Fig. 1 Geographical locations of the sampling sites. The color of the
circle indicates the dominant species of exotic plants
We sampled a total of 2267 quadrats in the 236 sites. For each quadrat,
first, plant species were
recorded. Then, the coverage of each species (C ) was
determined by visual
estimation on 22-degree scales:
0.5%, 1%, 5%, 10%, 15%, 20% … 100%. Next, all plant
materials, including shoots, leaves, and roots, in
the quadrat
were
collected by careful manual
digging. Finally, all plants were classified, washed, and dried at 70 °C
for more than 48 h to determine the biomass of each species (B ).
The total biomass of
native/exotic plants in each quadrat
(TBQN /TBQE ) =
∑B n, total coverage of native/exotic plants in
each quadrat (TCQ N/TCQ E) =
∑C n, n was the species number of natives or
exotics in a quadrat. The mean biomass of native/exotic plants at each
site
(MBSNMBSE )\(\ \frac{\sum\text{TBQ}_{i}}{i}\),
the mean overage of native/exotic plants at each site
(MCSN /MCSE ) =\(\frac{\sum\text{TCQ}_{i}}{i}\), and i is the number of quadrats at a
site. When the abundance of exotic plants in a site was too low to
appear in any quadrat, we determined the values ofMBSE and MCSE of the site
were zeros. In addition, the defoliation (Dleaf ,
% of leaf area removed) of exotic plants by herbivores was assessed.
10~20 fresh shoots (all shoots when the total shoots
< 10) of each exotic plant were randomly selected for
defoliation assessments in each quadrat, andDleaf was measured using our previously described
method (Fan et al. 2016).