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Creating safe woodchip for Westonbirt's trees

Woodchip sterilisation site in Silk Wood, Westonbirt ArboretumVisit the far end of Waste Drive in Silk Wood, and you’ll see a large shed-like structure housing piles of woodchip in the process of being made safe for use on site.

Simple as though this building may look, the science behind it will help protect Westonbirt’s trees from pests and disease.

The facility is the first of its kind in the UK to pasteurise raw woodchip without adding green matter. Adding green matter would cause the woodchip to become compost in the process.

Addressing the growing threat of plant pests and disease

Phytophthora RamorumTrees and plants face an increasing threat from new pests and disease. One of the ways plant pests and disease can spread is through the use of untreated woodchip.

Following the discovery of Phytophthora ramorum (known as Sudden Oak Death in USA) in a specimen rhododendron in 2009, DEFRA served a plant health notice to Westonbirt Arboretum. As a result, the use of woodchip produced onsite had to cease.

The Forestry Commission's tree team at Westonbirt could no longer use standard woodchip produced from trees felled or maintained as part of routine management of the collection. The plant health notice meant they would have to import pasteurise woodchip - this meant wasting material produced onsite and adding road miles and extra cost to the tree management process.

In order to reduce the risk of further infection, the decision was made to build a new woodchip facility.

A natural solution

Hot composting at the woodchip sterilisation facility at Westonbirt Arboretum.This new facility pasteurises the woody material produced from  everyday arboretum maintenance. The facility has been designed to cope with hundreds of tonnes of woodchip created during an average year at Westonbirt.

The process is simple and relies heavily on nature to do the hard work. Assorted freshly chipped material is immediately deposited into one of seven bays and covered over. Each bay measures 4.5m wide x 5.6m long and is filled to a depth of 1.5m.

To achieve pasteurisation, an entire pile of woodchip needs to reach a minimum of 45°C for five consecutive days, or 60°C for three days.  The Forestry Commission’s Forest Research department helped to establish a system of monitoring variations in temperature within each pile. 

Once a pile has reached the right temperature, it is turned into the next empty bay and the process is repeated for a second and third time to ensure every piece of material gets treated. Woodchip which is green at the start should turn to brown by the end of the process.

High quality, safe woodchip can now be used across the site - as mulch around new plantings and mature specimens and across the network of paths in Silk Wood. 

Interpretation will be added to the area around the facility to help visitors understand the important work taking place.

This project was funded by the Friends of Westonbirt Arboretum.

Last updated: 9th December 2016

What's of interest

Find out more about the national tree health work undertaken by the Forestry Commission

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England's Woods and Forests are cared for by Forest Enterprise England, an agency of the Forestry Commission.