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柳杉人工林疏伐對氣溫之時間序列效應

THINNING EFFECTS ON THE TIME SERIES OF AIR TEMPERATURE IN A JAPANESE CEDAR PLANTATION

摘要


為了探討疏伐對林地微氣候的效應,本研究蒐集林務局南投林區管理處人倫柳杉人工林樣區的氣溫監測資料進行分析。樣區採孔隙疏伐方式,疏伐強度分別為0%(對照樣區)、25%以及50%,資料蒐集期間從2006年7月至2011年10月。使用時間序列分析方法之自我迴歸整合移動平均模型(ARIMA模型),分析樣區月平均氣溫的季節性趨勢,以及使用介入模型分析疏伐對月平均氣溫的初期提升效應以及提升效應遞減率。結果顯示,對照樣區月平均氣溫最低溫出現在1、2月,最高溫出現在7、8月,且不同坡向樣區的氣溫季節性趨勢相當一致。疏伐後,夏季期間50%疏伐強度樣區氣溫明顯提升,而25%疏伐強度樣區則稍許提升;冬季期間50%疏伐強度樣區氣溫稍許提升,25%疏伐強度樣區則呈現氣溫降低。疏伐可提高各樣區月平均氣溫日較差及其變異,其中以50%疏伐強度樣區最為明顯,且不同疏伐強度樣區與對照樣區呈現顯著差異。以ARIMA模型分析結果,樣區的月平均氣溫呈現以12個月為周期的季節性趨勢,當月的平均氣溫與前兩個月具時間序列相依性,但不顯著。將疏伐視為脈動介入型態情況下,介入模型分析結果,在95%信心水準條件下,50%疏伐強度顯著提升樣區的月平均氣溫,疏伐初期約提升0.80~1.03℃,而25%疏伐強度對提升樣區月平均氣溫不顯著,疏伐初期約提升0.23~0.36℃。隨著疏伐後地被植群迅速生長及樹冠層的擴展,50%以及25%疏伐強度對提升氣溫的效應皆隨時間經過呈顯著遞減。

並列摘要


This research investigated the effects of thinning on forest microclimate. Air temperature data of thinning plots from July 2006 to October 2011 were collected in a Japanese cedar (Cryptomeria japonica D. Don) plantation at Renlun, Nantou Forestry District, Forestry Bureau. The plantation was conducted by gap thinning experiment which consists of 0% (control), 25% and 50% thinning intensities. Monthly average air temperature (AT) records of plots with different treatments were analyzed by autoregressive integrated moving average (ARIMA) model that to explore seasonal trend, and by intervention model that to explore the initial increase and rate of decay of AT after thinning. From analyzed results, AT of the control plot showed seasonal trend with minimum AT appeared in January or February and maximum AT appeared in July or August in a yearly round. The seasonal trend of plots with different aspects was quite consistent. Comparison of AT between thinning plots and control plots Showed that the 50% thinning intensity caused an obvious increase and 25% thinning intensity caused a slight increase in the summer season. In winter season, the 50% thinning intensity caused a slight increase and the 25% thinning intensity caused decrease. In addition, thinning could increase the range of monthly average air temperature (ATR) and its variation in particular plots of 50% thinning intensity. ATR of the thinning plot was significant difference with that of the control plot. Results of the ARIMA model analysis showed that AT of plots had seasonal fluctuant trend with a period of 12 months and AT of the current month was dependent on that of previous two months but the correlation was insignificant. Suppose the thinning treatment followed the pulse intervention pattern, under the 95% confidence level, the AT of 50% thinning intensity plots significantly increased about 0.80~1.03℃ and the AT of 25% thinning intensity plots insignificantly increased about 0.23~0.36℃ in initial stage. The effect of AT increasing would be significantly decrement over the time for both 50% and 25% thinning intensity treatments due to the rapid growth of ground vegetation and the expansion of canopy after thinning.

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