Tamarisk Alters Arthropod Composition, but has Little Negative Effect on Richness and Abundance in Southwestern Colorado

Riparian corridors are vulnerable to invasion by non-native plant species that can alter arthropod communities and ecological functions. Tamarisk (Tamarix4 spp. L.) replaced native riparian vegetation on 1.6 million acres in the southwestern United States. Our study investigated arthropod communities in three riparian habitats, two dominated by native vegetation (willow (Salix exigua5 Nutt.) in lower floodplain and mixed-native xeroriparian shrubs in upper floodplain) and one invaded by non-native tamarisk in lower floodplain. Tamarisk was predicted to lessen arthropod abundance and richness, change composition, and associate with nonnative arthropods. We sampled 41,124 arthropods identified to 258 taxa and seven functional groups during 2 years along the Dolores River in Colorado. Richness and abundance were not less in tamarisk, but composition differed among the three habitats. Trends varied across taxonomic and functional groups. Lower floodplain habitats, tamarisk and willow, were relatively similar in composition, with large numbers of beetles, hemipterans, detritivores, and herbivores. More ants, pollinators, and greater diversity were in upper floodplain shrub habitat. Tamarisk hosted several non-native arthropods: Armadillidium vulgare (Latreille)6, Cylisticus convexus (De Geer)7, Diorhabda carinulata (Desbrochers)8, and Coniatus splendidulus (Fabricius)9, while willow housed non-native weevils (Otiorhynchus spp. Germar)9. Tamarisk was favored by some non-native arthropods and altered community composition but did not lessen abundance or richness of functional or taxonomic groups. The results highlighted effects of non-native plants on arthropod communities and have implications for conservation of insectivorous riparian wildlife.