Ground vegetation contributes substantially to the carbon uptake of forests

Northern pine forests play a significant role in carbon uptake. So far, research has largely focused on the role of trees, but many ground vegetation species are effective assimilators and can therefore contribute substantially to the carbon uptake of forests. In her dissertation, Liisa Kulmala, M.Sc. (Agr. & For.), examines the carbon uptake of the most common ground vegetation species in pine stands of different age as well as various methods of measuring carbon uptake.

Ground vegetation, such as bilberry, lingonberry, heather, small-reed and mosses, is exposed to plenty of light in pine stands and clear-cut sites in particular. In older forests, ground vegetation represents approximately 10–15 percent of all carbon uptake. In forests less than 20 years of age, however, the proportion is much higher.

Ground vegetation, such as bilberry, lingonberry, heather, small-reed and mosses, is exposed to plenty of light in pine stands and clear-cut sites in particular. In older forests, ground vegetation represents approximately 10–15 percent of all carbon uptake. In forests less than 20 years of age, however, the proportion is much higher.

In her research, Kulmala enclosed plants in tight chambers in their habitat. Carbon dioxide content in the chamber was then measured to determine the amount of carbon bound by the plant. Kulmala studied the photosynthesis of ground vegetation species in five forests of different age and on two clear-cut sites with substantial differences in fertility.

“On the clear-cut sites, naturally, ground vegetation species were responsible for all carbon uptake, but they were affected by tough competition between plants and by being overshadowed by other plants,” Kulmala explains.

The biomass of evergreen species was highest on barren clear-cut sites and below canopies, whereas grasses and herbs predominated on fertile sites and open areas. Light, temperature history, soil moisture and recent frosts could explain the changes in the photosynthesis of low shrubs as well as some of the changes in the photosynthesis speed of other species. Light and the occurrence of rain explained most of the variation in the photosynthesis of mosses.

Liisa Kulmala presented her dissertation, Photosynthesis of ground vegetation in boreal Scots pine forests, for public examination on 11 November 2011. The event was held at Biocentre 2 on the Viikki Campus, with Associate Professor Sari Palmroth from Duke University as opponent and Professor Annikki Mäkelä as custodian.

The dissertation will be published as part of the Dissertationes Forestales series. The dissertation is also available on the E-thesis service.

More information: Liisa Kulmala, liisa.kulmala@helsinki.fi, tel. +358 (0)50 415 6722

Photo: Liisa Kulmala's collections