Large-scale estimation of carrying capacities in agricultural Crown lands of Manitoba, Canada using land cover datasets

Context There is growing interest in protecting the natural grasslands of North America's Great Plains, of which less than 30% in the Canadian Prairies, due to their vital ecosystem services, such as food production, nutrient cycling and climate regulation. The Prairies extend into southern Manitoba, where grasslands in agricultural Crown lands are primarily used for grazing beef cattle, specifically the cow-calf herd. The provincial government estimates carrying capacities, in animal unit months (AUM), to ensure the sustainable utilization of Crown lands and avoid overgrazing. Recently, there has been an increasing focus on maximizing forage use while conserving this valuable ecosystem. The availability of remote sensing datasets to monitor grassland cover and biomass productivity has expanded research opportunities in grassland conservation. Objective The objectives of this study are to estimate the carrying capacities of approximately 4000 km 2 of the agricultural Crown lands in Manitoba and compare them to those currently allowed by provincial lease contracts. Methods Forage yield data were obtained from aboveground biomass sampling carried out between 2004 and 2020 throughout Manitoba. Vegetation types in each Crown land parcel were identified using the remotely sensed Manitoba Grassland Inventory and Annual Crop Inventory. Due to limited data availability, estimated stocking rates, in animal unit months per hectare (AUM/ha), were assigned to Crown land parcels using a similarity index based on historical climate normals. A six-step hierarchical approach was adopted in assigning stocking rates, prioritizing direct observations when available and using imputation methods when necessary. Finally, carrying capacities were estimated using the assigned stocking rates and compared to those currently permitted by provincial lease contracts by calculating grazing rates. Results and conclusions The total estimated carrying capacity of the agricultural Crown land in Manitoba was 662,014 AUMs, approximately 10% higher than permitted under provincial lease contracts. This indicated that these lands were undergrazed by −8.85%. Grazing relative to lease allocations varied across parcels, with 50.6% undergrazed, 48.8% overgrazed and only 0.6% matching allocations. These results reflect regional and interannual variability, highlighting uncertainty in large-scale carrying capacity estimates. Significance This study provides the first attempt at a large-scale estimation of carrying capacities for agricultural Crown lands across Manitoba using biomass sampling and remotely sensed land cover datasets. The insights gained can support targeted management practices to optimize forage utilization and prevent overgrazing while maximizing the potential of underutilized areas. This also highlights the need for improved biomass estimation models using remote sensing approaches.