Sequoiadendron giganteum is renowned as the world’s largest tree and has been widely celebrated since the mid-1800s. The native range of Sequoiadendron occupies just 150 km2, occurring in distinct groves, whereas primary conifer associates have continuous distributions. Historically, Sequoiadendron forests experienced up to 30 fires per century, strongly influencing its own regeneration as well as the density and composition of co-occurring trees. Despite protection of many groves within national parks and monuments, more than a century of successful fire suppression has greatly altered the structure of these forests with large increases in shade-tolerant conifer abundance – particularly Abies lowiana. Five permanent reference plots were established in tall Sequoiadendron forests distributed across the range of the species to quantify elements of aboveground structure, biomass, and leaf area.
Results/Conclusions
Total aboveground biomass ranged from 1770 to 3290 Mg ha-1, of which 58-75% was decay-resistant Sequoiadendron heartwood. Two plots had Sequoiadendron bark mass exceeding biomass of all other species combined. Non-Sequoiadendron leaf area was very high (LAI 6.8–9.8), reflecting a positive response to fire suppression. Among the five plots, 50 giant trees were identified based on trunk diameter and crown size. Bark on these trees is resin-free and can be up to 78 cm thick (a global record), protecting trees from fire. But with trees that can live over 3000 years, fire eventually creates scars that often grow into fire caves. During fires, caves act as ovens, intensifying heat, increasing in size, and killing roots and cambium in and around the caves. Tree bases were mapped in detail, largely through photogrammetry, including inside caves. Among the 50 trees, 11 had no caves, but 63 caves were found among the other 39 trees. Spatial analysis of non-Sequoiadendron leaf area around giant trees was much lower when compared to plot averages, but within fire-cave zones non-Sequoiadendron leaf area was similar to plot averages. Sequoiadendron forests accumulate records of biomass and leaf area only surpassed by Sequoia sempervirens rainforests, and giant Sequoiadendron have managed to maintain control of their immediate surroundings despite more than a century of anthropogenic change.