Partner Profile: Creating a baseline

Thin canopy of dying hemlock.

More sunlight reaches streams when hemlock canopies thin.

NPS photo.

Understanding links between stream life & hemlock forests

In the stream
It’s hot hiking in waders, but this doesn’t stop USGS biologist Chuck Parker and NPS entomologist Becky Nichols from trudging through thick underbrush to some of the Park’s most remote streams. Their goal: to understand how stream life is affected when hemlocks die, as they are all over the Park due to the invasive hemlock woolly adelgid (HWA).

Dying hemlocks: what we know about their impact on waterways
Scientists have studied changes in stream life due to hemlock die-off in northern climates (where HWA started), but we don’t know if the same changes will happen in the Smokies. Known impacts in other ecosystems include:

  • Loss of the forest “ladder” of low and middle branches connecting ground to canopy
  • Different trees in the forest
  • Less shade
  • Changes in stream chemistry, habitat, and water levels
Mayfly larva.

Aquatic macroinvertebrates such as this mayfly larva can indicate overall stream health.

Photo courtesy of the North American Benthological Society.

Dying hemlocks in the Smokies: what’s the impact on waterways HERE?
To figure out what impact hemlock death will have on stream life in the Smokies, Becky Nichols and Chuck Parker began a monitoring study in 2008. For as many years as they have funding, they will create a baseline: a list of the species and numbers of aquatic macroinvertebrates living in their sample streams. Macro describes the size of these critters: macro is bigger than micro (which is often microscopic) but smaller than mega (which describes anything from a mouse-sized beast to a whale). Invertebrate means the animal doesn’t have a backbone. Aquatic macroinvertebrates in the Smokies include snails, water striders, and mayfly and caddisfly larvae, among many, many others.

With their baseline lists, they’ll be able to compare aquatic macroinvertebrates in healthy hemlock forests to those in dying hemlock forests, and also to notice changes in stream life over time.

They chose aquatic macroinvertebrates in particular because this group includes indicator species, which means that changes in their numbers or health indicate conditions in the stream are changing. They work well as indicator species because they require the right combination of temperature, acidity, and water clarity, among other factors, to survive. If hemlock death changes the streams, the macroinvertebrates will be the first to let us know.

Click here to read about Deciding on a research question.

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