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CR 39:261-274 (2009)  -  DOI:

Tree phenology and carbon dioxide fluxes: use of digital photography for process-based interpretation at the ecosystem scale

H. E. Ahrends1,2,*, S. Etzold2, W. L. Kutsch3, R. Stoeckli4, R. Bruegger1, F. Jeanneret1, H. Wanner1, N. Buchmann2, W. Eugster2

1Institute of Geography, University of Bern, Hallerstrasse 12, 3012 Bern, Switzerland
2Institute of Plant Sciences, ETH Zurich, Universitaetsstrasse 2, 8092 Zurich, Switzerland
3Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Strasse 10, 07745 Jena, Germany
4Federal Office of Meteorology and Climatology MeteoSwiss, Climate Services, Climate Analysis, Kraehbuehlstrasse 58,
8044 Zurich, Switzerland

ABSTRACT: Vegetation phenology is an important indicator of climate change and climate variability and it is strongly connected to biospheric–atmospheric gas exchange. We aimed to evaluate the applicability of phenological information derived from digital imagery for the interpretation of CO2 exchange measurements. For the years 2005–2007 we analyzed seasonal phenological development of 2 temperate mixed forests using tower-based imagery from standard RGB cameras. Phenological information was jointly analyzed with gross primary productivity (GPP) derived from net ecosystem exchange data. Automated image analysis provided reliable information on vegetation developmental stages of beech and ash trees covering all seasons. A phenological index derived from image color values was strongly correlated with GPP, with a significant mean time lag of several days for ash trees and several weeks for beech trees in early summer (May to mid-July). Leaf emergence dates for the dominant tree species partly explained temporal behaviour of spring GPP but were also masked by local meteorological conditions. We conclude that digital cameras at flux measurement sites not only provide an objective measure of the physiological state of a forest canopy at high temporal and spatial resolutions, but also complement CO2 and water exchange measurements, improving our knowledge of ecosystem processes.

KEY WORDS: Phenology · Growing season · Digital camera · Image analysis · Gross primary productivity · Forest

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Cite this article as: Ahrends HE, Etzold S, Kutsch WL, Stoeckli R and others (2009) Tree phenology and carbon dioxide fluxes: use of digital photography for process-based interpretation at the ecosystem scale. Clim Res 39:261-274.

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