Cycas micronesica leaf and strobili expansion patterns were measured in three locations and seasons on Guam and then were fitted with non-linear models to evaluate the use of the parameters for informing management decisions. All growth curves except for microstrobili height conformed to a negative exponential function. Microstrobili height development could not be fitted with any traditional linear or non-linear function, so spline models were used to smooth the effect of elapsed days. Leaf and leaflet expansion patterns were influenced by habitat and season, indicating development of the vegetative organ is plastic. In contrast, the models that described development of megasporophyll length, microstrobili height, and microstrobili diameter were not influenced by habitat or season. Moreover, seed diameter developmental patterns were only minimally influenced by location. These results indicate developmental patterns of the reproductive structures were primarily constitutive. We have demonstrated two empirical approaches to fitting models of Cycas micronesica organ growth and development and that both methods are useful for determining the influence of spatial or temporal factors in the timing of organ development. This approach may be used to inform horticultural or conservation questions of other rare cycad species.

Leaf litter chemical traits were measured for Cycas micronesica plants in Guam following leaf herbivory by the scale Aulacaspis yasumatsui, the butterfly Chilades pandava caterpillar, or the leaf miner Erechthias sp. to determine the influence of the non-native pests on litter quality. Scale herbivory increased litter phenols above those of undamaged leaves but did not influence lignin or cellulose concentrations. Butterfly caterpillar herbivory increased litter phenols above and decreased litter lignin below those of undamaged leaves, but did not influence cellulose concentrations. Leaf miner herbivory increased litter lignin concentrations above those of undamaged leaves, but did not influence phenols or cellulose concentrations. Herbivory influenced 8 of 12 essential elements that were quantified. Herbivory by all 3 insects increased nitrogen and potassium litter concentrations and decreased calcium and iron litter concentrations when compared with undamaged litter. The responses were idiosyncratic among herbivores for the remaining essential elements. Stoichiometry among the chemical constituents indicated that herbivory increased litter quality and predicted more rapid biogeochemical cycling in Guam's ecosystems as a result of these 3 non-native insect invasions.

An ex situ germplasm collection of the endangered Cycas micronesica was established in a transition zone between biodiverse native forest and mature stands of the invasive species Leucaena leucocephala. Soil chemical properties were determined for the 2 tree cover types to inform management decisions. Total carbon, total nitrogen, calcium, and net ammonification were greater in native forest cover than in L. leucocephala patches. Net nitrification and net mineralization were greater under L. leucocephala cover. Trace metals also differed between the 2 forest cover types, with chromium, cobalt, and nickel accumulating to greater concentration under L. leucocephala cover and zinc accumulating to greater concentration under native forest cover. The results indicated that L. leucocephala cover generated substantial changes in soil chemical properties when compared with native forest tree cover, illuminating one means by which understory vegetation may be affected by changes in invasive tree cover.

We used activated charcoal methods to test for the presence of phytotoxic substances in soils that had received inputs of decomposing Cycas micronesica K.D. Hill leaves and stems that were heavily infested with the armored scale Aulacaspis yasumatsui Takagi. Velocity of Momordica charantia Descourt. and Carica papaya L. seedling emergence was increased by the addition of charcoal to these soils. Furthermore, M. charantia and C. papaya seedling height and dry weight were among the response variables that were increased by the addition of charcoal. Legacy effects of scale-infested C. micronesica plant litter deposited in these soils resulted in phytotoxic compounds that inhibited seedling emergence and plant growth. Scale-infested Cycas leaves should not be used as mulch or in compost until phytotoxic causal mechanisms are more fully understood.

We studied the ability of Cycas micronesica roots to recognize the identity of competitor roots using pot culture. Pairs of seedlings were grown in single pots for 10.5 months, and morphological traits of the focal plant were determined when the non-focal plant was a half-sibling, a close relative from a mother 170 m away, a distant relative from a habitat 40 km away, or a different species (Cycas edentata) from Mindanao, Philippines. Most of the measured response traits exhibited similar trends and confirmed that C. micronesica plant roots were able to recognize the identity of competitors. For example, focal plants grown in pots with C. edentata competitors exhibited 66% increase in fine root dry weight, 54% increase in coralloid root dry weight, and 49% increase in total plant dry weight, compared to focal plants grown in competition with half-siblings. Our methods have shown that plot design in ex situ conservation and botanic garden settings would improve by positioning C. micronesica plants adjacent to non-relatives. Recruitment may improve within in situ conservation plots if managers distribute seeds away from the maternal parent so that emerging seedlings are not forced into immediate competition with half-siblings. These findings may be useful for designing more complex experiments to quantify the influence of these plastic root responses on plant nutrient status and physiology.