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Nitrogen (N) is a critical limiting nutrient that regulates plant productivity and the cycling of other essential elements in forests. We measured foliar and soil nutrients in 22 young Douglas-fir stands in the Oregon Coast Range to examine patterns of nutrient availability across a gradient of N-poor to N-rich soils. N in surface mineral soil ranged from 0.15 to 1.05% N, and was positively related to a doubling of foliar N across sites. Foliar N in half of the sites exceeded 1.4% N, which is considered above the threshold of N-limitation in coastal Oregon Douglas-fir. Available nitrate increased five-fold across this gradient, whereas exchangeable magnesium (Mg) and calcium (Ca) in soils declined, suggesting that...
Categories: Publication; Types: Citation; Tags: Ecosystems
This review article describes vectors for nitrogen and phosphorus delivery to riparian zones in semiarid African savannas, the processing of nutrients in the riparian zone and the effect of disturbance on these processes. Semiarid savannas exhibit sharp seasonality, complex hillslope hydrology and high spatial heterogeneity, all of which ultimately impact nutrient fluxes between riparian, upland and aquatic environments. Our review shows that strong environmental drivers such as fire and herbivory enhance nitrogen, phosphorus and sediment transport to lower slope positions by shaping vegetative patterns. These vectors differ significantly from other arid and semiarid ecosystems, and from mesic ecosystems where the...
Categories: Publication; Types: Citation; Tags: Ecosystems
This map layer shows Omernik's Level III ecoregions, derived from a 1:7,500,000 map created by J.M. Omernik in 1987 and from refinements of Omernik's framework that were made for other projects. Ecoregions describe areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources. Omernik's ecoregions are based on the premise that a hierarchy of ecological regions can be identified through the analysis of the patterns and the composition of both living and nonliving phenomena, such as geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology, that affect or reflect differences in ecosystem quality and integrity. All the characteristics are considered...

map background search result map search result map Omernik's Level III Ecoregions of the Continental United States Omernik's Level III Ecoregions of the Continental United States