Trees and grassland in agricultural landscapes help boost soil carbon storage

    ALES study shows surface soil gets up to 36 per cent increase

    By Helen Metella on December 7, 2015

    Alberta soils could store significantly more carbon if trees are integrated into cropland areas, new ALES research reveals.

    ALES scientists looked at the influence of shelterbelts, hedgerows and silvopastures to evaluate the role of trees and different land uses across the agricultural landscape in mitigating climate change, and to see which system is more conducive to carbon storage.

    They found that soils under trees stored 36 per cent more carbon.

    “The implication of these results for land management is quite straightforward,” said Chang, a professor of forest soils in the Department of Renewable Resources, and one of four researchers involved in the study, including his co-principal investigator Edward Bork, and researchers Mark Baah-Acheamfour and Cameron Carlyle.

    “If trees are beneficial in storing carbon, then we should be promoting tree planting within cultivated agricultural landscapes. We should also encourage government programs to assist farmers in planting trees.”

    During the study, which took place on plots in south-central Alberta over four years, the benefits of trees remained dependent on the adjacent land use. According to Bork, “trees had the greatest benefit in raising soil carbon levels in agroforestry systems where they were combined with neighboring annual cropland subject to cultivation, while perennial grassland maintained soil carbon levels similar to that of the natural forest.”

    However, he added that silvopastures remained the most effective agroforestry system as a whole for storing carbon, because trees and grassland, both permanent cover types, were able to accumulate and store large amounts of carbon.

    “Because of this, the conservation of existing perennial cover types and avoiding losses associated with cultivation are key to maximizing carbon stores,” he said.

    Both Chang and Bork note that it is important to communicate to farmers the benefits of forest and grassland retention as well as tree planting, which extend beyond increased carbon storage and stability.

    “The incorporation of trees decreases erosion losses and reduces leaching of nitrate. Trees can intercept nitrate leaching through surface soil before it gets into groundwater,” Chang explained.

    Additionally, farmers can diversify their income, by harvesting and replanting the trees for pulp wood production or saw lumber.

    Finally, there’s potential for future income derived from enhanced carbon storage, too.

    “If landowners increase carbon storage in the soil by having trees or maintaining perennial grassland, this increase may have value on the carbon market, which in Alberta is projected to rise to $30 per ton of CO2 emitted by 2017,” Chang said.

    The study, Carbon pool size and stability are affected by trees and grassland cover types within agroforestry systems of western Canada, was published in the journal Agriculture, Ecosystems & Environment.