up:: [[CKLA400 - Ecology and Sustainable Landscapes]] tags:: #source/course #on/design #on/landscape_design # CKLA400 M8 - Wetland Restoration in Severn Creek Watershed Case Study The focus is on the restoration of wetlands in a natural ravine in Toronto known as Severn Creek, encompassing various reaches such as Rosedale, Severn, Nordheim, and Cedarvale. While Severn Creek has been containerized as a storm sewer in its lower portions, the upper reaches feature naturalized areas, particularly wetlands. Some wetlands arose naturally post-excavation for the Spadina subway, while others were *deliberately constructed to manage surface runoff into the ravine*, serving as examples of fostering resilience in an urban context for sustainable landscape ecosystem management. ## Species Composition in the Historic Severn Creek Watershed Three wetland restorations in the Nordheim Reach of Severn Creek were established on shallowly sloped terraces with clay and silt soils, originally mown grass areas. The first restoration, downstream (wetland 3), was followed by the middle one (wetland 2) and finally the upstream, most extensive restoration. These areas were transformed into pocket wetlands due to the continuous moisture in the soil, making grass maintenance challenging. The regrading of the ground created naturalistic basins filling with spring meltwater but no standing water later in the year. These wetlands boast a high species richness from native woody and herbaceous plants, including both introduced and volunteer species. **Key Points:** - Restorations started in the mid-1990s, beginning with downstream wetland 3, followed by wetland 2 and the most upstream extensive wetland. - Ground regrading allowed for naturalistic basins filling with spring meltwater but no standing water later in the year. - High species richness from native woody and herbaceous plants, including introduced and volunteer species. The species richness and development of spatial structure in these small wetlands are notably high, fostering functional connections between the populations due to their proximity. The staggered restoration process introduced age diversity into species populations. Dominant tree and shrub species like Black Willow, Trembling Aspen, Red Maple, and others, along with herbaceous species like Cardinal Flower, Orange Lily, and more, contribute to the diverse plant community. While some species were introduced as part of the restoration, others naturally seeded in from the ravine, enriching the overall ecosystem. **Key Points:** - High species richness and spatial structure development due to close proximity and staggered restoration. - Dominant tree and shrub species include Black Willow, Trembling Aspen, Red Maple, Speckled Alder, etc. - Introduced herbaceous species like Cardinal Flower, Orange Lily, and naturally seeded species like Silver Maple, Cat-tail, etc., enrich the ecosystem. The resulting plant community is both structurally and spatially rich, contributing to the transition of wetlands into wet woodlands with diverse species representation. The clonal nature of introduced plant species ensures genetic uniformity within each species. ### Indicators of Ecological Resilience Three wetland restorations are being monitored for ecological indicators of resilience, particularly focusing on seral structure and dynamics. Key indicators of resilience include *high species richness, complex spatial physical structure, and an age-diverse species population*. However, there are concerns about genetic shallowness in introduced plant species, which can hinder resilience. **Key Points:** - **Indicators of Resilience:** High species richness, complex spatial physical structure, age-diverse species population. - **Concerns:** Genetic shallowness in introduced plant species. Seral dynamics play a crucial role in assessing ecological resilience. Key processes indicating resilience include stable water table annual fluctuation within a small range, balanced runoff release in restored wetlands, and significant decline in soil erosion rates linked to runoff. The presence of complex and robust arthropod and songbird populations, sustained by fruit and seed production from wetland plants, further indicates ecological resilience. Songbirds facilitate gene flow among habitats, enhancing overall resilience by limiting the spread of invasive species like Purple Loosestrife and Norfolk Reed. **Key Points:** - **Seral Dynamics:** Stable water table fluctuation, balanced runoff release, reduced soil erosion rates. - **Faunal Populations:** Complex arthropod and songbird populations sustained by wetland plants. - **Gene Flow:** Facilitated by songbirds, limiting invasive species spread. These indicators collectively showcase the success of wetland restoration efforts in fostering ecological resilience, emphasizing the importance of diverse species populations, stable hydrological processes, and interconnected habitats facilitated by key species like songbirds. ### Disturbance and Perturbation Regimes The behavior of wetland restorations in their initial years is characterized by wide oscillations, especially due to introduced plant species' unpredictable responses to soil moisture conditions. Some species exhibit poor growth initially but thrive later, while others grow rapidly before stabilizing to a core population. Competition among and between species must resolve before reliable change patterns emerge. Disturbances like prolonged drought during hot summers or snowless cold winters can reduce population sizes or individuals' robustness, altering reproductive behaviors and community structure. Different wetlands respond uniquely to drought due to varied hydrological regimes, contributing to overall group resilience against such disturbances. Flood risk is low due to stormwater diversion, with potential impacts on species preferring drier soil and soil-dwelling arthropods and vertebrates. Extreme winter conditions disrupt plant reproduction and insect populations, affecting population viability. **Key Points:** 1. **Wetland Restoration Dynamics:** - Initial years marked by wide behavioral oscillations. - Introduced plant species react unpredictably to soil moisture. - Growth patterns vary from poor to vigorous over time. - Competition within and between species determines stability. 2. **Disturbances and Impact:** - Prolonged drought and snowless cold winters reduce population sizes and reproductive vigor. - Different wetlands respond uniquely to drought based on hydrological regimes. - Flooding risk is low but can affect species preferring drier soil and soil-dwelling organisms. - Extreme winter conditions disrupt plant reproduction and insect populations, affecting viability. 3. **Community Resilience and Changes:** - Three wetlands' unique responses to drought enhance overall group resilience. - Major storm events disrupt breeding cycles for arthropods and birds. - Frequent spring frosts reduce reproduction in early flowering trees and shrubs, impacting population size. 4. **Species Dynamics:** - Species like red-berried elderberry and flowering raspberry show resilience and spread through seed dispersal by songbirds. - Insect populations and woody plants can suffer damage from extreme winter conditions, affecting reproduction and population viability. These points capture the nuanced dynamics of wetland restorations, their responses to disturbances, and the resulting impacts on species and community structures.