Westonbirt, The National Arboretum is managed by the Forestry Commission. Westonbirt Arboretum is located near the historic market town of Tetbury in Gloucestershire, England, and is perhaps the most important and widely known arboretum in the United Kingdom. Planted in the heyday of Victorian plant hunting in the mid-19th century, today Westonbirt Arboretum is one of the finest tree collections in the world, carefully laid out within a Grade One listed historic landscape.