Biotic Crust Project: joshua

Environmental Factors Influencing Distribution of Microbiotic Crust in Joshua Tree National Park

Participants: Nicole Pietrasiak and Valerie Flechtner

Sites Included in this Study: WJT2

Joshua Tree National Park was first sampled in 1998 as part of the Biotic Surveys and Inventories NSF grant to study algae of microbiotic soil crusts. Sites in the Pinto Basin (JT1), Cadiz Valley (JT2) and Lost Horse (JT3) areas were established as part of this effort. A number of isolates were made from our collections (by Val Flechtner, Klara Kubeckova, Jeff Johansen, and Hend Alwathnani) and one paper regarding these strains has been accepted for publication (Rehakova et al. 2007).

We began new studies when Nicole Pietrasiak (University of Leipzig), in collaboration with Johansen, studied the microbiotic crusts of Wonderland of Rocks in Joshua Tree National Park. This work was the subject of her diploma thesis at the University of Leipzig (Pietrasiak 2005). In 2006, with support from the California Desert Research Fund, Pietrasiak returned to JTNP to conduct an extensive survey of microbiotic soil crusts in wilderness areas throughout the park. She characterized 75 sites representing all wilderness segments of Joshua Tree National Park. Additional sites were characterized while hiking through the park with respect to microbiotic crust development. A map showing extent of crust cover based on all 200 sites was constructed for the entire park and appears below.

A total of eight vegetation community types were sampled. At all sites, one hundred 1.0 m² frequency plots and 250 cover points were scored for shrub vegetation (by species), cacti (by species), perennial grasses and forbs, annuals (cover only), rock, and several crust categories (algal, lichen, moss, mixed crust). Samples were taken at every site for subsequent soil analysis and algal isolation. Soil stability was also measured in the field (Herrick et al. 2001).

Figure 1. Map of Microbiotic Crust Development in 75 study sites and 140 other visited sites in Joshua Tree National Park. Areas lacking crust appear as small white dots. 0) absence of crust or presence of only incipient crust (some cohesion of soil and evidence of filaments, but no surface darkening of soil, soil breaks easily); A1), A2), A3) were dominated by algal crust, with 1, 2, and 3 representing increasing development; L1), L2), L3) were dominated by lichen crust (algae were also usually present) with 1, 2, and 3 representing increasing development; and M1), M2), M3) were the best developed crusts and required the presence of mosses.

Resulting Publications:

Rehakova et al. 2007