Shrub Trajectories


 There are no trends with time associated with the shrub structure (Figure 7.18) of
constructed wetland research sites. There appears to be a peak in stem diameter of early
successional species around 8-10 years.


Understory Trajectories

 There is a significant trend (p < 0.05) in herbaceous species richness (Figure
7.19a); however time explains only 29% of the variation. There are no trends with time
associated with richness, diversity or cover (Figure 7.19b, 7.19c and 7.19d) of combined
understory species.

 Species richness (Figure 7.20a) of seedlings of canopy tree species showed an
increasing trend with age (r2 = 0.45; p < 0.01). Species richness of subcanopy trees
(Figure 7.20b) differed very little between sites. Shrub seedlings showed no trends in
species richness (Figure 7.20c) with time. Vine species richness (Figure 7.20d) showed a
weak trend of increasing with age (r2 = 0.38; p < 0.01).

 Frequency of occurrence of canopy tree species showed a weak trend with time
(Figure 7.21a). Canopy species frequency of occurrence increased with time (r = 0.42; p
< 0.01). The frequency of occurrence of vines (Figure 7.21b) also increased with time (r2
= 0.31; p < 0.02). There was a weak trend in the frequency of occurrence of early
successional subcanopy species (Figure 7.21c). Early successional subcanopy species
increased with age, showing a peak in frequency around age ten and then declining.
Shrub seedlings showed no trends with time in frequency of occurrence (Figure 7.2 Id).


Soil Trajectories

 The only soil parameter to show a trend with time was bulk density. Figure 7.22b
shows that about 35% of the variation in bulk density can be explained by age (r2 = 0.35,
p = 0.05).


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