Determining Forage Weight on Southern Forest Ranges

Abstract

OPEN forests in the Louisana uplands I ) produce 2500 pounds or more of grass per acre per year (Fig. 1A). But adjacent 15-year-old plantations of pine or good stands of second-growth pine may not produce more than 250 pounds of green herbage per acre; most of it is covered by pine litter which weighs 6 to 10 tons per acre (Fig. iB). On southern forest ranges we are using actual weight of herbage as the basis for measuring forage production and ground cover. The method is simple, concrete, and well suited to conditions on the ground. It is an adaptation of the weight estimate method devised by Pechanec and Pickford (5), for use in determining grazing capacity on western ranges. Their method requires actual clipping and wveighing of herbage on training plots; then weight estimates only on temporary plots to inventory range forage by species. They used plots 100 square feet in size. Our adaptation of the method aims at weight measurements of vegetation as forage, as an ecological response to forest or range management, or as fuel, according to the purpose of the study. In inventorying herbage, our procedure is to actually clip and weigh the total yield by herbage classes, while the species weight composition is estimated. In 1944, the method was tried on plots ranging from 4.4 square feet (0.0001 acre) to 100 square feet in area. Weights for the smallest plots varied too greatly to yield significant results with a reasonable number of samples. The largest plots produced more herbage than could be harvested or weighed conveniently. The size plot finally selected after much trial, error, and analysis, was 9.6 square feet in area, or a square of 3.1 feet on a side about halfway between a square yard and a square meter (1). Under average herbage conditions, this size of plot gives a reasonably low error, and only 10 to 15 plots are needed to sample a vegetation sub-type. It is about the easiest size to work with, and its area is such that when herbage is weighed in grams, the production per acre can be calculated in pounds simply by multiplying the number of grams by 10, i.e., grams-per-plot times 10 equals pounds per acre. Obviously, small amounts of grass can be weighed more easily and accurately on gram scales than on pound-ounce scales. Moreover, metric weight values are better suited for field records and initial computations. Final values are in pounds per acre. It was found that plant density cannot be used as a satisfactory measure of forage production and ground cover. A range that usually has 0.6 to 0.8 density supports less than half that cover throughout the season following a spring burn, even though weight of herbage produced may actually be greater after the burn. The equipment used in determining forage yield by clipping and weighing is a pair of sheep shears, a spring scale of 500 grams capacity, a 3.1 feet square wire frame mgde of welding rods inch in diameter, paper bags in which to weigh and keep samples, and record forms. Field procedure is to place the wire frame on the sample point and to un-