marginal effect

A phenomenon exhibited by the plants at the edge of a stand of vegetation whereby they grow more vigorously than those in the centre. It has been well documented in advancing areas of bracken (Pteridium), where the fronds at the edge are significantly taller than those behind them. This is believed to be due to increasing rhizome age at the centre rather than to depletion of soil nutrients. Marginal effects may play a part in the *hummock and hollow cycle of vegetation.