Location: Livestock and Range Research Laboratory
Project Number: 3030-21630-005-08-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Oct 1, 2018
End Date: Mar 31, 2021
The 2017 Lodgepole wildlfire complex burned 270,200 acres of northern mixed grass and Ponderosa pine/bunchgrass habitat in north central Montana. Local economic impact was considerable displacing summer and fall grazing for nearly 9,000 head of livestock. As the 2018 grazing season nears, Bureau of Land Management (BLM) managers and livestock permittees are concerned about soil health and the interaction of grazing management decisions. Both groups need scientific information to formulate future grazing management decisions. Private landowners are equally interested in this information to direct recovery efforts on their own lands. Embedded within this larger question is a series of questions about the response of woodland and savanna ecosystems to prescribed fire used for treating hazardous fuel conditions. a) Describe soil organic matter levels in areas treated at different times with prescribed fire and similar landscapes burned under wildfire conditions. b) Describe native herbaceous and shrub cover, herbaceous biomass, plant height, soil surface litter, soil water content, soil nitrogen and soil texture at the same locations where soil organic matter is measured. c) Establish the relationship between the selected biological and physical attributes listed in b) and soil organic matter level. d) Identify those attributes with the highest predictability (R2> 0.60) of soil organic matter levels. These will become grazing management indicators.
Following the Lodgepole Complex wildfire Fort Keogh, BLM and MSU agreed to the importance of studying rangeland response to this more than 109,000-ha fire, designed an experiment and in 2018 identified study sites and applied initial treatments as described in the following so that research opportunities would not be missed awaiting funding. Work preceding funding serves as the basis for the funded work to follow and is described for that purpose. Burned ponderosa pine sites were identified for grazing and rest treatments the first post-fire growing season (2018). This work was done on private lands because federal policy did not allow grazing treatments during 2018 and 2019. Area selection was based on moderate fire intensity and similarity in landscape, soils, and likely pre-burn vegetation. Study plots were fenced to exclude cattle and paired with another left open to grazing. Exclosure size was minimized to limit elk use within exclosures. We used the same 0.01ha sized exclosures used in our study of northern mixed prairie response to wildfire and grazing (Gates et al. 2017). Stocking rate will target 50% utilization of the forage crop. Plant community diversity, standing crop, and composition will be measured at the end of the grazing period in the grazed and nongrazed plots. These measures were selected to address: 1) agency and conservation organization concerns about loss of biotic integrity if grazing is allowed too soon, 2) forage available to grazing livestock, and 3) the impact to long term sustainability of the system. To objectively describe the response of these ecosystem indices to grazing or rest, measurements will be collected near peak production (July) during 2018 and 2019 following methods of Gates et al (2017). During 2019, grazing will be deferred until sampling can be completed to ascertain the impact of grazing and rest on community recovery. A second set of exclosures will be established near the previously described paired plots to assess season of defoliation effects following the methods of Gates et al (2017). This study will indicate when grazing can begin following wildfire. Plots will be mowed during June, July, or August to approximate 50% biomass removal. Companion protected plots will not be mowed during 2018 and 2019. Diversity, biomass production, and species composition will be measured in mowed and untreated control plots near peak production during 2019. Two years of repeated seasonal defoliation will indicate plant community response to season of grazing use. Eight sites will be selected to monitor aboveground vegetation response to timing of defoliation after fire and effects of prescribed fire before wildfire. Defoliation treatments will be June, July and August mowing during the first post-fire growing season. Defoliation treatments will be factorialized with fire history (wildfire or wildfire preceded by prescribed fire). Four paired sites in the wildfire area and four paired sites in the prescribed fire area will be selected to compare grazing to first post-fire growing season rest. ARS will be responsible for biomass, cover/diversity data; will collaborate to incorporate data with soil variables.