Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2014
Publication Date: 12/1/2014
Citation: Longland, W.S. 2014. Biological control of saltcedar (Tamarix spp.) by saltcedar leaf beetles (Diorhabda spp.): effects on small mammals. Western North American Naturalist. 74(4):378-385.
Interpretive Summary: Exotic saltcedar trees have spread invasively along many rivers and streams throughout the western United States, and this has motivated a biological control program using an insect that feeds exclusively on saltcedar, the saltcedar leaf beetle. As part of an effort to determine whether saltcedar biological control affects native populations of wildlife, I used livetrapping to monitor small mammal populations for up to 12 years as saltcedar foliage was progressively removed over time at sites where saltcedar leaf beetles became established. There was no evidence of any effect of saltcedar defoliation over time on the number of small mammal species trapped. One small mammal species, the western harvest mouse, showed an increasing trend in population size at one site as biological control progressed but a decreasing trend at another site. Overall, my trapping results imply that saltcedar biological control is likely to have negligible effects on resident small mammal populations.
Technical Abstract: The spread of introduced saltcedar (Tamarix spp.) throughout many riparian systems across the western United States motivated the introduction of biological control agents that are specific to saltcedar, saltcedar leaf beetles (Diorhabda carinulata, D. elongata; Chrysomelidae). I monitored small mammal populations for up to 12 years as saltcedar defoliation progressed at three of the original saltcedar beetle release sites and an additional site where beetles established through dispersal. There was no evidence of any linear effect of increasing defoliation over time on small mammal species richness. Only one small mammal species, the western harvest mouse (Reithrodontomys megalotus), has shown any evidence of a linear population response to saltcedar defoliation, and that species showed an increasing population trend at one site but a decreasing trend at another site. This may be due to the affinity of harvest mice for dense vegetation cover, and differences among sites in understory cover as the saltcedar overstory was thinned by defoliation. Overall, my trapping results imply that saltcedar biological control is likely to have negligible effects on resident small mammal populations.