On the water relations of four heath species

Four species of heath, occurring in the heathlands of Brittany, are compared regarding their water relations: Calluna vulgaris, Erica ciliaris, E. cinerea and E. tetralix. E. cinerea is unable to establish itself in wet heathland because of its intolerance of prolonged waterlogging. It is the Erica species best adapted to dry habitat conditions in Brittany. E. ciliaris canot establish itself in dry heathland and is less tolerant of waterlogging than E. tetralix. E. tetralix is the species best adapted to wet heathland, being tolerant of waterlogging, but can also establish itself in dry heathland. Of the three E. species it has the widest ecological range. Calluna is tolerant of both wet and dry conditions and has a wide ecological range. E. cinerea is typical of dry- and E. tetralix of wet heathland. Although both species did best in moist aerated soil in experimental cultures, neither is abundant in mesophilic heaths where E. ciliaris is dominant. One explanation may be competition for aerial space. E. cinerea and E. tetralix both have an upright growth, whereas E. ciliaris rapidly adopts a straggling bushy habit, with long rooting branches. E. ciliaris thus establishes large interpenetrating clumps. With increasing dryness E. ciliaris disappears and may be replaced by E. cinerea and, with increasing wetness and especially waterlogging, E. tetralix will take over.