Plant colonization and soil properties on newly exposed shoreline during drawdown of Lake Mead, Mojave Desert

Abstract

Drawdown of Lake Mead from 1998 to 2011 reduced the lake's perimeter by more than 400 km while exposing more than 25,000 ha of formerly submerged land. To evaluate primary plant succession and soil properties in this new shoreline habitat, we sampled surfaces last submerged 3, 6, 9, or 13 years before sampling (including a never-submerged control) using 150, 100 m² plots at 3 sites varying in topography and soil parent material. Consistent with previous research, abundance of the exotic saltcedar (Tamarix ramosissima) declined with increasing surface age. Conversely, cover of native species was greatest overall on older surfaces across sites. Early successional native perennial species colonized the 13-year-old surface. Unexpectedly, multivariate soil properties did not differ between never-submerged and formerly submerged surfaces. Based on the first 13 years of plant colonization along the Lake Mead shoreline and previous research on longer term Mojave Desert vegetation succession, managers can likely anticipate (1) continued development of an early colonizing native shrubland persistent for several decades, and (2) eventual colonization by species of the mature vegetation inhabiting never-submerged surfaces. Moreover, we observed colonization of formerly submerged land by a rare plant of special conservation designation, California bearpoppy (Arctomecon californica), suggesting that even after many years of submersion, rare plant habitat along the Lake Mead shoreline may be reclaimed. While Lake Mead's drawdown might be viewed negatively from a perspective of maintaining full-pool water storage, it has re-exposed a vast area of new terrestrial habitat increasingly colonized by native species as invasive species abundance declines through time.

Key words:

• colonization
• primary succession
• species richness
• Tamarix ramosissima
• vegetation