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November in the Forest

November in the Forest

This year’s acorns are already beginning to sprout. They only need a modest amount of moisture and some thin forest soil to grow, but many are crushed on the forest tracks or shrivel on rocky outcrops (‘some fell on stony ground’). Others are taken by Grey Squirrels and eaten at once or buried for later consumption with their tips nibbled out to prevent germination. The loud Jays are busy burying too, unwittingly acting as woodland planters in return for a small percentage of acorns retrieved.

The baby oaks will come up thick and fast under those trees which have produced a good crop of seed but will have to escape the attentions of other hungry nibblers in order to reach maturity. The Fallow Deer browse seedlings and any branches within reach, and Rabbits may strip off bark in the hungry months of winter.  Not so obvious are the hordes of insects such as moth and fly caterpillars, weevils, leaf miners and gall wasps which shred and tunnel their way through the foliage but don’t usually cause a tree to die. Oaks are slow-growing compared to conifers and there is a useful rule of thumb which says that they put on an inch of girth (measured at breast height) on average for every year of their lives.

This brings me to my main subject, which is ‘Why are so many oaks in the forest dying?’  You may have noticed leaves yellowing, branches dying back and whole trees dying in the space of a few years. Chronic Oak Decline (COD) has probably been around for a century and, like Acute Oak Decline (AOD), may result in the death of a tree due to a combination of factors. Some trees die four to six years after the onset of symptoms while others seem to be checked for a few years but then continue to grow. The acute form (AOD) was first observed about 30 years ago but has been spreading rapidly in recent years, affecting our native pedunculate and sessile oaks and their hybrids (which account for most of the Wyre oaks).

As the photo shows, the trunks of affected trees can often show lesions oozing black, resinous liquid. There are at least 3 species of bacteria present in the fluid and involvement of some sort by the native Oak jewel beetle,  Agrilus biguttatus , whose larvae tunnel galleries under the bark of affected trees and leave characteristic D-shaped holes in the bark when they exit as adults. Heat, drought, fungal growth and damage to trunks and roots by woodland operations may all play a part.

What can be done about it? Nobody knows yet, but Sandra Denman of Forest Research (part of the Forestry Commission) and several academic bodies are working on it and we all hope that our oak woodland will be safe for generations to come.