Post-fire succession in heathland communities
A study was made of the post-fire development of several heathland community types in an -attempt to quantify and model the variations found in this development. Stands of various ages were subjected to experimental burning, and fire temperatures and severity were assessed. Fire severity was found to increase with stand age until the mature phase of Calluna, with a subsequent decline in the degenerate phase.Studies of the post-fire regeneration indicated that regrowth was more rapid and more diverse in stands which were young when burnt. Analyses of seed stores, substrates left by fire, and the ability of Calluna to regenerate vegetatively indicated that the potential of the vegetation to regenerate after fire decreased with stand age. Model analyses suggested that the age and composition of a stand before fire determined the initial floristic composition set up after fire, and this then determined the rate and direction of post-fire development.Chemical interactions between heathland species were investigated, and it was found that several species produced substances capable of inhibiting the growth or germination of other plants.Markov models were used to study the post-fire succession, but gave good predictions of development only for simple systems in which all the major species recolonised rapidly after fire. Statistical analyses indicated that the development shown by Calluna-Eriophorum bog after fire fits with the assumptions of a homogeneous first-order Markov chain.It was concluded that the vegetation development following fire is a complex probabilistic process of small-scale interactions between vegetation patches. The burning of old Calluna stands was considered to be unwise in terms of both management and conservation aims.