Kit Sutherland, of Queenstown, asks :-

If trees are the lungs of the Earth, what species of tree/s is the most beneficial?

Chris Lusk, a forest ecologist at the University of Waikato, responded.

Yes, in a sense, trees and other photosynthetic organisms are the lungs of the Earth. Their photosynthesis over millions of years formed the oxygen-rich atmosphere that has made human life possible – before photosynthesis evolved, Earth’s atmosphere had more carbon dioxide, and much less free oxygen.

Trees absorb carbon dioxide through photosynthesis, and use the carbon to build leaves, wood and roots. When the tree decays or is burnt, the carbon is released back to the atmosphere as carbon dioxide. But in the meantime, some of the carbon can be locked up in the tree’s wood for hundreds of years. There is a good diagram on the carbon cycle at wikipedia.org/wiki/Carbon_cycle

Since the industrial revolution, deforestation and burning of fossil fuels have increased the amount of carbon dioxide in the atmosphere by over 40% - and rising. Carbon dioxide acts like a blanket over the Earth, retaining heat – too much of it, and we’ll get cooked! This is “The Greenhouse Effect”. As Earth’s remaining forests contain about the same amount of carbon dioxide as the atmosphere, preventing further deforestation is important for controlling global warming.

To answer your question, diverse mixtures of tree species are probably the most beneficial. Fast-growing trees like Pinus radiata and mahoe absorb carbon quickly, but are mostly quite short-lived and their wood decays fairly quickly; so they don’t store carbon for very long.

Slow-growing trees like matai or rata absorb carbon only slowly, but are often long-lived and their wood is more resistant to decay. So they can store carbon for as much as a thousand years – not just in life, but after death too, as their logs can take centuries to decompose.

Recent research shows the greatest long-term carbon storage is in forests with diverse mixtures of tree species, including some fast-growing trees that respond quickly to opportunities, and others that store carbon slowly and steadily.