3:58 PM by Ann Vallee

by Andrea Williams, Vegetation Ecologist

This is installment nine of a 12-part series on grasses. Read the previous installment here.

I wrote earlier this year about how I thought fescues (Festuca sp.) were the best. And I do still believe that, but I also admit a growing fondness for the bromes (Bromus sp.) as well—a budding bromance, if you will.

For one thing, they have a couple of key features that make them quite recognizeable: downward-pointing hairs on the lower part of the stem, and distinctive multi-flowered spikelets arranged in a branching pattern called a panicle. And then, even though it is a large genus—we have nine or 10 species on the mountain—you really only need to know three more things about it to get to species: whether it is an annual or perennial, how flattened the spikelets are, and how long the awns are.
California brome 
 California brome (Bromus carinatus)

While we have around 10 species on the watershed, only two are native. This is the best time of year to tell our natives from the non-natives: Since the natives are perennial and the non-natives are annual, you can tell the natives by their remaining flower stalks and loose clump of green leaves at the base. The non-natives, if you see them at all, will be dead bleached husks with no green. Bromes, like many grasses, “shatter above the glumes,” which means when their seeds fall the lowest set of bracts (called glumes) stay on the flowering stalk. This is similar to oaks, where some species’ acorn caps stay on the tree instead of with the acorn. The height (3-4’) and pattern of the flowering stalks with glumes mean you can tell our native bromes apart even in winter—that, and their different habitats. California brome (Bromus carinatus) prefers open, sunny grasslands with its open, shiny panicle of flattened spikelets; forest brome (B. laevipes) usually grows in, well, forests and has a closed, drooping panicle of fuzzy fat spikelets.

Unlike fescues, our native bromes are rarely dominant where found. Rather, they are sprinkled across the landscape like fine spices. Some of the non-natives, though, are known for taking over entire ecosystems in certain areas. Cheat grass (B. tectorum) is sometimes titled “The grass that ate the West” for its predominance in the intermountain west sagebrush-juniper scrublands. These areas rely on infrequent fire (every decade or two) to keep the sagebrush-juniper balance, but once cheat grass comes in fires often happen every year: The cheat grass is annual, and produces enough fine, “flashy” fuels to carry fire that often; too-frequent fires kill sage and juniper, promote more cheat grass, and the problem grows ever larger. Our cheat grass “problem” is limited to a few plants occasionally showing up at Peters Dam or the south side of Mt. Tam. We have much more downy brome (B. hordeaceous), ripgut brome (B. diandrus), and red brome (B. rubens), none of which begin to reach the level of worrisome monoculture—we leave that to brooms, not bromes!


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