The importance of low atmospheric CO2 and fire in promoting the spread of grasslands and savannas

摘要: The distribution and abundance of trees can be strongly affected by disturbance such as fire. In mixed tree/grass ecosystems, recurrent grass-fuelled fires suppress tree saplings therefore control dominance. We propose that changes in atmospheric [CO2] could influence cover metastable ecosystems altering their postburn recovery rates relative to flammable herbaceous growth forms grasses. Slow sapling at low would favour the spread grasses a reduction cover. To test possible importance [CO2]/fire interactions, we first used Dynamic Global Vegetation Model (DGVM) simulate biomass grassy South Africa with without results indicate fire has major effect under higher rainfall conditions suggesting an important role for fire/[CO2] interactions. then demographic model effects on mesic savanna grass/tree differences rates. adjusted grass according DGVM output net primary production different current conditions. simulations predicted elimination typical last glacial period (180 ppm) because rate is too slow (15 years) grow fire-proof size ca. 3 m. Simulated produce adequate fuel load burn only 2 years. Simulations preindustrial (270 ppm) predict occurrence but densities. greatest increase occurs from (360 ppm). are consistent palaeo-records which disappeared sites currently savannas glacial. Savanna reappeared Holocene. There also been large over 50–100 years. suggest after fire, rather than differential photosynthetic efficiencies C3 C4 plants, might have significant factor Late Tertiary grasslands open, high light environments prerequisite Our further during times, slower regrowth disturbance, favouring