Nitrogen Deposition Along A California Freeway And Impacts On Central Valley Grassland Species

Author : Elise M. Tulloss
Publisher :
ISBN 13 : 9781303444036
Total Pages : pages
Book Rating : 4.4/5 (44 download)

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Download or read book The Effects of Nitrogen Deposition on Plant Community Dynamics in a Heterogeneous Savanna Landscape written by Elise M. Tulloss and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Urbanization and agricultural intensification in California has increased N emissions and, consequently, deposition to adjacent oak savanna landscapes. The total amount and chemical form of this deposition varies across the landscape at multiple spatial scales and through time. At a coarse scale, there is a non-linear gradient in N deposition across the California oak savanna region such that savanna sites closest to sources of N emissions receive greater deposition than sites in more remote areas. At a fine scale within savanna sites, a strong research foundation in oak woodland systems has described heterogeneity in soil resources created by the existence of oak canopies. This phenomenon, termed islands of fertility, is a net result of enhanced nutrient inputs and retention facilitated by the tree, with nitrogen deposition being recently suggested as a primary cause of enhanced inputs. The interaction between the regional-scale gradient of N deposition, the local-scale island of fertility, and the seasonal variability of N deposition results in heterogeneous soil N resources. Nitrogen availability is greatest beneath oaks and at sites on the high end of the regional gradient and during seasonal pulses of N deposition associated with precipitation events. These heterogeneous soil N resources play a critical role in structuring plant communities under current and increased N deposition. The aim of this dissertation was to investigate how N deposition varies at multiple scales depending on specific landscape drivers, such as site context and vegetation structure, and tease apart the effect of that heterogeneous N deposition on native and exotic competitive dynamics relative to multiple controlling factors. I quantified a gradient of N deposition across 6 oak savanna sites in north-central California. At the regional scale, sites closer to pollutant emissions received greater N deposition and sites in remote areas received less. At the local, within-site scale, the oak canopy was a hotspot of higher N deposition. The magnitude of the hotspot effect beneath oaks was not constant across the regional gradient, but rather oaks at the high end of the regional gradient received proportionally more N deposition than oaks at the low end of the gradient. This finding emphasized the importance of landscape context to within-site dynamics. The N deposition gradient was complex because several other soil and climate variables co-varied. Subsequent research was designed to experimentally tease apart the relative effect of N deposition on plant community dynamics from other factors that varied across this complex gradient, including soil type, which varied across the regional scale, and light availability, which varied between canopy and open areas at the local scale. A greenhouse experiment examined competitive interactions among native and exotic grasses in response to N fertilization, soil type, and light availability. Native and exotic grasses were both most sensitive to N deposition during the period of rapid vegetative growth in early spring. Invasive exotic grass was not becoming competitively dominant under increased N. Overall, N increased plant biomass, height, and seed mass altering the outcome of species interactions in a few cases, and thus, was important not as a single driving factor, but rather in the context of the other environmental factors I manipulated. This result indicated that N deposition must be considered together with the complex suite of environmental factors to predict effects to plant communities. In advancing our understanding of landscape and ecosystem ecology, the dissertation research highlighted the importance of landscape context and complex interactions among spatially and temporally heterogeneous factors in influencing dynamics within wildlands.