Facilitation Model - Models of Succession
This is considered as the classical model of succession. It is based on the assumption that species of a previous stage are replaced by the succeeding stage. And at each stage the species modify their own environment to make it progressively less suitable for themselves and increasingly more suitable for succeeding colonisers. Based on these characteristics Connell and Slayter (1977) proposed the facilitation model. To explain it better let us consider the example of succession in a pond.
Figure: Facilitation Model
You may have noticed that due to the death and decay of different species of plants, siltation takes place and bottom of ponds is raised and the conditions become less suitable for their own survival and more suitable for the establishment of succeeding species. The essence of the facilitation model is that species of early stages of succession modify their own environment in a way that inhibits their own regeneration but facilitates the entry and survival of species of next higher stage of succession. For many years this model was considered to be the only one. For the early stages of primary succession, it still seems to provide the best explanation of what is actually observed. But for later stages of primary succession and for secondary succession in forests or grasslands this model is not fully tenable.