The Impact of Urbanization on Southern California Ecosystems over the Past 100 Years Quantified by Stable Carbon Isotope Analysis
Abstract
The ecosystems of southern California have transformed within the last 100 years due to climate and land-use changes, yet these changes are currently poorly understood. In particular, the counties of Los Angeles, Orange, San Diego, Riverside, San Bernardino, and Ventura have been subject to rapid land-use changes and urbanization. Determining climate and vegetation changes on a regional scale will lead to a deeper understanding of the environmental impact of urbanization and will better inform future conservation and administration efforts of natural habitats. Using small mammal tissues, soils, and vegetation surveys, we investigated changes in local climate and environments over the past century in southern California. In this work, we analyzed stable carbon isotope ratios of deer mice hair (Peromyscus maniculatus) from historical and modern museum specimens in combination with high elevation soils sampled along a 10cm-deep soil profile and modern vegetation to quantify environmental and land-use change over the past 100 years. Stable carbon isotope ratios record the proportion of C₃ and C₄ plants incorporated into an animal's diet or that grew in the soil. These isotopes are preserved within the mouse's tissues when consuming food just as the isotopes are incorporated into soils as vegetation decays. Changes in stable carbon isotope ratios of mouse hair from the early 1900s to modern collections show a trend of carbon-13 enrichment in both high elevation meadows and populated valleys. Soil carbon isotope ratios also show a trend of increasing δ13C values towards the surface. Plant surveys of the soil collection sites provide additional evidence for vegetation shifts towards greater C₄ plants in areas with a history of C₃ dominance. Fire, disturbance, anthropogenic nitrogen fixation, and non-native plants/agriculture introduction likely caused the prior natural state of southern California ecosystems and animal diets to change, shifting towards more C₄ vegetation. This approach of a high spatial resolution analysis through time helps us understand the impact of land-use change events and environmental thresholds on local ecosystems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC21D1337P
- Keywords:
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- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 1632 Land cover change;
- GLOBAL CHANGE;
- 1655 Water cycles;
- GLOBAL CHANGE