Hemlock Woolly Adelgid in New England Forests: Canopy Impacts Transforming Ecosystem Processes and Landscapes
Hemlock Woolly Adelgid in New England Forests: Canopy Impacts Transforming Ecosystem Processes and Landscapes
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新英格兰森林中的铁杉羊毛阿德尔吉德：树冠影响改变生态系统过程和景观
DOI：
10.1007/s10021-003-0092-5
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发表时间：
2005
期刊：
影响因子：
3.7
通讯作者：
R. Cobb
中科院分区：
文献类型：
--
作者：
B. Stadler;T. Müller;D. Orwig;R. Cobb
外来害虫可能会严重破坏森林生态系统，并引发养分循环、结构和组成的重大变化。我们研究了这些不同的影响之间的关系铁杉绵球蚜（HWA，Adelges tsugae Annand）在新英格兰森林研究其对当地冠层过程的影响，在不同的侵扰水平，并将这些影响冠层养分循环和立场和景观效应的转变。HWA引发了冠层生物量和分布的重大变化。而未受感染的树木表现出显着下降，冠层生物量从中心到外围和针叶凋落物总量和估计的生物量之间的正相关性，受感染的树木有显着减少总冠层生物量，产生较少的新叶，脱落相对较多的针叶，并表现出凋落物和冠层生物量之间没有相关性。受害树叶片氮含量比对照树高20%-40%，其中幼叶增加最多，支持HWA的最高密度。叶片%C不受HWA或叶龄的影响。铁杉针叶上的附生微生物在林冠内的丰度变化不大，但细菌，酵母菌和丝状真菌的菌落形成单位的2-3个数量级更丰富的介质和严重侵染比未侵染的树木。HWA强烈改变了降雨的化学、数量和空间格局。在未受侵害的树木下，落叶具有很强的梯度，从树冠外围到树干的体积减少超过45%。穿透雨的数量在受侵害的树木下没有表现出空间格局，达到总降水量的80%-90%，其特征是显着较高浓度的氮化合物，溶解有机碳和阳离子。整个南部的新英格兰景观有一个强大的从南到北的梯度铁杉树和树苗死亡率和林下组成的变化，对应于虫害的持续时间。在区域上，黑桦（Betula lenta L.）从铁杉的减少中获益最多的是密度和覆盖率的显著增加。这些研究结果表明，有必要研究快速/小尺度过程之间的联系，如在树冠养分循环的变化和缓慢/综合的过程，如在森林林分和景观的化学循环和组成变化的变化，以更好地了解像HWA的外来有害生物物种对森林生态系统结构和功能的影响。
Exotic insect pests may strongly disrupt forest ecosystems and trigger major shifts in nutrient cycling, structure, and composition. We examined the relationship between these diverse effects for the hemlock woolly adelgid (HWA, Adelges tsugae Annand) in New England forests by studying its impacts on local canopy processes in stands differing in infestation levels and linking these impacts to shifts in canopy nutrient cycling and stand and landscape effects. HWA initiated major changes in canopy biomass and distribution. Whereas uninfested trees exhibit a significant decline in canopy biomass from the center to the periphery and a positive correlation between total needle litter and estimated biomass, infested trees have significantly less total canopy biomass, produce less new foliage, shed relatively more needles, and exhibit no correlation between litter and canopy biomass. Foliar N content of infested trees was 20%–40% higher than reference trees, with the strongest increase in young foliage supporting the highest densities of HWA. Foliar %C was unaffected by HWA or foliar age. Epiphytic microorganisms on hemlock needles exhibited little variation in abundance within canopies, but colony-forming units of bacteria, yeast, and filamentous fungi were 2–3 orders of magnitude more abundant on medium and heavily infested than uninfested trees. Throughfall chemistry, quantity, and spatial pattern were strongly altered by HWA. Throughfall exhibits a strong gradient beneath uninfested trees, decreasing in volumes from the canopy periphery to the trunk by more than 45%. The amount of throughfall beneath infested trees exhibits no spatial pattern, reaches 80%–90% of the bulk precipitation, and is characterized by significantly higher concentrations of nitrogen compounds, dissolved organic carbon, and cations. Across the southern New England landscape there is a strong south-to-north gradient of decreasing hemlock tree and sapling mortality and understory compositional change that corresponds to the duration of infestation. Regionally, black birch (Betula lenta L.) is profiting most from hemlock decline by significantly increasing in density and cover. These findings suggest that it is necessary to study the connections between fast/small-scale processes such as changes in nutrient cycling in tree canopies and slow/integrative processes like shifts in biogeochemieal cycling and compositional changes at forest stands and landscapes to better understand the effects of an exotic pest species like HWA on forest ecosystem structure and function.