Frequently cleared plantations may mitigate climate change

Forrest. Source: Reimo Lutter
Forrest. Source: Reimo Lutter

Silver birch and hybrid aspen plantations with a short rotation, i.e. frequently harvested and regenerated, present an excellent opportunity to find a use for abandoned agricultural lands, the production of raw timber, and the mitigation of climate change.

If short rotation forest plantations have thus far been established at latitudes where the climate is warmer, then over the last decades the idea has begun to gain popularity in Estonia and elsewhere along the Baltic Sea.

This trend is linked to the fact that there is a growing need for renewable energy and raw timber. At the same time, there is a pressure to reduce the intensity of clear-cutting in natural forests.. Silver birch and hybrid aspen are among the most suitable tree species for use in practising short rotation forestry under the conditions in Estonia, explains Reimo Lutter, author of the Doctoral thesis.

Since there has been little research conducted on the second part of the rotation cycle in ecology of fast growing forest plantations in Estonia, within the framework of his Doctoral thesis Reimo Lutter conducted repeat measurements on the growth of trees and the physico-chemical properties of the soil in permanent observation plots at 15 year old hybrid aspen and silver birch plantations.

The work revealed that after 15 years after planting hybrid aspen plantations are already carbon sequestrating ecosystems. Carbon sequestration has mainly taken place in the aboveground biomass of the trees, and the soils of former agricultural lands have greater potential to accumulated additional carbon than former grasslands.
While the carbon level in the upper layers of soil remained unchanged, an important discovery was that the carbon pool või storage of soil increased in the deeper layers.

‘The growth rate of both tree species after 15 years of growth on former agricultural lands was double in comparison with similar site-types for birch and aspen stands on forested land,’ said Lutter. He added that silver birch and hybrid aspen plantations grow faster on former agricultural land on soils corresponding to Oxalis, OxalisMyrtillus and Aegopodium site types. Both species of tree grow slower on a Hepatica site-type soils.

According to Lutter, the primary macronutrients of soil found in fast growing hybrid aspen and silver birch plantations has not decreased over the period of 15 years. The growth rate for both tree species was slower in soils in which the potential water supply and available phosphorous content were lower.

The Doctoral thesis Growth development and ecology of midterm hybrid aspen and silver birch plantations on former agricultural lands  was supervised by Professor Hardi Tullus, and Senior Researcher Arvo Tullus and the opponent is Professor Jürgen Bauhus (Chair of Silviculture, University of Freiburg, Germany). The dissertation can be examined at the Estonian University of Life Sciences Library and the University of Tartu Library.

The translation of this article from Estonian Public Broadcasting science news portal Novaator was funded by the European Regional Development Fund through Estonian Research Council