Park volunteer Larry Chaney cuts tamarisk in the Inner Canyon.
Invasive plants and weeds infest more than 2.6 million acres within the National Park system, threatening the complex native ecosystems for which the NPS serves as guardian and steward. In a coordinated response to the threats that invasive (exotic) plant species pose to biodiversity, the Park Service now deploys 17 Exotic Plant Management Teams throughout the country to assist in the inventory, control and monitoring of invasive plants.
Many individual parks – particularly the larger ones like Grand Canyon – also have invasive plant management programs.
Grand Canyon National Park began a very active invasive plant management program in 1993, when park biologists noted an increasing number of new plants here. Some species were found far outside of the park’s developed areas and primary trail corridors, which are usual areas for invasion. While there were only 116 known invasive plant species in the park in 1993, there are at least 170 today, comprising about 10 percent of the total flora.
Grand Canyon National Park’s vegetation program focuses control efforts on the highest priority species, including those demonstrating the greatest threats to the park’s native ecosystems and the speies for which containment or eradication is feasible. Park staff plan to devote more effort toward prevention with special focus on identifying areas with rich native species diversity, slowing the spread of invasive species into the backcountry of the park and increasing educational outreach.
One the park’s most successful invasive species control efforts is the Tamarisk Management and Tributary Restoration Program, which focuses on protecting the inner Canyon’s riparian areas, seeps and springs. These areas contain extremely valuable habitat for wildlife and plant species, and are among some of the most rare and threatened ecosystems in the southwest.
Tamarisk (Tamarix ramosissima), or salt cedar, is well-known to everyone who has spent any time along rivers in the desert areas of the southwest. Introduced to the United States in the 19th century as an erosion control agent and ornamental plant, the highly invasive tamarisk rapidly spread and caused major changes to natural environments as it formed dense monocultures.
Tamarisk reached the Grand Canyon area in the 1930s, where it occupied some pre-dam terraces and tributaries. It became a dominant species along the Colorado River following completion of Glen Canyon Dam in 1963.
Although some animals use tamarisk, and humans have used it for erosion control and shade, the impact that tamarisk exerts on native ecosystems are well-documented and present challenges for ecologists trying to preserve and restore riparian habitats.
A typical mature tamarisk produces about 600,000 seeds, and a large tamarisk may produce up to 250 million seeds. The plant’s roots can reach depths of more than 100 feet, exploiting water resources that had once been used by native cottonwoods and willows. Tamarisk often forms dense stands and a thick layer of salty leaf litter, both of which impede the growth of native plant species.
As tamarisk invades the beaches, side canyons and springs in Grand Canyon, native vegetation is crowded out, wildlife is sometimes displaced and fragile natural and cultural resources become vulnerable from increased fire hazard.
Prior to initiating a tamarisk control effort, park management evaluated the beneficial and adverse impacts of a tamarisk management project to natural, cultural and wilderness resources through a public review process and environmental assessment.
The approved action includes manual treatment (i.e. hand-pulling) and targeted chemical control of tamarisk in side canyons, tributaries, developed areas and springs. At this time, the project does not include control of tamarisk along the main river corridor due to the extent of its distribution, the difficulty of control along the 277 miles of the Colorado River within the park and the amount of funding required for such an extensive effort.
Grand Canyon’s tamarisk control project, which began in fall 2002, has been supported by the Arizona Water Protection Fund, the Colorado River Fund, the Grand Canyon National Park Foundation, the Grand Canyon Wildlands Council, the NPS and many thousands of hours of volunteer labor.
To date, crews have completed work in 70 project areas. In just over two years, crews have removed more than 124,000 tamarisk plants that infested over 4,500 acres, with only 12 percent of the initially controlled plants requiring follow-up treatment.
Prior to project implementation, biologists installed a long-term monitoring system that includes 22 transects and 376 fixed photo points to track changes in vegetation.
The vegetation transects have allowed biologists to document a 99 percent reduction of tamarisk cover in treated areas, and an increase in native plants. In many areas where tamarisk trees once formed dense thickets, native species of wildflowers, shrubs and trees now thrive. Park biologists will continue to monitor these project areas for five to 10 years.
For more detailed project information, refer to the Environmental Assessment/Assessment of Effect and project reports posted on the park’s Web page at www.nps.gov/grca.
If you would like more information about this project, contact the park’s Inner Canyon Vegetation Program Manager, Lori Makarick, at 928-226-0165 or Lori_Makarick@nps.gov.
The tamarisk management project is labor-intensive, but a great deal of progress has been made over the past two years largely due to the hard work and dedication of volunteers.
The NPS thanks all of the volunteers and welcomes new volunteers to the team. Those interested in this or other Inner Canyon Vegetation Management projects, should visit www.volunteer.gov/gov, look for the volunteer description and apply online.