Managing biodiversity for ecosystem services in apple orchards

Conventional intensive agriculture is largely reliant on high agrochemical inputs and has resulted in damaging environmental impacts including large scale biodiversity loss. More environmentally sustainable agricultural production methods are required. Ecological intensification is an approach which aims to sustainably increase production by using biodiversity-derived ecosystem services and replacing agrochemical inputs where possible. This can be achieved through modifying agricultural management practices to support ecosystem service-providing beneficial species. This thesis investigates the ecological intensification of commercial apple orchards in the UK. Apples are one of the most economically and nutritionally important fruit crops globally and their production relies upon a number of ecosystem services including pollination, pest regulation, and soil fertility services. Alleyway cover crops were trialled as a novel management practice which has the potential to improve a number of orchard ecosystem services. Three different cover crop species mixtures, all based on perennial legumes but each with a different rationale, were compared to a standard mown-grass control. Growing cover crops in the alleyways was provided improved habitat quality for beneficial species, attracting greater numbers of natural enemy taxa including predatory beetles, parasitoids, and active-hunting spiders, without increasing the abundance of crop pests. Greater numbers of pollinators were also observed in alleyways sown with cover crops. Despite the greater numbers of beneficial species recorded in the cover crop treatments, no increases in pest regulation or pollination services were detected and no change in production was observed during the timescale of the study. A second potential benefit of alleyway cover crops is the production of mulch material. Traditionally, organic mulches were used in orchards to help supress weeds underneath the trees, increase soil nutrients, and retain soil moisture, however many of these functions have now been replaced by agrochemical inputs. The cuttings from alleyway cover crops can provide an in-situ source of mulching material. Alleyway cuttings were compared to two traditional mulch materials, compost and straw, and a standard no-mulch control. Alleyway cover crop cuttings boosted numbers of earthworms and enhanced leaf litter decomposition, whilst the traditional straw and compost mulches improved some soil fertility measures including soil organic matter and moisture when compared to the control. In the final study of the thesis, the importance of pollination is quantified and the methods used to assess pollinator dependence and pollination deficits are tested, with recommendations made about the scale at which these experiments should be carried out. Following pollinator exclusion apple yields were found to fall to 55% whilst supplementary hand pollination led yields to increase to 167% of current ‘open’ pollination rates, showing that pollination deficits existed in the study orchards. This study also highlights the importance of pollination for fruit quality, a key deciding factor of a crop’s economic value. Alleyway cover cropping was found to have positive effects on ecosystem service providers both above and below ground. Even relatively inexpensive cover crop mixtures, combined with a reduction in mowing frequency and increase in mowing height, were found to increase numbers of beneficial species. The findings demonstrate the potential benefits of this multi-purpose habitat management method