Nature 2012 December

Ashes to ashes

The big news in the forestry world on late has been the confirmed arrival in the UK of Ash Dieback disease. There have been previous reports about disease attacking oak, chestnut and larch but these have been seen as less catastrophic on the whole population. Unlike the reporting in the UK of other outbreaks in trees the suddenness of this one seems to have taken everyone in authority a complete surprise. However, the death of ash trees had been attributed to an unknown fungus pathogen causing dieback in Polish ash trees way back in 1992. Thing is it was not until 2006 that the exact species of fungus was isolated and named as Chalara fraxinea – Fraxinus being the genus name of the ash tree. Unlike most of the flora and fauna we are used to dealing with, fungi are known to sometimes exist in two forms ‘sexual’ and ‘asexual’ and it is not unusual for only the latter of these two alternative forms to have been firmly identified and this frequently presents a problem for microbiologists tasked with isolating the offending pathogen as it is usually from studying the sexual form that any control measure are developed. In this case it took until 2010 before the essential information as to the offending species was found, by which time ash trees were succumbing across northern Europe as far as Germany. By early 2012 it had arrived in Scandinavia and in March it first appeared in the UK, within saplings imported from the Netherlands to a nursery in Bucks. Disease was identified in other nursery-supplied trees across the UK soon after, and the first wild infestation reports were in East Anglia in October. Whilst infection may not have arrived in wild trees around here yet as it is mainly transmitted on the wind it seems likely not to be far off. In the UK ash supports over 100 insect species that in turn support the woodland bird population. So the destruction of ash stands could have a significant wider impact on the local ecology. For information on identifying infected trees there is an excellent video from the Forestry Commission at www.forestry.gov.uk/chalara.

Sadly, in the absence of any way of combating it on the horizon it looks like we are in for a major catastrophe of similar proportions to the havoc that Dutch Elm Disease caused in the 1960s and 70s. Today there next to no mature trees in southern England. Locally, what has survived the scourge of elm bark beetles’ burrowing just below the surface of elm tree trunks, have been small bush elms located in hedgerows and the like. It turns out that however that whereas the English elm succumbed to the disease this is in fact a long ago introduced species of the tree. A whole number of so-called ‘native elms’ including, ones from Cornwall, Cambridgeshire and Essex being more resistant have largely survived the infestation. It is also apparent that there have been several previous elm disease outbreaks throughout both more recent and pre-historic periods which have wiped out much of the national heritage trees for a generation or so before more resistant stock has managed to re-supply our wild places once again. We can only hope this is the case this time!

Most insects are fast disappearing from the scene during late autumn. Except for the few species that are migrants to the UK all the others need to find a way to over-winter, be it as an egg, larva, pupa or adult, and a suitable place to hang out. Each to their own and nature provides these in abundance, however we provide plenty of opportunities too in dry or air conditioned, warm or cool, light or dark. Adult lacewings can be frequently found living out the colder months in our sheds and out houses. They are not social animals but usually they amass in choice locations. Their normal colouration is bright green, an essential camouflage kit to avoid predation. On taking up their winter roost their colour changes over a period of a few days from bright green to pale pink or cream. Opinions vary as to the rationale. Some say it’s the adoption of a more neutral hue to avoid detection Others suggest it’s the consequence of not feeding, whilst a third theory, which seems the most plausible, suggests its the natural process of slowing down the body clock and gradual re-adsorption and better utilisation of valuable proteins.

One consequence the impact of unusual and unseasonal weather has had on the fruit harvest has been the greater than normal quantities of both in situ and windfall fruit that has started to ferment. As these are a favourite foodstuff for both invertebrates and birds there have been reports of wasps caught in a drunk and disorderly state and a number of sightings of song birds such as blackbirds, song thrushes and redwings falling off their perches at dusk or becoming disorientated during flight and colliding with buildings.

If there was life insurance available for squirrels then premiums for January would be sky high. During that month grey squirrels don their best coats and go courting. This involves high-level gymnastic displays and the leaps from bough to bough have such a high degree of difficulty it results in many more miscalculations and accident which accounts for the larger than normal number of observed fatalities. Take care of low flying squirrels when out and about.