Split gills and Peruvian sleepersPosted: 06/09/2012
There has been a lot of discussion / argument about the management and sale of state owned assets over the last six months (see bowalleyroad). And over the last month the management of one of these assets, KiwiRail, has been subject to questions in Parliament. These questions have been triggered by a fungus, more specifically fungal decay in timber sleepers.
Of the six million sleepers in use in the New Zealand rail network of which 7000 (0.12%) are showing some degree of decay. These sleepers where obtained from Peru and initially the fungal decay was attributed to Schizophyllum commune. I have blogged about this species before. It is a common fungus on wood in New Zealand and was frequently intercepted at the ports on pallets, packing cases and dunnage. Sleepers are expected to an Australian standard requiring that they last at least 15 years. It is thought that new sleepers already had significant but not visible decay.
Since the mid 1990s wood has been considered as a possible pathway for pest insects and fungal pathogens to spread around the world. This has resulted in countries imposing standards for the treatment of wood either chemically or by heating before it is allowed entry. For instances the Ministry for Primary Production has issued a standard for the treatment of poles, piles, rounds, and sleepers. For instance new or unused wood items can be fumigated with methyl bromide at 80 g/m2 more than 24 continuous hours at 10°C or heated for 4 hours at a minimum continuous core temperature of 70°C. It can only be assumed that the treatment of these sleepers was not done correctly.
In itself Schizophyllum commune is not of concern to New Zealand however further testing of the sleepers has shown the presence of two other species not known to occur in New Zealand. Which species has not been said?
Historically there has always been a preference to use jarrah (Eucalyptus marginata) as it is very durable and resistant to decay, even in wet and weathered situations, making it a choice structural material for bridges, wharves, railway sleepers and telephone poles. Less durable timbers have also been used by treating them with chemicals.
Controversy over sleepers is not new and during the 1913 New Zealand Royal Commission on Forestry the commissioners examined alternative timbers for use as sleepers and chemical preservatives. One preserving process was Powellisation. According to a report in The Advertiser (Adelaide, 23 February 1914) this process required the sleepers to be boiled in an arsenic and sugar solution.
In The Age (Melbourne, 2 December 1913) there is a report of the Royal Commission’s hearing. Here it is noted that:
The evidence shows that both in the molasses vat for steeping green timber and expelling the sap, and in the drying kilns afterwards, the process needs to be applied with great care.
While he could not express a definite opinion as to its ultimatesuccess or failure, powellisation up to now had been anything but a success.
Powellisation was unsuccessful and the process and the name have been forgotten and it does not appear in any historical reviews on timber preservation.
However the virtues of jarrah were extolled:
The department [of Works] bought as many jarrah sleepers as they could get the Government to import, the cost being 4/9 each delivered. The latter, he considered, was the best timber for durability which they used. In one line 75 per cent. of the sleepers cut from this timber were found to be fit for use after being in the line for 30 years.
The suitability of eucalypt timber and the failure of the Peruvian timber has highlighted the potential to grow eucalypts on a bigger commercial scale then is done presently. One example is the New Zealand Dryland Forests Initiative which is selecting and breeding eucalypt species suitable for growing on drought- and erosion-prone farmland in Marlborough, Gisborne, Hawke’s Bay, the Wairarapa and Canterbury.
I have blogged before on the importance of eucalypts in the New Zealand landscape and the fungi associated with them.