Currently, the most damaging forest fires are in spring when dry brash and litter from the previous growing season can fuel the fires. In some parts of the country, such as south Wales, fires often spread from adjoining areas supporting tussocks of dead Molinia grass. The earlier growth of ground vegetation as a result of climatic warming might reduce the incidence of forest fires in spring and early summer. However, extended summer droughts such as those experienced in 1976 and 1995 result in a secondary fuel source in late summer as the ground vegetation dies and dries off. This is clearly demonstrated in fire statistics, which show peaks in years with extended summer droughts.
It has been noted that the large number of fires in 1976 may have been partly as a result of the age structure of the forest estate at that time, with a relatively high proportion of thicket stage woodland containing a large quantity of combustible material. The proportion of thicket stage woodland has since fallen. However, changes in woodland management, particularly conversion to continuous cover management systems may increase deadwood and forest floor litter, potentially increasing the risk of more intense or extensive fires. Improvements in approaches to fire-fighting may also have contributed to the improved fire statistics in recent years.
The predictions of an increase in the frequency and severity of summer droughts would thus be expected to lead a large increase in the number of fires and area affected in those years. Lifestyle changes and increased usage of woodland for leisure and recreation activities may exacerbate this problem through an increase in both accidental and malicious fires.