Effects of historical and current disturbance on forest biomass in Minnesota

Abstract

Context Historical carbon storage prior to widespread forest clearing is uncertain. We examined aboveground biomass in historical (1847–1908) and current (2004–2008) mixed and broadleaf forests of Minnesota. Objective Our objective was to compare aboveground forest biomass density and total aboveground carbon storage for two forest types with different historical and current disturbance regimes. Methods We used densities and diameter distributions from historical and current tree surveys and applied relationships between diameter and biomass to estimate biomass in historical and current forests for larger trees with diameters C12.7 cm. Results In the 8.5 million ha Northern Mixed Forest ecological division of Minnesota, historical forests ecosystems under a stand-replacing fire regime that produced high density forests contained greater aboveground biomass density (98 Mg/ha) than current forests (53 Mg/ha) disturbed by frequent tree cutting. Historical total carbon storage was 333 TgC and current carbon storage was 158 TgC; estimates depended on diameter distribution and historical forested extent. In the 4.5 million ha Eastern Broadleaf Forest division, historical forests under a frequent surface fire regime that produced low density oak savannas contained less biomass density (54 Mg/ha) than current dense eastern broadleaf forests (93 Mg/ha). Historical total carbon storage was 79 TgC and current carbon storage was 31 TgC, depending on diameter distribution and forested extent. Conclusions Total carbon storage appears to be unrealized due to potential for tree diameter increases in both divisions, stem density increases in the Northern Mixed Forest, and forested extent increases in the Eastern Broadleaf Forest.