Land Use, Land-Use Change and Forestry

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Fact Sheet 4.13. Forest Fertilization

Fertilization is the addition of nutrient elements to increase growth rates or overcome a nutrient deficiency in the soil. Fertilization can be divided into two sub-activities: increasing the quantity of fertilizer and improved fertilizing quality (i.e., timing and dosage) so that as much nutrient as possible is taken up by the trees and correspondingly less becomes waste to groundwater. Unintentional fertilization is occurring in many forests downwind of industrial centers, as a result of the deposition of nitrogen and sulfur from the atmosphere.

Fertilization leads to higher growth of aboveground and below-ground biomass, thus increasing carbon storage. The process is well understood except for some of the soil processes, and reliable models are available in many countries to predict the increased biomass growth. Among the few studies on forest fertilization and carbon sequestration are Hoen and Solberg (1994), Lunnan et al. (1991), and Nabuurs et al. (1999).

Use and Potential
This practice is used in most plantation management systems around the world, with varying intensity. In capital intensity forestry in Scandinavia, it represents one of the most profitable investments in forestry on low to medium site classes.

Lunnan et al. (1991) report the effects of carbon storage on boreal forests in Norway with (i) two applications of fertilizer, each with 173 kg N (as NH4NO3) ha-1; (ii) 10 and 15 years between the two fertilizations; and (iii) 30 years before clear-fellings. The table provides estimated carbon storage and costs in forest biomass (only in biomass of stem, branches, and root-not in soil and humus) by fertilizing stands of Picea abies and Pinus sylvestris in boreal forests.

Picea abies
Pinus sylvestris
Carbon storage (tC ha-1 yr-1 for 10 years)
Costs per fertilization (1999 US$ ha-1)
Cost efficiency (1999 US$ t-1 C)

* On relatively low site classes; costs and carbon fluxes (including end-use decays) discounted with 7-percent real annual rate of interest.

The rate of the carbon storage varies with many factors-such as species, site productivity, climate, soil conditions, the degree to which nutrition is the limiting growth factor, and fertilization amounts.

There are no global or regional statistics available regarding the total area to which forest fertilization may apply. This practice might be feasible at the country level, however. For example, Lunnan et al. (1991) estimate that the potential area for Norway per year is between 6 and 20 percent of the total productive forest area of the country.

Methods and Uncertainty
The same factors are valid here as those described in Fact Sheet 4.12. If yield tables or models are used, one needs to know the dose/response relationship between fertilization amount and stem volume increase. The ecological impacts of forest fertilization may not be fully understood yet for some ecosystems.

Monitoring, Verifiability, Transparency, and Permanence
The situation is similar to that described in Fact Sheet 4.12.

Associated Impacts
Associated positive environmental benefits are unlikely to result from this activity. In some areas, however, it may have several negative environmental impacts. The use of fertilization may increase the leakage/emission of N2O and NOX to air, ground, and water and influence soil processes (see other chapters in this Special Report). Impacts on jobs and income are about the same as described in Fact Sheet 4.13. The main barriers today for this activity are relatively high costs and the possibility of negative environmental impacts.

Relationship to IPCC Guidelines
See Fact Sheet 4.12.

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