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:Tidal freshwater marshes have been found to have higher rates of carbon storage than brackish or saline tidal marshes (Bridgham et al. 2006; Craft 2007; Trulio et al. 2007).
Category: