雪山翠池地區玉山圓柏植群動態之研究

臺灣之高山森林生態系中，玉山圓柏扮演著重要角色，亦為臺灣高山地區珍貴樹木，具有物種保存及水土保持之功能。本研究針對2006年設置之長期監測樣區進行13年後之複查，於F永久樣區 (玉山圓柏林)，以及A、B、C交會帶樣區 (玉山圓柏與臺灣冷杉交會帶)，記錄其樹木位置空間資訊及樹木生長性狀等，並分析玉山圓柏植群結構、樹木死亡及其死亡空間分布等，藉以建立玉山圓柏植群動態之生態資訊。於F永久樣區設置15個地被層樣區 (1 m × 1 m)，共記錄維管束植物14科21屬21種 (含種以下分類群)，含蕨類植物2種、裸子植物1種、雙子葉植物13種、單子葉植物5種；其中特有種14種，2種屬於2017臺灣維管束植物紅皮書名錄植物，分別為大霸尖山酢醬草與玉山唐松草，地被層樣區可劃分成川上短柄草型與髮草型。F永久樣區與交會帶樣區之胸徑、樹高、枝下高與樹冠長皆較2006年成長。應用TSTRAT分層可將F永久樣區之玉山圓柏區分為10個森林層次，玉山圓柏仍於該森林植群中居於優勢地位；F永久樣區與交會帶樣區之樹種組成，13年間無改變，樣區內樹木株數減少，但胸高斷面積則呈淨增加；死亡樹木之徑級結構呈現反J型分布。F永久樣區之空間分布於2019年與2006年相似，皆於距離尺度小於15 m呈現顯著集落分布，而大於15 m後呈現均勻分布，F永久樣區之玉山圓柏處於穩定階段；而於交會帶之空間分布則於2次調查間，整體皆呈現隨機分布，顯示交會帶之玉山圓柏與臺灣冷杉仍處於競爭階段。在最近鄰分析中，於A、B、C交會帶樣區內發現玉山圓柏大活樹不論對玉山圓柏小樹或臺灣冷杉小樹，都具有顯著之競爭壓力；C交會帶樣區則是臺灣冷杉對於種內有顯著競爭壓力，而種間則無顯著；F 永久樣區無論玉山圓柏大樹對玉山圓柏小樹或玉山杜鵑小樹都無呈現顯著競爭壓力。氣候方面以溫度趨勢來看，各樣區於2015~2019年間有逐漸增溫趨勢狀況，年平均溫度以樣區約增加1.5 ℃左右，年均最高溫與年均溫有同樣趨勢；降雨量於2009年後樣區之年降雨量不穩定，2010~2019年之平均年降雨量，是較1995~2009年間為低；樣區內之增強植生指數數值具有明顯季節性變化，12月至翌年1月是增強植生指數數值之低點，顯示樣區內玉山圓柏與臺灣冷杉活力較低，而樣區主要生長季是在2~7 月。雪山翠池地區之交會帶中玉山圓柏與臺灣冷杉仍持續競爭狀態，臺灣冷杉生長速度快於玉山圓柏，臺灣冷杉利用不斷更新與生長緩慢且生長年齡甚長之玉山圓柏競爭，但臺灣冷杉因生長快且對應氣候變化或颱風影響等因素，容易造成死亡，另一方面玉山圓柏氣候耐受性範圍較臺灣冷杉為大，13年間之2次調查，於F永久樣區之玉山圓柏維持穩定狀態，而於交會帶樣區之臺灣冷杉雖有競爭範圍擴大趨勢，但面對溫度升高、雨量減少或颱風干擾等因素下，氣候影響仍是主要未來監測動態變化主要原因之一。

關鍵字

玉山圓柏；植群動態；空間分布；樹木死亡

並列摘要

Juniperus morrisonicola Hayata plays an important role in Taiwan’s alpine forest ecosystem, which is not only a kind of precious tree species but also has the functions of species preservation and soil and water conservation. This study is based on the long-term monitoring of plots set in 2006 and their re-investigation after 13 years, which included F plot (permanent plot of J. morrisonicola) and ecotone A, B and C (permanent plots in the ecotone between J. morrisonicola and Abies kawakamii (Hayata)), recording their spatial distribution and growth traits. Ultimately, the ecological information of the dynamics of J. morrisonicola was established through analyzing the structure of vegetation, mortality of trees and the spatial distribution pattern of dead individuals. There were 15 permanent plots (1 m x 1 m) set in the F plot. In the result, 21 species (including taxa below species), 21 genera, and 14 families of vascular plants were recorded, including 2 species of ferns, 1 species of gymnosperms, 13 species of dicots, and 5 species of monocots. Among them, 14 species are endemic species, and 2 species are listed in The Red List of Vascular Plants of Taiwan, 2017, which are Oxalis acetosella L. subsp. taemoni (Yamamoto) S. F. Huang & T. C. Huang and Thalictrum sessile Hayata. The ground covers of plots were classified into Brachypodium kawakamii Hayata type and Deschampsia cespitosa (L.) P. Beauv. var. festucifolia Honda type. The diameter at breast height, height to crown base and crown diameter of the trees in the F plot and ecotone all increased slightly compared with that in year 2006. The TSTRAT stratification classified the J. morrisonicola in the F plot into 10 layers and indicated that J. morrisonicola still occupied a dominant position in the forest community. The composition of vegetation in the F plot and ecotone plots did not change in 13 years. The number of trees in the plots decreased, however, the basal area had a net increase. The diameter structure of dead trees showed an inverse J-shaped distribution. The spatial distribution of the F plot in 2019 was generally similar to that in 2006. Within the scale of distance of 15 meters, there was still a significant aggregation distribution, and it showed a uniform distribution 15 meters away, while J. morrisonicola in the F plot stayed in a stable stage. However, the spatial distribution of the ecotone was random in both investigations, which is suggested that the J. morrisonicola and A. kawakamii in the ecotone were still in the relationship of competition. Through the nearest neighbor analysis, it was discovered that the old living J. morrisonicola had significant competitive pressure to the young J. morrisonicola and young A. kawakamii in the ecotone A, B and C. In the ecotone C, A. kawakamii had significant intraspecific competitive pressure, but there was not significant interspecific competitive pressure. In the F plot, the old J. morrisonicola had no significant competitive pressure to the young J. morrisonicola or young Rhododendron pseudochrysanthum. As to climate, the temperature trends showed that it was gradually warming in each plot from 2015 to 2019 with the average annual temperature increased by about 1.5℃ in the plots. The average annual maximum temperature had the same trend as the average annual temperature. The annual rainfall in the plots was unstable after 2009. The average annual rainfall in 2010-2019 was lower than that in 1995-2009. The EVI value in the plots had significant seasonal variations. From December to January was the low point of the EVI value, indicating that the viability of J. morrisonicola and A. kawakamii in the plots was low, while the main growing season was from February to July. The J. morrisonicola and A. kawakamii in the ecotone in the Cuei-Chih area in Mt. Syue remained in a relationship of competition. A. kawakamii grew faster than J. morrisonicola, taking advantage of continuous regeneration to compete with slow-growing and much older J. morrisonicola. However, A. kawakamii was prone to death due to fast growth and countering climate change or typhoon, etc. On the other hand, J. morrisonicola had a better tolerance to climate. According to 2 investigations before and after 13 years, the J. morrisonicola in the F plot maintained in a stable state. Although the A. kawakamii in the ecotone tended to expand the range of being competitive, facing disturbances such as warming, rainfall reduction or typhoon interference, climate impact is still one of the main reasons for monitoring dynamic changes in the future.