Grazing and Plant Growth Interactions in a Semiarid Festuca pallescens Grassland (Patagonia)

BERTILLER, MONICA B.; DEFOSSE, GUILLERMO E.

JOURNAL OF RANGE MANAGEMENT

American Society for Range Management

Año: 1990 vol. 43 p. 300 - 303

0022-409X

The effects of grazing on relative (g l g-l l d-t) and absolute(g am-* l d-l) abo veground net primary productivity and senescence of coiron blanco (Festucapaflescens(St. Yves) Parodi) wereinvestigated in northwestern Patagonia. Aboveground net primaryproductivity under ungrazed and grazed conditions was estimatedby means of a simulation model fitted to biomass data. Relativeand absolute aboveground net primary productivity was greaterfor grazed than ungrazed plants during the early growing seasonwhile the inverse occurred during the late growing season (reproductive period). Grazing reduced the relative and absolute aboveground senescence during the late growing season. Relative andabsolute effective primary productivity, expressed as the differencebetween the corresponding primary productivity and senescence,were greater for grazed than ungrazed plants. This increase is inaccordance with the grazing optimization hypothesis. However,the increase was not of sufficient magnitude to compensate forlosses of green biomass caused by grazing. Results imply thatcurrent grazing intensities in this region reduce aboveground productivity of coiron blanco. It follows that a reduction in stockingrates would be necessary to increase aboveground primary productivity.