Growth form and reproductive effort in goldenrods (Solidago, compositae)

Abstract

Based on Gadgil and Solbrig's (1972) ideas concerning the distribution of resources between the reproductive and vegetative tissues, it is predicted that the ratio of reproductive biomass/total biomass (reproductive effort) will decline with the increasing successional maturity of the community. This prediction was confirmed in field studies utilizing four species of goldenrods. The distribution of resources among the various vegetative tissues should depend on the nature of the limiting factor and the growth form of the dominant plants competing for this limiting factor. Thus, it is predicted that the ratio of stem biomass/total biomass will decline and that of leaf biomass/total biomass will increase for light-limited plant populations as the growth form of competitors changes from being one of the same stature (herbs with herbs) to being one of greater stature (herbs with trees). These two predictions are likewise confirmed in goldenrods. The problem of how these differences in the distribution of resources among tissues are maintained in closely growing populations of a single species was examined. It was found that populations of a given species bloomed at different times, thus reducing the gene flow between these populations. This indicates some degree of isolation which could allow for the maintenance of ecotypic variation.