Detecting demographic patterns of old coast redwood forests in northern California

Forest demography is difficult to describe accurately. Tree recruitment and mortality are uncommon events, so that rates based on these observations often require long survey periods using large numbers of trees. Demographic rates can scale with tree size, so challenges describing demography are pronounced in coast redwood forests that are dominated by extremely large Sequoia sempervirens. Here, we present 10 years of observations from 15 1-ha plots in unmanaged primary coast redwood forests in northern California. The size distribution of live stems followed a “reverse-J” shape, with many small trees relative to large trees. Sequoia dominated these plots, particularly in terms of stem area. Mortality and recruitment rates varied among common species, with Sequoia having much lower mortality relative to co-occurring conifers and hardwoods. Mortality varied substantially among size classes and taxonomic groups, while little variability in recruitment occurred among taxonomic groups. Mortality rates were consistently greater than recruitment across taxonomic groups during our 10-year observation period. Our area experienced heavy winter storms in 2022–2023 resulting in numerous blowdowns, although mortality still outpaced recruitment when we excluded years affected by the storms. Simulations using current plot data found low statistical power to detect potential future changes in the mortality rate of Sequoia. We consider how these results could inform conservation of old Sequoia forests.