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:Trait data collection
 We used 10 plant functional traits related to growth, survival, and the response to environmental change (PeÃÅrez-Harguindeguy et al. 2013), including leaf area (LA; mm2), specific leaf area (SLA; mm2 g 1), chlorophyll content (measured by the SPAD device unit [see below]),‚Ä¶
Category: