Jamie Morton

Jamie Morton is science reporter at the NZ Herald.

Forest giants star in carbon-sucking stakes

Research finds growth of big, old trees doesn't slow down as they age

The global study has found for the first time that trees' growth does not slow as they get older and larger - instead, it keeps accelerating.
The global study has found for the first time that trees' growth does not slow as they get older and larger - instead, it keeps accelerating.

New Zealand researchers have helped to shatter a common assumption about how trees grow, finding that larger, older trees keep bulking up and can be "star players" at sucking carbon from the atmosphere.

The global study, published in leading journal, Nature, has found for the first time that trees' growth does not slow as they get older and larger - instead, it keeps accelerating.

Forests are major components of the global carbon cycle and the findings are held to have big implications for our understanding of the role of trees in greenhouse gas concentrations.

A team of 38 international researchers compiled the growth measurements of more than 673,000 trees belonging to 403 species in different temperature regions across six continents, including more than 45,000 trees across 22 species in New Zealand.

The results showed that for most tree species, mass growth rate increases continuously with tree size - in some cases, large trees appear to be adding the carbon mass equivalent of an entire smaller tree each year.

As was seen in other parts of the world, the proportion of large old trees measured in New Zealand which were found to have a high increasing mass growth rate was more than 95 per cent.

Stand-out New Zealand species included the rimu, kamahi, the silver beech, southern rata and Hall's totara.

"In human terms, it is as if our growth just keeps accelerating after adolescence, instead of slowing down," said the study's lead author, Nate Stephenson, a forest ecologist with the United States Geological Survey.

"By that measure, humans could weigh half a tonne by middle age, and well over a tonne at retirement."

The continuously increasing growth rate also meant that on an individual basis, large, old trees are better at absorbing carbon from the atmosphere.

But the researchers were careful to note that the rapid absorption rate of individual trees did not necessarily translate into a net increase in carbon storage for an entire forest.

Ecologists argue that young forests are better at tackling climate change, the mass of new trees collectively taking more carbon out of the air than the fewer older trees in mature forests.

Dr Susan Wiser of Landcare Research provided the New Zealand ecological perspective to the study.

The NZ results were taken from the National Vegetation Survey Databank, the world's sixth largest such resource.


Kiwis would pay for wildlife: study

A survey has suggested Kiwis would pay to support programmes that boost native wildlife in plantation forests.

New Zealand's planted forests provide a habitat for at least 118 of native species threatened with extinction, and studies suggest that these could be better managed to increase the population of many of these species at additional costs.

A study was recently conducted by a team of international scientists, led by Scion resource economist Dr Richard Yao, to estimate the value for a programme that would increase the biodiversity of native species in the 1.7 million hectares of New Zealand's exotic planted forests.

Dr Yao and his team conducted a nation-wide survey asking participants to place a value on the benefits they derived from an increased presence of native species.

Species included in the survey were the brown kiwi, bush falcon, Auckland green gecko, the giant kokopu (fish) and the kakabeak (plant).

More than 200 participated in the survey. Results suggested a proposed programme to enhance native biodiversity in New Zealand's forests would be valued. Respondents placed higher values on the conservation of birds than other species.

Typical respondents were willing to pay for native enhancement through an increase in income tax.

But the study authors said that given the small sample size of the survey, the results should "not be aggregated over the total New Zealand population".


Big and strong

38 international researchers compiled the growth measurements of more than 673,000 trees belonging to 403 species in different temperature regions across six continents, including more than 45,000 trees across 22 species in New Zealand.

- NZ Herald

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