Bottom-up regulation for protection and conservation of forest ecosystems in northern Japan under changing environments

Abstract Many studies have emphasized the essential role of the bottom-up regulation induced mainly by herbivores of stable forest ecosystems. Most plants species are able to change the quality of their leaves after having been grazed by insect herbivores. This alteration may further enhance the natural defenses of the plant as well as the stability of the biodiversity of forest ecosystems. The effects of defoliation on the defense responses of deciduous broad-leaved trees was summarized from the viewpoint of plant-animal interactions. An outbreak of biological damage to newly introduced species was found on larch plantations in northern Japan. Introducing the hybrid larch F I that developed by Hokkaido Forest Research Institute, prevented widespread damage to larch plantations. This is an example of bottom-up regulation of forest ecosystems. The defensive chemicals in leaves (condensed tannin and total phenolics) increase with a rise in foliar C/N. The defense chemicals in birch, willow and oak species were induced by grazing insect larvae, but not by mechanical cutting. Except for white birch, the amount of foliar defensive chemicals of three mid and late successional species (oak, elm and maple) was higher than, ash and alder. Under elevated CO2 conditions, the chemical composition of plant foliage changed greatly, which may affect the activities of insect herbivores. The potential for improving forest management systems in changing environments using the forest's own defenses against herbivores, especially in relation to plant-insect interactions, is discussed for keeping forest vitality and health.