NHS2022_TRCA

Description TRCA's Updated Natural Heritage System continues to build on the systems thinking and the guiding principles of the Terrestrial Natural Heritage System Strategy (TRCA 2007). It encompasses technical updates to the data and methods behind delineation of the target NHS to incorporate the latest science on integrated natural systems, especially in urban and near urban areas. This includes expanding the scope of the target NHS (i) to include terrestrial as well as aquatic and hydrologically important areas, and (ii) to consider contribution of existing and potential natural cover as well as contributing areas in the built portions of the landscape. In total, 36 criteria (and an additional cost parameter) were used in the Marxan analysis. Marxan is a science-based approach that aims to solve the minimum-set problem to include a certain amount of features (e.g., ecological) for the smallest possible cost to conservation targets for its reserve selection (Possingham et al. 2000). Criteria for the reserve selection process were based on the Provincial Policy Statement (2020) NHS defined by natural heritage features that are needed to support biodiversity, natural functions and terrestrial and aquatic ecosystems. The Natural Heritage Reference Manual (OMNR 2010) and Provincial Policy Statement (2020) defined natural heritage features including wetlands, wildlife habitat, woodlands, and valleylands for their environmental and social values as a legacy of the natural landscapes of an area. Eight criteria defined the locked-in criteria where the value was assigned that such significant natural features are automatically included in the final scenario solution. Criteria were ecological and natural heritage features within 1-hectare hexagonal planning units. Marxan sets the proportion of representation for each criterion to be included in the solution, which were set based on the amount of locked-in criteria and then any additional amount would be included with the proportion of representation of criteria. Th