E. Cayenne Engel

Early Post-Fire Plant Establishment on a Mojave Desert Burn

Abstract Fire has become more extensive in recent decades in southwestern United States arid lands. Burned areas pose management challenges and opportunities, and increasing our understanding of post-fire plant colonization may assist management decision-making. We examined plant communities, soils, and soil seed banks two years after the 2005 Loop Fire, located in a creosote-blackbrush community in Red Rock Canyon National Conservation Area in southern Nevadas Mojave Desert. Based on a spring sampling of 20, 0.01-ha plots, live + dead cover of the exotic annual Bromus rubens averaged nine times lower on the burn than on a paired unburned area. Perennial species composition shifted from dominance by late-successional native shrubs (e.g., Coleogyne ramosissima) on the unburned area, to dominance by native perennial forbs (e.g., Sphaeralcea ambigua, Baileya multiradiata) on the burn. Species richness of live plants averaged 26% (100 m2 scale) and 239% (1 m2 scale) greater on the burn compared to the unburned area. Only 5% of Larrea tridentata individuals resprouted, compared to 64% of Yucca schidigera and baccata. Fire and microsite (interspace, below L. tridentata, or below Yucca) interacted to affect several 0–5 cm soil properties, with higher pH, conductivity, and total P and K on burned Yucca microsites. Bromus rubens density in 0–5 cm soil seed banks was four times lower on the burn, and its distribution among microsites reversed. Below-shrub microsites contained the most B. rubens seeds on the unburned area, but the least on the burned area. Intense fire below shrubs may have increased seed mortality, an idea supported by >3-fold decreases we found in emergence density after heating seed bank samples to 100°C. Our study occurred after a post-fire period of below-average precipitation, underscoring a need for longer term monitoring that characterizes moister years.

Enhancing Quality of Desert Tortoise Habitat: Augmenting Native Forage and Cover Plants

Abstract Vegetation in habitat of the federally listed desert tortoise Gopherus agassizii in the Mojave and western Sonoran Desert is now partly or mostly dominated by nonnative annual plants. To i...

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 lakes 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 Meads 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.