Old trees boost biodiversity

In his PhD, Eivind Handegard studied how the age of boreal forests and trees impacts biodiversity. Results show that older forests and trees are vital for the diversity of lichens, fungi, mosses, and plants. They tend to host more species and different types than younger forests due to many habitats.

Aging makes trees more peculiar; parts of the wood may die, tree hollows can form, and the bark's texture becomes rougher, which benefit several lichen species. The age of the trees also influences how many and which lichen species grow on them.

“It’s important to protect large, old trees to preserve biodiversity,” Dr Handegard explains.

Various features can be used to estimate the age of old trees, including the bark's structure and the shape of the trunk. Previous studies have also shown other, less visible changes, such as increased stability due to slowed growth and altered bark chemistry. Several lichen species thrive particularly well on old trees.

“Some species are highly specialised and have adapted to the surface of old trees, such as the stems of spruce trees,” says Dr Handegard.

On old pine trees, we find the highest number of lichen species dead branches. The lichens on spruces, many which are pendulous, respond to both age and size.

“Lichens take time to grow, and not all of them can grow on large trees – they need old trees,” says Handegard. “In order to protect these lichens, we must conserve both large and old trees.”