銀合歡（Leucaena leucocephala (Lam.) de Wit.）為台灣危害力最高之入侵性木本植物，其具有優勢的繁殖特性及相剋作用，已快速入侵恆春地區，成為部分林地之優勢種，對森林生態系之生物多樣性造成影響。許多生態學家及地理學家應用航空照片進行判釋，並繪製其分布範圍，瞭解外來植物入侵範圍與擴散程度。本研究旨在應用1982、1992、2003、2007年所拍攝之四期航空照片，以尖山、後灣、關山、大尖石山等四區域為研究範圍，銀合歡及相思樹植群為研究對象，探討相同地點不同年度之土地利用情形及銀合歡分布狀況，瞭解銀合歡之擴散現象與土地利用之關係；以不同年度之擴散面積計算恆春半島山區及海岸地區銀合歡之擴散速率；利用立意取樣監測銀合歡與伴生樹種間之消長情形，探討銀合歡與其伴生樹種－相思樹（Acacia confuse Merr.）之間競爭狀況。研究結果顯示，恆春半島土地利用，1992～2003年間的森林面積有增加趨勢，其原因為銀合歡的擴散及人工造林，尤其是2003～2007年間裸露地明顯增加，形成銀合歡之入侵基地；由1982～2007年間之航空照片判釋得知，銀合歡有持續擴散之現象，其平均擴散速率為3.55 ha year^(-1)，藉由航空照片監測銀合歡與相思樹之競爭情形，顯示相思樹有漸漸取代銀合歡之趨勢。
Leucaena leucocephala (Lam.) de Wit. has been recognized as the most effectively invasive woody plant in Taiwan. Due to its strong reproduction and alleopathy, it has been a dominant invasive species in Henchun peninsula and caused negative impact to the biodiversity of the forest ecosystem. Currently the investigations into the invasive alien plants mostly rely on the application of aerial photography to monitor and to make a distribution map to study the dispersion of L. leucocephala. Therefore, aerial photography detection of plants has been used by many ecologists and land managers as a primary solution to invasive alien species. The aim of this study is to analyze the land use and the distribution of L. leucocephala in different years by utilizing the aerial photos of Jian Mountan, Hou Bay, Guanshan, and Dajianshih Mountain area which were taken in 1982, 1992, 2003 and 2007. The speed of dispersal and the competition of L. leucocephala with Acacia confusa Merr. were also studied. The result indicated that forest area had increased in 1992 to 2003 due to the dispersal spread of L. leucocephala and afforestation, and in 2003 to 2007 there were significant increase of the bare area which may become the base habitat for the invasion of L. leucocephala. Also according to the aerial photos taken from 1982 to 2007, L. leucocephala is continuously dispersing, and the average speed of its dispersal was 3.55 ha year^(-1). Meanwhile, the aerial photos also showed that A. confusa is gradually replacing L. leucocephala in these regions.
