Final Report for SW08-067
Ironwood trees (Casuarina equisetifolia) on the island of Guam began dying in 2002. By 2005, Ironwood tree decline (IWTD) was widespread and undiagnosed. With funding from Western SARE (Sustainable Agriculture Research and Education) in 2008, a research program commenced with preparations for a five-day IWTD conference in 2009. Research of conference attendees and others since then established that a complex of abiotic and biotic factors are involved in IWTD. Abiotic factors include host genetics, site environment and management practices. Biotic factors include Ganoderma wood rot, termites and xylem-residing bacteria Ralstonia solanacearum, Klebsiella oxytoca and K. variicola.
Objective 1: Develop a diagnostic key for all known injury, signs and symptoms that occur on Ironwood worldwide. Consultation: Five day meeting on Guam to finalize survey procedures and diagnostic key.
Objective 2: Determine the amount of change in Guam’s Ironwood population from 2002 to the present.
Objective 3: Categorize tree damage according to injury, signs and symptoms and record percent of each occurrence.
Objective 4: To inform the public of the survey finding and to form an Ironwood Tree Decline Committee.
Objective 5: Identify a source of seeds from superior Ironwood trees that the Guam Department of Agriculture can use in their give-away program.
Objective 6: Based an analysis of the data collected in Objectives 1-3 a conclusion will be drawn as to the cause or causes for ironwood decline.
Objective 7: Drawing from the results of objective 6 and the knowledge and expertise of others, the Ironwood Tree Decline Committee will develop management strategies for Ironwood decline and host a three half-day Ironwood tree workshops: one for government agency employees and two for farmers and the general public.
Causarina equisetifolia, locally known in the English language as Ironwood and in the Chamorro language as “Gago,” is known to be indigenous to Australia, the Malayan Islands, the east side of the Bay of Bengal and occurs on many islands of the Pacific, extending eastward to the Marquesa Islands and northward to the Mariana Islands (Safford, 1905). Pollen records indicated that Ironwood has grown on Guam for thousands of years (Athens and Ward, 2004) and is likely native to Guam (Fosberg et al., 1979; Stone, 1970). It has been continually propagated on Guam since the 1600s, possibly due its usefulness and low maintenance requirement. As a result of its tolerance to salt spray and typhoon damage and its ability to support nitrogen-fixing Frankia, endo- and ectomycorrhiza and protioid roots, the tree is able to thrive in the Mariana Islands where typhoons and coral sand beaches and other nutrient-poor soils are commonplace.
The tree is an evergreen. Its needle-like jointed branchlets bear the anatomical minute tooth-shaped leaves. As a result of limited leaves and floral structures, the tree has the ability to conserve moisture and tolerate drought. Within the Mariana Islands the average lifespan of Ironwood is estimated to be 35 to 90 years, with an average maximum height and circumference at breast height of 13.7 and 2.9 m, respectively. Due to damage from typhoons in the Mariana Islands, exposed trees are often topped with prolific epicormic shoots, which results in a shorter tree with a wider crown than what is typically seen in Hawaii, an area with few typhoons.
Ironwood thickets are a component of Guam's forestland, where it is considered a secondary forest species (Liu and Fischer, 2006). Ironwood trees do not compete with native tree species in undisturbed limestone forests (Moore, 1973), although it grows nearly everywhere; beaches, landfills, road shoulders, cleared land and vacant lots. In the Mariana Islands it grows both in the clay volcanic soils of savanna grasslands and calcareous and loamy sands of coastal strands. In large dense strands, trees produce a thick, slowly decomposed, allelopathic litter layer that eliminates nearly all understory vegetation.
Several prominent forest features of Ironwood on Guam were mentioned in a 2002 Guam Forest Bulletin (Donnegan et al., 2004). Ironwood trees were reported to be among the healthiest trees on the island with an estimated population of 115,924 for trees greater than five inches in diameter at breast height. C. equisetifolia was mentioned as a prominent member of the halophytic (sea-salt adapted vegetation type. This vegetation is found along beaches in the north and south, where it may be composed solely of ironwood or a mixtures of other species including Cocos nucifera, Guettarda speciosa, Hernandia sonora, Pandanus tectorius, Scaevola taccada, Thespesia populnea and Tournesfortia argentea. On the sandy beaches of the Mariana Islands, it has become an important perching tree for the white-collared kingfisher (Halcyon chloris) and the Mariana fruit-dove, Ptilinopus roseicapilla (Marshall, 1949). The white tern, Gygis alba, commonly lays eggs in ironwood trees.
Ironwood Tree Decline (IWTD) on Guam:
Decline was first noticed in 2002 by a local farmer, and since that time ithas been investigated by the PI of this project. The trees at that site were less than 10 years old and planted in single-row windbreaks of several hundred trees. Less than five trees were characterized as wilted with the following symptoms: acropetal progression of chlorosis, tip-burn of lower branchlets giving the tree a singed appearance, and tree death within six months. Roughly 15 trees had symptoms of decline, which included internal wood discoloration, thinning of branches and tree death after several years. Natural Resources personnel with Commander Navy Region Marianas (COMNAVMAR) became aware of trees dying in large numbers at the Naval Station in 2004. At that time approximately one third of all the Ironwood trees at the naval station were dead. By 2005, Ironwood Tree Decline was widespread on Guam.
Despite the myriad of utilities and merits of the Ironwood tree to the Pacific island of Guam, its future is in doubt as its health and survival rate has been deteriorating for years. Ironwood trees, like all trees, have a natural finite life span within a given ecosystem; however, Guam’s trees are dying at rates that far exceed the norm. What is happening on Guam fits the classic definition of tree decline: symptoms are nonspecific such as the thinning of branches; tree health gradually deteriorates leading to tree death over a course of several years; and decline is attributed to a complex environment of infectious and non-infectious agents. However, Guam’s trees deviate from the classic model where mature trees are more prone to decline.
Donnegan, J.A., S.L. Butler, W. Grabowiecki, B.A. Hiserote, D. Limtiaco. 2004. Guam’s forest resources, 2002. Resour. Bull.PNW-RB-243, Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station 32 p.
Duke, J.A. 1997. Casuarina equisetifolia J.R. & G. Fort. Purdue University Center for New Crops and Plant Products.
Elfers, S.C. 1988. Element stewardship abstract for Casuarina equisetifolia. The National Conservancy 13 p.
Elevitch, C.R., K.M. Wilkinson 2000. Information Resources of Pacific Island Agroforestry. Agroforestry guides for Pacific Islands #1. Permanent Agriculture Resources, Holualoa, Hawaii, USA.
GDAWR: Guam Department of Agriculture’s Division of Aquatic and Wildlife Resources. 2005. Fact Sheet: Birds of Guam
Ho, Kuen-Yih, Chern-Hsiung Ou, Jenq-Chuan Yang, and Ju-Ying Hsiao. 2002. An assessment of DNA polymorphisms and genetic relationships of Casuarina equisetifolia using RAPD markers. Bot. Bull. Acad. Sin 43:93-98
Marshall, J.T., Jr. 1949. The endemic avifauna of Saipan, Tinian, Guam, and Palau. Condor 51: 200-221
Mohanan, C., J.K. Sharma. 1993. Diseases of Cauarina equisetifolia in India. Commonwealth Forest Review. 72(1): 48-52
Moore, B. 2002. Hybrid poplars in natural buffer systems for agricultural pollution reduction and income enhancement. WSARE Research and Education Project SW98-006.
Ramsden, M., J. McDonald, and F.R. Wylie. 2002. Forest pests in the South Pacific region: a review of the major causal agents of tee disorders. ACIAR Project FST/ 2001/045: Development of Forest Health Surveillance Systems for south Pacific Countries and Australia
Sanfiorenzo, A. 2001. Demonstrating the benefits of agroforestry practices on family farms. WSARE Farmer/Rancher Project FS99-098
Taimanao, E. 2004. Luta windbreak/agroforestry project. WSARE Farmer/Rancher Project FW01-091
Wilson, K. L. and L. A. S. Johnson 1989. Casuarinaceae. In Flora of Australia, vol. 3, Australian
Young, F.J. 1985. Soil survey of Territory of Guam, Nation Cooperative Soil Survey
Diagnostic key: An ongoing literature search for disease and other information on Casuarina equisetifolia has been conducted, compiled and continuously updated (Appendix pg 1-8).
Ironwood tree decline conference: Participants and attendees included administrators, researchers, students, the general public and six off-island experts. Fourteen sites were visited during the five-day conference period where samples in the form of branches, cross-sections (roots, trunks and branches) and sporocarps were collected and brought to the laboratory at the University of Guam’s science building.
Ironwood tree decline (IWTD): Photographs of 44 randomly selected trees with varying levels of decline were categorized into saplings to small trees (DBH ? 32 cm) or large trees (DBH > 32 cm). These were then visually catalogued based on a five-scale decline severity (DS) rating. Percent bare branches (PBB) were determined by analyzing the photographs. Cross-sections of five small and three large tree trunks and of branch trunk intersections from 34 small and 26 large trees were examined for evidence of discoloration or wood rot. Four to five branches from randomly selected trees were removed (30 cm from branch tip) and growth parameters measured. The branch sections were stripped and branches and branchlets (needles) weighed. Cones were counted, weighed and placed in 20-cm diameter Petri dishes on the laboratory bench (temperature 24-25C and 50 – 55% relative humidity) to promote seed release.
Nematode extraction: Ten grams of roots were collected from the top 10 centimeters of soil around ironwood trees. Eight trees were surveyed: four were in decline and four appeared healthy. Roots were rinsed to remove soil. Roots were cut into sections of a centimeter in length. Ten grams of roots were placed in a flask with 200 ml of water and placed in a shaker at 200 rpm for a total of 57 hours of shaking. The water and roots were passed through a 140-mesh sieve to collect the roots, and a 400-mesh sieve to collect the nematodes. The 400-mesh sieve was flushed and nematodes were collected in 20 ml of water. Two ml of nematode suspension were placed in Petri dishes and identified under an inverted compound microscope. Nematode numbers are per one gram of root tissue.
One-hundred ml of soil were collected from the top ten centimeters of soil associated with Casuarina roots. The soil samples were processed using a modified Jenkins (1964) centrifugation and flotation technique, using 100 ml subsample. Twenty ml of the nematode suspension was placed in tubes and a 2.0 ml aliquot was placed in a cover slip-bottom dish and all the nematodes present were identified to the lowest taxon possible. The resulting numbers are in number of nematodes per 10 ml of soil.
DeLey’s and Blaxter’s (2002) system of classification was used for most of the nematode classification. Photographic images were taken of many of the nematodes taxa found in this study. An inverted Nikon compound microscopes and a Leica DM1000 compound microscope were used for taxon identification, and a Motic 2.0 camera and an imaging program were used for the pictures.
Gall wasp damage: The longest branches of a tree, attainable by a ladder and/or modified rope system, were cut 30 cm from branch tip. Four branches from each of five declined trees (DS=0,1,2,3,4) were removed and proportion of needles damaged by the gall wasp determined.
Tree survey: In 2008 and 2009, GPS-assisted surveys were conducted along Guam’s major thoroughfares, as well as a number of coastal intersecting roads to farmers’ fields, agricultural experimental stations, parks, beaches, cliffs and golf courses. For each sample tree, a set of measurements were taken and selected for analysis (Table 2). Sites were evaluated for stand origin (natural and planted) and management (slight, moderate and high). Slight management practices were those associated with tree stands (natural or planted) that were allowed to develop unattended. Moderate management practices were those associated with tree stands in parks and cemeteries. High management practices reflect conditions around Ironwood trees on golf courses and campuses. The GPS receiver (GPSmap 76CSx, Garmin International Inc.) was read 1 m above ground level held against the north-side of the tree. Each tree was given a decline rating by two researchers using the five-scale IWTD severity rating (Figure 8). A total of 1,398 trees at 38 sites were surveyed for decline from October 2008 to June 2009 (Survey I). From July 2009 to December 2009, a follow up survey of the original trees was conducted (Survey II). This survey was expanded to include additional characteristics, as well as 29 additional trees and six sites.
Statistical modeling: Modeling was used to evaluate a set of data from 1,427 individual trees, 44 sites and 16 GIS maps. The primary objective of using statistical models with the Ironwood tree data is to find possible factors that could be related to tree decline, in other words to find the parameters that have a positive or negative impact on the tree (Schlub, 2010). Various modeling techniques were applied to address data set issues. The logic model, which used dieback as the response variable, was found to be the best fit with the data.
Tree sites were examined using the original tree explanatory variables (Table 2) plus those derived from 16 GIS map characteristics (Kennaway, 2010): cemetery buffer, FIA trees with conks (multi-ring buffer); fire risk; fires per year; proximity to golf courses; land cover; management areas; school buffer, soil available water at 150 cm, available water at 25 cm soil depth; soil depth to restrictive layer; soil series; and vegetation. Some maps were dropped from the analysis because of correlations between regressors. A multiplicative change in the odds ratio of unhealthy vs healthy was calculated one regressor at a time by increasing the regressor one unit and holding all remaining regressors constant.
Sporocarp survey: Trees were only surveyed for sporocarps of basidiomycete, due to low infrequence of sporocarps of non-basidiomycetes wood rotters. A tree survey was conducted to quantitatively and qualitatively document existing basidiocarps of wood decay fungi on Ironwood trees in Guam and Saipan in January and February, 2012. The methodology used to document existing basidiocarps was developed, in part, to be consistent with previous surveys of ironwood on Guam (Schlub et al., 2010). Tree surveys were conducted in areas where trees were moderate to large in size, easily accessible and where their health was in question. Three areas on Guam were surveyed and six on Saipan. One-hundred and three Ironwood trees were inspected in three different locations in Guam and 44 trees in six locations in Saipan.
Testing for Ralstonia solanacearum (bacterial wilt): Declining trees at Bernard Watson’s farm were cut down with a chain saw. Three to six inch sections were cut from the trunk of the felled trees using a chain saw. The sections were brought back to the laboratory. All sections had discoloration and bacteria began to puddle on the cross sections. The bacteria was tested using Agdia Ralstonia solanacearum immunostrips following the directions from Agdia and showed positive. A LAMP test was done on the samples and this also gave positives for R. solanacearum. The LAMP method follows:
LAMP primers (primer sequences are proprietary) and Assimilating Probes (Kubota et al., 2011. probe sequences are proprietary) designed to selectively amplify and detect DNA from Ralstonia solanacearum were synthesized by Integrated DNA Technologies (Coralville, Iowa). LAMP reactions were performed in 25 ?L (total volume) reaction mixtures containing 1.6 ?M FIP and BIP, 0.2 ?M of the F3 and B3 primers, 0.8 ?M of the loop F primer, 0.08 ?M of the fluorescent strand of the assimilating probe, 0.16 ?M of the quenching strand of the assimilating probe, commercially available Isothermal Master Mix without dye (Catalog No. ISO-001nd, Diagenetix, Inc., Honolulu, HI), and template DNA. Reactions were carried out in capped 0.2 mL microtubes (Catalog No. 93001-118, VWR International LLC., Radnor, PA, USA) with temperature controlled in the block of a commercial real-time LAMP instrument (Smart-DART system, Diagenetix, Inc., Honolulu, HI), at 65C for 30 minutes and then terminated by heating to 80C for two minutes. Real-time fluorescence value of on-going reactions with Assimilating Probes were measured every 30 seconds of 30 minute reaction.
Pests and diseases: Guam's Ironwood tree insects and pathogens are generally considered incidental or opportunistic. Damage by incidental pests are precluded primarily by abiotic disorders. Drought periods, especially during the dry season, will primarily affect plants in poor planting sites where the trees become stressed and consequently become vulnerable to these insects and pathogens. Some pathogens may be agents of latent infections; therefore, the infection precedes environmental changes that trigger symptom production.
Scarab Beetles: Scarab larvae of the subfamily Cetoniinae, the group to which the beetles Protaetia pryeri and Protaetia orientalis belong, feed on organic matter in the soil, and some species damage the roots of plants (Borror et al., 1989). P. orientalis was first noted on the island in 1972 (Schreiner and Nafus 1986), and the first published discovery of a beetle matching the description of P. pryeri was in 1990 (Schreiner, 1991). Beetle larvae were found under C. equisetifolia, Pithocellobium dulce Roxb., and Leucaena leucocephala (Lam.) De wit, and in one instance under turfgrass. Larvae and frass were found under healthy and diseased Casuarina. Preliminary results from field research conducted by Campora in 2005 at the naval station and naval magazine in Guam showed no connection between the invasive beetles P. pryeri (Janson) and P. orientalis and dying Ironwood trees.
Termites: In India, termites feed on underground roots and stems of live C. equisetifolia. This type of damage is believed to be occurring in Guam as well. From past entomological surveys and reports there are at least six species of termites in Guam (Su and Scheffrahn, 1998). Colonies of Nasutitermes sp. and Microtermes sp. were found feeding on dead Ironwood trees (Moore, A., personal communication). The Philippine milk termite Coptotermes gestroi was responsible for killing ironwood trees transplanted onto a new golf course (Yudin, L.S., personal communication). The hollowing of trees by termites is often seen in sites with a high decline incidence (Figure 1). In some instances, it appears that old conks, serve as a food source and entry point for termites. It is also possible that termites are contributing to the high incidence of xylem residing bacteria and Ganoderma in declining trees through transmission and or the creation of points of entry for the pathogens.
Gall wasp: Damage to branchlet tips (Figures 2, 3 and 4) by an unidentified gall wasp (Figure 5) is known to reduce branchlet length and total banchlet mass (Mersha et al., 2009). The impact on tree health is probably negligible but may be significant on trees with thinning foliage (Figure 6). The wasp reared from branchlet tip galls was identified as belonging to the genus Selitrichodes (Eulophidae: Tetrastichinae) by John LaSalle, CSIRO, Australia.
Xylem residing bacteria: Ralstonia solanacearum the cause of bacterial wilt is among the most commonly worldwide reported pathogens of Casuarina. It is a xylem-resident bacterium mainly entering via roots. Though only occasionally reported as serious, bacterial wilt has emerged as the most serious disease of Casuarina in China (Huang et al., 2011) after its discovery in 1964.
Based on culturing from symptomatic tissues, immunostrip data, LAMP data, and other tests, R. solanacearum has now been confirmed on Guam. In addition, two companion bacteria (Klebsiella oxytoca and K. variicola) were found to be associated with the wetwood symptom, which is common in declined trees. Thus, two xylem-resident bacterial genera are associated with IWTD, Ralstonia and Klebsiella. In Guam, trees that harbor these bacteria do not manifest the same symptoms as those observed in China. In China, the field symptom is rapid tree death (Figure 7), which is triggered by severe environmental stress such as that caused by a typhoon or draught. On Guam, bacterial colonization of the xylem results in trees with thinning foliage, which is indistinguishable from symptoms associated with IWTD (Figure 8).
Differences between China and Guam diseases can also be seen in symptoms revealed in cross-sections of the trunks and limbs. In China, xylem vessels of trunk cross-sections contain diffused areas of slightly darker tissue and yield copious amounts of bacterial ooze (Figure 9).
On Guam, cross-sections of infected trees revealed uncontained areas of dark discoloration "wet-wood", with sharply defined borders that radiated from the center of the tree. Droplets of bacterial ooze may or may not appear and are generally restricted to the "wetwood" which has a high moisture content (Figure 10).
Nematodes: Not a great deal is known regarding the effects of nematodes on C. equisetifolia. However, certain species of nematodes do infect its roots: Helicotylenchus cavenessi, Radopholus similes, Rotylenchulus reniformis, Tylenchus sp., Xiphinema ifacolum; Angiospermae: Cuscuta campestris, Dendrophthoe falcata, Dendrophthoe lanosa. Nematode infections rarely result in the death of infected hosts, but it is not uncommon for certain root disease fungi to infect nematode-damaged roots, resulting in further damage, and even mortality in some cases.
To determine if there is a linkage between the presence of nematodes and Ironwood decline, Dr. Marisol Quintanilla extracted nematodes from Ironwood roots and associated soils. Helicotylenchus sp. was the only herbivore recovered from health trees roots. Tylencholaimellus sp., Aphelenchoides sp. and one unknown were recovered from trees with dieback. Helicotylenchus sp. and Tylenchus sp. were consistantly collected from healthy and dieback soil (Table 1). It was concluded that Helicotylenchus was the only nematode that was isolated consistently enough to be remotely implicated in Ironwood decline.
Fungal wood-rot: There are many fungi involved in wood rot or decay; one group are the basidiomycetes. The fruiting body or sporocarps of these fungi are called basidiocarps. The basidiocarps found in Guam and Saipan were either flat (resupinate) (Figure 11) or shelflike (conk) (Figures 12 and 14). Though usually present, the sporocarp (the fruiting body that bears spores) does not have to be present for wood rot to occur. To date, five conk-forming basidiomycete genera have been identified from Ironwood on Guam, all in the class Agaricomycetes: Ganoderma, Favolus, Pycnoporus, Phellinus and Sarcodon (Schlub et al., 2011). Distinguishing features for Guam's Ganoderma sp. sporocarp includes a cap that is unvarnished, gray to brown, and fan shaped, with an white pored under-surface that when young easily bruises brown (Figure 12). It invades woody tissue through an unrestricted mycelial network while sustaining themselves on cell and cell wall components (Figure 13). Descriptors for Guam's Phellinus sp. sporocarp includes a cap that is more or less fan-shaped, often formed in overlapping shelves, rusty-brown to dark-brown, cap margins when young are yellow-brown and pubescent, with a yellow-brown under-surface (Figure 14).
As a result of island-wide surveys, there were mainly two species of basidiomycetes on most affected trees; Ganoderma sp. (australe group) which fruits on tree roots, butt and less commonly on trunk (Figure 12) and Phellinus sp., which primarily fruited on the butt (Figure 14) (Schlub et al., 2012). Both are common on Guam (Figure 15) and infrequent on Saipan (Figure 16). The presence of Ganoderma is a consistent indicator of a tree in decline, and its occurrence is irrespective of tree size. Phellinus is found in association with Ganoderma or by itself on very large mature trees. On its own, Phellinus does not appear to be a contributor to Ironwood decline.
Ironwood tree decline conference: In accordance with this project's objectives, The Ironwood Tree Decline Conference was held from January 6, 2009 through January 10, 2009 (Figure 17). Participants and attendees included local producers, University of Guam administrators and researchers, students, the general public and six off-island experts. The participants reviewed research related to C. equisetifolia production worldwide and its growth on Guam (Mersha et al., 2010a, Mersha et al., 2010b; Schlub, 2010; Schlub et al., 2010). This working conference incorporated both field work and group discussion. Field work consisted of traveling to 14 different sites around Guam to survey declining and non-declining trees and to collect samples in the form of branches, cross-sections (roots, trunks and branches) and sporocarps. Field trips were taken each day of the conference. A trip to Western SARE grant participant Bernard Watson’s farm was taken, where over 1,000 Ironwood trees were in varying stages of decline. A backhoe was rented and used to uproot trees at the University of Guam Yigo Experiment Station and at the Anderson Air Force Base golf course so that the off-island plant pathologists could view and take root samples (Figure 18). A trip to Cocos Island, located two miles off of southern Guam, was undertaken so that participants could view trees that were not in any stage of decline. All field trip samples were brought back to the University of Guam Science Building laboratory for processing and analysis. On Wednesday, January 7, 2009, presentations and discussions were conducted at the University of Guam Science Building (see Agenda and Presentations Appendix pg 9-13). Findings of the conference were reported at the 4th International Casuarina Workshop (Schlub et al., 2011).
Tree survey: A total of 1,398 trees at 38 sites were surveyed for decline from October 2008 to June 2009 (Survey I) (Figure 19). From July 2009 to December 2009, a follow up survey of the original trees was conducted (Survey II) (Figure 19). For each tree and site, explanatory variables of decline were measured including tree circumference, fire damage, typhoon damage, presence or absence of termites, presence or absence of conks and various geographical or cultural conditions.
Symptoms: The presence of discoloration at the branch juncture of large branches of declining trees was consistent for large trees at all DS levels, where it discolored 80 to 100% of the branch cross-sections but was inconsistent for small trees at 1 and 2 DS levels. In healthy small trees, the cuts were clean and non-discolored. In large trees discoloration due to mature heartwood was occasionally observed. There was a clear, consistent gradient of discoloration within the tree trunk of declining trees (Figure 20). Linear functions derived from the average proportion of discolored wood at each sampling distance describe well the actual acropetal wood discoloration gradients recorded within small and large trees (Figure 20). Wood rotting fungi that produce “conks” are known to cause the internal discoloration and white soft rot commonly found in DS 3 level trees (Figure 13). The importance of these fungi in decline is also supported by the fact that the percentage of trees with “conks” increased with IWTD: 2, 18, 35, 47, and 66 % for DS 0, 1, 2, 3, and 4 level trees respectively.
At DS=1, the outward symptom of IWTD is indistinguishable from those produced by Guam's xylem-resident bacteria. Internal symptoms (as seen in trunk cross-sections) vary from tree to tree and with decline severity. Small trees (<50 CBH) and those at DS=1 generally have symptoms associated with bacterial infection of the xylem, others have no bacterial ooze and only a small area of centrally-located, contained discoloration. Medium size trees and those at DS=2 usually have bacterial symptoms (Figure 10), and less common signs of wood rots caused by Ganoderma (Figure 13) and termites. Trees in a severe state of decline harbor one or all of the following: bacteria, termites, various resupinate sporocarps (Figure 11) and conks of Ganoderma australe species complex (Figure 12), Phellinus (Figure 14) and other Agaricoymcetes.
Analysis of individual trees: For each sample tree, a set of measurements were taken and selected for analysis (Table 2). The primary objective of using statistical models with the Ironwood tree data is to find possible factors that could be related to tree decline, in other words to find the parameters that have a positive or negative impact on the tree (Schlub, 2010). Various modeling techniques were applied to address data set issues. The logic model, which used dieback as the response variable, was found to be the best fit with the data. Three explanatory variables were found to be significant and therefore could explain the Ironwood’s state of health (Table 2). Among the three regressors, presence of conks had the largest coefficient value at 3.31. The impact of each individual regressor was determined numerically by holding all other regressors constant. The odds favoring decline is 27.3 times greater for a tree with conks than without.
Conk reference to any resupinate or shelflike sporocarp of a basidiomycete appearing on a lower trunk (<0.25 tree height) or roots of an Ironwood tree (Casuarina equisetifolia).
Analysis of tree sites: Tree sites were examined using the original tree explanatory variables (Table 2) plus those derived from 16 GIS map characteristics (Kennaway, 2010): cemetery buffer, FIA trees with conks (multi-ring buffer); fire risk; fires per year; proximity to golf courses; land cover; management areas; school buffer, soil available water at 150 cm, available water at 25 cm soil depth; soil depth to restrictive layer; soil series; and vegetation. Some maps were dropped from the analysis because of correlations between regressors. A multiplicative change in the odds ratio of unhealthy vs healthy was calculated one regressor at a time by increasing the regressor one unit and holding all remaining regressors constant.
There were six positive dieback predictors: increasing circumference, increasing altitude, presence of conks, presence of termites, planted stand vs natural stand and urban land location.
There were four negative dieback predictors: increasing water availability at 25 cm soil depth, golf course location, forest location and decreases in latitude.
In summary, the most beneficial variable identified was soil moisture. Trees in areas with the highest moisture were 3.3 times less likely to be declined. Likewise, the most deleterious variable was the presence of basidiocarps. Trees with conks were 27 times more likely to be in a declined state.
Predicting tree size: As a result of multi-linear modeling, several factors were identified that may positively (+) or negatively (-) predict the average size of trees at a site (cm in circumference at 1.3 m). The size of a tree is restricted by tree stand density, altitude and soil depth.
Sites with large trees are more likely to be found in urban, forest, national parks and fire prone areas than in sites at golf courses or in close proximity to a school. It was also found that increased circumference is associated with trees having termites, conks, typhoon damage and multiple trunks. This suggests that large highly vigorous trees are able to tolerate stresses to which less vigorous trees would have succumbed.
Linking dieback with site productivity: Based on the premise that tree circumference in 2008 and 2009 is an indicator of site productivity, an association between IWTD and circumference was sought. The circumference map supports the concept that nearly the entire island is suitable for the growth of small trees (Figure 21). However, as the size of the trees increases, the area suitable for sustained growth decreases. When the map for dieback (Figure 22) is visually compared to the map for circumference (Figure 21), dieback appears poorly linked to site productivity (circumference) and strongly linked to the central area of Guam. This suggests that IWTD is not a natural progression of tree maturation and death. Many factors have been evaluated as possible causes or contributors to Ironwood decline. Those that have some perceived relevance by the authors are listed in Table 3.
Recommendations: Due to IWTD slow progression and general sporadic nature, decline on Guam could be reduced substantially through cultivar selection and cultural practices which promote health grow and preclude favorable conditions for pests (termites) and pathogens (wood-rots, root-rots and bacteria).
Cultivar selection: It was concluded, by attendees of the IWTD conference held on Guam in 2009, that the severity of the Ironwood decline was likely acerbated by the lack of genetic diversity of Guam's Ironwood tree population. Khongsak Pinyopusarerk recommended the evaluation of seedlots used in the 1991-1993 International Provenance trials of Casuarina equisetifolia (Pinyopusarerk et al., 2004). Though Guam's tree was planted in 21 countries at that time, the actual trial was never conducted on Guam. As a result of funding from the U.S. Forestry Service, a scaled down version of the international trial was planted at Bernard Watson farm (N 13.56545; E 144.87790) in 2012. This trial was planted in late July 2012, in an area of severe IWTD with the hope that, in the future, superior trees will be identifiable. The replicated trial (three blocks) consisted of 11 paired seedlots (similar geography) of four trees each from 12 countries including Guam, with 8 ft. tree spacing (Figures 23 and 24).
Site Evaluation and Soil Attributes: Site evaluation and soil care before planting ensures a healthy transplanted plant with increased tolerance to transplant shock as well as a tree that will reach its full maturity. Ironwood is suited for a range of sites and locations. Its growth habit dictates that it be planted 40 feet from houses and 20 feet from each other. In urban, windrow and agro-forestry situations closer spacing may be necessary.
The island of Guam has three broad landform categories, each with their own set of soil parent materials, which are responsible for the formation of eight major soil units, each with unique chemical and physical attributes (Figure 25). Chemical attributes of a soil are those related to the activity of ions within the soil solution; measurements include pH and Cation Exchange Capacity (CEC). Though Ironwood can grow across Guam's wide range of soil pH, soil nutrients are maximized between pH 6-7. Cation Exchange Capacity is a measure of the soil's ability to hold unto nutrients, which increases with a soil's fertility. Low CEC soils (<11) have a low capacity to hold on to nutrients and are subject to leaching of mobile anion nutrients. Landscape tree in low CEC soils are subject to nutrient deficiencies and will benefit with the addition of a slow-release fertilizers with micronutrients.
The physical attributes of a soil are those related to the size and arrangement of its solid particles. Measures of physical properties include soil bulk density, soil texture, soil porosity or percolation. Bulk density is an indicator of soil compaction, which is an indicator of root growth and soil porosity or percolation. The majority of the island of Guam has clay soils with bulk densities of 0.60-1.0 g/cm3, which are ideal for clayey soil. Unfortunately the soil is shallow; often no deeper than 16 cm. The permeability or percolation rate for Guam's soils vary widely from poor (0.1 inches or less / hour) to rapid (5.0 inches or more). Poor soils should be avoided or modified as they promote shallow rooting, poor growth and root rots. Rapid soils are fine for Ironwood, provided their roots can reached the water table, which will be critical for their survival in the dry season. Soil in an ideal state for tree growth contains 50% solids (45% mineral material and 5% organic matter) and 25% each of air and water.
Site remediation: Compacted soil in or near a planting pit should be remediated as necessary. The detrimental effects of compacted soil may include inadequacies in infiltration, aeration and water holding capacity. These factors could contribute to decreased root penetrability and thus increased susceptibility to drought and transplant shock. Remediation methods include soil aeration and incorporation of organic matter to improve porosity. Aeration is normally conducted using an air-tool or air-spade. Because Guam's productive layer is thin, vertical mulching also may add benefit to new planting sites. Vertical mulching consists of using an air-tool or drill to make vertical holes in the soil into which conditioned porous soil is added.
Tree installation: Plants should be installed in saucer-shaped hole/ pit that allow for expansion of the root zone with minimal substrate resistance (Figure 26). Soil should be removed with as little disturbance of the soil's profile as possible. Due to Guam's poor subsoil, mixing of topsoil and subsoil should be avoided. When backfilled, the site's profile should matching the original. To enrich the topsoil, amend with organic material. Large rocks on the side or bottom of the pit should be removed with a backhoe or cracked with an air-tool or auger. The hole should be free of rocks and debris. It is a misconception that adding rocks or gravel in the bottom of the planting hole improves drainage. Care should be taken to avoid planting in holes with steep sides or made with a corer that compresses the sidewalls, because in this scenario the roots could encircle amongst themselves leading to girdling roots. Balled or container trees must be carefully placed in the hole without disturbing the root ball. After installation, the tree should be staked.
Planting bare root plants: After planting bare rooted trees, gently tap the soil and backfill with water to remove air pockets. Additional staking may be required of bare rooted trees. Bare root plantings, although limited to smaller Ironwood plants, allow for earlier adaptation to the new site and faster transplant recovery. However, a drawback in using this technique is that initially roots and the planting pit must be kept sufficiently moist to prevent roots from drying out. It is estimated that in Guam during the dry season early care should by administered for at least three months and about one month in the wet/rainy season. Early care consists of providing tree transplants a stress free environment, which may include daily watering.
Nutrient management: Guam’s soils benefit from nutrient augmentation, especially in sandy soil and areas where soil has been disturbed. The soils of northern Guam are calcareous. Trees in these soils will likely benefit from the addition of chelated iron throughout their life time. Fertilizer needs to be use sparingly, as the development of nitrogen fixing Frankia and beneficial mycorrhizal will be held back with over application. A low nitrogen, slow release fertilizer with micronutrients is ideal. Alternatively, apply a small amount (50 to 100 g) of a low analysis complete fertilizer such as 10-10-10 at transplant.
Mulching: Mulching or placement of organic material around the base of a new plant can be one of the most beneficial cultural practices for young Ironwood trees. Mulch is anything used to cover the soil’s surface for the purpose of improving plant growth and development. To be suited for plant growth, mulch must allow the exchange of air between the soil and the atmosphere and allow water to infiltrate into the soil profile. The selected mulch (e.g. Ironwood needles) should be placed between 1-2 inches deep. Benefits of mulching include: conservation of soil moisture, moderation of soil temperature, improvement of soil quality (organic mulches), suppression of weeds, enhancement of landscape appearance, reduced maintenance and protection of plants from damage caused by maintenance equipment.
Fertilizing: Fertilizing (also see nutrient management), especially in the early stages of planting, helps root development and may improve drought tolerance, thereby reducing transplant shock.
Watering: Watering or irrigation needs should be a part of the planning process, especially if planting is to occur in the dry season. Any irrigation program implemented should be based on knowledge of the soil percolation rates for the site. Excess moisture could lead to root rot.
Pruning: Pruning for health and training the young tree for structurally optimal strength relies on the judicious removal of plant tissue in a manner, as much as possible, consistent with minimal invasiveness to the plant. Proper pruning practices will enhance the overall health of the plant and should be guided by established standards. Tool sterilization is critical in ensuring sanitation and reducing the potential transfer of pathogens. Wind damaged trees should be correctly pruned as quickly as possible to reduce the amount of deadwood and reduce the surface areas of branches ripped in strong wind. Removal of deadwood reduces the establishment of termites and wood-rotting fungi that contribute to hazardous trees in Guam's urban landscape. Trees broken from typhoons should be felled by excavation instead of sawing, where their colonization by a wood rotting fungus could possibly lead to infecting the root systems of neighboring healthy trees.
Athens, J.S. and Ward, J.V. 2004. Holocene Vegetation, Savanna Origins, and Human Settlement of Guam. In: Attenbrow, V. and Fullagar, R. (eds), A Pacific Odyssey: Archeology and Anthropology in the Western Pacific. Papers in Honour of Jim Specht. Records of the Australian Museum Supplement, 29:15-30.
Borror, D. J., C. A. Triplehorn, and N. F. Johnson. 1989. An Introduction to the Study of Insects. Saunders College Publishing, Florida, 875 pp.
Campora, C. 2005. Potential relationship between the decline of mature Casuarina equisitifolia L. on Guam Naval Station and the presence of two invasive beetles, Protaetia pryeri (Janson) and Protaetia orientalis (Gory and Percheron) (Coleoptera: Scarabaediae): Preliminary report, 13 pp.
De Ley, P. and M. Blaxter. 2002. Systematic Position and Phylogeny. In: The Biology of Nematodes. Lee, D. ed. Taylor and Francis, New York.
Donnegan, J.A., Butler, S.L., Grabowiecki, W., Hiserote, B.A. and Limtiaco, D. 2004. Guam’s Forest Resources, 2002. USDA, Forest Service, Pacific Northwest Research Station, Resource Bulletin, PNW-RB-243.
Fosberg, F. R., Sachet, M., and Oliver, R. 1979. A geographical checklist of the Micronesian dicotyledonae. Micronesica 15: 1-295.
Huang, J., He, X., Cai, S., Ke Y., Chen, D., and Tang, C. 2011. Current Research on Main Casuarina Diseases and Insects in China In: Zhong, C., Pinyopusarerk, K., Kalinganire, A., Franche, C. (eds), Proceedings of the 4th International Casuarina Workshop, Haikou, China 21-25 March 2010, pp 232-238.
Jenkins, W. R. 1964. A rapid centrifugal-flotation technique for separating nematodes from soil. Plant Disease Reporter 48:692.
Kennaway, L. 2010. Compiled spatial data from US Forestry Service, Dept. Defense, WERI, NOAA, Guam Planning & Statistics. USDA-APHIS-PPQ-CPHST Fort Collins CO.
Liu, Z., and Fischer, L. 2006. Guam vegetation mapping using very high spatial resolution imagery – Methodology. USDA Forest Service, Pacific Southwest Region, Forest Health Protection.
Marshall, J. T. 1949. The endemic avifauna of Saipan, Tinian, Guam, and Palau. Condor 51: 200-221.
Mersha, Z., Schlub, R.L. and Moore, A. 2009. The state of ironwood (Casuarina equisetifolia subsp. equisetifolia) decline on the Pacific island of Guam. Poster in 2009 APS annual proceedings Portland, Oregon: Phytopathology, 99:S85.
Mersha, Z., Schlub, R.L., Spaine, P.O., Smith J.A. and Nelson, S.C. 2010a. Visual and quantitative characterization of ironwood tree (Casuarina equisetifolia) decline on Guam. Poster in proceedings of 2010 APS annual meeting Charlotte, North Carolina: Phytopathology, 100:S82.
Mersha, Z., Schlub, R.L., Spaine, P., Smith, J., Nelson, S., Moore, A., McConnell, J., Pinyopusarerk, K., Nandwani, D. and Badilles, A. 2010b. Fungal Associations and Factors in Casuarina equisetifolia decline. Poster in proceedings of 9th International Mycological Congress Edinburgh, UK:IMC9:P3.268.
Moore, P. H. 1973. Composition of a limestone forest community on Guam. Micronesica 9: 45-58.
Pinyopusarerk, K. Kalinganire, A., Williams, E.R. and Aken, K.M. 2004. Evaluation of International Provenance trials of Casuarina equisetifolia. ACIAR Technical Reports Canberra. No. 58 106 pp
Safford, E. W. 1905. Useful Plants of Guam. U.S. Government Printing Office. Facsimile printing 2009 – Jillette Leon-Guerrero/Guamology Publishing, 416 pp.
Schlub, K.A. 2010. Investigating the Ironwood Tree (Casuarina equisetifolia) Decline on Guam Using Applied Multinomial Modeling. M.Ap. Stat. thesis, Louisiana State University.
Schlub, K.A., Marx, B.D., Mersha, Z. and Schlub, R.L. 2010.
Investigating the ironwood tree (Casuarina equisetifolia) decline on Guam using applied multinomial modeling. Poster in proceedings of 2010 APS annual meeting Charlotte, North Carolina: Phytopathology, 100:S115.
Schlub, R.L., Mersha, Z., Aime, C.M., Badilles, A., Cannon, P.G., Marx, B.D.. , McConnell, J., Moore, A., Nandwani, D., Nelson, S.C., Pinyopusarerk, K., Schlub, K.A., Smith, J.A., and Spaine, P.O. 2011. Guam Ironwood (Casuarina equisetifolia) Tree Decline Conference and Follow-up. In: Zhong, C., Pinyopusarerk, K., Kalinganire, A., Franche, C. (eds). Proceedings of the 4th International Casuarina Workshop, Haikou, China 21-25 March 2010, pp239-246.
Schlub, R.L., Mendi, R. C., Aiseam, C.C., Mendi, R. C. Davis, J.K. and Aime, M.C. 2012. Survey of wood decay fungi or Casuarina equisetifolia (ironwood) on the islands of Guam and Saipan. Phytopathology 102:P416.
Schreiner, I. H. 1991. Sources of New Insects Established on Guam in the Post World War II Period. Micronesia Supplement 3: 5-13, 1991.
Schreiner, I. H. and D. Nafus. 1986. Accidental Introductions of Insect Pests to Guam, 1945-1985. Proc. Hawaiian Ent. Soc. 27: 45-52.
Stone, B. C. 1970. The Flora of Guam. Micronesica 6: 1-659.
Su, N.-Y. and R.H. Scheffrahn. 1998. Coptotermes vastator Light (Isoptera: Rhinotermitidae) in Guam. Proc. Hawaiian Entomol. Soc. 33: 13–18.
Young, F.J. 1988. Soil survey of the territory of Guam. USDA Soil Conservation Service, National Cooperative.
- Figure 1. Picture: A cross-section of a small declined windrow tree (DS=3) infested with termites. Bacterial ooze positive for Ralstonia solanacearum was present on the cut surface. Basidiocarps were present.
- Figure 9. Picture: Cross-section of a tree in China with bacterial wilt reveals copious amounts of bacterial ooze and tissue discoloration. From a presentation of Huang Jinshui, He Xueyou, Ke Yuzhu, Cai Shouping, Chen Duanqin, and Tang Chensheng of Fujian Academy of Forestry Sciences at International Casuarina Workshop Haikou, China 21-25 March 2010.
- Figure 18. Picture: Ironwood Decline Conference attendees visit a declined tree site at Anderson Air Force Base, Yigo, Guam.
- Figure 3. Picture: Casuarina wasp exit hole on damaged branchlet tip of C. equisetifolia.
- Figure 4. Picture: Witches’ broom symptom on ironwood branch caused by infestation of gall wasp (foreground) in comparison to healthy branches (background).
- Figure 5. Picture: Unidentified Casuarina gall wasp belonging to the genus Selitrichodes (Eulophidae: Tetrastichinae) resting on branchlet of C. equisetifolia.
- Figure 7. Picture: Bacterial wilt of C. equisetifolia sapling in China (photo provided by Dr. Chonglu Zhong).
- Figure 8. Pictures: Representative photographs of small (above) and large (below) solitary trees from locations around Guam depicting five-levels of decline severity (DS) and percentage of bare branches (PBB).
- Figure 10. Picture: Cross-sections of infected C. equisetifolia tree revealed expanding areas of moist discolored wood (wetwood) that radiated from the center of the tree accompanied by droplets of bacterial ooze composed of Ralstonia solanacearum and Klebsiella spp.
- Figure 12. Picture: Sporocarp (conk) of Ganoderma australe species complex on C. equisetifolia. On Guam, 100% of the trees in decline sites may have conks on their roots or butts.
- Figure 13. Picture: Cross-section of rotted ironwood tree butt infected with Ganoderma australe species complex. Note expanding network of white mycelial strands.
- Figure 14. Picture: Sporocarp (conk) of a Phellinus sp. on C. equisetifolia trees. This fungus is likely a part of the normal decay process of the ironwood trees in the Mariana Islands and not a contributor to IWTD.
- Figure 15. Graph: Percentage of trees on Guam with root, butt, or lower trunk basidiocarps, which were identifiable as Ganoderma (australe complex) or Phellinus. The survey area and sites include trees flanking sidewalks on University of Guam campus (UOG 1 & 2), a woodlot at George Washington High School (GW), and windbreaks at Onward Mangilao Golf Course (OM 1, 2, & 3).
- Figure 17. Picture: Participants from the five-day IWTD conference.
- Figure 19. Map: Means of decline severity (DS) found at sites during Survey II (July to December 2009). Values in comparison to Survey I (October 2008 to June 2009) remained nearly the same (square), increased (up-triangle) or decreased (down-triangle).
- Figure 20b. Graph: Proportion of wood discoloration in trunk cross-sections fitted to a linear decay function for small (upper) and large (lower) trees and trunk cross-sections from two small trees, one declined (top) and one healthy (bottom).
- Figure 20. Picture: Proportion of wood discoloration in trunk cross-sections fitted to a linear decay function for small (upper) and large (lower) trees and trunk cross-sections from two small trees, one declined (top) and one healthy (bottom).
- Figure 21. Map of observed tree circumference in cm (CBH) over a longitude-latitude grid of the island of Guam; hence, areas of large trees sites (purple color) have habitats more suitable for ironwood growth irrespective of the presence of IWTD.
- Figure 23. Plot diagram of Guam’s Casuarina equisetifolia provenance trial.
- Table 1. Nematode counts per 10 ml soil samples from healthy ironwood trees and those with dieback.
- Table 2. Grouping and descriptions of ironwood tree variables, those in bold were found to be the most suitable for predictive purposes.
- Table 3. Likely contributors to ironwood decline and their perceived relevance from low * to high ****
- Figure 6. Graph: The proportion of ironwood tree branchlet tips damaged by the Casuarina gall wasp across the five-scale tree decline severity rating: 0 (healthy) to 4 (nearly dead).
- Figure 11. Picture: Multiple sporocarps of a unidentified resupinate polypore on an ironwood tree (Casuarina equisetifolia), on the campus of the University of Guam, Mangilao, Guam.
- Figure 26. Drawing: General hardware guidelines for tree installation.
- Figure 2. Picture: Healthy branchlet tip of C. equisetifolia (top) and a tip further magnified with gall wasp damaged (bottom).
- Figure 16. Graph: Percentage of trees on Saipan with root, butt, or lower trunk basidiocarps, of which were identifiable as Ganoderma (australe complex) or Phellinus. The survey area and sites on Saipan include trees in landscaped areas at American Memorial Park (AMP 1, 2, & 3), Fisherman Memorial (FM), Tennis courts (TC), Banzai Cliff (BC), Lau Lau Bay (LLB), and Public Works Beach (PWB).
- Figure 22. Map of the predicted probability of dieback using a logistic model. Areas in blue indicate regions where dieback is most likely to occur.
- Figure 24. Picture: Provenance trial 3.5 months after transplanting
- Figure 25. General Soil Map of Guam (Young et. al., 1988).
As the result of statistical modeling of survey data of 1,500 Ironwood trees (C. equisetifolia) at 50 sites on Guam and Saipan, it is now apparent that Guam’s Ironwood trees are dying as the result of a complex of biotic and abiotic factors. Survey calculations in 2008 and 2009 resulted in an estimated decline percentage of 51% for trees greater than 12.7 cm at breast height. With the reporting of this project, decline of C. equisetifolia on the island of Guam was brought to the attention of local, national and international organizations that are currently engaged in silviculture, agroforestry and tree improvement of this valuable pantropical tree. Many organizations and companies are now aware of Guam’s plight: APHIS, Arbor Global, Chinese Academy of Forestry, CNMI Forestry, CSIRO Plant Industry of Australia, Guam Forestry, The Davey Institute, Forestry Committee of the American Phytopathological Society, Guam Cooperative Extension Service, International Casuarina Workshop, RREA, University of Guam, U.S. Forest Stewardship program (RREA), and Western International Forest Disease Work Conference.
The broader awareness of ironwood decline in the scientific community has led to the building of alliances between Project Director Dr. Robert Schlub and researchers at institutions outside of Guam:
M. C. Aime: University of Purdue, West Lafayelle, IN 47907, USA
A. M. Alvarez: University of Hawaii at Manoa, Honolulu, HI 96720, USA
C. M. Ayin: University of Hawaii at Manoa, Honolulu, HI 96720, USA
K. Kubota: University of Hawaii at Manoa, Honolulu, HI 96720, USA
A. Badilles: Northern Marianas College, Rota, MP 96951, Northern Mariana Islands
A. Route: Northern Marianas College, Saipan, MP 96950
V. C. Guerrero, Jr.: CNMI Forestry, Saipan, MP 96950
P. G. Cannon: USDA Forest Service, Vallejo, CA 94592, USA
B. D. Marx: Louisiana State University, Baton Rouge, LA 70803, USA
D. Nandwani: University of the Virgin Islands, Kingshill, VI 00850 U.S.A.
M. Quintanilla: Formerly of Northern Marianas College, Saipan, MP 96950
S. C. Nelson: University of Hawaii at Manoa, Honolulu, HI 96720, USA
K. Pinyopusarerk: CSIRO Plant Industry, Canberra, ACT 2601, Australia
K.A. Schlub: Formerly of Louisiana State University, Baton Rouge, LA 70803, USA
J. A. Smith: University of Florida, Gainesville, FL 32611, USA
P. C. Spaine: APHIS, Riverdale, MD 20737, U.S.A.
M. L. Putnam: Oregon State University, Corvallis, OR 97331, U.S.A.
L. F. Kennaway: USDA-APHIS-PPQ-CPHST, Fort Collins, CO 80526, U.S.A.
K. K. Eckert: Arbor Global, Kaillua, HI 96734, U.S.A.
B. Rao: The Davey Institute, Kent, OH 44240, U.S.A.
A. B. Persad: The Davey Institute, Kent, OH 44240, U.S.A.
C. Zhong: Chinese Academy of Forestry, Guangzhou 510520, China
The building of alliances with researchers and their institutions have lead to new funding sources for Ironwood tree decline (IWTD) research.
Project Title: Mitigating the Impact of Ironwood Tree (Casuarina equisetifolia) Decline in the Mariana Islands
Funding agency: U.S. Forest Service Pacific Southwest Region
Amount of funding: $20,000
Project Title: Isolation and characterization of Ralstonia solanacearum strains and assessment of their role in decline of ironwood (Casuarina equisetifolia) on Guam.
Funding agency: USDA-NIFA #2011-51120-31149 sub-award # 201120630-GUAM4, Western Integrated Pest Management Center”
In the future it is anticipated that there would be additional funding sources identified to improve the current predictive Ironwood decline model through a new tree survey. This new survey will involve isolation of species-specific termites, fungi and bacteria. None of the original 1992-1994 provenance trial trees, other than the Guam trees, were ever planted or evaluated in Guam until 2012. From evaluation of the Guam’s international provenance tree trial, the body of knowledge of these trees will be strengthened.
Education and Outreach
Outreach year one
In accordance with this project's objectives, The Ironwood Tree Decline Conference was held from January 6, 2009 through January 10, 2009. Participants and attendees included local producers, University of Guam administrators and researchers, students, the general public, and six off-island experts. This working conference incorporated both field work and group discussion. Field work consisted of traveling to fourteen different sites around Guam to survey declining and non-declining trees and to collect samples in the form of branches, cross-sections (roots, trunks and branches) and sporocarps. Field trips were taken each day of the conference. A trip was undertaken to Western SARE grant participant Bernard Watson’s farm, where over 1,000 Ironwood trees are in varying stages of decline. A backhoe was rented and used to uproot trees at the Agricultural Experiment Station and at the Anderson Air Force Base golf course so that the off-island plant pathologists could view and take samples from roots. A trip to Cocos Island, located two miles off of southern Guam, was undertaken so that participants could view trees that were not in any stage of decline. All field trip samples were brought back to the University of Guam Science Building laboratory for processing and analysis. On Wednesday, January 7, 2009, presentations and discussions were conducted at the University of Guam Science Building (see Agenda and Presentations Appendix pg 9-13). The conference was highly successful and was well-received by the grant’s Cooperators and the Guam community. The conference was highlighted here on radio, television and newspapers.
Outreach activities for the general public included interactive Ironwood tree displays set up at the annual University of Guam’s Charter Day and at the Environmental Protection Agency’s Earth Day activities. Hundreds of students, teachers and members of the general public were informed of IWTD and Ironwood tree care during each day-long activity (Figure 27).
Outreach activities for the scientific community included a poster on Western SARE research to date that was presented at the annual meeting of the American Phytopathological Society in Portland, Oregon.
Outreach year two
Outreach activities for the general public included presentations on the importance of the Ironwood tree to the island's ecology and agriculture, how to care for Ironwood trees and how to identify and reduce the impact of IWTD. Activities included advisement of advanced high school biology students on Saipan on the tree species Casuarina equisetifolia (ironwood tree) and interactive displays at the University of Guam's Charter Day and at the Environmental Protection Agency's Earth Day. Hundreds of students, teachers, farmers and members of the general public were informed of IWTD and Ironwood tree care as a result of these activities. Approximately 52 landowners and managers were trained to develop Stewardship Plans during these events were. The number of direct contacts resulting in increased awareness of benefits and opportunities during these events was approximately 840.
Outreach activities for the scientific community included posters presented at three international professional meetings (the 4th International Casuarina meeting in Haikou, China the annual meeting of the American Phytopathological Society, Charlotte, North Carolina, and 9th International Mycological Congress Edinburgh, UK); a thesis from the Louisiana State University Experimental Statistics department by Karl A. Schlub “Investigating the Ironwood Tree (Casuarina equisetifolia) Decline on Guam Using Applied Multinomial Modeling”; a visit and review of our activities from the USDA Region 5 Forest Pathologist Dr. Phil Cannon; and a presentation on the Northern Marianas island of Saipan entitled “Studies on the Decline of the Tree Species Casuarina equisetifolia in the Marianas Archipelago” for the Asia Pacific Academy of Science, Education, and Environmental Management.
Outreach year three
Outreach activities for the general public included presentations on the importance of the Ironwood tree to Guam’s ecology and agriculture, how to care for Ironwood trees and how to identify and reduce the impact of IWTD. Activities included instruction of Cooperative Extension field agents and University of Guam Agriculture majors conducted by Dr. Schlub and Ms. Melody Putman of Oregon State University. Interactive displays were set up at the University of Guam's Charter Day and at the Environmental Protection Agency's Earth Day (Figure 28 and 29). As a result of these activities, hundreds of visitors, made up of students, teachers, farmers and members of the general public, were informed about Ironwood tree decline and Ironwood tree care. The number of landowners and managers trained to develop Stewardship Plans during these events was approximately 50. The number of direct contacts resulting in increased awareness of the benefits and opportunities during these events was approximately 930.
Outreach activities for the scientific community included two presentations at the Forest Pathology and Tropical Plant Pathology Special session of the 2012 Annual Meeting of the American Phytopathological Society and two accompanying abstracts.
Outreach no cost extension period
Outreach activities for the general public included an interactive Ironwood tree display set up at the annual University of Guam’s Charter Day activities. Hundreds of students, teachers and members of the general public were informed of IWTD and Ironwood tree care during full day-long activity.
Outreach to the scientific community included a presentation at the Proceedings of the 60th Annual Western International Forest Disease Work Conference. Also, an abstract and paper was presented. The publication is in press.
In January of 2012 three workshops were held under the theme “Tree Care Workshops for the Ironwood Tree and other trees of the Mariana Islands.” The objectives of the workshops were:
A. To improve Guam’s Ironwood tree health and its long-term outlook.
B. Promote good stewardship of the Ironwood tree and other agroforestry species.
C. To explore collaborative projects with The Davey Tree Expert Company.
Two full-day workshops were held for farmers, golf course superintendents, landscapers, government agencies and agriculture professionals. There were 40 participants who were in attendance for some or all of the workshops activities. Participants were from the University of Guam Cooperative Extension and Experiment Station; Guam Department of Agriculture; Guam Department of Parks and Recreation; Guam’s golf course superintendents; Anderson Air Force Base; Naval Station; Guam Division of Aquatic Wildlife Resources; Guam Natural Resource Conservation Service, U.S. Fish and Wildlife Service National Wildlife Refuge; Commonwealth of the Northern Mariana Islands Department of Agriculture Forestry; Northern Marianas College Cooperative Extension; and grant cooperator and farmer Bernard Watson represented the Farmers Association (Figure 30). Presenters for the two-day workshop included grant program investigator Dr. Robert Schlub and grant cooperators Dr. Aubrey Moore and Davey Tree Company representative Dr. Anan Persad. A 77-page manual created for the workshop and authored by Dr. Robert Schlub, Dr. Arnan Persad and Dr. Bao Rao titled “Plant Health Care: for Guam’s Gago/Ironwood (Casuarina equisetifolia) and other trees of the Marianas” was passed out to all participants of the workshops. The agenda for all three workshops can be found in Appendix pg 14-16.
The first day of the two-day workshop focused on Ironwood tree decline and Ironwood tree care. Classroom presentations were given during the morning hours, while field trips to in the the Mangilao Golf Course (Figure 31), Yigo Agriculture Experiment Station and Bernard Watson’s farm were accomplished in the afternoon. The purposes of the field trips were to have participants observe Ironwood trees in various stages of decline and to discuss the symptoms and signs of decline and Ironwood tree care.
The third workshop was a half-day workshop for the general public. Eighty participants including teachers, students, home gardeners and home owners attended the workshop (Figure 32). Presenters for the workshop included grant program investigator Dr. Robert Schlub and grant cooperators Dr. Aubrey Moore and Davey Tree Company representative Dr. Anan Persad. Presentations were on Ironwood tree decline and general tree care. The Guam Department of Agriculture Forestry, Landscape Management Systems and this grant's principle investigator gave away hundreds of Ironwood, palm, and native tree seedlings to the participants (Figure 33). Brochures on tree care and tree planting were handed out and participants were able to discuss trees and tree health care with the experts.
Workshop participants were asked to fill out a workshop true/false questionnaire designed to gauge knowledge gained and the overall success of the workshop. Fifty of the eighty participants turned in the questionnaire. The results follow:
90% of participants marked true - I feel I can more effectively monitor for disease/pests.
96% of participants marked true - I feel I can more effectively plant trees.
68% of participants marked true - I feel I can more effectively prune trees.
96% of participants marked true - I feel I can more effectively choose the right tree for the right place.
96% of participants marked true - I feel I know more about the Ironwood tree and what causes its decline on Guam.
Also, there was a section on the questionnaire that asked for additional comments. The following are all of the additional comments received (as written on the questionnaires):
-Excellent! Thank you very much. I live in Windward hills and I have watched an Ironwood on cross island road and wanted one and never knew what it was. I’m a school teacher on the navy base and only lived on Guam for a year and a half. I’m excited to help with your research and take care of trees in my yard.
- Great workshop! Thank you!
-Still more workshops on topic specific to Guam needs/conditions, what other plants/trees can be planted together. Thanks for doing!
-Thank you! Excellent class-more needed!
-Thank you for your interest in education us on the Ironwood tree.
-Thank you for this type of workshop. It’s a great opportunity to learn how to plant the proper way. Please continue to bring other workshops to the community. When you bring these workshops, people are intended to come. Everyone wants to keep Guam beautiful. Thank you/si yuos maase!
Final Educational Product: A Cooperative Extension Service educational publication titled “Gago, Guam Ironwood Tree (Casuarina equisetifolia): Past, Present, and Future” was completed. This 28 page publication will be available to the public at the CES/ANR office, given out at future workshops, and has been place online at http://www.uog.edu/admin/assetmanager/images/cnas%20anr/finalreducedwsare%20ironwood%20manual%2003-25%20.pdf
Schlub, R.L, ed. (2013). Gago, Guam ironwood tree, Casuarina equisetifolia: past, present, future (R.L. Schlub Ed.). Guam Cooperative Extension Service Publication. 28p.
Schlub, R.L., Schlub, K.A., Alvarez, A.M., Aime, M.C., Cannon, P.G., and Persad, A. 2012. Integrated perspective on tree decline of ironwood (Casuarina equisetifolia) on Guam. In: Brown, J., Comp. 2013. Proceedings of the 60th Annual Western International Forest Disease Work Conference; 2012 October 8-12, Lake Tahoe, CA. (In Press).
Schlub, R.L., Mendi, R. C., Aiseam, C.C., Mendi, R. C. Davis, J.K. and Aime, M.C. (2012). Survey of wood decay fungi or Casuarina equisetifolia (ironwood) on the islands of Guam and Saipan (abstract). Phytopathology 102:P416.
Mersha, Z., Aime, M. C., Cannon, P., Nandwani, D., Nelson, S., Spaine, P.C., and Schlub, R.L.2011. Decline of Casuarina equisetifolia (ironwood) trees on Guam: Ganoderma and Phellinus. Phytopathology 101:S216.
Schlub, R.L. (2011). Guam’s dying gago gain worldwide attention. In: Terral, O. (ed), 2010 Impact Report, Western Pacific Tropical Research Center, University of Guam, pp15-16.
Schlub, R.L., Mersha, Z., Aime, C.M., Badilles, A., Cannon, P.G., Marx, B.D. , McConnell, J., Moore, A., Nandwani, D., Nelson, S.C., Pinyopusarerk, K., Schlub, K.A., Smith, J.A., and Spaine, P.O. (2011). Guam ironwood (Casuarina equisetifolia) tree decline conference and follow-up. In: Zhong, C., Pinyopusarerk, K., Kalinganire, A., Franche, C. (eds), Proceedings of the 4th International Casuarina Workshop, Haikou, China 21-25 March 2010, pp239-246.
Schlub, R.L., Moore, A., Marx, B., Schlub, K., Kennaway, L., Quintanilla, M., Putnam, M., Mersha, Z., 2011. Decline of Casuarina equisetifolia (ironwood) trees on Guam: Symptomatology and explanatory variables. Phytopathology 101:S216.
Mersha, Z., Schlub, R. L., Spaine, P.O., Smith J.A., and Nelson, S.C. (2010). Visual and quantitative characterization of ironwood tree (Casuarina equisetifolia) decline on Guam. Poster in proceedings of 2010 APS annual meeting Charlotte, North Carolina: Phytopathology 100:S82
Mersha, Z., Schlub, R.L., Spaine, P., Smith, J., Nelson, S., Moore, A., McConnell, J., Pinyopusarerk, K., Nandwani, D., and Badilles, A., 2010. Fungal Associations and Factors in Casuarina equisetifolia decline. Poster in proceedings of 9th International Mycological Congress Edinburgh, UK: IMC9: P3.268
Schlub, K. 2010. iinvestigating the ironwood tree (Casuarina equisetifolia) decline on Guam using applied multinomial modeling. M. Ap. Stat., Louisiana State University, Baton Rouge
Schlub, K.A., Marx, B.D., Mersha, Z., Schlub, R.L. (2010). Investigating the ironwood tree (Casuarina equisetifolia) decline on Guam using applied multinomial modeling. Poster in proceedings of 2010 APS annual meeting Charlotte, North Carolina: Phytopathology 100:S115
Mersha, Z., Schlub, R.L. and Moore, A. (2009). The state of ironwood (Casuarina equisetifolia subsp. equisetifolia) decline on the Pacific island of Guam. Poster in 2009 APS annual proceedings Portland, Oregon: Phytopathology, 99:S85.
- Figure 27. Picture: Project Director Dr. Robert Schlub discusses ironwood tree decline and care with students attending the University of Guam’s Charter Day activities.
- Figure 28. Picture: Dr. Robert Schlub discusses IWTD with visiting students at the University of Guam Charter Day activities.
- Figure 29. Picture: Guam Lieutenant Governor Raymond Tenorio (left) visiting IWTD display at the EPA Earth Day activities, shown with UOG-CES lab technician Roger Brown.
- Figure 31. Picture: Field trip to the Mangilao Golf Course. Participants observed ironwood trees in various stages of decline and discussed the symptoms and signs of decline and ironwood tree care.
- Figure 33. Picture: Workshops participants begin proceeding out of the classroom to receive free tree seedlings and get expert advice on tree care.
- Poster APS meeting 2009
- Poster APS meeting 2010 Phytopathology 100S115
- Pub Proceedings 4th international casuarina worksop pg 239-246
- Pub Final Product – WSARE ironwood manual
- Pub in Forest Health – Casuarina Dieback on Guam Page 7
- Pub Karl Schlub Masters Thesis
- Pub WIFDC proceedings 2012a
- Poster APS meeting 2010 Phytopathology 100S82
- Figure 30: Picture: Some of the day one and two participants.
- Figure 32. Picture: Workshop participants from the general public begin filling up the classroom at the University of Guam prior to presentations.
- Poster APS meeting 2012 102P416
- Pub Abstracts APS annual meeting
Education and Outreach Outcomes
Areas needing additional study
Preliminary species identification of termites on Ironwood and the formulation of possible termite attack patterns through sampling and observations in healthy and declining tree stands are needed on Guam. Most of the severely declining trees on Guam are heavily infested with termites. We believe termites may be feeding on underground roots and stem of live Casuarina equisetifolia, but we lack the research to support this belief. In India, the damage occurs below the ground level mainly in the upper 20 cm where termites hollow out or severely ring bark on the taproot, which results in the death of the seedlings. Termites reported to occur on Ironwood trees include Guam genera of Nasutitermes, Microtermes and Coptotermes. The Formosan subterranean termite, Coptotermes formosanus (Shiraki), is known to attack live Ironwood trees and is reportedly found in Japan, Sri Lanka, Phillipines, Guam, Hawaii, South Africa and the continental United States. In Thailand, Coptotermes gestroi is a subterranean termite that is a destructive pest of standing Ironwood trees.
Presence of bacteria in declining Ironwood trees needs to be evaluated as a possible contributors to Ironwood decline. Bacterial colonization of the xylem is seen in trees with thinning foliage, which is indistinguishable from those attributed to Ironwood decline. Three bacterium were consistently isolated: Ralstonia solanacearum, Klebsiella oxytoca and K. variicola. We believe Kebsiella spp. are responsible for the wetwood symptom associated with Guam's declining trees and that both R. solanacearum and Klebsiella spp. play a role in tree decline. The current model will likely be strengthened with surveys that involve Ralsonia and Klebsiella.
Future studies should contain a control component. Due to Ironwood tree decline's slow progression and general sporadic nature, decline on Guam could be reduced substantially through cultivar selection and cultural practices which promote healthy growth and deny favorable conditions for pests (termites) and pathogens (wood-rots, root-rots and bacteria). It needs to be determined if treating Ironwood trees with termiticides will eliminate or reduce IWTD. Both liquid termiticides treatments and termite baits should be tested. Is it possible to protect tree saplings from becoming infested with termites and an eventual casualty to IWTD by creating conditions that repel termites at the time of planting, such as the application of wood ash? Can physical barriers such as basalt particles, sand, coral, etc. be an effective deterrent against termites? Can the application of copper fungicides or salt to the planting pit reduce wood-rots like Ganoderma? The efficacy of these and other possible treatments need to be determined.