Wednesday, 3 October 2012

Top 3 tree threats

The Woodland Trust claims that the UK stands to lose up to 30% of its woodland trees unless tougher biosecurity import laws are introduced.  This comes after DEFRA’s publication of ‘The Tree Health and Plant Biosecurity Action Plan’ a year ago, which aims to tighten controls but fails to take a strong stance on monitoring trade imports.

To control the speed and spread of introduced pests and diseases, it’s been suggested that the UK government should take a lead from other island nations by increasing checks, quarantining imports when required and dispensing heavy penalties for violations and infringements.

The Woodland Trust would like to start with an immediate ban on importing ash trees (Fraxinus excelsior), one of the three native trees worst hit.   Currently accounting for an astounding 30% of our woodland, the common ash is being struck by a fungal infection known as Ash Dieback Disease (Chalara fraxinea).  Already extensive throughout Europe it spreads rapidly, as the Danes have found to their cost, losing 90% of their ash trees in a mere seven years.  Will the common ash go the way of the elm?
Distribution of ash trees within Europe
(source: Wikipedia)
 Another established pathogen without a cure is Phytophthora ramorum.  Spread through spores and dispersed by rainwater, this is less discriminate in choosing a host and is responsible for the death of a variety of plants and trees.  The disease targets both deciduous and coniferous trees and is the cause of Sudden Oak Death.  Japanese larches (Larix kaempferi) in particularly vulnerable, as well as camellias, rhododendrons, pieris and viburnums.  At present there are at least three other destructive Phytophthora species recorded within the UK.

The effects of Sudden Oak Death

One of the UK’s three native conifers, the scots pine (Pinus sylvestris), is also at risk.  A fungal infection referred to as Red Needle Blight (Dothistroma septosporum) causing defoliation and weakening trees, is reaping havoc on a range of conifers, especially pines.

Example of Red Needle Blight
(source: Jarmo Holopainen (2008),

With global distribution behind the prevalence of destructive non-native organisms, surely there is a case for increasing levels of home-grown stock in UK nurseries?  Whilst not a short-term solution to meeting demand, this would boost jobs in the horticulture sector and in the long term maybe we could increase our exports with healthy, certified pest- and pathogen-free specimens.

During the ‘70s Dutch Elm disease decimated the elm population, killing an estimated 20 million trees.  Although very small at the time, I can just about recall the elms in our neighbourhood being felled and the sadness felt throughout the community.  Let’s try to avoid a similar scenario by urging the government to initiate a mandatory ban on ash tree imports until stricter measures are implemented; please sign this petition:

And if this article doesn’t convince you of the need for tighter controls, the Forestry Commission has a list of “top pest and disease threats” available here:

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