Remote Sensing of Tamarisk Beetle (Diorhaba Carinulata) Impacts along the Colorado River in Grand Canyon National Park And Glen Canyon National Recreation Area
Temuulen Sankey1*, Ashton Bedford1, Joel Sankey2, Barbara Ralston3, Laura Durning1
1Northern Arizona University, School of Informatics, Computing, and Cyber Systems, Flagstaff, Arizona, USA
2US Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, Arizona, USA
2US Geological Survey, Office of Science Quality and Integrity, Flagstaff, Arizona, USA
We present two recently completed remote sensing studies of tamarisk beetle (Diorhaba carinulata) impacts in the Colorado River ecosystem. Our objectives in the first, larger-scale study were to classify tamarisk stands along 412 km of the Colorado River from the Glen Canyon Dam through the Grand Canyon National Park (GCNP) using 2009 aerial, high spatial resolution multispectral imagery, and then quantify tamarisk beetle impacts by comparing the pre-beetle images from 2009 with 2013 post-beetle images. A total of 214 ha of tamarisk were detected in 2009. Tamarisk detection accuracies varied locally, but the combined overall accuracy was 74%. Using the Normalized Difference Vegetation Index (NDVI) changes from 2009 to 2013, we detected tamarisk defoliation due to beetle herbivory. The total beetle-impacted tamarisk area was 32 ha, where defoliation ranged 1–86% at the local levels. Our objectives in the second, smaller-scale study were to map tamarisk (Tamarix spp.) distribution and estimate effects of the beetle on tamarisk plant and leaf litter biomass in the Glen Canyon National Recreation Area (GLNRA), Arizona using fusion of airborne lidar data and multispectral imagery from 2013. We identified tamarisk beetle effects (overall accuracy of 86%) leading to leaf defoliation in a 4.9 ha area in GLNRA. On average, total aboveground tamarisk biomass was 8.68 kg/m2 (SD = 17.6). The tamarisk beetle defoliation resulted in a mean leaf biomass loss of 0.52 kg/m2 and an equivalent of 25,692 kg across the entire GLNRA study area. Our defoliated tamarisk maps and biomass estimates can help inform restoration treatments to reduce or remove tamarisk. Our remote sensing maps and methods can aid long-term efforts to monitor the spread and impact of the beetle along the river, the eventual mortality of tamarisk due to beetle impacts, and subsequent ecological succession.