Progress 10/01/02 to 09/30/05
Approximately 4100 NPP data were collected during the three year study. Prior to this study global NPP observations were based on < 500 data, with very poor coverage for tropical ecosystems. Biome averages for NPP differed dramatically between the older and revised estimates for tropical forests, with the older estimates being much greater than estimates obtained in this study, and boreal forests, with older estimates being much smaller than the estimates obtained in this study. Despite their small percent coverage of all terrestrial ecosystems, bamboo and mangrove forests had very high NPP, although not as high as tropical broad-leaf evergreen forests. Analysis of managed ecosystem NPP data clearly showed that management activities and land use changes have a far greater effect on NPP than responses of NPP to elevated CO2 experiment studies.
These data clearly illustrate that changes in land use (e.g. conversion from prairie to agriculture) and management practices (e.g. fertilization) have far greater effects on NPP than elevated atmospheric CO2 concentrations, suggesting more focus should be directed towards understanding land use change effects on biogeochemicstry of terrestrial ecosystems.
- Martin, J.L. and Gower, S.T. 2006. Boreal mixedwood tree growth on contrasting soils and disturbance types. Can. J. For. Res. (In Press)
- Martin JL, Plaut J, Gower ST & Holmes B (2005) Carbon content of boreal mixed-wood stands following logging. Global Change Biol. 11: 1883-1894.
Progress 01/01/04 to 12/31/04
The boreal forest logging studies conducted in central Saskatchewan and northern Manitoba did not show significant decreases in soil carbon content following logging, although there was evidence that detritic carbon content was redistributed from the surface litter to mineral soil. Coarse woody debris, an important component of forest carbon content, typically was greater immediately after harvest, reached a minimum approximatelt 20-40 years after harvest, and then increased.
The results are highly relevant to ecologists and earth system scientists modeling the global carbon cycle because many used the early NPP and carbon allocation data sets, the only ones available at the time, to parameterize and validate the NPP component of their terrestrial carbon cycling models. Additional logging studies are needed to better understand the effects of logging on soil carbon content and distribution.
- Howard, EA, ST Gower, JA Foley, and CJ Kucharik. 2004. Effects of logging on carbon dynamics of a jack pine forest in Saskatchewan, Canada. Global Change Biology 10:1267-1284.
Progress 01/01/03 to 12/31/03
Forests are an important source for fiber and fuel for humans, and contain the majority of the total terrestrial carbon. The amount of carbon stored in the vegetation and soil are strongly influenced by environmental constraints on annual carbon uptake and decomposition, and time since disturbance. Increasing concentrations of atmospheric carbon dioxide, nitrogen deposition, and climate warming induced by greater greenhouse gas concentrations in the atmosphere influence carbon accumulation rates of forest, but their effects will likely differ in direction and magnitude among forest ecosystems. The net interactive effect of global change on the forest C cycle is poorly understood. The growing demand for wood fiber and fuel by humans, and the ongoing anthropogenic perturbations of the climate have changed the natural disturbance regimes (i.e. frequency and intensity) and these changes influence the net exchange of CO2 between forests and the atmosphere. Net primary
production of terrestrial ecosystems, the annual accumulation of carbon in the form of vegetation organic matter, is an important determinant of the net exchange of carbon dioxide (CO2) between terrestrial ecosystems and the atmosphere. Here we summarize NPP and carbon allocation patterns for the major terrestrial biomes of the world and show the original values significantly underestimate the carbon sink strength for many of the major terrestrial ecosystems. On average, the Whittaker and Likens biome NPP averages were 124% smaller than averages compiled in this study, with the largest discrepancies occurring for croplands (474 to 717% for temperate and tropical crops, respectively), deserts (188%) and grasslands (121 to 189% for temperate and tropical grasslands, respectively). To date, the role of forest products in the global C cycle has largely been ignored, and important emissions associated with the production, transport and utilization of the forest products have been excluded
leading to erroneous conclusions about net C storage in forest products.
The results are highly relevant to ecologists and earth system scientists modeling the global carbon cycle because many used the early NPP and carbon allocation data sets, the only ones available at the time, to parameterize and validate the NPP component of their terrestrial carbon cycling models.
- Burrows, S. N., S. T. Gower, J. M. Norman, G. Diak, D. S. Mackay, D. E. Ahl, M. K. Clayton, 2003. Spatial variability of net primary production for a forested landscape in northern Wisconsin. Canadian Journal of Forest Resources 33:2007-2018.
- Gower, S.T. 2003. Patterns and mechanisms of the forest carbon cycle. Annual Reviews Energy and Environment 28:169-204.