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:, land use/cover change, agricultural expansion, bamboo harvesting) disturbances (Liu et al., 2001; Mackinnon and De Wulf, 1994; Viña et al., 2007; Wang et al., 2008).
Category: