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:…spectrum above-ground (i.e. trait syndromes associated with resource acquisition or conservation; see Reich 2014), the existence of a root economics spectrum is still a matter of debate, mainly because of a lack of consistency among and within studies (Mommer and Weemstra 2012; Weemstra et al.
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