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.