Evaluation of the Effect of Conifer Encroachment on Soil Organic Carbon Storage and Soil Properties in Aspen Ecosystems of Northern Utah

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Journal/Book Title/Conference

The ASA-CSSA-SSSA International Annual Meetings (November 4-8, 2007)

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In the Intermountain West, aspen (Populus tremuloides) has declined mainly due to a combination of successional processes, fire suppression and long-term use of ungulates which has led to replacement by conifers, sagebrush or other shrub communities. Conifer encroachment is believed to cause changes in the ecosystem properties such as water yield, biodiversity, and soil properties. The effect of conifer encroachment on soil organic carbon (SOC) storage is still largely unknown. The objectives of this study are to evaluate the influence of conifer encroachment on the soil chemical properties. The study is conducted in three catchments using 12 paired plots (aspen and conifer) established at Deseret Land & Livestock and T.W.Daniel Experimental Forest in Northern Utah. Pedons were fully described, and horizon samples were taken for C analysis and other chemical properties. Microclimate was measured in each plot and nutrient regime was evaluated using ion exchange membranes (PRS-probes). The soils under aspen are classified as Mollisols and Inceptisols while the soils under conifers are mainly Alfisols, Entisols, and Inceptisols. Soils under aspen contain more SOC than under conifers, ranging from to 184.7- 93.6 Mg/ha under aspen and 51.8- 103.2 Mg/ha under conifers (0-80 cm depth). The CEC in all soils is fairly low (/kg), decreases with depth, but is not affected by vegetation cover. Base saturation in all soil is >60%. Aspen soils have higher available K but lower available N than conifer soils, while other nutrients (Ca, Mg and P) are similar.

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