A Tale of Three Species: Invasive species control and endangered species management in the Southwestern US. Saltcedar, leaf beetles and the Southwestern willow flycatcher

Erik Grijalva

Abstract: Non-native Tamarix species were introduced into North America in the early 1800’s and by the mid-1900’s had expanded to cover over 0.6 million ha. Tamarix became a leading factor in the transformation of riparian corridors where it readily outcompetes natives, especially in the American Southwest. Species that relied on these corridors were either displaced or extirpated, leading to significant conservation efforts to restore or maintain native diversity. Chief among these species is the Southwestern willow flycatcher, a bird species which was heavily impacted by the changes to riparian habitats throughout its range. In the 1990’s, conservationists targeted the Tamarix infestation with an introduced biocontrol agent, the saltcedar leaf beetle, which can defoliate large stands of Tamarix once established. Though originally released at sites distant from known locations of the flycatcher, the beetles have expanded their range to overlap with that of the endangered bird. Beetle release was curtailed in 2010 out of concern that defoliation of Tamarix stands presented an unacceptable risk to the population of flycatchers by exposing nests in Tamarix to increased predation and nestling heat stress. Despite this, the beetle population continues to expand its range. Conservationists are now integrating new understanding of the ecological role of Tamarix and the presence of the beetle into restoration strategies for the flycatcher and other native species.