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The effects on non-vegetated wetland types have often been overshadowed by losses to vegetated wetland areas, but these wetlands provide crucial habitats for a variety of coastal bird species, including pelicans, cormorants, gulls, terns, and roughly 50 species of sandpipers, plovers, and their allies known as shorebirds. (Harrington and Corven [no date]) have described shorebird guilds, enumerating species and habitat types.) Some of these bird populations are at risk because of their dependence on narrow ribbons of marine and estuarine tidal habitats that are subjected to rapid and unpredictable changes resulting from coastal storms, habitat alteration by man, and other changes in marine ecosystems that can affect the availability of marine invertebrates (a food resource), water temperature, nutrients, and phytoplankton. Rising sea levels are expected to continue to inundate or fragment low-lying coastal areas including sandy beaches, barrier islands, and mudflats that support sea and shorebirds dependent on marine waters (North American Bird Conservation Initiative [NABCI] 2010).
Most recently, tidal beaches, shoals, bars, and barrier islands along the northern Gulf of Mexico were exposed to the impacts from the Deepwater Horizon oil spill. Although data on any wetland losses resulting from that event are not included in these results, the incident served to highlight the ecological and economic importance of these marine and estuarine resources.
Freshwater Emergent Marshes
The acreage of freshwater emergent marsh increased by an estimated 1.0 % between 2004 and 2009. There was a net gain of an estimated 267,800 acres (108,400 ha).
These gains resulted principally from wetland reestablishment or creation on upland agricultural lands and lands of other unspecified land use (primarily idle or set-aside lands with no discernible land use type). There were an estimated 367,000 acres (148,600 ha) of freshwater marsh gain from these two upland land use categories and these findings coincided with estimates that more than 59 % of wetland gains occurred Chapter 3 – Texas Wetlands Texas Outdoor Recreation Plan on agricultural lands between 1997 and 2007 (USDA 2010). Although freshwater marshes sustained some losses to urban and rural development (collectively 17,200 acres or 7,000 ha) and silviculture operations (28,500 acres or 11,500 ha), the increases noted above resulted in a net gain in acreage. Some of the gains in wetland emergent also came from areas previously classified as forested wetlands. If forested wetlands were clear cut but the hydrology remained, they were reclassified as emergent wetland. An estimated 421,000 acres of forested wetland were changed to emergent wetlands between 2004 and 2009.
Freshwater Shrub Wetlands
Freshwater shrubs increased in area by an estimated 180,100 acres (72,900 ha). This net gain came primarily from freshwater emergent wetlands. Shrub wetlands were composed of true shrub species as well as tree saplings less than 20 ft. tall (6 m). Many wetlands classified as shrub were located in areas of active silviculture management.
Consequently, wetland shrub areas that contained tree species have been subject to substantial change corresponding to managed forest harvest rotations as seen in longer term trend information.
There was relatively little natural succession of shrub wetlands leading to mature forested wetland as originally envisioned by Cowardin et al. (1979). Small pine trees as part of managed pine plantations matured to become larger pine trees in areas that retained wetland hydrological characteristics. These areas become economically mature and are used for their wood products before they become ecologically mature (deMaynadier and Hunter 1995). An estimated 142,600 acres (57,730 ha) of freshwater shrub wetland were lost (drained or filled) to become upland silviculture between 2004 and 2009.
Freshwater Forested Wetlands
Between 2004 and 2009, forested wetlands declined by an estimated 633,100 acres (256,320 ha). Forested wetlands experienced the largest change in area of any wetland type and reversed a trend where area had increased in the previous two eras of monitoring. Urban and rural development accounted for 26% or an estimated 102,400 acres (41,460 ha) of the forested wetlands losses to uplands. This area represented irreversible losses as wetlands have been filled, drained or otherwise developed for buildings or other support infrastructure. Historically, once these areas have been developed there is very little opportunity for wetland reestablishment and even less chance of successfully restoring mature forested wetlands.
An estimated 149,500 acres (60,500 ha) of forested wetland were lost to silviculture.
Although the tree removal process itself did not constitute wetland loss, a number of activities related to the timber removal resulted in more permanent changes. Some activities associated with forest plantations involved intensive site preparations and timber stand management practices that altered or eliminated site hydrology. Many of the forested plantations in the southeastern United States are even-aged stands
Texas Outdoor Recreation Plan Chapter 3 – Texas Wetlandsdominated by a single species of conifer, typically loblolly pine (Pinus taeda), (Miller et al. 2003). It has been estimated that loblolly-shortleaf pine forests cover 55 million acres in the southern states (Smith et al. 2009). By design, these plantations had relatively low diversity (deMaynadier and Hunter 1995) and specific management practices included clear cutting, stump and woody debris removal, ditching, drainage, and bedding. Specific actions that were deleterious to wetlands included construction of forest roads required to access cut timber sites (deMaynadier and Hunter 1995; Harms et al. 1998); installation of drainage ditches through a wetland (Sharitz and Greshan 1998; Wear and Greis 2002); bedding of sites; subsurface drainage; and levee construction, filling, and channelization.
Emerging Wetland Conservation Issues [Adapted from Dahl, T.E. 2011. Status and trends of wetlands in the conterminous United States 2004 to 2009. U.S. Department of the Interior; Fish and Wildlife Service, Washington, D.C. 108 pp.] Climate Change The analysis of climate change related impacts to natural resources and the potential responses to those impacts has become a priority for Federal agencies to address (U.S.
Department of the Interior 2009). Due in part to their limited capacity for adaptation, wetlands have been considered among the ecosystems most vulnerable to climate change (Bates et al. 2008). Because wetlands support a number of trust species and have been linked to water quality and other environmental values, their susceptibility to climatic changes are important to a number of federal and state agencies.
Direct and indirect environmental changes and related impacts resulting from climatic changes have been recognized and widely accepted by the scientific community (Twilley 2001; Field et al. 2007; Nicholls et al. 2007). The USEPA (2010e) identified erosion, water quality, salt water intrusion and changes in salinity, species composition, and wetland distribution as likely conditions exacerbated by climate and sea level changes. Some of these changes have the potential to influence all wetland types and biota. For example, increases in water temperatures as a result of climate change will alter fundamental ecological processes and the geographic distribution of aquatic species (Poff et al. 2002). Similarly, predicted changes in temperature and rainfall will likely reduce habitats vital for waterfowl species and many other wetland birds (NABCI 2010).
Deciphering how and if those changes manifest themselves on the landscape presents challenges for recognizing and following wetland ecosystem adaptations or modifications. This has been further complicated by several factors including decadal or cyclical change, and human induced changes to wetlands and surface waters that mask climate change effects on the landscape (e.g., increased level of farming of drier, shallow wetland basins). In addition, some important changes to species health or Chapter 3 – Texas Wetlands Texas Outdoor Recreation Plan distribution may go unrecognized by landscape or land use level survey techniques (e.g., disappearance of cold water fish species from their current geographic range).
Recognition of the increased or decreased occurrence and duration of water retention, depth, vegetation patterns, stress responses and community structure may require a refined suite of observables not yet fully understood. There has been acknowledgment that a major challenge of addressing climate change effects on wetlands involves identifying and addressing uncertainty in understanding how that change will affect ecological systems (USFWS 2010).
Wetlands are water dependent and many of the benefits they provide to fish and wildlife species (vegetation for food or cover, nesting and resting habitat, breeding grounds and water) are dependent on precipitation, and other surface and groundwater sources.
Changes in climatic conditions that affect water conditions (wetter, drier, more saline, etc.) will have a substantial impact on species that utilize wetlands and other ecological services wetlands provide, or make efforts to reestablish wetlands more challenging.
Climate change also may influence wetland habitats indirectly such as altered fire regimes, changes in farming techniques and duration, or changes in population concentrations and development patterns.
Researchers have pointed to some types of wetlands that may be particularly vulnerable to the effects of climate change (Guntenspergen et al. 2002; Johnson et al.
2005; Kirwan et al. 2010). Winter (2000) indicated that the wetlands most vulnerable to climate change are those dependent primarily on precipitation for their water supply.
These habitats are generally isolated either by lack of hydrological connectivity or by the uniqueness of community assemblage and structure. This makes adjustment to climate change in these areas unlikely and these wetlands face more immediate threats with little chance for adaptation.
In coastal regions such changes may include variations in ocean and air temperatures, acidification, increases or decreases in freshwater runoff (Kling and Sanchirico 2009), changes in species distribution and diversity, erosion of coastal sediments and beaches, inundation of coastal wetlands, increasing salinity of some brackish or freshwater systems, and increased storm frequency and intensity. Sea level rise is expected to have a large, sustained impact on future coastal evolution (Beavers 2002).
Changes in Sea Level and Coastal Processes
There is strong scientific consensus that climate change is accelerating sea level rise and affecting coastal regions, however, many researchers point to the uncertainties associated with predicting the response that increased sea level will have given other coastal processes and interactions (National Academy of Sciences 2008; Lavoie 2009).
Sea level rise directly threatens coastal infrastructure through inundation, increased erosion, more frequent storm-surge flooding, and loss of habitat through drowned wetlands (NOAA Congressional Budget Hearing 2009).
Texas Outdoor Recreation Plan Chapter 3 – Texas WetlandsCoastal habitats will likely be increasingly stressed by climate change impacts that have resulted from sea level rise and coastal storms of increasing frequency and intensity (Field et al. 2007). The difficulty in linking sea level rise to coastal change stems from shoreline changes not solely the result of sea level rise (Lavoie 2009). Natural and physical processes that act on the coast (e.g., storms, waves, currents, sand sources, sinks, relative sea level), as well as human actions that affect coastal processes in both the saltwater and freshwater systems, (e.g., development, dredging, dams, coastal engineering and modification), all have contributed to coastal changes.
In the conterminous United States, the Gulf of Mexico and mid-Atlantic coasts have experienced the highest rates of relative sea level rise and recent wetland loss (NABCI 2010). Stedman and Dahl (2008) found that in addition to the wetland losses already recognized, climate change models project additional wetland degradation in coastal areas as sea level continues to rise throughout this century. This trend has presented long-term challenges to managing and monitoring wetlands that abut the coast in coming decades.
Inundation of coastal wetlands by rising sea levels threatens wetland plants; particularly those not able to adjust to higher salinities or increased wave or tidal energy. For many of these systems to persist, a continued input of suspended sediment from inflowing streams and rivers is required for soil accretion (Poff et al. 2002). Migration or movement of coastal wetlands may offset some losses. The construction of levees and flood protection infrastructure may put some wetlands at additional risk by restricting water flow, sediment, and nutrient inputs.
Coastal development, urbanization, and infrastructure to support tourism throughout the coastal watersheds have an increased cumulative effect on the loss and modification of freshwater and estuarine wetland habitats. With continued growth and development, more shorelines have been cleared and stabilized, shallow waters dredged for navigation channels and marinas, wetlands filled and channelized, and land surfaces paved for buildings and parking lots (Riggs and Ames 2003).
Data from this study and others show that beach erosion due to sea level rise has increased along certain shorelines. This has constrained coastal plants to narrow stretches of beach and resulted in a breakdown of the succession processes that have been important for dune building, sediment binding, and reduction of erosion (Feagin et al. 2005).