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標題: | 南仁山亞熱帶雨林短期森林動態之研究 Short-term Dynamics of a Subtropical Rain Forest in Nanjenshan |
作者: | Shan-Huah Wu 吳姍樺 |
出版年 : | 1998 |
學位: | 碩士 |
摘要: | 南仁山三公頃樣區於設立後七年進行植被複查,旨在瞭解森林組成變化、死亡率、新增率、生長速率及徑級結構,進而探討森林所處之狀態。 樣區現有植株35561株,分屬45科86屬125種。七年間有2種消失,9種移入,淨變化率為9.4%;總株數成長0.74%;總底面積成長13.25%。四個微生育環境中,迎風坡之株數減少3.81%,底面積增加18.63%;緩風坡、背風坡及溪穀之植株數量及底面積則都有增加。森林之優勢科與優勢種組成皆沒有變化,僅在排名上稍有變動,族群數量稀少的植種優勢度變化也不大。 總植株群之死亡率為1.80%,四個植物社會之年死亡率依序為:溪穀(2.66%)、背風坡(2.00%)、緩風坡(1.75%)、迎風坡(1.70%)。以徑級1-2公分之個體死亡量最大,佔死亡總株數之42.53%,其年死亡率為2.33%,也大於其他徑級植株群,植株之死亡率隨徑級加大而遞減。死亡率在迎風坡隨著徑級的增加而下降,在溪穀則是隨著徑級增加而上升。植株群之年新增率為2%。各微生育地之年新增率依序為:溪穀區(3.58%)、背風坡(3.21%)、緩風坡(2.13%)、迎風坡(1.28%),各微生育環境之新增株數並無顯著差異。全樣區植種之平均年生長速率為8.98%,胸徑之淨增加量為2.29(mm/yr),前者隨胸徑之增加而遞減,後者則反之。大部份植種之年生長速率介於8.5-11.5%之間,胸徑之年淨增加量則多在2.5(mm/yr)以下。樣區林木之徑級結構為反J型分佈,且超過一半以上之種類的徑級結構也都屬於此一類型。 此樣區森林在七年間之變化可以大致歸納成以下幾個現象:一、植種組成與總植株數幾乎沒有變化;二、生長速率快,底面積成長量大;三、小徑級植株大量死亡且植株有向較大徑級推移的現象;四、新增個體較多的植種多為林下生長的種類;五、部份陽性樹種有底面積負成長的現象;六、徑級結構呈反J形連續分佈。推測此森林在植種組成與空間的利用上,應已趨近飽合,但提供植物生長的資源仍未達最大承載量,因此植物體在快速生長,少量死亡的情況下,使得總底面積有大量的成長,再加上小徑級的植株大量減少,此底面積的成長多來自於植株胸徑的增加,整個森林之植株向較大徑級推移。 受東北季風幹擾最大的迎風坡,在死亡率、新增率及生長速率三方面,都較其他生育環境為低,並沒有原先預測之高死亡率的發生,推測生存於其上之植種應具適應機制。此外,優勢種、先趨樹種與族群數量稀少的種類之生存策略各不相同,優勢種頃向於低新增率、低死亡率、低生長速率,先趨樹種則傾向高死亡率、高新增率、高生長速率,而族群稀少的種類則傾向於與優勢種類似之方式,但其生長速率有較快的表現。植種生存的方式不同,將有利於維持森林組成與歧異度之穩定。反J形之徑級結構反應出森林沒有大規模之幹擾破壞的發生,且由先趨樹種之徑級結構推測,樣區內提供植種進行演替之因數應為由1-2棵倒樹所造成之林冠孔隙。 此森林應仍在成長,未來的變化與動向,必需藉由長期的觀察與資料累積,才能加以研究與推測。 In 1990 and again 1997, trees over 1 cm DBH were measured and mapped to clarify stand dynamics in a 3-ha permanent plot in Nanjenshan. Considering these data, including mortality, recruitment, growth, size structure and change of the composition, we made some conclusions for these changes of this forest which faces the strong stress from northeasterly monsoon wind and typhoon disturbance. 12.58% of trees present during the first sampling were no longer alive at the second. This mortality was nearly balanced by recruitment, and the rate of mortality suggests a turnover time for this forest of 56 years. The mortality and recruitment were almost equal to each other in the 4 habitats (windward, intermediate, leeward and creek) with respect to wind exposure, and they decreased gradually from the creek to the windward slope. The individual numbers and species composition changed a little, but basal area increased 13.25% in this period. A similar pattern was also observed for each of the 4 habitats. Almost all species maintain the same abundance. The average diameter growth rate of all individuals was 2.29mm per year, and it decreased gradually from creek to windward. The size structure of this forest was a reversed J shape, and almost half tree species in this forest showed this pattern. The overall changes of this forest were as follows: 1. The total individual number and species composition changed only a little 2. This forest showed rapid growth rate and basal area increment 3. There was a shift of trees from small DBH size to large size. 4. Species with greater increment were shade-tolerant, and some shade-intolerant species showed a negative growth in total basal area. 5. The size structure of this forest was a reversed J shape. This forest is supposed to be serial, and would keep growing in the near future. Different strategies among the species would be necessary for the forest to keep diversity and stability. Based on the structure, this forest might not have been subjected to large-scale disturbances during the past few decades. Nevertheless, it's really difficult to predict the dynamics and the future of this forest just by one recensus. Several remeasurement will be needed to get insights into the long-term dynamics of this forest. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/76369 |
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顯示於系所單位: | 植物科學研究所 |
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