FIRE TEMPERATURES AND POSTFIRE PLANT COMMUNITY DYNAMICS IN ECUADORIANGRASS PARAMO

Three aspects of the paramo vegetation's response to fires were invest igated: the measurement of fire temperatures, general observations of changes in plant communities following fires, and monitoring the fate of individual plants after burning. Fire temperatures were strongly in fluenced by the physiognomy of the vegetation, dominated by tussocks o f Calamagrostis spp. Temperatures were highest amongst the upper leave s of the tussock (sometimes > 500 degrees C). The middle levels of the tussock experienced temperatures in excess of 400 degrees C, but in t he dense leaf bases temperatures were often below 65 degrees C. On the ground between tussocks, temperatures were variable, whereas 2 cm bel ow ground temperatures failed to reach 65 degrees C. Plant survival de pended on the intensity of the fire and the plant's position within th e tussock structure. Survival was often the result of high temperature avoidance (with buds shielded by other plant parts or buried beneath the soil surface). Post-fire Calamagrostis tiller mortality rates were high and tussock regrowth was slow. Some other species appear to main tain their populations by exploiting this recovery phase for seedling establishment on tussocks. Between tussocks, changes of occupancy at t he level of the individual plants were greater after fire than in cont rol vegetation. Most transitions were random. Those which departed fro m random often involved gaps and were related to post-fire mortality, regrowth from below-ground parts, colonisation or, in the case of a cl onal mat-forming species, to spatial rearrangement of rosettes. Recove ry was slower at higher altitude. Recovery was much slower in burned p lots when the upper 2 cm of soil was removed (along with buried plant parts) compared with burned plots. Qualitative observations suggest th at recovery may consist of a cyclical process, mediated by the serial dominance of several species that are physiognomically important. The frequency of fires determines the amount of fuel accumulated within gr ass tussocks and some plants may be unable to survive repeated burning . Chance survival of species in unburned patches of vegetation and ran dom colonisation of gaps may be important determinants of subsequent c ommunity structure.