PS 11-140 - Effects of Arundo donax removal on aerial invertebrates along the Salinas River, Monterey County, CA

Monday, August 7, 2023

5:00 PM – 6:30 PM PDT

Location: ESA Exhibit Hall

Presenting Author(s)

Savannah Y. Saldaña

Research Associate
California State University of Monterey Bay, California, United States

Coauthor(s)

JO

John Olson, PhD

Principal Investigator
California State University of Monterey Bay, United States

Abstract: The invasive riparian reed, Arundo donax, is a large perennial grass that severely threatens ecosystems and biodiversity in many coastal watersheds in California. The giant reed consumes approximately three times more water and has a lower nutritional value than native riparian vegetation, which can lead to lower biodiversity or food web effects. A. donax dramatically alters riparian vegetation composition, often approaching pure stands of the reed. The dense growth structure lowers the value of the reed as a habitat resource. Additionally, arthropod studies related to A. donax have shown that at sites where the giant reed was not present, the abundance and diversity were twice as high. A lower abundance of arthropods can lead to a decline in higher-level vertebrates (e.g., bats and birds) whose diets are primarily composed of invertebrates found in native vegetation. The extensive infestations and invasive root system causes A. donax to be extremely difficult and costly to eradicate, requiring a combination of mowing and herbicide to remove. However, there is little understanding of the effects of the removal of A. donax on aerial invertebrates. Therefore, we investigated the impact of A. donax treatments on aerial invertebrates at five sample locations along the Salinas River in Monterey County, California, both before and after removal. Pre-treatment samples were collected in the late summer of 2019, and post-treatment samples were collected in 2022. Five aerial adhesive traps were placed at each sample location and remained out for eight days. Diversity and evenness (Shannon-Wiener index) increased post-treatment, with the average diversity increasing from 2.38 at non-treated sites to 2.62 at treated sites. However, the abundance recorded in 2019 was twice as high as that in 2022. We also observed changes in flight direction following A. donax removal, with more invertebrates flying upstream, which is an essential pattern in adult aquatic invertebrates' life cycles. These results indicate that the invasion of A. donax reduces diversity in aerial invertebrates and thus may jeopardize energy transferred through trophic levels impacting higher-level vertebrates. While the removal of A. donax causes a temporary disturbance, results show the overall removal of the reed improves riparian ecosystems.