Effects of Fertilization on Wood Formation in Naturally Regenerated Juvenile Silver Birch in a Norway Spruce Stand in South Sweden

Josefin A Nilsson,Åsa Blom,Charlotta Håkansson,Grace Jones,Johan Bergh

doi:10.3390/f12040415

Abstract

This study investigates wood density and anatomy of juvenile silver birch stems in Sweden, grown in mixed conifer stands. Our aim is to investigate if fertilization provides increased growth, as well as an eventual reduction in stem wood density. Measurements of basic density, ring width, cell wall thickness, and vessels are analyzed for 20 birch trees. Bark to pith radial sections are analyzed using a light microscope and the freeware ImageJ to compare treatments and ages. The results show that trees with fertilizer treatment have wider growth rings and thinner cell wall thickness compared to unfertilized trees. The fertilized trees also have a lower cambium age at the same height and the same diameter, and a slightly lower stem mean density (420 kg m−3) than the unfertilized stems (460 kg m−3). Fertilizer is a significant determinant of density and cell wall thickness in nonlinear models. The fertilized trees have increased growth and reached a fixed diameter earlier. The age difference between the trees likely explains some of the differences in cell wall thickness. This study supports the use of fertilizer as a silvicultural option for increasing the growth rate of silver birch for a relatively small reduction of wood density.

Highlights

Forests 2021, 12, 415. https://In recent years, fertilization has been highlighted as a potential method to improve tree growth in boreal forests, increasing biomass production and providing more raw material for the bio-economy [1]
Limited attention has been paid to the self-regenerated broadleaf tree species which occur naturally in these stands, such as silver birch (Betula pendula Roth.) and downy birch (Betula pubescens Ehrh.), which are common in Sweden
The average ring width was slightly lower in 2016 (3.3 mm for fertilized, and 2.2 mm for unfertilized) than for 2017 (3.8 mm and 2.5 mm), which shows that the average ring width increased by 0.5 mm for the fertilized and 0.3 mm for the unfertilized trees. 2015 had the widest average ring width for both the fertilized (3.5 mm) and the unfertilized (2.5 mm) trees out of all the years in

Summary

Introduction

Forests 2021, 12, 415. https://In recent years, fertilization has been highlighted as a potential method to improve tree growth in boreal forests, increasing biomass production and providing more raw material for the bio-economy [1]. Limited attention has been paid to the self-regenerated broadleaf tree species which occur naturally in these stands, such as silver birch (Betula pendula Roth.) and downy birch (Betula pubescens Ehrh.), which are common in Sweden. The majority of these birches are commonly removed during precommercial thinning operations and left to decay, even though their diameters are large enough for further industrial processing to produce, for example, furniture or engineered wood products (EWP) [2]. This difference in plant phenology means deciduous birches must build up their canopies annually, while the native conifers retain needles between growing seasons and likely have a longer response time to fertilizer [7,8]

Objectives

Methods

Results

Discussion

Conclusion