Comparison of four methods for grassland productivity assessment based on Phytomass data

DEFOSSÉ G. E.; BERTILLER, M. B.

JOURNAL OF RANGE MANAGEMENT

Society For Range Management

Lugar: Lakewood; Año: 1991 vol. 44 p. 199 - 203

0022-409X

The relative utility of 4 methods for grassland above-ground primary productivity (ANPP) assessment were evaluated.  These methods, applied to a set of phytomass and litter data collected at about bimonthly intervals for 2 years in a Festuca pallescens (St. Yves) Parodi grassland  steppe of south western Chubut, Argentina, were: (1) summation of positive increments of green (live) biomass between harvests, (2) summation of positive increments of total biomass between harvests, (3) summation of positive increments of green biomass between harvests plus correction factors which accounted for the concomitant increases of dry, old dead, and litter, respectively, and (4) mathematical model of simultaneous differential equations which fitted the values of phytomass data obtained in the field. Method 1 gave consistently (p ≤0.05) the lowest ANPP values in both years. Productivity values obtained with methods 2,3, and 4 were highly correlated and did not differ significantly (p ≤0.05) with each other. Their estimates varied from 94.8 to 105.3 g of dry matter per m2 for the first and year and from 73.0 to 149.4 g of dry matter per m 2 for the second year. These values are within the range of productivity given for other climatologically and physiognomically similar semiarid grasslands of North America.  Each method except 1 provided reliable estimations of ANPP for the grassland studied.  Methods 2, 3, and 4 can also be used to assess ANPP in any other grassland with similar characteristics. Each one, however might have particular applications according to the specific objectives pursued.