Posts Tagged reforestation

Carbon Dioxide Fertilisation

Posted by on Friday, 11 March, 2011

The issue of carbon dioxide fertilization applies most immediately and understandably to managing forests and woodlands to reduce fire risk. In addition, carbon dioxide fertilization may have an effect on plant competition that contributes to shifts in species distribution, including post-fire recovery. This factor complicates projections about how southwestern forest and woodlands will be affected by global warming. Experiments testing the effects of carbon dioxide fertilization indicate rising atmospheric levels will result in an increase in herbaceous production (Nowak et al. 2004). This increase will translate into more fine fuels that can carry fire in forests and woodlands. Meanwhile, the improved growth of trees exposed to carbon dioxide fertilization indicates that rising levels of this greenhouse gas may exacerbate the tendency toward increasingly dense forests. Plants in lower light levels (i.e., understory plants) survive better in conditions of elevated carbon dioxide. The reintroduction of a surface fire regime can help counteract this tendency toward increased density.

Forest protection and reforestation are widely acknowledged means for sequestering carbon from the atmosphere and storing it in plants, at least until a stand-replacing fire occurs. Not only does a stand-replacing fire release carbon dioxide into the atmosphere as it burns plants and wood, it arguably may cause a reduction in the disturbed stand’s ability to sequester carbon until a full tree canopy is reestablished. Carbon dioxide fertilization may improve seedling survival rates after a large-scale disturbance, but this has not been tested in the field.

Reducing the risk of large-scale crown fires by treatments such as thinning understory trees could be seen as a means of keeping carbon sequestered in forests. Forestry practices such as thinning treatments, intermediate, shelterwood and seed-tree harvest cuts, as opposed to clear-cuts, also leave many mature trees standing. Carbon dioxide continues to be taken up by the remaining trees, which can grow better with the reduction of competition for limited resources. Meanwhile, carbon is also sequestered in the harvested lumber for decades or more. When small-diameter wood is used as biomass for heat or energy production, it displaces the need for using fossil fuels for this purpose.

Land managers may want to incorporate some of the information on carbon dioxide fertilization effects, including the value of intact forests for carbon sequestration, into their educational materials about the need to treat stands to reduce fire risk. They may also be interested in the scientific literature that contains many reports of carbon dioxide fertilization experiments involving different wildland species.

Carbon Fertilization