Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Carbon stock and plant communities across an elevation gradient of a semiarid grassland : a 58-year follow up

Auteur : Kramer, Alexander James

Université de soutenance : University of British Columbia

Grade : Master of Science – MSc 2021

Résumé
Soil and plant communities were examined across an elevation gradient of a grassland steppe ecosystem in the Southern Interior of British Columbia over 58 years (i.e., from 1961 to 2019). In 1961, three distinct zones were classified according to plant species composition and Chernozemic great groups. At the time, grasslands in the area had been in degraded states due to long-term overgrazing, but improved grazing management was put in place in mid-1970s. The objective of my study was to determine topographic, microclimate and soil variables that affect the distribution of Chernozemic great groups and associated soil carbon (C) (i.e., total, organic, active C) and plant communities over an elevation gradient at the Lac du Bois Grassland while reassessing the boundaries of three Chernozemic great groups as established in 1961 by the study of van Ryswyk et al. (1966). While soil C stock and plant composition at the lower grassland remained similar to 1961, the middle and upper grasslands have undergone notable changes. Both have progressed from early seral stage to late seral stage communities, showing recovery from the degraded state in 1961. The middle grassland, which used to be a unique grassland zone, has become a more mesic continuation of the lower grassland’s plant species composition with increased biomass and decreased bare soil. Similarly, soil C content only marginally increased from the lower to middle grasslands. Interestingly, during the 58-year period, soil C stock has not increased and may have even decreased in the middle and upper grassland despite the improved plant species composition. Soil organic C at the 0-15 cm depth showed a 7-fold increase (0.9% to 6.8%) from the lowest to highest elevation, while there was a 3-fold increase in C stock (2.87 to 8.51 kg m⁻²), indicating that elevation remains the primary factor that affects soil C distribution across this landscape due to its effect on effective precipitation and air temperature.

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