constructed wetlands. Comparing species diversity on the hummocks to that found
elsewhere in a wetland provides information on the ability of hummocks to increase
vegetation diversity. Table 5.2 shows data for hummock and off-hummock species
diversity indices for the Agrifos, Cargill and Iluka wetlands. In each sampling period, the
number of species was greater on the hummocks than in the surrounding wetland areas.
At least 8 more species were found on the hummocks during every sampling period
except for the 9/13/99 sampling of the Cargill wetland where only 5 more species were
found.

 Shannon diversities were greater on the hummocks in all sampling periods. In
 every case except the first Cargill sampling, the Shannon diversity is considerably higher
 on than off the hummocks. Data for Shannon evenness show a different trend. The
 evenness is higher on the hummocks in the Agrifos wetland in each sampling period, but
 is lower on the hummocks in the other two wetlands indicating a dominance by a few
 species.

 Percent cover was lower on the hummocks in the Agrifos wetland in each
 sampling period. The same trend was found in the Iluka wetland for the first two
 sampling periods. The third period percent cover on the hummocks was higher than off
 the hummocks. Percent cover in the Cargill wetland was higher on than off the
 hummocks in all sampling periods.

 Community similarities between habitats on and off the hummocks are shown in
Table 5.3. Values can range between 0 and 1.0, with a value of 1.0 meaning that all
species are found in both communities. Values are shown for each hummock type versus
the off hummock community as well as for the hummock community as a whole versus
off hummock habitat. Values appear to get lower throughout the growing season possibly
following increasing water level. None of the Sorensen coefficients show a high amount
of similarity between the hummock and off hummock communities, as all values fall
between 0.25 and 0.7. The ranges indicate some similarity in the communities. Some
species are found both on and off the hummocks, but the majority are found in only one
of the two community types. Low community similarities also can indicate a large
difference in the species richness in the community types.


Tree Growth

 The ability of hummocks two provide better growing conditions for tree saplings
than found in other wetland locations provides another reason why hummocks may be
valuable when incorporated into constructed wetlands. Table 5.4 contains data for trees
planted on and off hummocks in the Agrifos and Iluka wetlands. F. caroliniana growing
in the Agrifos wetland appear to be taller on the hummocks than off the hummocks in all
cases except for the one tree growing in organic soil. The trees planted off the hummocks
appear to be larger in basal diameter than those growing on the hummocks. Cypress trees
planted in the Iluka wetland show a clear trend in growth. Those trees planted on the
hummocks have a considerably larger DBH than the trees growing off the hummocks
(3.36 to 1.78 cm).


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