Twenty years ago people thought hurricanes occurred in other continents and killed trees. Learned writers treated ‘storm mortality’ as subtracting old trees from wildwood. Few remembered the ‘Great Storm’ of 26 November 1703 that sank the Fleet and destroyed the Eddystone lighthouse. Fewer remembered 15 January 1362, when (as Piers Plowman puts it), ‘pere-trees and plum-trees were poffed to þe erthe … beches and brode okes were blowe to þe grounde.’
Reality intruded with the events of 16 October 1987 and with storms in 1990. 1999 (on the Continent) and 2002. The chief lessons learnt (or not learnt) were:
- storm effects were greatest in the interior of woods and plantations, less on the edges; least among freestanding trees. Crowding predisposes to both breakage and uprooting
- Uprooting was commoner in planted than wild trees
- Both uprooting and breakage were commonest among big, young, fast-growing trees. Ancient trees were least affected.
- ‘Unsound’, rotten and hollow trees were no more affected – sometimes less – than ‘healthy’ trees. Narrow forks predisposed to breakage. A tree that broke one limb often broke others, suggesting a genetic predisposition.
- There was no great difference among species, although certain exotics were … often more uprooted
- Root systems where exposed, were unexpectedly shallow.
- Trees nearly always survived breakage, except sometimes at the base
- Most uprooted trees survived, especially where a swathe or area of trees toppled rather than single trees here and there. Fallen trees, responding to the change in the direction of gravity, sprouted at least from the base, and sometimes all along the trunk. If they died, this was usually due to the shade of neighbouring trees rather than drought. Thus lime (shade-tolerant) nearly always survived, whereas birch usually succumbed except in a swathe.
As in other countries, storms were an unmitigated benefit for wildlife. They broke up areas of monotonous shade and encouraged coppicing plants. They renewed the habitat of ground nesting birds and (in France) of deer. They call in question the assumption that the ‘normal’ state of a tree is upright.