植穴土壤與敷蓋對臺灣赤楊表現之影響──以武陵廢耕地為例

Effects of mud planting and mulching on the performance of Alnus formosana in Wuling abandoned farmland

臺灣赤楊是臺灣中海拔生態復育造林的重要樹種，然出栽於高含石率之廢耕地的表現不佳，為此本研究於苗木出栽前篩除土壤中之石礫，再分組以過篩土、泥漿土栽植苗木，並對栽植後苗木周邊土表進行敷蓋，區分為無敷蓋、敷蓋泥炭土、敷蓋生物炭等3組。相較於過去以石礫土栽植赤楊之存活率甚低（4.6％），本研究經3年之監測結果顯示，植穴土壤改善及敷蓋具有提升苗木存活率之趨勢（過篩土栽植存活46.7％、泥漿土栽植存活58.9％；無敷蓋48.3％、敷蓋泥炭土53.3％、敷蓋生物炭56.7％），在苗木生長方面，植穴土壤改善及敷蓋略有提升苗木生長，但未達顯著差異。整體而言，赤楊苗木於每年4-9月有較高的生長量，且第2年之生長明顯優於第1年，栽植3年後平均地徑從7.8mm生長至44.5mm、苗高從102.3cm生長至274.4cm。泥漿土栽植與敷蓋對赤楊苗木地徑與苗高生長雖無顯著助益，然對綜合存活率與生長之累加效應的累積表現指數（Accumulated Performance Index, API）則有顯著提升。由於高含石率及強烈的太陽輻射會使土壤嚴重乾旱並造成苗木大量死亡，因此本文建議在土壤多石礫的武陵廢耕地栽植臺灣赤楊時，需先篩除植穴土壤中之石礫，並進行打漿及敷蓋，可減緩苗木所面臨的水分逆境，提升在山區高石礫廢耕地之赤楊造林成效。

Alnus formosana is an important tree species for mid-altitude ecological reforestation in Taiwan. However, it does not perform well when planted on abandoned farmland with high gravel content. In this study, the soil were sieved to remove gravels and the A. formosana seedlings were planted in either sieved soil or muddy soil each with different mulched covers. They are un-mulched, mulched with peat, and mulched with biochar. Seedling survival rate were after 3 years were 46.7% for sieving soil, 58.9% for muddy soil, 48.3% for un-mulched soil, 53.3% for soil mulched with peat, and 56.7% for soil mulched with biochar. In terms of growth performance, although muddy soil planting and mulching showed a trend of increased growth but the difference were not significant statistically. The seedlings showed a higher growth rate from April to September annually. The growth in the second year is significantly better than that the first year. The average stem ground diameter of the seedlings grew from 7.8 mm to 44.5 mm and the average seedling height grew from 102.3 cm to 274.4 cm. Although muddy soil planting and mulching did not show significant benefit to the growth of the seedlings, the accumulation performance index (API) were significantly increased. Because of the soil with high gravel content could dry severely under strong solar radiation, and resulted in the death for a large number of seedlings, we recommend that when planting A. formosana in the gravel rich soil, the gravels in the planting hole should be sieve out, then water should be added to create mud and then covered with mulch to reduce the drought stress of the seedlings, so that the effectiveness of A. formosana reforestation in the abandoned farmland can be improved.