Geoscience Reference
In-Depth Information
of forestry are income from carbon sequestration, wood increment, rotation period
length, discount rates, planting costs, and wood prices. Main drivers for the net present
value of agriculture on current forest land are population density, agricultural suitabil-
ity, and risk adjusted discount rates.
These two values are compared against each other and deforestation is subsequent-
ly predicted to occur when the agricultural value exceeds the forest value by a certain
margin. When the model comes to the result, that deforestation occurs, the speed of
deforestation was constraint by estimates given by equation (24). The speed of de-
forestation is a function of sub-grid forest share, agricultural suitability, population
density and economic wealth of the country.
All symbols and abbreviations in the following equations are explained in the “List
of Symbols”.
Net Present Value of Forestry
The net present value of forestry is determined by the planting costs, the harvestable
wood volume, the wood-price, and benefits from carbon sequestration.
For existing forests which are assumed to be under active management the net
present value of forestry given multiple rotations (F
i
) over the simulation horizon is
calculated from the net present value for one rotation (f
i
) (equation 1). This is calcula-
ted by taking into account the planting costs (cp
i
) at the begin of the rotation period and
the income from selling the harvested wood (pw
i
·V
i
) at the end of the rotation period.
Also the benefi ts from carbon sequestration are included denoted as (B
i
).
The planting costs (equation 3) are calculated by multiplying the planting costs of
the reference country (cp
ref
) with a price index (px
i
) and a factor which describes the
share of natural regeneration (pr
i
). The ratio of plantation to natural regeneration is
assumed to increase with increasing yield for the respective forests (equation 4). The
price index (equation 5) is calculated using the purchasing power parity (PPP) of the
respective countries. The stumpage wood price (equation 6) is calculated from the har-
vest cost free income range of wood in the reference country. This price is at the lower
bound when the population density is low and the forest share is high and at the higher
bound when the population density is high and the forest share is low. The price is also
multiplied with a price index converting the price range from the reference country
to the examined country. The population-density and forest-share was standardized
between 1 and 10 by using equation (7) and equation (8) respectively.
The harvested volume (V
i
) is calculated by multiplying the mean annual increment
(MAI
i
) with the rotation period length (R
i
) accounting for harvesting losses (equation 9).
The rotation period length (equation 10) depends on the yield. Fast growing stands
have a short and slow growing sites a long rotation length. In this study the rotation
length is in the range between 5 and 140 years.
The mean annual increment (equation 11) is calculated by multiplying the esti-
mated carbon uptake (ω
i
) and a transformation factor which brings the carbon weight
to a wood volume (C2W
i
). The carbon uptake (ω
i
) is calculated by multiplying the net
primary production (NPP
i
) with a factor describing the share of carbon uptake from
the NPP (equation 12).
