Giant Sequoia (Sequoiadendron giganteum) Regeneration in Experimental Canopy Gaps

摘要

Restoration of giant sequoia populations is a high priority for managers, but few experimental studies have examined the efficacy of restoration treatments. To inform giant sequoia restoration treatment options, we assessed the response of giant sequoia regeneration (germination, mortality, and growth) to experimental gaps within a native giant sequoia grove. We created experimental gaps, ranging in size from 0.05 to 0.4 ha. Following gap creation, we sowed seeds and planted seedlings along north-south transects across gaps. Transects were planted on paired burned and unburned substrates. The seed-sowing treatment did not result in a cohort of established seedlings, although the amount of seeds sowed was far short of the potential amount released during intense fires. Mortality of planted seedlings did not vary with gap size (average 25% mortality). However, there was a distinct relationship between gap size and second year seedling growth. The relationship was best modeled with an asymptotic curve for both burned and unburned substrates. Relative seedling growth more than doubled as gap size increased from 0.05 to 0.2 ha, then increases in growth diminished. Growth rates of giant sequoia seedlings saturated above 70% light availability while increasing linearly with belowground resource availability. Long-lived pioneer species such as giant sequoia require restoration treatments that involve relatively severe disturbances to facilitate cohort establishment and recruitment.