In an ironic twist of fate, the federally endangered southwestern willow flycatcher has likely secured the survival of one of the most hated invasive plant species in the western United States, reports the Wildlife Management Institute.

Following years of controversy, the USDA Animal and Plant Health Inspection Service (APHIS) has shut down its highly successful tamarisk (also known as saltcedar) biological control program amid concerns over the destruction of critical nesting habitat used by the southwestern willow flycatcher. Paradoxically, dense monocultures of the non-native shrub are providing the only suitable nesting sites available for the flycatcher in pockets of the arid Southwest where tamarisk has choked out native willow and cottonwood communities.

According to a memo issued on June 15, APHIS will no longer permit the use of the saltcedar leaf beetle as a tamarisk control agent until "endangered species issues are resolved." Interestingly, only 2 of the 13 participant states of the 2005 APHIS saltcedar leaf beetle release program are within the historical breeding range of the southwestern willow flycatcher. As the moratorium only prohibits interstate movement and release of the tamarisk-eating beetles, states that currently contain established beetle populations may continue to use those beetles to control the invasive shrub within their borders.

Native to Asia and the Mediterranean, tamarisk was introduced to the United States in the latter part of the 19th century as a wind- and erosion-control measure. After successfully establishing populations along most of the major southwestern rivers, tamarisk rapidly invaded and replaced vast areas of native lowland riparian habitats that already were suffering from numerous human-caused hydrological changes. This loss and alteration of native riparian habitats has resulted in the decline of numerous sensitive fish and wildlife species, including the southwestern willow flycatcher.

Given the tamarisk's propensity to reduce groundwater and stream flow, increase soil salinity, and stifle plant and animal diversity, natural resource managers have waged war on the shrub for more than half a century. Unfortunately, removal of the estimated 1.5 to 2 million acres of the tenacious plant is a difficult and expensive proposition, because cutting and burning only result in denser and multiplied growth. According to experts, the saltcedar leaf beetle has been the most successful, desirable and cost-effective tamarisk-control method to date.

Nonetheless, controversy has surrounded the use of the beetles ever since the southwestern willow flycatcher was federally listed as endangered in 1995. Stripped of its native habitat in states such as Arizona, the flycatcher began using and even selecting for dense tamarisk stands in places where little or no natural plant communities existed. "The concern is that if the tamarisk were removed, the habitat won't be replaced with native vegetation because of other hydrological issues in addition to the extremely alkaline soil left behind by the tamarisk," said Terry Ireland, biologist with the U.S. Fish and Wildlife Service. Ireland is quick to note, however, that in the northern reaches of the flycatcher's habitat, the opposite is true; the birds seem to avoid tamarisk stands. "It seems to be an issue only in the southern areas of the flycatcher's range."

While there is little debate among biologists that tamarisk monocultures are a distant second to native riparian vegetation where optimal flycatcher habitat is concerned, the invasive shrub is, somewhat surprisingly, listed in the critical habitat designation of the bird's Endangered Species Act-mandated recovery plan. Thus, according to the official APHIS memo, "any unauthorized human-assisted movement of Diorhabda spp. (i.e., the saltcedar leaf beetle), particularly into the critical habitat of the southwestern willow flycatcher?may constitute a violation of the Endangered Species Act."

According to biologists, the veiled consequence of an endangered bird providing legal shelter for an invasive plant could be that other endangered species threatened by the tamarisk invasion, like the Colorado pikeminnow, may suffer on the flycatchers' behalf. "The costs and benefits of the moratorium on the use of biocontrol for tamarisk haven't been weighed out," cautioned Dr. Dan Bean, director of the Palisade Insectary.

Bean and his colleagues have voiced concern over the national implication of the APHIS moratorium, and point out the marked success that the saltcedar leaf beetle has had in curtailing the tamarisk. "All of the biologists we've worked with love the beetle. Its use is allowing us to win back critical habitat for a host of wildlife species that have been in decline due in large part to the tamarisk invasion." Additionally, Bean noted that 11 of the 13 states impacted by the biocontrol ban lie well outside of the flycatcher's historical range, whereas 6 of the 7 states within the bird's territory already have released the beetle with substantial success. Thus, the ban may do little to stop the beetles from affecting flycatchers, but do much to confound efforts to manage tamarisk.

Others agree. "Outside of tying the hands of northern states fighting tamarisk, I don't think a ban on the beetles will do anything for the big picture," said Levi Jamison, biocontrol specialist with the Tamarisk Coalition. Jamison has conducted extensive field mapping and monitoring of the saltcedar leaf beetle in the Southwest and has found that, in general, the bugs are doing fine on their own. "Where the beetles have established strong populations, we are seeing two to three reproductive cycles in a season. They are having a huge effect on tamarisk seed plants and ground shoots."

While the intertwined fates and uncertain futures of the southwestern willow flycatcher, tamarisk and saltcedar leaf beetle now are subject more than ever to the will of ecological processes, the more immediate result of the tamarisk biocontrol ban has been an abrupt check to many habitat biologists' ability to monitor the situation. "The timing couldn't have been worse," said Bean. "The ban came two weeks before our field season and caused significant setbacks to numerous tamarisk management actions." Jamison concurred: "Concern over running afoul of the Endangered Species Act has wrapped up a lot of money and resources that managers were depending on for tamarisk monitoring and management programs. No one wants to get wrapped up in ESA litigation." (mcd)