Below-ground response of Norway spruce to climate conditions at Mt. Brocken (Germany)—A re-assessment of Central Europe's northernmost treeline

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Abstract

Alpine treelines at medium high mountains are less abundant and thus have been less frequently studied than at high-elevation mountain ranges of the world. We studied mature Norway spruce stands along an extended elevation transect at Mt. Brocken (Harz Mountains, Central Germany) to analyse the altitudinal changes in climate-related growth conditions, and to evaluate the prevailing climate conditions at the treeline of medium high Mt. Brocken. A particular aim was to analyse the change in fine root biomass partitioning along the transect towards the treeline. Microclimate conditions at the treeline of Mt. Brocken were very similar to other treeline sites worldwide. Tree height and stem biomass strongly decreased from middle elevations towards the treeline. On the contrary, fine root biomass and the ratio of fine root/stem biomass strongly increased towards the treeline indicating a marked shift in carbon allocation in favour of the fine root system with elevation. A meta-analysis of literature data revealed that the elevation-related increase in dry mass partitioning to the fine root system is a general phenomenon for Norway spruce stands in northern and central European mountains. We conclude that the particularly large fine root system of Norway spruce at cold sites represents a mechanism to cope with unfavourable soil conditions such as reduced or temporally variable nutrient supply.

Introduction

Alpine treelines are most abundant in the world's large high-elevation mountain ranges as well as at lower elevations in the boreal regions of the southern and northern hemisphere. Accordingly, the vast majority of studies on alpine treelines were conducted in those regions (see reviews by Wieser and Tausz, 2007, Holtmeier, 2009). In contrast, alpine treelines at medium high mountains are less abundant and thus less frequently studied (e.g. the medium high mountains in Northeast America: Cogbill and White, 1991, Richardson et al., 2004). In Central Europe, only few medium high mountains exist apart from the high-elevation Alps and the Carpathian Mountains that show summits currently free of forest vegetation. Many of these treelines are thought to be anthropogenic rather than climate-driven (e.g. Hermes, 1955). Mount Brocken (1142 m a.s.l.) in the Harz Mountains – the northernmost medium high mountain range in Central Europe – shows a treeline built by Norway spruce (Picea abies). Though some authors have stated that this treeline might be natural (climate-driven), detailed analyses of the prevailing climate conditions and comparisons of the forest vegetation to other alpine treeline sites are still missing to confirm this assessment.

The obvious change in tree height and above-ground forest structure with elevation and near the alpine treeline has over decades stimulated a large number of investigations on the treeline formation (cf. reviews by Troll, 1973, Tranquillini, 1979, Körner, 2003, Wieser and Tausz, 2007, Holtmeier, 2009). Nevertheless, the ecological reasons for the formation of alpine treelines are still not fully understood. Traditionally, the marked decrease in tree height and above-ground tree biomass upslope towards the alpine treeline has been attributed to a reduced carbon gain due to a limitation in photosynthetic activity and/or an imbalance of annual C fixation vs. respiratory losses under the prevailing cold conditions. Other authors have emphasized the effects of strong winds, blowing ice, large snow charge, or winter drought for the formation of the alpine treeline (data reviewed by Stevens and Fox, 1991, Körner, 1998, Körner, 2003, Sveinbjörnsson, 2000, Grace et al., 2002, Holtmeier, 2009). More recent studies by Körner and co-workers have suggested that tree growth at (and above) the alpine treeline might not be source (carbon assimilates) but rather sink limited by reduced metabolic activity of the C allocation (Hoch et al., 2002, Hoch and Körner, 2003, Hoch and Körner, 2005, Shi et al., 2006, Patty et al., in press). Studies by these authors moreover revealed that the elevational position of alpine treelines worldwide coincides with a mean growing season root zone (10 cm soil depth) temperature of 6.7 °C (Körner and Paulsen, 2004). They conclude that the cold root zone temperatures bring about impaired root growth conditions that might significantly account for the adverse tree growth conditions at the alpine treeline (Körner, 1998, Körner, 2003).

In contrast to the large number of studies on the response of the above-ground tree organs to environmental conditions near the alpine treeline, effects of those conditions on the tree root system have been only occasionally studied. Elevational transect studies at boreal, temperate and tropical treeline sites have given evidence that high-elevation forest stands might be worldwide characterized by a particularly high fine root biomass (Kitayama and Aiba, 2002, Leuschner et al., 2007, Hertel and Wesche, 2008, Hertel et al., 2008). This phenomenon is in marked contrast to the response in above-ground tree compartments to the prevailing growth conditions at the alpine treeline and do not support the hypothesis of thermal constraints of root growth activity. However, it is not proven so far whether the fine root system of trees at treelines at medium high mountain ranges responds similarly.

We investigated four mature Norway spruce stands along an extended elevation transect at the northern hillside of Mt. Brocken (Harz Mountains, Germany). The stands were located at altitudes ranging from 390 to 1100 m a.s.l. with the highest stand representing the upper treeline at Mt. Brocken. We aim in our study (i) to investigate the elevational changes in various climatic parameters of Norway spruce stands along the transect, (ii) to thereby verifying the climatic status of the current elevational position of the treeline at Mt. Brocken, (iii) to analyse how the changing growth conditions along the transect affect the fine root biomass of the spruce stands, and (iv) to examine if a general dependence of the standing fine root biomass on elevation exists in Picea abies stands in central and northern Europe.

Section snippets

Location of the study sites

The study was conducted at the northern hillside of Mount Brocken (1142 m a.s.l., 51°48′N, 10°37′E), the highest peak of the Harz mountain range in Central Germany. Four mature stands of Norway spruce (Picea abies (L.) Karst.) were selected along an elevational transect spanning from the mountain basis near Ilsenburg town (ca. 300 m a.s.l., 51°52′N, 10°41′E) up to Mt. Brocken. The four stands were located at 390, 790, 990, and 1100 m a.s.l. with the uppermost forest stand (at 1100 m) representing

Microclimate of the spruce stands

Mean annual air temperature inside the forests decreased with elevation from 6.9 °C in the lowermost spruce stand to 2.1 °C in the treeline stand (Table 1). Air temperature minima also decreased along the elevational transect with the treeline stand experiencing a ca. 4 K lower minimum than the lowermost stand. Similarly, mean annual soil temperature at 10 cm soil depth as well as mean soil temperature during the growing season decreased linearly with elevation (Table 1). The altitudinal change in

Climate conditions of the spruce stands at Mt. Brocken: is there evidence for a natural treeline?

While the presence of natural (i.e. climate-driven) treelines at the prominent large high-elevation mountain ranges of the world (such as the Himalayas, Andes, or the Rocky Mountains) as well as at low-elevation sites at high latitudes are widely recognized, the natural status of treelines in medium high mountains has been the issue of a controversial debate from early decades to date. In Central Europe, this is particularly true for several medium high mountains that currently show treeline

Acknowledgements

We want to thank the national park administration for the permission to conduct the study in the Harz National Park. We are very grateful in particular to Gunter Karste for his skillful support of the study site selection. We thank Mechthild Stange and Marina Röderstein for their help of the soil sampling in the field. The contribution of Felix Norman to the analysis of the measured temperature data is also gratefully acknowledged.

References (104)

  • I. Schmid et al.

    Root distribution of Norway spruce in monospecific and mixed stands on different soils

    For. Ecol. Manage.

    (2002)
  • P.L. Shi et al.

    End of season carbon supply status of woody species near the treeline in western China

    Bas. Appl. Ecol.

    (2006)
  • E. Aichinger

    Die Waldverhältnisse Südbadens, eine pflanzensoziologische Studie

    (1937)
  • C. Ammer et al.

    An approach for modelling the mean fine-root biomass of Norway spruce stands

    Trees

    (2005)
  • R.G. Barry

    Mountain Weather and Climate

    (1981)
  • M. Beniston

    Future extreme events in European climate: an exploration of regional climate model projections

    Climatic Change

    (2007)
  • Beug, H.-J., Henrion, I., Schmüser, A., 1999. Landschaftsgeschichte des Hochharzes. Papierflieger,...
  • A.J. Bloom et al.

    Resource limitation in plants – an economic analogy

    Ann. Rev. Ecol. Syst.

    (1985)
  • A. Bolte et al.

    Interspecific competition impacts on the morphology and distribution of fine roots in European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.)

    Eur. J. For. Res.

    (2006)
  • W. Borken et al.

    Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands

    Plant Soil

    (2007)
  • H. Brockmann-Jerosch
    (1919)
  • A. Clemensson-Lindell et al.

    Fine-root vitality in a Norway spruce stand subjected to various nutrient supplies

    Plant Soil

    (1995)
  • C.V. Cogbill et al.

    The latitude-elevation relationship for spruce-fir forest and treeline along the Appalachian mountain chain

    Vegetatio

    (1991)
  • R.M.M. Crawford

    Ecological hazards of oceanic environments

    New Phytol.

    (2000)
  • A. Dengler

    Die Horizontalverbreitung der Fichte

    Mitt. forstl. Versuchsw. Preußens

    (1912)
  • A. Dengler

    Die Wälder des Harzes einst und jetzt

    Zeitschr. Forst- Jagdw.

    (1913)
  • Deutscher Wetterdienst, 2005. Monatliche Witterungsberichte 2005, Witterungsreport “Express”. Deutscher Wetterdienst,...
  • J. Doležal et al.

    Altitudinal changes in composition and structure of mountain-temperate vegetation: a case study from the Western Carpathians

    Plant Ecol.

    (2002)
  • J. Eichhorn

    Vergleichende Untersuchungen von Feinwurzelsystemen bei unterschiedlich geschädigten Altfichten (Picea abies Karst.)

    Forschungsber. Hessischen Forstl. Versuchsanstalt

    (1987)
  • F. Fankhauser

    Der oberste Baumwuchs

    Schweizer. Zeitschr. Forstw.

    (1901)
  • L. Finér

    Biomass and nutrient cycle in fertilized and unfertilized pine, mixed birch and pine and spruce stands on a drined mire

    Acta Forest. Fenn.

    (1989)
  • L. Finér

    Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

    Plant Biosys.

    (2007)
  • F. Firbas et al.

    Über die Bestimmung der Walddichte und der Vegetation waldloser Gebiete mit Hilfe der Pollenanalyse

    Planta

    (1934)
  • F. Firbas et al.

    Untersuchungen über die Entstehung der heutigen Waldstufen in den Sudeten

    Planta

    (1949)
  • F. Firbas et al.

    Untersuchungen zur jüngeren Vegetationsgeschichte im Oberharz

    Planta

    (1939)
  • M.C. Fisk et al.

    Nitrogen mineralization and microbial biomass nitrogen dynamics in three alpine tundra communities

    Soil Sci. Soc. Am. J.

    (1995)
  • D. Gaul et al.

    Effects of experimental frost on the fine root system of mature Norway spruce

    J. Plant Nutr. Soil Sci.

    (2008)
  • M. Genenger et al.

    Fine root growth and element concentrations of Norway spruce as affected by wood ash and liquid fertilisation

    Plant Soil

    (2003)
  • T.J. Givnish

    On the Economy of Plant Form and Function

    (1984)
  • D.L. Godbold et al.

    Root turnover and root necromass accumulation of Norway spruce (Picea abies) are affected by soil acidity

    Tree Physiol.

    (2003)
  • J.R. Gosz et al.

    Seasonal and annual variation in nitrogen mineralization and nitrification along an elevational gradient in New Mexico

    Biogeochemistry

    (1986)
  • J. Grace

    Plant Response to Wind

    (1977)
  • J. Grace et al.

    Impacts of climate change on the tree line

    Ann. Bot.

    (2002)
  • F.-K. Hartmann et al.
    (1970)
  • H.-S. Helmisaari et al.

    Fine root biomass in relation to site and stand characteristics in Norway spruce and Scots pine stands

    Tree Physiol.

    (2007)
  • K. Hermes
    (1955)
  • Hertel, D., 1999. Das Feinwurzelsystem von Rein- und Mischbeständen der Rotbuche: Struktur, Dynamik und...
  • D. Hertel et al.

    A comparison of four different fine root production estimates with ecosystem carbon balance data in a Fagus-Quercus mixed forest

    Plant Soil

    (2002)
  • D. Hertel et al.

    Tropical-moist Polylepis stands at the treeline in E-Bolivia: the effect of elevation on above- and below-ground structure, and regeneration

    Trees

    (2008)
  • D. Hertel et al.

    Above- and below-ground response of Nothofagus pumilio to growth conditions of the transition from the steppe-forest boundary to the alpine treeline in S Patagonia (Argentina)

    Plant Ecol. Divers.

    (2008)
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