Herbivory patterns in mature sugar maple: variation with vertical canopy strata and tree ontogeny


Sean C. Thomas, Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, M5S 3B3, Canada. E-mail: sc.thomas@utoronto.ca


1. Although leaf morphology and chemistry show profound changes as trees age, the consequences of such changes to herbivory have received little attention, particularly late in the ontogeny of canopy trees.

2. Using a mobile aerial lift for canopy access, patterns of leaf damage were evaluated in canopy-dominant mature sugar maple (Acer saccharum Marsh) trees ranging from ∼20 to 70 cm in diameter, corresponding to an age range of ∼40–180 years.

3. Herbivore damage patterns varied in relation to both vertical canopy position (among upper-, mid-, and lower-canopy positions) and with tree size. Damage types attributable to herbivores active on leaf surfaces, including leaf skeletonizers and leaf cutters (both principally Lepidoptera), and leaf stippling inducers (Hemiptera) showed decreases with tree size, and with increasing height in the canopy. In contrast, leaf damage from the most abundant gall-forming arthropod in the system, the eriophyid mite Vasates aceriscrumena, increased markedly with tree size.

4. The results indicate that herbivory patterns vary with both canopy stratum and with tree size in sugar maple, and that the relative strength of vertical stratification and tree ontogeny effects are similar in magnitude. The predominant patterns are of a decrease in herbivory with increasing height in the canopy and with tree size, but certain galling arthropods exhibit the reverse trends.