蓮華池天然闊葉林及杉木人工林試驗集水區水文與水質特性之探討

Studies on the characteristics of hydrology and water chemistry between natural hardwood and China-fir plantation forests in Lienhuachih experimental watersheds

黃正良(Jeen-Lian Hwong)

指導教授 ： 陳明杰

國立臺灣大學/生物資源暨農學院/森林環境暨資源學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.01846

摘要

以適應性、永續性概念之森林生態系經營是目前許多國家的森林經營理念，以期滿足生態、經濟及社會的需求。水文過程為森林生態系重要一環，與能量循環、養分循環、植群分佈，以及土壤化育等密切相關，故推行森林生態系經營時，了解該生態系的森林水文現象與過程是重要的事。林業試驗所自1966年起，陸續在蓮華池試驗林設置五座森林試驗集水區，進行森林水文研究；1979年更選定4號及5號集水區實施駢對集水區試驗，探討集水區森林經營 (伐木作業) 造成水文特性的差異，供說明森林對涵養水源、減緩洪害及過濾水質等效益，開創台灣森林水文研究新頁。本論文一方面依蓮華池森林水文特性之相關研究，將其區分成五大主題：氣象水文、地表水文、地下水文、土壤沖蝕及水化學與土壤化學等，進行文獻歸納整理及回顧分析。並且，進行天然闊葉林（5號集水區）與杉木人工林（4號集水區）之林下光環境與植群調查、土壤水力傳導度測定、降雨特性與森林經營對退水過程的影響、水化學等相關試驗研究。
本論文利用半球面影像取樣技術與林下植物多樣性分析，比較杉木人工林與天然闊葉林之林下光照環境，結果顯示杉木人工林林下光照指數較天然闊葉林高，林下植物多樣性指數變異程度也較天然闊葉林大，而天然闊葉林則因樹種多樣、冠層結構較複雜，其林下光照指數的變異程度較大。天然闊葉林植群型為九節木—黃杞型，樹冠層高度約12~18 m，優勢樹種為黃杞、鵝掌柴、紅皮、單刺苦櫧、捲斗櫟、香桂等，人工杉木林植群型為三腳虌—杉木型，林下小樹極多，且具有較多陽性樹種。植物社會的樹冠層高度約8~15 m，優勢樹種為杉木、白臼、墨點櫻桃、鵝掌柴、頷垂豆等。
土壤水力傳導度(soil hydraulic conductivity)與水分入滲、土壤水移動、逕流路徑及化學傳輸等密切相關，因此土壤水力傳導度常是研究森林水文特性之重要指標。本論文探討杉木人工林與天然闊葉林土壤水力傳導度之差異，以Guelph滲透計分別調查山頂、山腹及山谷之土壤水力傳導度之特性。結果顯示，杉木人工林與天然闊葉林土壤水力傳導度相似，且山頂、山腹及山谷之土壤水力傳導度亦無差異，但土深20 cm處之土壤水力傳導度則明顯高於土深40 cm處之土壤水力傳導度。
依據1976年至2006年間蓮華池氣象站之記錄，本區年平均雨量為2316.5㎜，每年降雨日數平均為132天，乾、濕季分明，雨量集中在5-8月份，佔平均年雨量的71.4%。主要因為中部地區受東北季風降雨之影響很小，大雨來源以颱風豪雨、鋒面型與夏季對流雨為主。
蒐集杉木人工林（4號集水區）於1973年至2007年間之雨量及流量資料，其間歷經1978年天然闊葉林皆伐作業、1982年杉木造林與1997年疏伐作業等，採用潘斯(Barnes, 1930)之退水曲線逕流分離法，來探討4號集水區歷經天然闊葉林、皆伐作業與人工林等森林經營方式對於逕流歷線之退水段造成的影響。結果顯示，皆伐與疏伐作業皆會使地表逕流、地中逕流與基底逕流之退水速度變快。地表逕流退水係數 在皆伐時期、疏伐時期受到降雨條件與地表植被狀況的影響較大。地表逕流終了時間 與降雨量有顯著的相關。而短時間的降雨量對地表逕流的影響大於地中逕流、基底逕流；基底逕流則受長時期季節性的總雨量影響較大。
在水資源的經營管理上，水量的多寡固然重要，但水質的優劣更是關鍵。最近水質的研究則快速發展，益加受到各方的重視，酸雨即是其中一例。雨水從樹冠、樹幹、土壤到溪流這一連串過程中，水化學的性質不斷地在改變，不同的區位或植生，其改變亦會有所不同。本論文探討天然闊葉林（5號集水區）與杉木人工林（4號集水區）之溪流水的水化學，在暴雨期及非暴雨期之差異。結果顯示，集水區的溪流水離子濃度與流量間的關係可分為三種，分別為：(1)稀釋作用：電導度、Na+、Ca2+、Mg2+、SO42、HCO3
−；(2)接近水文增加作用：NO3
−；(3)作用
不變：Cl−、NH4
+、K+、H+。NO3
− 與NH4
+不管在天然闊葉林與杉木人工林集水區
輸入皆大於輸出，且春夏二季的淨收入量約佔全年的80 %，顯示生態系在生長季
仍大量需要氮。而杉木人工林的淨收入都比天然闊葉林為高，表示4 號集水區杉
木在栽植24 年以後，仍需要比天然闊葉林更多的營養元素以供生長所需。皆伐後
的第24 年，4 號集水區的鹽基陽離子Na+、Ca2+、Mg2+年輸出量仍是5 號集水區
的1.4~1.8 倍之間。蓮華池天然闊葉林中的HCO3
−的淨輸出量(46.5 Kg/ha)低於福山
(250 Kg/ha.yr)及關刀溪(87.7 Kg/ha.yr) ，顯示了此處的天然闊葉林生態系統在緩衝
酸性沉降的能力可能低於其他地區。

關鍵字

蓮華池 ； 試驗集水區 ； 森林水文 ； 林下光照環境 ； 土壤水力傳導度 ； 水化學

並列摘要

Adaptive and sustainable management to meet ecological, economic and social demand has become the basic principle of forest ecosystem management in many countries. Hydrological process is an important component of forest ecosystems and is closely related to energy flow, nutrient cycling, vegetation distribution, and soil development. Therefore, understanding forest hydrology is indispensible in forest ecosystem management. Five experimental watersheds in Lienhuachih Experimental Forest has been set up by Taiwan Forestry Research Institute since 1996. The paired watershed No. 4 (WS4) and watershed No. 5 (WS5) were selected to examine the effect of forest management practice, clearcutting, on forest hydrology and serves as a model of illustrating the benefits of undisturbed forest ecosystems on water resource preservation, flooding mitigation, water purification and to advance studies of forest hydrology in Taiwan. Here I review and analyze five categories of forest hydrology including meteorological hydrology, surface hydrology, groundwater hydrology, soil erosion and water and soil chemistry.
Hemispherical photography was used to study understory light environments at WS4 and WS5 and analyzed its relation to understory plant biodiversity. The result indicates that understory light indices were higher at WS4 (China-fir plantation) than WS5 (natural hardwood forest) but the variability was higher at the WS5 possibly due to the more complex canopy structure resulting from the more diverse tree species. The vegetation of WS5 can be classified as Psychotria rubra-Engelhardtia roxburghiana type with canopy height ranging from 12 m to 18 m and dominate tree species include Engelhardtia roxburghiana、Schefflera octophylla、Styrax suberifolius、Castanopsis cuspidate var. carlesii、Cyclobalanopsis pachyloma、Cinnamomum randaiense. WS4 can be classified as Tetrastigma dentatum- Cunninghamia lanceolata type with canopy height ranging from 8 m to 15 m and dominate tree species include Cunninghamia Lanceolata、Sapium discolor、Prunus phaeosticta、Schefflera octophylla、Archidendron lucidum.
Soil hydraulic conductivity is closely related to water infiltration, soil water movement and the path of runoff so that is an important characteristic of forest hydrology. This study used Guelph Permeameter was used to measure soil hydraulic conductivity at the ridge, slope and valley at both WS4 and WS5. The result indicates that the two watersheds had similar soil hydraulic conductivity and there was no significant difference among different location on the slopes. However, soil hydraulic conductivity was higher at 20 cm than 40 cm in the soil profile.
Mean annual precipitation between 1976 and 2006 was 2316.5 mm with mean annual rainy days of 132days. There was distinctive dry and wet seasons with precipitation between May and August contributing to 71.4% of annual precipitation. Due to the lack of northeast monsoon heavy rainfall occurred mainly as typhoon storms, frontal storms and summer convective storms.
The precipitation and discharge data in the WS4 during this period from 1973 to 2007 are collected in this study. However, some forest practices are conducted during this period including natural hardwood forest clear-cutting in 1978, China-fir plantation in 1982, and forest thinning in 1997. In order to understand the effects of different forest managements including natural hardwood forest, clear-cutting practice, and plantation forest on the water resource utility, we apply the recession curve method (Barnes, 1930) to separate hydrograph. Results show that the recession curves of overland flow, interflow, and base flow are steeper due to the clear-cutting and thinning practices. The coefficient of recession curve of overland flow, , is significantly affected by precipitation condition and land vegetation cover when the clear-cutting and thinning practices are conducted. The time end of overland flow recession, , is closely related to the amount of rainfall. The overland flow is more significant affected by short period of rainfall than that for interflow and base flow. However, the base flow is more significant affected by the amount of seasonal precipitation.
The relationship between ion concentration and stream discharge can be classified into there groups: 1) dilution with conductivity, Na+, Ca2+, Mg2+, SO42and HCO3
−
belonging to this group, 2) hydrological access (NO3
−) and 3) hydrological constant Cl−,
NH4
+, K+, and H+.
Input of NO3
− and NH4
+ was greater than output at both the WS5 (natural
hardwood forest) and the WS4 (China-fir plantation) with net input during the spring
and summer contributing to approximately 80% of the annual net input. The net input
was greater at the WS4 than the WS5 suggesting that the China-fir plantation still has
higher demand for N than the natural hardwood forest two decades after the planting.
The output of Na+, Ca2+, and Mg2+ was 1.4 higher at the 24 year-old China-fir plantation
than the natural hardwood forest. The net output of HCO3
−,46.5Kg/ha was lower than
the levels at Fushan, 250Kg/ha/yr, and Kuandauchi 87.7Kg/ha/yr,suggesting that the
natural hardwood forest at Lienhuachih may have lower acid buffering capacity than the
other two forests.

並列關鍵字

Lienhuachih ； experimental watershed ； forest hydrology ； understory light environment ； soil hydraulic conductivity ； water chemistry

參考文獻

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