CO2 enrichment accelerates successional development of an understory plant community

Aims Rising concentrations of atmospheric carbon dioxide ([CO2]) may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional groups Here, we describe how elevated [CO2] (eCO(2)) affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge National Laboratory sweetgum (Liquidambar styraciflua) free-air carbon dioxide enrichment (FACE) facility in eastern Tennesee, USA We asked if (i) CO2 enrichment affected total understory biomass and (ii) whether total biomass response could be explained by changes in understory species composition or changes in relative abundance of functional groups through time Materials and methods The FACE experiment started in 1998 with three rings receiving ambient [CO2] (aCO(2)) and two rings receiving eCO(2) From 2001 to 2003, we estimated species-specific, woody versus herbaceous and total aboveground biomass by harvesting four 1 x 0 5-m subplots within the established understory plant community in each FACE plot In 2008, we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 5 x 5-m quadrats in each FACE plot Important findings Across years, aboveground biomass of the understory community was on average 25% greater in eCO(2) than in aCO(2) plots We could not detect differences in plant species composition between aCO(2) and eCO(2) treatments However, we did observe shifts in the relative abundance of plant functional groups, which reflect important structural changes in the understory community In 2001-03, little of the understory biomass was in woody species, heibaceious species made up 94% of the total understory biomass across [CO2] treatments Through time, woody species increased in importance, mostly in eCO(2), and in 2008, the contribution of herbaceous species to total understory biomass was 61% in aCO(2) and only 33%, In eCO(2) treatments Our results suggest that rising atmospheric [CO2] could accelerate successional development and have longer term Impact on forest dynamics