Effects of Fire Temperatures on Mojave Desert Native and Nonnative Seeds

Large-scale wildfires have been historically rare in hot deserts like the Mojave, largely due to the scarcity or uneven distribution of native plant biomass as fuel. Thus, native plants in these regions are ill-adapted to withstand spreading wildfire, resulting in slow post-fire recovery. Here, I test the hypothesis that nonnative grasses respond better to heat cues than native plant species. Seeds from 3 invasive and 13 native plant species were collected from research sites located in the eastern Mojave Desert, near surrounding Clark County Flood Control District weather stations. Seeds were buried in an artificial substrate mimicking field soil conditions and subjected to five different heat treatments. Seeds were grown in a greenhouse and germination rates were measured. Germination rates were not significantly different under treatments compared to controls, with some exceptions. Species with the greatest increase in germination compared to controls were Ambrosia dumosa, Salvia dorrii, and Xylorhiza tortifolia, all of which exhibited increased germination rates under a low extended heat treatment (thirty minutes at 100°C). Brassica tournefortii, an invasive winter annual displayed a 53% germination rate in response to the low extended heat treatment. Physaria tenella, a native annual species, did not germinate under any treatments. Temperatures mimicking fire conditions have a significant impact on the germination rates of some native and invasive plant species of the Mojave Desert. Invasive grasses had lower germination under heat treatments compared to native species. Future directions include testing seeds at different temperatures and durations and implementing these findings in field studies.