Crisis on the Prairies Revisited

Two stages of the Native Prairie Adaptive Management framework: the setup stage and the iterative stage. The setup stage consists of the foundational components of the decision framework that were developed between 2008 and 2010. The iterative stage consists of the recurrent steps of the annual decision-making, monitoring, and updating process.

Extent of the mixed-grass and tallgrass prairies within the northern Great Plains of the United States. The dashed line is the approximate demarcation of the mixed-grass (westerly) and tallgrass (easterly) grassland ecosystems. NPAM-enrolled units (n = 127) are located within the U.S. portion of the Prairie Pothole Region in Montana, North Dakota, South Dakota, and Minnesota, which includes two Service regions (3 and 6).

Relative weights for the A) four competing mixed-grass models and the B) six competing tallgrass models as they change across annual updating cycles between 2009 and 2022. In 2009, beginning weights on the competing models were set equal at 0.25 and 0.167 for mixed-grass and tallgrass, respectively. In 2020, after revising model parameters with empirical data from 2009–2019, model weights for 2019 were set to equal and annual updating cycles started anew with the 2019–2020 paired data. The competing models represent primary uncertainties in managing prairies and were parameterized and evaluated separately by grassland ecosystem. Model 1 hypothesizes that all forms of defoliation are equally effective, regardless of prairie condition, and result in a more desired native cover than does a rest treatment. Models 2 through 4 are additive in nature such that each model incorporates the structure of the prior model, but advances a new premise regarding treatment effectiveness; the models focus on the impact of dominant invader, defoliation history, and invasion level, respectively. Tallgrass prairies included two additional models that share the same structure as Model 3, but vary in their prediction regarding effectiveness of grazing within the phenological window when B. inermis is dominant (Model 5) and effectiveness of defoliation actions outside of the phenological window compared to rest (Model 6).

Mixed-grass decision policies of management recommendations based on expert-derived parameterized models. The two decision policies reflect A) equal weights of 0.25 first assigned to each of the four competing models in 2009 and B) updated weights of 0.56, 0.05, 0.14, and 0.25 on the four competing models in 2018 that evolved after nine annual updating cycles (2009–2018). The decision policy indicates the optimal management action (rest, graze, burn, or burn/graze combination) given the current state of a prairie unit and the current weight on the four competing models. The current state of a prairie unit is defined by its vegetation composition and defoliation history. We recognize four discrete states of native prairie cover (60–100%, 45–60%, 30–45%, and 0–30%) and four invasive dominance categories (SB=smooth brome, CO=co-dominant smooth brome and Kentucky bluegrass, KB=Kentucky bluegrass, RM=remainder), which results in 16 potential vegetation states. Defoliation history is captured by an index of how recent and frequent non-rest actions took place over the previous seven years; the index is then broken into three defoliation history levels of low, medium, and high. Additionally, we recognize three timeframes that describe the number of years since a prairie unit last received a non-rest action: one year ago, two to four years ago, and five or more years ago. Feasible combinations of the three defoliation history levels and the three timeframes result in seven potential defoliation history states. Combining the 16 vegetation and seven defoliation history states produces 112 prairie states in which a prairie unit can occur at any point in time.

Mixed-grass decision policy of management recommendations based on empirically derived parameterized models built in 2020. The decision policy reflects equal weights of 0.25 on each of the four competing models. Figure design and components are the same as those in Figure 5; see Figure 5 caption for further description.