Nitrogen deposition and forest expansion in the northern Great Plains

摘要: 1 Atmospheric nitrogen (N) deposition has become one of the most important agents vegetation change in densely populated regions, It may also contribute to forest expansion into grasslands at northern edge North American Great Plains. 2 We measured N and available soil with ion-exchange resin over years six national parks areas varying population density industrialization. was significantly higher four regions than two remote parks. 3 Available increased across all 4 mass N-15 abundance (delta N-15) parks: Elk Island, receiving 22 kg ha(-1) year(-1), Jasper, 8 year(-1). Differences between tissue concentrations were small, but five decades resulted increasing by 74% Island only 26% Jasper. delta lower suggesting that anthropogenic sources high rates entering ecosystem. 5 determined rate within using aerial photographs, Parks aspen parkland boreal showed a strong positive relationship deposition. The relationships found deposition, suggest even comparatively low accelerate temperate grasslands.