|Written for the Banstead Village Residents' Assoc. Newsletter, Summer 2020:
the 1960/70s, Dutch Elm Disease swept across Europe from North America,
devastating Elm trees in its path. The fungus that caused the disease simply
blocked the trees’ vascular system so blocking water and nutrient supply. Within
20 years, virtually all English Elms had disappeared from the UK, with only
scattered survivors in hedges and woods that start to grow as individual trees
but then die back because of chronic disease.
years on, a similar disease
(this time bacterial) hit the UK, this time affecting Ash trees. The
disease was cauised by infected trees imported from Europe, even at the
time disease was already destroying Ash
all over mainland Europe. The first evidence of disease is the death of
hence “die-back”. When it first appeared, the authorities decided to
trace, everyone was asked to report any trees that showed symptoms,
the disease spread rapidly and this approach became overwhelmed. The
still ongoing but evidence from Europe suggests that more than 90% of
affected with very few showing complete resistance and most dying.
where Ash is a common tree the effect so far has been mixed, nearly all trees
show some evidence of die back. It seems younger trees are worse affected than
larger specimens, in many places, large stands of saplings 4-8m high are dying
or dead. Larger trees appear to be able
to respond to die back early in the season by producing abnormal secondary
growth in early summer. Wherever you look however, you will find some
completely dead trees, some with dead branches but all will show some dead wood
even if only at the tips of branches. Certainly, over the past five years the
number of dead large trees has increased annually and it seems certain that our
Ash trees are going the same way as the Elm. In a lifetime we will have lost
two of our most iconic forest trees.
Even more worrying is that there are new threats to other tree species, both pests and diseases, such as Oak Processionary Moth. One thing is
certain just as with Elms and Ash, these lethal pandemics have the potential
to change our native woodlands for ever.