Defining species guilds in the Central Hardwood Forest,USA

Tree regeneration outcomes are challenging to generalize and difficult to predict. Many tree species can establish new propagules in a variety of post-disturbance environments and many different reproductive mechanisms may be used. In order to develop conceptual models that accurately reflect reproductive potential, we need a better understanding of the similarities in regeneration ecology among species. We used information from the forest ecology literature to evaluate the reproductive attributes of sixty-two tree species in the central hardwood region of the eastern United States. Each species was classified categorically for features such as flowering, seed production and dispersal, seed dormancy, germination requirements, seedling characteristics, and vegetative reproduction. Cluster analysis (Jaccard's similarity coefficient, complete linkage method) and ordination (homogeneity analysis) were used to separate nine groups (guilds) of species that had similar reproductive attributes. Individual attributes that had high variance in the first and second dimensions included: seed banking, seed dispersal, seedling shade tolerance, and seedbed requirements. Members of each guild had similar levels of reproductive specialization and guilds were either pioneer-like, opportunistic, or persistent. Pioneer guilds included: short-lived or fugitive species that colonize sites rapidly and are too shade intolerant to replace themselves; shade-tolerant species that colonize frequently disturbed sites; and stress-tolerant pioneers that survive on dry or nutrient-poor sites. Opportunistic guilds contained species that are remarkably versatile in their reproductive effort. The most flexible opportunists can colonize new sites, maintain seed in a seed bank, sprout from existing stems and persist as a seedling or sapling bank. Persistent guilds contain species that develop and maintain advance regeneration. These include: species with moderate understory tolerance that regenerate via cycles of dieback and resprouting; and more tolerant species that maintain seedling or sapling banks. Our regeneration guilds may provide a useful approach for more realistically representing large and diverse sets of tree species in forest ecosystem models.