Differential Responses of Herbivores and Herbivory to Management in Temperate European Beech

Abstract

Forest management not only affects biodiversity but also might alter ecosystem processes mediated by the organisms, i.e. herbivory the removal of plant biomass by plant-eating insects and other arthropod groups. Aiming at revealing general relationships between forest management and herbivory we investigated aboveground arthropod herbivory in 105 plots dominated by European beech in three different regions in Germany in the sun-exposed canopy of mature beech trees and on beech saplings in the understorey. We separately assessed damage by different guilds of herbivores, i.e. chewing, sucking and scraping herbivores, gall-forming insects and mites, and leaf-mining insects. We asked whether herbivory differs among different forest management regimes (unmanaged, uneven-aged managed, even-aged managed) and among age-classes within even-aged forests. We further tested for consistency of relationships between regions, strata and herbivore guilds. On average, almost 80% of beech leaves showed herbivory damage, and about 6% of leaf area was consumed. Chewing damage was most common, whereas leaf sucking and scraping damage were very rare. Damage was generally greater in the canopy than in the understorey, in particular for chewing and scraping damage, and the occurrence of mines. There was little difference in herbivory among differently managed forests and the effects of management on damage differed among regions, strata and damage types. Covariates such as wood volume, tree density and plant diversity weakly influenced herbivory, and effects differed between herbivory types. We conclude that despite of the relatively low number of species attacking beech; arthropod herbivory on beech is generally high. We further conclude that responses of herbivory to forest management are multifaceted and environmental factors such as forest structure variables affecting in particular microclimatic conditions are more likely to explain the variability in herbivory among beech forest plots.

Reading the Leaves’ Palm: Leaf Traits and Herbivory along the Microclimatic Gradient of Forest Layers

“…Typical leaf damage is determined about 6% for F . sylvatica in late summer [72]. Herbivory levels of our study were somewhat below this range for F .…”

How do herbivorous insects respond to drought stress in trees?

“…Classification of insects into these feeding guilds can be complex and somewhat arbitrary, as some insects change their feeding behaviour in different life stages (Stork, 1987) or opportunistically in response to available resources. For example, some ant species shift from a predatory or scavenging diet to feeding on extra-floral nectaries or homopteran honeydew (Blüthgen, Gebauer & Fiedler, 2003), many lepidopteran larvae change their feeding habits as they grow (Gaston, Reavey & Valladares, 1991), and some beetles such as the weevil Orchestes fagi have different habits as larvae (leaf miners) and adults (leaf chewers) (Gossner et al, 2014). Such complex behaviours and mutualisms may be common in tropical forests but we do not attempt to address them in our framework.…”

Beech forest management does not affect the infestation rate of the beech scaleCryptococcus fagisugaacross three regions in Germany

“…Infestation was categorized into three infestation classes: 1, no visible attack; 2, few individuals, no clusters (weak attack); 3, many individuals, forming dense clusters (heavy attack). Our assessment of beech scale infestation was part of a large‐scale general herbivory assessment in the sun‐exposed canopy (Gossner et al , ), and thus the estimation of beech scale infestation (with three levels) was slightly simplified compared with other assessments (with five infestation levels; Rhumbler, ; Braun, ).…”

“…These trees also reflect the dominant tree size of each stand. The present study arose from a large‐scale herbivory assessment mainly in beech canopies (Gossner et al , ), in which the BBD complex as a whole was not considered.…”