Blackthorn sloe (Prunus spinosa)

Are we drinking in the last chance saloon for sloe gin?

11 November 2009 

It’s that time of year when sloe gin enthusiasts will be out in the hedgerows gathering this popular berry to make a delicious alcoholic treat for Christmas.

However, a collaborative study carried out on the Game and Wildlife Conservation Trust’s research farm in Leicestershire, shows that further declines in pollinating insects could seriously reduce the berries produced by many important fruit-bearing hedgerow plants, particularly, blackthorn (Prunus spinosa), which produces sloes as well as hawthorn (Crataegus monogyna) and ivy (Hedera helix). The study was recently published in the Annals of Botany.

As well as being the foundation of an alcoholic treat, the fruits of hedgerow plants, such as sloe berries are also a source of winter food for fruit eating farmland birds. The Trust is therefore concerned that recent declines in pollinating populations of insects could threaten the fruit-set of these important hedgerow plants and thus impact on a vital winter food supply for many farmland birds.

The flowers of blackthorn, hawthorn, dog rose, bramble and ivy are visited for pollen or nectar by many insect species, such as bees, wasps, flies, moths and butterflies and it is likely that these visits result in the pollination, seed set and fruit-set of these plants. The aim of this study was to investigate the role of insect pollination for a range of fruit-bearing hedgerow plants and to establish whether a lack of insect pollination limits fruit-set in a selection of British hedgerow plants.

Significantly, the results of the study showed that the development of mature fruits was reduced when insects were excluded from the flowers of blackthorn, hawthorn and ivy by using fine mesh bags. However fruit-set in bramble and dog rose were unaffected when insects were excluded.

This collaborative study by the Game and Wildlife Trust, Rothamsted Research and Stirling University was carried out by Jenny Jacobs as part of a CASE PhD studentship and jointly funded by The Game and Wildlife Conservation Trust and the Biotechnology and Biological Sciences Research Council (BBSRC).

Dr. Jacobs said "Hedgerows are a vitally important habitat, sustaining farmland wildlife throughout the year. They provide a supply of flowers producing nectar and pollen for insects from March to November, and it appears that for some of these plants, insect flower visits are essential for good fruit set. After pollination, fruits develop and ripen in succession, providing a continual supply of food for fruit-eating birds from late summer, through autumn and winter and into spring, when other food is scarce."

Dr Chris Stoate, head of research at the Trust’s Allerton Project in Leicestershire was a joint supervisor of this study, and said, "Many pollinating insects have declined in abundance in recent decades and this work shows how such declines could have ecological effects on other wildlife such as fruit-eating birds. Anything we can do to boost insect numbers will increase the fruit available for birds such as wintering fieldfares, and redwings, as well as for sloe gin production."

The results of this study clearly demonstrate the importance of understanding the links between insect pollinators, fruits and fruit-eating birds to determine whether habitats for pollinators in agricultural areas need to be improved. This study also provides strong evidence that hedgerow plants, particularly blackthorn and hawthorn are dependent on pollinating insects to produce fruit.

Dr Stoate explains, "Our study shows the importance of pollinating insects on farmland and every effort should be made to carry out appropriate management. Sensitive hedge management and the provision of habitats for pollinators on farmland such as growing pollen and nectar flower strips along field margins should be given priority in order to help ensure a healthy winter supply of fruits for many declining birds."

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Rothamsted Research is an institute of the Biotechnology and Biological Sciences Research Council