Stand structure and woody species composition along a fire chronosequence in mix pine

Although forest fires have become a critical question in Mexico following the fire season of 1998, there is little knowledge regarding the effects of fire events on forest structure, composition, and dynamics in mixed pine-oak forests in northern Mexico. Objective of this study was to determine how fire has shaped forest structure and composition in mixed pine-oak forests and to describe trends and stages of natural succession. First of all, a chronosequence of forest fires was reconstructed by carrying out tree ring analysis and inventories in different sites of increasing time since fire. Increments cores were taken from P. teocote and P. pseudostrobus. Stand level vegetation characteristics, environmental data (solar radiation, slope, aspect, and elevation) were analysed along a 134 year chronosequence at 23 sites in mixed forests of the Ecological Park "Chipinque" in the Sierra Madre Oriental. Detrended canonical analysis confirmed that the time since fire was correlated to most biotic variables and indicates that the disturbance regime is tightly coupled to ecosystem functions. The study revealed that there were important differences between post-fire cohorts in terms of species richness, stand composition, and structure. High tree diversity was generally found in young stands, while the intermediate and major ones showed the lowest woody plant diversity. In old stands, tree diversity was increased again. In turn, the forest structure was less divers in young stands compared to intermediate, major and old stands. By exploring forest stand structure and composition in the context of ecosystem functions an overlook of fire ecology in northern Mexican pine-oak forests was gained. The occurrence of forest fires is natural part of these mixed forests and sustainable forest management should include the natural forest fire incidence to maintain forest health and the possibility to benefit from this natural resource.