Soil seed bank characteristics measurements
The density of SSB was expressed as the number of seeds per
m2 and SSB richness was measured as the number of
species for each soil sample.
SSB species diversity indices were calculated for each individual
under-shrub using greenhouse data. The Shannon index is most frequently
used to characterize the diversity of communities; it is sometimes
referred to as the Shannon-Wiener index (Equation 1).
Equation 1 H’ =\(\sum_{i=1}^{s}\text{pi}\log\text{pi}\)
Where pi is the relative abundance of SSB of the ith
species in a soil sample, and S is the number of detected species in SSB
in that sample (Chernov et al., 2015). Another diversity index
frequently used in ecology is the Simpson index, which is frequently
determined as the probability of belonging to different taxa for two
plant species randomly selected from an indefinitely large community.
The Simpson index was calculated from the equation 2 (Chernov et al.,
2015).
Equation 2 SI\(=\)\(\sum_{i=1}^{s}\frac{ni\ (ni-1)}{N(N-1)}\)
Where ni is the individual number of each plant species
in the SSB in a sample, and N is the total number of all germinants of
all plant species in SSB in that sample.
The diversity indices were calculated using the Past software.
In addition, during the growth season, we recorded the presence of all
plant species within each of the patches sampled for SSB. Species
abundance of the AGV was not estimated because it was not possible to
place a sampling frame beneath the shrubs and we used presence-absence
data for AGV in the analyses. Qualitative similarity between the species
composition of the AGV and the SSB was assessed using the Jaccard
similarity index (Kent and Coker 1994) in each patch using equation 3.
Equation 3\(\text{IS}_{j}=\left[\frac{C}{\left(C+A+B\right)}\right]\times 100\)
Where C is the number species common between AGV and SSB, A, the number
of species found only in the AGV and B, the number of species found only
in the SSB.
We also estimated the mean canopy surface of our shrubs on ground and
the height of each individual shrub using metal tape measure.