Understory/overstory species patterns through a Sierra Nevada Ecotone
Mellmann-Brown, Sabine; Barbour, Michael G.
Distribution patterns of understory and overstory species were determined using 45 forest plots within a 6 km2area that spanned 290 m of elevation change in a major vegetational ecotone of the central Sierra Nevada of California. Overstory composition ranged from dominance by Abies concolof to A. magnifica. Understory composition was analyzed in relation to overstory composition and abiotic site factors. While only 10 herbaceous species were restricted to a single forest type, others exhibited distribution patterns that reflected overstory dominance, overstory cover, litter depth, soil chemistry, elevation, and aspect. Turnover of herbaceous species parallelled the turnover of tree species and change in community physiognomy that characterizes this ecotone between the lower and upper montane zones. However, species turnover within either A. concolof or A. magnifica forests was nearly as large as between them. We conclude that understory species behave independently of the tree species which dominates the overstory.