Recent increases in the magnitude and occurrence of insect-induced tree mortality are disruptingevergreen forests globally. To resolve potentially conflicting ecosystem responses, we investigatedwhether surrounding trees exert compensatory effects on biogeochemical signatures following beetleinfestation. To this end, plots were surveyed within a Colorado Rocky Mountain watershed that expe-rienced beetle infestation almost a decade prior and contained a range of surrounding tree mortality(from 9 to 91% of standing trees). Near-surface soil horizons under plot-centered live (green) and beetle-killed (grey) lodgepole pines were sampled over two consecutive summers with variable moistureconditions. Results revealed that soil respiration was 18e28% lower beneath beetle-infested trees andcorrelated to elevated dissolved organic carbon aromaticity. While certain edaphic parameters includingpH and water content were elevated below grey compared to green trees regardless of the mortalityextent within plots, other biogeochemical responses required a higher severity of surrounding mortalityto overcome compensatory effects of neighboring live trees. For instance, C:N ratios under grey treesdeclined with increased severity of surrounding tree mortality, and the proportion of ammonium dis-played a threshold effect with pronounced increases after surrounding tree mortality exceeded ~40%.Overall, the biogeochemical response to tree death was most prominent in the mineral soil horizonwhere tree mortality had the largest affect on carbon recalcitrance and the enrichment of nitrogenspecies. These results can aid in determining when and where nutrient cycles and biogeochemicalfeedbacks to the atmosphere and hydrosphere will be observed in association with this type of ecological disturbance.
