Cattle-Breeding Valley Plains and C₄ Spontaneous Grasses in North Patagonia

The climate of North Patagonia (Argentina) is semiarid and the region periodically suffers severe droughts that may last several years, decreasing forage offer and consequently cow livestock and productivity. In most of the cattle fields extensive grazing is usually continuous through the year-long. The absence of pasture rotational schemata affects rangeland health changing the composition of plants communities in detriment of the valuable species. When under a severe drought, the appreciated forage Leptochloa crinita (= Trichloris crinita) stopped reproduction and the population became scarce, a grazing schedule was designed in a cattle farm to avoid foraging during spring and summer in a paddock located in the valley plains, where the species was disappearing. Besides L. crinita populations, the sympatric presence of the Poaceae Aristida mendocina, Distichlis spicata and Distichlis scoparia is expected, each one in slightly different patches within the same area. The forage value differs between species but all of them are eaten by bovines. For ten years the plant communities were studied with the aims of determining the incidence of the patches on the paddock carrying capacity in early autumn and estimating the contribution of the four C₄ species to bovine diet by microhistology. Free of grazing during its growing period, L. crinite enhanced the area of its patches and the biomass production of its good quality forage and was consumed preferently. A. mendocina is not prized by cattle but contributed to the diet at the end of the foraging period. Distichlis spp. is important component of the cows’ diet, especially in dry years. Management actions to preserve a valuable species may have side effects involving other community members.