Vegetation sampling and trait measurements
We compiled a full list of species, based on the list provided on Estrada-Castillón et al. (2010), for each subplot. Plant cover for each species was estimated using a modified Daubenmire plot and its cover scale method (Daubenmire, 1968) where each species is individually assessed and classified within one of 6 designated cover classes and assigned a midpoint value: (1) 0-5% = 2.5%; (2) 5-25% = 15%; (3) 25-50% = 37.50; (4) 50-75% = 62.50%; (5) 75-95% = 85%; (6) 95-100% = 97,50%. Daubenmire cover estimates were also compared against species and total cover results of the line-point-intercept method (Herrick et al. 2005) in Agri sites. This method consisted of point readings at every meter of three 30m transects that were 8 meters apart within the site, marked by a measuring tape. Both methods gave very similar results in identifying the site’s cover and species, so the Daubenmire method was selected because it was easier and faster to implement in the field. A total of six traits (Table 1) were selected due to the feasibility to obtain them in the field (Reich, 2014) and their relationship with key grassland functions in vegetation studies (Garnier et al. 2007). Three traits, namely vegetative height, leaf area, and habit, were assessed in the field following the guidelines by Pérez-Harguindeguy et al. (2013), i.e. all measures were taken from at least 5 healthy individuals of each species. Leaf area was measured using the app LeafByte, version 1.3.0. (Getman-Pickering et al. 2020). Due to the COVID-19 virus restrictions in Mexico, the measurement of leaf dry mass was not possible, so leaf area was used instead of SLA. Plant habit was considered as erect or prostrate to further specify the species life form. Traits obtained from the literature were life history, photosynthetic pathway and life form (Table 1). We did not use other traits because it was difficult to find information even for the traits commonly used in plant trait studies (Blumenthal et al. 2020). Many of the plant species in GPCA El Tokio have been poorly studied. We could obtain traits for 63 out of 92 of the species, which together accounted for 96% of the total cove.
Table 1. Selected plant functional traits, and classification levels (if applicable) or values.