Regeneration und Invasibilität des montanen Metrosideros-Regenwaldes auf der Insel Hawaii

夏威夷大岛 Metrosideros 山地雨林的再生和入侵

• 批准号: 5289000
• 负责人: Privatdozent Dr. Hans Jürgen Böhmer
• 金额: --
• 依托单位: Interdisziplinäres Lateinamerikazentrum (ILZ)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2001
• 资助国家: 德国
• 起止时间: 2000-12-31 至 2003-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5289000?language=en
• 关键词: Regeneration; und; Invasibilit; des; montanen

About 50,000 hectares of Metrosideros polymorpha(Myrtaceae) rain forest on the island of Hawaii were affected by a decline of the canopy ("´ohi"a dieback") in the 1970s. A twenty-seven year study of permanent plots has shown that a new cohort of Metrosideros polymorpha trees is replacing the old canopy layer, confirming the predictions of a stand-structure model. The density of healthy trees in former dieback stands has now reached the density in rain forest stands that did not undergo dieback in the 1970s.The large extent of the forest decline is attributed to a uniform age and stand structure ("cohorts") initiated by primary succession following volcanic eruptions. This uniform cohort structure resulted in the simultaneous aging and death of most of the trees in the cohort ("cohort senescence"). We postulate that the decline was a natural demographic phenomenon, whereby synchronized senescence acted as the major predisposing cause. Climatic fluctuations may have acted as dieback triggers, particularly on sites with poor drainage. In these habitats, extreme rainfall events and droughts, eg. during an episodic lifting of the cloud layer in ENSO years, may have caused abiotic stress, particularly a cavitation dysfunction of the xylem.As mentioned above, the density of healthy Metrosideros trees per hectare has almost reached the level of unaffected forest stands again " except for those stands invaded by certain invasive alien plant species. Results show a significant impact of Psidium cattleianum(Myrtaceae) and Hedychium gardnerianum (Zingiberaceae) on the regeneration of indigenous plant species. Both species were not present on the plots in 1976. Today, Psidium cattleianum makes up about 25% of all understorey trees on the study sites, apparently replacing the expected new cohort of Metrosideros polymorpha. Dense stands of Hedychium gardnerianum displace any Metrosideros regeneration as well as numerous other indigenous, endemic, or alien plant species. Both species are probably capable of completely changing structure and species composition of Hawaii´s montane Metrosideros rainforest.

20世纪70年代，夏威夷岛上约50,000公顷的桃金娘(桃金娘科)雨林受到树冠衰退的影响。一项对永久地块长达27年的研究表明，新的多形Metrosideros树群正在取代旧的冠层，证实了林分结构模型的预测。以前的枯萎林中健康树木的密度现在已经达到了热带雨林林分的密度，这种密度在20世纪70年代没有经历过枯萎。森林衰退的很大程度归因于火山喷发后的初级演替所引发的统一的年龄和林分结构(“队列”)。这种统一的队列结构导致队列中的大多数树木同时老化和死亡(“队列衰老”)。我们假设，这种下降是一种自然的人口统计现象，同步衰老是主要的诱因。气候波动可能起到了枯萎的触发作用，特别是在排水不佳的地点。在这些栖息地，极端降雨事件和干旱，例如。在ENSO年的一次周期性的云层抬升期间，可能造成了非生物胁迫，特别是木质部的空化功能障碍。如上所述，健康的Metrosideros树的密度几乎再次达到了未受影响的森林林分的水平“，除了那些受到某些外来入侵植物入侵的林分。结果表明，桃金娘科植物Psidium cattleianum和姜科植物Hedychum gardnerianum对乡土植物更新有显著影响。1976年，这两个物种都没有出现在这些地块上。今天，卡特兰约占研究地点所有落叶乔木的25%，显然取代了预期的新的多形Metrosideros队列。密林中的白花蛇舌草取代了任何Metrosideros的更新，以及许多其他本土、特有或外来植物物种。这两个物种可能完全改变了夏威夷S山地Metrosideros热带雨林的结构和物种组成。