Fine roots of overstory Norway spruce (Picea abies):

I Catalin Petritan,B Von Lupke,A M Petritan

doi:10.5424/fs/20112003-11136

Abstract

The horizontal and vertical distribution of live fine roots (diameter < 2 mm) of overstory Norway spruce [Picea abies (L.) Karst.] and their influence on diameter and height growth of underplanted beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) saplings were studied on experimental plots in the Solling Mountains (Germany). The aims of this study were to investigate how overstory fine root density varies with stand density, and how it influences growth of the underplanted saplings to changes in belowground resources availability in connection with simultaneously changing light availability. Most fine roots were concentrated in the humus layer (more than 45%) and in the top mineral soil (0-5 cm, about 15%). Fine root biomass increases with overstory basal area and decreases with rising distance from the nearest overstory tree, reaching about zero within ca. 8 m distance. Over the whole two-year study period, light availability alone was the decisive factor for growth of the beech saplings (5 resp. 6 years of age) while growth of the Douglas-fir saplings in the first study year (6 years of age) was additionally affected by a shortage of belowground resources due to root competition in a season with less than average rainfall. This species-specific response of underplanted saplings to changes in above and belowground resources is of silvicultural importance for the establishment of a mixed stand beneath a mature canopy: the more sensitive Douglasfir should be planted on the central parts of openings with little or none belowground competition while the less sensitive beech can be placed below the denser parts of the overstory.

Highlights

As a consequence of the high susceptibility of pure Norway spruce [Picea abies (L.) Karst.] stands to abiotic and biotic stress factors (Spiecker et al, 2004), the conversion into mixed stands has gained an increasing importance in Central Europe over the last decades (Lüpke et al, 2004)
In the present study we investigated the vertical and horizontal variation of fine root parameters of Norway spruce in two cutting types —target diameter and strip cutting— with the following objectives: (1) To describe the relationship between overstory fine root biomass and measurable aboveground characteristics
A large-scale and long-term research experiment with various logging and regeneration treatments – established in autumn 2003 by the Northwest German Forest Research Station in Göttingen to test different methods in converting pure Norway spruce stands into mixed stands —offered the opportunity to carry out the planned investigation on the interaction between above— and belowground resources availability

Summary

Introduction

As a consequence of the high susceptibility of pure Norway spruce [Picea abies (L.) Karst.] stands to abiotic and biotic stress factors (Spiecker et al, 2004), the conversion into mixed stands has gained an increasing importance in Central Europe over the last decades (Lüpke et al, 2004). For this purpose, beech (Fagus sylvatica L.) and other native or non-native species with high adaptive and productive capability such as Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] are often planted under the canopy of Norway spruce stands (Weihs and Klaene, 2000; Lüpke, 2004, 2009). Whereas the effect of light interception has been widely studied, the influence on belowground resources remains poorly investigated several studies described a strong belowground competition between overstory and understorey vegetation for water and nutrients (Riegel et al, 1992; Walters and Reich, 1997; Lindh et al, 2003; Machado et al, 2003)

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Conclusion