The concentration of phenols, procyanidins, and protein in pine foliage was determined at two and eight weeks following mechanical defoliation of 0, 25, 50, and 75% in this greenhouse study. The lowest level of defoliation (25%) produced the largest increase in phenols; 75% defoliation caused the largest increase in procyanidins. The number of phenolic compounds in mature foliage doubled following 25% defoliation. Maximum protein production also occurred at moderated defoliation levels. Mechanical defoliation had a significant effect on the production of all compounds tested. The time required to induce the observed changes in plant metabolism is short enough to influence the feeding behavior of pine herbivores during seasonal attacks. It is suggested that an increasing concentration of allelochemicals is not necessarily an indication of low forage quality. Large increases in protein may be more nutritionally advantageous than defensive chemicals are limiting, and may offset any deleterious effects. It is apparent that defoliation can rapidly alter plant primary and secondary metabolism in ponderosa pine (Pinus ponderosa).
Citations and enhanced abstracts for journals articles and documents focused on rangeland ecology and management. RSIS is a collaboration between Montana State University, University of Idaho, and University of Wyoming.