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ecologists began to note the huge build-up of flammable fuels in the understory 

 of the Giant Sequoia groves. Dead limbs, logs, standing tree snags all littered 

 the ground surface, and dense thickets of young white fir saplings were 

 widespread. The appearance of this understory was sharply different from that 

 described by John Muir and others in the last century and portrayed in early 

 photographs. Then, the understory appeared more open and dead fuels were 

 much less obvious. Worse, giant sequoia seedlings which had once been 

 relatively common seemed now rare. These observations led ecologists to 

 question the fire protection policies of resource management, and develop a 

 clearer understanding of the importance of fire as an ecosystem factor in the 

 establishment, growth, and survival of Giant Sequoias. 



Giant Sequoias and Fire 



The establishment of Giant Sequoia' is closely tied to fire, and this factor has 

 been significant in the evolution of many life history traits of Giant Sequoia. The 

 thick bark of Giant Sequoia makes mature trees relatively immune to the 

 damaging effects of fire. Furthermore, the convective heat of ground fires is a • 

 critical element in causing the release of Giant Sequoia seeds from closed 

 cones high in the canopies of mature trees. Seeds falling onto bare mineral soil 

 germinate readily and grow rapidly, ensuring the next generation of Giant 

 Sequoias. Recent studies have shown that relatively infrequent intense fires 

 are particularly important in the establishment of dense groupings of Giant 

 Sequoias. This effect is shown diagrammatically in Figure 1 , where the small 

 x's in mixed conifer forest starids after fire indicate the location of dense groups 

 young Giant Sequoias where fires have killed overstory conifers and created 

 light gaps with bare mineral soil. 



The complexities of Giant Sequoia establishment and survival in relation to fire 

 can be seen in the empirical model presented in Figure 2. Fire occurrence in 

 the Giant Sequoia groves is a function of many biotic and abiotic factors. The 

 presence of lighting or other source of ignition, environmental conditions of 

 temperature and humidity, fuel biomass, and interval since the last fire are all 

 important factors in fire occurrence. Without fire, there is little or no release of 

 Giant Sequoia seeds and seedling establishment is rare, even if bare mineral 

 soil is available. Light fires reduce woody litter and expose mineral soil and 

 produce a light rain of seeds from mature Giant Sequoias nearby. Seedling 

 survival is poor under these conditions, however, since canopy openings are 

 not established for light, and competition with surviving saplings of White Fir for 

 water and nutrient resources increases mortality for Giant Sequoia seedlings. 

 High rates of survivorship for giant sequoia seedlings normally requires intense 

 fires which open the canopy, kill young fir saplings thereby increasing the 

 availability of water and nutrients. Regional climatic factors here play an 

 important role in determining if these Giant Sequoia seedlings will survive to 

 become mature trees. Drought years following fire severely increase mortality 

 of saplings. Wet conditions in subsequent years, however, removes this 

 drought stress and leads to high survivorship. 



