ST. GEORGE – Sometimes environmental concerns compete. The goals of preservation of an endangered species are not always best met by the radical removal of non-native species. Utah’s Division of Wildlife Resources in St. George faces a balancing act between these two interests when it comes to the preservation of the Southwestern Willow Flycatcher (Empidonax traillii extimus) and the invasive Tamarisk (the common name for the salt cedar shrub derived from the Latin tamarix).
The Willow Flycatcher is a small songbird placed on the federal endangered species list in 1995 by the U.S. Fish and Wildlife Service. It is threatened by habitat loss and is thought to thrive best in “a native community of willows, cottonwood and seep willow” said Rob Dobbs, native biologist in bird and riparian restoration with Wildlife Resources.
The tamarisk is an invasive species, which is fire-adapted, and has long tap roots that allow it to intercept deep water.
When it comes to controlling a non-native plant species, there are essentially three methods: Bio-control – the introduction of an insect, for example; chemical; and mechanical – burning, razing. In 2006, the United States Department of Agriculture, through its Animal and Plant Health Inspection Services program, or APHIS, began a periodic release of the tamarisk beetle, also known as the salt cedar beetle, along areas of the Virgin River in St. George.
Christian Edwards, a native aquatics biologist with Utah’s Wildlife Resources, said, “APHIS has been studying the tamarisk beetle for as much as 20 years. They made sure that it would only feed on the tamarisk.”
The present challenge for Wildlife Resources comes as a result of a collaborative ongoing study by three organizations – The federal Bureau of Reclamation, Utah’s Division of Wildlife Resources, and SWCA Environmental Consultants. Edwards said the study, which seeks to identify the effects of the tamarisk beetle on the willow flycatcher, has produced some interesting observations.
“The first thing we found is that the tamarisk beetle is causing widespread defoliation – that’s a good thing, essentially it’s doing its job. But,” Edwards said, “what we found in our 2010 study is that the willow fly catcher has experienced higher nesting success where there is a higher percentage of tamarisk to willow. So that’s the big debate: Even though the flycatcher is called the willow flycatcher, we’re finding it has good success in tamarisk dominated habitat (among other possible reasons).”
The tamarisk holds a lot of debris among its branches, which the willow flycatcher uses for its nest, Edwards sad. Now that the beetle is killing the tamarisk it could negatively impact the willow flycatcher.
Edwards’ concern, he said, is:
As the willow flycatcher migrates and builds its nest in the tamarisk, the beetles cause the tamarisk to brown and drop their leaves early, which creates an overly hot microclimate for the flycatcher’s nest which may affect the growth of the embryos within the eggs.
One way Wildlife Resources balances these concerns is by replacing the non-native tamarisk with more native vegetation, willows and cottonwood. Dobbs said these are “difficult to establish during a period of successive floods.”
“In December 2009, we made about 1,200 willow stem plantings in Bloomington below Man of War … and more in winter 2010,” Dobbs said.
Most of those were wiped out by the December 2010 flooding of the Virgin River. Although Wildlife Services plans to replant in that region sometime this year, Edwards said that it is currently focusing on the “Riverside Marsh” north of Riverside Drive.
“Essentially the flood totally changed the river, created big sand banks and new water pools,” Edwards said. “There are a couple of inflows that come off the fields north of Riverside Drive and drainage is now coming in from some of the neighborhoods. It’s good because the willows like water pools, and the willow flycatcher likes to breed in habitats and territories near water; and the Riverside Marsh is an area where they have had existing breeding habitats. By planting a bunch of willows we can connect these patches of breeding habitats, improving the willow flycatcher’s success in nesting.”
The goal of Wildlife Resources, to perpetuate the connective habitats with willow planting over time, more slowly replacing the invasive tamarisk, seems to be a plan that will serve both interests well without the eradication of the tamarisk inhibiting the perpetuation of the songbird.
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