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研究模擬臺灣櫸生物量分配  有望設計最適育林法增加碳吸存

 

       林木碳儲存為生態系服務中之獨特效益,2015年「巴黎協定」即宣告森林碳吸存於氣候變遷扮演關鍵角色。台大森林系副教授林增毅與台大實驗林助理研究員陳潔音、農委會林業試驗所助理研究員柯淑惠合作,研究臺灣櫸(Zelkova serrata(Thunb.))如何將大氣中的碳轉化為生物量後分配於林木之不同部位,發現如需將生物量集中於林木主幹以及增加臺灣櫸使用率,需預先規劃修枝作業以控制樹冠比例,模型也可用以評估整個臺灣櫸造林地之碳存量的分配。

       臺灣櫸為臺灣重要造林五種闊葉樹之一,根據第四次全國森林資源調查,2008至2012年之間,臺灣櫸造林面積達到1785公頃,其造林地每公頃可儲存452.2公噸之二氧化碳。然而,目前較少研究瞭解及模擬臺灣櫸林木生物量的分配策略,以設計最適育林法,增加臺灣櫸之碳吸存功能。

       因此研究團隊選擇於實驗林內茅埔營林區臺灣櫸9年生人工林林分進行實驗及取樣,使用進階統計模式「彷彿無相關迴歸模型」(Seemingly Unrelated Regressions, SUR)結合「構成比例法」(Component Ratio Method, CRM),模擬臺灣櫸如何分配生物量於林木主幹、大枝條、小枝條及葉部。

       研究結果顯示,臺灣櫸將46%的生物量儲存於林木主幹以及40%於大枝條,不過當臺灣櫸的直徑增加1公分時,林木主幹的生物量將減少1.9%,大枝條的生物量反而增加2.2%,顯示大棵的臺灣櫸較注重樹冠的發展及擴大。

       研究團隊指出,如果需將生物量集中於林木主幹以及增加臺灣櫸使用率,需預先規劃修枝作業以控制樹冠比例。另外,研究開發的臺灣櫸SUR-CRM模式也可以套用在林分層次上,評估整個臺灣櫸造林地之碳存量的分配。研究全文發表於《Scientific Reports》期刊。

Chen C-Y, Ko S-H, Lam TY.2021. Modeling biomass allocation strategy of young planted Zelkova serrata trees in Taiwan with component ratio method and seemingly unrelated regressions. Scientific Reports 11, 7536. https://doi.org/10.1038/s41598-021-87129-7

 

臺大實驗林內茅埔營林區臺灣櫸9年生人工林林分。

 

林木直徑於林木主幹、大枝條及小枝條生物量比例之關係。

Modeling Biomass Allocation Strategy of Zelkova serrata

 

       Trees are unique in that they accumulate biomass by sequestrating atmospheric carbon. As such, the Paris Agreement in 2015 finally and formally recognizes that forests play an important role in addressing the impact of climate change.

       To protect Taiwan from natural disasters and to maintain quality watershed in provision of water resources, a Taiwan National Reforestation Program was established in 1996 to conduct massive reforestation operations. Moreover, corporates are interested in the reforestation efforts to promote their Corporate Social Responsibility policies. Thus, there has been an ongoing cooperation between National Taiwan University Experimental Forest and corporates in reforestation projects with up to 70 hectares of forests being planted. However, there is a still a lack of research into the effects of this cooperation in promoting carbon sequestration.

        This research attempts to understand biomass allocation strategies of Zelkova serrata (Thunb.) that is how the tree species allocates sequestrated carbon to main stem, large branches, small branches and leaves.  Z. serrata is a major reforestation species. According to the 4th National Taiwan Forest Resources Inventory, about 1,785 ha of land has been reforested with the tree species with the forest having the capability of sequestrating 452.2 tons of CO2.

       However, there has been little modeling work on understanding how Z. serrata in allocating its biomass to different components. The research was carried out in a nine years old plantation located in the National Taiwan University Experimental Forest Neimaopu Forest Management District. In this study, Component Ratio Method (CRM) was applied to related biomass component ratios of main stem, large branch, twig, and foliage to tree attributes of Z. serrata, and the CRM models were fitted with Seemingly Unrelated Regression (SUR) to account for model correlations. Results show that the species allocates about 46% and 40% of total tree biomass to main stem and large branch, respectively. However, with every 1-cm increase in dbh, main stem biomass decreased by 1.9% but large branch biomass increased by 2.2%. This implies that larger Z. serrata trees tend to invest in more in crown development. Thus, a pruning treatment needs to be scheduled properly on dominant trees to maintain crown ratio and ensure wood quality. Lastly, the developed SUR-CRM model could be used to predict biomass allocation on plantation level.

       This study is a cooperation between Associate Professor Tzeng Yih Lam from the National Taiwan University School of Forestry and Resource Conservation, Assistant Researcher Dr. Chieh-Yin Chen from the National Taiwan University Experimental Forest, and Assistant Researcher Shu-Hui Ko from Taiwan Forestry Research Institute. The research has been published in Scientific Reports.

 

Chen C-Y, Ko S-H, Lam TY.2021. Modeling biomass allocation strategy of young planted Zelkova serrata trees in Taiwan with component ratio method and seemingly unrelated regressions. Scientific Reports 11, 7536. https://doi.org/10.1038/s41598-021-87129-7

Figure 1. The nine years old Zelkova serrata plantation in National Taiwan University Experimental Forest Neimaopu Forest Management District.

 

Figure 2. Relationship between tree diameter and component ratio of main stem, large branch, and small twigs of Zelkova serrata.

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