Biodiversity: Added disclosure of the LEAP approach to Mitsui’s Forest

Biodiversity assessment

[Action] Assessment of the current state of Ishii Forest and its surrounding area

[Results]

Using the Japan Biodiversity Mapping Project, a project created by Think Nature Inc. that provides big data related to biodiversity, including information on the distribution of a wide range of organisms, we checked what parts of the target area have been designated as nature reserves and the current conservation priorities based on information on the distribution of species. As a result, we confirmed that the conservation priority level of biodiversity in Ishii Forest is higher than in surrounding areas.

[Distribution of vascular plant species]

The median number of vascular plant species in Ishii Forest is five species higher than in the planted forests surrounding it and roughly the same as in the natural forest located to the East.
Representative species include coniferous species that make up planted forests, such as Japanese larch and Sakhalin fir, broad-leaf species such as Japanese elm and Japanese white birch, and herbaceous species such as Japanese pachysandra, Japanese primrose, and Sasa nipponica.

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[Distribution of mammal species]

The median number of mammal species in Ishii Forest is one species higher than in the planted forests surrounding it.
Representative species include the brown bear, Yezo sika deer, Sakhalin fox, and Ezo flying squirrel.

© Think Nature, Inc. 2023, All Rights reserved.

Impact of forest management on biodiversity

[Action] Assessment of the impact of appropriate forest management methods on the number of living species

[Results]

We carried out analyses and assessments based on the three scenarios shown below and then compared the outcome of each of the scenarios in terms of biodiversity conservation. Note that we set 2011, the year we acquired Ishii Forest, as the base year, but analysis was carried out using data from 2009, the closest year to this base year that we were able to obtain data for.

Scenario	Premise
Current management	Continuous implementation of the forest management methods currently in use at Ishii Forest, including a long-rotation system that avoids clear cutting, enabling the forest to sustainably demonstrate its public benefits.
Unmanaged forest	No forest management methods implemented. Assumes that Ishii Forest was not designated as a privately-owned protected area and development therefore progressed at the same rate as in other privately-owned land in the surrounding area.
Clear-cutting	Clear-cutting carried out to obtain timber. Assumes that clear-cutting was carried out on 50-year-old trees, in line with the Hokkaido Regional Forest Office's standard of 50 years for the cutting of planted Sakhalin firs, followed by replanting.

The forestry management we are implementing at Ishii Forest is classified as non-clearcut / retention forestry. This means that in planted forests, cutting is carried out in a way that retains the healthiest broad-leafed trees, enabling the forest to replenish its natural capabilities as much as possible without the need for clear-cutting. The use of this management method at Ishii Forest has curbed the decline in forested area compared to land with different designations in the surrounding area, and prevented development for non-forestry purposes(such as agriculture).

Soil retention effects

[Action] Assessment of the quantity of soil loss in cases of forested and unforested land

We assessed the quantity of soil loss in cases of forested and unforested land based on the Universal Soil Loss Equation (USLE)*, a widely-used formula for predicting soil loss.

• Developed primarily by the United States Department of Agriculture and adopted as a standard for agricultural land conservation in the U.S.
• Recommended as an appropriate method in official land improvement guidelines pertaining to agricultural development in Japan
• Estimates average annual soil loss based on rainfall characteristics, soil characteristics, slope length and steepness, surface vegetation, and effects of conservation activities (does not estimate soil loss volumes for each type of rain)

* Universal Soil Loss Equation

[Results]

This involved analysis and assessment based on two scenarios, a current management scenario and a deforestation scenario.

Scenario	Premise
Current management	Continuous implementation of the forest management methods currently in use at Ishii Forest, including a long-rotation system that avoids clear cutting, enabling the forest to sustainably demonstrate its public benefits.
Deforestation	Deforestation leads to the area becoming bare ground.

(t/year)	Current management scenario	Deforestation scenario
Volume of soil loss	111	22,165

We found that the conservation of Ishii Forest reduced the annual volume of soil loss in the area to just 0.5% of the potential loss. Soil loss has a huge impact on the natural environment, including damaging water recharge functions, reducing water quality, and destroying ecosystems, but the analysis showed that forest management can mitigate this impact.

Carbon sequestration effects

We gained an overall assessment of the annual amount of carbon fixation at Ishii Forest by combining two calculations: 1) the amount of carbon absorbed by trees (carbon fixation by trees) and 2) the amount of carbon release prevented by curbing soil runoff (carbon sequestration by forested soil).

[Action] 1.Carbon fixation by trees

Assessment of the amount of carbon fixation calculated using the Forest Agency's Carbon Dioxide Absorption and Fixation Visualization Calculation Sheet

[Results]

We calculated the amount of carbon dioxide absorbed by the forest based on location, tree species, tree age (using five-year intervals), area, tree density, tree height, and average diameter.

We estimated that Ishii Forest can absorb about 292 tons of carbon per year (equivalent to about 1,072 tons of CO2 per year). This is roughly the same as the annual emissions generated by 391 regular households.

Ishii Forest contains many Japanese larches and Sakhalin firs, and in regard to carbon absorption and fixation, we know that the peak carbon absorption volume is reached at around 11 to 15 years old for Japanese larches and at 16 to 20 years old for Sakhalin firs. We continue to carry out forest management practices that promote forest renewal by appropriately thinning forests that have reached an advanced stage of maturity. This is believed to be effective in maintaining carbon sequestration effects.

Source: MS&AD InterRisk Research & Consulting, Inc. edit of data from the Hokkaido Regional Forest Office's website (https://www.pref.hokkaido.lg.jp/sr/srk/81225.html)

[Action] 2.Amount of carbon release prevented by curbing soil runoff

Assessment of the amount of carbon sequestered by forested soil by using the difference in sediment yields between forested and unforested land to calculate the amount to which forested land reduces carbon release through soil runoff, including the amount of carbon released in erosion caused by soil runoff

[Results]

We calculated the volume of carbon sequestered in soil by multiplying the volume of soil retained through curbing runoff by the carbon content of one ton of soil. According to Forest Research and Management Organization's Hokkaido Research Center, the brown forest soil that comprises most of Ishii Forest's area contains 140 tons of carbon per hectare at depths of up to 70 cm. Based on this, we made the assumption for this analysis that one ton of brown forest soil contains 0.025 t-C.

We found that the amount of carbon retained in soil by preventing runoff through forestry management was 551 tones per year, equivalent to a reduction of about 2,020 tons of CO2 emitted through runoff per year.

Although it is difficult to considerably raise the amount of carbon sequestered by trees using the retention forestry method being implemented at Ishii Forest, it can prevent soil runoff, particularly compared to clear-cutting, which severely destabilizes the ground, and therefore enables carbon to be retained within the soil for long periods.

(t-C/year)	Carbon fixation by trees	Carbon sequestration by forested soil
Volume of carbon absorbed (equivalent in t-CO2)	292(1,072)	551(2,020)

Water recharge effects

[Action] Assessment of recharge functions enabled by forest management based on a visualization of the water cycle in the target area

[Results]

Water recharge functions demonstrated by forests include flood mitigation, water resource accumulation, and water purification. In recent years, abnormal weather patterns have made the flood mitigation functions demonstrated by healthy forests more important than ever for environmental conservation.

In this analysis, we defined the water recharge volume as the volume of water passing downward through the ground surface. This was calculated based on soil infiltration capacity (the ability of forest soil to allow infiltration by rain) and the amount of aboveground evapotranspiration (calculated using a forest evapotranspiration model that takes into account factors such as precipitation volume, air temperature, global solar radiation, tree species, tree height, and forest density). For the purposes of this study, only the average recharge volume (the volume of water passing downward through the ground surface) was considered, and we did not consider temporal changes over the last 10 years. Therefore, conditions such as the permeability of the topsoil will affect the values.

For each of the three scenarios shown below, we carried out a quantitative assessment of water recharge volumes by simulating the water cycle. The difference in recharge volumes for each scenario was quantified based on the current management scenario. (Note that this analysis does not quantify all of the other water source recharge functions of the forest, such as flood runoff reduction during heavy rainfall events by controlling sediment runoff and storing groundwater.)

Scenario	Premise
Current management	Continuous implementation of the forest management methods currently in use at Ishii Forest, including practicing a long-cut non-thinning operation that can continuously demonstrate the forest's public benefit value.
Pre-management condition	The condition Ishii Forest was in when first acquired.
Clear-cutting	Clear-cutting carried out to obtain timber. Assumes that 51% of Ishii Forest area has been developed since 1977, the same as in the surrounding area, and that clear-cutting of the developed area has led to soil loss.

(m3/year)	Current management	Pre-management condition	Clear-cutting
Difference in water recharge volume	- (Base)	- 71,800	- 384,400

In addition to the volume of water recharge maintained by Ishii Forest, which was quantitatively analyzed in this study, it is generally considered that deforestation results in long-term soil loss. This then leads to a decrease in infiltration capacity, reduced water recharge volumes, increased flood flow volumes, and a decline in the volume of groundwater reaching downstream areas.