Determining the mechanism of 'protective effects' of hardwoods on spruce budworm defoliation of balsam fir

香脂冷杉云杉的易感性和脆弱性云杉芽虫落叶减少硬木的存在。当硬木成分超过30-60%时，冷杉林分承受较少的蚜虫落叶。更高的硬木含量的最大影响是减少冷杉死亡率，认为是由于较高的寄生率的芽虫或更大的损失分散的第一和第二龄云杉芽虫幼虫在更大的硬木含量的立场。硬木成分对落叶的影响也影响冷杉云杉树的生长，因为较高的硬木可以观察到较低的平均径向生长减少。 硬木含量减少落叶、生长减少和 云杉芽虫暴发期间宿主物种的死亡率很高。但仍有几个问题： 1)其机制是由于较高的寄生率或更大的损失分散第一和 二龄云杉芽虫幼虫在更大的硬木含量的立场，或两者兼而有之？2)硬木树种之间的“保护”效应是否不同，特别是耐荫树种（糖枫、黄桦）与不耐荫树种（白色桦、颤白杨、红枫等）之间的差异？3)硬木的“保护作用”如何在一个夜蛾爆发的过程中变化，以及它应该如何被纳入林分生长模型和决策支持系统预测的立场和森林发展？解决这些问题的时机是正确的，因为加拿大东部的云杉芽虫数量正在上升。魁北克的落叶面积在过去4年中每年都翻了一番，2012年超过240万公顷，信息素诱捕器显示北方新玩法的云杉芽虫种群有所增加。我建议，以确定机制的“保护作用”的硬木对芽虫落叶冷杉云杉，并解决上述三个问题，使用混合的芽虫人口和树木的测量在新玩法或魁北克在预期即将爆发的永久地块。

Balsam fir-spruce susceptibility and vulnerability to spruce budworm defoliation are reduced by the presence of hardwoods. Fir stands sustain less budworm defoliation when >30-60% hardwood composition is exceeded. The greatest effect of higher hardwood content is reduction of fir mortality, thought to result from higher parasitism rates of budworm or greater losses of dispersing first- and second-instar spruce budworm larvae in stands with greater hardwood content. Hardwood composition effects on defoliation also influence fir-spruce tree growth, as lower mean radial growth reductions have been observed with higher hardwoods. The evidence for a 'protective effect' of hardwood content reducing defoliation, growth reduction, and mortality of host species during spruce budworm outbreaks is strong. But several questions remain: 1) Is the mechanism due to higher parasitism rates of budworm or greater losses of dispersing first- and second-instar spruce budworm larvae in stands with greater hardwood content, or both? 2) Does the 'protective' effect between differ among hardwood species, in particular between shade-tolerant (sugar maple, yellow birch) versus shade-intolerant species (white birch, trembling aspen, red maple, etc.)? 3) How does the 'protective effect' of hardwoods vary over the course of a budworm outbreak, and how should it be incorporated into stand growth model and decision support system projections of stand and forest development? The timing is right to address these questions because spruce budworm populations are on the rise in eastern Canada. Area of defoliation in Quebec has generally doubled in each of the last 4 years, to over 2.4 million ha in 2012 and pheromone traps have shown increases in spruce budworm populations in northern New Brunswick. I propose to determine the mechanism of 'protective effects' of hardwoods on budworm defoliation of fir-spruce and to address the above three questions, using a mix of budworm population and tree measurements in permanent plots in northern New Brunswick or Quebec during the expected upcoming outbreak.