Large herbivores play a key role in terrestrial ecosystems, and their populations alter the plant composition in many ecosystems. One example is deer, whose populations in the Northern Hemisphere have increased over the last decades. This has resulted in increased browsing pressure on saplings and, as a consequence, has hampered forest regeneration in some areas. Such herbivore-induced changes in the regeneration of forest stands have changed their composition and biodiversity. Although there is an established link between the deer population density and the level of damage caused by browsing, the question remains open: What is the effect of increasing deer density over years on the regeneration of palatable and less browsing-resistant tree species? In this study, we investigated the relationships between the regeneration dynamics of five tree species (European beech Fagus sylvatica, silver fir Abies alba, sycamore Acer pseudoplatanus, hornbeam Carpinus betulus, and oak Quercus spp.) and browsing pressure in two years with low and high red deer (Cervus elaphus) density and at similar roe deer (Capreolus capreolus) density. We set up experimental plots in Roztocze National Park (central-eastern Poland), a protected area where natural predators of deer are constantly present. In addition to deer density, we analysed parameters that may affect browsing intensity: height of saplings, forage availability (sapling density), sapling diversity and light intensity (canopy openness). We found that increasing red deer density significantly increased browsing on all tree species, with saplings taller than 50 cm being under the strongest pressure. Moreover, higher deer density altered deer forage selection – it increased their selection for unpalatable European beech and decreased for highly preferred sycamore. Additionally, more species-diverse patches and closed canopy attracted deer and increased the probability of browsing on saplings. Contrary to our predictions, sapling density decreased browsing intensity. The study confirms that high ungulate density has significant effects on tree recruitment and may alter tree species composition of the forest stand. We provide clear evidence that deer herbivory plays a crucial role in tree regeneration in top-down processes in natural ecosystems.

大型食草动物在陆地生态系统中发挥着关键作用，它们的种群改变了许多生态系统中的植物组成。一个例子是鹿，其在北半球的数量在过去几十年中有所增加。这导致对树苗的浏览压力增加，结果阻碍了某些地区的森林再生。这种由食草动物引起的林分更新变化已经改变了它们的组成和生物多样性。尽管鹿种群密度与浏览造成的损害程度之间存在确定的联系，但问题仍然存在：多年来增加鹿密度对可口且耐浏览性较差的树种的再生有什么影响？在这项研究中，我们调查了 5 种树种（欧洲山毛榉Fagus sylvatica、银冷杉Abies alba、美国梧桐Acer pseudoplatanus、鹅耳枥 Carpinus betulus和橡木Quercus spp.）在两年低和低浏览压力之间的关系。高马鹿（Cervus elaphus ) 密度和类似狍 ( Capreolus capreolus)） 密度。我们在 Roztocze 国家公园（波兰中东部）设立了试验区，该保护区是鹿的天敌经常出没的保护区。除了鹿密度之外，我们还分析了可能影响浏览强度的参数：树苗高度、草料可用性（树苗密度）、树苗多样性和光照强度（树冠开放度）。我们发现，增加马鹿密度显着增加了对所有树种的浏览量，高于 50 厘米的树苗承受的压力最大。此外，更高的鹿密度改变了鹿草料的选择——它增加了它们对难吃的欧洲山毛榉的选择，减少了对高度偏爱的梧桐的选择。此外，更多种类多样的斑块和封闭的树冠吸引了鹿，并增加了浏览树苗的可能性。与我们的预测相反，树苗密度降低浏览强度。该研究证实，高密度有蹄类动物对树木补充有显着影响，并可能改变林分的树种组成。我们提供了明确的证据，表明鹿食草在自然生态系统自上而下的过程中在树木再生中起着至关重要的作用。