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University of California Los Angeles (2017)

Plant and Soil Recovery Along Transmission Power Line Corridors in the Colorado Desert of Southern California

Setal Sridhar Prahbu

Titre : Plant and Soil Recovery Along Transmission Power Line Corridors in the Colorado Desert of Southern California

Auteur : Setal Sridhar Prahbu

Université de soutenance : University of California Los Angeles

Grade : Doctor in Environmental Science and Engineering (2017)

Résumé
The desert habitats of southern California have been subject to numerous anthropogenic disturbances. Recovery of the disturbed habitat can occur naturally or through human intervention (active restoration). Increasing energy demand and a push towards renewable sources like solar thermal and wind, often located in desert regions, will continue to impact the deserts of southern California. Electricity generated at the source (e.g. solar plant) is transported over long distances to the customer using transmission power lines which also traverse the desert habitat. This dissertation focuses on the natural recovery of vegetation and soil following impacts from transmission power line construction. The main objectives of this dissertation are to : 1. Evaluate vegetation recovery in sites impacted by transmission line construction using Landsat imagery and normalized difference vegetation index (NDVI) ; 2. Evaluate vegetation recovery about thirty years after construction using field survey data ; and 3. Evaluate natural soil recovery in sites impacted by transmission line construction. The study area, dominated by creosote bush (Larrea tridentata) and white bursage (Ambrosia dumosa), is in the lower Colorado Desert in southern California. Data are collected in areas impacted during transmission power line construction and in areas undisturbed during construction. I assess vegetation recovery in the field by measuring species richness, plant density, and percent cover. Soil recovery is assessed by comparing soil characteristics such as infiltration rate, texture, bulk density, soil compaction, salinity, pH, soil organic matter, carbon stocks, and soil moisture content between impact and control sites. The dissertation is subdivided into the following five chapters : an introduction (chapter 1), three chapters of original research addressing the main objectives listed above (chapters 2–4), and a conclusion of the work (chapter 5). In chapter 2 I evaluate the impact of transmission power line construction on vegetation by comparing the NDVI measured before construction and immediately following construction. There is no significant difference in NDVI immediately after construction compared to NDVI before construction in disturbed sites implying that the impact is not detected in the Landsat images. In chapter 3 I evaluate vegetation recovery with field survey data thirty-three years after construction by comparing impact and control sites. Results indicate no significant differences between the control and impact sites. In chapter 4 I evaluate soil recovery thirty-one years (old impact) and less than one year (new impact) after construction. The results show no significant differences in soil characteristics between control and old impact, except with soil compaction at 3 cm from surface. The new impact differed significantly from control in soil organic matter, carbon stocks to a depth of 8 cm, and compaction at 3 cm. Though not significant (p > 0.05) bulk density, pH, and salinity at new impact are slightly different (p < 0.1) from control sites implying that there may be some immediate effects from construction. Confirming the “fertile island” effect, significant differences are observed between the data collected under shrubs compared to the data collected in the bare ground between shrubs. In chapter 5, I present the overall conclusion, suggest some research opportunities, and discuss land management implications.

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Page publiée le 19 octobre 2017, mise à jour le 19 novembre 2018