Relationships Between Basal Cover and Forage Production

Percentage composition by species is an important measurement used in range ecology. It can be based on either basal cover or forage production. Most range managers are interested in composition based on production although composition by basal cover is easier and quicker to determine. Therefore, if the relationships between these two measurements were known, it would be possible to obtain date rapidly on basal cover and convert them to data representing production. The purpose of this project was to study the relationship between these two measurements. However, it must be considered preliminary as many years' data will be necessary to establish an accurate correlation. This experiment was conducted on an ungrazed area of the mixed prairie situated near the Cedar Bluff reservoir in Trego County, Kansas. Data were gathered from two range sites, the upland and the break site. The upland soil was a deep, heavy, silty clay loam and supported a typical short grass vegetation dominated by blue grama (Bouteloua gracilis) and buffalo grass (Buchloe dactyloides). The break site was located on a gradual west-facing slope near the upland site. The calcareous soil was relatively shallow and supported primarily mid-grass vegetation dominated by blue grama, side-oats grama (Bouteloua curtipendula), little bluestem (Andropogon scoparius) and big bluestem (Andropogon gerardi). Square-foot quadrats, randomly located, were used to sample the vegetation. One hundred sampling units from the upland and 300 from the break site were taken. Data gathered included actual basal cover of all species, percentage composition based on basal cover by each species, and height of each species. The grasses were then clipped by species and bagged separately. When air dried, they were weighed to the nearest one-tenth of a gram. Composition by forage production was then calculated and available for comparison. Calculations were made of the mean, standard deviation, and standard error. Correlation coefficients were used to compare the relationship of basal cover, forage production and height of the dominant grasses. The upland site had a basal cover of 56.0 per cent. Percentage composition by basal cover was 66.1 per cent buffalo grass, 33.3 blue grama, and 0.6 per cent sand dropseed (Sporobolus cryptandrus). Percentage composition calculated from forage production was 53.4 per cent buffalo, 44.8 per cent blue grama and 1.8 per cent sand dropseed. The multiple correlation coefficients among basal area, height and yield for blue grama were 0.89 and for buffalo grass 0.93. Total basal cover on the break site was 16.1 per cent. Of this, blue grama made up 21.5 per cent, side-oats grama, 40.8, big bluestem 17.7, and little bluestem 11.7 per cent. Eight minor grasses accounted for the remaining 8.7 per cent. When per centage composition was based on forage production, blue grama made up 14.9 per cent, big bluestem 21.1, little bluestem 20.3, and side-oats grama 35.2 per cent. The multiple correlation coefficients among basal area, height and yield on this break site were 0.91 for big bluestem, 0.89 for little bluestem, 0.93 for blue grama, and 0.85 for side-oats grama. Although no definite conclusions could be reached from one year's data, tentative multiple regression equations were derived for each of the major species. If their validity could be established, they could permit estimation of yield from date about basal area and height. Continued research is necessary to establish such a relationship.