Removal of predators and creation of early seral habitat has, in many systems, caused substantial population growth of herbivores. Hyperabundant herbivores, in turn, induce cascading ecosystem effects, but few studies have investigated long-term browser density trends in relation to succession and stochastic climate events. Here, for the first time, we use annual population estimates of a forest browser to relate forest succession to the long-term decline of an herbivore that prefers early seral habitat. From 2007 – 2021, concurrent with reduced timber harvest, we used line-transect distance sampling to document annual changes in Columbian black-tailed deer (Odocoileus hemionus columbianus) density on a mid-sized (17.3km²) predator-free island. We documented successional changes associated with forest aggradation and decreased forage quality for deer: early successional shrub/scrub habitat declined 3.8%/year; timber volume increased 4.5%/year; and canopy coverage increased 2.5%. In 2007 – 2008, deer densities were the greatest observed (~44/km²), but then an historic snowstorm reduced deer density by 39%. Density increased slightly in 2010 but from 2010 – 2021, as forests matured, deer density decreased 4.0% per year, declining to 20 deer/km². Despite declines, deer density on the island exceeds mainland densities, and overbrowsing likely continues to disrupt ecosystem processes.

The distance sampling data are formatted to be used in Program DISTANCE.