[APWG] Remote sensing of tamarisk beetle (Diorhabda carinulata) impacts along 412 km of the Colorado River in the Grand Canyon, Arizona, USA

[Davis, Scott]

fyi

Scott

*Scott Davis*
*Senior Soil Scientist*
*Program Officer*
*BLM*
*Denver Federal Center*
*Denver CO 80225*
*303-236-6646*






Remote sensing of tamarisk beetle (Diorhabda carinulata) impacts along 412
km of the Colorado River in the Grand Canyon, Arizona, USA
https://pubs.er.usgs.gov/publication/70196440

2018, Ecological Indicators (89) 365-375

Ashton Bedford, Temuulen T. Sankey, Joel B. Sankey, Laura E.C. Durning,
Barbara Ralston

Tamarisk (*Tamarix* spp.) is an invasive plant species that is rapidly
expanding along arid and semi-arid rivers in the western United States. A
biocontrol agent, tamarisk beetle (*Diorhabda carinulata*), was released in
2001 in California, Colorado, Utah, and Texas. In 2009, the tamarisk beetle
was found further south than anticipated in the Colorado River ecosystem
within the Grand Canyon National Park and Glen Canyon National Recreation
Area. Our objectives were to classify tamarisk stands along 412 km of the
Colorado River from the Glen Canyon Dam through the Grand Canyon National
Park 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. We classified tamarisk presence in
2009 using the Mahalanobis Distance method with a total of 2500 training
samples, and assessed the classification accuracy with an independent set
of 7858 samples across 49 image quads. A total of 214 ha of tamarisk were
detected in 2009 along the Colorado River, where each image quad, on
average, included an 8.4 km segment of the river. Tamarisk detection
accuracies varied across the 49 image quads, but the combined overall
accuracy across the entire study region was 74%. Using the Normalized
Difference Vegetation Index (NDVI) from 2009 and 2013 with a
region-specific ratio of >1.5 decline between the two image dates
(2009NDVI/2013NDVI), we detected tamarisk defoliation due to beetle
herbivory. The total beetle-impacted tamarisk area was 32 ha across the
study region, where tamarisk defoliation ranged 1–86% at the local levels.
Our tamarisk classification can aid long-term efforts to monitor the spread
and impact of the beetle along the river and the eventual mortality of
tamarisk due to beetle impacts. Identifying areas of tamarisk defoliation
is a useful ecological indicator for managers to plan restoration and
tamarisk removal efforts.
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