Hard wood natural regeneratin and rehabilitation in a serious Nematode-damaged Luchu pine (Pinus luchuensis) plantation

A widespread nematode (Bursaphelenchus xylophilus) epidemic has occureed in northeastern Taiwan in past 5-10 yr. Most of the Luchu pine plantations almost completely died back; this caused them to look like early developing secondary hardwood stands dominated by Mallotus paniculatus but interpersed with scattered standing dead Luchu pines. In order to estimate the potential natural regeneration capability of these nematode- damaged stands and determine rehabilitation measuers, a typical plantation of this kind was selected in the Pinglin area, northern Taiwan and its structure was studied. Afterwards, a completely random block design wtith 3 treatments and 4 replicates was applied to the plantation. The 3 treatmentsincluded control,weeding,and weeding with enrichment planting. Each treatment area was 40X25 m. The total area was 1.0ha. Within the plantation, 72 hardwood tree species were identified, and amonh them, goodnatural regeneration ability was found for importanttimber species, such as Michilia compressa, Machilus thunbergii,Mac.zuihoensisand Scheflera octophylla. The results show that within this secondary stand, weeding treatment did not significantly increase the basal area growth of the residual hardwood trees in the stand, which might have been affected by the disturbance of typhoons and damages caused by cutting practices of the nematode-damaged pines. However, weeding did increase the new occurrence of tree seedlings to an average of 132seedling/ plot compare to 34 seedling/plot in the control.as to the weeding with enrichment planting, the increase in new seedling was lowerthan in the control. The high weeding frequency in the treatment may have caused thisresult. the dominant naturally occurring seedlings were 2 pioneer species Mal. paniculatus and Mal. iaponicus. For 4 native tree species used for enrichment planting, the net height growth ofmac.zuihoensis reachon average of 199 cm in 4 year, but the height growth of the remaining 3 tree species was still below 138 cm on a average of the sa,me period. The survival rates of seedlings were all above 82.6%, indicating the under-canopy bright is not a limiting factor in such stands. Weeding or weeding with enrichment planting can accelerate the restorationof this secondary forest.

过去5至10年间，中国台湾东北部地区爆发了大面积松材线虫（Bursaphelenchus xylophilus）疫情。当地多数琉球松（Luchu Pine）人工林几乎完全枯败，林分外观类似以粗糠柴（Mallotus paniculatus）为优势种的早期演替次生阔叶林，仅零星残存枯立的琉球松植株。为评估此类受线虫侵染林分的潜在天然更新能力并制定林分修复措施，研究团队在中国台湾北部坪林地区选取了一处典型的此类人工林，并对其林分结构展开研究。
本试验采用完全随机区组设计，设置3种处理、4次重复，处理组分别为对照组、除草组、除草+补植组。每个处理样地面积为40m×25m，总试验面积达1.0公顷。本次调查共鉴定出72种阔叶树树种，其中重要用材树种如台湾含笑（Michelia compressa）、红楠（Machilus thunbergii）、乌心石（Machilus zuihoensis）以及鹅掌柴（Schefflera octophylla）均表现出优良的天然更新能力。
研究结果表明，在该次生林分中，除草处理并未显著提升林分内残存阔叶树的胸高断面积生长量，这可能与台风扰动以及受线虫侵染的枯松采伐作业带来的干扰有关。但除草处理可显著提升幼苗新增数量，对照组样地平均幼苗数为34株/样地，除草组则达到132株/样地。而除草+补植组的幼苗新增量却低于对照组，这可能是由于该处理组的除草频率过高所致。林分内天然更新的优势幼苗为两种先锋树种：粗糠柴（Mallotus paniculatus）和野梧桐（Mallotus japonicus）。
在用于补植的4种乡土树种中，乌心石（Machilus zuihoensis）在4年内的平均树高净生长量达到199cm，而其余3个树种在同期的平均树高生长量仍低于138cm。所有补植幼苗的存活率均高于82.6%，表明林冠下光照并非该类林分的限制因子。除草或除草+补植措施均可加速该次生林的修复进程。