Decline of Casuarina equisetifolia: A Loss to Pacific Island Agroforestry

Project Overview

Project Type: Research and Education
Funds awarded in 2008: $140,680.00
Projected End Date: 12/31/2013
Region: Western
State: Guam
Principal Investigator:
Roger Brown, Jr.
University of Guam
Dr. Robert Schlub
University of Guam

Annual Reports


  • Additional Plants: trees, ornamentals


  • Crop Production: windbreaks
  • Education and Training: technical assistance, decision support system, extension, focus group, on-farm/ranch research, participatory research
  • Pest Management: disease vectors, field monitoring/scouting, genetic resistance, integrated pest management, prevention, sanitation
  • Sustainable Communities: public participation, sustainability measures

    Proposal abstract:

    Statement of Problem:

    Guam is in the midst of a tree decline that is threatening Guam’s environmental sustainability. Being indigenous to the region and traditionally pest and disease free, the ironwood tree, Casuarina equisetifolia, is one of the dominant naturally occurring and propagated agroforestry species in the Pacific. Thousands of trees, on hundreds of acres, are drying on Guam for reasons or reason unknown. Without intervention the decline is likely to spread to Rota and the island of Saipan.


    The aim of this project is to survey ironwood trees on Guam in both agriculture and natural settings, to determine possible causes of decline, to find resistance and to advise farmers, agroforesters and landscapers on the planting and care of this tree.


    1) Develop a diagnostic survey key to measure tree health in locations collected in 2002 by the USDA Forest Service and on present day farms;

    2) sample the environment for abiotic (soil, storm damage, age) and biotic conditions (pathogens and pests) known to cause damage to ironwood and to collect seeds from trees that show signs of resistance;

    3) analyze data for causality;

    4) educate Guam and the neighboring islands on ways to safeguard the Pacific region’s ironwood trees.

    Experimental design:

    1) Off-island forest experts will be brought to Guam to finalize the diagnostic key and survey procedures;

    2) Guam’s 2002 forest inventory sites will be surveyed along with eight farm windbreaks;

    3) The data will be analyzed using multiple regression or another appropriate method to determine correlations between environmental conditions and tree decline.

    Outreach plan:

    Three half-day workshops will be given in the final year of the grant. Two-thousand ironwood seedlings with planting instructions will be distributed to school children during the University of Guam Charter Day celebrations in March of each year.

    Educational products:

    This project will produce three reports/manuals:

    1) Ironwood Forest Inventory Update Report:

    2) Correlative Models of Associated Stress Factors and Ironwood Decline;

    3) Ironwood Tree Care Manual.

    Short- and medium-range outcomes:

    The cause of the decline will be determined and an effective course of action will be devised to reduce its impact on Guam and lower the risk that decline will spread to neighboring islands. In the long-term, Guam’s susceptible cultivar will be replaced with a resistant one and large stands of healthy trees will once again return to Guam.

    Measurable impacts:

    This project will result in a measured reduction in the rate of ironwood decline on Guam in managed areas such as schools, parks and farms.

    Producer involvement:

    Three growers with windbreaks will participate in all phases of the project, from the development of the ironwood survey key in year one to assisting with the field day in year three.

    Evaluation plan:

    A faculty member in the College of Natural and Applied Sciences, who is not directly involved in the project, will evaluate progress on the project bi-monthly. Two months after the field days, half the attendees will be surveyed for long-term gains in their knowledge of ironwood tree decline and tree care.

    Project objectives from proposal:

    Relevance to Western SARE goals:

    This project is directly addresses Western SARE goals 1 and 3 and indirectly addresses 2, 4 and 5.

    1) It promotes good stewardship of a valuable natural resource.

    2) The project enhances the quality of life of farmers by protecting a valued windbreak species.

    3) It protects the health and safely of those involved in food and farm systems by reducing the impact of trade-winds and typhoons on crops and farm buildings afforded by the presence of ironwood trees.

    4) The project’s improvement of Guam’s ironwood tree health increases enterprise diversification because the tree buffers the farm acreage from environmental limiting facts such as salt spray and soil and beach erosion.

    5) This project examines the implications of losing a long-time sustainable agriculture practice of planting ironwood for windbreaks and for reforestation and erosion protection programs.

    Objective 1: Develop a diagnostic key for all known injury, signs and symptoms that occur on ironwood worldwide.

    Method 1: To reduce the chance that an important injury, sign or symptom is overlooked, literature on ironwood will be reviewed for diagnostics reports and a diagnostic key developed linking various injury, signs and symptoms with causal agents. Project Principal Investigator (PI), cooperators and participant producers will meet on Guam for five days in November of the first year. During this time members will have a chance to meet each other and exchange ideas. They will finalize the diagnostic key and survey procedures. For some members, this will be an opportunity to see the decline firsthand.

    Objective 2: Determine the amount of change in Guam’s ironwood population from 2002 to the present.

    Method 2: A field survey of the 32 plots established in 2002, as part of a USDA Forest Service, Pacific Northwest Forest Inventory and Analysis Program (Donnegan et al. 2004), will be conducted. The forest inventory method used in 2002 to record ironwood tree numbers and health will be followed: thirty-two 1.5-acre footprints with four 24 foot radius subplots for trees over five inches in diameter and four eight-foot radius microplots for measurement of ironwood seedlings and saplings. The 2007 survey results will be compared to those collected in 2002.

    Objective 3: Categorize tree damage according to injury, signs and symptoms and record percent of each occurrence in the 32 USDA Forest Service plots as well as eight windbreak plantings.

    Method 3: All trees examined as part of the field survey in Objective 2 will be examined extensively for additional damage indicators using the diagnostic key developed in Objective 1. Findings will then be compiled into a survey record data form. Because a tree can exhibit secondary damage caused by another agent, damage reporting will be for primary and secondary damage agents. The age of the tree will also be noted because different causal agents contribute to mortality at different stages of an ironwood tree’s development. The trunk, branches and shallow roots of trees will be examined. To assist in this process, extensive digital photos will be collected and categorized.

    In addition to the 32 USDA Forest Service plots, eight farms where ironwood tree windbreaks were planted will be examined. For the farm survey, 20 percent of the windbreaks will be examined by random examination of 100 row feet sections. Participant producers will assist in the survey of the selected windbreaks. The progress of decline will be monitored for two years in two of the Forest Service plots on a monthly basis using survey and sampling techniques.

    Objective 4: To inform the public of the survey findings and to form an Ironwood Tree Decline Committee.

    Method 4: Principal Investigator (PI) will publish survey results in the local newspaper. The PI and producer participants will develop an Ironwood Tree Decline Committee to assist the PI in the development of the Ironwood Tree Care Manual for Guam and the Mariana Islands and in informing the public on ironwood tree care. Members of the committee will include PI, producer participants and individuals from the public. The committee will meet at the beginning of the second and third years.

    Objective 5: Identify a source of seeds from superior ironwood trees that the Guam Department of Agriculture can use in their give-away program.

    Method 5: There have never been any restrictions on introductions of ironwood to Guam; therefore, it is reasonable to assume that genetic exchange has occurred and that small isolated gene pools do exist. A DNA assessment of 142 Casuarina equisetifolia from Taiwan and Pacific islands, by Kuen-Yih Ho and associates (Ho et al. 2002) revealed two major groups: C. equisetifolia var. incana and C. equisetifolia var. equisetifolia. Their study revealed that there is large enough genetic variation among the native accessions of C. equisetifolia to be useful in selection of particular traits. The variety incana is distributed in Australia from Darwin to the north coast of New South Wales, while the variety equisetifolia is widely distributed from Malaysia to subtropical Australia, Melanesia, Micronesia, Philippine, and Polynesia (Wilson and Johnson, 1989).

    Information collected for objective 2, will be reviewed for mention of stands of large healthy trees among diseased ones. From trees that have a high probability of resistance, seeds will be collected and given to the Department of Agriculture. This process will diversify the germplasm distributed by the department and improve the odds that some of the seedlings will have resistance or tolerance to ironwood decline. Seeds from sources outside of Guam such as the Australian Tree Seed Center will be solicited for new varieties of C. equisetifolia. The Department of Agriculture will record and keep track of the seed sources for future reference.

    Objective 6: Based on an analysis of the data collected in objectives 2 and 3, a conclusion will be drawn as to the cause or causes for ironwood decline.

    Method 6: Data from objectives 2 and 3 will be analyzed using multiple regression or another appropriate method to find correlations between environmental conditions, casual agents and tree decline. Those trees with injuries, signs, insects or diseases that correlate highly with known causes will be sampled when possible and forwarded to experts for verification.

    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 three half-day ironwood tree workshops.

    Method 7: The PI and graduate student will compile a guide of possible control recommendations based on the literature. This material will be presented to the Ironwood Tree Decline Committee for discussion and possible inclusion in the Ironwood Tree Care Manual for Guam and the Mariana Islands. Project PI and selected cooperators and producers will meet for five days to establish a course of action to remediate ironwood decline, to finalize changes to the Ironwood tree care manual for Guam and the Mariana islands and to participate in the ironwood tree workshops. Dr. Rao, with assistance from the project PI and a local arrangement committee, will conduct three half-day ironwood workshops. One workshop will be given to government agency employees and two to farmers and the general public. Possible topics and activities include cause and control, tree pruning tips, stump removal, tool safety, planting and caring for ironwood and alternative tree species.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.