Why the biomass of over-crowded populations of Galium aparine L. does not increase during density-dependent mortality? An experimental approach

Abstract

Biomass accumulation, mortality, growth allometry and size-hierarchy development over time were assessed for an experimental, over-crowded population of Galium aparine . Individual plants were labelled according to emergence time and initial size. The allometry of growth of 54-day old G. aparine populations at different densities with or without the addition of physical support was analysed for another experiment. The significant decrease in population density over time in the over-crowded population was not accompanied by a significant increase in biomass. The biomass/stem length allometry differed between large and small plants within this population. Initial size had a more clear effect on plant survival and growth than emergence time. The slope of the biomass/length allometric line increased with population density in the second experiment, but was not significantly affected by support availability. The absence of biomass accumulation over time in G. aparine populations could be due to the shift in the hierarchy of resource exploitation of the population caused by the progressive increase in elongation of the largest individuals and their subsequent lodging.