December Prairie

Even though most of the top growth in the prairies has turned brown, you still get an impression of freshness when you look out over the dry grass stalks. That image will change as winter weather works to bring the stalks down. Exposed west facing hillsides usually suffer most from winter storms and wind. This patch of grass will be one of the earliest to break down.

Scattered cedars in the prairie help to buffer the grass from the wind. At the same time, the trees can funnel and accelerate the wind, causing increased damage in certain areas. This is an example of the canyon effect experienced in cities when moving air must crowd together and increase speed in order to pass down a city street. Randomly scattered trees are not as effective as buildings in producing the wind currents, but it’s quite noticeable when it does occur.

Each species of grass exhibits a different level of resistance to the elements. At this time of year the different grasses share the same general color and are hard to distinguish at a glance. Textural differences help to distinguish patches of each species. On the right we have triple-awn grass forming a solid mass containing so many fine stems that it appears out of focus. To the left is the tough stemmed Big Bluestem. A winter dominated by wind will flatten the bluestem and leave the triple-awn relatively untouched. Heavy snow loads will flatten the triple-awn to the ground and leave the bluestem standing. A combination of the two weather types will flatten everything.

It may appear that the fate of the dead grass stalks is of little importance to the overall health of the prairie, but locked in that dead vegetative material are the nutrients that will nourish the prairie next year. Nutrients are released from the plant material through decomposition. Decomposition occurs most rapidly when the temperatures are warm and the vegetation is moist. These conditions are most prevalent in early summer, which is the exact time that prairie plants are growing most rapidly. Plants are ready to make use of the nutrients as soon as they become available.

But there’s another factor besides weather that determines the rate and timing of decomposition and that is the position of the vegetation. Material that is densely packed close to the ground will decompose earlier more rapidly than standing material. This tends to favor the early growing forbs. More upright material tends to decompose during the later part of the season and most favors the grasses. Of course, some of that material takes more than one year to completely break down and that extends and moderates the seasonal release of nutrients.

As I walk through a winter prairie, I tend to make predictions of how I think the summer prairie will look. It’s really too early to make any sound guesses, but by the end of February, I’ll have a pretty good idea of how things are going to progress. Naturally that’s assuming average weather conditions, which seems to be a rarity anymore.