PARENT SESSION
Oral Session #69: Elevated CO₂ and Global Change. Presiding: L. Gough.
Thursday, August 9, 2001. 1:00 PM to 4:45 PM. Hall of Ideas H.

How will increased atmospheric CO₂ and mammalian herbivory affect forest succession?

Mohan, Jacqueline¹, Schlesinger, William¹, Clark, James¹, ¹

ABSTRACT- Forest diversity and productivity depend on species-specific responses to increasing atmospheric CO₂ and mammalian herbivory. We examined growth and mortality of understory woody plants in response to elevated CO₂ in both the presence and absence of mammalian herbivores. In a two-year study, Pinus taeda and Robinia pseudoaccacia growing in herbivore exclosures were the only tree species to show positive growth responses in both seasons to elevated CO₂ (1999: RGR increase 32%, p=0.03 and 59%, p=0.03, respectively; 2000: 72%, p=0.08 and 646%, p=0.003). In the second year, various shade tolerant and intolerant species exhibited positive growth responses to CO₂: Acer barbatum (RGR 57%, p=0.10), Acer rubrum (38%, p=0.05), Cercis canadensis (64%, p=0.04), Liquidambar styraciflua (50%, p=0.004), Pinus echinata (717%, p=0.04), Ulmus alata (24%, p=0.07), and Quercus phellos (50%, p=0.02). CO₂ effects on mortality of protected plants were species-specific (p=0.01) and depended on the initial plant size (CO₂-by-Year-by-Species-by-Initial Biomass interaction, p<0.0001). When available to mammalian herbivores, fewer species responded to CO₂ but the percent increase in RGR of responsive plants was large, suggesting that increased CO₂ may augment the ability to withstand herbivory. Future forest impacts of atmospheric CO₂ may depend on the abundance of mammalian herbivores.

KEY WORDS: Atmospheric CO₂, Herbivory, Biodiversity, Global Change