- 學位論文
紅樹林疏伐對碳吸存之影響
Effects of thinning on carbon sequestration in mangroves
摘要
紅樹林主要分布於河口與海岸地區，為重要的碳吸存(carbon sequestration)場所。但紅樹林過度生長對生物多樣性與洪患調節恐造成負面影響，許多地區開始進行疏伐或全面移除紅樹林。但疏伐後可能會影響紅樹林的碳吸存量，因此本研究的目的為建立芳苑紅樹林的碳收支模式，並探討疏伐後紅樹林的樹密度與碳吸存之間的關係。本研究於2014年2月在彰化芳苑設立三個測站，包括近海海茄苳(Seaward Avicennia marina, SA)、近陸海茄苳(Landward Avicennia marina, LA)與水筆仔(Kandelia obovata, K)，並在各測站進行三種不同程度的疏伐，分別為控制組的不伐(Control, C)、中度疏伐(Medium thinning, MT)以及高度疏伐(High thinning, HT)，MT處理砍去該測站一半數量的植株；HT處理則於測站中心處留一棵植株。藉由累加法(summation method)來估計芳苑紅樹林的淨初級生產力(Net primary productivity, NPP)與碳吸存量，並建構芳苑紅樹林的碳收支模式。結果顯示芳苑紅樹林的碳吸存量為15.4、14.7、27.6 Mg C ha-1 yr-1(依序為SA、LA、K)，而生態系統碳儲存量為434、607、533 Mg C ha-1。將芳苑紅樹林碳吸存及各項碳輸出的結果彙整，可計算出其淨生態系統生產量為5.03、4.38、19.27 Mg C ha-1 yr-1 (依序為SA、LA、K)，顯示芳苑紅樹林為一個碳匯系統。疏伐後的三個紅樹林測站之碳吸存量，HT處理最低，為4.4、5.0、4.5 Mg C ha-1 yr-1(依序為SA、LA、K)；MT處理次之，為11.6、14.3、19.2 Mg C ha-1 yr-1，其中MT處理與C處理(15.4、14.7、27.6Mg C ha-1 yr-1)的差異較小，顯示HT處理顯著減少單位面積的碳吸存力，MT處理減少的幅度較小。若以單棵植株的角度來看，疏伐後的三個紅樹林測站之碳吸存量，以HT處理最高，為3.6、4.8、1.9 Mg C tree -1 yr-1(依序為SA、LA、K)，且顯著高於MT處理及C處理。綜合上述結果，若全面移除芳苑紅樹林，可能導致其生態功能的喪失，因此中度疏伐應為解決紅樹林過度擴張的最佳選擇。雖然HT處理能增加單棵植株的碳吸存量，但以整個紅樹林生態系的觀點，並期望在生態系服務中獲得最高的碳吸存量，MT處理則為最佳疏伐密度。
並列摘要
Mangroves distribute in estuary and coastal region, and mangroves are one of the most important carbon sinks. Mangrove thinning or afforestation has been initiated in many countries because of its negative effects on biodiversity and flood prevention in estuarine ecosystems. However, this may reduce its function as carbon sequestration. Our study tried to quantify mangrove carbon budget and examine the relationship between tree density and carbon sequestration after thinning. We conducted a field study from February 2014 in Fangyuan, Changhua, at 3 sites, including Avicennia marina at seaward zone (SA) and landward zone (LA) and Kandelia obovata (K). Each site was conducted 3 treatments of thinning, including non-thinning as the control (C), medium thinning (MT) by cutting half number of trees, and high thinning (HT) by leaving only one tree in the center. Net primary production and carbon sequestration of mangroves were estimated by the summation method. The results showed that carbon sequestration was 15.4, 14.7, 27.6 Mg C ha-1 yr-1 (in SA, LA, and K, respectively), and carbon stock was 434, 607, 533, Mg C ha-1. These data indicate that Fangyuan mangrove function as carbon sequestration. The estimated net ecosystem production of Fangyuan mangrove was 5.03, 4.38, 19.27 Mg C ha-1 yr-1 (in SA, LA, and K, respectively). Carbon sequestration was lower in MT treatment (11.6, 14.3 and 19.2 Mg C ha-1 yr-1 in SA, LA, and K respectively) and lowest in HT treatment (4.4, 5.0, and 4.5 Mg C ha-1 yr-1). HT treatment reduced areal carbon sequestration, but MT and C treatments had no significant difference. Furthermore, the results showed that individual carbon sequestration was highest in HT treatment (3.6, 4.8, and 1.9 Mg C tree-1 yr-1 in SA, LA, and K respectively). Individual carbon sequestration in HT treatment was significantly higher than that in MT and C treatment. Overall, Fangyuan mangroves was important carbon sinks. Because mangrove afforestation may destroy ecosystem function, we suggest that MT treatment would be the best choice if we are to reduce the loss of carbon sequestration in whole mangrove ecosystem.