The role of woodlands in the diversity and resilience of pollinator communities in agricultural landscapes

科学背景集约化农业是授粉昆虫数量和授粉服务下降的关键驱动因素。为减轻这些影响而进行的生态强化主要集中在恢复田间规模的半自然生境，包括花带和草原和野花的其他生境斑块。这些农业环境计划对花卉资源的促进作用通常只跨越授粉昆虫群落的季节性活动期的一部分。在农田上提供授粉服务也取决于更广泛的景观背景，相对较少关注林地斑块对传粉者群落的影响。对于哪些植物物种是传粉者物种最有价值的食物资源，以及它们的相对价值如何随季节变化，仍不确定。虽然与草原相关的野花对蜜蜂的益处是众所周知的，但在农业景观中，树木和林地在缓冲传粉者资源(花蜜和花粉)方面的互补作用研究较少。林地可以为英国的主要栖息地提供最高水平的花蜜生产，授粉昆虫对树种的利用可能与景观中林地的丰富程度不成比例。林地树种组成也会影响其他植物，对传粉者造成影响。景观中的林地和木本走廊(树篱)为一系列传粉昆虫物种提供了筑巢和幼虫的微型场所。目的和目标本项目将调查林地在农业景观中传粉昆虫群落的维持和恢复中的作用。昆虫抽样将在诺福克选定的研究景观中进行，横跨一系列密度的林地斑块和树篱网络。该项目着手解决以下关键研究问题：(1)林地冠层中的传粉者群落与地面、林地内部和更开阔的农田生境中的传粉者群落有多相似？我们将调查哪些传粉者物种在林地冠层中相对于更开阔的生境出现的比例最大，并测试冠层出现与林地冠层中花粉和/或花蜜来源的可用性之间的相关性。(2)在林地冠层或林冠附近是否发现传粉者在觅食树木花粉资源？我们将使用分子技术来确定传粉昆虫分类群的身份，以及它们相关的花粉，这些花粉是从林地树冠上采集的，距离林地栖息地不同。这项工作将确定使用了哪些树种的花粉(如果有的话)。我们将测试大约20种常见的林地树种，包括一些风媒授粉树种。(3)林地地区是否促进了传粉者多样性和周围景观丰富度的季节稳定性？研究设计将侧重于在研究区域内重要的林地斑块内进行采样，以及在农业景观中与这些斑块的不同距离进行采样，包括沿有树和无树的树篱不同距离进行采样。春季和夏季的重复采样将捕捉到传粉者群落的季节性变化。(4)对于在农业景观中维持有弹性的传粉者群落，从而提供授粉服务，最佳的林地和木质走廊管理建议是什么？在这里，我们将集中讨论木质走廊在景观中作为线性特征的作用，以及如何优化它们在林地斑块和耕作景观之间传粉者组合的连接中的作用，并维持授粉服务。

Scientific backgroundIntensive agriculture is a key driver of declines in pollinating insect populations and pollination services. Ecological intensification to mitigate these effects has focused largely on restoring field-scale semi-natural habitat including flower strips and other habitat patches for grassland and wildflowers. The boost to floral resources provided by these agri-environment schemes typically span only a portion of the seasonal activity period for pollinating insect assemblages. Provision of pollination services on farmland is also dependent on wider landscape context, with relatively little attention being paid to the influence of woodland patches upon pollinator communities.Uncertainty remains over which plant species are the most valuable food resources for pollinator species, and how their relative value varies seasonally. While the benefits to bees of grassland-associated wildflowers is well-established, the complementary role of trees and woodland in buffering the provision of pollinator resources (nectar and pollen) is less well-studied in agricultural landscapes. Woodlands can provide among the highest levels of nectar production for a major UK habitat, and the use by pollinating insects of tree species may be disproportionate to the abundance of woodland in the landscape. Woodland tree species composition also influences other plants, with consequences for pollinators. Woodlands and woody corridors (hedgerows) in landscapes provide nesting and larval microsites for a range of pollinator species.Aims and objectivesThis project will investigate the role of woodland in the maintenance and resilience of pollinator insect communities in agricultural landscapes. Sampling of insects will be carried out in a selected study landscape in Norfolk spanning a range of densities of woodland patches and hedgerow networks. The project sets out to address the following key research questions:(1) How similar are pollinator assemblages that occur in woodland canopies compared with those that occur at ground level, in woodland interiors and in more open farmland habitats? We will investigate which pollinator species show the greatest proportional occurrence in woodland canopies relative to more open habitats, and test for correlation between canopy occurrences and availability of either pollen and/or nectar sources in woodland canopies. (2) Are pollinators found in or close to woodland canopies foraging on tree pollen resources? We will use molecular techniques to determine the identity of pollinator insect taxa, and their associated pollen, sampled from woodland canopies and at varying distance from woodland habitat. This work will establish which species of tree pollen, if any, are being used. We will test for circa 20 common woodland tree species, including some wind-pollinated species.(3) Do woodland areas promote seasonal stability in pollinator diversity and abundance in the surrounding landscape? The research design will focus on sampling within significant woodland patches within the study area, and at varying proximities to these patches within agricultural landscapes, including varying distances along hedgerows with and without trees. Repeat sampling in spring and summer will capture seasonal variations in pollinator assemblages. (4) What are the optimal woodland and woody corridor management recommendations for maintaining resilient pollinator communities, hence pollination services, in agricultural landscapes? Here we will focus on the role of woody corridors as linear features in the landscape, and how to optimise their role in connectivity of pollinator assemblages between woodland patches and cultivated landscapes and maintain pollination services.