Papers by Christian Körner
Trends in Ecology & Evolution
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Ecology Letters, 2015
The tendency of trees to grow taller with increasing water availability is common knowledge. Yet ... more The tendency of trees to grow taller with increasing water availability is common knowledge. Yet a robust, universal relationship between the spatial distribution of water availability and forest canopy height (H) is lacking. Here, we created a global water availability map by calculating an annual budget as the difference between precipitation (P) and potential evapotranspiration (PET) at a 1-km spatial resolution, and in turn correlated it with a global H map of the same resolution. Across forested areas over the globe, Hmean increased with P-PET, roughly: Hmean (m) = 19.3 + 0.077*(P-PET). Maximum forest canopy height also increased gradually from ~ 5 to ~ 50 m, saturating at ~ 45 m for P-PET > 500 mm. Forests were far from their maximum height potential in cold, boreal regions and in disturbed areas. The strong association between forest height and P-PET provides a useful tool when studying future forest dynamics under climate change, and in quantifying anthropogenic forest disturbance.
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Advances in Global Change Research, 2005
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Science
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Biologie in unserer Zeit, 2008
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Frontiers in plant science, 2014
Temperate climates are defined by distinct temperature seasonality with large and often unpredict... more Temperate climates are defined by distinct temperature seasonality with large and often unpredictable weather during any of the four seasons. To thrive in such climates, trees have to withstand a cold winter and the stochastic occurrence of freeze events during any time of the year. The physiological mechanisms trees adopt to escape, avoid, and tolerate freezing temperatures include a cold acclimation in autumn, a dormancy period during winter (leafless in deciduous trees), and the maintenance of a certain freezing tolerance during dehardening in early spring. The change from one phase to the next is mediated by complex interactions between temperature and photoperiod. This review aims at providing an overview of the interplay between phenology of leaves and species-specific freezing resistance. First, we address the long-term evolutionary responses that enabled temperate trees to tolerate certain low temperature extremes. We provide evidence that short term acclimation of freezing ...
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Alpine Botany, 2014
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Biologie in unserer Zeit, 2014
ABSTRACT Die kältebedingte obere oder polare Verbreitungsgrenze von Bäumen folgt global einer ers... more ABSTRACT Die kältebedingte obere oder polare Verbreitungsgrenze von Bäumen folgt global einer erstaunlich gleichförmigen Isotherme, unabhängig davon, ob die Wachstumsperiode drei oder 12 Monate dauert und ob es das Phänomen Winter gibt oder nicht. Diese potenzielle, biologische Lebensformgrenze lässt sich über Klimadaten vorhersagen und hat nichts mit der zufälligen, störungsbedingten lokalen Abwesenheit von Bäumen an dieser Grenze zu tun. Der aufrechte Wuchs zwingt Bäumen die Temperatur der freien Atmosphäre auf, während kleinwüchsige alpine Pflanzen von der Wärme in der bodennahen Luft profitieren. Physiologisch sind diese viel höher steigenden Arten nicht robuster als Bäume.Why are there alpine and polar treelines?The low temperature, high elevation or polar range limit of trees falls at a surprisingly uniform global isotherm, irrespective of whether the growing season lasts 3 or 12 month, or whether 'winter phenomena' occur or not. This potential 'life-form' limit is predictable from climate data and is not to be confused with random, disturbance effects that may cause the local absence of trees from that boundary. The upright stature of trees exposes them to free atmospheric circulation, whereas small stature alpine plants profit from the warmer conditions near the ground, the reason why these plants can reach much higher elevations than trees. Physiologically, these plants are not more robust than trees.
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The anthropogenic rise in atmospheric CO2 is expected to impact carbon fluxes not only at ecosyst... more The anthropogenic rise in atmospheric CO2 is expected to impact carbon fluxes not only at ecosystem level but also at the global scale by altering carbon cycle processes in soils. At the Swiss Canopy Crane (SCC), we examined how 7 years of free air CO2 enrichment (FACE) affected soil CO2 dynamics in a c. 100-year-old mixed deciduous forest. The use of 13C-depleted CO2 for canopy enrichment allowed us to trace the flow of recently fixed carbon (C). In the seventh year of growth at ~550 ppm CO2, soil respiratory CO2 consisted of 39% labelled C. During the growing season, soil air CO2 concentration was significantly enhanced under CO2-exposed trees. However, elevated CO2 failed to stimulate cumulative soil respiration (Rs) over the growing season. We found periodic reductions as well as increases in instantaneous rates of Rs in response to elevated CO2, depending on soil temperature and soil volumetric water content (VWC; significant 3-way interaction). During wet periods, soil water s...
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Trees, 1995
... 9 Springer-Verlag 1995 Increase in tree-ring width in subalpine Pinus cembra from the central... more ... 9 Springer-Verlag 1995 Increase in tree-ring width in subalpine Pinus cembra from the central Alps that may be CO2-related Kurt Nicolussi*, Sigmar Bortenschlager, Christian K~irner** Institut ftir Botanik, Universit[it Innsbruck, Sternwartestrasse 15, A-6020 Innsbruck, Austria ...
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Plant Ecology & Diversity, 2011
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Plant and Soil, 1996
... Pascal A. Niklaus and Christian K6rner Institute of Botany, University of Basel, SchOnbeinstr... more ... Pascal A. Niklaus and Christian K6rner Institute of Botany, University of Basel, SchOnbeinstrasse 6, CH-4056 Basel, Switzerland* ... storage structures (which was not found) and used for enhanced regrowth in the next year (which also was not observed; Sch~ippi and KOrner, pers ...
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Oikos, 2001
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Oikos, 2005
ABSTRACT The effect of low host plant nitrogen (N) content on herbivore performance has rarely be... more ABSTRACT The effect of low host plant nitrogen (N) content on herbivore performance has rarely been studied together with the herbivore's feeding behaviour. We explored this relationship with juvenile Omocestus viridulus (Orthoptera: Acrididae) grasshoppers using fertilized and unfertilized host grasses. Due to lower growth rates, grasshoppers reared on N-poor grasses exhibited slightly prolonged development and smaller adult size, while mortality was similar among the fertilizer treatments. This was found both in the laboratory and in outdoor cages under natural climatic conditions. A parallel analysis of feeding behaviour revealed that the grasshoppers counterbalance N shortage by compensatory feeding, and are capable of selectively feeding among grasses of contrasting nutritional quality when given a choice. This indicates a striking ability of O. viridulus to regulate nutrient intake in the face of imbalanced food sources. Although the species exploits a relatively very poor autotroph nutrient base in the wild, as underpinned by N analysis of natural host grasses and grasshopper tissue, our data suggest that natural food quality imposes no relevant constraint on the herbivore's performance. Our study thus challenges the importance of simple plant-mediated control of herbivore populations, such as N limitation, but supports the view that herbivores balance their intake of N and energy.
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Oecologia, 1996
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Papers by Christian Körner