Logging and Edaphic Factors in the Invasion of an Asian Woody Vine in a Mesic North American Forest

Factors contributing to an invasion of the Asian woody vine Celastrus orbiculatus in a mesic forested Massachusetts (USA) sanctuary were investigated. Planting germinated C. orbiculatus seeds in the field revealed that, although they tolerate a wide range of conditions, seedlings grow largest in moist circumneutral soil under high irradiance. A study of naturally occurring vines in a logged forest suggested that C. orbiculatus invaded two years after harvest, and invasion may have been triggered by logging disturbance. Vine stems were more abundant on former logging roads than in surrounding selectively logged areas. Former logging roads had a significantly higher soil pH than surrounding areas and, due to the direction of construction, a significantly more southerly aspect. Fourteen years after harvest, logging roads continued to provide this aggressive exotic with superior habitat for establishment and growth.     

Leaves of Lianas and Self-Supporting Plants Differ in Mass per Unit Area and in Nitrogen Content

Abstract: The aim of this study was to test the hypothesis that the reduction in supporting tissues in climbers compared to self-supporting plants is also true for their leaves, and that climbers generally require higher leaf nitrogen than self-supporting plants to accomplish fast growth. This hypothesis was tested using paired samples of both growth forms with assessment of leaf area index above the sampled plants (LAI_a) in a tropical rain forest in Gabon. The sampling protocol ensured that within a highly fluctuating low canopy environment, the growth conditions were identical for each pair sampled. The results confirmed the hypothesis. Lianas had significantly lower leaf mass per unit leaf area (LMA) than their supporters. Liana leaves also contained significantly more nitrogen than host tree leaves. The differences in nitrogen concentration between liana and tree leaves reversed for the most shaded sites, when nitrogen was expressed on a leaf area base (N_area). Significant regression between leaf nitrogen and LAI_a was found for the climbers on the shaded sites but not for their supporters. This indicated better acclimation of climbers to prevailing light conditions. Better nitrogen allocation at low LMA, together with lower carbon costs for building supporting tissues, makes lianas highly competitive, especially where high nitrogen availability is assured.