Thorny Shrubs Limit the Browsing Pressure of Large Herbivores on Tree Regeneration in Temperate Lowland Forested Landscapes

Abstract

Thorny shrubs are considered as an important driver in the natural development of temperate forest structures, particularly in European lowland forests. We assessed the current role of thorny shrubs in the regeneration of deciduous tree species under heavy browsing pressure in a central European temperate forested landscape. The study’s military training area offered a unique opportunity to investigate the processes in which deciduous tree seedlings grew under thorny shrubs and in the close vicinity of thorny shrubs in a landscape with a high density of large herbivores (red deer and sika deer). We assessed the number of seedlings, species composition, seedling height, and degree of browsing damage, and their relationship to study plots elevation, thorny shrub species, coverage, and height. The regenerated tree seedlings were mostly detected as common ash (Fraxinus excelsior) and wild cherry (Cerasus avium). The species of thorny shrubs were blackthorn (Prunus spinosa), hawthorn (Crataegus sp.), and wild rose (Rosa sp.). We found that the thorny shrubs protected the tree seedlings from browsers to a large extent. However, the effects of thorny shrubs on the tree seedlings' characteristics varied among the shrub species. While results revealed significant effects of hawthorn and wild rose on the tree seedlings' abundance and survival, blackthorn’s negative effect of shading the tree seedlings outweighed its protective role. These results indicated a possible mechanism that enabled the regeneration of deciduous tree species under large herbivore pressure. These results can be applied in the landscape planning and forest management of deciduous tree regeneration and forest restoration in temperate forested lowland landscapes, where high densities of large herbivores (without the presence of large predators) usually occur.

To be browsed or not to be browsed: differences in nutritional characteristics of blackthornPrunus spinosasubject to the long-term pressure of herbivores

“…Also, the structural response of a particular plant to ungulate browsing may vary to such an extent that some parts of the tree will be readily eaten, while other parts will be less attractive (Hartley et al 1997); furthermore, the differences within one tree may be greater than those between two separate trees. On the other hand, the blackthorn’s spinescences are part of a well-known structural defence mechanism used against biotic stress factors (Pisani and Distel 1998; Scogings et al 2011; Salek et al 2019). We noticed that all heavily browsed blackthorns had thick, hard and well-developed thorns located on twigs of the external parts of the crowns, whereas on unbrowsed bushes such structures were less developed only on older twigs situated in the inner regions of the plants.…”

“…In a scenario where browsing is intense, individual plants can react by increasing the secretion of defensive compounds (Wigley et al 2015), developing structurally induced defences (Salek et al 2019), increasing foliar nitrogen (N) levels (Scogings et al 2011) or changing resource allocation patterns (Orians et al 2011; Scogings et al 2014; Peschiutta et al 2018). As plant defence systems may limit foraging preferences, ungulates have developed a number of strategies to counteract such systems, like avoidance behaviour, reducing the intake of certain food types (Iason and Villalba 2006) or physiological adaptation to tolerate toxic plant products with the aid of specific binding enzymes (Clauss et al 2003; Iason and Villalba 2006; Mlambo et al 2016; Perkovich and Ward 2022).…”

“…Blackthorn is listed among the woody species preferred by foraging red deer Cervus elaphus during summer and autumn (Dumont et al 2005; Salek et al 2019). It commonly grows on ecotones and abandoned farmland (Szafer and Zarzycki 1977), where it usually adopts the shrubby form (Seneta and Dolatowski 1997) or develops a dwarf form, apparently in response to long-term, high browsing pressure.…”

Mitigation of Deer Herbivory in Temperate Hardwood Forest Regeneration: A Meta-Analysis of Research Literature

“…Studies from Europe have shown that dense cover of some thorny shrubs, such as wild rose and hawthorn (Crataegus spp. ), can deter browsing of shade-tolerant regenerating hardwoods by red deer and sika deer (Cervus nippon), but that the protective effects of other shrubs, such as blackthorn (Prunus spinosa), are outweighed by competitive effects [88]. A study in Michigan found that weeding reduced the height of fast-growing hardwood species in harvest gaps by exposing them to browsing by white-tailed deer, but that slow-growing species did not benefit [41].…”

Neighborhood Competition and Understory-Associated Vegetation Are Important Factors Influencing the Natural Regeneration of Subtropical Mountain Forests

“…On the other hand, the impact of understory-associated vegetation on natural regeneration is complex. The diversity of shrubs and herbs contributes to the forest's water-holding capacity and nutrient retention [21]; for example, thorny shrubs can reduce browsing by herbivores [22], thereby increasing the survival rate of seedlings and saplings. However, shrubs may compete with tree seedlings [23].…”