Fuel load and heat effects on Northern mixed prairie and four prominent rangeland graminoids

Abstract

Plant mortality following fire has been a concern of many people and agencies. There is little information, relating to the direct effect fire has on grass mortality, biomass production, and tillers at the community and individual levels. The objectives of this research were to determine the survival, tiller numbers, and biomass response to fuel load and direct measures of heat of four prominent graminoid species at the individual and community levels. The community level consisted of 24 plots measuring 20 X 20 meters. The plots were burned in autumn 2008 and 2009. Regression analyses were used to assess relationships of fuel load, degree-seconds, duration of heat, and maximum temperature, with relative biomass and frequency of species and species groups. The results illustrated fuel load, degree seconds, and duration were good predictors of total biomass. Threadleaf sedge increased in biomass to pre-treatment measures. Threadleaf sedge and needle-and-thread biomass was negatively related to fuel load, degree-seconds, and duration of heat. Neither blue grama nor western wheatgrass changed in biomass. A burn cage was used to apply the burn treatments for the individual plant study using range of fuel loads 500-9000 kg X ha -¹. Relationships of fuel load with degree-seconds, heat duration, and maximum temperature were tested independently. Probabilities of plant mortality were estimated based on fuel load, duration of heat, maximum temperature, and degree-seconds. Of 120 plants of each species, only one western wheatgrass and one threadleaf sedge plant died following fire. Mortality occurred for 20 blue grama plants and 17 needle-and-thread plants. Degree-seconds, duration, maximum temperature, and fuel load were good predictors of mortality for blue grama and needle-and-thread. Neither duration of heat or maximum temperature explained changes in biomass or tillers for any species. Plant response was less in the field than the burn cage even at heavier fuel loads. This study found that as fuel load increased, degree-seconds, duration, and maximum temperature increased. Fuel load was the primary factor increasing degree-second, duration, and maximum temperature and provided an alternative way to predict plant mortality following fire. Understanding direct fire effects on plants will provide better management decisions following a fire.