Plant Self-Thinning and Leaf Area Dynamics in Experimental and Natural Monocultures

Abstract

The gradient of the relationship between mean plant weight and density for many species in self-thinning monocultures is known to be -3/2. There is evidence in the literature that this gradient may decline as light intensity falls. A recent controversy has centred upon whether or not the -3/2 gradient can be restored at low light intensities by graphing mean leaf area per plant against density. An experiment was conducted, using Trifolium pratense L. grown at three light intensities, to establish the gradient of this relationship. Whereas the mean weight vs. density gradient remained near -3/2 at all light intensities, the mean leaf area vs. density gradient approximated to -1.0, indicating that leaf area index stays constant as thinning proceeds. Thus, the results do not support the proposal that alterations in leaf area ratio act to restore the -3/2 gradient to the mean leaf area vs. density graph at low light intensities. Support for these findings is discussed, including data from field monocultures of Mercurialis perennis L.