Bunchgrass Growth Pattern

On  winter walks Leonard and I notice things we often ignore during the spring and summer when the abundance of flora and fauna are sometimes almost overwhelming. During this time of greys and browns we tend to look a little closer.

Our pastures contain many different grass species, each fascinating in its own way. Bunchgrasses (orchardgrass, some fescues, some bluegrasses, some ryegrasses, and some wheatgrasses, among others) grow as clumps or tufts of vegetation with empty spaces existing between the clumps. Often the tufts grow in roughly a circular pattern. A close examination of one isolated clump sometimes reveals a circular fringe of grass with a dead center.

Bunchgrasses grow by what is called intravaginal tillering. Tillers are new grass shoots. If the tiller remains within the leaf sheath of the mother plant (intravaginal) the plant has an erect growth pattern and very little space between the tillers, resulting in the compact plant arrangement.

Individual grass tillers have a short life span, usually less than two years and must be replaced nearly annually by buds near the base of the established tillers. As the basal area of the bunchgrass increases, the shoots or tillers at the periphery of the clump increase in density and the tiller density at the interior of the base declines. The nutrients are primarily directed to the younger tiller generations.  The oldest tiller generations at the center of the bunchgrass basal area die and decompose. For this reason individual tussocks of bunchgrass often are a fringe of grass shoots surrounding a dead and decomposing center as shown in two of the pictures.

As the original tiller generations die and decompose from the center the bunchgrass “circle” becomes larger and eventually begins to fragment with the tufts  separating yet still maintaining a suggestion of the original circular pattern, as in two of the other pictures.

These irregular bunchgrass circles and tussocks with decomposing centers are easily observed in the winter.

These bunchgrasses were photographed in our pastures (Lookout CA). Although the grass is difficult to identify in the winter, Leonard believes the photographs are of Idaho fescue (Festuca idahoensis).

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