Do spatial variation in leaf traits and herbivory within a canopy respond to selective cutting and fertilization?

Abstract

Within a canopy, spatial variation in leaf traits may be determined by light and nutrient availabilities. Such environmentally caused changes in leaf traits may be an important cause of changes in leaf palatability to herbivores. We conducted a factorial experiment with fertilization and selective cutting in a northern Japanese forest dominated by oak ( Quercus crispula Blume). Fertilization increased the nitrogen content of upper canopy leaves. Leaf mass per area (LMA) was greater in the upper canopy than in the lower canopy. Selective cutting and all interactions had significant effects on LMA. Total phenolics and condensed tannin in leaves were also greater in the upper canopy than in the lower canopy. The interaction of selective cutting × position in the canopy (upper or lower) had a significant effect on total phenolics; a similar trend was seen for condensed tannin. Herbivory was greater in the lower canopy than in the upper canopy. Also, fertilization increased herbivory, whereas selective cutting decreased it. These results imply that human activities, such as logging and nitrogen deposition, may strongly influence spatial variation in herbivory through changes in leaf traits.