ABSTRACT
The natural resistance of plants is a mechanism commonly exploited in agriculture, horticulture, and forestry. It is mainly employed against microorganisms such as virus, bacteria, and fungi. The common image of plant defense relates probably to mechanical devices such as spines and hairs to deter grazing animals. Another older aspect of natural defense is a decreased content of nutritional substances, foremost protein, in exposed tissues, thereby affecting the preferences, or reproduction, of attacking animals. The North American Lodgepole pine has been introduced to Finland and Sweden as a fast-growing and productive species. It has been badly damaged by voles, especially the field vole. Many or most natural plant defense chemicals effective against herbivorous mammals are also toxic to humans and their livestock. Several severe diseases are caused by resistant plant species or varieties. Biomass production is of little or no concern to ornamental plants but is vital for forestry plants.
