Delayed effects of fire and logging on cicada nymph abundance

Abstract

The degradation of the root system after fire and logging entails alteration of belowground biodiversity. Nymphs of Cicada orni feed on the sap of roots and can be indicators of the fate of the root-feeding fauna. I studied the cicada population of a pine forest which was affected in 2010 by a wildfire that burned all the vegetation aboveground and was subsequently logged. I hypothesized that the effect of these disturbances on the forest root system would negatively affect nymph abundance and length, due to the consequent food limitation. I used a BACI (before-after control-impact) design approach, assuming that root degradation, taking place around 1 year after the death of aerial structures, was the main impact on cicada nymphs. Cicada exuviae attached to vegetation were collected as a proxy for nymphs. From 2011 to 2012, the relative abundance of exuviae increased from 12.6 to 23.3 exuviae/100 m2 in the control area, but decreased from 18.0 to 3.6 exuviae/100 m2 in the burned area, probably as a consequence of progressive root degradation and/or to the absence of 2-year-old nymphs due to the destruction of eggs by fire. However, interannual trends in exuviae length of males and females cicadas were not significantly different between areas. This population crash illustrates a previously undescribed time lag in the response of belowground animals to fire and logging which may have consequences for the ecosystem as a whole.