It isn’t competition for nutrients that make densely planted trees give a worse yield per hectare. The problem is actually genetics. So said World Bioenergy Award winner Professor Laércio Couta at the World Bioenergy conference in Jönköping, Sweden.
Laércio Couta won the World Bioenergy Award for his work on eucalyptus cultivation in Brazil. At the conference in Sweden he described in more detail one of the most recent projects being done by his group of researchers.
At issue is the question of how significant the distance between the eucalyptus trees is to their growth per hectare. In natural stands, trees compete with each other and over time the stands become thinner. One explanation usually given for this is that the trees are competing for a limited amount of nutrients.
Brazil is uniquely well suited to answer this question. People began planting eucalyptus there in 1904 to ensure fuel for the railway steam engines. Over time, this fast-growing tree has gained increasing importance in other areas too – as a raw material for the forest industry, as fuel, and for making charcoal for the steel industry.
Extensive research into eucalyptus is being done in Brazil. One result is that cloning is now widely used. Forest owners have their own varieties of eucalyptus but within an individual plantation most of the trees are genetically identical.
Laércio Couta’s researchers planted the eucalyptus seedlings various distances apart and monitored their growth for five years. The seedlings planted most closely were
3 x 0.5 metres apart, and the most thinly planted were 3 x 3 metres apart. It turned out that the trees grew equally quickly whatever the distance between them.
“The production per hectare increased in a linear manner,” said Laércio Couta, who pointed out that there is a limit to how densely one can plant. The conclusion is that the obstacle is not the amount of nutrients. In a normal plantation plants have different characteristics: some grow faster and outcompete the others. But in this plantation the plants all had the same genetic makeup and they all grew equally quickly without outcompeting each other. “One big advantage with planting more densely is that the number of stems increase and there are fewer branches and leaves,” Laércio Couta explained. “This means we can export wood and not nutrition.”
Most of the nutrition is in the leaves, but it is the stems that are the most interesting to export in the form of cellulose products, sawn timber, biofuel, etc.