The dynamics of carbon following forest disturbance have enormous potential impact on landscape- and regional-scale carbon cycling and storage. Many of the trends have been well-studied following harvesting, fire, and insect outbreaks. However, very few examples are known of long-term biomass and carbon accumulation following major windstorms. A category F4 tornado in May 1985 struck the Tionesta Scenic Area in northwestern Pennsylvania, a well-known primary northern hardwoods forest. I began studying the damage patterns and regeneration in 1986, with annual surveys during the first several years and occasional surveys later until 2010. Using both surviving pre-storm trees and regeneration, it is possible to reconstruct biomass and carbon for nine snapshots during the first 25 years post-disturbance. The following questions are addressed:
(1) What are temporal trends in rate of biomass and carbon accumulation (linear, increasing, asymptote) during the first 25 years?
(2) How much of the intact primary forest carbon vegetation carbon is stored by year 25?
(3) Given the arrival of beech bark disease in the late 1990s, is biomass accumulation in this formerly beech-dominated forest reduced from its likely pre-disease trajectory?
Results/Conclusions
The intact primary forest at the Tionesta Scenic area supports 249.3 Mg ha-1 of woody biomass, and 124.6 Mg ha-1 of carbon. Immediately after the 1985 disturbance, regeneration biomass and carbon were negligible, while 5.6 Mg ha-1 of biomass remained standing it the disturbed area. Regeneration biomass alone in 1987 was 21.7 Mg ha-1, increasing to 61.9 Mg ha-1 in 1999. By 2010, regeneration and survivors together totals 154.71 Mg ha-1 of biomass and 77.36 Mg ha-1 of carbon, suggesting that regeneration and survivors together surpassed 0.5 of the intact forest values in 2007 or 2008 (22 or 23 years post-disturbance). These values are broadly similar to live-tree biomass reported at 71 years post-hurricane in a New England pine-hemlock forest, and appear to slightly exceed biomass in a southern Appalachian watershed at 20 years after clear-cutting. Rates of accumulation did not show any sign of reaching an asymptote during the study period, and annual increment increased roughly threefold between years 2 to 3 and years 17 to 25. These trends do not suggest that biomass and carbon accumulation is suppressed by beech bark disease.