NATIONAL PARK SERVICE Giant Sequoia Ecology: Fire and Reproduction

This study of giant sequoia ecology concentrated on the role of fire as it affected succession and sequoia seedling survival in the mixed-conifer forest of the Sierra Nevada of California. In addition, special consideration was given to the interaction of animals with giant sequoia reproduction, particularly as they affected cones, seeds and young seedlings.

The removal of the litter and duff layers, by fire or manipulation, from the forest floor facilitated the establishment of annual herbs, shrubs and giant sequoia seedlings. Those seedlings growing in soil which had experienced the hottest fires survived at a higher rate than those on other soils. The former seedlings also grew at a faster rate than those on other substrates, reaching a height of over a meter in eight years.

Vertebrate animals were not greatly affected by the fire manipulations and their numbers fluctuated in response to environmental factors other than fire. Most of the vertebrates present in the giant sequoia groves that were studied had little to no effect on sequoia reproduction, with the exception of one species. The Douglas squirrel plays an intimate role in reproduction by feeding on giant sequoia cone scales and thus aiding in seed dispersal. No vertebrates selected fallen sequoia seeds as a preferred food.

Arthropods associated with the giant sequoia were found to number over 150 species. A few fed on the young seedlings and many were associated with the foliage, bark and wood of mature trees. Cone inhabitants were also few in number, with one beetle playing a significant role in the release of seeds from the cones. The beetle, Phymatodes nitidus, mined the main axis of cones causing drying of normally serotinous cones, thus causing them to drop their seeds.

The giant sequoia appears to have a fauna which have evolved a partitioning of the cone substrate. The Douglas squirrel uses the relatively young cones for food while the beetle uses the older cones.

The implications for management of the giant sequoia are that prescribed fires should be employed judiciously and that hot localized fires are best for seedling development. The ultimate objective should be to allow natural forces to range free throughout the groves, thus enabling the giant sequoia ecosystem to be perpetuated much as it was in millennia preceding man's intrusion on the scene.