The RIC Good Wood Guide

(What We Need to Grow are...)

Durable Native Softwoods - the Ethical Solution to Toxic Timber Treatments

by Trevor Lane

With the benefit of hindsight, the incalculable risks involved in using pesticides and herbicides over the long-term, points to a cumulative disaster, as the Australian timber consumption trend veers more and more toward non-durable timber species.

The seeming necessity for using such toxic chemical preparations as copper chromium arsenate (CCA) or Light Organic Solvent Preservative (LOSP) for treatment of the more common (non-durable) plantation timbers, is creating an annual accumulation of millions of cubic metres of hazardous waste as the impregnated timber reaches the end of its 'shelf-life' of 20 years or so.

End-of-life disposal of hundreds of millions of cubic metres of treated timber, which leaches 3.5 percent of its chemical content for each month of rain 1, is a disaster for our underground and surface waterways, their inhabitants and associated life-support systems.

The obvious alternative is to grow durable timbers (ie, that don't require toxic treatments) in mixed-species plantations on degraded land for environmental repair-work. This 'repair-work' also provides a future timber supply.

Trees such as White Beech (Gmelina leichhardtii), Rosewood (Dysoxylum fraseranum), Cypress Pine (Callitris spp), Brown Pine (Podocarpus elatus), heartwood of the Hoop Pine (Araucaria cunninghamii), Red Cedar (Toona australis), and other similarly durable, light, easy to work timbers can be grown as dominants (ie, main, but not only components) in a mixed-species plantation format. This would allow the replenishment of the soil in the form of mulch, created by the deciduous tendency of a large number of these species. At the same time, these trees could create natural fire-breaks due to the resultant increase in relative humidity.

Growth-rate analysis 2 shows promising timber-production rates, whilst thinnings (culled, immature timber-trees - for chipping?), seed and fruit production each represent an interim source of income.

Just because Red Cedar and White Beech are renowned for cabinetmaking, doesn't mean they can't be grown in large numbers now (as can other durable, non fire-regime species whose use would also obviate CCA treatment-requirements).

Meanwhile, future import volumes of radiata and other exotic pines are set to escalate to relieve pressure on our native forest logging processes. These softwoods will require treatment and thus the CCA problem will just be exacerbated and further perpetuated.

Since the 1920's, huge tracts of rainforests have been logged for red cedar, then for hoop pine, and subsequently burnt, thus allowing fire-hardy eucalypts to take precedence in the regrowing forests. (Very few rainforest species can self-regenerate after fire: wildfires do not normally penetrate old growth rainforests.) Areas which were predominantly rainforest at the turn of the century are now eucalypt-dominant forest and farming country.

The dry sticks and leaves dropped by eucalyptus trees don't decompose as quickly as those from the original forest species and create a much greater fire risk, with the accumulation of extra fuel on the forest floor. To reduce this fuel build-up, it became the practice to put a low-temperature fire through these forests. These fires, moving unseasonably across the ground, then burnt the bases of the tree trunks, which has allowed diseases to enter ever since, resulting in what we call 'dieback'. The low-temperature fires also suppressed the regeneration of fire-retardant rainforest species.

This process of converting forest species-types from rainforest to eucalyptus is a conscious practice of the State Forests Departments in NSW and Queensland, due to the perceived demand for hardwood eucalypts.

Unfortunately, these management methods have created a huge fire-hazard for Australia and now also are notable for their creation of vast areas of dieback eucalypt.

One solution could be to selectively log the non-habitat trees damaged through this hazard-reduction burning (ie, the dieback trees) and then interplant with the original rainforest species, which would reduce future fire-hazards and rejuvenate the damaged areas.

Note: There have been massive amounts of timber wasted in land-clearing in Central NSW and Queensland. In 1994 alone, a mind-boggling 500,000 hectares was cleared to make way for cows and crops. All the massive quantities of trees pushed into piles could instead have been utilised as millable timber and/or woodchips.

Due to past mismanagement, our short-term supply options are severely limited if we are to avoid threatening our next generations with toxic chemical accumulation from treated softwood.

It will take 30 to 40 years before supply from a durable softwood plantation can come on-line to replace the existing quotas.

Alternatives do exist to avoid the export woodchipping industry removing our constantly dwindling forest resources. A thorough reappraisal of forest-interaction must be rapidly sought and implemented.

Alternatives, such as fast-growing fibre and chip crops must be sought as soon as possible, not forgetting the need for massive planting of mixed species plantations to ensure a safe supply of preservative-free, durable timbers for the future.

1. Ref. Qld Health Dept.

2. (ref. D. Cameron, CSIRO)

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