DISSERTATION RESEARCH: Substrate Limitations to Tsuga Canadensis and Betula Allegheniensis Seedling Establishment

论文研究：加拿大铁杉和阿勒格尼桦幼苗建立的基质限制

• 批准号: 0410748
• 负责人: Michael Walters
• 金额: $ 0.85万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-15 至 2005-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0410748&HistoricalAwards=false
• 关键词: DISSERTATION; RESEARCH; Substrate; Limitations; Tsuga

In northern Michigan and Wisconsin, eastern hemlock trees often grow in dense stands bordering sugar maple forests. These borders are remarkably stable, sometimes not changing for thousands of years. Because hemlock trees cast such dense shade, sugar maple is unable to invade hemlock stands. But why can't hemlock expand into sugar maple forests? Part of the reason is that hemlock seedlings cannot survive more than a few years on the forest floor. Older hemlock seedlings (and yellow birch seedlings) are usually found growing on rotting logs and stumps, which stay moister than the surrounding soil and also shed leaf litter. Previous work by these investigators has found that both hemlock and yellow birch seedlings prefer hemlock logs to those of sugar maple and other deciduous species. This may explain not only why hemlock trees are unable to "invade" sugar maple forests, but also why hemlock and yellow birch (a slow-growing conifer and a faster-growing deciduous tree) are commonly found so close together that their roots are intertwined. Having already counted and measured seedlings on logs and the forest floor, the investigators are now measuring water, light, and nutrient levels of logs, along with wood decay rate, to explain why hemlock and yellow birch seedlings prefer hemlock logs. This research may eventually be used to help restore hemlock forests destroyed by hemlock woolly adelgid, a pest from Asia that has invaded the east coast. The preliminary results of this study are currently being used to improve management of old-growth hemlock forests in Michigan.

在北方密歇根州和威斯康星州，东部铁杉树经常生长在密集的立场接壤糖枫林。这些边界非常稳定，有时数千年都没有变化。由于铁杉树投下如此密集的阴影，糖枫是无法入侵铁杉林。但是为什么铁杉不能扩展到糖枫树林呢？部分原因是铁杉幼苗不能在森林地面上存活超过几年。较老的铁杉幼苗（和黄桦树幼苗）通常生长在腐烂的原木和树桩上，这些原木和树桩比周围的土壤更潮湿，也会脱落落叶。这些研究人员以前的工作发现，铁杉和黄桦幼苗都喜欢铁杉原木，而不是糖枫和其他落叶树种。这不仅可以解释为什么铁杉无法“入侵”糖枫树林，也可以解释为什么铁杉和黄桦树（一种生长缓慢的针叶树和一种生长较快的落叶树）通常被发现如此接近，以至于它们的根相互缠绕。在已经计算和测量了原木和森林地面上的幼苗之后，研究人员现在正在测量原木的水分、光照和营养水平，沿着木材腐烂率，以解释为什么铁杉和黄桦幼苗更喜欢铁杉原木。这项研究最终可能被用来帮助恢复被铁杉绵球蚜破坏的铁杉森林，铁杉绵球蚜是一种来自亚洲的害虫，已经入侵了东海岸。 这项研究的初步结果目前正在用于改善密歇根州古老的铁杉林的管理。