Letter: Favoured by fire

From John Etherington

It is labouring the point to explain the present distribution of the redwoods
by differences in mycorrhizal fungi or water transporting ability. There is
little experimental support for either
(“How the north was won”, 20 June, p 34).

It has long been known that adult sequoias and coastal redwoods are
specifically fire-tolerant and that they need fire to aid germination and
establishment. By contrast, most of the firs and pines with which they grow are
sensitive to fire.

The obstruction of the proto-Gulf Stream would have reduced transpiration and
probably increased rainfall, making fire less frequent and favouring
regeneration of pines and firs. When occasional dry years came, there would have
been an accumulation of fuel so that fire would devastate the tree community,
favouring the spread of grass-shrub cover.

Bottomland trees such as swamp cypress need a long warm summer and the dawn
redwood is frost-sensitive. The climatic shift would have directly disadvantaged
both species.

This explanation, based on silvicultural experience and forestry practice,
seems less speculative.

Pembrokeshire