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

Carbon dioxide efflux (Es) 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 Es. Minimal variation of Es occurred among the four locations with healthy plants, and Es 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 Es was 0.59 µmol·m-2·s-1. This is the first known report of Es for any cycad species, and the values for the unique pachycaulous stem form fit in the lower half of the range of published Es for woody trees. The results illuminate the potential for using Es to screen in situ C. micronesica populations to identify the individual trees with the greatest likelihood of surviving conservation measures.