Through enhanced tree dynamics carbon dioxide enrichment may cause tropical forests to lose carbon.
The fixation and storage of C by tropical forests, which contain close to half of the globe's biomass C, may be affected by elevated atmospheric CO2 concentration. Classical theoretical approaches assume a uniform stimulation of photosynthesis and growth across taxa. Direct assessments of the C balance either by flux studies or by repeated forest inventories also suggest a current net uptake, although magnitudes sometimes exceed those missing required to balance the global C cycle. Reasons for such discrepancies may lie in the nature of forest dynamics and in differential responses of taxa or plant functional types. In this contribution I argue that CO2 enrichment may cause forests to become more dynamic and that faster tree turnover may in fact convert a stimulatory effect of elevated CO2 on photosynthesis and growth into a long-term net biomass C loss by favouring shorter-lived trees of lower wood density. At the least, this is a scenario that deserves inclusion into long-term projections of the C relations of tropical forests. Species and plant functional type specific responses ('biodiversity effects') and forest dynamics need to be accounted for in projections of future C storage and cycling in tropical forests.
Körner
Christian
C
Institute of Botany, University of Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland. ch.koerner@unibas.ch
D044822:Biodiversity; D018533:Biomass; D002244:Carbon / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D008954:Models, Biological; D010788:Photosynthesis / Q000502:physiology; D018521:Plant Physiological Phenomena; D014197:Trees; D014329:Tropical Climate; D014867:Water / Q000502:physiology; D014934:Wood
D014867:Water; D002245:Carbon Dioxide; D002244:Carbon