Image caption Tropical timber production exceeds forests' ability to replace the felled trees, the study says

Current tropical timber practices are not sustainable and nations should consider the "implications of 'peak timber'", a study has suggested.

A team of researchers says the standard cutting cycle of 30-40 years is too short to allow trees to grow to a volume required by commercial loggers.

As a result, they add, the pressure to harvest primary forests will continue, leading to ongoing deforestation.

The findings have been published in the journal Biological Conservation.

The scientists used logging on the Solomon Islands as an example because it was, in some respects, "a microcosm of the challenges facing sustainable forest management in the tropics".

They said the industry had been a major source of government revenue for a number of years.

Yet, they added: "For nearly a decade, the nation had been warned that the volume of timber annually harvested from native forests was too high and, if unchecked, that timber stocks would be seriously depleted by 2012.

"In 2009, the Central Bank of the Solomon Islands asserted that (the) exhaustion of timber stocks had arrived even earlier that predicted and its economic consequences were likely to be severe."

Pushing the limit

The team - made up by Dr Phil Shearman and Jane Bryan from the Australian National University, and Prof William Laurance from James Cook University, Australia - said the trajectory of the country's timber production (a rapid increase in production, followed by a peak and then a decline) was akin to the 'Hubbert curve', which has been observed in the exploitation of non-renewable resources, such as oil.

"It is occurring in the Solomons because timber extraction has occurred at a rate far in excess of the capacity of the forests to regenerate commercial timber stocks," they wrote.

The researchers suggested that there were three main factors that made it difficult to find examples of sustainable forestry in the tropics:

Low level of marketable timber production - many tree species having unsuitable wood properties, and the slow growth rate of commercially viable specimens is another factor

- many tree species having unsuitable wood properties, and the slow growth rate of commercially viable specimens is another factor Collateral damage - while logging in the tropics tends to focus on a small fraction of the trees, many others are damaged or killed as a result of the network of access roads to the area being logged

- while logging in the tropics tends to focus on a small fraction of the trees, many others are damaged or killed as a result of the network of access roads to the area being logged Second-wave clearance - the "labyrinths of logging roads have opened up vast swaths... for colonisation, hunting, illegal mining and other destructive activities"

As well as these factors, the problem of illegal logging was also threatening primary forest cover in many nations.

Image caption Deforestation accounts for up to 20% of annual greenhouse gas emissions from human activities

A joint World Bank and Interpol project called Chainsaw produced a report in 2010 that highlighted the widespread nature of the problem.

"Illegal logging is one, very significant, component of a complex array of problems that are leading to a worldwide crisis of forest loss and degradation," it reported.

It went on to say that Interpol estimated that an area of forests "equivalent in size to the territory of Austria" disappeared worldwide every year as the result of illegal logging.

The report added: "They also estimate that the percentage of timber marketed worldwide of illegal origin stands at between 20% and 50% of all marketed timber products."

Prof Laurance and the team said that the Redd (Reducing emissions from deforestation and forest degradation) concept could be an avenue that offered some hope in the future.

Redd is essentially a way of paying developing countries or communities within them to preserve their forests.

"We believe that some Redd+ funds should be directed at initiatives designed to keep loggers and their associated road networks out of forests, rather than merely modifying logging operations," they wrote.

The team concluded with a stark warning: "Unless something fundamental changes... we believe that logged tropical forests will continue to be over-harvested and, far too frequently, cleared afterwards, leading to an inevitable global decline in native timber supplies.

"It has become common these days to speak of 'peak oil'. In the tropics, we assert, we should also begin to seriously consider the implications of 'peak timber'."