Open AccessNitrogen deposition across scales: hotspots and gradients in a California savanna landscape
Author(s) -
Tulloss Elise M.,
Cadenasso Mary L.
Publication year - 2015
Publication title -
ecosphere
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.255
H-Index - 57
ISSN - 2150-8925
DOI - 10.1890/es14-00440.1
Subject(s) - spatial ecology , deposition (geology) , environmental science , grassland , ecology , spatial variability , spatial heterogeneity , physical geography , ecosystem , vegetation (pathology) , temporal scales , landscape ecology , context (archaeology) , geography , hydrology (agriculture) , habitat , geology , biology , medicine , statistics , mathematics , geotechnical engineering , archaeology , pathology , sediment , paleontology
Nitrogen (N) deposition is a key component of global change. In order to predict the consequences of those changes, the spatial and temporal patterns of N deposition need to be quantified. We investigated patterns of inorganic‐N deposition across two spatial scales—regional and local—in six oak savanna sites across north‐central California during the 2008–2009 wet season. We found a regional‐scale deposition gradient in which sites closer to urban and agricultural sources received higher rates of deposition than more remote sites. Additionally, sites closer to urban sources received a greater proportion of N as NO 3 − ‐N. At the local, within‐site scale, canopy understories received greater N inputs compared to the adjacent open grassland. Temporal heterogeneity in N deposition was also found. Deposition exhibited a strong seasonal pattern, corresponding to the distinct wet‐dry cycles characteristic of this Mediterranean ecosystem. While these spatial and temporal results were expected, it was surprising that the magnitude of the hotspot effect under oaks changed across the regional gradient. At the high deposition end of the regional gradient proportionally more N was received beneath canopies than at the low end of the gradient. This nonlinearity between local and regional scales demonstrates the importance of landscape context for understanding within‐site dynamics and the need for multi‐scalar research approaches. Incorporating regional‐scale landscape context and local‐scale vegetation structure, as well as temporal variability, into our understanding of deposition patterns is crucial for monitoring efforts as well as addressing potential ecological effects of increased N deposition.