Monitoring
Biweekly field monitoring of seed germination was conducted over a year
from April 2020 to May 2021. During each monitoring session, we recorded
and labelled each seed germinated. Overall, over 90% of the geminated
seeds were recorded within 1-3 months after seed sowing. Very few seed
germination (< 5%) was observed beyond 6 months after seed
sowing.
2.4 Statistical analysis
We used generalized linear mixed models (GLMM) to analyse the results of
the seed coating and surface soil treatment experiments. These were
performed using R version 3.6.3 with the ‘nlme’ package (Pinheiro et
al., 2021). We used germination rate as the response variable in both
experiments, while the three seed coating treatments (clay-dominant,
biochar-dominant and control) and two surface soil treatment (biochar
and control) were considered as fixed covariates respectively. In order
to incorporate the dependency among observations in the same site and
nested structure of our experiment, we used site and species as random
effects. We did not include any interaction term due to small sample
size. Moreover, due to the poor seed viability, some of the species such
as Eurya nitida, Tetradium glabrifolium and Zanthoxylum
avicennae failed to germinate in both nursery and field trials and were
excluded from further analyses.
We separated the analysis into two parts: 1) across all species and 2)
each species independently. For all species, we ran four models by
including different covariates and selected the model with the lowest
Akaike information criterion (AIC) value (Table 2). For the species
models, we modelled the relationship between germination rate and
treatment with site as a random factor. Model assumptions of normality
and homogeneity of variances were verified by plotting model residuals.
Post hoc analyses for pair-wise comparisons of means were undertaken
using least square means using the lsmeans package (Russell, 2016).
Additionally, to test the effect of seed size and successional stage on
germination rate of native seeds on landslide scars, data from the
controls of the two experiments were pooled and analysed. We used linear
mixed models to compare seed germination rate of different successional
groups and seed sizes. All analyses were conducted using R version 3.6.3
(R Core Team, 2020) for GLMM.