2.1. FOROM
The FOrest Resource Outlook Model (FOROM) is a partial equilibrium model of the world’s forest sector that includes forest resources, timber supply, demand for intermediate and final products, and international trade (see [
33]). The modelling framework enables investigations into the influence of external shocks and changes in future socioeconomic conditions on the production, consumption, trade, and prices of raw material, intermediates, and final products, controlling for changes in forest land area and forest standing stock. The FOROM was originally designed to provide the outlook of the global and U.S. forest sector for the U.S. Forest Service 2020 Resource Planning Act (RPA) Assessment.
The current version of the FOROM represents the global wood product market in terms of 20 distinct interconnected products (
Figure 1;
Appendix A,
Table A1) across 55 countries and regions of the world (
Appendix A,
Table A2), although additional regions and products may be included (see [
34]). The model tracks the complex relationships between wood products, which is of particular importance to certain product categories, such as wood pellets, which may receive feedstock from various sources including coniferous and non-coniferous industrial roundwood, fuelwood, or chips, particles, and residuals from sawmilling activities.
The FOROM consists of solving a series of static equilibria that are connected through dynamic exogenous assumptions. In the static phase, the model maximizes economic welfare for all products in all countries following the law of one price, consistent with the spatial price equilibrium (SPE) framework, where differences in prices between regions are assumed to arise from differences in transport costs (including tariffs and other non-tariff barriers). The most relevant equations of the FOROM model for this study are described below, while the broader modelling framework is presented in
Appendix A.
The objective function maximizes the sum of consumers’ and producers’ surpluses net of transport costs, subject to various constraints related to material balance, resource feasibility, and equilibrium conditions:
where
and
refer to the price and quantity of wood product
k consumed by region
j, while
and
refer to the manufacturing cost and production in region
i. The cost of moving product
k from region
i to
j,
, is a function of the shipping and handling cost,
, and the associated tariffs,
.
The supply of final demand products
f from all regions
i to region j, including domestic supply, must be greater than or equal to the demand in region
j:
where the shadow price gives the demand price,
.
It follows that the sale of wood products
k from region
i to all regions
j must be no larger than what is produced in region
i:
where the shadow price gives the demand price,
.
Consumers’ behavior is represented by a set of constant elasticity demand functions for each final demand product:
where symbols embellished with a bar indicate benchmark levels, and
≤ 0 is the price elasticity of demand. Demand can be linearly approximated by first finding the tangency with the benchmark price and quantity demanded, where small changes in price and quantity are given by:
and then rearranged into an inverse constant elasticity of demand curve:
or simply, in reduced form:
Similarly, each supply region
i is assumed to have a set of constant elasticity supply curves for each product
k, with price elasticity of supply
≥ 0:
which can be linearly approximated in a similar fashion as described for final product demand using benchmark manufacturing costs and quantities:
or simply, in reduced form:
To satisfy material balance in any given region and product, production plus imports must equal the sum of consumption, exports, and the input of product
k required in manufacturing output
n, given as
:
The manufacture of byproducts (i.e., sawmilling byproducts, recycled paper) are a function of primary product manufacturing, represented by:
where
is the amount of byproduct
b ⊆
k recovered per unit of manufactured output
n.
In the static phase, equilibrium prices, quantities, and net trade levels are obtained by solving the problem of maximizing the objective function subject to various economic and engineering constraints. Once a solution for the current period, t, is determined, the model will enter the dynamic phase, in which the parameters of the model are updated based on exogenous drivers (e.g., GDP growth, population growth, changes in productivity, and changes in trade openness) and endogenous variables (e.g., harvest levels, standing stock levels, etc.) in preparation for the next iteration cycle.
Demand is assumed to change over time through exogenous shifts to GDP per capita,
, and translated through the growth rate of per capita GDP,
, and the elasticity of demand with respect to the growth rate of per capita GDP,
:
Supply of harvestable inputs (i.e., industrial roundwood, fuelwood, other roundwood) are assumed to change over time through exogenous shifts to forest area and forest stock:
where
is an exogenous change in the growth rate of forest area at time
t;
is an endogenously determined growth rate of forest inventory, which changes over time based on the specified nonlinear negative relationship between forest growth and stocking density; and
and
are elasticities associated with forest area and inventory, respectively.
The main data source for reference prices, quantities, and trade is FAOSTAT (see
Table A2). Data on production, import value, import quantity, export value, and export quantity are directly recorded in the database. Consumption is calculated as apparent consumption, equal to production plus import minus export. Data on prices of all 20 forest products are not available in the FAOSTAT database. We follow the method proposed in Buongiorno et al. [
35] and choose the unit values of imports or exports (import or export value in US dollars divided by import or export quantity) as the prices. Data on forest areas and stocks are obtained from the FAO’s 2010 and 2015 Global Forest Resources Assessments (FRA).
We employ a goal programming approach for reconciling apparently inconsistently reported data (e.g., negative apparent consumption, gaps between total imports and exports) and missing data for the reference year. This approach also re-estimates input–output coefficients and the manufacturing costs for each country/region. The calibrated manufacturing costs are equal to the price of the output minus the cost of wood and fiber input under the zero-profit assumption in each market. The details of the goal programming approach are explained in [
33].
The United States is disaggregated into six Resources Planning Act (RPA) Assessment regions (
Figure 2) from country-level data, with the primary means of disaggregation based on data from the USDA Forest Service’s Timber Product Output (TPO) program and the United States International Trade Commissions (USITC). These supplemental datasets provided the basis for calculating regional shares, from which FAOSTAT country level data are reconciled.
2.2. IPCC Shared Socioeconomic Pathways
The global research community has developed five Shared Socio-economic Pathways (SSPs) describing alternative changes in economic, social, and environmental factors up to 2100 [
36,
37]. The five broader narratives have been translated into quantitative assumptions in the IIASA SSPs database [
35]. Furthermore, as mentioned above, Daigneault et al. [
32] developed detailed narratives for how the global forest sector, in particular, could vary across the five SSPs. These narratives serve as key inputs into the modeling process. A brief narrative for each is described follows.
The SSP1 (often referred to as the “Sustainability”) scenario characterizes a more sustainable world where consumption is oriented toward less resource-intensive energy. The world focuses more on low-consumption growth and improved energy efficiency. More sustainable awareness reduces damages to the environment. Land use is strongly regulated. Globalization is developing rapidly. All these factors lead to relatively high economic and urbanization levels, and a moderate level of international trade, but the lowest population level. In this scenario, the world faces low challenges to both mitigation and adaptation.
The SSP2 (“Middle of the Road”) scenario describes a world where social, economic, and technological development will not divert markedly from historical trends. This pathway foresees a moderate growth of the global population and economy. Energy generation continues to rely on fossil fuels at a similar rate as today. The global economy is characterized as semi-open by reduced trade barriers. Land use is incompletely regulated. This scenario faces medium challenges to adaptation and mitigation.
SSP3 (“Regional Rivalry”) describes a world with high challenges to adaptation and mitigation, the opposite of sustainability. This pathway features the lowest economic growth and highest population growth. There is only minor improvement in technologies and energy efficiency. Land use change is hardly regulated. Countries focus on achieving energy objectives within their own region. De-globalization severely restricts international trade, and development becomes fragmented across regions.
The world in the SSP4 (“Inequality”) scenario portrays stagnating economic growth among the poorer countries of the world, leading to a persistent and growing divide in the socioeconomic development prospects of rich versus poor countries. High-income nations have high land use change regulations, while low-income nations have weak land use change regulation. In this divided pathway, the world faces low challenges to mitigation for modest climate targets, but it will be quite difficult to adapt to it.
The SSP5 (“Fossil-fueled Development”) scenario envisions a strongly globalized and fossil-fuel-intensive world with high energy use and greenhouse gas emissions. This pathway features a relatively low growth rate of population but an unconstrained growth in economic output. Accelerated globalization leads to a high level of international trade and market connectivity. Land use change is modestly regulated. This “fossil-fueled development” faces high challenges to mitigation, but low challenges to adaptation.
The SSPs were operationalized within the dynamic phases of FOROM through exogenous changes in gross domestic product (GDP), population, technological development, trade openness, and bioenergy demand preferences (
Figure 3 and
Table 1). Wear and Prestemon [
38] developed a method to jointly downscale national-scale income and population projections to counties within the United States. Technological development implies the degree to which the global forest sector becomes efficient in transforming raw materials into finished products. Trade openness relates to the frictions embedded in the model as it relates to the movement of goods between foreign regions of the model. These later two exogenous drivers are stylized to reflect the storylines of the SSPs, consistent with what is outlined in Daigneault et al. [
32].
The demand for bioenergy in the form of fuelwood as well as wood pellets in FOROM is assumed to be driven not only by economic development assumptions, but also by differences in consumer preference and policy assumptions underpinning the IPCC’s shared socioeconomic pathways. For fuelwood demand, FOROM incorporates trends consistent with global primary energy from biomass from the IPCC SSP scenarios (
Figure 4). Similarly, the evolution of wood pellet consumption in FOROM is not only driven by changes in GDP per capita, but also constrained using trends in global secondary biomass energy production to capture SSP-related preference and policy differences (
Figure 5). Global growth rates of secondary energy were used to scale recent regional growth rates. Secondary energy is energy that has been converted, and in the case of bioenergy, this could represent energy sourced from biomass, including wood pellets.