Cottonwood understory zonation and its relation to floodplain stratigraphy

Publication Type:

Journal Article

Authors:

Merigliano, Michael F.

Source:

WETLANDS, Volume 25, Issue 2 (2005)

Call Number:

A05MER01IDUS

Keywords:

floodplain stratigraphy, gradient analysis, narrowleaf cottonwood, understory species composition, water availability

Abstract:

Species composition in floodplain vegetation is often related to initial floristics, succession, and disturbances such as flooding and herbivory. However, on a braided, cobble-bedded river with contrasting sediment facies, much of the composition of understory vegetation within a cottonwood forest was related to edaphic factors controlled by stream-deposit stratigraphy. Large shifts in understory species composition were more related to soil texture and water availability than deposit age or hydroperiod. Finer-textured and thicker overbank deposits had greater water availability and supported mesic species, while sites with coarse sediments to the surface supported only xeric species. A strong gradient of site moisture corresponded to a gradient in species composition. Soil water potential (Ψ8) indicated by pre-dawn xylem water potential (XWPPD) in a shallow-rooted grass reached 4.2 MPa on xeric-species sites in mid-summer; on mesic species sites, XWPPD was always greater than 1.5 MPa for the same grass species. Deep-rooted plants had a narrower range of XWPPD across all sites, and XWPPD was typically between 0.0 and 1.0 MPa. Ψ8 derived from actual soil water content followed the same pattern indicated by species composition, soil texture, and XWPPD.