Impacts of wildfires and grazing on the recovery of forage quality in mixed native prairies

Background/Question/Methods

Fires in grasslands promote heterogeneity of vegetation structure and maintain the ecological stability of the prairies. While the productivity and forage quality recovery after wildfires in native prairies is typical of great interest in rangeland management, there is still scarce information on the post-burn effect on forage nutrient availability in mixed prairies. We, therefore, assessed the nutritional profile of grazed grasslands during plant recovery after wildfire occurrence. We investigated the post-burn annual variation of the nutrient content of two plant groups (i.e., forbs and graminoids) in a four-year timeframe. We asked: i) to what extent the effect of the wildfire remains on forage quality four years after fire, and ii) whether the effect of fire on the functional plant groups depends on grazing activities. Sampling was conducted annually at 12 selected locations affected by wildfires in Alberta and Saskatchewan, including burned and unburned plots and in grazing exclosures. Grasses and forbs were clipped separately, dried, ground, and later processed for crude protein and fiber (neutral detergent fiber - NDF and acid detergent fiber - ADF).

Results/Conclusions

Both crude protein and fiber varied annually after the wildfires, with no effect of grazing on forage quality. In the first and second years, burned sites displayed higher protein content than unburned locations. Fire did not affect crude protein between plant functional groups; however, forbs showed higher nutrient values than grasses throughout the four years. Additionally, our data also showed that fire affected fiber content. There was a positive relationship between fiber (NDF and ADF) and litter in burned sites. Lastly, grasses exhibited consistently higher fiber than forbs. Overall, these results indicate no long-term effect of wildfire on protein content, which seems to stabilize in the third-year post-burn. The apparent improvement of forb digestibility and retention of protein under dry conditions could modify the grazing capacity of the prairies at large scales. This may also change the foraging behaviour of large ungulate grazers such as bison through mechanisms such as increasing patch re-selection (i.e., intensified grazing cycles) and broadening feeding preferences to forbs when grasses are limited or have high fiber content.