REGENERATION BY FRAGMENTATION IN TROPICAL MONTANE FOREST SHRUBS

Abstract

The ability of neotropical forest shrubs to reproduce by establishment of severed fragments was demonstrated experimentally in a lower montane forest in Costa Rica. Twigs (N = 307) broken from 78 individual shrubs or large herbs (representing 22 species, 14 genera, and eight families) were individually marked, dropped to the forest floor, and measured periodically over 5 years. Ninety‐two percent of the fragments and all but one species persisted for 4 months (rainy season) or more. Adventitious roots were produced after the first month. For all fragments, both the net number of leaves and total stem length declined initially. Mortality was concentrated in a 10‐month period (that included the first dry season), in which 35% of the fragments (average by species) and 85% of the species survived. Species’ survivorship then was steady or declined slowly. Fourteen species, representing seven genera in three families (Piperaceae, Rubiaceae, and Acanthaceae) persisted for all 5 years of the study. A fragment's original size did not affect the likelihood that it would survive. Although there was continuous production of new leaves, few fragments showed a net gain in leaf number by 5 years. In contrast, most fragments showed a net gain in stem length (up to five‐fold), with vertical growth accounting for the gain. By the third year, most surviving fragments were upright plants and some had flowered and borne fruit. Several, broken again by falling branches, fragmented naturally. Regrowth from fragments is likely to be important in the persistence of individuals and in the structure and dynamics of populations of shrubs in tropical wet forests.