Contrasting effects of vineyard type, soil and landscape factors on ground‐ versus above‐ground‐nesting bees

Abstract

Agricultural intensification and abandonment of traditional agricultural practices are main drivers of current insect declines. The resulting loss of feeding and nesting opportunities has led to a decrease in pollinator populations like wild bees. While the restoration of floral resources has been widely implemented in wild bee conservation, nesting resources, particularly for ground‐nesting species, are barely considered. We assessed wild bee diversity in a wine‐growing area in Germany in 15 study sites along a soil gradient and evaluated whether wild bees were distinctly affected by different vineyard types (vertically oriented, terraced, abandoned), local conditions (e.g. shrub and flower cover) and landscape factors in response to divergent nesting needs (above‐ground vs. ground‐nesting). We found that wild bees responded more strongly to the availability of nesting sites than to flower resources. While ground‐nesting bees were determined by the suitability of soil aspects for nesting irrespective of vineyard management types, above‐ground‐nesting bees profited from vineyard abandonment and shrub encroachment in vineyard fallows and were enhanced by the availability of semi‐natural habitats (SNHs) in the surrounding landscape. In contrast, floral resource availability in managed vineyards had only marginal effects on above‐ground‐nesting bees. Synthesis and applications: Life‐history traits like nesting strategies have long been neglected in wild bee conservation approaches, but proved to be highly relevant, especially for ground‐nesting bees. For this, agri‐environmental schemes can no longer solely focus on the restoration of floral resources, but should equally address nesting resources. Therefore, management efforts for enhancing wild bees in vineyard landscapes should aim at complementing nesting resources for ground‐nesting bees (e.g. exposed bare ground patches) and above‐ground‐nesting bees (e.g. woody elements, hedges) in addition to floral resources. At the landscape level, conserving heterogeneous landscapes at a mixture of actively managed vineyards and semi‐natural and woody elements is significant to maintain diverse bee communities.

Crossing Old Concepts: The Ecological Advantages of New Vineyard Types

“…Similarly, flower strips in the agricultural landscape are well known to promote wild bee and butterfly populations by providing a continuous supply of floral resources [56][57][58]. In contrast to our study, Wersebeckmann et al [59] found no differences in bee abundance between vertically oriented vineyards (comparable to NEVs) and terraced vineyards (comparable to GEVs). However, this study was based on pan trap sampling, which has been cautioned against for providing unreliable abundance measures, especially when there is a contrast in flower cover [60].…”

“…However, this study was based on pan trap sampling, which has been cautioned against for providing unreliable abundance measures, especially when there is a contrast in flower cover [60]. Corroborating our results, Wersebeckmann et al [59] observed a trend of higher bee species diversity in terraced compared with vertically oriented vineyards using a sampling method complementary to our method with regard to representativeness of the sampled bee community [21].…”

“…The preservation of steep-slope vineyards therefore has mutual benefits, hence also achieving one of the important objectives of the National Biodiversity Strategy. Although the results of this study require confirmation by a more extensive analysis as soon as more terraced vineyards become available, they are confirmed by a similar study from another wine-growing region [59]. Consequently, the establishment of biodiversity-friendly GEVs should be of vital interest to winegrowers, conservationists, and landscape planners.…”

Annually mulched wild flower strips increase the observed wild bee (Apiformes) species richness and abundance in vineyard fallows in the short term

“…Since the soil of the vineyard fallows remained undisturbed after sowing of the WFS, and because wild bees use WFS as nesting habitats under low soil disturbance (Boetzl et al, 2022), it is likely that the annually mulched WFS served as a nesting habitat for wild bees. Most native bee species in viticultural landscapes are ground nesting (Krahner et al, 2018;Wersebeckmann et al, 2023), and creation of sun exposed ground spots with scarce vegetation is an important conservation measure for promoting bees (Gardein et al, 2022).…”

“…For maintaining suitable bee habitats on vineyard fallows, prevention of bush encroachment is pivotal. Without management, vineyard fallows are generally overgrown by shrubby vegetation (Wersebeckmann et al, 2023). This may negatively affect floral resources, because important food plants are replaced by dominant, less bee attractive plants (Kirmer et al, 2018).…”