Mechanisms maintaining productivity in a chronosequence of Northern forests

Mechanisms maintaining productivity in a chronosequence of Northern forests

Project Abstract: 

Increasing concentration of atmospheric carbon dioxide (CO2) since the Industrial Revolution is prompting global climate change. Uptake of atmospheric CO2 by forests has the potential to mitigate this rise, but the role of old forests in the global carbon budget is uncertain. Previous work demonstrates that old forests are substantially more productive than expected but mechanisms underlying maintained productivity are poorly understood. To test the hypothesis that canopy structure is more complex in old forests, boosting light interception and thus productivity, we characterized canopy structural complexity, nitrogen availability, and forest productivity in forest stands spanning more than 150 years of development and succession. Canopy structural complexity was measured as rugosity, an integrated measure of vertical and horizontal variability in the distribution of canopy elements. Canopy structural complexity increased with stand age and correlated with above ground productivity (r2=0.69, p<0.05). Total canopy leaf area, however, was static once stands were older than ~50 years, suggesting that the 3D arrangement of leaf area plays a more important role in determining productivity of aging forests than increases in total leaf area. The oldest stands surveyed were more productive per unit of canopy structural complexity than expected based on a linear relationship, indicating that other factors besides canopy structure are influencing productivity. Foliar nitrogen concentration and natural abundances of 15N indicate greater nitrogen availability and faster nitrogen cycling rates in these old forests with structurally complex canopies. We posit that this greater relative availability of nitrogen and the increase in canopy structural complexity with age in these stands together maintain productivity in old forests. These trends suggest that as forests age their productive potential, and thus CO2 storage capacity, may continue to be significant in the global carbon budget. Management strategies that facilitate and promote development of old forests will increase their carbon storage potential.

Funding Agency: 
Years Active: 
2009 - 2011

Research Sites:

Colonial Point OSP: Wooded peninsula on W shore of Burt Lake. Most of property owned by UMBS.
UMBS AmeriFlux Tower The UMBS AmeriFlux Tower, a 46 m tall, self-supporting tower with associated lab building, power, and communication lines was completed in June, 1998...
UMBS Burn Plots There is a set of natural and experimental burn plots on our property that now creates a hundred year chronosequence of plant succession after fire....