Translating ecological drought into resource management: giant sequoias
Giant sequoia is an iconic species that stores vast amounts of carbon and inspires awe and curiosity about the natural world. Much of its limited range is protected within federal, state, and tribal lands. Sequoia can live more than three millennia and have shown considerable resistance and resilience to drought, fire, insects, and disease. However, their limited distribution reflects narrow environmental tolerances, high moisture demand, and vulnerability to climate change. Indeed, giant sequoias were probably near extinction during a period of slightly warmer temperatures from about 10,000 to 4,000 years ago. Given a trajectory of rapid warming, the sustainability of this long-lived species is uncertain. Despite the high social value of this species, managers face critical problems that constrain our ability to manage giant sequoia forests sustainably in the face of increasing drought. What are these challenges and how can managers and scientists work together to overcome them?
Fire management is one of the few tools we currently can use to reduce vulnerability of forests to climatic change. However, capacity to use fire is very limited and it is usually prioritized to protect the most socially valued sequoia groves. Managers might shift their focus to a longer term view of protecting likely climate refugia (i.e., low vulnerability areas) if we had reasonable confidence in how to identify them. Climate envelope models are one way to identify possible refugia, but they are not enough to convince managers to invest limited resources in these locations. Additional tools also are needed to identify areas that are not occupied by sequoia now, but might be suitable in the future.
Currently, managers have very limited means to understand early warning signs of drought stress in giant sequoia. We don’t know what moisture thresholds will lead to mortality. It is critical that we develop efficient monitoring programs to detect subtle warning signs before loss is imminent. Proxies developed through remote sensing products could become a powerful tool to monitor moisture condition if we can validate and calibrate them with field data.
We understand very little about genetic variability of giant sequoia and whether or not genotypes vary in their drought tolerance. This information is important to develop climate adapted seedbanks for future planting.