Maintain and restore wetland structure

This approach addresses the importance of maintaining and restoring wetland structure to support ecosystem processes such as soil microclimate, light regime, moisture regime, and fire regime. Wetland 'structure' is characterized by how the various physical elements of a given wetland (e.g., trees, shrubs, herbs, substrate microtopography) are arranged both horizontally and vertically. Changing precipitation patterns and increased evapotranspiration rates are anticipated to decrease water levels in some wetlands, favoring woody species invasion and spread. Woody species (both native and non-native) can exert significant influence on the plants that grow beneath them by competing for light, water and nutrients. The cool, moist microclimate that they create can also alter fuel characteristics and fire behavior for prescribed burns. Higher evapotranspiration rates associated with woody species invasions can also contribute to altered water budgets. Conversely, flooding and elevated water levels can cause mortality of woody species, leading to conversion of shrub-dominated wetlands to open wetlands. Where feasible, maintaining historic proportions of herbaceous to woody species in open wetlands will support a diverse herbaceous flora and associated fauna, and will keep more options open for using prescribed fire as a management tool. In some situations, allowing open wetlands to convert to shrub-dominated or forested wetlands may be the only feasible scenario if management options are limited; in these cases, controlling the trajectory of change will be the priority. Microtopography plays an important role in community structure and resilience to changing environmental conditions. For example, microtopographical variation promotes species richness in sedge meadow and minerotrophic peatlands; it also confers resilience to fluctuating moisture levels by expanding available microsites for plants. Increasing sedimentation associated with changing precipitation patterns can reduce or eliminate this microtopography, facilitating invasions of non-native plants such as reed canary grass (Phalaris arundinacea) and lowering native species richness and diversity.

This strategy addresses the strong influence of plant community structure and composition on wetland ecological integrity and function, and outlines approaches that managers can take to resist climate change influences and build resilience into the sites that they manage through purposeful vegetation management. Wetland plant communities have evolved over millennia as dynamic systems that respond to a range of natural disturbance regimes. Changes in precipitation and temperature regimes may push these plant communities outside of their natural range of variability, resulting in changes in plant community structure and composition. For example, changing precipitation patterns and evapotranspiration rates are anticipated to decrease water levels in some wetlands, favoring woody species growth. In fire-dependent wetlands, wetter springs and prolonged droughts may present new challenges and opportunities for conducting prescribed burns, which can further influence community composition and structure. Increasingly frequent and intense floods may scour wetland substrates and vegetation, rendering them vulnerable to non-native invasives. Early spring warming, poor synchronization between seedling emergence and precipitation, and prolonged inundation may lead to seedling mortality and exhaustion of a wetland’s soil seed bank. Increasing sedimentation associated with increasing precipitation and intense storm events can also bury wetland seed banks to the extent that native species are lost. In identifying approaches that bolster wetland plant community structure, managers will need to consider tactics that reduce imbalances in species dominance (e.g., woody or invasive species encroachment) and altered microtopography. Approaches relating to plant community composition emphasize limiting invasive species while maintaining and promoting taxonomic and functional diversity of native species and seed banks that are adapted to current and future conditions. Applying fire where appropriate will further support efforts to achieve target community structure and composition. Managing for diverse wetland plant communities with intact structure will promote resistance to invasions, support vegetative flexibility as environmental conditions change, and provide habitat for broad suites of fish and wildlife species.