Decline of Casuarina equisetifolia: A Loss to Pacific Island Agroforestry

Decline of Casuarina equisetifolia: A Loss to Pacific Island Agroforestry

Summary

Major inroads were made in finding the extent and severity of Ironwood Tree decline on Guam during the first year of this grant. A literature search was conducted and a list compiled of all known injury, signs, and symptoms that occur on ironwood worldwide. A conference was held that brought scientists from the Mainland and Australia for consultation and field study. A decline rating scale was created and a survey conducted over the entire island to determine the extent and degree of decline. Also, symptoms and signs of decline were identified, photographed, and analyzed.

Objectives/Performance Targets

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.

Accomplishments/Milestones

Sept 1, 2008 –
Hired Dr. Zelalem Mersha as project’s Post Doctoral Research Associate.

Sep 1, 2008 to Feb 15, 2008 – Purchasing of Materials
In accordance with the first year request for materials and supplies, we have purchased materials and supplies including the following: a chain saw, saws, shovels, hoes, tree augers, parts for a seedling greenhouse, marking tape, tape measures, machete, gloves, scales, pruners, loppers, GPS and software, etc. Also, a backhoe and a bush cutter were rented for one and two days respectively. All materials purchased and rented have been used extensively to this point.

October 1, 2008 to August 31, 2009 – Literature Search
An ongoing literature search for disease and other information on Casuarina equisetifolia has been conducted, compiled, and continuously updated (Appendix 1).

January 6, 2009 through January 10, 2009 – Ironwood Tree Decline Conference
In accordance with this grants objectives, The Ironwood Tree Decline Conference was held. Grant participants from Australia, Northern Marianas Islands, Georgia, Florida, and Hawaii were brought to Guam to attend the conference with local professionals and producers. This working conference incorporated both field work and group discussion. Field work consisted of traveling to different areas of the island to survey declining and non-declining trees and to collect samples for laboratory processing and analysis. Field trips were taken each day of the conference. A trip was undertaken to grant Participant Bernard Watson’s farm where over one thousand Ironwood trees are in varying stages of decline (Picture 1). 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. On Wednesday, January 7, 2009, presentations and discussions were conducted at the University of Guam Science Building (Picture 2). 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.
During the conference, some aspects of survey methods and procedures were finalized. These included setting standard visual methods of estimating the decline severity, pinpointing the most vulnerable spots on the island for decline, and taking samples for diagnostic purposes.

October 1, 2008 to June 31, 2009 – Ironwood decline survey of Guam
Visual methods for classifying decline symptoms are commonly employed because they incorporate all causes of decline characteristics regardless of their causes (McLaughlin et al., 1992). A visual rating of decline severity on a scale of 0 (healthy) to 4 (nearly dying) was chosen to characterize the extent of ironwood tree decline on Guam. A survey was conducted at 38 sites across Guam in both natural growth sites and sites planted by man. These sites included farmer participant windbreaks, agricultural experimental stations, parks and beaches, cliff lines, golf courses, and sites in and around Guam’s villages. A Garmin GPS76CSx receiver was used to identify the locations of the survey sites, digital photographs of trees were taken at the sites, and the diseases rating scale was applied to ironwood trees located at these sites. Picture 3 shows the disease rating scale of trees in decline at two of the survey sites. Also, using GPS coordinates, these sites were place on a map of Guam along with their respective mean decline rating (Figure 1). Overall, it is estimated that 40 percent of the ironwood trees on Guam are in some stage of decline. In a 2002 forestry inventory, it was estimated that Guam had 115,924 Ironwood trees that were larger than 5 inches in diameter at breast height and it was the healthiest tree species on island (Donnegan, et al. 2004).

January 1, 2009 to June 31, 2009 – Discoloration of tree branches and trunks as an indicator of decline
Small and large trees from the UOG experimental station, UOG campus, and a farm windbreak were felled and cross-sectioned. These included small trees with and without decline, as well as large trees with decline. Trees were felled by cutting the tree at the base of the trunk. Then, cross-sections of 5-cm thickness were removed first from the base (0 m), at 1.3 m, and then at 2 m intervals. Trunk cross-sections and cut wedges were digitally photographed and discoloration quantified.
Trunk sections from small and large healthy trees did not show any discoloration, except a case with a large tree with limited discoloration, which was not attributed to decline as it was not characteristic of that seen in declined trees (Picture 4).
There were variations in patterns and types of discoloration encountered. Some appear to originate from the edge and others from the center of cross-sections. The discoloration ranged from slight to intense and most of the section from the base and the roots showed a white soft root-rot symptom, which in some cases could even be pulled out by hand. Advancing edges of these discolorations varied from smooth to serrated (Picture 5).

August 2, 2009 – Presented poster on Western SARE research to date for this project at the annual American Phytopathological Society (Appendix 2)

March 10, 2009 and April 16, 2009 – Educational outreach for Guam’s general public
Ironwood tree displays were set up at the University of Guam’s Charter Day in March of 2009 and at the Environmental Protection Agency’s Earth Day activities. Hundreds of students, teachers, and members of the general public were informed of ironwood tree decline and ironwood tree care during each day long activity (Picture 6).

Impacts and Contributions/Outcomes

It is likely that a complex of biotic and abiotic factors are responsible for the decline. Possible biotic candidates include fungi of the genera Ganoderma, Pestalotia, Botryosphaeria and Fusarium and several yet unidentified fungi and bacteria. Insects that may play a role in the decline are termites and a newly discovered Eulophid wasp, which forms galls in branchlet tips. Among the abiotic factors are the major typhoons, Chataan on July 4 and Pongsona on December 5, 2002, and the intervening severe drought, as well as proximity to urban development. Decline prevalence was highest on manmade plantations (windbreaks, beaches, parks, and golf courses). The healthiest ironwood trees are located on Cocos Island, a Casuarina dominated island just 1.6 miles off the southern tip of Guam, and at Ritidian Point, a National Wildlife Refuge located on the northern tip of Guam.
Producers, golf course superintendents, park managers, village mayors, NRCS, Guam Department of Agricultural, University of Guam scientists and extension personnel, Mainland scientists, teachers, students, and the general public have been made aware of the progress of this ironwood tree decline Western SARE project through active participation in the grants objectives, conferences, site visits, educational activities, and newspaper and radio announcements. This awareness is an essential building block going forward in this grant as we further define the causes of decline and come up with management strategies in the next two years that can be passed onto the people of Guam and the neighboring region.

Collaborators: