桉樹人工林皆伐地更新策略之研究Study on regeneration strategy of Eucalyptus clearcut land

桉樹萌芽更新二代林林分之留存根株經5年之生長調查，於前二年每公頃存活根株數，由平均820株/ha減少至574株/ha；林分處理後，至二年生以上，直至目前之存活根株株數則維持穩定。對照區維持546株/ha，除蘗處理區為603株/ha。每公頃總萌蘗株數，對照區每公頃1809株，除蘗處理區，每公頃則留存1119株。對照區單一根株， 平均萌蘗株數為3.3±2.0 株、平均胸徑生長10.0±3.8cm，樹高生長10.5±4.5m；除蘗處理區單一根株萌蘗株數為1.9±1.1株、平均胸徑生長12.0±3.5cm，樹高生長11.6±3.8m。雖由DBH換算之總胸高斷面積，分別為對照區16.7m2/ha，除蘖處理區為13.6m2/ha，主因對照區留存總萌蘖枝數較高的影響所致，但就單一林木生長，除蘗處理後平均胸徑及樹高生長均優於對照區。尤其平均胸徑生長可高達120%。在桉樹萌芽更新二代林林分之天然更新幼苗動態調查顯示，於對照區出現林下更新物種有22種363株，而除蘖處理區出現林下更新物種有27種567株，在兩處理區同時出現較多之數量植種，包括耳莢相思樹、血桐、山油麻、山漆莖、月橘等，於出現之植種，僅零星分不如樟樹、苦棟、山黃槴等，險是更新物種變化不大，但除蘗處理後所釋放出的環境資源可提供林下較多物種的發生機會，甚至有利尾葉按天然更新幼苗的發生。林下栽植相思樹、桃花心木、烏心石以及黃連木等台灣重要經濟造林樹種，至2015年止，總成活率達64%。林下栽植桃花心木平均成活率達87%，平均苗高已達406.5±121.1cm，4年生的高生長率達372%；黃連木之成活率79%，平均苗高193.6±73.1cm，高生長率247%；相思樹平均苗高在303.2±12 0.5cm，成活率73%，高生長率達318%；而烏心石平均苗高115.9±105.9cm，但成活率僅有17%，較其他三樹種苗高生長及成活率均不佳，烏心石造林木主因蟲害嚴重及乾旱而導致成活率逐年下降，顯示該樹種不適合當地生育地環境之生長。
We investigated the growth of 5-year-old Eucalyptus sp. Regenerated secondary stand of sucker shoots. The results indicated that the survival shoot number 2 years after cutting varied widely. The surviving shoots decreased from the original 820 existing shoots per hectare to an average of 574 shoots. After 2 years, the surviving shoot number remained stable.In which the control plot has 546 plants per hectare; deshooting treatment retained 603 plants per hectare.In the 5-year forest, control plot retained 1809 shoots/ha; the deshooting plot retained 1119 shoots/ha. In the control plot, a single stump averaged 3.3±2.5 shoots with average dbh of 10.0±3.8cm and shoot length of 10.5±4.5 m ; in the deshooting plot, each stump retained 1.9±1.1 shoots with average dbh of 12.0±3.5 cm and shoot length of 11.6±3.8 m. The sults also indicated that the dbh and height growth of shoots in deshooting plot was better than the control plot. The total dbh cross-sectional area in the control plot was 16.7 m2/ha; and in the deshooting plot was 13.6 m2/ha; The more shoots retained on the control plot, caused that the total dbh crosssectional area of the deshooting plot was still poorer than did the control. However, the net dbh and tree height growths after deshooting were greater. In subsequent investigations, we hope to establish more clearly the effect of deshooting treatment. In a survey of natural regenerated seedlings in the secondary Eucalyptus sp. shoot forest, there were 363 plants belonging to 22 species; whereas in the deshooting forest, there are 567 plants of 27 species sprouting from seeds. The species appeared both in the control plots and deshooting include Acacia auricuriformis , Macaranga tanarius, Breynia officinalis, Aleurites montana, Murraya paniculata etc. The other plants present only scattering, such as Cinnamomum camphora, Melia azedarach and Gardenia jasminoides, indicating renewable species showed little variation. However, the post-sprouting treatment released environmental resources can provide forest trees with a more varied regeneration opportunity,even facilitating seeding renewal of Eucalyptus urophylla. Comparing the emerging plant species, we found that the environmental resources released by deshooting treatment apparently allowed more plant species to take hold. Secondary planting of important endemic reforestation species of high economic values such as Acacia confusa, Swietenia macrophylla,Michelia compressa, and Pistacia chinensis in understories was also carried out. In 2015, the total survival rate after 4-year of all species averaged 64%. S. macrophylla had the highest surviving rate of 87% with average sapling height of 406.5±121.1 cm, the highest of all species;Acacia confusa had survived rate of 73%, with average sapling height of 303.2 ±120.5 cm . The survived rate of P. chinensish droped from 97% to 79% ,with tree height only of 193.6±73.1cm; M. compressa grew to a height of 83.4±65.2 cm, with survival rate of only 45%. These results are useful reference for selecting trees for understory planting in local planting programme.