UMBS Forest Carbon Cycle Research Program

1. Forecasting Carbon Storage in Aging Forests of the Upper Mid-West: New Insights From the Forest Accelerated Succession ExperimenT (FASET) Peter S. Curtis, Christopher M. Gough, Lucas E. Nave, Brady Hardiman, Gil Bohrer, Abby Halperin, Christoph S. Vogel, Kyle Maurer, Knute Nadelhoffer, James Le Moine, Jed Sparks Ohio State University, University of Michigan, Virginia Commonwealth University, Cornell University UMBS Forest Carbon Cycle Research Program

2. Current Status of the Great Lakes Forests • They cover about half of their original area. • They bear little structural or compositional resemblance to the original forest. • They are mostly young and homogeneous. www.nrs.fs.fed.us UMBS Forest Carbon Cycle Research Program

3. WE ARE HERE Many Stands Are Now at an Ecological Transition, Between Young and Potentially Old Community Types UNEVEN-AGED (maple, oak, pine) Succession ASPEN MORTALITY natural senescence, pathogens, insects EVEN-AGED (mostly aspen) Forest age (years)

4. Potentially Old Timberland (80-120 yrs) in the Lakes States Northern Minnesota: 369,000 ha (10% all timberland) Southern Superior Uplands: 830,000 ha (16% all timberland) Northern Superior Uplands: 104,000 ha (9% all timberland) Northern Great Lakes: 643,000 ha (13% all timberland) Eastern Broadleaf Forest: 672,000 ha (19% all timberland) All timberland: 19,494,000 ha Potentially old: 2,747,000 ha (14%) Old: 464,000 ha (2%) (after Schmidt et al., 1996)

5. Although some forests accumulate C for centuries, the mechanisms behind sustained rates of C storage in aging deciduous forests have not been identified. Luyssaert et al. (2008) Gough et al. (2008) UMBS Forest Carbon Cycle Research Program

6. Conventional theory suggests declining productivity and C storage in over-mature stands. • Increasing biotic and structural complexity with age could alter this trajectory. UMBS Forest Carbon Cycle Research Program

7. The UMBS Forest Carbon Cycle Research Program • Peter Curtis, Ohio State Univ. • Gil Bohrer, Ohio State Univ. • Chris Gough, Virginia Commonwealth Univ. • Chris Vogel, Univ. Michigan • Knute Nadelhoffer, Univ. Michigan • DaniloDragoni, Indiana Univ. This research is supported by the Office of Science, U.S. Department of Energy, through the Midwestern Regional Center of the National Institute for Global Environmental Change, and the National Institute for Climate Change Research.

8. The UMBS landscape is a mosaic of forest stands varying in age and disturbance history Sampling transects Burn chrono-sequence

9. More Diverse Forest Plots Are More Resilient to Carbon Storage Declines With Age Gough et al. (2010) UMBS Forest Carbon Cycle Research Program

10. Older Plots That Are More Structurally Complex Have Higher Wood Production • Examples of canopies with Low (A), Medium (B), and High (C) rugosity but with equivalent Leaf Area Index (LAI). • Canopy features are marked with roman numerals. We measure canopy complexity (rugosity,r) with a portable canopy lidar system. UMBS Forest Carbon Cycle Research Program Hardiman et al. (in review)

11. Relationship Between Canopy Complexity, Stand Age, and Wood NPP • Rugosity reaches a maximum value at 70-80 yrs. • Wood NPP is exponentially related to rugosity. • Rugosity is largely independent of LAI and is more strongly correlated with wood NPP. UMBS Forest Carbon Cycle Research Program

12. The Forest Accelerated Succession ExperimenT (FASET) Conceptual model of NEP before, during, and following aspen and birch mortality. N availability will have an important effect on final NEP. UMBS Forest Carbon Cycle Research Program

13. Increasing Aspen and Birch Mortality: • Accelerated fine root turnover • Reduced soil respiration • Prompted the redistribution of N from the foliage of early to later successional species. Effects on fine root NSC and turnover. UMBS Forest Carbon Cycle Research Program Effects on soil respiration, temperature, and moisture.

14. Leaf N content decreased in senescing (EM) aspen but increased in neighboring (AM) maple. • Leaf δ15N increased significantly in neighboring maple and oak. Effects on leaf %N in aspen, maple, and oak Effects on leaf δ15N in aspen, maple, and oak UMBS Forest Carbon Cycle Research Program

15. Soil N availability increased with increasing aspen/birch mortality. • Hydrological and gaseous N losses were small, but measureable. Effects on Ion Exchange Resin Bag (IERB) recoverable NH4 and NO3 UMBS Forest Carbon Cycle Research Program Effects on hydrologic (left) and gaseous (right) N losses.

16. Growing season NEE was reduced as aspen/birch mortality progressed. • This was due to lower GPP in the FASET plot. Mortality effects on growing season (top) and dormant season (bottom) NEE. UMBS Forest Carbon Cycle Research Program

17. Conclusions • Increased N availability and canopy complexity work in concert to support increases in production as these forests age • Likely mechanisms are improved light capture and light use efficiency. • These results provide new insights into the mechanisms by which deciduous forests maintain high rates of production into late succession • They suggest that forests of the upper Mid-West will continue to be important C sinks for decades into the future. UMBS Forest Carbon Cycle Research Program