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Wetland Succession

Plant diversity in the Point au Sauble lagoon, is heavily dependent on seasonal, annual, and long-term water level fluctuations. The Point has an inlet/outlet on it's southeast side which connects it directly to the bay, but isolates it from the heavy storm surges from the north. This connection to the bay allows for changing water levels to affect the plant diversity within the lagoon. Scroll down for a short explanation of the effects that fluctuating water levels can have on aquatic plant communities. It's important to remember that each change in the water cycle is accompanied by a new set of conditions that may or may not have occurred on the bay before. In addition, invasive species such as Reed Grass (Phragmites australis) or Purple Loostrife (Lythrum salicaria) may disrupt the successional stages that are listed below.

Wetland Plant Identification

This picture, taken in 1973, shows the large areas of open water that develop during periods of high water. The high water levels disturb the system enough to remove the persistent stands of Cattail (Typha spp.) and other more persistent wetland plant communities. The last high water stage occurred in 1997, and afterward water levels dropped very quickly.
The low water levels and mud flats (as shown on the right) are very important to overall wetland plant diversity. Most emergent plant species are dependent upon exposed substrate for germination. If low-water levels persist, annuals such as Bidens spp.and Scirpus spp. will quickly colonize the area. If water levels continue to decrease for an extended period of time, a shrub-carr system will develop. However, if water levels increase fairly rapidly, it will drown out most of the emergent seedlings and result in an open-water ecosystem.
Persistent low-water levels, such as those that occurred in 1999 and 2000, allow pioneer species such as Bidens spp., Scirpus validus, and Polygonum spp. to colonize an area. Their domination of a wetland is entirely dependent on fluctuating water levels. The large stand of Bidens spp. that you can see in the background will look much differently next year as the annual plants are replaced by the more dominant perennials.
The picture to the right shows one of the possible late successional wetland plant communities in the lagoon. What you see are large stands of Cattail (Typha spp.) with small pockets of open-water. This ecosystem will persist until the next high water system 'uproots' the Cattail from the bottom and removes it from the system. Extreme low-water periods could also select for shrubs such as Willow (Salix spp.) or Alder (Alnus spp.) to gradually outcompete the Cattail.

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