THE PRIMARY SUCCESSION OF VEGETATION ON THE 2006 PYROCLASTIC FLOWS OF THE TUNGURAHUA VOLCANO

Tungurahua, a stratovolcano located in the Tungurahua province, Ecuador produced a series of pyroclastic flows in August 2006. A year and a half after the eruption, a study of the vegetative growth (plant type, quantity, and age) on the pyroclastic flows revealed that plant growth was young and scarce. To determine the type of plants, and the mechanisms which control the dynamics of vegetative recovery, two transects on the pyroclastic flows were made; one in Cusúa gorge and the other in the Bascún gorge. As a control, a third transect of vegetation not directly affected by the 2006 flows was made adjacent to the Bascún gorge. At Cusúa and Bascún gorges, a total of 47 species were found; 19 in Cusúa and 28 in Bascún, the majority of which possessed special adaptations for growing in poor conditions. The dominant species at Cusúa gorge was Baccharis latifolia (Asteraceae) and at Bascún gorge, Alnus acuminate (Betulaceae) dominated-followed by B. latifolia. The results indicate that the principal mechanisms of primary succession include the amount of water and sunlight available, ecological micro-niches, and the proximity of unaffected vegetation. A preliminary estimate indicates that vegetation on the pyroclastic flows should take 8 to 15 years to fully recover under stable conditions. Studies of this type may help in the interpretation of biostratigraphic markers in volcanic terrains.