Indicator Species

An indicator species is a plant or animal that is used to gather information about an environment. Foresters, biologists, ecologists, outdoorsmen and women use indicator species to quickly gain information about the natural community that they are viewing.

Some plants and animals are very characteristic of certain habitats and make good indicator species, while others, such as red maple, black gum, or deer, are ubiquitous, and their presence or absence may not tell the whole story about a particular area.

Knowing some common indicator species will help you read the landscape the next time you are out in nature. Suppose you are walking down slope and you see some willows, alders, cattails, and reeds at the bottom. Knowing a little bit about these plants allows you to surmise that you are entering a swampy area.

Likewise, if you see large sycamore, silver maple, boxelder, or pin oak on the horizon, you may surmise that there is likely a large stream or river nearby, since these trees normally grow in lowlands or at the edge of waterways.

Sycamore along the bank of Catoctin Creek

Credit: Jan Barrow, Myersville, MD

Fisheries managers and ecologists can deduce if water is clean, cold, and well-oxygenated if the water contains brook trout, damsel flies, and stoneflies, because these aquatic species cannot tolerate warm or polluted waters. Conversely, when a stream has a preponderance of bottom-feeding fish such as catfish, midges, and worm-like insects, it’s probably safe to say that water quality is not too good.

There are a whole suite of animals and plants that are collectively known as FIDS, or Forest Interior Dwellers. These indicator species require large, unbroken stretches of forest to thrive and feel secure.

Have you ever noticed that there are a lot of cedar, redbud, hackberry, walnut, and elm growing around Walkersville, Woodsboro, Keymar, and Emmitsburg? These trees grow well in limestone soils, and there is a large belt of limestone located here.

At the other extreme, when you see a preponderance of oaks, pine, or mountain laurel growing in an area, it’s a pretty good bet that you have dry conditions and acid soils, because these are indicator species of those conditions.

The southwest-facing slopes of a mountain receive a lot of sunlight throughout the day, and as a result, these areas are drier than the north and east slopes. If you see a lot of pitch pine, upland oak, and gum on a mountain slope, you are probably looking at the southwesterly side, whereas if the slope has hemlock, sugar maple, and yellow birch, you can deduce that this is a north or eastern slope.

Foresters and ecologists can spot a young forest in its early stages of development by looking for the presence or absence of “pioneer” species: those plants that typically seed into and become established where there has been a disturbance or where farmland has been left fallow.

Examples of early successional indicator species are black locust, eastern red cedar, black cherry, elm, and persimmon.

When outdoors, looking for indicator species can offer a lot of insights into a particular community, its relative health, underlying soils, and historical influences.

Article by Mike Kay, FCFCDB

Nature Notes for 1/22/21

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