淡水河口水筆仔與蘆葦兩植叢間演替機制之探討

Abstract

作者研究1978年至1990年之航空照片發現關渡水筆仔（Kandelia candle）叢在1982年後曾急劇增加，且有向蘆葦（Phragmites communis）擴張之現象，在此期間除了蘆葦叢大量退卻而水筆仔將其露出之裸地再次覆蓋外，亦可發現部分水筆仔由蘆葦叢邊緣入侵。在竹圍地區亦可由前人之文獻及航空照片得知，曾遭人為破壞而產生裸地，水筆仔亦能由邊緣侵入漸漸取代先驅進入裸地的蘆葦。由兩地演替的現象均可確知水筆仔對蘆葦入侵的能力。 本研究首先對水筆仔胎生苗存活的情況進行探討，發現不論人為植入或自然散佈的胎生苗均難在蘆葦中存活。由人工植入之實驗得知，於蘆葦叢中的胎生苗於植入兩個月後即遭螃蟹全數啃食，而紅樹林林隙及林內皆有胎生苗之存活，且林隙之啃食率低於林內；而在林內存活之植入苗亦在一年後全數死亡，使得植入之胎生苗僅能存活於林隙中，而有63％的存活率。 本研究另一部分則是探討遮蔭及相剋作用對蘆葦的生長是否有抑制作用，進而產生對水筆仔擴張有利之裸地。經由十個月的遮蔭實驗後，發現蘆葦的生物量及株高有顯著的升高，而地下根莖的萌芽並未下降，動物啃食的現象也無上升。在相剋作用方面，發現水筆仔樹皮及葉的水溶萃取液對蘆葦的萌發具抑制效果，且樹皮內之毒物質對蘆葦之根莖具強抑制能力。但是，此植物毒物質在野外的作用效果仍未有直接的證據。

Studing the aerial photographic pictures which were taken from 1978 to 1990, it was found that kandelia candle were not only increasing sharply but also extending to reed (Phragmites communis) area after 1982, covering the exposed area because of backward movement of the reed. The Kandelia began intruding from the edge of the reed. After reviewing the aerial photograph and also references of the Chu-wei district, it was found that the Kandelia would gradually replace the reed area, starting from the edge of the reed area where it was created by mans disturbance. The pheonomenon of succession in Tan-shui river can be concluded that the ability of Kandelia succeed the reed occurs in the mouth of the river. In the begining, this research was to investigate the surviving status of the viviparous seedling of kandelia. It was hard for either the plant or the spread for the viviparous seedlings needed to survive. With test plants, all the viviparous seedling planted in the reed were biten by crabs within two months. The viviparous seedlings planted in the understory were all dead, however, there were surviving seedlings in the understory and gap of mangrove trees, and the bited rate was lower in the gap than in the understory. The planted viviparous seedlings only survived in the gap at a 63% rate. An other part of this investigation was to explore whether shading of the reed and finding the allelopathy between the reed and Kandelia would inhibit the growth of the reed. Thus, it might create a better environment for Kandelia to diffuse. After ten monthes in the shade, there was an increase of reed in quantity and extent of growth. The budding of the rhizome did not decrease, and the consumed rate by animal, did not increase. In allelopathy, the extracts of bark and leaf of Kandelia might inhibit the budding of reed. The phytotoxins of the bark can inhibit the growth of rhizomes of the reed, but these is no direct evidence in field.