INVASIVE SPECIES OF OUR REGION
Main sources: Tellman, Barbara, ed., 2002, Invasive Exotic Species in the Sonoran Region, Tucson: University of Arizona Press and the Arizona-Sonora Desert Museum; Chambers, Nina & Trica Hawkins, n.d., Invasive Plants of the Sonoran Desert.
PLANTS
For access to a variety of links providing further information on the kinds of exotic invasive species in Arizona and elsewhere, consult the following:
http://tncweeds.ucdavis.edu/esadocs.html; (this takes you to the "Invasive Species" page of TNC. To search for specific plants, scroll down the left-hand side of the page, to the column "For Staff", under which find "Control Info on Specific Invasives" -- click on that and you can then enter the page of your chosen species, see plant images, then under "File Format" click on MSWord for extensive text on the species in question.)
http://aznps.org/html/exotics.html; (this takes you to info from the Arizona Native Plants Society)
http://usgssrv1.usgs.nau.edu/swepic/ (Southwest Exotic Plant info from USGS and Northern Arizona University)
By "invasive species" we mean those exotic species (introduced -- usually by humans -- from outside the reference environment) which have become so well adapted to their new environment that they interfere with the species that are native there (here we follow the definition provided by Tellman et al (2002) pp. xix-xx). As a general rule, the more disturbed a habitat is by human activity, the higher the number and percentage of non-native species will be. Other factors support the invasion of exotics. For example, in the Southwest, most native plants (cactuses, shrubs, and trees) have evolved so they do not form continuous stands, and so most of them do not support wildfires, and consequently such plants have not fire-adapted and are seriously damaged by fire. In contrast, many invasives cluster into continuous stands, support wildfires and thrive on them.
The purpose of the present pages is to identify the invasives appearing on Saguaro Juniper lands so that we may identify relevant locations and be prepared to act if and when these forms appear to be threatening our natives or are otherwise damaging the ecosystem.. What follows below is structured mainly by the list provided by Tellman et al (op.cit.), of "the most invasive exotic species in the Sonoran Desert Region", supplemented by additional exotics specifically present in our area as we identify them.
(Click on names printed in blue and underlined below for elaborations on the relevance of these life forms to Saguaro Juniper.)
Tamarisk (Tamarix ramosissima)
They are spreading along the San Pedro River, and they are appearing along Saguaro Juniper watercourses (see the "Tamarisk" link above).
Bermuda Grass (Cynodon dactylon)
This invasive grass is wideswpread in all of our major washes and in all the old earthen tanks of Saguaro Juniper land. See the link for further details.
Lehmann lovegrass (Eragrostis lehmanniana)
This invasive grass is found in a number of our washes. See the link for further details.
Red brome, foxtail brome (Bromus ruben)
This invasive grass is found in a number of our washes and water tanks. It is probably spreading as we speak. See the link for further details.
Johnson
Grass (Sorghum
halapense)
Originally native to the Mediterranean, Johnson Grass now occurs all over the world in warm-temperate regions. It entered the U.S. southeast early in the 19th century and by the 1890s was becoming a problem in Arizona's Salt River Valley. It is now common throughout the state below 6,000 feet.
African
sumac (Rhus lancea)
An arid-land tree of South Africa, Rhus lancea was originally imported into the U.S. by the landscape industry and was introduced to Tucson in the 1920s by a UA botanist. Its pollens disperse from November to February and are highly allergenic. Female trees produce large quantities of seeds, which are distributed by the birds who eat them.Once established along a wash or roadside, it spreads quickly, and since its canopy produces very deep shade it tends to crowd out native species. Since its root system is invasive and deep, the plant is hard to remove, and has now become a common weed in Pima County urban areas (though not yet in our SJ area). Click on Rhus and Rhus-2 for detailed images.
Tree of Heaven (Ailanthus altissima)
Tree of Heaven was introduced from China, into the east in the 1780s and into California in the 1850s as a host tree for the silk-moth. It can be confused with native sumacs, having large compound leaves 1-4' long. It reproduces both sexually and through lateral-rooted suckers, so existing plants are hard to remove. It grows rapidly, is a prolific seed-producer, overwhelms native vegetation and forms thickets. These plants are invasive mainly in Santa Cruz County, but have also been found in Cochise County near the Mexican border. For images and details, see Heaven.
Buffelgrass (Pennisetum ciliare)
Buffelgrass is a water-efficient C-4 African grass which is actively invading our Sonoran Desert. First introduced into the U.S. in the 1940s for erosion control, it was then planted on a large scale in Mexican drylands in an effort to augment pasturage for cattle, and efforts continue in Sonora to clear large areas (by means of chain and blade bulldozing) for seeding it. It is a fairly large, ragged perennial bunchgrass which produces long, bristly brown seed-heads whose numerous seeds are wind-dispersed, and it forms dense stands (unlike most desert grasses and other plants). Buffelgrass thrives with fire, and has spread into the Tucson area where it has become a significant pest.
The following link will take you directly to a link to a PDF file describing buffelgrass: http://aznps.org/html/exotics.html
Mustard species
Camelthorn
Crystal iceplant