Framework / Assessment California Forests and Rangelands: 2015 Assessment Summary During an outbreak, forest insects and diseases can cause moderate to high rates of mortality (>1% of forested area) in short periods. This indicator is a comparison of mortality rates as area or volume compared to a 1% threshold. The reporting units for this indicator may include ownership, species or plant type, type of insect/disease, and by exotic/native insect/disease type. It may also be reported as a percentage of area or volume.