© 2007 Heron Publishing—Victoria, Canada
Drying and wetting of Mediterranean soils stimulates decomposition and carbon dioxide emission: the “Birch effect”
Paul Jarvis (1, 2), Ana Rey (1, 3), Charalampos Petsikos (1), Lisa Wingate (1), Mark Rayment (1), João Pereira (4), João Banza (4), Jorge David (4), Franco Miglietta (5), Marco Borghetti (6), Giovanni Manca (7) and Riccardo Valentini (7)
1. School of GeoSciences, The University of Edinburgh, The King’s Buildings, West Mains Road, Edinburgh, EH9 3JN, Scotland, U.K. / 2. Corresponding author (margaretsjarvis@aol.com) / 3. Present address: Department of Desertification and Geoecology, Estacion Experimental de Zonas Aridas (EEZA-CSIC), General
Segura 1, Almeria 04001, Spain / 4. Instituto Superior de Agronomia, Lisbon, Portugal / 5. Institute of Biometeorology, IBIMET, P. le della Cascine 18, 50144, Firenze, Italy / 6. Department of Crop, Forest and Environmental Sciences, University of Basilicata, v. le dell’Ateneo Lucano 10, Potenza, Italy / 7. Department of Forest Science and Environment, University of Tuscia, Viterbo, Italy / Received November 27, 2006; accepted December 1, 2006; published online April 2, 2007
Summary
Observations on the net carbon exchange of forests in the European Mediterranean region, measured recently by the eddy covariance
method, have revived interest in a phenomenon first characterized on agricultural and forest soils in East Africa in the 1950s
and 1960s by H. F. Birch and now often referred to as the “Birch effect.” When soils become dry during summer because of lack
of rain, as is common in regions with Mediterranean climate, or are dried in the laboratory in controlled conditions, and
are then rewetted by precipitation or irrigation, there is a burst of decomposition, mineralization and release of inorganic
nitrogen and CO2. In forests in Mediterranean climates in southern Europe, this effect has been observed with eddy covariance techniques and
soil respiration chambers at the stand and small plot scales, respectively. Following the early work of Birch, laboratory
incubations of soils at controlled temperatures and water contents have been used to characterize CO2 release following the rewetting of dry soils. A simple empirical model based on laboratory incubations demonstrates that
the amount of carbon mineralized over one year can be predicted from soil temperature and precipitation regime, provided that
carbon lost as CO2 is taken into account. We show that the amount of carbon returned to the atmosphere following soil rewetting can reduce significantly
the annual net carbon gain by Mediterranean forests.
Keywords:
carbon balance, carbon mineralization rates, Mediterranean climate, Mediterranean forest, rain pulse, soil rewetting, soil
temperature, soil water, summer rainfall events.
