# Guam’s Forest Resources, 2002

Joseph A. Donnegan, Sarah L. Butler, Walter Grabowiecki, Bruce A. Hiserote, and David Limtiaco

United States Department of Agriculture Forest
Service Pacific Northwest
Research Station Resource Bulletin

PNW-RB-243

November 2004The 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.

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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.

### 1 **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).

### 2 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.

### 3 **Guam’s Forest Resources, 2002**



### A v e r a g e M a x i m u m a n d M i n i m u m T e m p e r a t u r e

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 74 76 78 80 82 84 86



### Monthly Precipitation Totals

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecPrecipitation (inches)

2 4 6 8 10 12 14 

## Anderson Air Force Base, Guam, 1953–2001Temperature (°F)

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).

### 4 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, nonnative insects and pathogens, invasive weeds, historical military actions, and

historical timber harvest.

The northern half of the island is generally flat limestone plateau with abrupt

dropoffs and cliffs toward the ocean. Locally the limestone can be strongly weath

ered into rugged karstic terrain. Soils are related to vegetation communities in

Guam. The limestone soils in the north are covered with forest in areas not culti

vated or urbanized. The southern part of the island features rolling to mountainous

terrain in the deeply weathered volcanic soils. The volcanic soils on the southern

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. Significant disturbance

agents have shaped

the vegetation on

Guam. Humans

and tropical storms

continue changing

forest structure and

composition.

### 5 **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., Thespesia populnea (L.) Soland. ex Correa, and Tournefortia argentea L. f. (Fosberg

1960). Areas of swamp, mangrove, and marsh are also found on Guam.

### 6 RESOURCE BULLETIN PNW-RB-243



### Table 1—Scientific and common names and estimated specific gravities **a** 

### of species measured as trees
on Guam



### Scientific name Common name Specific gravity (for biomass) Number

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.

### 7 **Guam’s Forest Resources, 2002**



### Regions of barren, eroding soil are prevalent in the southern part of the island.

The erosion problem is being addressed individually by multiple agencies and

coordinated jointly through a multiagency consortium working on the vegetation

strategy for southern Guam (Bell et al. 2002).



## Field Methods

This inventory was based on the national FIA inventory design that was implemented across the mainland United States. Adaptations were made to the national

design to use topography to define site productivity and to include additional

branching and rooting forms, additional tree crown measurements, and specialinterest species ranging from invasive plants to pathogens to culturally or economically important species of various life forms. In the mainland FIA Program,

plots are spaced within forest land on a 3.3-mile grid. With the assistance of the

Government of Guam, Division of Forestry, plots were spaced across all vegetation

types at 1.9-mile intervals, yielding a triple intensification of the mainland inventory

plot grid.

The FIA plot-cluster is composed of four 24-foot-radius subplots (fig. 3). Three

of those subplots are equally spaced, as if on spokes of a wheel, around the central

subplot. The distance from the middle of the central subplot to the middle of each

subplot on the three spokes was 120 feet.

A variety of information was collected at the plot, subplot, and tree levels

(USDA Forest Service 2002). Differences in forest-type conditions are also mapped.

For example, roads that intersect subplots are mapped, as are clear boundaries in

forest tree size classes. The primary variables collected include plot location, slope,

aspect, elevation, subplot slope position and shape, tree species, diameters, heights,

damages, branching and rooting forms, decay, epiphytic loadings, crown character

istics, tree locations, and regeneration information. The fieldwork for this inventory

was performed February to April 2002, before the two major typhoons, Chata’an

and Pongsona, struck the island in July and December of 2002, respectively.



## Analysis Methods

The FIA estimates of forest land are based on a system that uses aerial photogra

phy or satellite imagery to define different types of land (strata) across the land

scape. The simplest stratification is separating land into forest and nonforest strata.

However, stratifications can be assisted or refined by using ancillary data such as

topography, soil information, life zone or climatically based information, and prior

inventories of vegetation groups.

The Guam stratification was conducted via a classification of 2002 IKONOS

satellite data, masking out and replacing clouds by using aerial photography taken The FIA inventory

design was adapted

for the conditions and

vegetation in Guam.

### 8 RESOURCE BULLETIN PNW-RB-243



### in 1994. The initial land cover classification divided the landscape into forest,

urban, nonforest vegetation, barren, and water land types. At least 10 percent cover

of trees was used as the basis for the forest land classification, and includes both

agroforests and mangrove forests. Nonforest vegetation includes other vegetation

types with less than 10 percent cover of trees. A geographic information system

(GIS) was used to sum acreage for each type. Forest was further classified into

volcanic and limestone forest types by overlaying a soils layer (USDA NRCS 1988)

on the land-cover-classification layer in a GIS. We used the GIS to individually 

## F o r e s t I n v e n t o r y a n d A n a l y s i s

P a c i f i c I s l a n d s P l o t D e s i g n

N Overall plot footprint ~1.5 acres
Distance between subplot centers: 120 feet

D i s t a n c e f r o m s u b p l o t c e n t e r t o m i c r o p l o t c e n t e r : 1 2 f e e t



# 1 2

4 3 P l o t

S u b p l o t M i c r o p l o t 6.8-foot-radius microplot: seedlings + saplings 

### K ey

24-foot-radius subplot: all trees ( � 5 inches in diameter at breast height)

Figure 3—Forest Inventory and Analysis Pacific Islands plot design.

### 9 **Guam’s Forest Resources, 2002**



### sum the acreage of limestone and volcanic forest types. From this limestone/

volcanic stratification, field plot condition types were expanded to the landscape

level. The acreage each field plot represents was derived by dividing the total

acreage of forest in each of the limestone and volcanic soil types by the number of

field plots that fell within the geographic bounds of that specific type. Average stand

size was expanded from the plots to the landscape level by using the same expan

sion factors. The forested areas on our initial land cover classification will be

further refined into more detailed forest types in an ongoing project by the USDA

Forest Service, Pacific Southwest Region, Remote Sensing Laboratory.

Wood volume was estimated for individual trees by using tree height and two

stem diameter measurements. These measurements are expanded to tree-level

volume estimates by using equations for sections of a cone. Both gross stem volume

and net stem volume estimates were calculated. Net stem volume subtracts dam

age and rotten defects from gross stem volume. Biomass for individual tree stems

was estimated by using the specific gravity for known species (31 out of 50 species

measured on Guam have known specific gravities). For species where specific grav

ity was not known, an average specific gravity, according to forest type, was used.

These estimates of aboveground tree biomass are derived from bole volume and

include only biomass for the main stem, excluding branches, roots, and foliage.

An additive combination of relative density and relative basal area (importance

value IV) was used to classify forest types and assess the species dominance in a

stand. Traditional site productivity estimates require forest stand age, derived from

the annual rings of forest trees. Because tropical trees do not produce consistent

annual rings, a modified topographic relative moisture index (TRMI) (Parker 1982)

was used as a proxy for site productivity. The TRMI used a weighted, additive com

bination of slope steepness, slope shape, and slope position to assess the potential

moisture retention in a forested stand. The TRMI serves as a proxy for productiv

ity until we can obtain growth rate data from remeasurement of these plots. We

recognize moisture is not likely to be the only factor limiting tree growth and that

an excess of moisture can be detrimental to tree growth.



## Reliability of FIA Data

The area of land cover types mapped from the IKONOS classification was assumed

to be accurate and was used as the basis for the expansion of the numbers of trees,

tree volume, and tree biomass from the plot scale to the forest-type scale. Possible

sources of error not accounted for in our estimates include errors in the land cover

map owing to incorrect interpretation of the image, errors from rounding when

working with pixel-based imagery, and measurement errors on field plots. Standard Because tropical

trees do not produce

consistent annual

rings, an index

based on slope

characteristics

affecting moisture

retention was used

as a proxy for site

productivity.

### 10 RESOURCE BULLETIN PNW-RB-243



### errors for the expansion of our estimates from field plots to the forested landscape

were calculated according to the proportion of area occupied by either volcanic or

limestone forest types. Volcanic and limestone forest areas were treated as known

rather than estimated, and variance was calculated by using methods in Cochran

(1977). Using one standard error as our basis for evaluation gives a 68 percent

chance that the true total gross tree stem volume on Guam lies between 83,229,532

and 99,520,878 cubic feet. There is a 68-percent chance that the true number of

trees (>1 inch diameter) on Guam lies within the range of 68,809,072 to 84,733,366.



# Resource Highlights

Land Cover

Based on the IKONOS satellite imagery, we estimate that Guam is approximately

48 percent forested, with an additional 33 percent covered by grass and shrublands.

Barren lands account for slightly over 1,500 acres (1 percent), and urban lands total

approximately 24,000 acres (18 percent) (figs. 1 and 4, table 2).



## Productivity

Forest land productivity was approximated as the potential of a site to retain mois

ture (TRMI) (Parker 1982) relative to that particular broad soil-based forest type

(limestone vs. volcanic; table 3). Topography at each plot was used to rank sites

within a forest type in terms of whether water would be expected to accumulate

on or flow from the site. The limestone forests tended to occur on lands that would

be classified predominantly (80 percent) as moderately high productivity (fig. 5).

However, when basing potential productivity on topography, one must consider

that limestone soil and parent material quickly drain water owing to high porosity.

This may lead to an overestimate of productivity depending on the moisture-hold

ing capacity of the soil. Sixty percent of the area of volcanic forest was classified

as moderately high productivity or higher (fig. 6).



## Forest Structure

Stand size class summarizes the predominant diameter of all live trees in a forested

condition. In Guam, trees tend to be somewhat small in diameter, with the majority

of forested area having trees in the 5- to 10.9-inch category (fig. 7). No stands were

sampled in this inventory for the 20+ inch category. Such large-diameter stands are

expected to be rare on Guam owing to frequent disturbance by typhoons.

The diameter distribution for trees on Guam follows a typical “reverse-J”

pattern (fig. 8). More individuals are found in the smallest tree size classes (tables

4 and 5), which through time either grow into larger trees, die in the understory Based on satellite

imagery, we estimate

that Guam is 48

percent forested.

In Guam, trees tend

to be relatively small

owing to disturbance

by typhoons and

historical land use

practices.

### 11 **Guam’s Forest Resources, 2002**



## Guam's Land Cover, 2002

1%

14%

34%
33% 18%

Barren

Volcanic forest

Limestone forest

Nonforest vegetation

Urban

Fresh water <1%

Figure 4—Land cover was mapped for Guam by using high-resolution satellite imagery. Guam is currently about 48 percent forested and 18 percent urban.



### Table 2

— 

### Estimated land area by land status

Land status Area

Acres

Accessible forest land:

Unreserved forest land—

Limestone forest 44,704

Volcanic forest 19,129

Total unreserved 63,833

Reserved forest land 0

All accessible forest land 63,833

Nonforest and other area:

Nonforest urban 23,956

Nonforest savanna or fernland 44,455

Barren lands 1,539

Area not classified 1,622

Water 255

All nonforest and other 71,827

Total forest and nonforest area 135,660

Area not included in field sample:

Access denied 2,096

Hazardous conditions 1,716

### 12 RESOURCE BULLETIN PNW-RB-243



### Table 3—Estimated area of accessible forest land by forest-type group and productivity class



### Site productivity class a



### Forest-type group 0–4.9 5–9.9 10–14.9 15–19.9 20–24.9 25–29.9 30–40 All classes

Acres Limestone forest — — 6,020 3,010 35,675 — — 44,704 Volcanic/ravine forest — 2,455 4,911 254 6,953 3,328 1,228 19,129

Total — 2,455 10,930 3,264 42,628 3,328 1,228 63,833

a Classes are based on topographic relative moisture index. Higher numbers correspond to greater potential moisture retention on a site.



## Limestone Forest Potential Productivity

(Percentage of forest-type acres)

80% 7% 13%

Medium low

Medium

Medium h igh

Figure 5—The majority of forest on limestone soils was estimated to be moderately high productivity. However, owing to the rapid runoff expected in karstic topography, produc

tivity will depend greatly on the depth of soil present locally.



### as other individuals outcompete them for space, or are killed by typhoon or other

damaging agents. Likewise, cubic-foot volume (fig. 9, tables 6, 7, and 8), biomass

(fig. 10, table 9), and carbon mass (table 10) follow similar trends, with the major

ity of each distributed among the smaller tree size classes. For trees greater than or

equal to 5 inches in diameter, the mean tree height is approximately 25 feet with a

standard deviation of 11.3 feet. Approximately 63 percent of the trees fall within the

height range of 15 to 30 feet, and about 30 percent of the trees are greater than 30

feet tall.

### 13 **Guam’s Forest Resources, 2002**

Figure 6—Much of the forest on volcanic soil occurs on steeper slopes. Productivity on these steeper slopes is expected to be lower than in areas where the moisture collects.

Figure 7—The majority of Guam’s forests are characterized by small-diameter stands of trees. 

### 26%

1% 37% 17% 6% 13% 

## Volcanic Forest Potential Productivity

(Percentage of forest-type acres)

Low

Medium low

Medium

Medium high

High

Hi ghest

Stand size class 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000

Less than

5 inches 5–10.9

inches 11–19.9

inches 20+ inches All sizesArea (acres) 

### Lime stone forest

Volcanic/ravine forest

Forest t otal

### 14 RESOURCE BULLETIN PNW-RB-243

Figure 8—The distribution of number of trees by size class indicates Guam’s forests tend to be dominated by smaller individuals.

Figure 9—The woody stem volume for trees in Guam is concentrated in the smaller size classes. 

## Number of Trees by Size Class

Total trees in all classes: 76,771,219

0 5 10 15 20 25 30 35 40 45

1.0–2.9 3.0–4.9 5.0–6.9 7.0–8.9 9.0–10.9 11.0–12.9 13.0–14.9 15.0–16.9 17.0–18.9 19.0–20.9 21.0–22.9 23.0–24.9 25.0–26.9 27.0–28.9 29.0+



### Diameter (inches)Estimated number of trees (millions) 50

0 2 4 6 8 10 12 14 16

5.0–6.9 7.0–8.9 9.0–10.9 11.0–12.9 13.0–14.9 15.0–16.9 17.0–18.9 19.0–20.9 21.0–22.9 23.0–24.9 25.0–26.9 27.0–28.9 29.0+



### Diameter (inches)Gross volume (million cubic feet) 18



## Volume by Size Class

Total volume, all classes: 59,937,557

### 15 **Guam’s Forest Resources, 2002**Table 4—Estimated number of live trees on forest land by species group and diameter classDiameter class (inches)Species group 1–2.9 3–4.9 5–6.9 7–8.9 9–10.9 11–12.9 13–14.9 15–16.9 17–18.9 19.0+ All classesNumber of treesLimestoneforest type 42,779,542 14,079,343 3,622,623 1,275,163 652,072 231,848 130,414 57,962 28,981 72,452 62,930,401Volcanic/ravineforest type 5,338,023 4,601,744 2,039,186 620,622 502,408 413,748 192,097 73,884 44,330 14,777 13,840,818Total 48,117,565 18,681,087 5,661,809 1,895,785 1,154,480 645,596 322,512 131,846 73,311 87,229 76,771,219

### 16Table 5—Estimated number of live trees on forest land by species and diameter classDiameter class (inches)Species5.0–6.97.0–8.99.0–10.911.0–12.913.0–14.915.0–16.917.0–18.919.0–20.921.0–22.923.0–24.925.0–26.927.0–28.929.0+All classesNumber of treesAdenanthera pavonina—14,49014,49014,49014,490————————57,962Aglaia mariannensis260,82928,981———————————289,810Annona reticulata86,943————————————86,943Areca catechu29,553—14,777——————————44,330Artocarpus altilis58,53414,77714,777——————————88,088Artocarpus mariannensis14,490————————————14,490Averrhoa bilimbi57,962————————————57,962Barringtonia asiatica—14,490———————14,490———28,981Barringtonia racemosa14,777———14,777————————29,553Calophyllum inophyllum44,330————————————44,330Cananga odorata——————14,490——————14,490Carica papaya43,47143,47114,490——————————101,433Casuarina equisetifolia43,47143,47114,49014,490—————————115,924Ceiba pentandra—14,490———————————14,490Cerbera dilatata101,43328,98128,981——————————159,395Cocos nucifera43,758117,927498,974339,292132,99014,77714,777——————1,162,494Cyathea lunulata14,77714,777———————————29,553Cycas micronesica900,700510,316117,06928,98114,490————————1,571,556Eugenia thompsonii29,553————————————29,553Ficus prolixa43,471—14,490——44,04414,777—————14,490145,764Ficus tinctoria14,49014,490———————————28,981Guamia mariannae86,94343,471———————————130,414Hernandia ovigera72,452—43,47114,490—————————130,414Hernandia sonora14,490—14,490——————————28,981Heterospathe elata1,075,552————————————1,075,552Hibiscus tiliaceus437,291115,92414,490——————————567,705Intsia bijuga14,49014,490——43,471————————72,452Kleinhovia hospita43,47114,490———————————57,962Leucaena leucocephala729,390146,05014,777——————————890,217Macaranga thompsonii43,47157,96228,98143,471—14,490———————188,376Mangifera indica—29,55314,77788,66044,33029,55314,77714,777—————236,427Morinda citrifolia58,821————————————58,821Neisosperma oppositifolia—14,490———————————14,490Pandanus tectorius527,668249,48714,490——————————791,646Premna obtusifolia405,734159,39543,471—————14,49014,490———637,582Spathodea campanulata28,981—14,490——14,490———————57,962Vitex parviflora306,018189,808218,502101,72057,96214,49014,490——————902,990Xylosma nelsonii14,490————————————14,490Total5,661,8091,895,7851,154,480645,596322,512131,84673,31129,26714,49028,981——14,4909,972,568

### 17 **Guam’s Forest Resources, 2002**



### Table 6—Estimated gross volume of all live trees on forest land by forest-type group and diameter class

Diameter class (inches)

Forest-type group Less than 5 5–10.9 11–19.9 20+ All sizes

Cubic feet Limestone forest type 25,000,018 22,194,860 8,278,410 3,937,467 59,410,755 Volcanic/ravine forest type 6,437,631 14,069,581 11,457,238 31,964,450

Total 31,437,648 36,264,441 19,735,649 3,937,467 91,375,205



### Table 7—Estimated net volume of all live trees > 5 inches in diameter on forest land by forest-type group and diameter class

Diameter class (inches)

Forest-type group 5–10.9 11–19.9 20+ All sizes

Cubic feet Limestone forest type 21,467,757 8,248,484 3,756,956 33,473,197 Volcanic/ravine forest type 14,048,885 11,318,163 25,367,048

Total 35,516,642 19,566,647 3,756,956 58,840,245

3 00

250

200

150

100

50

0 5.0-6.9 7.0-8.9 9.0-10.9 11.0-12.9 13.0-14.9 15.0-16.9 17.0-18.9 19.0-20.9 21.0-22.9 23.0-24.9 25.0-26.9 27.0-28.9 29.0+



### Diameter (inches)Stem biomass (thousand tons) 

## Biomass by Size Class

Biomass total, all classes: 1,000,200 tons

Figure 10—Small-diameter trees account for the greatest relative share of biomass in Guam’s forests.

### 18Table 8—Estimated gross volume of all live trees on forest land by species and diameter classDiameter class (inches)Species5.0–6.97.0–8.99.0–10.911.0–12.913.0–14.915.0–16.917.0–18.919.0–20.921.0–22.923.0–24.925.0–26.927.0–28.929.0+All classesCubic feetAdenanthera pavonina—101,166215,151237,852295,831————————850,000Aglaia mariannensis745,310147,832———————————893,142Annona reticulata243,248————————————243,248Areca catechu66,619—62,911——————————129,529Artocarpus altilis166,08762,78187,091——————————315,959Artocarpus mariannensis69,114————————————69,114Averrhoa bilimbi170,238————————————170,238Barringtonia asiatica—94,617———————678,079———772,696Barringtonia racemosa36,026———185,433————————221,459Calophyllum inophyllum162,457————————————162,457Cananga odorata——————481,325——————481,325Carica papaya97,698153,709147,836——————————399,244Casuarina equisetifolia158,514212,708156,081171,682—————————698,985Ceiba pentandra—68,581———————————68,581Cerbera dilatata324,750168,655212,986——————————706,391Cocos nucifera157,742598,0265,659,6574,275,0062,066,260284,146578,822——————13,619,659Cyathea lunulata27,99256,791———————————84,783Cycas micronesica1,735,7011,810,718724,419265,754165,066————————4,701,658Eugenia thompsonii78,386————————————78,386Ficus prolixa258,381—251,358——685,362210,436936,398————1,238,1053,580,041Ficus tinctoria42,56171,029———————————113,590Guamia mariannae197,414259,918———————————457,332Hernandia ovigera165,222—361,133178,057—————————704,413Hernandia sonora65,398—115,645——————————181,043Heterospathe elata3,562,810————————————3,562,810Hibiscus tiliaceus1,233,493610,80781,339——————————1,925,638Intsia bijuga63,48859,862——916,945————————1,040,296Kleinhovia hospita126,46283,586———————————210,048Leucaena leucocephala2,071,080654,66584,420——————————2,810,165Macaranga thompsonii128,274343,322274,918567,175—256,535———————1,570,224Mangifera indica—109,580192,5081,284,968945,215746,063473,038520,927—————4,272,299Morinda citrifolia167,806————————————167,806Neisosperma oppositifolia—53,968———————————53,968Pandanus tectorius1,531,3751,140,927140,841——————————2,813,143Premna obtusifolia1,185,221797,452393,112—————483,181601,705———3,460,670Spathodea campanulata98,688—114,276——334,289———————547,254Vitex parviflora1,040,617938,3462,161,9151,444,5601,181,825457,650525,425——————7,750,339Xylosma nelsonii49,624————————————49,624Total16,227,7998,599,04611,437,5968,425,0545,756,5762,764,0452,269,0471,457,325483,1811,279,783——1,238,10559,937,557

### 19Table 9—Estimated aboveground dry stem weight of all live trees on forest land by species and diameter classDiameter class (inches)Species5.0–6.97.0–8.99.0–10.911.0–12.913.0–14.915.0–16.917.0–18.919.0–20.921.0–22.923.0–24.925.0–26.927.0–28.929.0+All classesTonsAdenanthera pavonina—1,5783,3563,7104,615————————13,260Aglaia mariannensis11,6272,306———————————13,933Annona reticulata3,795————————————3,795Areca catechu1,039—981——————————2,021Artocarpus altilis2,5919791,359——————————4,929Artocarpus mariannensis1,078————————————1,078Averrhoa bilimbi2,656————————————2,656Barringtonia asiatica—1,476———————10,578———12,054Barringtonia racemosa562———2,893————————3,455Calophyllum inophyllum2,889————————————2,889Cananga odorata——————4,355——————4,355Carica papaya1,5242,3982,306——————————6,228Casuarina equisetifolia4,1545,5754,0914,499—————————18,319Ceiba pentandra—492———————————492Cerbera dilatata5,0662,6313,323——————————11,020Cocos nucifera2,4619,32988,29166,69032,2344,4339,030——————212,467Cyathea lunulata437886———————————1,323Cycas micronesica27,07728,24711,3014,1462,575————————73,346Eugenia thompsonii1,223————————————1,223Ficus prolixa4,031—3,921——10,6923,28314,608————19,31455,849Ficus tinctoria6641,108———————————1,772Guamia mariannae3,0804,055———————————7,134Hernandia ovigera2,577—5,6342,778—————————10,989Hernandia sonora592—1,046——————————1,638Heterospathe elata55,580————————————55,580Hibiscus tiliaceus21,93610,8631,447——————————34,246Intsia bijuga990934——14,304————————16,229Kleinhovia hospita1,420939———————————2,359Leucaena leucocephala41,35513,0721,686——————————56,113Macaranga thompsonii2,0015,3564,2898,848—4,002———————24,496Mangifera indica—1,7783,12320,84715,33512,1047,6758,452—————69,314Morinda citrifolia2,618————————————2,618Neisosperma oppositifolia—842———————————842Pandanus tectorius23,88917,7982,197——————————43,885Premna obtusifolia18,48912,4406,133—————7,5389,387———53,986Spathodea campanulata770—891——2,607———————4,269Vitex parviflora22,72720,49347,21631,54925,8119,99511,475——————169,267Xylosma nelsonii774————————————774Total271,673145,576192,590143,06897,76743,83335,81723,0597,53819,965——19,3141,000,200

### 20Table 10—Estimated aboveground weight of carbon for stems of all live trees on forest land by species and diameter classDiameter class (inches)Species5.0–6.97.0–8.99.0–10.911.0–12.913.0–14.915.0–16.917.0–18.919.0–20.921.0–22.923.0–24.925.0–26.927.0–28.929.0+All classesTonsAdenanthera pavonina—7731,6451,8182,261————————6,497Aglaia mariannensis5,6971,130———————————6,827Annona reticulata1,859————————————1,859Areca catechu509—481——————————990Artocarpus altilis1,270—666——————————2,415Artocarpus mariannensis528————————————528Averrhoa bilimbi1,301————————————1,301Barringtonia asiatica—723———————5,183———5,906Barringtonia racemosa275———1,417————————1,693Calophyllum inophyllum1,416————————————1,416Cananga odorata——————2,134——————2,134Carica papaya7471,1751,130——————————3,052Casuarina equisetifolia2,0362,7322,0042,205—————————8,976Ceiba pentandra—241———————————241Cerbera dilatata2,4821,2891,628——————————5,400Cocos nucifera1,2064,57143,26232,67815,7942,1724,425——————104,109Cyathea lunulata214434———————————648Cycas micronesica13,26813,8415,5372,0311,262————————35,939Eugenia thompsonii599————————————599Ficus prolixa1,975—1,921——5,2391,6097,158————9,46427,366Ficus tinctoria325543———————————868Guamia mariannae1,5091,987———————————3,496Hernandia ovigera1,263—2,7611,361—————————5,385Hernandia sonora290—513——————————803Heterospathe elata27,234————————————27,234Hibiscus tiliaceus10,7495,323709——————————16,780Intsia bijuga485458——7,009————————7,952Kleinhovia hospita696460———————————1,156Leucaena leucocephala20,2646,405826——————————27,496Macaranga thompsonii9812,6242,1014,335—1,961———————12,003Mangifera indica—8711,53010,2157,5145,931—4,141—————33,964Morinda citrifolia1,283————————————1,283Neisosperma oppositifolia—413———————————413Pandanus tectorius11,7068,7211,077——————————21,504Premna obtusifolia9,0606,0963,005—————3,6934,599———26,453Spathodea campanulata377—437——1,278———————2,092Vitex parviflora11,13610,04223,13615,45912,6474,8985,623——————82,941Xylosma nelsonii379————————————379Total133,12071,33294,36970,10347,90621,47817,55011,2993,6939,783——9,464490,098

### 21 **Guam’s Forest Resources, 2002**



## Number of Canopy and Understory Species

The field sample of this inventory considers both overstory and understory vegeta

tion. Understory vegetation cover was surveyed on field plots for individual species

that occupy at least 3 percent cover on an entire subplot (tables 11 and 12). Rela

tively rare species are not documented on plots unless they have been identified

as a special-interest species by island foresters. More species were found in the

limestone forest sample than in the volcanic forest sample (fig. 11). However, the

limestone sample area was over twice the area of the volcanic forest sample, and

the number of species found tends to increase with the area sampled. These species

figures are only a rough estimate of cover and species counts for the most common

plants. Stone (1971) details 931 species in the flora of Guam.

On a per-plot basis, using the sum of FIA subplot area of approximately onesixth of an acre (summing four subplots at 24-foot radius = 7,238 square feet), the

distribution of tree species numbers reveals a pattern of a relatively high number

of species per plot (fig. 12). Plots where only one or two species are found are often

plots dominated by the widespread Hibiscus tiliaceus

, Casuarina equisetifolia , or the recently broadcast (aerial seeded after World War II) Leucaena leucocephala

.


## Tree Damage and Mortality

We estimate that about 20 percent of the individual trees on Guam have been

damaged (table 13). These damages include mechanical damage from storms and

people, diseases, insects, decay, and damage by other plant species. Approximately

one-third of the damaged trees show signs of decay with visible growth of woodrotting fungus (conks) (fig. 13).

Tree damages are categorized according to causal agents. Because a tree can

exhibit secondary damages caused by another agent, we have classified damages

according to frequency for the primary and secondary damage agents. Thirty-six

percent of primary tree damages in Guam forests are attributed to weather (fig.

14). Damage caused by other vegetation, insects, and diseases follow in declining

frequency for primary damage types. Insects frequently play a secondary role fol

lowing damage or weakening by another damaging agent (fig. 15).

Tree damages can contribute to mortality at different rates for different species.

Some species are more sensitive than others to insects, some to fungal, viral, or

bacterial pathogens that gain entry into plant tissues through mechanical wounding.

Overall, about 2 percent of the trees in our sample were dead. However, by species,

the percentage dead ranges as high as 33 percent for breadfruit trees (Artocarpus

altilis ) in the inventory (fig. 16). About 20 percent of

the trees on Guam

have been damaged—

most from weather,

other vegetation, and

insects.

### 22 RESOURCE BULLETIN PNW-RB-243



### Table 11—Average nontree understory cover **a** 

### on FIA field subplots by species and forest type



### Forest type

Species Limestone Volcanic

Percent
Unknown 12

— Abutilon indicum (L.) Sweet

— 3 Aeschynomene indica L.
— 10 Allophylus timoriensis (DC) Bl. 3

— Alocasia macrorrhiza (L.) Schott

— 5 Antrophyum plantagineum (Cav.) Kaulf.

— 5 Antigonon leptopus Hook. & Arn. 20 17 Arundina graminifolia (D. Don) Hochr.

— 3 Asplenium laserpitifolium Lam.
— 7 Axonopus compressus (Sw.) Beauv. 9 15 Bambusa vulgaris Schrad. ex J.C. Wendl. 10

— Belvisia spicata Safford 3 4

Bidens alba (L.) DC. 27 8 Blechum pyramidatum (Lam.) Urban 33

— Bothriochloa pertusa (L.) A. Camus

— 32 Buddleja asiatica Lour. 5

— Calopogonium mucunoides Desv. 11 5 Calyptocarpus vialis Less. 10

— Cassytha filiformis L. 3

— Centotheca lappacea (L.) Desv. 5 11 Centrosema pubescens Benth. 9

— Chamaecrista nictitans (L.) Moench

— 3 Chamaesyce sp. S.F. Gray 3

— Chamaesyce hirta (L.) Millsp.

— 3 Chamaesyce hypericifolia (L.) Millsp. 3

— Chloris barbata Sw.

— 8
Chloris radiata (L.) Sw. 30

— Chromolaena odorata (L.) King & H.E. Robins. 13 12
Clerodendrum inerme (L.) Gaertn. 5

— Colubrina asiatica (L.) Brongn. 28

— Conyza canadensis (L.) Cronq. 4

— Cynodon dactylon (L.) Pers. 10 3 Cyperus ligularis L. 3

— Davallia solida (Forst.) Sw. 3

— Decaspermum fruticosum Forst.
— 3 Dendrobium guamense Ames

— 9 Desmanthus virgatus (L.) Willd. 8

— Desmodium umbellatum (L.) DC. 10

— Dichanthium bladhii (Retz.) Clayton

— 75 Dicranopteris linearis (Burm.) Underwood

— 19 Digitaria bicornis (Lam.) Roemer & J.A. Schultes ex Loud. 10 28 Digitaria ciliaris (Retz.) Koel. 30

— Dimeria chloridiformis (Gaud.) K. Schum. & Lauterb.

— 36 Discocalyx megacarpa Merrill

— 5 Elephantopus mollis Kunth

— 6

Eleusine indica (L.) Gaertn. 36 5 Entada phaseoloides (L.) Merr. 5 22

### 23 **Guam’s Forest Resources, 2002**



### Table 11—Average nontree understory cover **a** 

### on FIA field subplots by species and forest type (continued)



### Forest type

Species Limestone Volcanic

Percent Entada pursaetha DC. 12

— Epipremnum pinnatum (L.) Engl. 27

— Eragrostis tenella (L.) Beauv. ex Roemer & J.A. Schultes 60

— Euphorbia chamaesyce L. 10

— Eustachys petraea (Sw.) Desv.

— 8 Fimbristylis dichotoma (L.) Vahl 8

— Fimbristylis sp. Vahl

— 10 Flagellaria indica L. 28 14 Flemingia strobilifera (L.) Ait. & Ait. f. 36

— Freycinetia reineckei Warb.

— 15
Gleichenia linearis (Burm.) Clarke

— 16
Glochidion mariana Mueller-Arg., L.

— 3 Gossypium hirsutum L. 5

— Grasses

— 10 Heterogonium pinnatum (Copel.) Holtt.

— 3 Humata heterophylla (Sm.) Desv.

— 5 Hyptis capitata Jacq.
— 9 Hyptis pectinata (L.) Poit.

— 15 Hyptis rhomboidea Mart. & Galeotti

— 5 Ipomoea indica (Burm. f.) Merr. 13 5 Ipomoea littoralis Blume 5 3 Ipomoea obscura (L.) Ker-Gawl. 3

— Ipomoea triloba L. 7 3

Jasminum marianum DC. 10 25 Lepturus repens (G. Forst.) R. Br. 75

— Lycopodium cernuum L.
— 7 Lygodium microphyllum (Cav.) R. Br. 10 11 Macroptilium lathyroides (L.) Urban 3

— Mariscus javanicus (Houtt.) Merr. & Metcalfe

— 70 Maytenus thompsonii Fosb. 5

— Medinilla sp. Gaud

— 8

Melastoma malabathricum L.
— 4 Merremia peltata (L.) Merr. 7

— Microlepia speluncae (L.) T. Moore

— 8

Mikania micrantha Kunth 7 18

Mikania scandens (L.) Willd. 9

— Mimosa pudica L. 9 3 Miscanthus floridulus (Labill.) Warb. ex K. Schum. & Laut. 22 47

Momordica charantia L. 11 70 Myrtella bennigseniana (Volk.) Diels

— 3 Nephrolepis biserrata (Sw.) Schott 10 12 Nephrolepis hirsutula (J.R. Forst.) K. Presl 7 8
Ochrosia mariannensis A. DC. 7

— Oplismenus compositus (L.) Beauv. 14 20 Oplismenus sp. Beauv.
— 23

Panicum maximum Jacq. 34

— Paspalum conjugatum Berg. 10

—

### 24 RESOURCE BULLETIN PNW-RB-243



### Table 11—Average nontree understory cover **a** 

### on FIA field subplots by species and forest type (continued)



### Forest type

Species Limestone Volcanic

Percent Paspalum longifolium Roxb. 3 7 Passiflora foetida L. 11 6 Passiflora suberosa L. 8

— Pennisetum polystachyon (L.) J.A. Schultes 17 27 Pennisetum purpureum Schumacher 39 10 Phragmites karka (Retz.) Trin ex Steud.

— 44 Phyllanthus saffordii Merrill

— 3 Phymatosorus scolopendria (Burm. f.) Pic. Serm. 7

— Pilea microphylla (L.) Liebm. 19

— Piper guahamense DC. 10 3

Pluchea carolinensis (Jacq.) G. Don

— 3 Polygonum minus Huds.

— 25 Polypodium punctatum (L.) Sw. 5 5 Polypodium scolopendria Burm. f. 19 13 Premna serratifolia L.
— 3 Pteris ensiformis Burm. f.

— 50 Pteris quadriaurita Retz.
— 8 Pteris tripartita Sw. 3

— Pycreus polystachyos (Rottb.) Beauv.

— 15 Pyrrosia lanceolata (L.) Farw. 9 6 Pyrrosia sp. Mirbel

— 7 Rhynchospora rubra Domin

— 13 Saccharum spontaneum L.
— 28 Scaevola frutescens (Miller) Krause

— 3 Scleria polycarpa Boeck. 15 11
Senna alat (L.) Roxb. 6

— Unknown shrub 10

— Solanum americanum P. Mill.

— 3 Spathoglottis plicata Blume

— 3 Stachytarpheta jamaicensis (L.) Vahl 16 4 Stachytarpheta urticifolia Sims 19 6 Stacytharpheta jamaicensis (L.) Vahl 3 4 Stictocardia tiliaefolia (Desr.) H. Hallier

— 8 Stylosanthes guianensis (Aubl.) Sw.

— 7 Syngonium augustatum Schott 8

— Thelypteris gretheri (Wagner) Stone 13

— Thelypteris maemonensis (Wagner & Grether) Stone 3

— Thelypteris opulenta (Kalfuss) Fosberg 5 10 Thelypteris parasitica (L.) Fosberg

— 9 Thelypteris subpubescens Blume

— 13 Thelypteris unita (L.) C.V. Morton

— 6 Trichomanes brevipes (C. Presl.) Baker

— 5
Waltheria indica L. 17 8 Wikstroemia elliptica Merr. 6 3 Zoysia matrella (L.) Merr. 7

—

a The cover estimates are averaged among subplots where each species was found.

### 25 **Guam’s Forest Resources, 2002**



### Table 12—Average understory tree cover on FIA field subplots by species and forest type



### Forest type

Species Limestone Volcanic

Percent Adenanthera pavonina 3

— Aglaia mariannensis 4

— Annona muricata L. 7 3

Annona reticulata 8

— Areca catechu

— 8 Artocarpus altilis 3

— Averrhoa bilimbi 5

— Barringtonia racemosa
— 3

Bauhinia monandra

— 10 Calophyllum inophyllum

— 4 Cananga odorata 3

— Carica papaya 3

— Casuarina equisetifolia

— 3

Cerbera dilatata 4

— Cocos nucifera 7 14 Cycas micronesica 8 6 Diospyros kaki L. f. 3

— Eugenia reinwardtiana 3

— Ficus prolixa 7

— Guamia mariannae 11 3 Heterospathe elata 20 10

Hibiscus tiliaceus 7 5 Kleinhovia hospita 8

— Leucaena leucocephala 11 4 Mangifera indica

— 3 Morinda citrifolia 7 6 Neisosperma oppositifolia 3

— Pandanus tectorius 5 8 Pipturus argenteus 3

— Polyscias grandifolia

— 7 Premna obtusifolia 6

— Psidium guajava 3 4 Triphasia trifolia 11 13 Vitex parviflora 5 10

### 26 RESOURCE BULLETIN PNW-RB-243

90

80

70

60

50

40

30

20

10

0 

### Tree species Understory species Number of plotsNumber of species 

### Lime stone

Volcanic

Figure 11—Forty-eight tree species and about 140 understory species were measured on 46 plots in

Guam.



### 1–2 3–4 5–6 7–8 9–10 11–12 12

10

8

6

4

2

0Number of plots



### Number of tree species on FIA plots Lime stone

Volcanic

Figure 12—The average number of tree species per sixth-acre plot on both limestone and volcanic

soils was four.

### 27 **Guam’s Forest Resources, 2002**



### Table 13—Number of trees by primary damage type and species for all trees ( > 5 inches diameter at breast height; includes dead trees)

Species No damage Broken

bole Broken

branches Broken

roots Conks Damaged

shoots Lost apical
dominance Open

wound Vines in

crown All damage s
Number of trees
Adenanthera pavonina 14,490

— 28,981

— 14,490

— — — — 43,471
Aglaia mariannensis 275,319 14,490

— — 14,490

— — 14,490

— 43,471

Annona reticulata 72,452

— — — 14,490

— — — — 14,490

Areca catechu 44,330

— — — — — — — — — Artocarpus altilis 73,311

— — — — — 43,758

— — 43,758
Artocarpus mariannensis 14,490

— — — — — — — — — Averrhoa bilimbi 57,962

— — — — — — — — — Barringtonia asiatica 14,490

— — — — — — 14,490

— 14,490
Barringtonia racemosa

— — — — 29,553

— — — — 29,553
Calophyllum inophyllum 59,107

— — — — — — — — — Cananga odorata 14,490

— — — — — — — — — Carica papaya 57,962

— 28,981

— — — 14,490

— — 43,471
Casuarina equisetifolia 115,924

— — — — — — — — — Ceiba pentandra 14,490

— — — — — — — — — Cerbera dilatata 144,905

— — — 14,490

— 28,981

— — 43,471
Cocos nucifera 1,074,979

— — — 29,553 14,490

— 58,248

— 102,292
Cyathea lunulata 29,553

— — — — — — — — — Cycas micronesica 1,280,888 14,490 43,758

— 115,924

— — 72,452 87,515 334,140
Eugenia thompsonii 29,553

— — — — — — — — — Ficus prolixa 131,273

— — — — — 14,490

— — 14,490

Ficus tinctoria 14,490

— — — — — 14,490

— — 14,490

Guamia mariannae 86,943

— — — — 14,490 14,490 14,490

— 43,471
Hernandia ovigera 115,924

— 14,490

— — — — — — 14,490

Hernandia sonora

— — — — 28,981

— — — — 28,981
Heterospathe elata 1,045,998

— — — — — — 29,553

— 29,553

Hibiscus tiliaceus 219,933

— 101,433

— 159,682 101,433 14,777 14,490

— 391,816
Intsia bijuga 57,962

— — — 14,490

— — — — 14,490
Kleinhovia hospita 57,962

— — — — — — — — — Leucaena leucocephala 772,576

— — — 58,534

— 14,777 44,330

— 117,641
Macaranga thompsonii 144,905

— — — 14,490

— 14,490 14,490

— 43,471
Mangifera indica 177,321 14,777

— — 14,777

— 29,553 29,553

— 88,660
Morinda citrifolia 29,267

— 29,553

— — — — — — 29,553
Neisosperma oppositifolia 14,490

— — — — — — — — — Pandanus tectorius 688,781 58,248 29,267

— — — — — 44,330 131,846
Premna obtusifolia 376,753 14,490

— 43,471 130,414

— 14,490 14,490 57,962 275,319
Spathodea campanulata 57,962

— — — — — — — — — Vitex parviflora 743,022 29,267 58,248

— 28,981

— 57,962 14,490

— 188,949
Xylosma nelsonii 14,490

— — — — — — — — —
Total 8,138,752 145,764 334,712 43,471 683,343 130,414 276,750 335,571 189,808 2,139,834

### 28 RESOURCE BULLETIN PNW-RB-243

Figure 13—Broken boles, branches, and roots accounted for 25 percent of the damages on Guam. An additional 31 percent of the damages were due to rot evidenced by shelf-fungus conks. 

### 31%

16% 16% 9% 6% 7% 2%

13% 

## Tree Damages

8.1 million no damage 2.1 million with damage

C onks

Open wound

Lost apical dominance

Broken branches

Vines in crown

Damaged shoots

Broken bole

Brok en roots

Figure 14—Weather and mechanical impacts by other vegetation accounted for 64 percent of the primary damages. 

### 36%

16% 10% 8% 1%

28% <1% 1% 

## Primary Damage Agent

Weather

Vegetation

Insect

Disease

Physical

Unknown

Human

Animal

### 29 **Guam’s Forest Resources, 2002**

Figure 15—Secondary damage was generally attributed to weather.

Figure 16—Soft-wooded species, such as Artocarpus altilis , tended to suffer high mortality. 

### 82% 8% 6% 2%

2% 

## Secondary Damage Agent

Weather

Insect

Vegetation

Physical

Disease

Artocarpus altilis Calophyllum inophyllum Cerbera dilatata Mangifera indica Aglaia mariannensis Hibiscus tiliaceus Pandanus tectorius Vitex parviflora Cycas circinalis Premna obtusifolia Cocos nucifera 35

30

25

20

15

10

5

0Dead trees (percent) 

## Percentage Dead by Species

### 30 RESOURCE BULLETIN PNW-RB-243



## Epiphytes

Epiphytic plants growing on trees use space and moisture that might otherwise be

available for the growth of the host tree. Physical breakage of tree limbs can occur

depending on the amount and species of plants growing in the branching network

of the host tree. In extremely wet areas, the weight loading of epiphytes can be

tremendous, stunting the growth of individual trees. We rated each tree sampled in

the inventory according to epiphyte loading. The majority of trees on Guam show

little evidence of epiphyte loading (table 14). Frequent storm damage to trees may

prevent the accumulation of epiphytes to the point of tree limb damage on Guam.



# Acknowledgments

The FIA Pacific Island inventories are the result of cooperative effort between

a number of groups and agencies. The USDA Forest Service, State and Private

Forestry in the Pacific Southwest Region has been a strong supporter of natural

resource assessments in the Pacific Islands. Many thanks to the Pacific Islands Im

agery Consortium partners for sharing costs on imagery and interpretation. Thanks

to the University of Guam (UOG) for logistical support, to Lynn Raulerson at UOG

for species identification and training, to Lisa Fischer at the Remote Sensing Lab in

the Pacific Southwest Region for imagery interpretation and mapping support, and

to Walter Grabowiecki, Dale Baer, Falaniko Mika, Ritofu Lotovale, Tony Gaison,

Patrick Quenga, Vince Tenorio, Albert Blas, De’rick Baza, D’wuane Baza, and

Vince Perez for field assistance and logistical support. We also thank Dale Weyer

mann, John Chase, Chuck Veneklase, and Ron Wanek with FIA for GIS, program

ming, and technical support. Tom Brandeis, Dave Azuma, and Chuck Bolsinger

offered very helpful comments on prior drafts.



# Metric Equivalents

When you know: Multiply by: To find:

Inches 2.54 Centimeters

Feet .3048 Meters

Miles 1.609 Kilometers

Acres .405 Hectares

Cubic feet .0283 Cubic meters

Tons 907 Kilograms

Tons per acre 2.24 Tonnes or megagrams per hectare

Cubic feet per acre .06997 Cubic meters per hectare

Trees per acre 2.471 Trees per hectare

### 31 **Guam’s Forest Resources, 2002**



### Table 14

— 

### Estimated number of trees on forest land by epiphyte loading (amounts of nontree vegetation in the canopy and branches) and species (includes dead trees)

Epiphyte loadings

Species None Low Moderate High All loadings

Number of trees Adenanthera pavonina 28,981 — 28,981 — 57,962 Aglaia mariannensis 217,357 72,452 28,981 — 318,791

Annona reticulata 43,471 28,981 14,490 — 86,943

Areca catechu 44,330 — — — 44,330 Artocarpus altilis 58,248 — 44,044 14,777 117,069 Artocarpus mariannensis — 14,490 — — 14,490

Averrhoa bilimbi 14,490 43,471 — — 57,962 Barringtonia asiatica 14,490 14,490 — — 28,981 Barringtonia racemosa 14,777 14,777 — — 29,553 Calophyllum inophyllum 44,330 — 14,777 — 59,107 Cananga odorata 14,490 — — — 14,490 Carica papaya 101,433 — — — 101,433 Casuarina equisetifolia — 115,924 — — 115,924 Ceiba pentandra 14,490 — — — 14,490

Cerbera dilatata 101,433 72,452 — 14,490 188,376 Cocos nucifera 499,832 515,181 73,597 88,660 1,177,271 Cyathea lunulata — — — 29,553 29,553 Cycas micronesica 565,415 596,686 379,043 73,884 1,615,028 Eugenia thompsonii — 29,553 — — 29,553 Ficus prolixa 73,311 28,981 43,471 — 145,764

Ficus tinctoria 28,981 — — — 28,981

Guamia mariannae 86,943 43,471 — — 130,414 Hernandia ovigera — 86,943 43,471 — 130,414

Hernandia sonora 14,490 14,490 — — 28,981 Heterospathe elata 883,454 177,321 14,777 — 1,075,552

Hibiscus tiliaceus 450,923 160,827 — — 611,749 Intsia bijuga 14,490 57,962 — — 72,452 Kleinhovia hospita 57,962 — — — 57,962 Leucaena leucocephala 247,769 350,920 277,037 14,490 890,217 Macaranga thompsonii 144,905 14,490 28,981 — 188,376 Mangifera indica 73,884 162,544 14,777 14,777 265,981 Morinda citrifolia 58,821 — — — 58,821 Neisosperma oppositifolia — 14,490 — — 14,490

Pandanus tectorius 351,493 248,628 176,176 44,330 820,627 Premna obtusifolia 202,867 202,867 202,867 43,471 652,072 Spathodea campanulata 28,981 28,981 — — 57,962 Vitex parviflora 566,560 306,876 28,981 29,553 931,971 Xylosma nelsonii 14,490 — — — 14,490

Total 5,077,896 3,418,252 1,414,451 367,987 10,278,586

### 32 RESOURCE BULLETIN PNW-RB-243



# Literature Cited

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Agriculture, Forest Service; U.S. Department of Agriculture, Natural Resources

Conservation Service, Government of Guam Division of Forestry. 11 p.

Cochran, W.G. 1977. Sampling techniques. New York: John Wiley and Sons.

428 p.

Fosberg, F.R. 1960. The vegetation of Micronesia: 1. General descriptions, the

vegetation of the Marianas Islands, and a detailed consideration of the vegetation

of Guam. Bulletin of the American Museum of Natural History. 119: 1–76.

Mueller-Dombois, D.; Fosberg, F.R. 1998. Vegetation of the tropical Pacific

Islands. New York: Springer-Verlag. 733 p.

Parker, A.J. 1982. The topographic relative moisture index: an approach to

soil-moisture assessment in mountain terrain. Physical Geography. 3: 160–168.

Stone, B.C. 1971. The flora of Guam. Micronesica. 6: 1–657.

U.S. Department of Agriculture, Forest Service [USDA FS]. 2002. Field

instructions for the inventory of the Pacific Islands. Portland, OR: Pacific

Northwest Research Station, Forestry Sciences Laboratory, Forest Inventory and

Analysis. 256 p.

U.S. Department of Agriculture, Natural Resources Conservation Service

[USDA NRCS]. 1988. Soil survey of Territory of Guam: soil survey geographic

(SSURGO) database for Territory of Guam. Washington, DC. 166 p. +117 maps.

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