Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Regardless of these differences, the results from both studies that used sites located in the 2004/2005 Alaska fire events were substantially different from previous findings from research in Canada, where the residual organic layers under trees were substantially shallower than the organic layers from across the plot (Miyanishi and Johnson, 2002; Greene et al., 2007).
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