VOLUME 3 ISSUE 2 SUMMER 1993

THE PHYSIOGEOGRAPHIC ARGUMENT FOR A MIXED PLANTING

Each of the hundreds of native plants have evolved to take advantage of a specific niche in the environment. This can be demonstrated by the physical characteristics of the plants, site specific adaptation and response to environmental influences.
Native prairies are dynamic systems whose complexion and visible composition can change dramatically from year to year depending upon the environmental influences acting upon that prairie. Rainfall - timing and amount, presence or absence of fire and timing of burn, removal of vegetative growth during the growing season, plus previous year's influences, all act to determine the outward appearance of a prairie.

Each native plant responds differently to a given set of environmental influences, however there are exceptions to this general statement. There are a number of native plants which respond similarly to the same conditions but most generally there are physical and physiological characteristics unique to those plants which reduce competition between the plants for the available resources allowing them to co-exist. A mixed planting of native grasses and forbs can be more productive, on the average, than a pure stand.

With a mixed planting there is a greater opportunity for one or more of the plants in the mix to take advantage of the existing conditions and influences. It is important to understand that if the management is the same every year it will favor certain plants best adapted to that management and over time the planting will be dominated by those plants. For this reason it is important to vary the timing and implementation of management practices to maintain a diverse mixture.

The physical and physiological characteristics that allow some native plants to co-exist on the same site are also responsible for the site specific adaptation of an individual plant. From wet to dry there are native plants adapted to a zone everywhere along that slope. (See THE NATIVE GRASS MANAGER, Summer '92, Native Warm Season Grass Species Applied.)

Even within species there are variations, some adapted to wet conditions while others are more commonly found on upland sites. Local genotypes account for the differences within species. In a mixed planting, the plants will sort out which species will dominate at any point along the moisture gradient. It will take a number of years for this to be sorted out but eventually each plant will dominate its own niche.

The advantage of introducing a mixture of seeds in a planting is the establishment of a plant base. Over time the forces of nature and the site specific geography will work on the planting to determine its own equilibrium.