Guam’s Forest Resources, 2002 Joseph A. Donnegan, Sarah L. Butler, Walter Grabowiecki, Bruce A. Hiserote, and David Limtiaco Resource Bulletin United States Forest Pacific Northwest PNW-RB-243 Department of Service Research Station November 2004 Agriculture The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation’s forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, cooperation with the States and private forest owners, and management of the National Forests and National Grasslands, it strives—as directed by Congress—to provide increasingly greater service to a growing Nation. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326- W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer. USDA is committed to making its information materials accessible to all USDA customers and employees. Authors Joseph A. Donnegan is an ecologist, Sarah L. Butler is an ecologist, Walter Grabowiecki is a quality assurance technician, and Bruce A. Hiserote is an information management specialist, Forestry Sciences Laboratory, 620 SW Main Street, Suite 400, Portland, OR 97205-3028; David Limtiaco is the chief of forestry for the government of Guam, 192 Dairy Road, Mangilao, Guam 96923. Abstract Donnegan, Joseph A.; Butler, Sarah L.; Grabowiecki, Walter; Hiserote, Bruce A.; Limtiaco, David. 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. The Forest Inventory and Analysis Program collected, analyzed, and summa- rized field data on 46 forested plots on the island of Guam. Estimates of forest area, tree stem volume and biomass, the numbers of trees, tree damages, and the distribution of tree sizes were summarized for this statistical sample. Detailed tables and graphical highlights provide a summary of Guam’s forest resources and a baseline from which to detect future change following remeasurement of the permanent field plots. Keywords: Guam, biomass, damage, FIA, forest inventory, volume. Summary The Forest Inventory and Analysis (FIA) Program established a systematic sample of forest field plots on Guam to estimate forest area, tree stem volume and biomass, tree damages, and associated understory vegetation. Thirty-two permanent field plots were established in limestone forest and 14 in volcanic forest. Land cover was mapped from high-resolution satellite data and merged with the soil layer in a geographic information system to stratify the field sample. The forest area on Guam occupies approximately 63,830 acres, with limestone forest accounting for about 70 percent of that total. About 18 percent of Guam was classified as urban land and includes roads, towns, airstrips, and military facilities. We estimated gross tree stem volume to be about 91 million cubic feet, inclusive of all tree size classes. Aboveground stem weight for all trees greater than or equal to 5 inches in diameter at breast height was estimated to be about 1 million tons. About 21 percent of the trees sampled exhibited some form of physical damage. Of those damaged trees, evidence of decay was found in nearly one-third of the individuals. Physical break- age owing to weather and damage by falling trees were cited as the primary damag- ing agents in approximately 64 percent of the damage cases. The average number of tree species per sixth-acre plot was about four in both limestone and volcanic forest types. Forty-eight tree species and about 140 understory species were measured on 46 sixth-acre plots. Guam’s Forest Resources, 2002 Introduction This summary of forest resources on the island of Guam (fig. 1) was based on a forest inventory conducted in 2002 by the USDA Forest Service, Pacific Northwest Forest Inventory and Analysis Program (FIA) in cooperation with Pacific Island foresters. The key inventory objectives were to help answer local and national questions about the status and trends in tropical forested ecosystems and to share forestry skills among cultures and agencies. The fieldwork for this inventory was conducted by a multinational crew including students and foresters from Guam, foresters from American Samoa, and mainland U.S. foresters and ecologists. This systematic, sample-based field inventory on Guam was the first of its kind to be conducted across the island to establish estimates for the area of forest types, tree size distribution, volume, biomass, and damages for living and dead trees. It was designed to provide resource managers with information about the current situation so they can better manage their forested and nonforested lands and, after remeasurement, better manage or mitigate any changes in the resource. Empirically based knowledge of the status and trends in forest vegetation can help managers plan sustainable supplies of wood, control invasive species, control erosion, and manage disturbances such as fire and animal damage. Objectives 1. Estimate the area of forest land by forest type group and stand size class. 2. Estimate the volume, biomass, and carbon storage for tree species by diameter class. 3. Estimate the numbers of trees affected by damaging agents, such as insects and diseases, and estimate the number of dead trees. 4. Share measurement and analysis techniques among groups involved in the inventory. Methods Site Description The island of Guam is the largest and farthest south in the north-south sweeping Marianas archipelago (fig. 1). The highest point on Guam is Mount Lamlam with an elevation of 1,332 feet. Guam is an unincorporated territory of the United States with significant income generated from tourism. The climate is tropical marine with little annual variation in temperature, but a pronounced dry season from January to June (fig. 2). 1 RESOURCE BULLETIN PNW-RB-243 Figure 1—The unincorporated Territory of Guam is in the North Pacific Ocean approximately 1,600 miles east of Manila and 3,500 miles north of Melbourne, Australia. 2 Guam’s Forest Resources, 2002 Anderson Air Force Base, Guam, 1953–2001 86 Average Maximum and Minimum Temperature 84 82 ) F ° ( e ur 80 t a r e p m 78 e T 76 74 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 14 Monthly Precipitation Totals 12 ) s e 10 h c n (i n o 8 ti a t pi ci e 6 r P 4 2 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 2—Average maximum and minimum temperature, and total monthly precipitation for Anderson Air Force Base, Guam. Note the pronounced seasonality in precipitation (Western Regional Climate Center, http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?piande). 3 RESOURCE BULLETIN PNW-RB-243 A significant portion of land on Guam is occupied by the U.S. military. On a portion of these lands, a system of refuges and wildlife reserves are overlain on the military lands. For example, Ritidian Point, approximately 22,500 acres at the northern tip of Guam, is administered by the U.S. Fish and Wildlife Service as a national wildlife refuge. Significant disturbance agents have shaped vegetation in Guam, including frequent tropical storms and typhoons, human-caused grassland and forest fires, animal rooting, browsing and trampling, mass soil movements and erosion, non- native insects and pathogens, invasive weeds, historical military actions, and Significant disturbance historical timber harvest. agents have shaped The northern half of the island is generally flat limestone plateau with abrupt the vegetation on dropoffs and cliffs toward the ocean. Locally the limestone can be strongly weath- Guam. Humans ered into rugged karstic terrain. Soils are related to vegetation communities in and tropical storms Guam. The limestone soils in the north are covered with forest in areas not culti- continue changing vated or urbanized. The southern part of the island features rolling to mountainous forest structure and terrain in the deeply weathered volcanic soils. The volcanic soils on the southern composition. half of Guam are covered primarily by grassland, with some ravine forest occur- ring in sheltered and leeward sites. Vegetation Types The vegetation of Guam was categorized (Mueller-Dombois and Fosberg 1998) according to the major underlying soil types: (1) northern limestone vegetation, and (2) southern volcanic vegetation. The limestone vegetation was further broken down into five classes by Fosberg (1960): Artocarpus-Ficus forest, Mammea for- est, Cordia forest, Merrilliodendron-Ficus forest, and Pandanus forest. A brief description of each forest community follows. Pure examples of these forest types are now rare on Guam; instead these forests tend to be mixtures with secondary species predominating. The FIA inventory does not currently provide sufficient plot density to reliably classify vegetation types in these highly diverse tropical forests but provides plot-level data to help refine remotely sensed estimates of forest type acreage and developmental stage. Some of the forest types discussed below may not be represented in the plot-level information provided from this inventory owing to the systematic sampling design having missed the forest type. Ongoing mapping efforts will provide greater spatial detail and better refinement of forest types. 4 Guam’s Forest Resources, 2002 Limestone forest types Artocarpus-Ficus— A widespread forest type on limestone in Guam with canopy dominants including Artocarpus mariannensis (breadfruit) and Ficus prolixa (banyan). Mammea forest— Mueller-Dombois and Fosberg (1998) characterize this forest type as dominated by Mammea odorata and by its occurrence on the eastern escarpment of the northern limestone plateau. Cordia forest— This is an open scrub-forest type on steep slopes and cliffs dominated by Cordia subcordata Lam. Merrilliodendron-Ficus forest— Merrilliodendron megacarpum (Hemsley) Sleumer and Ficus prolixa dominate this tall forest type. Pandanus forest— This moderate-height forest is dominated by Pandanus tectorius. Other common genera include Flagellaria, Cestrum, Triphasia, and Nephrolepis (Fosberg 1960). Volcanic Types The southern, volcanic half of the island is vegetated with a mix of grassland and patchy forest. The forest tends to follow topographic features, such as river drain- ages, sheltered depressions, and ravines. Grassland savannas are dominated by the dense, sharp-leaved Miscanthus floridulus (Labill.) Warb. ex K. Schum. & Laut. (swordgrass), and smaller areas of Pennisetum polystachyon (L.) J.A. Schultes (mission grass) and Dimeria chloridiformis (Gand.) K. Schum. & Laut. Common ravine forest trees include Areca catechu, (see table 1 for common names of trees) Ficus prolixa, Glochidion mariana Mueller-Arg., L., Hibiscus tiliaceus, Pandanus tectorius, P. dubius Sprengel, and Premna serratifolia L. (Fosberg 1960). Low-lying, halophytic (sea-salt adapted) vegetation is found along beaches in the north and south, and may be composed solely of Casuarina equisetifolia or a mixture of species including Casuarina, Cocos nucifera, Guettarda speciosa, Hernandia sonora, Pandanus tectorius, Scaevola taccada (Gaertn.) Roxb., Thes- pesia populnea (L.) Soland. ex Correa, and Tournefortia argentea L. f. (Fosberg 1960). Areas of swamp, mangrove, and marsh are also found on Guam. 5 RESOURCE BULLETIN PNW-RB-243 a Table 1—Scientific and common names and estimated specific gravities of species measured as trees on Guam Specific gravity Number Scientific name Common name (for biomass) measured Adenanthera pavonina L. kulalis 0.50 7 Aglaia mariannensis Merrill mapuñao .50 54 Annona reticulata L. annonas .50 8 Areca catechu L. puguá .50 9 Artocarpus altilis (Park.) Fosb. lemai, breadfruit .50 8 Artocarpus mariannensis Trec. dugdug, Marianas breadfruit .50 1 Averrhoa bilimbi L. bilimbi, pikue .50 9 Barringtonia asiatica (L.) Kurz puting .50 2 Barringtonia racemosa (L.) Spreng. langaasag .50 2 Bauhinia monandra Kurz Saint Thomas tree, mariposa .50 3 Calophyllum inophyllum L. daok, Alexandrian laurel .57 5 Cananga odorata (Lam.) Hook. f. & Thoms. ilang-ilang .29 7 Carica papaya L. papaya .50 23 Casuarina equisetifolia L. gagu,australian pine .84 9 Ceiba pentandra (L.) Gaertn. algodon de manila .23 1 Cerbera dilatata Markgraf chuite .50 19 Citrus aurantifolia (Christm.) Swingle lime .50 1 Cocos nucifera L. niyok, coconut palm .50 81 Cyathea lunulata (Forst. f.) Copel. chacha, tree fern .50 2 Cycas micronesica K.D. Hill fandan (C. circinalis L.) .50 112 Cynometra ramiflora L. gulos .70 5 Eugenia reinwardtiana (Benth.) a’abang .50 2 Eugenia thompsonii Merrill atoto .50 2 Ficus prolixa Forst. f. nunu .50 11 Ficus tinctoria Forst. f. hoda, tagete .50 2 Guamia mariannae Merrill paipai .50 47 Guettarda speciosa L. pano .50 1 Hernandia ovigera L. .50 9 Hernandia sonora L. nonak .29 2 Heterospathe elata Scheffer palma brava .50 80 Hibiscus tiliaceus L. sea-hibiscus, pago .57 104 Inocarpus fagifer (Park.) Fosb. budo buoy, Tahitian chestnut .50 1 Intsia bijuga (Colebr.) O. Ktze. ifit, ifil .50 5 Kleinhovia hospita L. .36 5 Leucaena leucocephala (Lam.) de Wit tangantangan .64 147 Macaranga thompsonii Merrill .50 13 Mangifera indica L. mango .52 18 Morinda citrifolia L. lada, Indian mulberry .50 41 Neisosperma oppositifolia (Lam.) Fosb. & Sachet faag .50 3 Pandanus tectorius Park. aggag .50 61 Pipturus argenteus (Forst.) Wedd. amahazan .50 2 Polyscias grandifolia Volk. .50 1 Premna obtusifolia R. Br. ahgao .50 50 Psidium guajava L. guava, abas .50 3 Spathodea campanulata Beauv. African tulip tree .25 4 Triphasia trifolia (Burm. f.) P. Wils. limon de China .50 38 Vitex parviflora Juss. .70 92 Xylosma nelsonii Merrill .50 1 a Specific gravity was used to calculate biomass and carbon mass. 6