Date of Award:

1-1-1967

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Department name when degree awarded

Range Science

Abstract

Practical assessments of range production and utilization are based on forage weight estimates. In preparing these estimates moisture content in green vegetation offers some problems. The moisture component is not likely to be constant for a given species. Diurnal, seasonal and site variability have been well illustrated for agronomic and tree species (Salisbury, 1848; Jenkins, 1879; Miller, 1917; Pearson, 1924; Watkins, 1940; Parker, 1951; Ackley, 1954; Werner, 1954; Zohary and Orshan, 1956; Slatyer, 1959; Kozlowaki, 1965 and Jame son, 1966). Since variability is also likely for range plants, computations made on green weights are apt to be fallacious. It is a common practice, therefore, to express production on "water free" or "dry weight" basis. But the estimates of dry weight are made difficult by variations in herbage moisture. A variety of factors, relevant both to the vegetation and the site it occupies, would seem to account for variable moisture content. The prevalent methods for estimating moisture, however, seem to be more of a legacy from the past than an appreciation of ecological influences.

Earlier investigators of pastures and fodder crops were largely agronomists interested in comparing yields. They were concerned primarily with irrigated crops where soil moisture is not a limiting factor and the ecological influences, such as humidity, rain, cloudy weather, dew, shade, exposure etc. are far from dominant (Atwater, 1869; Collier, 1881; Richardson , 1884; Ladd, 1888; Richardson, 1889; Morse, 1891 and Widstoe, 1897). The variations in water content and other components were accordingly related to stage of growth. Taking a cue from these studies agencies such as the United States Forest Service and Soil Conservation Service came to use certain reducing factors to convert green weight of range forage into dry weight. In developing these factors the type of vegetation and growth phases have been considered but ecological features and context have been neglected. The methodology adopted from pasture conditions became the accepted basis for making range management decisions (Range Memo, SCS-8, Soil Conservation Service, 1963; Range Analysis, Region IV, Forest Service, 1964).

The influence of features of environment, particularly aspect, on growth differential, has long been recognized by foresters (Schlich, 1905; Champion, 1928 and Tourney, 1928). Plant physiologists have been aware of the significance of time-of-day on plant water for some time (Shreve, 1914; Miller, 1917). It is very probable that these influences express themselves in moisture content of herbage also.

The investigations reported herein were conducted to define and assess the scope and intensity of some of these ecological features in modification of the moisture component of herbage. The objective is to determine whether differences in ecological context influence range herbage moisture to a sufficient extent to warrant consideration in developing conversion factors for deriving dry weights from green weights of vegetation samples. The appraisal should reaffirm present assumptions applied or yield more accurate adjustments for estimating forage production. In either circumstance the results should enhance the scientific basis of range management decisions.

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