Ecological theory predicts the strongest ecosystem effects of herbivory when dominant and ecologically important species are consumed. Bilberry, Vaccinium myrtillus, is such a key plant species, attractive to many other species in the boreal forests, for example ungulate and invertebrate herbivores. Large herbivores may remove substantial biomass and alter plant quality and therefore affect abundance and populations of invertebrate animals sharing the same food plant. We combined experimental exclusion of ungulates with a browsing intensity gradient to investigate the 15-year effect of ungulate (Cervus elaphus and Ovis aries) browsing on bilberry plant size and on bilberry-feeding herbivorous larvae (Lepidoptera and Symphyta), in a Norwegian old growth boreal forest ecosystem. Bilberry ramets in exclosure plots had nearly nine times higher dry mass and three times higher abundance of invertebrates feeding on them than in ungulate-access plots. Sweep-netting data verified these findings as larval numbers were twice as high in exclosure plots. The pattern in the large herbivore effects on bilberry size and abundance of herbivorous larvae were identical along the browsing gradient. Differences in larval abundance between treatments, as indicated by leaf-chewing, increased during the 15-year study period, and the community fluctuations were larger when ungulate herbivores were excluded. The browsing effect was moderated by plant quality as larval densities were lowest on both heavily-browsed and non-browsed plants, and highest on ramets that had 50–74% of annual shoots browsed. Our study supports previous findings in that bilberry is relatively disturbance tolerant and may recover quickly, but that ungulates may compete with herbivorous larvae for food biomass. Additionally, our results strongly indicates that population insect community peaks and fluctuations are dampened by ungulate consumption. Our findings add to the understanding on how ungulates may structure forest ecosystems directly and indirectly.

生态理论预测，当主要和生态重要的物种被食用时，食草动物的生态系统影响最强。越橘，Vaccinium myrtillus，就是这样一种重要的植物物种，对北方森林中的许多其他物种具有吸引力，例如有蹄类动物和无脊椎动物食草动物。大型食草动物可能会去除大量生物量并改变植物质量，从而影响共享同一食用植物的无脊椎动物的丰度和种群。我们将有蹄类动物的实验排除与浏览强度梯度相结合，以研究有蹄类动物（Cervus elaphus和Ovis aries) 在挪威古老的北方森林生态系统中浏览越桔植株大小和以越桔为食的食草幼虫（鳞翅目和共生植物）。与有蹄类动物接近的地块相比，围场中的越橘分株的干重高出近 9 倍，以它们为食的无脊椎动物丰度高出 3 倍。扫网数据证实了这些发现，因为围栏地块中的幼虫数量是原来的两倍。大型食草动物对越橘大小和食草幼虫丰度的影响模式沿着浏览梯度是相同的。在 15 年的研究期间，不同处理之间幼虫丰度的差异（如咀嚼叶所示）有所增加，并且当排除有蹄类食草动物时，群落波动更大。浏览效果受植物质量的影响，因为幼虫密度在重度浏览和未浏览的植物中最低，在有 50-74% 一年生枝条浏览的分株上最高。我们的研究支持先前的发现，即越橘相对耐受干扰并且可能会迅速恢复，但有蹄类动物可能会与食草幼虫竞争食物生物量。此外，我们的结果强烈表明，有蹄类动物的消费会抑制昆虫种群的峰值和波动。我们的发现增加了对有蹄类动物如何直接和间接构建森林生态系统的理解。但有蹄类动物可能会与食草幼虫竞争食物生物量。此外，我们的结果强烈表明，有蹄类动物的消费会抑制昆虫种群的峰值和波动。我们的发现增加了对有蹄类动物如何直接和间接构建森林生态系统的理解。但有蹄类动物可能会与食草幼虫竞争食物生物量。此外，我们的结果强烈表明，有蹄类动物的消费会抑制昆虫种群的峰值和波动。我们的发现增加了对有蹄类动物如何直接和间接构建森林生态系统的理解。