We report on a long-term study of changes in the diameter distribution of red and white oaks in old-growth forest of Indiana. We expand the scope of a prior 50-year demographic study of a 20.6-ha stand by (1) extending the census period, (2) comparing diameter distributions in the large stand with those of a smaller (2.3-ha) stand, and (3) examining small-diameter ingrowth of red oaks into both stands. Oaks displayed bell-shaped or even-aged diameter distributions in 1926, suggesting a history of disturbance from timber removal, grazing, and fire. These exogenous disturbances were suppressed starting in 1917 with acquisition of the property by Purdue University. Subsequent censuses indicated considerable ingrowth of nonoak stems into both stands. Oaks that were mid-sized in 1926 gradually moved through the size classes and were replaced by younger individuals in the small stand but not in the center of the large stand. The survey of red oak saplings confirmed this pattern, revealing numerous recruits in the small stand but virtually none in the large stand. These data support the view that oaks are failing to regenerate in part due to shade-intolerance and a waning disturbance regime in the large stand interior.
Aldrich, Preston R.; Parker, George R.; Severson-Romero, Jeanne; Michler, Charles H. 2005. Confirmatin of oak recruitment failure in Indiana old-growth forest: 75 years of data. Forest Science. 51(5): 406-416.