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提供: 広島大学デジタル博物館
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Recent rapid increases in ambient CO2 are largely attributed to deforestation in tropics. However, the carbon emissions from terrestrial ecosystem are mostly based on the area-wise statistics of “forest land” which is defined as an area with minimum crown coverage >10%, while extensive biomass (more than 50%) has been removed through “forest degradation” processes resulted from the over-harvesting in legitimated logging regime or illegal logging. Therefore, if the carbon losses accompanied by the forest degradation had been added on the forest statistics, actual carbon losses and emissions could have been larger than those were reported. Therefore, recovery process accompanied after forest degradation needs to be thoroughly monitored and reviewed in order to evaluate long term NET carbon losses.<br>  
 
Recent rapid increases in ambient CO2 are largely attributed to deforestation in tropics. However, the carbon emissions from terrestrial ecosystem are mostly based on the area-wise statistics of “forest land” which is defined as an area with minimum crown coverage >10%, while extensive biomass (more than 50%) has been removed through “forest degradation” processes resulted from the over-harvesting in legitimated logging regime or illegal logging. Therefore, if the carbon losses accompanied by the forest degradation had been added on the forest statistics, actual carbon losses and emissions could have been larger than those were reported. Therefore, recovery process accompanied after forest degradation needs to be thoroughly monitored and reviewed in order to evaluate long term NET carbon losses.<br>  
 
In these respects and backgrounds, we studied biomass and canopy structural changes in a lowland tropical rain forest in the Pasoh Forest Reserve (PFR) of Peninsular Malaysia after selective logging in 1950s, and found that total aboveground biomass (AGB) has not fully recovered yet to the level observed in a primary forest plot within PFR. On this site, we also conducted canopy height mapping using an airborne light detection (LiDAR) in 2003 and 2011, and found that the average canopy height in the logged forest was still lower than that in the primary forest. The coefficient of variation of canopy height was also lower in the logged forest plot, suggesting that the highly heterogeneous features in canopy surface height commonly seen in the pristine old growth forest, known as typical features tropical rain forest, has not fully recovered yet. These studies suggest delay of recovery process, not only in AGB but in forest structures will possibly result in underestimate of the carbon emission from forest sectors, and “forest degradation” needs to be thoroughly studied and should be incorporated properly into the climate mitigation measures.
 
In these respects and backgrounds, we studied biomass and canopy structural changes in a lowland tropical rain forest in the Pasoh Forest Reserve (PFR) of Peninsular Malaysia after selective logging in 1950s, and found that total aboveground biomass (AGB) has not fully recovered yet to the level observed in a primary forest plot within PFR. On this site, we also conducted canopy height mapping using an airborne light detection (LiDAR) in 2003 and 2011, and found that the average canopy height in the logged forest was still lower than that in the primary forest. The coefficient of variation of canopy height was also lower in the logged forest plot, suggesting that the highly heterogeneous features in canopy surface height commonly seen in the pristine old growth forest, known as typical features tropical rain forest, has not fully recovered yet. These studies suggest delay of recovery process, not only in AGB but in forest structures will possibly result in underestimate of the carbon emission from forest sectors, and “forest degradation” needs to be thoroughly studied and should be incorporated properly into the climate mitigation measures.
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*<正義>の生物学―生物多様性を保全する理由―
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山田俊弘<br>
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広島大学大学院統合生命科学研究科<br>
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演者は、2007年から広島大学で担当してきた講義、「保全生物学」の中で、多くの生き物が絶滅しかけている。私たちは彼らを絶滅から守るべきだろうか?それとも特別なことをする必要などないのだろうか? どちらかを理由とともに選べ。という問いを学生に投げかけ、学生とともにその答えを模索してきた。そして、探し当てた問いへの(ひとつの)解答を2020年、『<正義>の生物学 トキやパンダを絶滅から守るべきか』にまとめ、上梓した。<br>
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演者がたどり着いた答えは、生物多様性の保全は必要であり、その理由は、(1)生き物の恵み(特に供給サービス)を得るため、(2)生き物の恵み(特に基盤サービス)を得るため、(3)それが正しい行いだから、という3つだった。<br>
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『<正義>の生物学』では、これら3つについて解説したが、3つの理由のそれぞれがとても大きなテーマなため、本シンポジウムですべてを紹介することができない。そこで本シンポジウムでは、3つ目の理由である、「それが正しい行いだから」に注目し、この考えを紹介したい。<br>
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生物多様性の保全が正しい行いだと考える立場は、命の重さを尊重する。ここでいう命にはヒトのものだけでなく、すべての種のものが含まれる。ヒトの命は当たり前に大切なものである。対してヒト以外の命は、ヒトの 命ほどの重みはないと考えられがちである。本発表ではまず、ヒトとそれ以外の種の命の重みに差があるかどうかを考えてみたい。そして、その考察の上、これからのヒトがもつべく思考態度について議論したい。
    
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