Herbarium Records Reveal Hidden Gaps in Prairie Sedge Conservation

More than half of the rare sedge species in Saskatchewan have never been recorded inside a single protected area, according to a new conservation assessment of the genus Carex in the province. The study, which drew on thousands of georeferenced herbarium specimens, found that 12 of 21 rare sedges, or 57.1 percent, have no documented occurrences within Saskatchewan’s Protected and Conserved Areas Network, while another five species are known from only one protected area. Only one species, C. garberi, was recorded in three protected areas, making it the most protected sedge in the provincial network.

The research team assembled occurrence records for 105 Carex species present in Saskatchewan, combining data from the Global Biodiversity Information Facility with the Flora of Saskatchewan Association dataset, which includes material from the W.P. Fraser Herbarium at the University of Saskatchewan. Specimens from major herbaria across North America contributed to the pooled dataset, including collections held by the Canadian Museum of Nature, the New York Botanical Garden, the Smithsonian Institution, McGill University, the University of Alberta and the University of Michigan. After taxonomic verification against the Database of Vascular Plants of Canada and the Plants of the World Online database, and after filtering out records lacking coordinates, unclear identifications or duplicated points, the researchers validated 2,655 occurrences in total. From these, 49 target species were selected for detailed assessment, represented by 277 occurrence records.

The target list was built from the 40 Carex species that the Saskatchewan Conservation Data Centre currently lists as at risk in the province. Thirty-six of those species entered the spatial analysis, while four, C. hallii, C. lapponica, C. pachystachya and C. paleacea, were classified as Data Deficient because of conflicting information on their taxonomy or occurrence in Saskatchewan. The team also added nine species with very low record counts, between two and eleven occurrences each, that had not previously been included in the provincial assessment, bringing the spatially analysed total to 45 species.

To evaluate conservation status, the researchers applied the IUCN Red List criteria, focusing on geographic range under Criterion B. Two standard measures anchored the analysis: extent of occurrence, the imaginary boundary enclosing all known records of a species, and area of occupancy, the area actually occupied within that boundary, calculated on the IUCN-recommended grid of 2-kilometre cells. Both statistics were computed with the Geospatial Conservation Assessment Tool, and where a species had fewer than three records, its extent of occurrence was set equal to its area of occupancy, following IUCN guidance. Thresholds were then applied to assign categories: Critically Endangered for species with an extent of occurrence below 100 square kilometres, Endangered below 5,000, Vulnerable below 20,000, with Near Threatened and Least Concern designations for species approaching or missing those limits.

Because detailed species-specific habitat information was unavailable for most sedges, the team modified the IUCN sub-criterion B2b(iii), which concerns the area, extent and quality of habitat. They combined two measures into a five-point scoring system: local rarity, based on the number of ecoregions a species occupies, and habitat vulnerability, based on how heavily threatened by human activity those ecoregions are. Saskatchewan’s ecoregions were ranked by threat level, with the prairie ecoregions, including the Aspen Parkland, Moist-Mixed Grassland, Mixed Grassland and Cypress Upland, scoring highest because they face the greatest extent and severity of anthropogenic threats. Species confined to a single, highly threatened ecoregion received the maximum score, while widespread species in lightly threatened boreal ecoregions received the minimum.

The integrated assessment produced a substantially revised picture of sedge conservation in the province. Six species emerged as Critically Endangered, including C. raynoldsii, C. meadii, C. heleonastes, C. leptonervia, C. mackenziei and C. projecta. Four species were assessed as Endangered, eight as Vulnerable, three as Near Threatened and 24 as Least Concern, with four remaining Data Deficient. Notably, the approach cut the provincial list of rare sedges nearly in half, from 40 species, about 38.1 percent of the genus in Saskatchewan, to 21 species, or 20.0 percent. Most species were effectively downgraded relative to the previous provincial ranking, a shift the authors attribute to the standardized, evidence-based application of range criteria to specimen data.

Mapping the results against protected areas revealed stark gaps. Saskatchewan contains 323 protected areas covering 6,390,710 hectares, about 9.8 percent of the provincial land area, which falls below the Canadian national average of roughly 12.1 percent and well short of the federal goal of conserving 30 percent of the country’s land and water by 2030. Rare sedges were recorded in only 13 of those protected areas, just 4.0 percent of the network. The Wildlife Habitat Protection area held the highest sedge occurrence, with three records of two species, C. garberi and C. hoodii, while sites such as Prince Albert National Park, Clearwater River Provincial Park and Wildcat Hill Provincial Park each contained a single occurrence of a single rare species.

Overlaying species ranges with provincial land cover data added a habitat dimension to the analysis. Seven rare sedge species primarily occupy agricultural areas within their extent of occurrence, a finding that underscores how far prairie sedges have been pushed into transformed landscapes. Several species, including C. houghtoniana, C. sterilis, C. glacialis and C. pedunculata, are associated with four or more habitat types, ranging from mixed softwood and spruce forests to wetlands, water bodies and cutover areas. Others are far more restricted: C. leptonervia was recorded only in mixed softwood forests, C. mackenziei only in shrub fen wetlands, and both C. bicolor and C. bigelowii subsp. bigelowii only in closed-canopy spruce forests. C. meadii, C. gravida and C. petasata were recorded in agricultural fields and grasslands.

The study situates these findings against a backdrop of intensive land use. Almost 80 percent of the native grassland in the Prairie ecozone, which contains 68 Carex species, has been lost, and in some prime cropland areas less than 2 percent of original habitat remains. In the Boreal Plain ecozone, a sedge diversity hotspot with 85 species including ten rare ones, conversion of aspen-dominated forest to agriculture has reached roughly 73 percent since European settlement, and the annual deforestation rate of 0.89 percent over the past 28 years is approximately three times the world average. Urbanization around Saskatoon and Regina, along with industrial mining, oil and gas extraction, and associated road infrastructure, adds further pressure on remaining natural habitats, and Saskatchewan’s population, now over 1.2 million, is growing at its fastest pace in more than a century.

The authors propose expanding the provincial protected areas network and adopting complementary tools such as Important Plant Areas, micro-reserves and Other Effective Area-Based Conservation Measures, approaches that have only recently begun to be explored in Saskatchewan. They also call for a culture of adaptive management within the conservation community, including training workshops on sedge morphology and identification, since Carex species can confuse even experienced botanists and citizen-science observations of sedges remain very low in the province. The team acknowledges limitations: the analysis rests entirely on herbarium vouchers and therefore reflects collecting bias, threat knowledge is incomplete for some taxa, and the assessment relied on geographic range criteria alone, which capture threats only partially. Even so, the work delivers the first comprehensive, specimen-based conservation assessment of Saskatchewan’s largest plant genus and a spatial blueprint for where future protection efforts are most needed.

Subject of Research: Spatial conservation assessment of the sedge genus Carex in Saskatchewan using herbarium data and modified IUCN criteria

Article Title: Integrating herbarium data with spatial biodiversity assessment into conservation plans: A case study of the genus Carex L. ( Cyperaceae ) in Saskatchewan, Canada

Article References: Kricsfalusy, V., Chakma, K., & Godfrey, A. (2025). Integrating herbarium data with spatial biodiversity assessment into conservation plans: A case study of the genus Carex L. (Cyperaceae) in Saskatchewan, Canada. Nature Conservation, 59, 65-88. https://doi.org/10.3897/natureconservation.59.149423

Image Credits: AI Generated

DOI: 10.3897/natureconservation.59.149423

Keywords: Carex, sedges, Saskatchewan, herbarium specimens, IUCN Red List, protected areas, conservation planning, biodiversity, extent of occurrence, area of occupancy, land cover, prairie grasslands