Chapter 4: Assessing Grassland Condition

The term "condition" describes the present species composition and vigor of the plant community compared to its potential. Condition refers to the health of the grassland and long-term productivity, but not to annual production which is largely an influence of current precipitation and temperatures.

Once determined, the condition of your grassland will have a direct bearing on the management objectives you wish to establish and the means you choose to achieve them.

The grassland condition concept has been developed to account for the impact of grazing, although other types of disturbances can influence condition in similar ways. For example, fires, trampling or hay cutting can reduce soil moisture and change species composition.

Grazing and other forms of disturbance have a direct bearing on grassland potential and, hence, on condition. Even a prolonged drought will change the species composition of a grassland by favouring less-productive, drought-resistant species. A site in poor condition will support fewer cattle and/or different species of wildlife, and produce fewer pounds of beef than can be supported on good-to-excellent sites. As well, sites in poor condition cannot withstand climatic variation such as drought. Generally poor sites have lost a good proportion of the more productive, desirable plant species which, in turn, have been replaced with less desirable, often poorer-producing invaders.

The key to maintaining or restoring near pristine condition is to manage for a proper balance between use of, and rest for, plants.

Photo: G. Trottier, Canadian Wildlife Service
Repeated, untimely disturbance of any kind will favor certain plant species over others and reduce grass vigor. The Fescue grassland on the left was burned 3 times in 8 years compared to the right which was burned 5 times. Note the shorter, less vigorous growth and unprotected ground on the right. Ground-nesting birds and small mammals were more abundant in the less frequently burned area.

Grassland plants have been classified depending on whether they become more abundant or less abundant in a community when there is disturbance or rest.

Decreasers:

These are desirable forage plants most liked and sought after by livestock. Repeated, excessive disturbance (defoliation) causes them to decrease in abundance and vigor.

Increasers:

These are plants not as readily eaten by livestock, or affected by other disturbances. Initially, they increase in abundance following disturbance, then decline if excessive disturbance continues.

Invaders:

These are largely weeds or introduced exotics which appear and increase if excessive disturbance weakens and kills increaser/decreaser species. Invaders are very resistant to disturbance and are usually less productive.

Proper Use:

This is the balanced use and the resting of the plant community which will maintain increasers and decreasers in balance, and generally discourage invaders.

To rate condition of grassland, follow these steps:

1. Identify and roughly estimate the relative cover of the dominant grass and forb species in each range site or plant community.
2. Refer to the species lists in the published Range Guide for your area to see which species are typically decreasers, increasers, or invaders, and what proportion these occupy in the potential or climax community.
3. Compare the estimated proportions of these three groups in your range sites to the potential or climax community and calculate range condition.

Range Condition Classes Graph: Black and white graph depicts along the vertical axis the realtive contribution to total yield (%) ranging from 0 to 100 and across the horizontal axis lists four range condition classes in order left to right as excellent, good, fair and poor. On the graph, three lines representing increasers, decreasers and invaders show that as range condition decreases, the proportion of decreaser plant species in the community declines, while the invaders increase.

As range condition decreases, the proportion of decreaser plant species in the community declines, while the invaders increase. Increaser species become more abundant under light to moderate grazing pressure, but they are grazed out of overgrazed pasture in poor condition (Abougouendia and Copeland 1985).