Abstract

The annual pattern of above-ground live biomass, recent dead standing biomass, old dead standing biomass, and standing crop of big sacaton (Sporobolus wrightii Monro) grassland community in semiarid Arizona was studied over a 3-year period. Live biomass was produced throughout the year but peak production, over the 3 2 years, was in August. Peak biomass production was 296 g m in 1 wet summer and averaged 133 g mover 2 dry summers. Recent dead standing biomass was greatest in spring and least in summer, over the 3 years. Transfer of recent dead standing biomass to old dead standing biomass was precipitation and temperature dependent. Old dead standing biomass was greatest in summer, least in winter, and was primarily composed of dead seed stalks. Livestock management of big sacaton grasslands should possibly be distinct from adjacent upland areas. Big sacaton (Sporobolus wrightii Monro) is a robust perennial warm-season bunchgrass that begins growth in early spring and usually produces a limited amount of green herbage in winter (Haferkamp 1982). The species grows on low alluvial flats and flood plains (Wooten and Standley 1912). It usually is excluded from alkaline and saline playas and lowlands dominated by alkali sacaton [Sporobolus airoides (Torr.) Torr.]. Big sacaton is distributed from southeastern Arizona to central Texas and Author is range scientist, Arid Land Ecosystems Improvement, USDA, Agricultural Research Service, 2000 East Allen Road, Tucson, Ariz. 85719. Appreciation is extended to R.M. Madrigal and B.B. Buck for field assistance; Drs. H.L. Morton and T.N. Johnsen, Jr., for technical assistance; the Donaldson family at the Empire Range for their cooperation; and ANAMAX Mining Company for permission to use their land. Manuscript received August 17, 1983. south into the northern Mexican Frontier States; however, stand development is greatest in southeastern Arizona (Kearney and Peebles 1960). Dense stands of big sacaton formerly dominated alluvial flats and bottomlands along the Santa Cruz and San Pedro Rivers in Southeastern Arizona and supported more than a million cattle in 1890 (Humphrey 1958). Big sacaton bottoms have been, and continue to be burned and grazed (Bock and Bock 1978), plowed and sown to agricultural crops (Griffiths 1901), channelized to provide irrigation water and drainage (Cooke and Reeves 1976), and covered with houses and asphalt (Renard et al. 1983). Today the species occupies less than 5% of its original area (Humphrey 1960). Big sacaton stands were usually associated with perennial, surface water and new growth was readily consumed by livestock in spring when upland grasses were dormant (Thornber 1910). Dead standing big sacaton biomass is coarse and stands have been burned or mowed in either late fall, winter, or early spring for at least the past 100 years (Thornber 1910, Humphrey 1970). The animal-carrying capacity of semiarid grazing lands is dependent on net primary production and the amount of plant biomass which is available to be converted into animal biomass. Previous investigators have been interested in big sacaton production after natural and man-caused fires (Humphrey 1960, Bock and Bock 1978, Gavin 1982). However, net primary production rates under nonburned conditions have not been measured. The first step in a program to evaluate carrying capacity should be to quantify the annual accumulation and decomposition characteristics of live biomass and standing litter in big sacaton grassland communities. JOURNAL OF RANGE MANAGEMENT 37(4), July 1984 377 This content downloaded from 157.55.39.223 on Wed, 24 Aug 2016 05:07:16 UTC All use subject to http://about.jstor.org/terms This paper reports on studies in which the above-ground live biomass production, recent dead standing biomass, and old dead standing biomass were examined over 3 years. The relative differences in yield accumulation and decomposition in response to climate were also studied.

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