This data package describes a forest restoration management trial in young conifer forests of the western central Cascade Range in Washington State, USA. Young second-growth forests often regenerate as very dense homogeneous stands following harvesting. These forests have low species diversity and often trees experience strong competition for resources. To increase tree vigor and growth and stimulate development of diverse understory shrub species stands are thinned with the long-term goal to restore diverse functional older forests that provide habitat and are resilient to disturbance. The Restoration Thinning Program under the Cedar River Habitat Conservation plan conducted thousands of acres of thinning with varying prescriptions. This trial was part of the restoration thinning program and was designed to test what type of prescription would lead to better tree growth and understory development. We tested two different thinning densities as well as uniform and clumped distribution of residual trees. The trial areas were sampled twice following treatment and tree and understory data were collected. Thinning prescriptions differed in response of overstory tree growth and understory response. Initial trial design and overstory measurement reports are included in the data package.