Impacts of drought on biomass production and species composition in the Northern Mixed Grass Prairie

Background/Question/Methods

Precipitation drives biomass production. Rancher’s livelihoods rely on this biomass production for livestock grazing and wildlife production. In years when drought occurs ranchers need to adjust management and utilization plans to maintain rangeland quality. Drought is any annual reduction of rainfall greater than 25%. Historically, annual drought occurs in the Northern Mixed Grass Prairie (NMGP) one out of five years. The objective of this study is to simulate 50% spring or summer droughts on vegetation resistance and resilience using 3.3 x 2.2 m stationary rainout shelters. We hypothesize that sites with high-productivity/high-diversity (HPHD) will be more resistant and resilient than low/diversity/low productivity (LPLD) sites to drought. To address this objective, rainout shelters were placed in HPHD and LPLD areas on three separate ranches. Treatments within each study area include spring drought, summer drought, ambient, and 100% (“control”). In 2014 rainout shelters were placed on all spring and summer treatments. Supplemental water was added, based on the 30-year average, to the spring and summer treatments and “control”. Spring drought was implemented from April 1^st to June 30^th and summer drought was from June 1^st to August 31^st. Biomass clippings were collected after the first frost event for all replicates and treatments.

Results/Conclusions

Analysis for this data set is a 3-way ANOVA with replication, site and treatment as the main effects that were tested against total biomass. Proc-Mix in SAS was used to test all main effects and interaction terms. Results on total biomass fail to support our hypothesis. Treatment had no effect on total biomass (P-Value - 0.2079). The three ranches were not compared to one another because it was inappropriate based off soil type and precipitation regime. Total biomass was significantly different between high diversity and low diversity plant community sites for all treatments and ranches (P-value - 0.0169). The main effect of Ranch had no effect on overall total biomass (P-value - 0.2911). No interactions of total biomass (ranch*community, ranch*treatment, ranch*community*treatment) were significant at an alpha level of 0.05. These results can be explained by possible microclimate effects being present or windblown precipitation occurring underneath the rainout shelters. These data can serve as baseline data for ranchers preparing drought management plans.