Forest biomass growth is almost universally assumed to peak early in stand development, near canopy closure, after which it will plateau or decline. The chronosequence and plot remeasurement approaches used to establish the decline pattern suffer from limitations and coarse temporal detail. We combined annual tree ring measurements and mortality models to address two questions: first, how do assumptions about tree growth and mortality influence reconstructions of biomass growth? Second, under what circumstances does biomass production follow the model that peaks early, then declines? We integrated three stochastic mortality models with a census tree-ring data set from eight temperate forest types to reconstruct stand-level biomass increments (in Minnesota, USA). We compared growth patterns among mortality models, forest types and stands. Timing of peak biomass growth varied significantly among mortality models, peaking 20-30 years earlier when mortality was random with respect to tree growth and size, than when mortality favored slow-growing individuals. Random or u-shaped mortality (highest in small or large trees) produced peak growth 25-30 % higher than the surviving tree sample alone. Growth trends for even-aged, monospecific Pinus banksiana or Acer saccharum forests were similar to the early peak and decline expectation. However, we observed continually increasing biomass growth in older, low-productivity forests of Quercus rubra, Fraxinus nigra, and Thuja occidentalis. Tree-ring reconstructions estimated annual changes in live biomass growth and identified more diverse development patterns than previous methods. These detailed, long-term patterns of biomass development are crucial for detecting recent growth responses to global change and modeling future forest dynamics.
Bibliographical noteFunding Information:
Acknowledgments Funding for this research was provided by the american revenue recovery act and the Us Department of Interior northeast climate science center. nick Jensen, mike reinikainen, John segari, Kyle gill, amy milo and others collected field data and/ or measured and cross-dated tree rings. We thank Bruce anderson and the superior national Forest for logistical support and shawn Fraver and two anonymous reviewers for reviewing this manuscript. any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.s. government.
- Net primary productivity
- Stand dynamics
- Sub-boreal forests
- Temperate forests