Litter decomposition & Type-Conversion

For my undergraduate thesis (advisor: Prof. Wallace Meyer), I examined abiotic (UV radiation) and biotic (litter type and macroinvertebrate presence) factors influencing regional leaf litter decomposition in native California Sage Scrub (CSS) and non-native annual grassland in the LA Basin (study site: the Bernard Field Station). Type conversion (in this case, the transformation of native scrub land to non-native grassland) is dramatically changing the landscape of California and is expected to become more pervasive with climate change and continued urbanization. In our study, we found that both abiotic and biotic factors significantly affected decomposition and nutrient loss, but UV was the most important. However, the primary driver of decomposition processes varied seasonally. In contrast to studies limited to grass-invaded CSS (which retain both native and non-native species diversity), we observed faster rates of decomposition and nutrient loss in the grassland than in native sage scrub. This fits with our nutrient sequestration work and further highlights the importance of preventing type conversion to avoid drastically altering the C and N dynamics. With this research, my hope is to inform management of native and invaded CSS and to provide an organized framework for understanding the mechanisms controlling early stages of decomposition in semiarid systems.

Nutrient Sequestration in Css & Grassland

At Pomona, I worked on a carbon and nitrogen sequestration project that began as an undergraduate thesis (M. Wheeler, HMC '14), but after expanding in scope, has been submitted for publication and is under review (Wheeler et al., under review). Terrestrial vegetation and soil are potential nutrient sinks that are heavily influenced by anthropogenic activity, including the introduction of non-native species and urbanization. For this study, we compared C and N storage in litter, aboveground biomass, and surface soil in CSS, type-converted grassland, and "transitional" (i.e. recovering CSS) habitats. We found that both CSS and transitional areas stored more C and N in stable pools than the grasslands, providing support for preservation of intact and recovering CSS patches and partial restoration of CSS to improve sequestration ability.

 Sage Scrub (dominated by  Artemisia californicus ) at the Robert J. Bernard Biological Field Station.

Sage Scrub (dominated by Artemisia californicus) at the Robert J. Bernard Biological Field Station.

Arthropod Assemblages & Habitat Modification

 Jerusalem Cricket ( Stenopelmatus   sp.)   & other arthropods in a pitfall trap.

Jerusalem Cricket (Stenopelmatus sp.)  & other arthropods in a pitfall trap.

The Meyer Lab ground-dwelling arthropod survey project at the Bernard Field Station involved long-term seasonal pitfall trap monitoring to understand how assemblages respond to different types of disturbances: type conversion of native CSS to non-native grassland and rampant (sub)urbanization throughout the LA Basin. In doing so, we hope to aid conservation efforts of native, endemic species at risk of local or regional extirpation. So far, the Meyer Lab has published one paper about patterns of ant species richness and composition among habitat types (Staubus et al., 2015) and is in the process of preparing a second paper on spider community responses to habitat changes and fire (Spear et al., in prep).

From our ant data, we found that maintaining a mosaic of CSS and non-native grassland patches is critical for preserving biodiversity of native species, which display high habitat specificity for low-elevation areas. The spider populations at the BFS displayed remarkable resiliency to type conversion and to fire, but were sensitive to (sub)urbanization. Although maximizing spider species richness requires both suburban and non-suburban areas, our focus should be on preserving non-suburban habitat to protect the species that rely on these threatened environments for their survival.