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.
Highlights
As reforestation and forest restoration grow in importance in Europe and around the world [1], the debate concerning the appropriate reference points and ecological conditions continues to evolve [2,3]
The correlation analyses between the number of seedlings and saplings, and thorny shrub characteristics showed that the number of seedlings and saplings correlated positively with the hawthorn composition and negatively with the blackthorn composition
Our study contributes to the debate about the important ecological relationships between some species of large herbivores and temperate forest regeneration
Summary
As reforestation and forest restoration grow in importance in Europe and around the world [1], the debate concerning the appropriate reference points and ecological conditions continues to evolve [2,3]. Veras theory is based on the assumption that most of light-demanding deciduous trees were not able to regenerate naturally in closed and dark mature forests. The tree-dominated phase followed, during which shrubs disappeared from the shaded closed mature forest, and large herbivores returned and prevented tree regeneration. Some authors highlighted the neglecting of the ecological effects of large carnivores as an important shortcoming of Vera’s theory [10]. This theory has been widely debated [11,12], but there is difficulty to test it under current natural conditions, as the European lowland landscape has changed substantially [13,14,15]
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