Effects of Low-Intensity Prescribed Burning with Minimal Soil Heating on Soil Properties and Mycorrhizal Infectivity in an Inter-Andean Montane Shrubland of Southern Ecuador

Fire is a recurrent ecological process in Andean ecosystems, yet its effects on soil properties and arbuscular mycorrhizal fungal (AMF) infectivity under low-intensity conditions remain poorly understood. The study was conducted with limited spatial replication (n = 3 plots per treatment) in an inter-Andean montane shrubland of southern Ecuador, with nine plots assigned to upslope burning, downslope burning, or an unburned control. Fire behavior, soil physicochemical properties, and AMF infectivity using the MSI50 bioassay were assessed. Maximum soil temperatures at 5 cm depth reached only29.2 to 35.8 °C in burned plots, compared to a baseline of 20.8 °C in unburned controls, confirming minimal soil heating. No, statistically detectable changes in soil chemical properties were observed, although the limited statistical power precludes ruling out ecologically meaningful variations. Upslope fires spread faster and had shorter heat residence times than downslope fires, though these differences were not statistically significant (p = 0.10). Median MSI50 values were 9.74%, 9.75%, and 18.08% under downslope burning, upslope burning, and the unburned control, respectively, with no significant treatment effect (p = 0.668). The downslope-burning treatment included one exceptionally high value (82.42%) visible as an outlier. Multivariate ordinations and correlation analyses are presented strictly as exploratory due to the small sample size and did not reveal statistically supported associations between fire behavior variables and mycorrhizal infectivity. Overall, low-intensity burning with minimal soil heating produced limited short-term changes in soil properties and no detectable decline in AMF infective potential, suggesting the functional AMF propagule bank remains resilient under these conditions.