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.
|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 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.