Abstract
Most forests are exposed to anthropogenic management activities that affect tree species composition and natural ecosystem processes. Changes in ecosystem processes such as herbivory depend on management intensity, and on regional environmental conditions and species pools. Whereas influences of specific forest management measures have already been addressed for different herbivore taxa on a local scale, studies considering effects of different aspects of forest management across different regions are rare. We assessed the influence of tree species composition and intensity of harvesting activities on arthropod herbivores and herbivore-related damage to beech trees, Fagus sylvatica, in 48 forest plots in three regions of Germany. We found that herbivore abundance and damage to beech trees differed between regions and that – despite the regional differences - density of tree-associated arthropod taxa and herbivore damage were consistently affected by tree species composition and harvest intensity. Specifically, overall herbivore damage to beech trees increased with increasing dominance of beech trees – suggesting the action of associational resistance processes – and decreased with harvest intensity. The density of leaf chewers and mines was positively related to leaf damage, and several arthropod groups responded to beech dominance and harvest intensity. The distribution of damage patterns was consistent with a vertical shift of herbivores to higher crown layers during the season and with higher beech dominance. By linking quantitative data on arthropod herbivore abundance and herbivory with tree species composition and harvesting activity in a wide variety of beech forests, our study helps to better understand the influence of forest management on interactions between a naturally dominant deciduous forest tree and arthropod herbivores.
Highlights
Most forests have been considerably modified by human activities [1,2,3]
Leaf damage by chewing herbivores differed considerably between regions (Fig 1, Table 1), and both the proportion of F. sylvatica and harvest intensity affected the amount of leaf damage and the density of different taxonomic groups of herbivores when the regional differences were accounted for (Fig 2, Table 1)
Our results demonstrated that herbivore damage on beech trees may decline with decreasing beech dominance and that it may decline with increasing harvest intensity
Summary
Most forests have been considerably modified by human activities [1,2,3]. Anthropogenic influences affect forest ecosystems indirectly via activities including hunting, livestock grazing, environmental pollution, human-assisted biological invasions and climate change, and directly via forest management activities [4,5,6]. Herbivore diversity and abundance on host plants is modified by an array of different factors such as abiotic conditions [28, 29], the quality of host plants [30,31,32], and the exposure to competitors and natural enemies [33,34,35]. In forests, these factors may show strong vertical stratification within individual trees [36], and they may be strongly influenced by tree species composition [37, 38]. A distinct stratification of arthropods has been described for both tropical and temperate forests, stratification seems to be no static characteristic of canopy arthropod assemblages, but it may vary between seasons and with tree species identity, tree age and tree neighborhood [36, 41, 42]
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