The independence of clonal shoot’s growth from light availability supports moso bamboo invasion of closed-canopy forest

Abstract

Forests with closed canopy are generally thought to resist invasion by other species because of the low light conditions under the canopy. However, moso bamboo (Phyllostachys edulis) is capable of invading adjacent intact forests, including Chinese fir (Cunninghamia lanceolata) forest, broad-leaved forest, and mixed broadleaf-conifer forest. How does moso bamboo manage to expand and grow under the deep shade of forest canopies? To test this question and explore the light conditions in which bamboo shoots survive, we experimented with shading treatments under field conditions. The levels of shading included total shading of young bamboo shoots, shading with light only to the tip of the shoots (tip light), and no shading (full light). Treatments were applied to shoots developing in pure stands of moso bamboo, and shoots that were invading Chinese fir stands. Shoot survivorship, height, and diameter at breast height (DBH) were measured weekly. Total shading of bamboo shoots led to mortality of all shoots, compared with >90% survival for shaded shoots with tip light and for unshaded shoots. Bamboo shoots elongated over a 60day period, reaching heights of more than 10m. Height growth was 8–13% higher for shaded shoots with tip light than for unshaded shoots, with no significant effect of stand type. The elongation of bamboo shoots is largely independent of the light environment that would influence current photosynthesis of the shoot, indicating that shoot elongation likely depends on supplies of carbohydrates from the clonal root system. The deep tolerance of shade that results from clonal of new shoots appears to be a key factor allowing its invasion of intact forest stands.