Approximately 170,000 ha have been logged on the Tongass National Forest since the early 20 th century, resulting in a vast network of young, and even-aged Sitka spruce-western hemlock stands. Many of these stands are in a stem exclusion phase, with dense overstories that competitively shade out understories. In 2001, a USDA Forest Service planning committee convened to develop multiple resource treatments to examine the effects of precommercial thinning, resulting in a collaborative, long-term

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... project to improve knowledge and catalyze the Tongass-Wide Young Growth Studies (TWYGS) project. This project was designed collaboratively, implemented by partners across the Tongass, and monitored via the Forest Service's Pacific Northwest Research Station. Of the four TWYGS experiments, one has been measured three times in 16 years since treatment. We examine forest development following three levels of precommercial thinning in 15-to 25-year-old stands: unthinned, 4.3 m spacing, and 5.5 m spacing. Results from 5, 10, and 16 years highlight key differences in understory cover and forage biomass between thinned and unthinned treatments. We identify tradeoffs between overstory and understory development following treatment, which will have impacts on future management planning. TWYGS is a hallmark of management-research collaboration, and provides much needed insight into young-growth silviculture throughout the temperate rainforest.