How general is ‘constant final yield’ in herbaceous plants?

Background/Question/Methods

Plant populations are often influenced by competition and the resulting density-dependent effects on their structure and behaviour. When plants are sown at a range of densities and harvested at a given point in time, total biomass production at low densities shows a linear increase with density, begins to level off at higher densities as the growth of individuals is reduced by competition, and at even higher densities reaches a constant level. This phenomenon, called ‘Constant Final Yield’ (CFY), results from the modularity of plant growth, plasticity in allometric growth patterns and size-asymmetric competition. While CFY is commonly referred to as a universal pattern, there has been no extensive review of literature to support this claim, thus we conducted a literary review to determine how general CFY is in herbaceous plants.

Results/Conclusions

Data from 272 density trials on herbaceous plants from 12 families, showed CFY in 39% of the experiments, in 33% the densities were not high enough to determine if the populations would eventually reach constant final yield, 21% showed a reduction in total biomass of 5% or more, and 7% showed unusual patterns. Though the majority of the studies seem to be consistent with CFY, there are interesting exceptions from this pattern that should be investigated further, for example from studies conducted in extreme environments where facilitation has been documented. As total biomass is often measured only at final harvest, declining total biomass at high densities could be caused by lost biomass during the growth, or alternatively be a result of non-recorded root biomass. Our review shows that CFY is a general phenomenon, suggesting that natural selection of individuals usually results in maximal biomass production at the population level over a wide range of densities.