Microenvironment Variations under Canopy Gaps and Responses of Broad-leaved Tree Seedlings

溪頭第二林班的柳杉人工林於2002年清理麻竹後，形成不同大小之冠層孔隙，於2005至2009年期間，觀測45個孔隙樣區之冠層開闊度及其中10個孔隙樣區之微氣候變化，其平均冠層開闊度範圍為13.2至30.6%，孔隙相對大小（孔隙直徑/樹高）範圍為0.1至1.6，生長季（3至9月）光量範圍為平均日累積光量介於1.5至10.4 mol m-2 day-1之間，於2006年4月至2008年9月間另觀測兩樣點之孔隙冠層開闊度及微氣候變化，平均開闊度範圍為35.3至38.1%，生長季光量範圍為平均日累積光量介於12.3至18.8 mol m-2 day-1之間。最大與最小孔隙之平均日累積光量絕對值差異在生長季時達17.3 mol m-2 day-1，在非生長季為15.5 mol m-2 day-1，全年平均則為16.5 mol m-2 day-1。迴歸分析結果顯示孔隙的冠層開闊度與孔隙相對大小間具有線性關係，且直接影響孔隙的生長季平均日累積光量及土壤水勢，並間接影響孔隙的空氣溫度、日夜氣溫差、土壤溫度及空氣濕度、土壤水勢，同時受到季節效應的影響。 孔隙樣區內於2005年栽植6種1年生闊葉樹苗：瓊楠、大葉釣樟、狹葉櫟、青剛櫟、三斗石櫟、栓皮櫟，經過4年生長良好，且可觀察到各樹種生長特性差異，於2009年4至8月調查45個樣區苗木之生長表現與其中架設微環境觀測站之10個樣區的苗木生理反應。隨著冠層開闊度的擴大，大葉釣樟、狹葉櫟、青剛櫟及三斗石櫟的苗高、基徑生長量均隨著增加，因此適合栽植於相對較大冠層孔隙。其中狹葉櫟、青剛櫟及三斗石櫟生長量的增加主要來自日累積光量的增加，大葉釣樟則受土壤可用水分的影響甚於累積光量的效應，故適合選擇在濕潤的生育地栽植。栓皮櫟在此開闊度範圍內因生理活性已受限，應更適宜栽植於冠層開闊度>30%之孔隙。瓊楠的高生長緩慢且不受冠層開闊度影響，然栽植於較大孔隙之苗徑較粗壯。4種殼斗科苗木狹葉櫟、青剛櫟、三斗石櫟、栓皮櫟的冠幅也隨冠層開闊度顯著擴大，狹葉櫟與青剛櫟側枝數亦隨開闊度增加而增加，若能進行更長期的生長觀察在育林作業之參考更具價值。Gaps of various sizes were made in Japanese Sugi (Cryptomeria japonica) plantation at Chi-tou, Central Taiwan after removed Ma Bamboo (Dendrocalamus latiflorus) 2002. Canopy openness was measured on 45 gaps, and the irradiation, temperature of air and soil, diurnal air temperature fluctuation, relative air moisture, and soil water potential were measured on 10 of the 45 gaps during the period of 2005 to 2009. The average openness ranged from 13.2 to 30.6%, and the gap size ranged from 0.1 to 1.6, and the irradiation intensity ranged from 1.5 to 10.4 mol m-2 day-1 in the growing season(from March to September). Two additional gaps were observed during Apirl 2006 to September 2008. In which the average openness ranged from 35.3 to 38.1%, and the irradiation intensity ranged from 12.3 to 18.8 mol m-2 day-1. The maximum absolute difference of average openness between all gaps was 17.3 mol m-2 day-1 in the growing season, 15.5 mol m-2 day-1 in the non-growing season, and it was 16.5 mol m-2 day-1 in the whole year. We found that it appeared to be a linear relationship between gap size and canopy openness. We also found that the irradiation intensity and soil water potential were directly determined by the canopy openness. However, the variations of other microenvironmental conditions were indirectly determined by openness and affected by seasonal changes at the same time. 6 species of 1 year old seedlings, Beilschmiedia erythrophloia, Lindera megaphylla, Cyclobalanopsis stenophylloides, Cyclobalanopsis glauca, Pasania hancei var. ternaticupula and Quercus variabilis were planted and growing well in 45 gaps from 2005 to 2009. The growth of height and basal diameter, crown width, number of lateral stems, growth of height/diameter ratio, SLA (specific leaf area) of 45 gaps and leaf physiological activities of 10 gaps were measured from April to August 2009. The results showed that the growth of height and basal diameter of L. megaphylla, C. stenophylloides, C. glauca and P. hancei var. ternaticupula were proportional to the increase of canopy openness, which suggested that they would be more suitable to planted in larger gaps. The growth of C. stenophylloides, C. glauca and P. hancei var. ternaticupula were due to the increase in accumulation of irradiation. Nevertheless, the growth of L. megaphylla was mainly determined by soil moisture. As a result, it would be appropriate to plant in moisture habitats. The physiological activities of Q. variabilis had been limited, which implied that it would be more appropriate to plant in larger gaps with canopy openness being >30%. In B. erythrophloia, there was no significant effect on the growth of height on canopy openness, but on the growth of basal diameter was. The crown width of 4 Fagaceae species, C. stenophylloides, C. glauca, P. hancei var. ternaticupula and Q. variabilis increased as the canopy openness increased. The number of lateral stems of C. stenophylloides and C. glauca also grew in the same pattern. A longer period of survey would be more useful for silviculture strategies