PARENT SESSION
Oral Session #62: Forest Carbon Dynamics.
Presiding: R. Norby
Wednesday, August 7. 1:00 PM to 4:45 PM. Greenlee Meeting Room, TCC.

Carbon allocation and interannual variability of net primary production in a temperate mixed deciduous forest.

Newman, Gregory^*,1, Arthur, Mary¹, Muller, Robert¹, ¹ Department of Forestry, Lexington, KY

ABSTRACT- Strong relationships have been found between ANPP and both LAI and soil nitrogen availability, although, it is unclear whether these relationships hold for total NPP. Additionally, the range of interannual variability in productivity and above- and belowground carbon allocation is rarely addressed. We measured ANPP over three years and total NPP over two years in a temperate mixed deciduous forest to examine the relationship between productivity and LAI and soil nitrogen availability, and to document interannual variability in net primary production and carbon allocation. ANPP was significantly and positively related to both LAI (p=0.017) and nitrogen mineralization (p=0.001). However, total NPP was not correlated with LAI (p=0.891) due to a negative correlation between BNPP and LAI (p=0.003). There was no correlation between nitrogen mineralization and BNPP, resulting in a moderately significant relationship for total NPP (p=0.067). Mesophytic hardwood species, on mesic slope aspects, responded more strongly to interannual variations in growing season precipitation than Quercus spp.-dominated xeric slope aspects. A moderate drought during the first study year resulted in 50% (p=0.002) and 18% (p=0.191) decreases in the following year's litter mass for mesic and xeric stands, respectively. Mesic stands returned to previous levels the next year while xeric stands did not change. BNPP on xeric stands was consistently greater and showed less variability between the two study years than on mesic stands. Annual patterns of carbon allocation showed distinct shifts from belowground to aboveground sinks on mesic stands and no differences on xeric stands in response to increased soil water availability. High interannual variability of NPP observed on mesic stands was largely attributable to differences in leaf production and was accompanied by dramatic shifts in carbon allocation between leaves and roots. This study suggests that mesophytic hardwoods in the southeastern U.S. are more responsive to changes in annual precipitation patterns and may be highly susceptible to increasing occurrence of drought associated with global climate change.

KEY WORDS: forest productivity