Blaeberry (Vaccinium myrtillus) is a key component of the Caledonian Forest ground flora, and an important food source for a wide range of wildlife.
Blaeberry is circumboreal in distribution, and occurs in Europe, the northern parts of Asia, including Japan, and in North America, where there are two disjunct ranges, between British Columbia and New Mexico. It also occurs in Greenland, although this is thought to be the result of an introduction from Europe, possibly in Viking times.
In Europe, blaeberry is an important plant in both coniferous and deciduous forests, and it is found in greatest abundance in the northern and western parts of the continent – in southern Europe it only occurs on mountains. It is closely related to a number of other species, such as cowberry (Vaccinium vitis-idaea) in Europe (with which it can hybridise) and several types of huckleberry (Vaccinium membranaceum andVaccinium parviflorum, amongst others) in North America. In Britain it has a number of common names, including bilberry, whortleberry and whinberry.
Distribution in Scotland
In Scotland, blaeberry occurs throughout the country, but it is most abundant in the Highlands, particularly in the north and west. It occurs in both moorland and woodland, and grows at elevations from sea level up to 1,250 metres, although it is very stunted in growth at over 1,000 metres. It typically grows on areas of better-drained, acid soils, and does best in shady conditions, underneath the canopy of trees. It occurs in oakwoods, but reaches its greatest size in the birchwoods and pinewoods of the Caledonian Forest, where it can form extensive patches. It is also a common plant on the hummocks (raised mats of vegetation growing over old tree stumps or rocks) which are a characteristic feature of the forest floor. On moors and heaths, blaeberry typically occurs under heather (Calluna vulgaris), and in some cases can be an indicator of the former presence of woodland there.
In the past, blaeberry was more widespread and abundant, but it has declined with the loss of Scotland’s native forest cover. The large-scale husbandry of sheep in the Highlands during the past 300 years has also contributed to this decline. Although blaeberry can survive grazing, it is reduced to a close-cropped sward in which its ability to flower and fruit is substantially curtailed.
Blaeberry is a small perennial shrub in the heather family, Ericaceae. It grows to a height of up to 90 cm. in woodland, but is usually only 60 cm. tall, and on heaths and moorland it rarely exceeds 25 cm. It has green angular stems which grow from a rhizomatous root system, and individual stems can persist for up to 15 years. The leaves are 1-3 cm. in length, oval to elliptical in shape, and have serrate or toothed edges. Blaeberry is deciduous, and in the pinewoods the new leaves appear in late April or the beginning of May, and are shed in late September or October.
Like deciduous trees, the leaves undergo a colour change before being dropped, as chlorophyll production ceases and other pigments are revealed. These colours are a dull yellow-brown in many cases, but some blaeberry patches turn brilliant shades of orange and red – this is possibly due to the presence of specific nutrients in the soil at those sites.
The flowers appear in May, soon after the new leaves, and are waxy and pinkish-red in colour. They are bell-shaped, with the open end facing downwards, and are up to 6 mm. in diameter. Pollination is mainly by bumble bees (Bombus spp.), although other insects such as wasps also serve this function. In addition, blaeberry can be self-pollinated, with the pollen being transferred from one flower to another by gravity and wind.
Berries begin to develop soon after pollination, and are spherical in shape and up to 1 cm. in diameter. They ripen to a dark blue colour in July and August. Each berry can contain up to 40 seeds, although on average only about half of these are viable. Berries are only borne on stems which are at least three years old.
Because most of the berries are eaten by birds and mammals which do not excrete viable seeds, blaeberry’s main method of reproduction is vegetative, with new shoots growing off the rhizomes of mature plants. The rhizomes, which are underground stems, can live for up to 25 years, although rhizomes older than 15 years rarely produce new aerial shoots. Individual plants expand outwards as a result of rhizome growth, which can be up to 40 cm. per year, and the rhizomes enable blaeberry to regenerate quickly after disturbance, such as fire.
In autumn, before the leaves are shed, blaeberry transfers some of the nutrients from them into its rhizomes – this time, along with spring, is the main period of rhizome growth. Blaeberry also has the ability to utilise the sun’s energy in winter, through photosynthesis in its green stems.
Blaeberry is a key constituent of the field layer in the native pinewoods of the Caledonian Forest, and it plays a significant role for a number of other species, particularly of birds and mammals. As a result, blaeberry abundance has been used as an indicator of biodiversity within the pinewoods.
As with other members of the Ericaceae family, blaeberry has mycorrhizal associations with fungi. In these mutually-beneficial relationships, the fungi gain sugars and carbohydrates which the blaeberry has photosynthesised, and the fungi in turn provide nutrients from the soil, which the blaeberry cannot access itself. Nutrient exchange between plant and fungus takes place where the hyphae (white filaments of the fungus body) wrap around the root tips of the plant.
In another mutually-benefical relationship, blaeberry provides a food source for the bees, wasps and other insects which pollinate it. In contrast to those symbiotic associations, common cow-wheat (Melanpyrum pratense) is partially-parasitic on the roots of blaeberry (and other plants such as heather) – it takes nutrients from the blaeberry roots, but gives nothing back.
Blaeberry foliage is highly palatable, and is an important food source for birds such as red grouse (Lagopus lagopus), ptarmigan (Lagopus mutus) and black grouse (Tetrao tetrix). The capercaillie (Tetrao urogallus) in particular depends on blaeberry, and it eats the stems and buds in winter, as well as the leaves in spring and summer. More insects feed on blaeberry than any other understorey plant in the Caledonian Forest, and these insects are a vital food supply for young capercaillie chicks in the first few weeks after they hatch. Blaeberry also provides cover and shelter for the chicks.
A variety of mammals feed on blaeberry foliage, including red deer (Cervus elaphus), roe deer (Capreolus capreolus) and mountain hare (Lepus timidus), while species which feed on the berries include the pine marten (Martes martes), wood mouse (Apodemus sylvaticus) and bank vole (Clethrionomys glareolus). The latter two in particular consume large numbers of berries, but the seeds they excrete are no longer viable.
A number of birds eat the berries, including black grouse, capercaillie and members of the thrush family such as the fieldfare (Turdus pilaris). In the past the berries must also have been relished by the European brown bear (Ursus arctos) before it was extirpated from Scotland about 1,000 years ago.
Blaeberry has long had an important role in human cultures. In addition to the nutrient-rich berries providing food, blaeberry has been used as a herbal remedy for digestive problems and diabetes, and to strengthen capillaries in the circulatory system. The juice of the berries has also been used as a dye, providing a blue colour for both linen and paper.
The expansion of the Caledonian Forest, through current regeneration initiatives, and a renewed interest in blaeberries as an edible wild food, should ensure that this important component of the forest thrives and increases in abundance again.