My objective is to understand the nature of stability in old-growth forests, particularly in eastern mesic old-growth forests in which the dominant canopy species also reproduce well in the understory. I wish to quantify changes that occur and variations in those changes over time. How bounded is the internal variation of such forests? The present study addressing these concerns originates in 1977 when I established transects through an old-growth beech-sugar maple stand in Hueston Woods, southwest Ohio. I recorded information on treefall gaps and canopy trees (point-centered quarter method for trees ³25 cm dbh). I have resampled the site every four years since then.
Gaps have closed or been rejuvenated by new disturbances. Canopy trees have grown, died and been replaced. Snags (>2.5 m ht) formed by the death of canopy trees have deteriorated or remained standing. Both trends (long term consistent changes, though at different rates) and fluctuations (changes that vary from time interval to time interval) occur though cannot always be distinguished. Tree density went from 171/ha in 1977 to 159 in 1991 but has remained roughly constant (157-164) since. Tree basal area decreased from 1977 to 2001 but was near 1977 levels in 2005 (36.5 m2/ha). From 1977 to 1997 beech declined in density and basal area while sugar maple increased. From 2001 to 2005 the two stayed at about the same relative values. Annual mortality rates of canopy trees have varied from 1.3% (1977 to 1991) to 1.3% (1991 to 1997) to 1.5% (1997 to 2001) to 0.7% (2001 to 2005). Snags deteriorate (fall to become logs and stumps) at different rates: annual disappearance rates went from 6.2% (1991 to 1997) to 19.0% (1997-2001) to 8.3% (2001 to 2005). After 32 years of study I still have much to learn and Hueston Woods has much to teach.