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Invasive Species

Arundo donax chokes riversides and stream channels, causing flood control problems. It also crowds out native plants, resulting ina loss of habitat for native species. In fact, this reduction in habitatisone of the factors contributing to the low populations of the endangeredLeast Bell's Vireo. Inaddition, Arundo increases the risk of fire in riparianhabitats which further reduces the numbers of native plant species. Finally, Arundorequires more water than the native vegetation, stressing an area thatalready has little available water. Arundo is an extremely prolific weed.It reproduces vegetatively, through rhizomes which root and sprout readily.This type of reproduction allows Arundo to reproduce very quickly, andthus build large stands in an area. Once established, the underground rootscan reproduce new plants despite efforts at removal. In order to successfullykill Arundo, the underground network of roots must be completely removed,or killed with pesticides.

SAWA has been actively involved in projects to remove Arundo from theSanta Ana watershed.

Tamarisk,or saltcedar, is an invasive weed found within the Santa Ana River Watershed.Saltcedarshave deep tap roots which allow them to access deep water tables. Thisability to use deep water can cause small streams and springs to dry up.Saltcedar also out competes natives species, promotes wildfires, increasessoil salinity, and increases sedimentation and channel blockage. The lossof native riparian habitat is a major threat to the survival of animalsin the
infested areas. While saltcedar provides someamount of shelter to native animal species, it is little food value forthe native wildlife.

Mechanical, chemical, and biological control have all been used in themanagement of saltcedar. For extensive areas of saltcedar, chemical control(herbicide) has been the most effective. Systemic herbicides (those thatkill from the root up) are recommended: they can be applied as a foliaror aerial spray, or applied to cut saltcedar. Mechanical methods (cutting,bulldozing) can be effective, but can also cause problems with soil erosionin the removal area. Biological control, by introducing insects that eatthe saltcedar, can gradually reduce the amount of saltcedar in the area,but approximately 15-25% of the original infestation can be expected toremain perpetually with biological control methods.

SAWA has performed some Tamarisk removal withinthe Santa Ana Watershed, often in conjunction with Arundo removal.

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