Utilization of above ground net Primary production by herbivores in Mukogodo rangelands, Laikipia,Kenya

Abstract

The amounts and proportion of above ground net primary production of the herb layer utilized were investigated in the Mukogodo rangelands of Laikipia Kenya. Two private (01 Jogi and Loldaiga) and two conununal group ranches (II Polei and Makurian) were compared in the study by investigating the herb layer cover, tree and shrub composition and density, standing crop biomass, production and productivity. The twig count and Jensen and Urness' (1981) methods for assessing browse use were also compared. The ratios of browse to grass to forbs eaten by cattle, goats zebras and giraffes were monitored by the microhistology technique. Herb layer cover, standing biomass, and biomass production and productivity were significantly higher in the private ranches (01 Jogi and Loldaiga) compared to the communal group ranches, (II Polei and Makurian) and varied with the season. Biomass in the private ranches under trees were in the range of 1.15 to 3.37 tlha, and 0.81 to 2. l7t1ha in the open area. In the communal ranches, biomass ranged from 0.39 to 2.73 and, 0.0 to 0.94 tJha under the trees and in the open area respectively. There was significantly more biomass production under tree canopies than in the open area (p < 0.05). Utilization varied from 0.0 to 2.18 tlha and was similar across the ranches. The twig count and Jensen and Urness' (1981) methods used to determine browse use were not to be different (p > 0.05). Browse use was heavier in II Polei than in the other ranches and it's level of use also varied with the season. Microhistology results indicated that Cattle and Zebras significantly (p < 0.001) ate more grasses (averaging 60 to 96 %) than either forbs or browse, while Giraffes browsed more than grazed in all the seasons (p < 0.001) (80 to 90 %). Goats were mixed feeders, browsing and grazing on an equal basis.