Does expansion of western snowberry enhance ecosystem carbon sequestration and storage in Canadian Prairies?

Aerial expansion of woody species in grasslands is common in arid and semiarid areas. The ecological consequences of shrub expansion, including ecosystem function and carbon sequestration, are complex and dependent on local environmental conditions. This research was conducted in the Northern Mixed Prairie of Canada to determine the effects of western snowberry (Symphoricarpos occidentalis) expansion on phytomass production and ecosystem carbon storage in grass-dominated plant communities. Total aboveground phytomass in western snowberry communities was more than triple that of the ecotone and 6-times greater than that of the grassland. Similarly, the mass of large roots was greatest in the western snowberry community (1.2 ± 0.19 kg m−2, mean ± SE), intermediate in the ecotone (0.5 ± 0.08 kg m−2), and least in the grassland (0.1 ± 0.04 kg m−2). Conversely, the mass of fine and medium roots was not different (P > 0.05) among the three communities, averaging 0.7 kg m−2 in all communities. Greater aboveground phytomass did not correspond with greater organic carbon in the soil (SOC) in the western snowberry community possibly due to the poor quality and slow decomposition rate of shrub litter. Soil organic carbon in the upper 50 cm averaged 8.3 ± 0.7, 7.9 ± 1.0, and 7.9 ± 0.7 kg m−2 in western snowberry, ecotone, and grassland communities, respectively. The SOC in fine- and coarse-textured soils averaged 10.4 ± 0.6 and 6.2 ± 0.4 kg m−2, respectively. Expansion of western snowberry into grass-dominated plant communities does not appear to conflict with goals related to maintenance of SOC in the Northern Mixed Prairie. Soil texture had a greater effect on SOC than that of western snowberry. Therefore, the management of western snowberry in the Northern Mixed Prairie should be site specific and focus on aspects other than SOC pools.