Broom

Do You Sell Broom?

By Sally de Becker
Excerpted from the East Bay Chapter's Bay Leaf, August 1995. Sally, President of the East Bay Chapter, was a speaker at one of our recent general meetings.

At last fall's plant sale, I was asked a question to which even I knew the answer: "Do you have French broom for sale?" After weighing the possibilities--this is a jokester trying to outrage my refined sensibilities, or an earnest member of the public just trying to plant something colorful in his yard--and taking a few deep breaths, I slowly answered that we sold only plants that were native to California. "Oh," he said, "I grew up around here and there was always lots of broom around so I assumed it was native." By now I was assured that he really was interested in plants, but just didn't happen to have been exposed to information on problems with many non-native plants. After some more deep breaths so that I wouldn't sound as shrill and as near hysteria as I felt, I gave him a little background on non- natives. He listened, if not attentively, then at least with patience, and then wandered off (I hope) to buy some of our gorgeous natives.

So what is the problem with non-native species? In 1993, the US Office of Technology Assessment issued a 400-page volume titled Harmful Non-Indigenous Species in the United States, which neatly categorizes the economic, health, and environmental consequences of the nearly 4,500 plant and animal species of foreign origin that have established free-living populations in this country in the last 100 years. Economic costs alone are high. Between $3.6 billion and $5.4 billion annually in agricultureal crop losses and expenditures for weed control can be attributed to non-native plants; an estimated $100 million a year is spent to control non-native aquatic weeds such as hydrilla (Hydrilla verticillata) which blocks canals, impedes navigation, and can reduce the productivity of recreational fisheries; and non-native species such as Klamathweed (Hypericum perforatum) and cheatgrass (Bromus tectorum) have invaded millions of acres of rangeland in California alone, making the land worthless for grazing.

Though health costs are clearly more of an issue for non- native animals, such as African honey bees, non-native plants bring about health problems too. The Brazilian pepper tree (Schinus terebinthifolius) causes respiratory difficulty and contact dermatitis as it spreads through Florida. Over half the poisonous plants of eastern North America are non-native.

Finally, the environmental costs are enormous. Nearly all plants are very specific about where they will and will not grow (my garden is living and dead proof). This includes non-natives, most of which could never establish free-living populations outside a tended garden. But the non-native plants that cause problems have no such fussiness. They share other characteristics too. They grow quickly, they become large, they reproduce phenomenally, either by seed or vegetatively, and because they left their predators and diseases behind, they have a real advantage and compete successfully with native species. These traits can lead to decline of native species and species extinction. In Hawaii, invasion by non-native weeds is considered one of the biggest threats to the remaining native plant species.

Non-natives also can transform and degrade ecological communities and ecosystems, quickly converting a biologically diverse assemblage of plants and animals into a sterile monoculture. Giant reed (Arundo donax) from Europe invades riparian areas in the Sierra Nevada foothills, central and south coast, San Gabriel Mountains, and the desert, converting groves of willow, cottonwood and mulefat that support songbirds and other wildlife to solid giant reed stands that provide little food or cover for native animals, increase the fire hazard, impede flood control by clogging channels, and consume three times as much water as native vegetation. And on top of all that, the giant reed stands provide cover for the terribly destructive non-native feral pigs. French broom and cheatgrass both increase fire hazard, and in fact cheatgrass burns so much more readily and recovers so much more swiftly than the native sagebrush it invades, that once it gets a toehold, it increases the frequency of fire. This rapidly eliminates any remnant sagebrush and makes return to natural conditions very unlikely.

More and more attention is now focused on the problem posed by some non-native species. The important steps to take are to stop even more non-natives from getting into our natural landscape, focus control efforts on the species that are most harmful, and help the general public understand the nature of the problem. The successes to date should keep us hopeful. For example, the Marin CNPS Chapter and the California Exotic Pest Plant Council (CalEPPC) have convinced the Marin Board of Supervisors to pass a resolution discouraging the import, sale, or cultivation of five invasive non-natives. The CNPS Invasive Exotics Committee works closely with CalEPPC to effect similar legislation statewide. In 1992, ecological weeds were added to the plant pests that are controlled under mandate of the State Food and Agriculture code. CalEPPC has published a list of the highest-priority non-natives of ecological concern in California.

But public awareness of the problem has not kept pace with these other promising developments. I am my own most disappointing example. I saw Pennisetum setaceum, fountain grass, at several local nurseries this summer and was thinking of incorporating it into a perennial grass bed this year, until I simultaneously noticed it growing along the roadside of Highway 13 below the Caldecott Tunnel and noticed it on the CalEPPC List A-1-Most Invasive Wildland Pest Plants: Widespread. It is originally from Africa, and in California, invades grasslands, desert canyons, and is spreading along roadsides. We will select something else for the perennial grass bed.

If you are interested in the issue of invasive non-natives, watch for the reports that Jake Sigg provides in the state Bulletin on the CNPS Invasive Exotics Committee. You might also be interested in CalEPPC (write c/o Sally Davis, PO Box 1045, Cambria, CA 93428-1045; phone 805 927-7187).