Invasive giant reed shifts riparian habitat mosaics, with stronger effects on birds than butterflies across spatial scales

Giant reed (Arundo donax) has colonized riparian corridors in warm and arid regions globally, yet its impacts on wildlife are poorly resolved across taxa, spatial scales, and relative to native vegetation. We quantified effects of giant reed and other dominant vegetation types on bird and butterfly site occupancies along the Rio Grande in west Texas, USA. We surveyed birds and butterflies at 168 sites, visiting each site three times per year in 2016 and 2017. A fourth butterfly survey was added in 2017 to better capture monsoonal activity. We used occupancy models to relate species occupancy to remotely sensed vegetation quantified at local (100-m radius) and floodplain (500-m radius) extents. Five of 16 bird species studied (31%) showed negative giant reed effects, whereas no butterflies showed direct negative effects. However, most positive vegetation effects for butterflies were tied to mesic tree-shrub and herbaceous cover, the cover types most displaced by giant reed and most likely to benefit from control efforts. Xeric tree-shrub cover, including gallery forest, was the strongest predictor of bird and butterfly occupancies overall, with mostly positive effects for birds and mostly negative for butterflies. Vegetation effects were broadly consistent between scales. In particular, negative effects of giant reed on birds persisted at the floodplain scale even though its cover was mostly confined to mesic, near-channel habitats. Full methods, results, and implications are reported in the peer-reviewed journal article that this dataset supports.