Abstract
Tamarix spp. (tamarisk), native to Eurasia, is an invasive woody species in the arid regions of North America. Tamarix is widely distributed along the major rivers in the western U.S. Tamarix forms dense monocultures and thus influences biodiversity in the riparian ecosystems. The presence of Tamarix may also influence soil properties and microbes. In order to eradicate Tamarix as well as to enhance restoration of native tree species, the tamarisk leaf beetle (Diorhabda spp.), an exotic biological control agent, was recently introduced in several Tamarix habitats in the southwestern U.S. Herbivory by beetles has caused early defoliation of Tamarix stands in many places. The herbivore defoliation causes Tamarix growth reduction and improves understory light environments during the growing season, increasing opportunities to establish understory vegetation. In contrast, herbivore defoliation alters timing and amounts of leaf litters, and thus may influence soil conditions in the beetle affected stands. Under the altered conditions, other invasive species may become more abundant than native species. Until now, large areas of Tamarix stands have been influenced by beetle herbivory and caused large scale defoliations. However, it is unclear how this defoliation changes ecosystem nutrient cycling and alters plant composition in future. Studies focusing on ecosystem responses to herbivore defoliation are necessary for restoration success using native tree species in the regions.
