Science - January 14, 2016

Successful growth of trees explained

Roelof Kleis

The success of a tree is judged all around the world by three fundamental characteristics, says ecologist Lourens Poorter and 40 colleagues in Nature. In a study involving three million trees they identified how the trunk diameter at a height of 130 metres depends on the surrounding trees.

The growth success was linked with three functional characteristics: the density of the wood, the leaf surface per gram of leaf and the maximum adult height of the tree. Taken together, these three characteristics explain how a tree fares, standing alone or in competition. And that came as a surprise. Poorter: ‘Actually we expected a big difference between the habitats. That the relations would be very different in a tropical deciduous forest than in a cold coniferous forest, for instance.’

This was not the case, however. The above-mentioned characteristics predict worldwide and in a predictable way the result of competition between trees. The key factor is wood density. Species with high wood density are more tolerant  - they cope with competition from their neighbours better – as well as more competitive – they more effectively prevent the neighbour from growing. Poorter: ‘If you have to compete with a beech, you are in trouble. A beech has dense wood and forms a thick leaf canopy.’ Those competitive advantages far outweigh the disadvantages of slow growth.

Theoretically ecologists can use these natural laws in creating a forest. Poorter: ‘We know which species characteristic are successful early in the process and which at a later stage. If for instance we want to restore a forest, we now know which trees to plant.’