4.2.2.2 Driving Forces for Land-Use Change
| Box 4.2. Disturbance, Age-class Distribution, and their
Implications for Forest Carbon Dynamics
At the stand scale, disturbance events (both natural and anthropogenic)
have three main impacts on the carbon budget (Apps and Kurz, 1993). First,
they redistribute the existing carbon by transferring carbon from living
material, above and below ground, to the dead organic matter pools. Second,
they transfer some of the carbon out of the ecosystem (e.g., into the
atmosphere as combustion products, in the case of fire, and/or into the
forest product sector as raw feedstock, in the case of harvest). Third,
by opening the forest canopy, the disturbance changes the site micro-environment
and restarts the successional cycle for new stand development.
At the scale of forests (typically comprising many stands), the disturbance
regime determines the age-class structure (e.g., the even-age structure
associated with stand-replacing disturbance regimes or the uneven-age
structures associated with individual tree mortality and gap-phase replacement),
and age-class structure of stands and trees making up the forest. The
C stocks in a forest landscape, and the changes in these stocks over time,
are strongly influenced by the age-class distribution (Kurz et al.,
1995b; Turner et al., 1995; MacLaren, 1996; Apps et al.,
2000; Bhatti et al., 2001). In managed plantation forests, the
age-class distribution is controlled by the management regime and harvest
cycle (Heath and Birdsey, 1993; MacLaren, 1996), while in natural forests
other mortality agents play a major role. See Heath et al. (1996)
and Kurz et al. (1995a) for examples.
|
Land management decisions are influenced by many factors.
In the temperate zone, and in the European parts of the boreal zone, these are
mainly technological and economic. Agricultural production is, for example,
heavily influenced by evolving technologies, economic opportunities, subsidies,
and restrictions on international trade. Forestry practices are similarly influenced
by economic returns, trade, and pressures from society (Clawson, 1979; Waggoner,
1994; Wernick et al., 1998). It is within these pressures and opportunities
that carbon mitigation possibilities may be found, and preferably they would
be region specific. Table 4.2 gives an overview of some
of the specific issues of importance in the temperate and boreal zone of the
world.
Competition for land between forestry and agriculture has become less severe.
Forest area is increasing in many regions of the boreal and temperate zone, partly
because agricultural yields have improved or because the profitability of marginal
agriculture has declined. The ability to produce agricultural goods has grown
faster than demand, resulting in a downwards trend in prices (Alig et al.,
1990; Waggoner, 1994). Much abandoned agricultural land has reverted to forest,
either naturally or through deliberate planting. Superimposed over these land
conversions is a transition in forestry from a foraging and gathering operation,
dependent upon primary forest, through a stage of more intensively managed forest,
to total forest ecosystem management. The latter occurs when urbanized societies
press for nature-oriented forest management. Continuously improving technologies
allow low-cost establishment and higher productivity from planted and plantation
forests (Sedjo, 1983; 1999a). In agriculture, also, practices are changing towards
maintaining site fertility or decreasing the risk of erosion.
Silvicultural practices have increased forest growth in many boreal and temperate
regions. The increasing concentration of atmospheric CO2 may also have
contributed to the enhanced growth of forests.
Incentives for planting forests are provided by a combination of market factors
and public policy. Remaining wild forests, such as the public forests in the
US National Forest System and in British Columbia, are becoming less accessible
and have increased harvesting restrictions. Subsidies to harvesting of natural
forests are also being withdrawn elsewhere. For example, large subsidies for
harvesting Russian forests were prevalent during the Soviet era, largely through
subsidized transportation, but have now disappeared. The economic structures
are in transition and industrial production has declined. As a result, harvests
have fallen dramatically in Russia since the 1990s (Nilsson and Shvidenko 1998).
Market forces, reflecting industrial needs for wood, have provided financial
incentives for expansion of commercial forests (Sedjo and Lyon, 1990). This
is a trend expected to continue, because of growing demand for industrial wood
and low profitability in agriculture (Sohngen et al., 1999). Early analyses
suggested that economic returns from plantations (in the tropics as well as
in the temperate and boreal zone) justify investment in a number of regions
(Sedjo, 1983). Recent studies confirm that forest plantations are being established
at a rate of 600,000ha/yr (Pandey, 1992; Postel and Heise, 1988; UN-ECE/FAO,
2000). However, industrial plantation forestry is new in many tropical areas
and yields vary considerably across ecosystems. In many locations where plantations
have only recently been established, little is known about the potential capabilities
for increasing productivity as well as the potential problems that may limit
yields.
Table 4.2: Overview of biological carbon
mitigation issues and opportunities in selected countries/regions
(Based, in part, on Sedjo and Lyon, 1990; Fujimori, 1997; Nilsson and Shvidenko,
1998; De Camino et al., 1999; Sohngen et al., 1999; Zhang,
1996) |
 |
| Region |
Issues |
Options to store carbon arising from the issues |
|
| USA/Canada |
- Primary forest based forestry and second rotation forestry
- High tech forest industry
- Fierce environmental debates
- Large impacts of natural disturbances
- Agriculture under pressure that restore soil C
(excess agricultural land)
|
- Fire management
- Afforestation
- Efficient use of wood products
- Bioenergy
- Farming practices (e.g., reduced tillage)
|
|
| Europe |
- Agriculture under pressure, afforestation of agricultural lands
- Changing ownership
- Forest health problems
- Move towards nature-oriented forest management
- High tech forest industry
- In eastern Europe, privatization of forest ownership that restore
soil C
|
- Nature-oriented forest management
- Nature reserves
- Afforestation
- Efficient use of wood products
- Bioenergy
- Farming practices (e.g., reduced tillage)
|
|
| Russia |
- Transition to market economy
- Bad financial situation of forest service
- Large impacts of natural disturbances
- Low levels of fellings
|
- Natural regeneration on abandoned agricultural land
- Fire management
- Capacity building
- Farming practices that restore soil C
|
|
| Japan |
- Plantation-based forestry and managed secondary forestry
- High tech forest industry
- Forest health problems
- Move towards nature-oriented management
|
- Efficient use of wood
- Nature-oriented forests
- Reserves
- Bioenergy
|
|
| China |
- Transition to market economy
- Transition from non-wood fibre sources to using wood fibre
- Floods resulting from loss of forest
|
- Afforestation with plantations
- Protecting primary forests
- Flood protection
- Farming practices (e.g., reduced tillage) that
restore soil C
|
|
Australia/
New Zealand |
- Plantation-based forestry and some primary forest based forestry
- High tech forest industry
- Afforestation of agricultural lands
|
- Fire management
- Afforestation with plantations
- Efficient use of wood products
- Bioenergy
- Halting deforestation
- Farming practices (e.g., more forages) that enhance soil C
|
|
| Argentina, Chile, Brazil |
- Plantation-based forestry and some primary forest based forestry
- High tech forest industry developing
- Plantations are not able to reduce deforestation because they provide
different set of products
|
- Afforestation with plantations
- Efficient use of wood products
- Bioenergy
- Halting deforestation
- Farming practices (e.g., reduced tillage) that
and services. enhance soil C
|
|
| Mexico |
- Forestry largely based on native forests
- Large deforestation rates
- Economic incentives favour agriculture/cattle over forestry
- Afforestation of degraded lands mostly for restoration
|
- Halting deforestation
- Sustainable forest management of native forests
- Social forestry
- Afforestation with local species
- Bioenergy
|
|
|