Document: JAS-3-34-5

Insect herbivory in an intact forest understory under experimental CO₂ enrichment.

HAMILTON, J.G.*, A.R.ZANGERL, M.R.BERENBAUM and E.H.DELUCIA

University of Illinois, Urbana, Il 61801 ¹

Abstract:
Elevated atmospheric CO₂ may lead to changes in levels of insect herbivory. However, it has remained a matter of speculation how results from experiments with only a few species of insects and plants in controlled environments will generalize to natural ecosystems. We measured leaf damage from herbivory in an intact forest understory in an ongoing FACE (free-air CO₂ enrichment) experiment. Using digital photography and image analysis, we quantified leaf damage to three species of deciduous trees over a growing season from insects representing three distinct feeding guilds. The total amount of leaf tissue damaged varied little between treatments both early in the season (ambient 5%, elevated 3.5%) and late in the season (ambient 9%, elevated 7.5%). Overall, the greatest amount of leaf damage came from herbivores that removed tissue, with skeletonized tissue next and galled tissue covering the least amount of leaf area. We found a significant interaction between tree species and CO₂ treatment . Red maple (Acer rubrum) experienced the same amount of leaf damage in the two treatments. Winged elm (Ulmus alata) experienced significantly greater damage in the ambient treatments, whereas, sweet gum (Liquidambar styraciflua) showed a trend toward more damage in the elevated treatments. Correlations between leaf damage and total leaf nitrogen, total phenolics, starch and soluble sugars are also discussed. The results of this study demonstrate that CO₂ effects on herbivory cannot be generalized to a whole forest.

Keywords: Herbivory, elevated CO2, Insects

This abstract is being presented at: 9:00 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.