Effects of proximity to highways and highway construction on the threatened Valley elderberry longhorn beetle

Background/Question/Methods Roads not only divide remnant habitats, they also contribute particulates, mineral nutrients, and noise from traffic and construction activities. Particularly susceptible to the effects of roads are species like the Federally threatened Valley elderberry longhorn beetle (Desmocerus californicus dimorphus), a subspecies endemic to California's Central Valley whose habitat has been bisected by roads, but whose relatively short movement distances may limit it to these roadside habitats. Threats to the beetle are thought to include dust and noise produced from the network of highways bisecting its historic habitat. Until now, however, the effects of proximity to highways and highway construction had not been tested. Results/Conclusions Field studies revealed that proximity of the beetle's host shrub, blue elderberry (Sambucus mexicana), to highways or construction did not obviously influence leaf dust levels or foliar concentrations of elements commonly found in vehicle exhaust. Increases in shrub size, or age, shrub stress and C:N ratios occurred with increased distance from highways. Occupancy rates of the beetle in sites was low (20%), but comparable to rates in remnant riparian woodlands along several rivers in the northern Central Valley. Furthermore, beetle emergence occurred following construction activities in 2 of 3 construction sites illustrating that the beetle's life cycle could be completed in the presence of nearby construction. Consideration of using roadside areas as habitat connecting existing populations is discussed along with suggested management actions. Our understanding of the relationships between urban land use and rare species is often hampered by difficulties in obtaining data but collaborative studies such as this one can reveal important information for optimizing remaining impacted habitats.