Sustainable management of planted landscapes: lessons from Japan

Abstract

In Japan, 42 % of forests are planted forests, and most of them were established after World War II (1950–1980) to meet increased wood demands. Although Japanese planted forests are now reaching their planned harvest age, they have not been managed, and their restoration is now being discussed. Japanese foresters have not cut their own forests, and the country’s high wood demands have been met by imports during recent decades. The decline of young forests due to the stagnation of forestry activity is suggested to be partly responsible for the nation-wide decline in early-successional species, which is referred to as the “second crisis of biodiversity.” As a timber-importing nation, it is suggested that Japan has underused the nation’s own forests and has overused forests elsewhere. A revival of Japanese plantation forestry may contribute to the restoration of early-successional species because young planted forests are likely to provide suitable habitats. Furthermore, only 30 % of the current planted forests in Japan will be needed to meet the expected future domestic demand for lumber and plywood without imports. The remaining 70 % of the current planted forests may be restored to natural forests with or without harvesting. The history of Japanese planted forests suggests that some natural trees/forests should be retained, even in the landscapes that specialize in wood production, because part of the planted forests may be economically marginalized in the future, and their restoration to natural forests would then be needed.

Appendices

Appendix 1

See Table 1.

Table 1 Qualities of land uses other than old-growth forest for forest birds (σ)

Appendix 2 Calculation of lower and upper limits for annual harvested areas of planted forests

Lower limit: 10.4 million ha (i.e., 10.4 × 1000 thousand ha) of forest are presently planted in Japan. Suppose that 70 % of the planted forests are targeted for timber harvest and that the maximum harvesting age is 200 years. Further suppose that the initial condition of the planted forest has areas of young stands that are equal to or larger than those of the fully regulated forest on a 200-year rotation. Then, the lower limit of the annual average final harvested area of planted forest is

$$ 10.4 \times 1000 \times 0.70/200 = 36.4 \, \left( {\text{thousand ha}} \right). $$

Because we do not have sufficient data to determine the maximum age at harvest, if the maximum harvesting age is conservatively 160, instead of 200, then the lower limit of the annual average final harvest area of planted forest is

$$ 10.4 \times 1000 \times 0.70/160 = 45.5 \, \left( {\text{thousand ha}} \right) $$

Other factors being equal, if the initial condition of planted forests has small areas of stands <40 years, then the lower limit of the annual average final harvest area of planted forests is

$$ 10.4 \times 1000 \times 0.70/(160-40) = 60.7 \, \left( {\text{thousand ha}} \right). $$

The area of final harvest has not recently been reported in Japan. From the reported amount of 17,587 thousand m³ log production in 2009, assume 80 % is from planted forest and 75 % of that is from final harvesting. Further assume that 300 m³ ha⁻¹ of logs are produced on average from final harvesting. Then, the area of final harvest in 2009 can be calculated as follows:

$$ 17,587 \times 0.80 \times 0.75/300 = 35.2 \, \left( {\text{thousand ha}} \right). $$

The annual area of final felling must be increased from the level in 2009 to harvest at least 70 % of the planted forests before the 160-year-old mark.

Upper limit: The consumption of lumber and plywood in Japan in roundwood equivalents was 31,564 thousand m³ in 2009. Per capita consumption of lumber and plywood is trending downward. The population is estimated to decrease about 20 % by 2050 and may be halved by 2100 if the current birth rate trend continues without substantial immigration. Here, we assume the average final harvesting age to be about 100 years and the average amount of final harvest to be 400 m³ ha⁻¹, with annual thinning production comprising 20 % of the production by final harvest.

If we assume that the long-term upper limit of demand for logs from planted forests is 30 million m³ year⁻¹, then the upper limit of the long-term annual average final harvesting area is

$$ 30,000,000\,({\text{m}}^3\,{\text{year}}^{-1})/400\,({\text{m}}^3\,{\text{ha}}^{-1})/1.20=62,500\,({\text{ha}}\,{\text{year}}^{-1}) $$

If we assume that the long-term upper limit of demand for logs in planted forests is 20 million m³ year⁻¹, instead of 30 million m³ year⁻¹, then the upper limit of the long-term annual average final harvest area is

$$ 20,000,000\,({\text{m}}^3\,{\text{year}}^{-1})/400\,({\text{m}}^3\,{\text{ha}}^{-1})/1.2 = 41,667\,({\text{ha}}\,{\text{year}}^{-1}).$$

Appendix 3 Required amount of planted forest in Japan

Suppose that the target of the national forestry program is to sustain the saw log and veneer log production capacity of planted forests at the level that meets domestic demand for lumber and plywood in roundwood equivalents. Suppose that the productive planted forests are capable of producing 7 m³ ha⁻¹ year⁻¹ of saw logs and veneer logs on average. Further suppose that 90 % of saw logs and veneer logs are from planted forests. If domestic demand for lumber and plywood in roundwood equivalents decreases to 20 million m³ year⁻¹ in the long run, then the required area of productive planted forest for saw logs and veneer logs in Japan is

$$ 20 \times 0.9/7 \, = 2.57 \, \left( {\text{million ha}} \right). $$

If domestic demand for lumber and plywood in roundwood equivalents is maintained at 30 million m³ year⁻¹ (32 million m³ year⁻¹ in 2009), instead of decreasing to 20 million m³ year⁻¹, then the required area of productive planted forests for saw logs and veneer logs is

$$ 30 \times 0.9/7 = 3.86 \, \left( {\text{million ha}} \right) $$

The current area of planted forests in Japan is 10.4 million ha, which clearly exceeds domestic demand for saw logs and veneer logs. Thus, substantial planted forest areas could be restored to natural vegetation after harvest.

Appendix 4 Full description of graphical approach

Let us assume that yield (timber production per area) and the component of biodiversity (e.g., species richness, density of species/functional group) are functions of land-use intensification (proportion of planted trees among canopy trees; Fig. 2a). We also assume that yield increases linearly with intensification and that biodiversity decreases in a convex or concave manner. These land-use intensity–yield–biodiversity relationships are then converted into a yield–biodiversity relationship (Fig. 2b). Because yield is a linear function of intensification, the shapes of the biodiversity responses are conserved. Utility (evaluated in monetary terms) could be described as follows:

$$ U = aB + bY $$

(1)

where a and b are values of biodiversity (B) and yield (Y), respectively. This equation can be rewritten in terms of B:

$$ B= (U/a)- (b/a) Y $$

(2)

which is a straight line in Fig. 2b. Under particular values of a and b, we seek a maximum value of U, i.e., identifying the line that intersects the yield–biodiversity line and has a maximum intercept on the B axis. For the convex yield–biodiversity relationship, we seek a single line (gray solid line in Fig. 2b), and the intersected point indicates the timber yield and biodiversity, which are optimally produced and conserved, respectively. Optimal points change with shifts in the value of timber and biodiversity (a and b). If the timber value declines and biodiversity is valued more, the optimal proportion of planted trees would decrease (tentative Japanese trajectories of these two products are depicted; Fig. 2c). When biodiversity responds to the proportion of planted trees in a concave way, the situation changes dramatically. In this case, only two optimal strategies exist, depending on the timber and biodiversity values: produce timber and ignore biodiversity when the timber value is higher than that of biodiversity or conserve biodiversity and ignore timber production when the value of biodiversity is higher than that of timber. Only when we value timber and biodiversity equally are these two strategies equally optimal (lower gray dotted line, Fig. 2b). However, this is an unstable and unrealistic solution. When our valuation of these two products crosses this threshold rate, the optimal strategy suddenly changes (Fig. 2d).