CARBON ALLOCATION IN AN OLD-GROWTH FOREST IN THE GREAT LAKES REGION OF THE UNITED STATES

We measured components of ecosystem respiration and biomass from wood, foliage and roots in two stands in an old-growth hemlock-northern hardwood forest. Respiration was measured by the chamber method and upscaled to the stand level. Wood production was calculated from the increase in tree size. Foliage biomass was measured from litterfall. Root production was measured from in-growth root cores. Based on the measurements of respiration and biomass we calculated gross primary production (GPP) and net ecosystem production (NEP). The annual GPP was estimated as 1144 and 1089 g C m y in the hardwood and hemlock stands, respectively. GPP was partitioned into 131, 115, 270, 168, 257, 203 g C m y of wood, foliage, and root respiration, and wood, foliage, and root production, respectively, in the hardwood stand, and 206, 72, 155, 190, 139, 327 g C m y of wood, foliage, and root respiration, and wood, foliage, and root production, respectively, in the hemlock stand. The percentage of GPP allocated to wood, foliage and roots for growth and respiration was 20%, 23%, and 57%, respectively, for the hardwood stand, and 31%, 14%, and 55%, respectively, for the hemlock stand. The ratio of net primary production (NPP)/GPP was 30% in the hardwood stand and 33% in the hemlock stand. INTRODUCTION Large-scale ecosystem carbon modeling has been constrained by our limited knowledge in carbon allocation from GPP to respiration and biomass production. The fixed ratio of carbon allocated to wood, foliage and roots that many modelers used may be biased due to the variation in the ratio with forest stands or over the course of stand development. Studying carbon allocation is also important in understanding forest growth, succession, and responses to environmental stresses. Studies on carbon allocation and complete annual carbon budgets are limited relative to incomplete carbon budget studies such as carbon fluxes or biomass inventories. Combining eddy covariance measurements of NEP, chamber measurements of flux, and biometric measurements is necessary for detailed information on carbon allocation. MATERIALS AND METHODS The study area is located on the boundary of the Sylvania Wilderness and Recreation Area in the upper peninsula of Michigan, USA (46° 14' 31'' N, 89° 20' 52'' W). It is a hemlock – northern hardwood forest dominated by either eastern hemlock (Tsuga canadensis) or sugar maple (Acer saccharum). Trees ranged from 0-350 years old, but old trees dominated the canopy. The first study stand was dominated by sugar maple with DBH of 25.9 cm, basal area of 33.1 m ha, and leaf area index (LAI) of 4.1. The second stand was dominated by hemlock with DBH of 38.8 cm, basal area of 83.8 m ha, and LAI of 3.8. Leaf biomass was measured from litterfall. DBH was measured with band dendrometers. Growth of roots was estimated with in-growth root cores. We measured soil, woody debris, stem, and leaf respirations using the chamber method (LI6400, LI-COR, Inc., Lincoln, NE, USA). We used exponential equations to analyze the relationship between respiration and temperature. RESULTS AND DISCUSSION The hardwood stand stored 12,548 g C m of carbon, less than the hemlock stand that stored 14,232 g C m of carbon. Wood, foliage and roots accounted for 94%, 1%, and 5%, respectively, of total carbon in both stands. The root/shoot ratio was 0.052 for the hardwood stand and 0.046 for the hemlock stand.