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Background and Aims Previous molecular dating studies revealed historical mass extinctions and recent radiations of extant cycads, but debates still exist between palaeobotanists and evolutionary biologists regarding the origin and evolution of Cycadaceae. Methods Using whole plastomic data, we revisited the phylogeny of this family and found the Palawan endemic Cycas clade was strongly related to all lineages from Southeast Eurasia, coinciding with a plate drift event occurring in the Early Oligocene. By integrating fossil and biogeographical calibrations as well as molecular data from protein-coding genes, we established different calibration schemes and tested competing evolutionary timelines of Cycadaceae. Key Results We found recent dispersal cannot explain the distribution of Palawan Cycas, yet the scenario including the tectonic calibration yielded a mean crown age of extant Cycadaceae of ~69–43 million years ago by different tree priors, consistent with multiple Palaeogene fossils assigned to this family. Biogeographical analyses incorporating fossil distributions revealed East Asia as the ancestral area of Cycadaceae. Conclusions Our findings challenge the previously proposed Middle–Late Miocene diversification of cycads and an Indochina origin for Cycadaceae and highlight the importance of combining phylogenetic clades, tectonic events and fossils for rebuilding the evolutionary history of lineages that have undergone massive extinctions.

An understanding of leaf nutrient relations is required for tree conservation and horticulture success. The study of cycad leaf nutrient dynamics has expanded in recent years, but direct comparisons among reports remains equivocal due to varying sampling protocols. We used Cycas micronesica K.D. Hill and Cycas nongnoochiae K.D. Hill trees to determine the influence on leaf nutrient concentrations of in situ versus ex situ locations and orientation of leaves within the tree canopy. Nitrogen, phosphorus, and potassium concentrations of leaves from ex situ plants exceeded those from in situ plants, and the differences were not explained by soil nutrient differences. Calcium concentrations of leaves varied among the site pairs, with differences primarily explained by soil calcium. Magnesium concentrations of leaves were not different among all location pairs even though soil magnesium concentrations varied among the sites more than any of the other elements. Differences in leaf macronutrient concentrations among four C. micronesica provenances were minimal when grown in a common garden. Lateral orientation of leaves did not influence any of the essential elements for either of the species. These findings indicate that the lateral orientation of cycad leaves does not influence leaf nutrient concentrations, leaf nutrient relations of cycad plants in managed ex situ settings do not align with leaf nutrient relations in habitat, and these differences are not explained by soil nutrition for most elements. We suggest that leaf nutrient concentrations should be determined in all niche habitats within the geographic range of a cycad species in order to fully understand the leaf physiology of each species.

Plants that enter symbiotic relationships with nitrogen (N)-fixing microbes contribute some of their N to the community through leaf litter decomposition and mineralization processes. The speed of these processes varies greatly among tree species. Mesocosm methods were used to determine the speed of N and carbon (C) release from Cycas micronesica, Intsia bijuga, and Serianthes nelsonii leaf litter. Microcosm methods were used to determine soil respiration traits in soils containing the leaf litter. The speed of leaf litter N and C release during decomposition occurred in the order C. micronesica < I. bijuga < S. nelsonii. Soil carbon dioxide efflux was increased by adding leaf litter to incubation soils, and the increase was greatest for S. nelsonii and least for C. micronesica litter. Ammonium, nitrate, total N, organic C, and total C were increased by adding litter to incubation soils, and the differences among the species converged with incubation duration. The rate of increases in available N and decreases in organic C were greatest for S. nelsonii and least for C. micronesica litter. These findings indicate that S. nelsonii litter released N and C rapidly, C. micronesica litter released N and C slowly, and the leaf economic spectrum accurately predicted the differences.

Mixtures of species in natural or agricultural systems can increase the performance of individuals or groups relative to monocultures, often through facilitative mechanisms. Mechanisms include root communication by which plants can interrogate the identity of adjacent plants and respond negatively or positively. Alternatively, mixtures of species can ameliorate the harmful effects of soil biota that are pronounced in monocultures, thereby improving plant productivity. Limited investments into roots by shade-grown Serianthes plants in nurseries have been correlated with reduced survival after transplantation to forested habitats. We used companion container cultures in two studies to determine if heterospecific neighbor, or “stranger” roots could experimentally increase the root growth of Serianthes grandiflora plants used as surrogates for the critically endangered Serianthes nelsonii. In one study, native sympatric eudicot and pteridophyte companions increased relative root growth and conspecific companions decreased root growth in comparison to control plants that were grown with no companions. In a second study, the phylogeny of companion plants elicited different root growth responses following the order of congeneric &lt, eudicot = monocot &lt, gymnosperm &lt, pteridophyte. We propose the use of stranger roots that are experimentally maintained in production containers as a passive protocol to improve relative and absolute root growth, leading to improved post-transplant growth and survival of container-grown Serianthes plants.

Guam’s established population of non-native coconut rhinoceros beetle (CRB, Oryctes rhinoceros L.) began creating burrows in stem apices of several cycad species in a managed garden. We conducted an island-wide survey to determine the spatial patterns of CRB burrowing of stems of in situ Cycas micronesica. We also measured starch of healthy and unhealthy coconut leaf tissue and compared this with starch of cycad stem tissue. The starch concentration of the central unexpanded leaf in healthy Philippine coconut trees was ≈90 mg·g−1, and that of unhealthy Guam coconut trees was ≈40 mg·g−1. The starch concentration of the tissue within the CRB burrow locations on C. micronesica trees was 145 mg·g−1. Burrowing of C. micronesica was restricted to female CRB adults and was found throughout the full latitudinal gradient of Guam. Our findings indicate Guam’s unhealthy coconut trees are no longer nutrient-dense, and the female CRB population may have exhibited a phylogenetically distant host shift to the abundant C. micronesica plants for a starch-rich diet within the concepts of the ‘ecological fitting’ hypothesis. We add proximity to coconut tree habitats as a new threat to Guam’s endangered C. micronesica population.

Ubiquitous Aulacaspsis yasumatsui Takagi infestations of Guam’s Cycas micronesica K.D. Hill trees cause direct herbivory of most exposed organ surfaces, including developing naked ovules and seeds. The nonstructural carbohydrates of infested vs. noninfested seeds were quantified to understand more fully the influences on seed quality for propagation purposes. Two studies compared seeds from healthy trees with those of unhealthy trees suffering from whole-tree A. yasumatsui infestations. The sugars fructose, glucose, maltose, and sucrose were in greater concentrations and herbivory reduced these free sugars by a greater percentage in sarcotesta tissue than in sclerotesta and gametophyte tissues. Starch concentration was greatest in gametophyte tissue, but herbivory reduced starch by a greater percentage in sarcotesta tissue. A third study was used to manipulate seeds of unhealthy infested trees such that some seeds were uninfested and some seeds were infested and revealed the nonstructural carbohydrates of the uninfested seeds were greater than those of the infested seeds in patterns that were similar to those when the entire tree was protected from herbivory. The combined results indicated that both source and sink relations were involved in the reductions of seed carbohydrates by A. yasumatsui herbivory. The reduction in seed resource pool by the herbivore feeding may be one of the mechanisms that results in reduced germination percentage and increased seedling mortality.

The diel cycle of Serianthes nelsonii leaflet movements was characterized under four levels of shade from full sun to 22% sunlight transmission to determine the photoprotective components of diurnal leaflet movements and the relationship to patterns of nocturnal leaflet movements. Treatments also included negating paraheliotropism by re-orienting plants every 15min throughout the photoperiod such that the plants never experienced a predictable solar vector. The timing of leaflet closure to avoid high light, the shape of the diurnal curve depicting leaflet angle, and the maximum extent of leaflet closure were influenced by the shade treatments. Protection of leaf function by paraheliotropism was also influenced by shade treatment, with the full sun plants exhibiting the greatest level of protection. Leaflet heat gain was reduced 50% by leaflet movement as determined by direct measurements of leaf-to-air temperature differences. Midday quantum efficiency of photosystem II was increased 120% by leaflet movement as determined by direct measurements of pulse modulated chlorophyll fluorescence. The extent of nyctinastic leaflet closure was greatest in the high light plants that moved the most midday and least in the shaded plants that moved the least midday, indicating the extent of diurnal paraheliotropism controlled the amplitude of nocturnal leaflet movement. Serianthes nelsonii is highly skilled at using movement to reduce leaflet exposure to the solar vector, providing instantaneous behavioral control over heat gain and photoinhibition. This case study of an endemic tree species in Micronesia has added to the nascent field of conservation physiology, and indicated that heliotropism of S. nelsonii leaves may provide the species with the ability to minimize high light damage during increased temperatures associated with climate change.

The literature covering the biology, ecology, horticulture, and conservation of the critically endangered tree Serianthes nelsonii Merr. was reviewed. The roots, stems, and leaves of this charismatic legume tree revealed highly plastic traits and responded positively to horticultural manipulations to improve the quality of container-grown transplants. Pre-sowing seed treatments of seed coat scarification and 1 h of imbibition generated 85% to 90% germination at a temperature optimum of 26 °C. Adventitious root formation on air layers and successful unions on approach grafts were 100%. Seedling and sapling growth was maximum under 25% to 50% sunlight transmission, limited irrigation to ensure adequate root zone aeration, repetitive stem tip pruning to increase root:shoot quotient, and thigmic stress to retain an orthotropic orientation of stems. In situ regeneration on Guam was substantial but recruitment from seedling to sapling was nil. High quality leaf litter chemistry enabled rapid decomposition, and soils beneath the tree exhibited unique chemical traits that increased ecosystem health by creating spatial heterogeneity. The greatest unanswered questions focus on plant mortality. Research is needed to determine the reasons for the mortality of in situ seedlings, mortality within transplantation projects on Guam, and the mortality of 60% of the mature in situ tree population during the 26-year implementation of the national recovery plan. Horticultural researchers are ideally positioned to answer these urgent questions.

Simple Summary Effective conservation of endangered plant species requires identifying their greatest threats to formulate management protocols. Invasive species are a result of global change and are a major threat to biodiversity. We used the island cycad Cycas micronesica K.D. Hill as a model that represents the global issues of conservation science and invasion biology. In Guam, several non-native insect invasions began in 2003 and have combined to threaten the island population of this cycad species. In this article, we summarize the history of reported invasions and the reported non-native insect herbivores that have recently increased the threat status. We also discuss the interactions among herbivores that threaten the sustainability of C. micronesica on the island of Guam. Abstract Invasions of non-native species can threaten native biodiversity, and island ecosystems are ideal for studying these phenomena. In this article, first, we report on the invasive species that combine to threaten the island cycad Cycas micronesica by reviewing the history of previously reported invasions and providing an update of recent invasions. Then, we prioritize the threat status of each herbivore and the interactions among them. Plant damage was initiated in 2003─2005 by the non-native Aulacaspis yasumatsui Takagi armored scale, Erechthias sp. Meyrick leaf miner, and Luthrodes pandava Horsfield butterfly, which elicited unprecedented irruptions of the native Acalolepta marianarum Aurivillius stem borer and increased herbivory by feral pigs (Sus scrofa L.). The combined impact of these five consumers represents the greatest sustained threat to the cycad tree species. Mitigation of the damage caused by phytophagous non-native species is urgently needed to conserve this unique gymnosperm tree.

The United States is currently home to five native cycad species. We provide a discussion on these five cycad species to illuminate how evolutionary and geopolitical processes influence phytogeography and published checklists of threatened plants. The number of threatened species in need of protection within any given country is a product of speciation that is contingent with evolutionary processes. However, this number may change instantaneously along with shifting of geopolitical boundaries brought about by armed conflict between rival states and multilateral negotiations. There are five contemporary cycad species within the United States, and the various historical bilateral and multilateral agreements that have generated this list are reviewed. Three of these five cycad species are threatened and in need of urgent protection. A discussion on the history of United States cycads as a microcosm of worldwide conservation issues is presented, with a focus on how federal conservation endeavors of individual nations may influence the world’s biodiversity crisis.

The literature containing which chemical elements are found in cycad leaves was reviewed to determine the range in values of concentrations reported for essential and beneficial elements. We found 46 of the 358 described cycad species had at least one element reported to date. The only genus that was missing from the data was Microcycas. Many of the species reports contained concentrations of one to several macronutrients and no other elements. The cycad leaves contained greater nitrogen and phosphorus concentrations than the reported means for plants throughout the world. Magnesium was identified as the macronutrient that has been least studied. Only 14 of the species were represented by data from in situ locations, with most of the data obtained from managed plants in botanic gardens. Leaf element concentrations were influenced by biotic factors such as plant size, leaf age, and leaflet position on the rachis. Leaf element concentrations were influenced by environmental factors such as incident light and soil nutrient concentrations within the root zone. These influential factors were missing from many of the reports, rendering the results ambiguous and comparisons among studies difficult. Future research should include the addition of more taxa, more in situ locations, the influence of season, and the influence of herbivory to more fully understand leaf nutrition for cycads.

Growth dynamics of pachycaulous stems of arborescent cycad plants are not well understood, and most observations have been made in cultivated garden plants. We studied Cycas micronesica plants in Guam, Tinian, and Yap to understand the influences of geography, plant size, sex, and herbivory on stem growth. We also determined the changes in demography of Guam’s population after 15 years of damage by non-native insect herbivores. The height increment (HI) was similar for plants within the height range from 100 cm to more than 600 cm, so the relative growth rate declined with height. Female tree HI was 68% of male tree HI, and Yap tree HI was 87% of Guam tree HI. Chronic herbivory by non-native insect herbivores caused a mean 44% decline in HI. Plants in managed gardens grew more rapidly than plants in a wild habitat. The HI was used to estimate that Guam has experienced a complete loss of ≈70 y of demographic depth resulting from the selective mortality of small plants since 2005. When future conservation interventions successfully mitigate the ubiquitous biological threats, our HI may be useful for empirically quantifying recovery of plant health.

Simple Summary Trees are not able to move in order to avoid stressful conditions. Therefore, trees have developed elaborate methods for modifying their organs to benefit the tree under prevailing conditions. For low light and high light conditions, most studies have looked at how the leaf blade is modified. We have shown that the entire leaf should be observed for modifications rather than just the leaf blade. Abstract Numerous leaf traits exhibit developmental plasticity in response to irradiance, an attribute that maximizes performance in the prevailing light. The use of leaflets to represent whole leaf traits of tree species with compound leaves is common in the acclimation literature. These methods ignore the potential for whole leaf plasticity to augment leaflet plasticity. We grew Serianthes nelsonii plants in incident light ranging from 6% to 100% of sunlight and quantified numerous leaflet and leaf traits to determine plasticity index (PI: (maximum-minimum)/maximum)) of each. Leaflet acclimation such as changes in length of palisade mesophyll occurred as expected. However, leaf-level morphometric traits such as rachillae insertion angle also exhibited acclimation potential. The leaf-level plastic behavior enabled acclimation approaches that simple-leaved species do not possess. We illuminate the need to look at the entire leaf when quantifying acclimation potential of tree leaves, and indicate that the historical use of leaflets to represent species with compound leaves under-estimated the acclimation potential when compared to species with simple leaves.

Cycas micronesica is a foundation species in several Micronesian islands and its seeds have been a historical source of starch for the island residents. The species has become endangered by invasive specialist insect herbivores and conservationists struggle with the inability to estimate the age of observed seeds. To inform this agenda, we evaluated numerous Cycas micronesica seed traits to determine if any exhibited a relationship with age and a substantial change in absolute value. Of the 30 direct and derived seed traits that we evaluated, most of them were non-linear and exhibited minimal change after about 12 months in age. The only traits that emerged as unambiguous estimators of age were the quotients derived as gametophyte fresh weight/total seed fresh weight and sarcotesta dry weight/sclerotesta dry weight. These two simple metrics can be used to accurately estimate seed age for this arborescent cycad species.

Leaf gas-exchange responses to shadefleck–sunfleck and sun–cloud transitions were determined for in situ Cycas micronesica K.D. Hill plants on the island of Guam to add cycads to the published gymnosperm data. Sequential sunfleck–shadefleck transitions indicated understory leaves primed rapidly but open field leaves primed slowly. Time needed to reach 90% induction of net CO2 assimilation (PN) was 2.9 min for understory leaves and 13.9 min for open field leaves. Leaf responses to sun–cloud transitions exhibited minimal adjustment of stomatal conductance, so PN rapidly returned to precloud values following cloud–sun transitions. Results indicate bi-directional leaf acclimation behavior enables mature C. micronesica trees to thrive in deep understory conditions in some habitats and as emergent canopy trees in other habitats. These data are the first nonconifer gymnosperm data; the speed of gas-exchange responses to rapid light transitions was similar to some of the most rapid angiosperm species described in the literature.

Large stem cuttings were removed from Cycas micronesica K.D. Hill trees and used for asexual propagation to more fully understand resource factors that influence adventitious root formation success. Healthy source trees had received insecticide protection from ubiquitous Aulacaspsis yasumatsui Takagi infestations and unhealthy source trees had suffered from chronic A. yasumatsui infestations. Nonstructural carbohydrates were quantified from stem tissues at the base of each 1-m cutting, and induction of adventitious roots was attempted using field soil as the medium. Carbohydrate concentrations were increased in healthy, protected tree cuttings above those in unhealthy, infested tree cuttings. The relative increase was greatest in the hexoses, intermediate in sucrose, and least in starch. The total nonstructural carbohydrate concentration in cuttings of infested trees was 54% of that of protected trees, and the sugar/starch quotient of infested trees exceeded that of protected trees. Asexual propagation success was 30% for the unhealthy tree cuttings and 100% for the healthy tree cuttings. These manipulative experiments confirm that chronic A. yasumatsui herbivory of C. micronesica trees reduces stem carbohydrates and decreases asexual propagation success. The results indicate that the use of large cuttings from unhealthy C. micronesica trees to rescue tree populations from construction sites is not a wise conservation decision in habitats where A. yasumatsui herbivory has been uncontrolled. Protocols for future rescue operations designed to transplant C. micronesica trees from construction sites may be improved by this new knowledge.

Premise of research. The armored scale Aulacaspis yasumatsui Takagi has invaded numerous geographic regions to devastate cultivated populations of Cycas L. and the native population of Cycas micron...

Mount Pinatubo, Philippines (15.14°N, 120.35°E) erupted violently in 1991 to initiate significant primary succession. Aspect, the direction faced by a slope, affects patterns of vegetation at higher latitudes, but such effects remain unreported in the wet tropics. Therefore, we monitored species composition and cover in established plots during 2006, 2010, and 2013 to characterize how aspect affected primary succession. We used redundancy analysis (RDA) to assess vegetation change in response to time and environmental factors. Vegetation cover increased from 153 to 245% on north-facing slopes, and from 174 to 230% in south-facing slopes while species richness and diversity indices also increased. From 38 to 63% of the species were restricted to one aspect, depending on the year of study. Redundancy analysis demonstrated that aspect strongly affected species composition and that its effects persist. Fabaceae was concentrated on south-facing slopes, which suggested that aspect effects might be accentuated due to enhanced soil nitrogen. Vines, grasses, and forbs, all typical of habitats with greater insolation, were more abundant on south aspects, while trees and ferns were more common on the north aspects. This is the first survey of vegetation dynamics using permanent plots on new volcanic surfaces in this region. Aspect differences produced distinct insolation and moisture patterns that enhanced habitat diversity and altered species composition. This effect has not been noted in monsoon forests. Aspect may continue to initiate divergence in succession trajectories as soils and vertical canopy structure develop differentially in response to differential dominance.

The diel patterns of stem carbon dioxide efflux (E(s)) were determined for cycads, monocots, and woody eudicot and gymnosperm tree species. Stem E(s) at a height of 30–40 cm was measured every 2 h throughout 31-h campaigns. Our range of E(s) was 1.5–4.0 µmol·m(−2)·s(−1) for cycads, 1.0–3.5 µmol·m(−2)·s(−1) for arborescent monocots, and 1.5–4.5 µmol·m(−2)·s(−1) for woody eudicot and gymnosperm trees species. Time of day did not influence E(s) of cycads or monocots. In contrast, the woody stems of eudicots and gymnosperms exhibited diurnal E(s) that was 36% to 40% greater than nocturnal E(s). The established literature based on E(s) of woody tree species cannot be used to estimate habitat carbon cycles in habitats which contain cycad or monocot trees. Time of day must be included for accuracy of research on E(s) of woody tree species. Failures to account for the spatiotemporal differences of E(s) may explain some of the disparity in outcomes of published stem respiration studies.

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.

Information on the best methods for producing endangered Serianthes nelsonii plants for use in species recovery projects is lacking. Plants of this species behave similarly in a nursery setting to plants of the congeneric Serianthes grandiflora and Serianthes kanehirae. Container-grown plants of these two species were repeatedly pruned in the nursery to determine if a more favorable root:shoot ratio would result, then to determine if performance after out-planting would benefit from the enhanced root growth. Repetitive pruning increased absolute root dry weight 43% to 61% and root:shoot ratio 55% to 56% above that of control plants that were not pruned. One year after out-planting, the pruned plants were greater in shoot dry weight and plant height than the control plants. More importantly, control plants exhibited 70% to 80% mortality, but the pruned plants exhibited 100% survival. This new knowledge from two surrogate species indicated that repetitive pruning of S. nelsonii plants in conservation nurseries would greatly increase the quality of the resulting transplants and therefore nurseries may add pruning as a prescribed production protocol to improve species recovery success.

The profile of nonstructural carbohydrates (NSC) was quantified to determine sugar and starch relationships of megagametophyte tissue during Cycas micronesica K.D. Hill seed ontogeny. Field work occurred in northern Guam where megastrobili were marked and dated as they emerged from stem apices of plants in a natural population. Seeds were harvested beginning 6 months after megastrobili emergence and continuing until 28 months, and gametophyte tissue was separated from the remainder of each seed. Carbohydrates within lyophilized gametophyte tissue were quantified by high-pressure liquid chromatography. The levels of glucose and fructose declined from a high at 6 months to a homeostasis at 11 months, and the levels of sucrose similarly declined from 6 months to a homeostasis at ≈14 months. Starch content exceeded sugar content and increased from 6 months to reach a homeostasis at ≈18 months. Maltose was not detected in any sample. Stoichiometric quotients changed dramatically until ≈14 months, when they became fairly stable until 28 months. Starch concentration was ≈5-fold greater than sugar concentration at 6 months, and increased to ≈15-fold greater than sugar concentration by 28 months. Total NSC in mature megagametophytes was almost 70% on a dry weight basis. Our results are in agreement with the biological function of this haploid tissue, as copious carbohydrate resources are readily available to support embryo and seedling growth.

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.

Background and Aims Research required to clarify leaf nutrient relations of cycad species has been inadequate. Common garden studies are useful for determining the influence of genetics on leaf traits because of the homogeneous environment among experimental units. To date, there have been no common garden studies which included all ten genera of cycads. The full phylogenetic breadth has, therefore, not been included in this important area of study. Methods We examined macronutrient and micronutrient content of leaves from one representative species from each of the ten cycad genera at Nong Nooch Tropical Botanical Garden in Thailand. Nitrogen content was determined by dry combustion, and the remaining nutrients were quantified by spectrometry. Results The least variable elements were nitrogen and phosphorus, and the most variable elements were boron and sodium. Nutrient content based on leaflet area was more variable than based on leaflet mass, reflecting species differences in specific leaf area. There were no universal macronutrient or micronutrient signals indicating clear phylogenetic distinctions. Implications for Conservation: Active management of threatened cycad taxa requires research to develop the knowledge to enable evidence-based decisions. This common garden study inclusive of all 10 cycad genera creates a foundation to determine leaf nutrient sufficiency ranges to inform management decisions.

Growth dynamics of pachycaulous stems of arborescent cycad plants are not well understood, and most observations have been made in cultivated garden plants. We studied Cycas micronesica plants in Guam, Tinian, and Yap to understand the influences of geography, plant size, sex, and herbivory on stem growth. We also determined the changes in demography of Guam's population after 15 years of damage by non-native insect herbivores. The height increment (HI) was similar for plants within the height range from 100 cm to more than 600 cm, so the relative growth rate declined with height. Female tree HI was 68% of male tree HI, and Yap tree HI was 87% of Guam tree HI. Chronic herbivory by non-native insect herbivores caused a mean 44% decline in HI. Plants in managed gardens grew more rapidly than plants in a wild habitat. The HI was used to estimate that Guam has experienced a complete loss of ≈70 y of demographic depth resulting from the selective mortality of small plants since 2005. When future conservation interventions successfully mitigate the ubiquitous biological threats, our HI may be useful for empirically quantifying recovery of plant health.

Global research agendas on plant nutrient relations attempt to illuminate biotic and abiotic factors that mediate nutrient relations. We contend that cycad species are not adequately represented in these global agendas. Little is known about how various cycad traits such as phylogenetics, growth form, latitudinal range, or ecological niche influence concentration, stoichiometry, and resorption dynamics of leaf nutrients. The addition of cycad species data to the global research dataset will address a critical knowledge gap and benefit global research needs to improve our systemic understanding of biotic and abiotic influences on plant nutrition.

Cycad plants possess uncommon morphological, chemical, and ontogenetic characteristics and they may introduce localized changes in soil traits that increase habitat heterogeneity. We used mature Cycas micronesica K.D. Hill trees growing in a range of soil types in Guam, Rota, and Yap to quantify differences between the soils beneath target trees and paired non-target soils away from cycad trees. The chronic presence of a C. micronesica tree introduced numerous localized changes in soil traits, increasing the heterogeneity of elemental stoichiometry in the community. Nitrogen, carbon:phosphorus, and nitrogen:phosphorus were increased in target soils among every soil type. Carbon increased and phosphorus decreased in most target soils. The habitats revealing the greatest number of elements with differences between target and non-target soils were the habitats with acid soils. The greatest number of metals exhibiting differences between the target and non-target soils occurred in the impoverished sandy habitat. This is the first report that indicates a cycad tree increases community spatial heterogeneity by localized changes in soil chemistry. Contemporary declines in cycad populations due to anthropogenic threats inadvertently decrease this spatial heterogeneity and its influences on primary producers in the landscape then cascading effects on the food web.

Chemical traits of Terminalia catappa L. leaves were determined on the island of Guam to understand the changes caused by beetle leaf herbivory. Green leaf chemistry indicated nitrogen was the most limiting nutrient in the climate and soils of Guam. The changes in leaf chemistry following beetle damage were extensive. Senesced leaf chemistry indicated beetle damage decreased some traits that predict lower leaf litter quality, such as lignin, but also decreased some traits that predict higher leaf litter quality, such as nitrogen. The stoichiometric traits based on carbon:macronutrient and lignin:macronutrient generally predicted higher quality leaf litter following beetle herbivory. The beetles that produce this form of T. catappa leaf damage on Guam are non-native, and overall, the results indicate these pests will increase the rate of litter decomposition and nutrient turnover in habitats where T. catappa is prevalent.

We compiled Red List data from all listed cycad taxa to determine the current status of the world's most threatened plant group. Each Red List threat category had different proportions of genera, and the genera comprised different proportions of threat categories. Each Red List threat category consisted of different proportions of Red List criteria. Each genus was composed of different proportions of Red List criteria, and every genus was represented by different proportions of listed versus non-listed species. Differences among the genera and categories were substantial, revealing no canonical characteristics that define the members of this plant group. Species that are missing from the Red List or Data Deficient deserve high priority for completion of assessment and listing. Cycas is the genus that may change the most as taxonomy and Red List threat assessments continue to be modified. Distinctive overviews of the Red List data such as this one provide a unique snapshot of the conservation status of the world's cycads, and should be repeated as trends evolve.

The leaf nutrient status and stoichiometry of nitrogen (N), phosphorus (P), and potassium (K) were determined for Elaeocarpus joga trees in Guam’s dominant calcareous soils to understand nutrient limitations in limestone soils of Oceania and contribute to global databases on leaf economic spectrum studies. Supplemental N, P, or K was added to soils to determine plant growth and nutrient concentration responses. Leaf and soil quantifications of nutrients enabled multiple trait comparisons. Supplemental N stimulated growth of young cultivated plants without affecting leaf N concentrations. Supplemental K increased leaf K concentration but did not generate a growth response. Supplemental P did not affect growth or leaf P concentration. N:P, N:K, and K:P were most influenced by K additions. Leaf N and P concentrations of mature trees in unmanaged settings were similar to unfertilized young plants in the controlled study, but leaf K concentration was greater in the mature trees. Leaf nutrient relations were not overtly related to soil nutrient relations for mature trees. Results indicate that N and K are the limiting factors in calcareous soils of the Mariana Islands for this endemic tree species, age and size of trees do not greatly influence leaf nutrient content, and leaf stoichiometry is constrained and less variable than soil stoichiometry.

Premise of research. The role of specialist insects in the pollination of cycads is well established, with wind playing little to no role. Questions remain for species within the Cycas rumphii complex that have dispersed via floating seeds to islands far from mainland ancestors. One such species, Cycas micronesica, resides in habitats on the island of Guam that are exposed to trade winds that enhance the potential for wind pollination.Methodology. We examined the distance and direction of horizontal pollen movement either from microstrobili or from experimentally released pollen relative to wind direction and velocity in several different Guam cycad habitats. Wind-dispersed pollen was also captured around megasporophylls and then examined relative to wind and distance from dehiscing microstrobili.Pivotal results. Wind velocity, trap direction, and trap distance from the pollen source were the most important factors affecting pollen capture. In habitats where C. micronesica grows in the deep understory wit...

We have investigated the potential movement on air currents of pollen from Guam’s native cycad, Cycas micronesica, proposed as ambophilic. We measured wind velocities and directions in different cycad habitats that vary in their exposure to trade winds, determined pollen settling velocities, and then modeled the potential horizontal pollen drift distance in each habitat. Similar measurements were performed on several entomophilous Zamia cycads and six zoophilous tropical trees used in horticulture or landscaping. All cycad species’ pollen exhibited relatively slow mean settling velocities (0.73–1.29 cm·s−1) with C. micronesica pollen in the middle of this range. Our models predicted that wind in more open habitats with wind directions east northeast (ENE) to northeast (NE) and velocities >2 m·s−1 could transport C. micronesica pollen, either single grains or clumps, hundreds of meters downwind from the pollen source before falling 1 or 2 m. In forested habitats and at typical heights of cycad cones in the understory, the mean wind velocities ranged from −1 to ≈1 m·s−1. In habitats with mean winds ≥0.2 m·s−1, models predicted pollen transport distances of tens of meters from the pollen source. In sheltered habitats with velocities near 0.03 m·s−1, the potential wind transport of pollen was limited to less than a few meters, suggesting that wind would be an ineffective vector in such areas. Pollen grains of all angiosperm species were larger except one, and the species with larger grains had settling velocities 3–26 times faster than that of cycad pollens. Even so, winds in most Guam environments could transport pollen of most angiosperm species over 50 m before falling 1 m. In summary, the results suggested that pollen size, clumping tendencies, and drift of most of these species do not preclude a role for wind in moving pollen in habitats exposed to trade winds, and that other physical and plant characteristics affect their pollination mode. For C. micronesica, these pollen and plant attributes do not preclude entomophily, and insects are likely required in the deep understory where cycads are present.

Chilades pandava (Lepidoptera: Lycaenidae) larval food quality was studied to determine its influence on adult life history traits. A wild population from Cycas nongnoochiae (Cycadales: Cycadaceae) endemic habitat behaved similarly to the population collected from a garden setting. Cycas micronesica, Cycas revoluta , and Cycas seemannii leaves were used as high-quality food, whereas C nongnoochiae, Cycas taitungensis , and Cycas condaoensis leaves were used as low-quality food. The daily oviposition rate was not influenced by food quality, but longevity and lifetime fecundity of females were increased by high-quality larval food. These results indicate that in situ Cycas species impose a physiological constraint on the genetic capacity to produce offspring by C pandava . The removal of that constraint by high-quality novel Cycas species may be one reason this butterfly can increase in population rapidly after an invasion event and express greater herbivory of Cycas species within invaded regions.

Chilades pandava (Lepidoptera: Lycaenidae) larval food quality was studied to determine its influence on adult life history traits. A wild population from Cycas nongnoochiae (Cycadales: Cycadaceae) endemic habitat behaved similarly to the population collected from a garden setting. Cycas micronesica, Cycas revoluta, and Cycas seemannii leaves were used as high-quality food, whereas C nongnoochiae, Cycas taitungensis, and Cycas condaoensis leaves were used as low-quality food. The daily oviposition rate was not influenced by food quality, but longevity and lifetime fecundity of females were increased by high-quality larval food. These results indicate that in situ Cycas species impose a physiological constraint on the genetic capacity to produce offspring by C pandava. The removal of that constraint by high-quality novel Cycas species may be one reason this butterfly can increase in population rapidly after an invasion event and express greater herbivory of Cycas species within invaded regions.

Contemporary reviews of leaf responses to sunflecks indicate gymnosperms exhibit slower photosynthetic inductions times than angiosperms, but the gymnosperms were represented exclusively by conifers. I recently reported that the gymnosperm Cycas micronesica exhibited photosynthetic induction times in conformity with some of the most rapid angiosperms and opined that representatives from non-conifer gymnosperms must be added to the published conifer database before gymnosperm-wide conclusions can be formulated. Guiding principles for this urgently needed research will maximize relevance and improve accuracy of conclusions.

Research Highlights: Established stands of Leucaena leucocephala (Lam.) de Wit, Spathodea campanulata P. Beauv., and Vitex parviflora Juss. modified soils in Guam&rsquo, s limestone forests, reducing storage pools of carbon, nitrogen, and phosphorus. Background and Objectives: Invasive plants may engineer negative changes in ecosystem properties. This study was conducted to determine changes in soil chemistry following infestations of three problematic tree species on Guam. Materials and Methods: Minerals, metals, and mineralization dynamics were measured in invaded sites and paired sites with biodiverse native tree cover. Results: Most soil properties were significantly changed by long-term infestations of the invasive tree species. The soils within invaded sites exhibited total carbon, total nitrogen, and available phosphorus that were less than native sites. In contrast, the carbon/nitrogen ratio increased for every species-site combination. The other chemical properties were idiosyncratic among the sites and species. Conclusions: Mitigation and restoration activities that include the removal of these trees from project sites may require many years for the below-ground ecosystems to return to their native state. These three invasive trees decrease the ability of Guam soils to sequester recalcitrant forms of carbon, nitrogen, and phosphorus.