Northern Backswamp - PROVISIONAL

Description

Perhaps no other landform or ecological system conjures such strong images of the Southeast than the iconic backwater alluvial swamp forest. Towering cypress and broad buttressed tupelo trees provide deep shade over the calm waters that “feed” this venerated system. Yet, this ecological site has experienced tremendous impacts from a variety of activities and uses over the past few centuries. Among the most irrevocable impacts is the draining of these low-lying landforms and converting them to completely different uses. Additional impacts include the disconnection of this site from the rivers and streams that developed it through channelization and levee construction. Therefore, reference conditions for this site are modeled after existing swamps within naturally meandering and free-flowing stream systems.

A key characteristic of this ecological site is periodic flooding that generally occurs on a frequent basis. Flood duration of this site may vary by location, landform within the floodplain (e.g., linear slough, lake-edge oxbow swamp, etc.), stream size, and the extent of the drainage basin. In general, flood duration on this site is very long, lasting most if not all of the growing season. Plants that can withstand such long term inundation and such extreme anoxic conditions are relatively few. Two species that can withstand these conditions often co-occur and form the characteristic and dominant natural vegetation of this site, bald cypress and water tupelo. Dominance by either or both of these species and additional associates, such as swamp tupelo, may vary by location and across a range of local hydrodynamics. For instance, swamp tupelo may co-occur with water tupelo along the shallower margins of some sites, or the former may be dominant in smaller stream systems and in the upper reaches of local watersheds. Yet, water tupelo may be the dominant species in some sites and cypress forming an almost monoculture in other locations (Eyre, 1980). Determining the causes of these varying patterns are not always clear, but some dominance patterns may have explanations associated with former disturbances and/or land use actions.

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Description

This state is characterized by the regeneration or regrowth of a pre-existing forest stand following a major, stand-replacing disturbance. Scale of the disturbance is at the stand level and is greater than one acre in size (Johnson et al., 2009). Potential types of disturbances include catastrophic windstorms, silvicultural clearcuts, and particularly destructive ice storms. Fire may be an additional disturbance, although fire in this hydric system is considered to be very rare (Conner and Buford, 1998; Mitsch and Gosselink, 1993). The resulting even-aged stand (or single-cohort) is set on a new course of development, which is highly dependent upon several critical factors including: the composition and structure of the stand prior to the disturbance; the degree or intensity of the disturbance; size and configuration of the disturbed area (Oliver and Larson, 1990); and sedimentation or deposition rates into the site (Hodges, 1997).

Following the destruction of the overstory, a series of seral stages or community transitions and transforms will occur. Depending on water depths and length of the hydroperiod, a predominantly open herbaceous marsh with a secondary shrub-scrub component may represent the first major stage. Later stages will include a predominant small tree – shrub component followed by a transition to young wetland forest. The rapidity or length of these major transitions (seral stages) again, depend directly upon flooding frequency and duration.

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Description

This state represents the breadth of forest management activities on this site. Various management or silvicultural methods can lead to very different structural and compositional results within a managed stand. The range of methods are diverse and include even-aged (e.g., clearcut and shelterwood) and uneven-aged (single tree, diameter-limit, basal area, group selection, etc.) approaches. Included within these methods is an option to reduce competition and achieve maximum growth potential of the desired species. Inherently, these approaches result in different community or “management phases” and possibly alternate states, depending on local floodplain dynamics. This state, as indicated, occurs within floodplains that have not been modified through drainage, channelization, or levee construction.

A major limitation of this site is frequent flooding and ponding over long to very long durations. Management activities may need to be adjusted to accommodate those natural conditions. Care should be taken on this site to avoid unscrupulous impacts to the soils and natural vegetation during management and extraction activities.

Finding the appropriate approach for a given stand and environment necessitates close consultation with trained, experienced, and knowledgeable forestry professionals. If there is a desire to proceed with this state, it is strongly urged and advised that professional guidance be secured and a well-designed silvicultural plan developed in advance of any work conducted.

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Description

Forests in this state have undergone repeated select harvests over time. Actions leading to this condition consist of removing the biggest and best trees of the most desirable species and leaving low-quality trees (damaged and deformed) and undesirable species. This action, conducted repeatedly, can cause tremendous shifts in species composition and can decrease the vigor and health of the residual stand. Without implementing carefully prescribed management actions, species composition of extreme high-graded stands may remain in a highly altered condition for many decades, even after large, stand-replacing disturbances resets “successional opportunity.”

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Description

This state is included and intended to capture the range of modifications to the natural hydrology of this site. The largest and most significant alteration to this site has been channelization and levee (or spoil bank) construction. Such hydrologic alterations have become the norm for floodplains in MLRA 134. This action results in a disconnection between the stream - floodplain environment, which interrupts and alters the ecological processes and functions of the system as a whole. Mitsch and Gosselink (1993) noted that the productivity of swamps were inextricably linked to the local hydrologic conditions. Sites that exhibited the greatest productivity were associated with a pulsing hydroperiod – one directly associated with seasonal overbank flooding followed by a period of drier conditions. Sites that had the poorest productivity were drained areas and/or swamps that were continuously inundated. This is particularly concerning for alluvial swamps that have become disconnected from the associated stream or river through channelization and levee construction. When periodic flooding of an alluvial river swamp is prevented, nutrient rich sediment that is so important to the system may be reduced or halted altogether. In cases where inundation is retained due to artificial means or through the actions of beaver, these continuously flooded low spots may stagnate, which ultimately decreases productivity and limits germination and future stand recruitment.

Categorizing all modified sites as non-functioning is altogether inaccurate. There are many altered floodplains that still support exemplary stands of southern bottomland hardwoods, and those areas provide numerous resources and incredible benefits. Managed and water-manipulated back-lying swamps and inundated wetlands provide habitat for numerous wildlife species as well as some State-protected rare, threatened, and endangered plants. Because the vast majority of floodplain environments, including backswamps, have incurred some form of modification, the various altered states and major uses warrant recognition. Tremendous conservation benefits can be established in many of these altered areas.

The altered hydrology state is “provisionally” included here to begin the process of gathering and tracking additional uses of this site where the natural processes have been modified. Future iterations and inventories should provide full description of the various uses and the conservation measures and actions that are applicable to this site.

Of note, a restoration or return pathway from this state to reference conditions is not provided. Too few evidences exist where channelized, leveed, and/or drained backswamps have been restored to the historic, natural hydrodynamics and hydroperiod. However, examples may exist and restoration seems plausible. Wetland environments can be forgiving following former disturbances and modifications. However, the time period required before reference conditions of the bald cypress – water tupelo swamp is realized could be exceedingly long with much management effort involved. Successful restoration ultimately depends on the level of degradation and disruption of a given site.

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