Thomas E Marler

University of Guam | UOG · Western Pacific Tropical Research Center

Translocation of endangered plant species and facilitating in situ regeneration require knowledge of the factors that define suitable habitat characteristics. Four approaches were employed to define how antecedent and contemporary plant identity influenced Cycas seedling growth and survival in Guam, Yap, and the Philippines. Cycas micronesica K.D....

Stem cuttings are often exploited for asexual propagation of cycad plants, and impaired health of the source plants may reduce success. A reliable procedure that screens potential source plants for predicted success would benefit conservationists. The cut surfaces of Cycas revoluta stem cuttings obtained from source plants that had endured 0–39 wee...

Cycad transplantation and asexual propagation by stem cuttings are highly successful horticultural procedures because the manoxylic stems contain copious nonstructural carbohydrates. The success of these horticultural procedures may be impaired by antecedent abiotic or biotic stress that decreases stem nonstructural carbohydrate content. The armore...

Background and Research Aims Conservationists aiming to establish seed orchards or restoration plantings benefit from methods that reduce tree juvenility. Previous studies suggest that seedling and sapling mortality is the major limitation to natural population recovery of the critically endangered Serianthes nelsonii. To enable effective restorati...

The pachycaulous stem of cycad plants enables the storage of abundant nonstructural carbohydrates. Cycas revoluta Thunb. and Zamia furfuracea L.f. stems were analyzed for starch and 15 sugars to determine carbohydrate richness. All 15 sugars were detected in both species. The tetrasaccharide stachyose and the disaccharide sucrose comprised most of...

Tabernaemontana rotensis (Kaneh.) P.T. Li is an attractive small tree that is endemic to the islands of Guam and Rota. Conservation efforts of the threatened population are constrained by lack of research. Understanding the ecology of flower and fruit development is fundamental to successful conservation of threatened angiosperms. This study determ...

Aulacaspis yasumatsui Takagi invaded Guam in 2003 and caused the widespread mortality of the indigenous Cycas micronesica K.D. Hill population. The regeneration of the surviving tree population continues to be constrained 20 years later, and a look at the changes in megastrobili traits may inform future conservation management decisions concerning...

The diel patterns of stem carbon dioxide efflux (Es) were quantified for 8 lignophyte tree species using paired trees, with one tree surrounded by hardscape from the bole to the canopy perimeter and the second tree surrounded by grass or mulch. Stem Es was measured at a height of 30 to 40 cm on the boles, and measurements were made about every 2 ho...

Understanding the mechanisms that epiphytic orchids use to sustain plant nutrition may benefit horticulturists and conservationists. Nutrient concentrations of green and senesced leaves and pseudobulbs of Bulbophyllum guamense and Bulbophyllum raulersoniae were quantified to more fully understand the differences between ephemeral and persistent pse...

Plant leaf litter decomposition is directly influenced by the identity of the source plants and the leaf age. Defoliation of forests by tropical cyclones (TC) transfers copious amounts of high-quality green leaf litter to soils. We used a soil amendment approach with the incubated buried bag method to compare carbon (C) and nitrogen (N) mineralizat...

Exposure to environmental toxins may be partly responsible for mammal neurodegenerative disorders. Consumption of seeds from Guam’s cycad tree has been linked to the disorder known as amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS-PDC). The unambiguous identification of causal agents of ALS-PDC has been elusive. We have examined t...

Trees contribute to ecosystem nutrient cycling through the amount, timing, and composition of litterfall. Understanding the nature of this contribution from endangered tree species may aid in species and habitat recovery efforts. Serianthes nelsonii is an endangered tree species from the Mariana Islands, and little is known about litterfall dynamic...

Soils from the rhizosphere of perennial plants accumulate microorganisms that influence the growth of other plants. This microorganism biodiversity may be exploited by using these soils as an inoculum in new planting sites. Soils collected from the rhizosphere of mature Serianthes trees were subjected to treatments designed to reduce or increase mi...

The genus Serianthes has not received adequate research attention, leaving large gaps in the knowledge required to inform conservation decisions. For example, nutrient management protocols are not understood due to lack of research. Serianthes grandiflora, Serianthes kanehirae, and Serianthes nelsonii plants were grown in container culture to deter...

Conservation of the endangered Serianthes nelsonii is constrained by lack of research. Transplanted containerized plants die in the competitive in situ environment. This study determined if foliar applications of nutrient solution could replace edaphic fertilizer applications for mitigating competition for soil nutrients. Weekly sprays with 0.1× Ho...

Knowledge about the position of tree roots is needed to understand tree biology and inform management decisions. Cycad species produce pachycaul stems and are not represented in the published studies on the relationships between aboveground tree traits and root system spread. We measured the radius of root egress from 6-year-old Cycas edentata de L...

Tree stem CO2 efflux (Es) can be substantial and the factors controlling ecosystem-level Es are required to fully understand the carbon cycle and construct models that predict atmospheric CO2 dynamics. The majority of Es studies used woody lignophyte trees as the model species. Applying these lignophyte data to represent all tree forms can be inacc...

The invasion of numerous countries by the armored scale Aulacaspis yasumatsui Takagi has caused widespread mortality of host Cycas species. Few studies have looked at reproductive biology responses of host plants to the herbivore. This study was conducted to determine the influence of direct Cycas seed integument infestation of A. yasumatsui on ger...

Aulacaspis yasumatsui Takagi invaded Guam in 2003, and the influence on survival and demography of the host Cycas micronesica K.D. Hill population has been well-studied. To more fully understand how A. yasumatsui has threatened the host cycad species, we determined the microstrobilus size and number of pollinators per microstrobilus from 2001 to 20...

Greater knowledge concerning the interspecific diversity of the plant leaf ionome is required to effectively understand the spatiotemporal dynamics of biogeochemistry, but Micronesia has been ignored in this literature. The objectives of this study were to quantify the leaf ionome, resorption efficiency, and stoichiometry of leaves from 25 plant sp...

Background and Aims Previous molecular dating studies revealed historical mass extinctions and recent radiations of extant cycads, but debates still exist between paleobotanists and evolutionary biologists in revealing the origin and evolution of Cycadaceae. Methods Using whole plastomic data, we revisited the phylogeny of this family and found th...

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 c...

The literature covering the biology, invasion chronology, host plant responses, and control efforts of the armored scale Aulacaspis yasumatsui Takagi (Hempitera: Diaspididae) is reviewed. The small size of this cycad pest and complex surface morphology of the host cycad organs combine to make visual detection of every cryptic infestation difficult...

A long-term reciprocal garden study was used to determine adaptive variation between Cycas micronesica K.D. Hill plants from north versus south Guam. Half-siblings from each location were planted as one-leaf seedlings in north and south gardens and monitored for 15 years. Stem height and diameter, and leaf number and maximum length were measured ye...

In this short review, we summarize much of the past and current data on the neurological disease spectrum of ALS‐parkinsonism dementia complex (ALS‐PDC) of Guam and the Western Pacific. Once highly prevalent on Guam, ALS‐PDC comprises two overlapping neurological conditions. The first described appeared to be a classical form of ALS first described...

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 transplan...

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 c...

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. T...

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 specia...

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 demograp...

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 th...

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 lea...

Improved horticultural practices may help to reduce demand for wild cycads threatened by unsustainable collection. We determined the influences of leaf retention with or without anti-transpirants on the success and speed of adventitious root development of Zamia furfuracea L.f. and Zamia integrifolia L.f. stem cuttings. Root formation success for b...

The number of branches in male and female plants of Cycas micronesica K.D. Hill, Cycas edentata de Laub., Cycas wadei Merr., and Zamia encephalartoides D.W. Stev. were counted in Guam, Philippines, and Colombia, to confirm earlier reports that female plants develop fewer branches than males. Cycas plants produce determinate male strobili and indete...

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 determ...

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,...

The influences of indole-3-butyric acid (IBA) concentrations of 0–30 mg·g ⁻¹ on the success and speed of adventitious root development of Zamia furfuracea L.f. and Zamia integrifolia L.f. stem cuttings were determined. Root formation success for both species was greater than 95%. The IBA concentrations did not influence the speed of root developmen...

Three groups of beetles inhabit cones of cycads (Cycadales) in the northern hemisphere and are believed to be involved in their pollination. The primitive weevil subtribe Allocorynina (Coleoptera: Belidae) is restricted to the New World cycad genera Dioon Lindl. and Zamia L. One group of weevils (Curculionidae), found only in Cycas L., appears to b...

Methods in sunfleck research commonly employ the use of experimental leaves which were constructed in homogeneous light. These experimental organs may behave unnaturally when they are challenged with fluctuating light. Photosynthetic responses to heterogeneous light and leaf macronutrient relations were determined for Cycas micronesica, Glycine max...

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 unh...

Cycad stem cuttings will develop adventitious roots if the open wound is first treated with a sealant to protect the exposed parenchyma tissue. The commercial pruning wound sealant that is often employed for this purpose is not available in many locations. We used commonly available products as a prophylactic sealant on Cycas edentata, Cycas micron...

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 evaluate...

Island invasions may cause severe changes in biodiversity, but the factors that influence these changes are not well understood. We established 120 plots in Cycas micronesica habitats throughout Guam in 2005 following the invasion of the armored scale Aulacaspis yasumatsui, then observed plant mortality through 2020. We used transects in Yap as ben...

The growth of synchronized leaf flushes or male cones on Cycas trees is an ephemeral event, and non-structural carbohydrates (NSCs) are likely deployed from stem and root storage tissues to support their construction. The relationships among various stem NSCs and these rapid growth events have not been studied to date. Monosaccharides, disaccharide...

The influences of Cycas micronesica and Zamia integrifolia plants on soil chemistry were determined in Tinian and Florida in order to more fully understand how cycad plants affect the environments in which they grow. The introduction of C. micronesica plants into a karst habitat generated decreases in soil phosphorus after five years and increases...

Research Highlights: Established stands of Leucaena leucocephala (Lam.) de Wit, Spathodea campanulata P. Beauv., and Vitex parviflora Juss. modified soils in Guam’s limestone forests, reducing storage pools of carbon, nitrogen, and phosphorus. Background and Objectives: Invasive plants may engineer negative changes in ecosystem properties. This stu...

The diel patterns of stem carbon dioxide efflux (Es) were determined for cycads, monocots, and woody eudicot and gymnosperm tree species. Stem Es at a height of 30–40 cm was measured every 2 h throughout 31-h campaigns. Our range of Es 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 w...

Stem respiration is influenced by the vertical location of tree stems, but the influence of vertical location on stem respiration in a representative cycad species has not been determined. We quantified the influence of vertical strata on stem carbon dioxide efflux (Es) for six arborescent Cycas L. species to characterize this component of stem res...

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 wit...

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 propagatio...

Recent conservation actions for Serianthes nelsonii Merr. and Cycas micronesica K.D. Hill in the Mariana Islands have illuminated some negative consequences associated with ill-informed agents representing permitting and funding agencies. Several cases from the islands of Guam and Tinian are discussed as ineffective conservation examples, and these...

The need for improved knowledge on conservation and management of cycad species has generated recent interest in compiling a database on leaf nutrient concentrations. However, the sampling protocols have not been consistent among reports and the influences of some plant and habitat traits on the plasticity of cycad leaf nutrient concentrations has...

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 p...

The soils beneath and surrounding mature Artocarpus mariannensis, Elaeocarpus joga, and Serianthes nelsonii trees were studied in northern Guam limestone forests to determine the role of these trees in maintaining spatial heterogeneity of biogeochemistry. The soils beneath S. nelsonii were nutrient-enriched compared to soils away from S. nelsonii....

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 nurse...

Cycas micronesica K.D. Hill trees on the island of Yap were used to determine the influence of position along the leaf rachis on macro- and micro-nutrient concentrations and how leaf age affected the results. The outcomes revealed improvements to sampling protocols for future cycad leaf research. The concentration of every element except carbon and...

The direct role of physical dormancy in delaying germination of Serianthes grandiflora Bentham, Serianthes kanehirae Fosberg, and Serianthes nelsonii Merrill seeds has not been adequately studied, nor has the role of temperature on germination behaviors. Imbibition testing indicated seeds with scarified testa absorbed water for the duration of a 24...

The role of seed imbibition and light during germination are not known for the critically endangered Serianthes nelsonii Merr. Scarified seeds were pre-soaked in gibberellic acid (GA3) up to 300 mg/L and nitrate solutions of 3000 mg/L to determine if germination was influenced by these treatments. Scarified and imbibed seeds were incubated in high...

The influences of stem flexure on shade-grown Serianthes nelsonii Merr. stem growth and strength were determined in a container nursery setting. Treated stems were bent 90° two times daily for a 14 wk nursery production period. Plant height, internode length, and slenderness were decreased by stem flexure when compared with control plants that rece...

The seasonal aspects of Guam’s Serianthes nelsonii seed rain quantity, new seedling emergence, and lifespan of newly emerged seedlings were determined by direct observations. Two high wind events in January and September 2013 generated 63% of the annual number of new seeds collected in litterfall. A defoliating tropical cyclone in May 2015 generate...

The scale predator Rhyzobius lophanthae Blaisdell was introduced to Guam and Rota to control invasive Aulacaspis yasumatsui Takagi armored scale infestations on the native Cycas micronesica K.D. Hill populations. The predator demonstrated a clear preference for A. yasumatsui infesting adult plants, resulting in 100% seedling mortality due to the la...

Plant size influences the leaf nutrient relations of many species, but no cycad species has been studied in this regard. We used the arborescent Cycas micronesica K.D. Hill to quantify leaf nutrient concentrations of trees with stems up to 5.5-m in height to determine if height influenced leaf nutrients. Green leaves were sampled in a karst, alkali...

Epiphytic orchid species grow in stressful conditions that include nutrient deficiency. A greater understanding of the factors that influence epiphytic orchid nutrition may benefit conservationists and horticulturists. Green and senesced leaf nutrient concentrations of the epiphytic Dendrobium guamense were quantified among six host tree species to...

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 influenc...

Essential nutrients and metals have been quantified in stems of many tree species to understand the role of stems as storage and source organs. Little is known about stored stem resources of cycad tree species. Cycas micronesica tissue was collected from apical and basal axial regions of stems; and pith, vascular, and cortex tissues were separated...

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 an...

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 indica...

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 suff...

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 200...

The pachycaulous stem of arborescent cycad species exhibits unique traits and has received limited research. To date, nothing is known about the axial and radial spatial patterns of non-structural resources within cycad stems. Cycas micronesica K.D. Hill stem tissue was collected from apical and basal axial positions of ca. 100-cm tall plants to se...

The coconut rhinoceros beetle (CRB, Oryctes rhinoceros L.) is a serious pest of coconut (Cocos nucifera L.) in many tropical regions, however the influences of CRB herbivory on the coconut leaf chemistry are unknown. This limits our ability to predict the afterlife decomposition dynamics of the damaged coconut leaf litter. Mature green and senesced...

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 micronesica K.D. Hill on the islands of Guam and Rota. Questions remain as to how this small hemipteran insect can so rapidly kill a large cycad tree. One poss...

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...

Conservation agencies charged with care of threatened plant species should be governed by the concepts that conservation actions should do no harm. Adaptive management research progresses in imperfect situations due to incomplete knowledge. Interpreting new experimental or observational evidence for inclusion in conservation plans should first cons...

Best protocols for cycad propagation require more research

The population size and structure of Cycas wadei were assessed along with habitat traits to update the current level of knowledge for conserving this Critically Endangered endemic species. Direct measurements of plant density and size, chemical analyses of soil and leaf tissue samples, and surveys of sympatric plants were conducted. The adult popul...

Mature Cycas micronesica trees were among the forest trees that were destined to be removed from a 2012 construction site in northern Guam. Forty-nine of these trees were cut at the base and transported to nursery conditions to determine if adventitious root development could be stimulated as a means of saving the trees. Fungicide and auxin were ap...

The chemical changes in soils following the use of non-native Acacia trees to mitigate soil erosion from barren scars within Guam’s grassland savanna were determined and compared to continuously vegetated sites. Chemistry of the soils in a 20-yr-old Acacia site was dissimilar to that of the grasslands and adjacent native forest sites. Stoichiometry...

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