Document: JAC-3-67-19

Will rising CO₂ affect forest succession?

MOHAN, J.E.*, J.S.CLARK and W.H.SCHLESINGER

Duke University Durham, NC 27708, USA ¹

Abstract:

Understanding the effects of rising CO₂ on forest succession and diversity requires studies on how different species respond to CO₂ enrichment in a forest setting. At the Duke Forest FACE site, we show that elevated CO₂ increases the relative growth rate of naturally-recruited understory vines by 40% (p=0.06) and tree seedlings by 15% (p=0.05). The twenty-four tree species represent different functional groups, which respond differently to increased CO₂. Shade tolerant trees under CO₂ enrichment showed a 40% growth increase (p=0.03), whereas intermediately tolerant and intolerant trees showed no significant growth effects. These results suggest that increased growth of understory trees and vines, and potentially increased turnover of early- and mid-successional understory trees, will hasten future forest succession. However, these CO₂ results were confounded by the effects of mammalian herbivory and dispersal limitation. To isolate CO₂ effects, seedlings of fourteen tree species (2352 trees) were planted in 1997 and protected from mammalian herbivory. Among these species, and in the absence of herbivory, there was a trend towards a 35% increase in overall relative biomass growth under CO₂ enrichment. There were large differences between species. Liquidambar styraciflua exhibited a 70% growth increase (p=0.02); Quercus alba, a 27% increase (p=0.04); and Prunus serotina, a 20% increase (p=0.10). Liriodendron tulipifera, however, experienced a 35% decline in growth (p=0.05). No other species, including an N-fixer (Robinia pseudoaccacia), showed a significant growth effect. Survivorship also differed among species. Whereas elevated CO₂ increased survivorship of Pinus echinata and Prunus serotina (p=0.09 and 0.10, respectively), it decreased survivorship of Quercus alba and Acer rubrum (p=0.09 and 0.10, respectively). Future CO₂ effects on forest succession may be unpredictable and uncorrelated with functional groupings.

Keywords: atmospheric carbon dioxide, forest succession, species diversity, shade tolerance, herbivory

This abstract is being presented at: 10:15 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.