# Research Trends and Future Direction for Utilization of Woody Biomass in Japan
## 3 Supply Potential and Availability of Woody Biomass
### Methods and Results of Availability Estimation
#### 3.2.2 Results and Influencing Factors of Availability Estimation  
The availability of woody biomass, as estimated by the reviewed papers, is presented in Table 1, showing significant variations in results due to the different estimation methods. To facilitate comparisons among the studies, the availability rate was calculated by dividing the estimated availability by the respective supply potential (Figure 4). Notably, the restrictions considered in these studies were not uniform. The maximum availability rate was 40% in the absence of government subsidies, indicating that nearly half of the potential was inaccessible. It is nearly impossible to achieve self-sufficiency in many areas of Japan. However, with the implementation of appropriate improvement measures, the availability rate demonstrated notable improvements, with mean and median values reaching 65% and 70%, respectively, albeit with a wide range of variation. Furthermore, in certain areas of Japan, the full supply potential of woody biomass can be utilized effectively. To identify ways to increase the availability of woody biomass, we summarized the improvement measures proposed by the reviewed papers and identified three measures, which are described below. It should be noted that some studies examined the availability in relation to changes in selling prices. However, because selling prices are typically determined by the market, an increase in selling prices was excluded from the improvement measures. (1) Government subsidies  
Government subsidies, the most intuitive improvement measures, directly offset the production costs of woody biomass and ensure profitability. The effects of subsidies are examined in the four examples presented in Table 1, Cases 6 through 9. Implementing government subsidies can significantly increase the availability rate, enabling the utilization of approximately 80% of the supply potential [22]. (2) Aggregated forests  
In Japan, this sub-compartment is a fundamental unit for forest management and harvesting. The concept of Aggregated Forests revolves around economies of scale achieved by expanding the fundamental unit through the aggregation of smaller adjacent sub-compartments. This expansion enhances operational efficiency and reduces indirect costs. The overhead costs of woody biomass utilization include significant fixed expenses, such as machinery transportation and garage management costs (further discussed in Chapter 4). Because fixed expenses occur only once per harvest area, the overall fixed costs decrease with an increase in operational area. However, with the expansion of the operational area, the distance over which trees are forwarded also increases. Therefore, the scale of the Aggregated Forests should be carefully considered. [PERSON] et al. [30] investigated the optimum area of Aggregated Forests and recommended limiting the area of aggregated sub-compartments to 6 hectares or less because production costs would rise if the area exceeded 6 hectares. Figure 4: Availability rate relative to supply potential. Almost no studies consider only Aggregated Forests, but Cases 2 and 3 in Table 1 demonstrate that Aggregated Forests can increase the availability rate from 38% to 100% and from 48% to 99%, respectively, when subsidies are applied [19]. In Case 26 in Table 1, when no subsidies are applied and the selling price of woody biomass is 6000 yen/m\({}^{3}\), Aggregated Forests can enhance the availability rate from 6.6% to 9.6%. When the selling price is 10,000 yen/m\({}^{3}\), the availability rate increases from 25.0% to 56.1% [17]. Additionally, Cases 19 through 24 in Table 1, which consider regional trade, show that Aggregated Forests effectively improve woody biomass availability [24]. Notably, these studies considered only fixed expense reductions and omitted operational efficiency improvements when estimating the effects of Aggregated Forests. Therefore, the improvement effects of the Aggregated Forests may be even greater.