Why is timber a renewable resource?

Wood is the most widely available building material derived from a renewable source.

Sustainable management of forests and plantations is the only efficient way to meet society’s demand for wood in perpetuity.

Forests themselves are able to be replenished, since the major inputs that contribute to their growth are sunlight (energy), air, water, and nutrients from soils in which they grow.

It is therefore vital that forests are carefully managed to avoid over-harvesting and that man’s intervention does not reduce the sustainable, long term potential of the resource. If we ensure that forests are regenerated after each harvest of wood products, they will be around for future generations to use and enjoy.

It has been estimated that around 40% of Australia’s forests and woodlands have been harvested for wood and timber at some stage over the past 200-years, but remain essentially intact (State of the Forests Report, BRS, 2003).

Of Australia’s 147 million hectares of native forests (2008 data) around 20% is now managed primarily for conservation in formal nature conservation reserves and national parks on public land, and conservation covenants and other reserves on lease-hold and private land. In addition, huge areas of other forest that is not formally reserved, is effectively reserved by being unsuitable or too remote for resource use.

Most native hardwood production occurs within just the 6% of forest on public land designated as State Forest for multiple uses, although only about half of this is actually being managed for sustainable timber supply due to productivity constraints and management reserves. Timber production in these multiple use State Forests is conducted on a sustainable basis because state government agencies have gathered sufficient data about forest growth and productive area to be able to match the level of harvest to the annual growth across the area of usable forest.

A much higher level of leasehold and privately-owned forest is theoretically accessible for wood products (DAFF, 2008), but most is either unsuitable or too remote from industrial infrastructure to be usable, or is being managed specifically for other purposes. It is more difficult to ensure sustainable harvesting on private or leasehold land because there are many different owners or managers with a range of intentions, and it is hard to get an overall picture of the size and growth rate of such a disparate privately-managed resource.

While most developed countries such as Australia are able to harvest timber sustainably from their public forests, this is not the case in many developing countries where forest management is more primitive and there is a lack of data about forests and their growth. This, coupled with different systems of land ownership, makes it harder to determine a sustainable level of harvest and to regulate its implementation. This is a major reason why it is preferable for Australia to produce its own timber rather than rely on imported timbers.    

The establishment of new forests, plantations or woodlots, using native or exotic tree species adds to our renewable resource. In Australia, hundreds of thousands of hectares of new tree cover has been established on land that had been cleared of its original vegetation. In broad terms, during the period 2003 to 2008, the nation’s area of plantations increased by 12% from 1.63 million hectares to 1.82 million hectares.

Native forests are harvested either in consolidated patches or by selective removal of trees subject to the silvicultural requirements of the species. Generally, the wetter and more productive forest types are harvested more intensively followed by the burning of harvesting debris to fit their regeneration requirements of full sunlight on a burnt ash seed-bed. Drier forest types are often able to regenerate under partial shade and so are more suited to selective harvesting which creates gaps in which seedlings can regenerate without the need to burn the debris.

The only energy inputs into native forest harvesting systems are the fuels used by harvesting machinery and log trucks, and equipment used in artificially seeding areas where natural regeneration is unlikely to be sufficient. There are generally no fertilisers, herbicides, or insecticides used in native forest systems.

In plantations and agroforests (woodlots on farms), improvements in soil cultivation and early management (silvicultural) techniques including the judicious use of fertilisers and herbicides, along with tree breeding (genetic science), has driven a dramatic increase in the amount of wood able to be grown and drawn upon for a whole range of societal needs. Most plantations and woodlots are single species monocultures and on good sites they can produce hundreds of cubic metres of wood from every hectare, harvestable at 25 to 40 year intervals, and often with intermediate thinning along the way.