Spatio-temporal impacts of fire on soil nutrient availability in Larrea tridentata shrublands of the Mojave Desert, USA

•Fire effects on soil nutrient availability were assessed over time by measuring ion flux rates.•Increased availability of N, K, Mg, and Ca around burned shrubs 7 months after fire•Lower N, K, and S around burned shrubs 7 years after fire•Potential disappearance of L. tridentata fertility islands over time in burned areas•Redistribution of desert soil nutrients may pose cascading effects at community-level scale.

Soil nutrients and herbaceous plant growth are patchily distributed in desert ecosystems, often restricted to “fertility islands” created by perennial shrubs. Although fire has been historically uncommon in southwestern American hot deserts (e.g., the Mojave), these regions have experienced more severe fires due to recent invasions of exotic species that increased proneness to fire. Nevertheless, the effects of fire on soil nutrients in SW deserts, including via the removal of shrubs by fire, remain unclear. We assessed the spatio-temporal impacts of fire on soil nutrient availability in burned and unburned areas of the Mojave Desert. The study was conducted in shrublands dominated by Larrea tridentata. We investigated both the short (seven months after fire) and long (seven years after fire) term effects of fire on soil nutrient availability within a microhabitat gradient spanning from under the shrub canopy to open inter-shrub areas. We found that nitrogen (N) and potassium (K) were higher under the canopy of burned L. tridentata seven months after fire. In contrast, seven years after fire, N and K availability were lower around shrubs that were killed by fire. Over the short-term, fire had a positive effect on soil nutrients. However, over the long-term, the fertility island effect diminished after removal of shrubs by fire, and the differential availability of nutrients such as N and K became more similar under shrubs and in open inter-shrub areas. This reinforces the key role of L. tridentata in influencing the distribution of soil nutrients and provides support for the hypothesis that post-fire herbaceous plant growth will be less restricted to areas under shrubs.