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Comparison of the Reference Unit Method and Dimensional Analysis Methods for Two Large Shrubby Species in the Caatinga Woodlands

1985; University of Arizona; Volume: 38; Issue: 5 Linguagem: Inglês

10.2307/3899714

2162-2728

Robert D. Kirmse, Brien E. Norton,

Forest ecology and management

The reference unit technique was compared with the dimensional analysis approach for estimating large shrub foliige biomass in Northeast Brazil.The techniques were tested on coppicing jurema (Mhosa acutistipula Benth.) and pau branco (Auxemma oncocalyx [Fr.Alem.]Taub.).Both methods provided good esti- mates of foliage weight.The coeffkients of determination for the reference unit approach ranged from .890 to .985.The P values obtained in applying the dimensional analysis method were .937and .948.Improvements in estimates with the reference unit method were obtained when (1) a branch unit of 19% of total plant foliage was used versus a unit of only 7%, (2) the branch unit resembled the appearance of the branching of the plant being estimated, and (3) estimations of 3 judges were averaged.Total foliage production on shrubs and trees is one of the most difficult parameters to measure or estimate on native rangelands.The woody material and variable growth form renders most traditional sampling methods, largely derived for agronomic conditions, impractical for shrubs.As a consequence, vegetation sampling technique manuals ha,ve made only passing reference to or given insignificant information on biomass estimation of shrub foliage or current growth (Brown 1954, NAS 1962, Newbold 1967, Pieper 1973, t'Mannetje 1978).Efficient estimations of browse availability are required for research on brush control and grazing animal diet studies.Shrub measurement techniques used in other semiarid areas of the world were examined with the prospect of adapting a suitable method for the caatinga species.The criteria for selection were that the method be nondestructive, time efficient, and relatively precise.Traditional 'clip-and-weigh' methods (e.g., Whittaker 1961) were eliminated from consideration because of the labor and cost required (Gimingham and Miller 1968, Rutherford 1979), and because the associated research design did not permit destructive sampling.The twig count method of Shafer (1963) and methods relating foliage weight to the dimensions of individual branches (Whittaker 1962, Ovington et al. 1963, Provenza and Urness 1981) were considered inappropriate because of the high density of coppicing branches sprouting from the stumps of the test species.Two sampling techniques were selected for testing on large shrubs of Northeast Brazil.The first of these employs the principle of matching standards against samples (Hutchinson et al. 1972, Andrew et al. 1979), such as estimating the number of multiples of the reference unit (e.g., leafy branch) present in the entire plant.This technique was tested by Andrew et al. (1981) on 2 small Australian shrubs (Atriplex vesicaria Heward ex Benth.and Maireana sedifolia F. Muell.) and compared favorably with other techniques for estimating shrub biomass.The second technique, dimensional analysis, requires establishing a relationship between