Disturbingly Undisturbed

Too much of the same is rarely a good thing.

For the most part we have a very narrow concept of what native rangeland vegetation should look like. That view tends to be very static. We don’t realize that what we see on a single visit is not necessarily what it will look like on the next visit. What we lack awareness of is how the plant communities vary over time depending on what is taking place on the landscape.

Plant communities can look very different from one time to the next depending on the timing and nature of the latest disturbance. It doesn’t mean that anything is wrong - simply that a different aspect of that community is being expressed.

After a fire on the landscape, depending upon the timing of that fire, there may be an abundance of annual forbs - “weeds”. The fire didn’t cause the “weeds”. They were already a part of that community, but weren’t being expressed. It isn’t that they weren’t present and suddenly invaded from elsewhere. They were patiently waiting for the return of favorable environmental conditions. After the fire removed the overhead canopy and some of the litter from the surface - the annual forbs were able to germinate and grow. As recovery from fire continues they will drop out and grasses will again predominate. Well, you may ask, what good are they? Bobwhite, along with other grassland vertebrates, depend on the larger seeds from forbs for a lot of their food needs - either as a direct food source - the seeds, or as a food source for prey species - insects. Looking at the root systems of the forbs vs grasses provides some insight as to another roll the annual forbs are playing in soil health. A tap root creates a small whole in the soil and then dies and decays - leaving the hole. If you consider how many holes are left by the tap roots of all the annual forbs in a pasture after a fire - this is not an inconsequential impact on water infiltration and gas exchange.

Having a dense stand of broomweed appear after a fire, even though it offends our bias toward manicured lawns, is not a bad thing.

Removing the litter allows for much greater mobility of a species who spends most of their time on the ground but has legs only 2 inches long. I’ve got long legs and I’m particular about where I go and the paths I take to get there. Imagine trying to travel through dense grass and litter accumulation when you can’t get your foot more than a couple inches off the ground. How about trying to catch a bug for lunch or evade a coyote or a hawk in that mess.

Dense grass and litter do make for good nesting structure for ground nesting birds so we don’t want fire across all of the landscape at the same time. In fact, in a healthy range ecosystem, occurrence of fire at different times of year and at different return intervals is what maintains the diversity of habitat necessary to support healthy wildlife populations.

Although we don’t often think of it as such, grazing is a necessary disturbance as well as fire. Large herbivores exert grazing pressure mostly on the perennial grasses which allow other plant species to persist, providing food for vertebrates and invertebrates. Grazing distributes organic material which again provides a food source for various invertebrates (dung beetles, fly larvae), who in turn, serve as food for grassland birds. The dung beetles are incorporating organic matter directly into the soil as well as aerating and improving water infiltration in the soil. Hoof action from large herbivores can, if stock density is high enough, impact those plants that aren’t directly grazed so that everybody gets abused equally and no plant species or group of species gains the upper hand. Most of the plants either get chewed on or stomped on although there’s a couple of others things that could happen to them as well. Fire operates in a similar manner in this respect.

Each type of disturbance, fire or grazing, has an influence on the other which adds to the ecosystem complexity and biodiversity.

If all of these disturbance effects are taking place across the landscape, the soil should be in good shape. If they’re not, soil health is going to suffer. The same can be said for the grassland birds. Grassland birds can act as a barometer of rangeland ecosystem health. If they are in good shape, everything else is as well. If they are struggling, there’s a problem somewhere, likely with the disturbance regime.