Remote sensing of tamarisk biomass, insect herbivory, and defoliation: Novel methods in the grand Canyon region, Arizona

Tamarisk is an invasive, riparian shrub species in the southwestern USA. The northern tamarisk beetle (Diorhabda carinulata) has been introduced to several states to control tamarisk. We classified tamarisk distribution in the Glen Canyon National Recreation Area, Arizona using 0.2 m resolution, airborne multispectral data and estimated tamarisk beetle effects (overall accuracy of 86 percent) leading to leaf defoliation in a 49,408 m²area. We also estimated individual tamarisk tree biomass and their uncertainties using airborne lidar data (100 points/ m2). 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/m²and an equivalent of 25,692 kg across the entire study area. Our defoliated tamarisk map and biomass estimates can help inform restoration treatments to reduce tamarisk. Continued monitoring of tamarisk and tamarisk beetle effects are recommended to understand the currently-unknown eventual equilibrium between the two species and the cascading effects on ecosystem processes.