Ungulates have become abundant in many temperate forests, shifting tree species composition by browsing and altering soil physical conditions by trampling. Whether these effects cascade down to other trophic levels and ecosystem processes is poorly understood. Here, we assess the paths through which ungulates have cascading effects on other trophic levels (regeneration, litter, invertebrates, rodents and organic matter decomposition). We compared ungulate effects by comparing 15 response variables related to different trophic levels between paired fenced and unfenced plots in twelve temperate forest sites across the Netherlands, and used pathway analysis model to identify the (in)direct pathways through which ungulates have influenced these variables. We found that plots with ungulates (that is, unfenced) compared to plots without (that is, fenced) had lower litter depth, sapling diversity, sapling density, rodent activity, macro-invertebrate biomass, decomposition rate of tea bags, pine and birch litter and higher soil compaction. These findings were used in a path analysis to establish potential causal relationships, which showed that ungulate presence: decreased sapling density, which indirectly decreased rodent activity; decreased litter depth, which indirectly reduced invertebrate diversity; increased soil compaction, which also decreased invertebrate diversity. Soil pH decreased invertebrate biomass, which also increased nitrogen mineralization. Yet, we did not find cascading effects of ungulates on decomposition rates. Importantly, an increase in ungulate abundance strengthens the cascading effects in this system. Our results suggest that ungulates can trigger cascading effects on lower trophic levels, yet decomposition and mineralization rates are resilient to ungulate browsing and trampling. Therefore, temperate forests conservation could benefit by limiting ungulate abundance.

在许多温带森林中，松g变得越来越丰富，通过浏览和通过践踏来改变土壤物​​理条件，从而改变了树种的组成。这些影响是否会降级到其他营养级别和生态系统过程，人们对此知之甚少。在这里，我们评估有蹄类动物对其他营养水平（再生，凋落物，无脊椎动物，啮齿动物和有机物分解）的级联影响的路径。我们通过比较15个与不同营养水平相关的15个响应变量对有蹄类动物的影响进行比较，该变量在荷兰的12个温带森林站点中的成对的围栏和无围篱地块之间进行了比较，并使用路径分析模型来确定有蹄类动物通过这些路径影响这些变量的（间接）路径。我们发现与有蹄类动物（即无围栏）相比，有蹄类动物的地块（即无围栏）围栏）具有较低的凋落物深度，幼树多样性，幼树密度，啮齿动物活动，大型无脊椎动物生物量，茶袋，松树和桦树凋落物的分解率以及较高的土壤压实度。这些发现被用于路径分析，以建立潜在的因果关系，这表明有蹄类动物的存在：树苗密度降低，从而间接降低了啮齿动物的活动；凋落物深度的减少，间接降低了无脊椎动物的多样性；增加土壤压实度，这也降低了无脊椎动物的多样性。土壤pH降低了无脊椎动物的生物量，这也增加了氮的矿化作用。但是，我们没有发现有蹄类动物对分解率的连锁影响。重要的是，有蹄类动物数量的增加会增强该系统的级联效应。我们的结果表明，有蹄类动物可以在较低的营养水平上引发级联效应，但是分解和矿化速率对于有蹄类动物的浏览和践踏具有弹性。因此，温带森林的保护可以通过限制有蹄类动物的数量而受益。