This swamp milkweed (Asclepias incarnata) is one of the summer-blooming native wildflowers used in the wetland restoration project. (photo credit: Paul Meyer)

 

What is a "wetland", anyway?  A wetland is a plant community that is defined by the presence of water, either at the surface or just beneath the surface of the soil, for at least part of the year.  The wetland that has been constructed at the Arboretum contains water all year long, unless there has been a serious drought.  Much of the wetland is "squishy" and if you walked in it without boots or waders, your feet would get wet.  Certain kinds of plants, called obligate wetland species, thrive in this kind of soggy soil, and are not found in drier locations.  Other plants, called obligate upland species, cannot grow at all where the soil is so wet.  Some plant species, called facultative wetland species, can actually grow in soggy soil as well as in drier soil.  All three of these types of plant can be found in or near the wetland at the Morris Arboretum.  (You can see a partial plant list from the wetland.)

This snake was photographed swimming to shore. (photo credit: Brice Dorwart)

 

Together with the animals that inhabit the wetland, the plants help to form a diverse community which is intended to emulate the natural ecosystem that was originally found in this location before the land was converted to pasture for livestock in the early Twentieth Century.  Wetlands are just one of the managed land uses demonstrated at the Arboretum.  In the Wissahickon Valley, wetlands help to clean Philadelphia's drinking water, and retain flood water during storms.

Many of the plants that can be found in the wetland are native to the area, and are encouraged to grow there by the horticulture staff and volunteers at the Arboretum.  Native wetland plants are an essential part of the local ecosystem, and provide food and habitat for native birds, amphibians, and insects that require wetlands to live.   Some plants are considered weeds, and are intentionally removed.  Many of these weeds are invasive, which means that they can quickly take over an area by out-competing the plants that are already there.  Invasive plants can dominate a plant community by producing large amounts of seeds quickly, or by spreading by root runners, effectively cloning themselves many times over.  Some of the invasive plants that have become a nuisance at the Arboretum's wetland are also not native to the area, which adds to their competitive edge over native plants, because often the animals living here do not (or cannot) eat them.  These exotic species are either descended from horticulturally grown plants, or from seeds that were imported accidentally by people.  Either way, invasive exotic plants quickly take over land that is not tended by people (and sometimes land that is tended), especially land where the soil or existing plant life has been disturbed in some way.  The problem of invasive exotic plants is fairly common near cities in the United States, and is becoming more common all over the world.  The most problematic weeds in the Morris Arboretum's wetland are cat-tails (Typha sp.), common reeds (Phragmites australis), and purple loose-strife (Lythrum salicaria).  A fairly recent noxious weed to show up at the wetland is goat's rue (Galega officinalis), and efforts are under way to try to eliminate this plant entirely from the Arboretum before it can become widespread.

The major work for the wetland restoration project was done in the autumn of 2001, but more native trees and shrubs are planted each spring.  Click here to see photos from the construction; click here to see comparison photos from the project before, during, and after.

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