A Comparison of Seasonal Primary Production of Mojave Desert Shrubs During Wet and Dry Years

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Abstract
Estimates of net primary productivity were made for major shrub species in the northern Mojave Desert [California, USA] during 2 yr of contrasting moisture regimes using harvest and gas exchange techniques. Prodouction increased by 224% (harvest) to 260% (gas exchange) in 1973 over 1972. Production gains varied among species, depending on whether the species was favored by the cool, moist spring of 1973. Lycium andersonii and L. pallidum, which have high photosynthetic rates and start growth in the early spring, showed the greatest increases. Larrea tridentata and Krameria parvifolia, species adapted to warmer, drier conditions, exhibited the smallest changes in production. Ambrosia dumosa, which has high photosynthetic rates but responds more favorably to warmer spring temperatures than the Lycium spp., had moderate production gains. Reasons for the different estimates obtained by these 2 methods are discussed.