Approach
Diverse communities may be less vulnerable to climate change impacts because risk is distributed among multiple species. In a changing climate, conditions may change and some species at the southern extent of their range or with a narrow tolerance to edaphic conditions may be vulnerable or lost. One can diversify a site's flora by simply increasing the base number of species, or one can diversify the plant traits represented by various species). These plant traits may reflect diverse life histories, ecological niches, and phenologies. This ‘functional redundancy’ allows fluctuations of favored species and guilds in response to climate variations and other disturbance factors and ensures that all microhabitat niche are occupied at all times, thus maintaining ecosystem services (e.g., securing substrates) and limiting non-native species invasions. Recruitment of these diverse species and functional groups may be impacted by climate change as changing precipitation patterns and rising temperatures can affect seed dormancy, germination, and seedling survival. Wetlands also rely heavily on robust and diverse soil seed banks to ensure consistent vegetative cover as water levels and soil moisture fluctuate, and as plant assemblages shift in response to disturbance such as muskrat herbivory. Early spring warming, poor synchronization between seedling emergence and precipitation, heavy precipitation and prolonged inundation may lead to seedling mortality and exhaustion of a wetland’s soil seed bank, while increasing sedimentation can bury wetland seed banks to the extent that native species are lost. Promoting a soil seed bank with species that have diverse germination strategies will build resiliency into wetlands.
Tactics
- Increase the number of native species in wetland plant mixes or in established wetlands to increase the odds that a high number of native plants will occupy all microhabitat niches under variable and changing environmental conditions.
- Adjust species lists for inclusive representation of various life histories, wetland rankings (FACW, FAC, OBL; USACE 2016), seed germination strategies and phenologies that enhance plant trait diversity of wetland planting mixes or existing sites.
- Release existing wetland seed banks, e.g., by restoring historic water levels, or by removing legacy sediment overlying the original substrate.
- Favor and restore native species local to a given wetland that are most likely to be to be adapted to future conditions, e.g., avoid species that are at the southern edge of their range.
- In low-diversity plantings or degraded wetlands, interseed following prescribed burns to boost diversity.
- Maintain and enhance microsite complexity and heterogeneity by burning, mowing, or planting in irregular patterns and by establishing rotational management units.
- Promote phenological diversity by conducting prescribed burns in different seasons.
- Restore tussock sedge (Carex stricta) in degraded wet meadows. Tussocks provide microsite complexity and thus contribute to floristic diversity.
Strategy
Strategy Text
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.