Structure and Growth of Century-Old White Pine Plantations in Saginaw Forest, Southeastern Michigan, USA

Saginaw Forest in Ann Arbor, Michigan, includes the second-oldest eastern white pine plantation in the United States, with pioneering thinning experiments among the oldest in the country. With no additional silvicultural treatments occurring since at least the 1950s, we report on the current condition of four planting lots near their century mark to provide silvicultural, cultural, and historical perspectives. Stand density and tree diameter in 2017 were similar across the four lots, all having a significant number of trees > 50 cm diameter at breast height. Tree ring widths suggest that diameter growth was responsive to thinning treatments that occurred before 1955. Today, management geared towards site preservation as a cultural and historical landmark, with an emphasis on intensive invasive species and hardwood ingrowth control and native tree species regeneration, are likely more appropriate than a focus on silviculture. Study Implications: Saginaw Forest in Ann Arbor, Michigan contains the second-oldest eastern white pine plantation in the United States. It underwent pioneering forest thinning experiments that pre-dated similar experiments in the oldest eastern white pine plantation at the Biltmore Estate in Asheville, North Carolina. Silvicultural treatments have not occurred since the 1950s, but the effects of historical thinning treatments are evident today across four planting lots. We summarize the current conditions of this important forestry site, noting a serious threat by invasive species and hardwood ingrowth that should be targeted as a means of preserving this important cultural and historical landmark.