Spatial Dynamics of a Primary Succession: Nucleation

Yarranton, G; Morrison, R

Two stages are recognized in the sand dune succession at Grand Bend: a colonizing stage characterised by open grassland with scattered Juniperus virginiana and Quercus prinoides bushes and a persistent stage taking the form of an oak-pine forest. The first stage lasts for 1600 years and the second begins at 2900 years; from 1600 to 2900 years there appears to be a transition. Persistent species first appear under Juniperus virginiana where a humus layer first accumulates and soil maturation proceeds rapidly; such sites act as nuclei for the subsequent growth of patches of persistent species which eventually coalesce at the onset of the persistent stage. As the individual oaks mature into trees they dominate the developing patches and the association of J. virginiana with the patches disappears. Species of the colonizing stage are eliminated between the growing patches of incipient oak forest. The nucleation model suggests that Greig-Smith's suggested sequence of changes in spatial pattern during a succession is repeated during each stage of the process. The clump size of species of the invading stage will increase as they establish themselves and nucleation occurs and the rate of increase will become asymptotic to infinity as the patches coalesce; the clump size pattern of the disappearing species will be exactly the reverse as they suddenly cease to constitute the overall matrix of vegetation and become confined to gradually decreasing patches.

Spatial Dynamics of a Primary Succession: Nucleation

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