Print PageDesert shrubs create an environment that supports high densities of native annual species under their canopies, particularly under the North facing side of the shrub. Non-native species invading deserts, however, can have high densities in the open areas between shrubs. Our objective was to compare patterns of seedling recruitment in Larrea tridentata (creosote bush) dominated areas in the Mojave and Sonoran deserts. In both deserts, we identified focal L. tridentata individuals and established transects on either the North or South side of the shrubs. Several weeks after the first winter rains, we counted seedlings in four different microhabitats along each transect: under the canopy (UC), the canopy drip line (CD), in the open near to the focal shrub (ON), and in the open far from the focal shrub (OF).
Results/Conclusions
Overall, seedling density was approximately 10 times higher in the Mojave desert than in the Sonoran desert. In the shrub influenced microhabitats UC and CD, seedling densities were higher on the North side of the shrubs in the Mojave desert, but densities were similar between the N and S sides of the shrubs in the Sonoran desert. In the Mojave desert, native seedling density was highest in CD plots; however, in the Sonoran desert, native seedling density was highest away from the shrub canopy (in ON and OF plots). Non-native seedling density was highest in the ON and OF plots in the Mojave desert; whereas, non-native seedling density was more similar among microhabitats in the Sonoran desert. We found that patterns of native and non-native seedling recruitment differed between our Mojave and Sonoran desert sites, suggesting that the factors controlling seedling recruitment differ between the Mojave and Sonoran deserts. High native seedling recruitment under the North side of shrubs in the Mojave desert is consistent with findings from other studies that document the formation of fertility islands, but creosote bushes do not appear to have similar effects in the Sonoran desert.
