Environmental Engineering Reference
In-Depth Information
Fig. 5.1 The National Wetlands Inventory map of an estuarine system in Maine. Information
includes dominant system (e.g., palustrine, estuarine), vegetation life form (e.g., shrub-scrub,
emergent, forested), and limited detailed subclass modifiers (e.g., evergreen type, inundation
permanence, and some water chemistry information)
simply use the inventory as a starting point for site visits. In any case, it is critical to
keep the purpose of your study in mind while selecting wetlands and to avoid
“reinventing the wheel” when possible.
Questions to ask yourself when choosing wetlands:
1. Is it important to have an unbiased sample of wetlands?
2. Is it important to identify representative or reference-type sites using profes-
sional judgment?
5.2.2 Where in the Wetland?
With some exceptions, (e.g., monocultures or some large peatlands), wetlands tend
to have highly heterogeneous vegetation. This heterogeneity is often due to hydro-
logic differences at multiple different scales within the wetland. For example, some
wetlands have distinctive bands, or zones of vegetation corresponding to large-scale
hydrologic gradients (Fig.
5.2a
). Each of these zones could be considered a differ-
ent community within the wetland. Within each zone, vegetation can be further
influenced by microtopographic features such as hummocks, tussocks, deep holes,
or trees (Fig.
5.2b
, (Ehrenfeld
1995
)). Disturbance factors, such as herbivory,
pollution, fire, or animal trails can lend further heterogeneity to vegetation, often
in less predictable patterns.
Wetland vegetation heterogeneity can initially be explored using high-quality
aerial photography, which can provide a good idea of large-scale patterns. This
