Responses of Englemann spruce forests to nitrogen fertilization in the Colorado Rocky Mountains

Ecological Applications
By: , and 



Two old-growth coniferous forests in Colorado with differing initial soil conditions responded differently to four years of low-level fertilization with ammonium nitrate. The site (Fraser) with an average initial organic horizon soil C:N ratio of 36 and nitrogen (N) pool of 605 kg/ha showed no significant increase in net N mineralization rates. At the Fraser site, foliar and organic horizon soil percentage N increased significantly. In contrast, N mineralization rates and inorganic soil N increased significantly at the site (Loch Vale) with greater soil N (C:N of 24, N pool of 991 kg/ha), while foliar N and soil percentage N in the organic layer did not change. We predict continued fertilization at Fraser will narrow the soil C:N ratio to a point where increases in biogeochemical N cycling and fluxes will be detected. Additional N inputs to the site with already low soil C:N ratios will enhance N mineralization rates and leaching losses. The coniferous forests at Fraser and Loch Vale are similar in species composition, stand age, substrate, aspect, and climate. The differences in soil conditions strong enough to cause contrasting responses to fertilization could be due to differences in atmospheric N deposition. Regardless of the reason, the size of the organic soil N pool and C:N ratio of mature coniferous forests in Colorado controls the responsiveness of N pools and fluxes to fertilization, and even low levels of fertilization are sufficient to initiate measurable biogeochemical changes.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Responses of Englemann spruce forests to nitrogen fertilization in the Colorado Rocky Mountains
Series title Ecological Applications
DOI 10.1890/1051-0761(2003)013[0664:ROESFT]2.0.CO;2
Volume 13
Issue 3
Year Published 2003
Language English
Publisher Wiley
Contributing office(s) Fort Collins Science Center
Description 10 p.
First page 664
Last page 673
Country United States
State Colorado
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