Document: DAV-3-59-95

Carbon balance of long-term experimental pine forests in the Nebraska Sandhills: A tradeoff between net carbon storage and soil carbon losses.

WEDIN, D.A.* ¹, M.BULLERMAN ¹ and T.J.MINNICK ²

University of Nebraska, Lincoln, NE 68583 USA ¹
Nebraska Wesleyan University, Lincoln, NE 68504 USA ²

Abstract:
Expansion of woody vegetation in the Great Plains may significantly affect the region's ecosystem carbon (C) storage. We measured long-term C storage in a site with relatively uniform soils and documented site history, an 11,000 ha experimental Pinus ponderosa forest (average age 70 years) in the Nebraska Sandhills . 20 plots (each 40m by 40m) spanned a canopy cover gradient from C₄-dominated grassland to closed-canopy forest (maximum basal area 40 m²/ha). Total ecosystem C increased across the gradient from ca.2,700 g/m² in the grassland to 10,800 g/m² in the densest forest. The pine duff layer accounted for roughly 5% of this increase, while aboveground pine biomass accounted for 95%. Herbaceous aboveground biomass decreased from >300 g/m² in the grassland to <50 g/m² at basal areas greater than 20 m²/ha. Decreases in fine root biomass across the gradient were matched by increases in belowground woody biomass. Soil C (measured to 35cm depth) decreased from ca 2000 g/m² in the grassland to ca 1000 g/m² in the densest pine forest (r²=0.30, p = 0.019, regression of soil C and pine basal area). Stable C isotope analyses indicated that roughly 20% of the soil C in the forest is new C₃ carbon (post pine establishment). We suggest that these large losses of soil organic matter may not be an acceptable tradeoff to C sequestration by trees in the drought and fire prone Sandhills.

Keywords: carbon storage, Pinus ponderosa, Nebraska Sandhills, grasslands

This abstract is being presented at: 10:30 AM in session:
CARBON STORAGE