Wet Depressional Forest

Description

Northern white cedar and yellow birch often find their primary rooting substrate on downed woody debris associated with these openings. Both species regenerate well on mossy, rotting wood (i.e., nurse logs) that have consistent moisture (Smith, 2008 Erdmann, 1990; Johnston, 1990). Eventually, initial rooting media from downed woody debris can leave roots exposed to air and result in poorly formed trees. Northern white cedar can also regenerate by vegetation reproduction. These stems usually are developed from fallen trees and root from branches that come in contact with moist rooting media and are extremely shade tolerant (Erdmann, 1990). Hummocks and micro depressions resulting from windthrown trees are an important component of the Reference State. This variability in microsites provides opportunity for obligate wetland species in ponded micro depressions and facultative or even some upland species on the drier hummocks.

Submodel

Description

The Flooded State develops as a result of dammed or blocked waterways. Flooding and more permanent forms of inundation (i.e., ponding) are caused by either beaver activity or development associated with road building. Only drainageway landforms are affected, and isolated depressions do not go through this state. Sites that have blocked water drainage from roads may become perpetual open water wetlands. In natural settings, the Flooded State can last for many years, but it ultimately depends on maintenance of high quality habitat conditions for beaver to proliferate. Once a site is abandoned, dams will gradually decline and ultimately drain, thereby beginning the transition to the Inundated State.

Beaver populations in North America were drastically reduced by broad scale fur trapping during the Colonial time period, into the 1800s (Mitsch and Gosselink, 2007). As a result, natural conversion of these sites to the Flooded State may be less common today than it was prior to European settlement.

Submodel

Description

Sites can transition to this state by relatively sudden and complete loss of the tree canopy, thereby losing the transpiration of water from trees that would normally occur later in the growing season to keep water tables at bay (i.e., drawdown; Slesak et al., 2014). This can happen as a result of intensive logging, forest pests, or general forest decline. Since water tables on these sites mimic annual rainfall graphs, the primary change in hydrology occurs later in the growing season, when overstory tree species would normally be causing drawdown in the Reference State. This state will likely become very common in this MLRA if the invasion of the exotic and completely destructive emerald ash borer beetle is not halted (Slesak et al., 2014; Palik et al., 2012). Plant community species composition will shift from primarily facultative wetland species to primarily obligate wetland species, such as lake sedge (Slesak et al., 2014).

Other than a few scattered trees, these sites do not seem to regenerate forests well. The probability of transitioning to the Reference State is largely unknown; it will probably require many decades to produce a closed canopy forest again. There is limited evidence that these communities succeed to a forested structure within a reasonable time frame (SNF, unpublished report b), but non-forested wetland conditions may persist for decades, and even centuries (Naiman et al., 2005; Terwilliger and Pastor, 1999). Viability of black ash seeds is only 8 years (Wright and Rauscher, 1990), so that initial seedbank is extirpated from the site. And since most sites are small and isolated, there may not be a reliable seed source nearby. The loss of important mycorrhizal relationships is also likely to impede succession to forest trees. It has been shown that long-term flooding kills symbiotic mycorrhizae; these fungi form essential relationships with tree species on most ecological sites, forested wetlands included, and recolonization following draining may be inhibited (Terwilliger and Pastor, 1999), which is likely the case on this ecological site as well. All of the aforementioned factors, in combination with extreme competition for light, nutrients, and growing space with fibrous rooted resident vegetation, make succession to a forested state very difficult.

Submodel