Stem CO₂ efflux of Cycas micronesica is reduced by chronic non-native insect herbivory

Carbon dioxide efflux (E_s) from the base of Cycas micronesica K.D. Hill stems was quantified in four locations containing healthy populations and in one location with populations threatened by non-native insect herbivores in order to determine the influence of reduced plant health on E_s. Minimal variation of E_s occurred among the four locations with healthy plants, and E_s ranged from 1.68 to 1.79 µmol·m^-2·s^-1. The threatened in situ populations were on the island of Guam, where recent invasions of non-native insects have caused epidemic plant mortality, and the E_s was 0.59 µmol·m^-2·s^-1. This is the first known report of E_s for any cycad species, and the values for the unique pachycaulous stem form fit in the lower half of the range of published E_s for woody trees. The results illuminate the potential for using E_s to screen in situ C. micronesica populations to identify the individual trees with the greatest likelihood of surviving conservation measures.