Invasive Plants in Aravaipa Canyon, Arizona: Invasion History, Life History, Problems, and Control.

Invasive plant species can have many detrimetal impacts on native vegetation in natural areas. Here we examine the impacts of giant reed, buffelgrass, Sahara mustard, tamarisk, tree of heaven, and vinca in the Aravaipa Canyon Wilderness and surrounding areas in Arizona. All six of these species can form monotypic stands, thereby excluding native vegetation and gready changing the natural environment and native species diversity. The three invasive species with the earliest known introductions in the mid-20th century into Aravaipa Canyon, giant reed, tree of heaven, and vinca, were planted around homesteads as ornamentals or for shade. Although these species are quite different plant types, giant reed and vinca reproduce vegetatively in Aravaipa and tree of heaven has extensive vegetative reproduction. Giant reed and vinca might represent novel life forms in western US riparian environments, potentially enhancing their success as invasive species. In contrast, the three species with later introductions, buffelgrass, Sahara mustard, and tamarisk, were introduced either by long distance seed dispersal or by movement on vehicles. In addition, Aravaipa Canyon experiences periodic disturbance and scouring by high volume flooding and these impacts appear to play an important role in the establishment and spread of these invasive plants in Aravaipa Canyon. An element that is troubling for both public safety and the native environment is that giant reed, buffelgrass, and tamarisk can all fuel very hot fires. In addition, these three species are highly adapted to fire and the survival and reproduction of these invasive species is enhanced while native vegetation is killed, thereby resulting in a positive feedback for the numbers and distribution of the invasives. The two species that are most likely to be eliminated from Aravaipa are giant reed and tree of heaven. The two plants that appear to be long-term and widespread challenges to control are Sahara mustard and tamarisk. Tamarisk is well established, has very high seed production, and has long distance dispersal. Sahara mustard also has very high seed production and appears to be spreading despite extensive efforts to control it. The other two species, buffelgrass and vinca present other challenges even though they presently have restricted distributions. Understanding the factors contributing to the presence and elimination or control of these six invasive plant species in the Aravaipa Canyon Wilderness and the surrounding area might help to inform efforts to control invasive plant species in other natural areas. [ABSTRACT FROM AUTHOR]