Long-term Dynamics of Giant Sequoia Populations: Implications for Managing a Pioneer Species

My colleagues and I have analyzed the age structure of four populations of giant sequoia (Sequoiadendron giganteum [Lindl.] Buchholz). We have found the following: (1) The amount of successful reproduction in a grove cannot be judged by the sizes of its trees. (2) Sequoia populations almost certainly were near equilibrium or increasing before the arrival of European settlers. (3) In this century, there has been a massive failure of sequoia reproduction in groves protected from fire but otherwise meant to be maintained in a natural state. (4) Before the arrival of European settlers, successful recruitment of mature sequoias depended on f ires intense enough to kill the forest canopy in small areas. Thus, sequoia is a pioneer species, and this conclusion has specific management implications. On walks I have taken through sequoia groves with members of conservation groups and the general public, our discussions raised several questions relevant to the preservation of sequoia groves. Here I will address four of these questions-four that I consider to be among the most important for understanding the dynamics and management of sequoia groves. (1) Can we determine whether a grove is successfully reproducing by the sizes of its sequoias? Small sequoias, some less than 1 m (3.3 ft) tall, can be found in nearly any sequoia grove protected from logging and fire. Does this not contradict the popular and scientific literature, which abound with declarations that sequoias have not been reproducing successfully in otherwise undisturbed groves? (2) Were sequoia populations increasing, decreasing, or near equilibrium at the time of European settlement? The answer to this question is critical as a backdrop for interpreting sequoia population trends during the postsettlement period. (3) Is reproduction sufficient to maintain sequoia populations in the absence of fire? Even though sequoia seedling establishment declines precipitously in the absence of fire, might establishment on bare mineral soil exposed by treefalls be sufficient to maintain sequoia populations? After all, John Muir recognized that bare mineral soil was a necessary prerequisite for sequoia reproduction, and that fire created mineral soil seedbeds, but clearly stated that "[t]he fall of old trees ... furnishes fresh soil in sufficient quantities for the maintenance of the [sequoia] forests" (Muir 1878, in Jones 1977). Thus, is there really any reason for concern over sequoia reproduction, and is fire really necessary? (4) What were the key factors in the maintenance of sequoia populations before the arrival of Europeans? This is the most all-encompassing question, and we must know Presented at the Symposium on Giant Sequoias: Their Place in the Ecosystem and Society, June 23-25, 1992, Visalia, California. Research Ecologist, Sequoia and Kings Canyon National Parks, Three Rivers, California 93271. the answer if our goal is to maintain groves in as nearly a natural state as possible.