PARENT SESSION
Oral Session 5: Disturbance Ecology I: Scaling, Wind, and Ice.
Presiding: D McKenzie
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 113.

Ice storm impacts on carbon cycling in pine forests under elevated CO₂, nutrients and thinning.

McCarthy, Heather^*,1, Oren, Ram¹, Johnsen, Kurt ², Kim, Hyun-Seok¹, ¹ Duke University, Durham, NC, USA² USDA Forest Service, RTP, NC, USA

ABSTRACT- Ice storms are common events over large parts of the U.S., including the southeast. After a moderately severe ice storm event, measurements of storm effects were made in an unthinned free air CO₂ enrichment experiment in a 21-year-old loblolly pine forest and an adjacent thinned loblolly stand to judge the impacts of elevated CO₂, differing nutrient supplies and thinning on the initial damage caused by the storm and the subsequent recovery of carbon sequestration capacity. The measurements of initial damage showed that plots under ambient CO₂ suffered significantly (p=0.055) more damage than plots exposed to elevated CO₂, with fertilization having no impact (p=0.75). The average biomass lost under ambient CO₂ was 206 C g m^-2, while plots under elevated CO₂ lost an average of 78 C g m^-2. This difference resulted from fewer trees being damaged under elevated CO₂ (20% damaged vs. 30%), and less biomass being lost from each tree that was damaged (averaging 2383 g C vs. 4190 g C). As expected, the thinned stand suffered much greater damage as a result of the ice storm than any of the unthinned treatments, with an average of 436 g C m^-2 lost, as a result of a greater proportion of trees being damaged (42%) and the average damage per tree being much greater (13,883 g C). In addition, ambient treatments (including fertilized and thinned) lost more leaf area than elevated CO₂ treatments with 0.4 m² m^-2 lost vs. 0.18 m² m^-2. The greater loss of biomass and leaf area under ambient CO₂ resulted in a greater reduction in biomass production in the year following the storm (48% vs. 33%) and a greater increase in ecosystem respiration. Both of these factors contribute to a reduction in carbon being sequestered in the ecosystem, so that elevated CO₂ by reducing the severity of the initial ice storm damage consequently reduced the negative effects of the storm on carbon storage.

Key words: ice storm, loblolly pine, elevated CO₂, carbon storage