Skip to main content
SLU publication database (SLUpub)

Conference abstract2011

The Effect of Intensive Fertilization of Height Development in Young Unthinned Scots Pine (Pinus Sylvestris L.) Stands

Ulvcrona, Kristina; Ulvcrona, Thomas


Demands for forest biomass, mainly for use as biofuels and energy generation, have been rising for several years. Growth of trees are affected by environmental factors. For example, competition for light affects the allocation of growth along the stem, and competition for water and / or nutrients affects the overall growth rate [1, 2, 3, 4]. However, few studies have been investigating the effect of intensive fertilization on height development in young unthinned stands. Therefore the aim of this study was to determine the principal effect of fertilization on height development in young Scots pine trees (Pinus sylvestris L.). The hypothesis being that Scots pine trees from intensively fertilized unthinned stands have a higher both absolute and relative hight development than trees from unfertilized unthinned stands. Within this study, in all 101 trees from three field trials in Northern Sweden, investigating fertilization and spacing in young Scots pine dominated stands, were felled and measured. 68 trees from the unthinned treatment and 33 trees from the unthinned intensively fertilized treatment (100 kg ha-1 annually from 1997 onwards). Total height in spring 2009 and annual height growth ( topp shoot) for the years between 1999 and 2008 were measured with measuring tape. All investigated trees were within the same range of height in year 1999. Differences regarding total height year 2008, mean height year 1999 and annual height growth for years 2000 - 2008 were analyzed with standard GLM procedure. Used model was "site" and "treatment". Significantly higher total height increment was found for the intensively fertilized treatment during the investigated period. Fertilized trees had a 3% higher mean height (5.3 m) than unfertilized trees (5.2 m) at the start in the year 1999. After the growing season year 2008 fertilized trees mean height (9.45 m) was 12% higher than unfertilized trees (8.53 m).Generally during the period, the fertilized trees expressed both higher total and relative annual height increment than the control (Figure 1). Figure 1. Development of relative annual height increment for unfertilized (C) and intensively fertilized (c+F2) sites between years 2000 to 2008. The figure clearly describes both the overall trends that fertilization generally increases relative annual height when compared to control and that the difference in relative increment is higher during the first years of intensive fertilization than later in the cycle. Fertilized trees showed significantly higher relative height increment during all years except for the last year 2008 when the relative increment was the same as for unfertilized trees. Note that the fertilized trees then was significantly higher than unfertilized trees. In absolute values differences between treatments regarding height increment varied between 17% and 28%. Site had significant effect on relative height increment during the years 2000, 2002 - 2003 and 2005 - 2006. No apparent trend could be found explaining this when examining individual tree and site variables. However, variable site was not significant during years 2007 and 2008 when also the difference in relative height increment was the smallest. Total height and relative increment was as described above significantly higher in fertilized trees when compared to unfertilized thus supporting the hypothesis. Both the absolute and relative difference between treatments was largest in the beginning of the studied period and then generally decreased over time. This pattern indicates that the studied net effect of the intensive fertilization on height development is a result of interactions not included in this study. This is interesting and in need of further studies since the literature describing these and other related growth factors in very young dense stands is sparse. The effect of site was significant in only 5 of the 9 years included within the study. Probably will future studies using the combination of this type of data together with information concerning climatic and soil interactions be useful for development of more knowledge regarding tree and stand height development. Many studies have been investigating height development in young stands in relation to pre-commercial thinning and recent studies include those by [5] and [6]. The general conclusion from these and earlier studies is that the mean height is likely to decline with higher stem densities due to a higher number of suppressed trees in the stand. The results presented here indicates that fertilization is a treatment that increases site index and thus might allow development of silvicultural management schedules that can use higher stem densities without as pronounced negative effects on stand height development. 1 Cannell, M.G.R., Rothery, P. & Ford, E.D. 1984 Competition within stands of Picea sitchensis and Pinus contorta. Ann. Bot. 53: 349-362. 2 Nilsson, U. and Albrektson, A. 1993 Productivity of needles and allocation of growth in young Scots pine trees of different competitive status. For. Ecol. Manag. 62: 173-187. 3 Nilsson, U. and Gemmel, P. 1993 Changes in growth and allocation of growth in young Scots pine and Norway spruce due to competition. Scand. J. For. Res. 8(2): 213-223. 4 Nilsson, U. 1994 Development of growth and stand structure in Norway spruce stands planted with different initial densities. Scand. J. For. Res. 9: 135-142 5 Ruha, T. and Varmola, M. 1997 Precommercial thinning in naturally regenerated Scots pine stands in Northern Finland. Silva Fenn. 31(4): 401-415. 6 Varmola, M. and Salminen, H. 2004 Timing and intensity of pre-commercial thinning in Pinus sylvestris stands. Scand. J. For. Res. 19: 142-151.


biomass, tree height, fertilization, young stands

Published in

Rapport fra Skog og landskap
2011, number: 14, pages: 49-50 Title: Forest Management and Silviculture in the North - Balancing Future Needs : Book of abstracts for the conference in Stjørdal, Norway, September 6-8, 2011
ISBN: 978-82-311-0136-9
Publisher: Skog + Landskap, Norsk Institutt for skog og landskap


Forest Management and Silviculture in the north-balancing future needs