Tropical Forests in a CO2-Rich World

Abstract

Tropical forests resemble, besides their enormous genetic diversity, the single largest biomass carbon pool in the world. Only a ‘small’ annual increase of this pool could trap the current surplus of atmospheric CO2. The fact that this is not happening already today (after the world has seen a 27% increase in atmospheric CO2 in only 150 years) sets the boundaries of the likely trends to be expected in the future. In contrast to the possibly small overall responses of the tropical forest carbon pool, individual plant responses to CO2 enrichment will be significant. Since species and their genotypes will not respond in identical ways, selective processes will be induced which will lead to new community structures and alterations of numerous plant-plant, plant-animal and plant-microbe interactions. Examples are provided for such subtile CO2 effects, measured both in the greenhouse and in the field. From what is known currently it is concluded that in closed humid tropical forests leaf area index is unlikely to increase, mineral nutrient and water demand may (at least temporarily) become reduced, and leaf tissue quality plus associated consumer behavior will be altered. The big unknown is the behavior of tropical soils and their microflora and fauna. There is a realistic possibility that carbon turnover will be increased in tropical forests in a CO2-enriched world, which would have substantial implications for nutrient cycling.