BOTANICAL FIRST-RESPONDERS FROM THE CARBONIFEROUS THROUGH THE MID-TERTIARY: THE EVOLUTION OF PIONEERING POST-DISTURBANCE TERRESTRIAL PLANT ASSEMBLAGES

Disturbance, ranging in scale from individual wind-throws to devastation from impact events, has been ubiquitous in the history of terrestrial vegetation. In extant post-disturbance vegetation recovery/succession, the pioneering taxa in the case of large-scale events are characterized by distinctive traits that favor long-range dispersal and establishment. In the peat-forming mire forests of the Carboniferous, successions appear to have been unique in their character and analogs of extant pioneering stages cannot be readily distinguished. During the Mesozoic, pioneering guilds were dominated by ferns and other free-sporing plants, which continued in this role until the mid-Tertiary. Modern guilds, dominated by herbaceous Angiosperms, do not become significant elements in earliest vegetation recovery until essentially the Paleogene-Neogene transition. Disturbance thus appears to have had little impact on early Angiosperm diversification and, particularly in very mesic settings, ferns and fern allies may still dominate the earliest stages of post-recovery vegetation. The presence and composition of pioneering successional stages are best documented using high resolution palynology. In general, small-scale events cannot be resolved. In the case of larger-scale disturbance, early recovery stages will generally be recognized only when sample sites are within or immediately proximal to the disturbed zone. The characteristic elements of early post-disturbance recovery stages of any region and time tend to be constant at any particular scale, irrespective of the disturbance mechanism.