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Licentiate thesis, 2014

Long-term effects of nitrogen (N) fertilizer and simulated N deposition on boreal forest growth

From, Fredrik;

Abstract

The studies presented in this thesis aims to increase our understanding of the long-term effects of anthropogenic nitrogen (N) input via fertilization or atmospheric N deposition on tree growth in boreal forest. Firstly, I studied carry-over effects of forest fertilization between tree generations. Growth of 10 years old trees on sites fertilized during the previous tree generation was measured. On sites that were previously fertilized twice (25 and 33 years prior to the study), the young Norway spruce (Picea abies [L.] H. Karst.) and Scots pine (Pinus sylvestris L.) trees were 24% taller than trees on similar sites that were only fertilized once (25 years prior to the study) or on sites that had never been fertilized. Furthermore, the soil N mineralization rates were 3.7 times higher and the amount of available soil-N 2 times higher on sites that were previously fertilized twice than on other sites. Secondly, I studied the effects of low annual N addition simulating atmospheric N deposition on tree growth and variables linked to site fertility in two different forest ecosystems, i.e. on one P. abies dominated site and on one P. sylvestris dominated site. On the P. abies dominated site tree growth and needle N concentration were higher on plots treated with 12.5 and 50 kg N ha⁻¹ year⁻¹ than on control plots, which only received background N deposition (1 to 2 kg N ha⁻¹ year⁻¹). P. abies growth increased linearly with 2.5% for every kg of N added, which corresponded to a net sequestration of approximately 19 kg of C per kg N. On the P. sylvestris dominated site tree growth and needle N concentration increased only on plots with the 50 kg N ha⁻¹ year-1 treatment, whereas the low N addition treatments (3, 6 and 12.5 kg N ha⁻¹ year⁻¹) had no effect on tree growth. In conclusion, I present data suggesting that commercial forest fertilization can have long-term effects on site productivity and consequently tree growth in the tree generation following the one fertilized. I also show data that supports a positive tree growth response to N addition rates similar to those of atmospheric N deposition. However, further studies are needed of how tree growth in naturally nutrient poor P. sylvestris dominated forests respond to low annual N addition rates.

Keywords

Annual N addition; Carbon sequestration; Fertilization; Forest growth

Published in


ISBN: 978-576-9225-2, eISBN: 978-91-576-9226-9
Publisher: Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences

Authors' information

From, Fredrik
Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology

UKÄ Subject classification

Forest Science

URI (permanent link to this page)

https://res.slu.se/id/publ/54917