Feathermoss seedbeds facilitate black spruce seedling recruitment in the forest-tundra ecotone (Labrador, Canada)
Feathermoss seedbeds facilitate black spruce seedling recruitment in the forest-tundra ecotone (Labrador, Canada)
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羽毛苔苗床促进森林苔原生态交错带黑云杉幼苗的补充（加拿大拉布拉多）
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
P. Marino
中科院分区：
文献类型：
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作者：
J. Wheeler;L. Hermanutz;P. Marino
随着气候变暖，针叶树的活动范围预计将扩大到高山苔原，那里的生态因素，如苗床可用性、传播后种子和幼苗的捕食，可能会控制当地的补充。苗床组成可能会影响微生境、营养物质、物理结构和捕食水平，从而影响针叶树补充的成功，从而为未来的扩张提供模板。在北方森林中，苗床与幼苗的竞争占主导地位，因此苗床的移除增加了黑云杉的补充。在米利山脉北方针叶林-苔原交错带（加拿大拉布拉多）气候更加恶劣的情况下，应力梯度假说（SGH）预测促进作用可能主导苗床-幼苗的相互作用。本研究调查了三个针叶树苗床（侧耳草、石蕊属、裸土）的苗床促进（温度、水、养分、物理保护）的潜在机制，并检查了三年内种子捕食和/或幼苗食草是否存在变化。种子出苗率总体较低（所有处理均< 10%），但侧耳草属最高（6.3%），其次是裸地（4.6%）和石蕊属（0.3%）。观察到侧耳草和黑云杉之间的促进作用，苗高增加 (31%) 和成活率 (55%) 最高；与石蕊和裸地苗床相比，草食性、种子捕食和越冬死亡率最低。与封闭的冠层北方森林不同，裸露土壤上的幼苗补充效果较差，幼苗高度增加和成活率分别为 20.5% 和 26%。各苗床的温度和水分利用率相似，而侧耳草的养分利用率较高。侧耳草的物理结构可能保护一到三年的幼苗免受极端温度和捕食者的侵害。随着气候变暖和种子供应量的增加，侧耳草可能会促进黑云杉的补充和树线的扩张。
As climate warms, conifers are expected to expand their ranges into alpine tundra where ecological factors such as seedbed availability, and post-dispersal seed and seedling predation may control local recruitment. Seedbed composition may influence microhabitat, nutrients, physical structure, and predation level and, therefore, affect the success of conifer recruitment, thereby providing the template for future expansion. In the boreal forest, seedbed–seedling competition dominates such that seedbed removal increases black spruce recruitment. In the harsher climate of the Mealy Mountains boreal forest–tundra ecotone (Labrador, Canada) the Stress gradient hypothesis (SGH) predicts that facilitation may dominate seedbed–seedling interactions. This study investigated potential mechanisms of seedbed facilitation (temperature, water, nutrients, physical protection) in three conifer seedbeds (Pleurozium schreberi, Cladonia spp., bare soil) and examined whether seed predation and/or seedling herbivory varied among seedbeds over three years. Seed emergence was low overall (< 10% on all treatments), but highest on Pleurozium (6.3%), followed by bare ground (4.6%) and Cladonia (0.3%). Facilitation was observed between Pleurozium and black spruce as seedling height increase (31%) and survival (55%) were highest; herbivory, seed predation and overwinter mortality were lowest compared to both Cladonia and bare ground seedbeds. Unlike in the closed canopy boreal forest, seedlings recruited poorly on bare soil as seedling height increase and survival were 20.5% and 26%. Temperature and water availability were similar across seedbeds, while nutrient availability was higher on Pleurozium. The physical structure of Pleurozium likely protects first to third-year seedlings from temperature extremes and predators. As climate warms and seed availability increases, Pleurozium may facilitate black spruce recruitment and treeline expansion.