Old and potential old forest in the Lake States, USA

Data from the last two inventories of timberland in the Lake States, USA were used to determine the area, ownership, distance from roads, and changes in average stand age of existing and potential old forests in the region. Inventory dates, by state, were 1980 and 1993 for Michigan, 1977 and 1990 for Minnesota, and 1968 and 1983 for Wisconsin. In this paper, timberland is considered forest land that is capable of growing at least 1.4 cu m per ha per year of wood under natural conditions and that is not reserved from harvesting. (Old forests are more than 120 years old, and potential old forests are between 80 and 120 years old.) During the most recent inventory, 2% of the total area of timberland was old forest and 14% was potential old forest. The maple-beech-yellow birch (Acer-Fagus-Betula alleghaniensis) forest type accounted for about 40% of both old forest and potential old forest. Private landowners owned more than 70% of all old forest timberland in the previous inventory and 64% in the most recent inventory. On average, old forests and potential old forests were found significantly farther from maintained roads than other timberland. As a result of increased stand age, more than 200 thousand ha of potential old forest in the previous inventory were reclassified as old forest in the most recent inventory. Natural disturbances resulted in a decrease of almost 14 thousand ha of old forest between inventory periods. Human-induced disturbances accounted for most of the area of old forest lost between inventories. Plant succession, natural stand aging, improved stocking levels, or reclassification to timberland resulted in more than 1.2 million ha being reclassified as potential old forest.