Differences between understorey and canopy in herbivore community composition and leaf quality for two oak species in Missouri

1. From July 1994 to September 1995, at six censuses, the herbivore communi ty associated with understorey (<2.5m height) and canopy (15-20m) leaves of Quercus alba and Q. velutina was sampled in south-eastern Missouri, US,A. 2. Across all censuses, herbivore densities were not significantly differen t between canopy arid understorey for Q. alba and Q. velutina, except in Au gust 1994 when herbivore densities were 60% higher in the canopy on Q. alba . Little significant spatial variation in herbivore densities or community composition was found during the study years. 3. The herbivore community was diverse, consisting of 138 species of leaf-c hewing insects. Species richness was significantly greater (by 5-20%) in th e understorey than in the canopy for both tree species, and the relative ab undance of the main families, different feeding guilds, and most common spe cies differed significantly between. understorey and canopy. 4. To determine the extent to which leaf quality explained the observed pat terns, percentage nitrogen and protein binding capacity were measured in ca nopy and understorey leaves of Q. alba and Q. velutina. Per cent nitrogen w as higher in canopy leaves for Q. velutina while protein binding capacity w as higher in canopy leaves for LT. alba. 5. These results suggest that the herbivore community associated with these two species of Quercus comprises species that appear to respond individual ly to environmental and biological conditions encountered in the understore y and the canopy.