Decline of Casuarina equisetifolia: A Loss to Pacific Island Agroforestry

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.

REFERENCES

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 &amp; 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 ****
• Appendix
• 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).