Methods for preventing the invasion of Leucaena leucocephala in coastal forests of the Hengchun Peninsula, Taiwan.
Leucaena leucocephala, which originates from Central America, has severely invaded the western Hengchun Peninsula and the Penghu Archipelago in Taiwan. This study conducted several physical and chemical control experiments aimed at preventing invasion by this species. Regarding physical control, although adult L. leucocephala trees were cut down and new sprouts were cut out once a month for 12 times, sprouting could still not be inhibited. After felling adult trees, the stumps were covered with a thick black plastic sheet. No sprouting occurred in the covered area, yet new sprouts emerged from an uncovered area nearby. Shading treatment using shading nets to reduce the relative light intensity to 5% significantly reduced 63% of the amount and 30% of the length of the sprouts, and rendered L. leucocephala seedlings unable to survive. Girdling treatment caused the upper trunk and branches above the girdled area to wither; however, sprouts still grew from the lower edge of the girdled area. Regarding chemical control, smearing herbicide (glyphosate) either on the cut surface of the stumps or on the girdled area of trunks did not inhibit sprouting. However, injection of 3 ml of glyphosate into the trunk of L. leucocephala during the dry season considerably inhibited the crown sprouting ratio (to <10%), but during the rainy season, the injection was less effective (with a sprouting ratio of >22%). Thus, this study suggests that injection of glyphosate into the trunk is the most effective method to eliminate L. leucocephala. However, if herbicide usage is not an option, further investigation could focus on the effectiveness of felling adult trees, shading the stumps, and intensively cutting out new sprouts to inhibit the sprouting of L. leucocephala.