What is chronic oak decline?
British oaks have been affected by a condition now known as chronic oak dieback or decline for much of the past century. Pedunculate oak (Quercus robur) tends to be the most commonly affected. This disorder is widespread, prolonged and complex, often involving abiotic factors such as recurrent drought. Biotic agents, such as root disease fungi are known causes of chronic oak decline.
Typically, the first symptom observed on a declining tree is a deterioration of the foliage. Leaves may be smaller than normal, and are often pale green or yellowish. In some cases the foliage may be sparse or thin over the entire crown.
Over the next year or so, death of fine twigs may be followed by the death of small branches; at this stage the foliage can be very thin. In some cases the process continues through to death of large branches, and eventually the whole tree may die.
However, some trees can make a partial recovery through the production of epicormic shoots on the trunk and surviving branches.
The dieback may occur over many years, even decades, and some individuals may stabilise and make a partial recovery. Typically trees affected in this way are described as ‘stag-headed’ with skeleton branches protruding from the crown.
Very often the smaller area of the remaining crown has leaves of normal colour and size showing there has been recovery, although further episodes of dieback can strike resulting in chlorotic leaves and further twig and branch dieback which accumulate over time.