First Decadal Response to Treatment in the Acadian Forest Ecosystem Research Program

Maintenance of late-successional structures to enhance biodiversity and sequester carbon has been a major focus of forest research over the past two decades. Several long-term, disturbance-based silvicultural trials have been installed to try to balance the maintenance of complex forest conditions yet allow for economical extraction of timber. One of the oldest of these contemporary efforts is the Acadian Forest Ecosystem Research Program (AFERP) located in central Maine. AFERP is now nearly 15 years old and, having received its second harvest entry, allows for a decadal review of its long-term sustainability in terms of forest growth, regeneration response, and maintenance of complex forest structure. AFERP includes two versions of ‘expanding gap’ treatments on a 100-year rotation: a ‘large-gap’ system that encourages regeneration of species with intermediate shade tolerance by using 0.2 ha gaps expanded every 10 years; and a ‘small-gap’ system that encourages shade-tolerant species with smaller 0.1 ha gaps expanded every 20 years. AFERP also includes an unharvested control and is replicated three times across nine 8.7-11.3 ha units. Prior to treatment, there was no significant difference among units in either total volume or basal area (275±11 m3 ha-1 and 37.7±1.1 m2 ha-1, respectively [mean± 1 S.E.]). Following treatment, there were significant differences in both volume and growth, often due to differences in regeneration response and differential mortality patterns among the treatments. For example, basal area growth averaged 0.22±0.04 m2 ha-1 yr-1, -0.08±0.13 m2 ha-1 yr-1 and -0.27±0.15 m2 ha-1 yr-1 for the large gap, small gap and control treatments, respectively; this resulted from higher levels of balsam fir and paper birch mortality in the small gap and control treatments. Further, there were strong treatment effects on regeneration composition, with both gap systems having much denser Pinus strobus and Picea spp. regeneration than controls.