- 學位論文
神木溪天然闊葉林孔隙微環境與苗木之生長表現
Gap Microenvironment and Seedling Growth in a Natural Broad-leaved Forest at Shen-Mu Area, Centeral Taiwan
摘要
冠層孔隙在森林更新循環中，扮演著很重要的角色，已有釵h相關研究陸續投入瞭解孔隙大小與形狀對林木更新的影響。本研究目的在瞭解神木溪天然闊葉保護林，在冠層出現孔隙後，孔隙內微環境因子的動態變化及其對於苗木生長的影響。研究對象為兩個不同大小的冠層孔隙，面積約分別為550及250m2。在孔隙內、孔隙邊緣與冠層下，以定點方式長時間監測光量、氣溫、土溫與土壤水勢等環境因子的變化，並栽植七種闊葉樹之一年生苗木，觀察其適應情形。由結果得知，冠層孔隙形成後將使林地太陽輻射比率增加，且於每年3-9月最為明顯，大、小孔隙光量皆可超過冠層下方10倍以上。惟因孔隙位於北迴歸線附近有緯度效應，導致在不同樣點間的光量出現梯度差異，北側樣點月平均光量皆高於南側樣點。孔隙內的氣、土溫在日間上升之幅度皆比冠層下方大，夜間熱能散失降溫的情形亦較冠層下快速，因此日照充足的3-9月，孔隙內平均氣、土溫會高於冠層下，其它的月份中則後者高於前者。土壤水勢在孔隙內樣區者內通常高於冠層下方，樣點位置越接近孔隙的周邊冠層，則平均土壤水勢越低，乾旱水逆壓的程度越為嚴重且乾燥持續的時間越長。在陽光直射光量較高的季節，也會使土壤水勢下降。受試的七種闊葉樹一年生苗木，在孔隙樣區栽植一年後之生長皆比冠層下良好，顯示孔隙形成後的環境條件對苗木生長有所幫助，但不同樹種受適應度在生長率的表現上則不盡相同。各樹種苗木生長於孔隙內有偏好的區塊，顯示受試的兩孔隙之內部環境條件，別是樣點的光量，對苗木生長已出現篩選的作用並表現在生長量上，差別僅在篩選強度於樹種間各有不同。
並列摘要
Canopy gaps play an important role in forest regeneration cycle. Many researches were performed to understand the effects of gap size and form on tree regeneration. The study was aimed to understand the Microenvironment conditions and their effects on seedling growth in two gaps in a natural broad-leaved forest at Shen-Mu area, Centeral Taiwan. Gaps sizes were 550m2 and 250m2 each. Solar radiation, air temperature, soil temperature, and soil moisture in both gaps were monitored. 1-year-old seedlings of seven different species were planted within gaps and their growths were monitored. The results showed that formation of gap would increase the solar radiation, especially from March to September. Light intensity under both large and small gap was 10 times higher than that in the understory. Meanwhile, the solar radiation was different among plots in gaps because of the effects of latitude. The average solar radiation in northern plots inside of the gap is higher than the average of those of southern ones. The changing ranges of air temperature and soil temperature were higher in gaps than those under the canopy. Also, the lost of heat in gaps was faster than those under canopy. In March to September when solar radiation was higher, the air and soil temperature were higher in the gaps. The results varied and were different between two gaps in the rest of the year. In general, soil moisture in the gaps was higher than that under canopy. Based on the results, we found that the closer the plots were to the canopy, the lower the moisture and the drier the soil. In season with higher radzation, direct sun light in the gaps increase the evaporation of surfice soil and decrease the soil water potential. The seedlings grew better in gaps than under canopy, which shows that the formation of gaps is beneficial to the growth of seedlings, and this study also showed that the internal environmental conditions provide the screening factors on seedlings of different species that affect of growth rate of those seedlings.