United States

Department of

Agriculture

Forest 

Service

Pacifi c Northwest

Research Station

Resource Bulletin

PNW-RB-261

October 2011

Commonwealth of the 

Northern Mariana Islands’ 

Forest Resources, 2004

Joseph A. Donnegan, Sarah L. Butler, Olaf Kuegler, and Bruce A. Hiserote

Saipan

Tinian

Rota
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 

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Authors

Joseph A. Donnegan is an ecologist, Sarah L. Butler is an ecologist,

Olaf Kuegler is a statistician, and Bruce A. Hiserote is an information management specialist, Forestry Sciences Laboratory, 620 SW Main Street, Suite 400, 

Portland, OR 97205-3028.
Abstract

Donnegan, Joseph A.; Butler, Sarah L.; Kuegler, Olaf; Hiserote, Bruce A. 2011.

Commonwealth of the Northern Mariana Islands’ forest resources, 2004. Resour. 

Bull. PNW-RB-261. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station. 40 p.

The Forest Inventory and Analysis program collected, analyzed, and summarized 

field data on 37 field plots on the islands of Rota, Tinian, and Saipan in the Commonwealth of the Northern Mariana Islands (CNMI). 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 the CNMI’s forest resources and a 

comparison to prior vegetation mapping work.

Keywords: CNMI, biomass, damage, Forest Inventory and Analysis, forest 

inventory, volume, land cover.
Summary 

The Forest Inventory and Analysis (FIA) program conducted a systematic inventory 

of the forests of Rota, Tinian, and Saipan in the Commonwealth of the Northern 

Mariana Islands (CNMI) in 2004 to estimate forest area, tree stem volume, biomass, carbon storage, tree damages, and the composition and percentage cover of 

understory vegetation species. Thirty-five permanent field plots were installed in a 

variety of forest types. By using recently acquired high-resolution satellite imagery, 

land cover was mapped into five broad classes: forest, nonforest vegetation, urban, 

barren, and inland water. Soil survey information was used to help refine the 

classification of forests. Our estimates for this inventory are derived from a sample 

based on 75,407 acres on the three main islands in the CNMI. About 12 percent of 

the landscape was classified as urban land, the largest percentage found on Saipan 

(21 percent). We estimated gross tree stem volume to be about 66.5 million cubic 

feet for all size classes including seedlings and saplings. Aboveground dry biomass 

for tree stems 5 inches and greater was estimated to be about 563,000 tons. About 

32 percent of the trees sampled in the inventory had some form of damage. Vines in 

the crown were the most prevalent damage type, followed by lost apical dominance, 

and conks. The most frequently identified damaging agents were damage from 

other vegetation (e.g., strangling or smothering vines) and weather. The CNMI’s 

forests are composed of small-diameter trees and have relatively low species diversity compared to other Pacific Islands. In total, 57 tree species and 107 understory 

species were measured on the FIA plots. The average number of tree species per 

one-sixth-acre plot was five. The CNMI foresters and ecologists were especially 

helpful with species identification in the field.
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Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Introduction

This report on the forest resources of the three main islands of the Commonwealth 

of the Northern Mariana Islands (CNMI) (fig. 1) was based on a cooperative forest 

inventory conducted in 2004 by the USDA Forest Service, Pacific Northwest Forest 

Inventory and Analysis (FIA) program1 and Pacific Island foresters. This work is 

an adaptation of the national FIA inventory system and was tailored to help answer 

local, national, and international questions about the status and trends in tropical 

forested ecosystems. Our partnership has concentrated on sharing technical forestry 

skills among cultures and agencies. The fieldwork for this inventory was conducted 

by a multinational crew including foresters from the CNMI, American Samoa, and 

mainland U.S. foresters and ecologists.

The FIA partnership yeilded a systematic, sample-based field inventory on the 

CNMI in conjunction with support for updating prior vegetation mapping work 

(Falanruw et al. 1989) to estimate land cover and forest-type area. We include new 

information on species composition, tree size distribution, stem volume, biomass, 

carbon mass, and damages for living and dead trees. The inventory was designed 

to provide resource managers with a broad overview of the current situation so they 

can better manage their forested and nonforested lands, and manage or mitigate any 

changes in the resource. The summarization of the field data is intended to help 

managers plan sustainable land use practices as well as plan sustainable supplies of 

wood, control invasive species and erosion, manage disturbances such as fire, and 

to track and mitigate damage from animals.

Objectives

The objectivs of this inventory are to:

• Estimate the current area of forest land by forest-type group and stand size 

class.

• Estimate the volume, biomass, and carbon storage for tree species by diameter class.

• Estimate the numbers of trees affected by damaging agents, such as insects 

and diseases, and estimate the numbers of dead trees.

• Share measurement and analysis techniques among groups involved in the 

inventory.

1

 The Forest Inventory and Analysis program is now part of the Resource Monitoring and 

Assessment program of the Pacific Northwest Research Station.
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RESOURCE BULLETIN PNW-RB-261

Figure 1—The Commonwealth of the Northern Mariana Islands is an archipelago in the northwestern Pacific Ocean about 470 miles east of the Phillipines. Land cover was mapped from 2005 QuickBird satellite data. The Forest Inventory and Analysis program collected data on the three larger and southernmost islands of Rota, Tinian, and Saipan.

Phillipines
3

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Methods

Site Description

The archipelago of the Commonweatlh of the Northern Mariana Islands is a U.S.-

associated political entity that parallels the Mariana Trench in the northwestern 

Pacific Ocean. Over an ocean distance of approximately 400 miles, the CNMI’s 14 

islands stretch from about 14 to 20 degrees north latitude: Rota, Aguijan, Tinian, 

Saipan, Farallon de Medinilla, Anatahan, Sarigan, Guguan, Alamagan, Pagan, 

Agrihan, Asuncion, Maug (three islets), and Farallon de Pajaros. The U.S. Territory 

of Guam, a separate political entity from the CNMI, lies to the south of Rota by less 

than 50 miles, and is the southernmost island in the Mariana Archipelago. Land 

area of the CNMI totals about 184 square miles. However, the forest inventory only 

covers the three largest, southern islands of Rota, Tinian, and Saipan, making up 

about 117 square miles (64 percent) of the land area.

The nine northern islands are geologically younger than the five southern 

islands (Fosberg 1960). The vegetation of the northern islands has been disturbed 

by volcanic activity, browsing by goats, and typhoon damage. A mixture of forest types and abundant sword grass (Miscanthus floridulus (Labill.) Warb. ex K. 

Schum. & Lauterb.) were described in a detailed survey by Ohba (1994). Currently 

the northern islands host little to no human settlement owing to relocation of locals, 

disturbance risk, isolation, and the harsh environment.

The three older, southern islands of Rota, Tinian, and Saipan have developed 

deep soils where the underlying volcanic parent materials have been exposed and 

weathered. Limestone areas tend to have shallow, highly weathered soils. Owing 

to relatively rapid water infiltration and consequently limited stream development, 

the limestone landscapes are characterized by plateaus and a series of steep escarpments (Young 1989) (fig. 2). Although deep, soil developed on volcanic parent materials have very low fertility, most of which resides in the topsoil. The abundance of 

calcium in the limestone and coral sand on these landscapes creates soils that are 

inherently more fertile than soils on volcanic landscapes.2

Rota, Tinian, and Saipan have a long history of human disturbance, with human

settlement dating back as far as 4,300 years (Athens et al. 2004). The large population of Chamorro natives and Micronesian settlers likely was a significant impact 

on the vegetation of the CNMI even prior to European visit by Magellan in 1521 

and subsequent Spanish occupation in the 1600s. The southern islands also were 

profoundly disturbed for agriculture by German and Japanese occupation in the 

2

 Gavenda, R. 2010. Personal communication. Soil fertility in Pacific Island Landscapes, 

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

Office, FHB Building, Suite 301, 400 Route 8, Maite, GU 96927-2003.
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RESOURCE BULLETIN PNW-RB-261

early 1900s and by heavy fighting during World War II (Young 1989). Coupled with 

regular natural disturbance from typhoons, the CNMI forests are in a continuous 

state of recovery.

The climate of the CNMI is warm and moderately humid (fig. 3). Mean annual 

temperature in Saipan is about 78.9 °F, with mean annual minimum and maximum 

about 74.5 °F and 83.3 °F, respectively. Total annual precipitation averages 82.3 

inches with a pronounced wet season July to November (Western Regional Climate 

Center 2009).

The CNMI is located in a typhoon belt and often experiences major typhoons 

annually to semiannually. The typhoons are characterized by heavy rainfall, strong 

winds, and coastal surges that inundate low-lying areas. Changes in sea level and 

the frequency of coastal surges have become an immediate concern for Pacific 

Island inhabitants.

Vegetation Types

The native composition and structure of vegetation on Rota, Tinian, and Saipan 

mostly has been replaced over a long history of agroforestry, agricultural practices, 

and disturbances including typhoon, nonnative plants and animals, and World War 

II. What currently exists is a mixture of native and nonnative species, primarily of 

smaller tree size classes, with intact remnants of native limestone and ravine forest. 

Figure 2—The islands of Rota, Tinian, and Saipan are composed of volcanic cores capped by 

limestone, forming a series of plateaus and steep escarpments.

Joseph Donnegan
5

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

The vegetation types described below use the mapping work of Liu and Fischer 

(2007) as the basis for classification with the species composition derived by 

overlaying the 2004 forest inventory plot data onto the mapped types. We purposely 

avoid the terms “primary” and “secondary” forest for this most recent mapping and 

summary; these terms suggest a dichotomy between disturbed and undisturbed 

forest when in reality, the majority of the forests on Rota, Tinian, and Saipan have 

been disturbed by humans continuously over several thousand years. Additionally, 

that terminology is somewhat arbitrary because of an unknown history of land use 

and the uncertainty surrounding the time required to recover from secondary back 

to an undocumented primary forest.

Native limestone forest—

Where limestone has not been cleared by humans recently, dense forest tends to 

develop. Owing to the widespread disturbance across the three southern islands, the 

label “native limestone forest” cannot be equated with intact, undisturbed forest. 

Instead, this type refers to forest occuring on limestone substrates where higher 

numbers of native species are found. Listed in descending abundance (as is the 

case for all forest types except ravine forest in this section) the following species 

Figure 3—Both the annual maximum and minimum temperatures in the Commonwealth of the 

Northern Mariana Islands differ seasonally only by about 4 °F. However, average monthly precipitation totals vary from a low of about 3 inches in March, to over 12 inches in August with a distinct 

summer wet season and a dry winter/early spring (Western Regional Climate Center 2009).
6

RESOURCE BULLETIN PNW-RB-261

were found on forest inventory plots within native limestone forest: Citrus hystrix, Pandanus tectorius, Guamia mariannae, Cynometra ramiflora, Ficus prolixa, 

Discocalyx ponapensis, Eugenia palumbis, Aglaia mariannensis, Hibiscus tiliaceus, 

Carica papaya, Drypetes spp., Hernandia sonora, Premna obtusifolia, Psychotria 

mariana, Barringtonia racemosa, Allophylus timorensis, Claoxylon marianum, 

Pipturus argenteus, Cocos nucifera, Elaeocarpus joga, Intsia bijuga, Pandanus 

dubius, Guettarda speciosa, Artocarpus altilis, Barringtonia asiatica, Ficus spp., 

Neisosperma oppositifolia, Mammea odorata, Morinda citrifolia, Ficus tinctoria, 

and Mangifera indica (see table 1 for scientific names of tree species).

Ravine forest—

Only 204 acres of ravine forest were mapped for the CNMI (Liu and Fischer 

2007); all of it occured on the southernmost part of Rota where the volcanic core 

has weathered into highly dissected ravines with relatively impermeable soils. No 

forest inventory plots fell inside of the ravine forest type. The vegetation in this 

area is primarily swordgrass (Miscanthus floridulus (Labill.) Warb. ex K. Schum. 

& Lauterb.) savanna mixed with shrubs. However, a variety of tree species occur 

in sheltered ravines. Dominant species (alphabetic listing) include Areca catechu

L., Artocarpus altilis, Bambusa vulgaris (Schrad. ex J.C. Wendl.), Barringtonia 

asiatica, Calophyllum inophyllum, Cananga odorata (Lam.) Hook. f. & Thomson, 

Cocos nucifera, Cynometra ramiflora, Hernandia labyrinthica Tuyama, Hibiscus 

tiliaceus, Intsia bijuga, Ixora triantha Volkens, Macaranga thompsonii, Mangifera 

indica, Melastoma malabathricum, Morinda citrifolia, Pandanus tectorius, and 

Scaevola sericea Vahl.

As typified for the region, savanna areas are regularly ignited by arsonists, 

killing tree seedlings, burning into forested areas, and leaving soils barren for 

increased erosion and mass soil movement. Foresters on Rota currently are planting 

native species on the steep slopes with barren soils throughout the ravine badlands 

in an effort to reforest and stabilize these soils (fig. 4). The primary species planted 

recently include Paspalum notatum Flueggé, Vetiveria zizanioides (L.) Nash, Acacia confusa, Calophyllum inophyllum L., Morinda citrifolia, Barringtonia asiatica, 

Scaevola sericea, Hernandia labyrinthica, and Dodonaea viscosa (L.) Jacq.

Mixed introduced forest—

This forest type is a mixture of native and nonnative species representing forests 

recovering from disturbance, native forests invaded by nonnatives, and forests that 

are establishing in disturbed areas from a mix of seed sources. Tree species include 

Leucaena leucocephala, Cynometra ramiflora, Ficus prolixa, Melanolepis multiglandulosa, Pandanus tectorius, Albizia lebbeck, Ficus tinctoria, Guamia mariannae, Eugenia palumbis, Carica papaya, Premna obtusifolia, Hibiscus tiliaceus, 
7

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 1—Scientific names, common names, estimated number and gross volume, and standard errors for estimated totals of species measured as trees in the Commonwealth of the Northern Mariana Islands

Estimated Standard Gross

Number error for volume Standard error

Number (≥ 1 inch estimated (≥ 5 inches for estimated

Scientific name Common name measured diam.) number (

±) diam.) volume (

±)

Acacia confusa Merr. formosa acacia 1 132,241 148,100

Adenanthera pavonina L. kulalis 3 34,199 36,870 1,108,736 1,195,315Aglaia mariannensis Merr. mapuñao 8 1,011,607 550,109 27,663 27,946Aidia cochinchinensis Lour. smak, sumac 1 142,004 153,093Albizia lebbeck (L.) Benth. mamis 27 1,792,671 973,227 1,687,721 1,146,098Allophylus timorensis (DC.) Bl. 1 132,241 148,100Annona spp. 1 142,004 153,093Artocarpus altilis (Park.) Fosb. lemai, breadfruit 3 31,848 35,667 1,060,613 1,187,810Barringtonia asiatica (L.) Kurz puting 3 31,848 35,667 176,601 197,781Barringtonia racemosa (L.) Spreng. 2 142,857 159,989 14,185 15,887Bruguiera gymnorrhiza (L.) Lam. 2 22,800 24,580 162,424 175,107Carica papaya L. 22 2,522,276 1,101,626 224,167 131,323Cassia fistula L. 1 11,400 12,290 45,838 49,417Casuarina equisetifolia L. 17 215,063 183,622 2,822,173 2,532,776Cerbera dilatata Mgf. chuti 1 11,400 12,290 21,138 22,789Citrus ×aurantifolia (Christm.) Swingle 2 330,374 324,801Citrus hystrix DC. 47 6,215,306 6,960,696Claoxylon marianum Muell.-Arg. katteknau, katot 1 132,241 148,100Cocos nucifera L. niyok, coconut palm 16 176,910 102,146 2,213,227 1,311,222Cynometra ramiflora L. 75 6,899,858 3,450,790 1,250,248 720,320Delonix regia (Boj.) Raf. flame tree, arbol del fuego 7 732,821 790,045 422,586 455,584Discocalyx ponapensis Mez 13 1,906,823 1,266,316Drypetes spp. 

4 528,962 592,400

Elaeocarpus joga Merr. joga 5 53,080 47,344 174,853 168,294Erythrina variegata (L.) Merr. gabgab, coral tree 10 113,998 122,900 1,267,520 1,366,499Eugenia palumbis Merr. 12 1,586,887 1,184,799Eugenia stelechantha (Diels) Kaneh. luluhut 10 1,651,872 1,624,006Ficus prolixa Forst. f. 66 3,809,830 2,295,211 5,355,185 4,617,736Ficus spp. L. 2 21,232 23,778 48,825 54,680Ficus tinctoria Forst. f. hoda, tagete 7 732,038 777,846 112,779 94,147Guamia mariannae (Safford) Merr. paipai 39 5,099,250 2,863,701 97,072 62,077Guettarda speciosa L. pano 7 75,879 53,344 255,091 192,854
8

RESOURCE BULLETIN PNW-RB-261 Table 1—Scientific names, common names, estimated number and gross volume, and standard errors for estimated totals of species measured as trees in the Commonwealth of the Northern Mariana Islands (continued) Estimated Standard Gross Number error for volume Standard error Number (≥ 1 inch estimated (≥ 5 inches for estimated

Scientific name Common name measured diam.) number (±) diam.) volume (±)

Hernandia sonora L. nonak 23 365,792 274,392 2,296,609 1,688,288

Heterospathe elata (Becc.) Becc. 1 11,400 12,290 34,661 37,368Hibiscus tiliaceus L. 17 1,058,426 841,806 401,349 381,486Intsia bijuga (Colebr.) O. Ktze. ifil 22 572,025 470,986 997,715 651,708Leucaena leucocephala (Lam.) de Wit tangantangan 300 38,815,714 10,814,962 1,727,600 649,115Mammea odorata (Raf.) Kosterm. chopak 1 12,769 12,899 25,099 25,356Mangifera indica L. 1 10,616 11,889 91,305 102,255Melanolepis multiglandulosa (Muell.-Arg.) Fosb. alom 24 1,448,730 762,417 549,154 323,323Morinda citrifolia L. lada, indian mulberry 8 850,607 590,073 152,420 102,631Morus alba L. 2 330,374 324,801Musa spp. 12 136,798 104,926Neisosperma oppositifolia (Lam.) Fosb. & Sachet faag 6 192,733 148,112 227,565 130,711Pandanus dubius Spr. pahong 29 326,675 218,109 1,499,415 1,047,583Pandanus tectorius Park. kafu 115 4,626,326 1,741,831 3,079,227 1,198,506Pipturus argenteus (Forst. f.) Wedd. amahazan 2 297,428 219,790Pisonia grandis R. Br. amumo 9 363,807 392,216 458,175 493,954Pithecellobium dulce (Roxb.) Benth. kamachiles 4 46,968 39,061 136,276 123,868Pouteria obovata (R. Br.) Baehni lalahag 1 11,400 12,290 75,945 81,876Premna obtusifolia R. Br. ahgao 57 1,073,804 396,058 3,404,918 1,409,201Psychotria mariana Bartl. ex DC. aplohkateng 10 403,207 305,073 312,235 315,435Spathodea campanulata Beauv. 12 136,798 147,480 830,487 895,338Unknown 14 1,729,743 1,937,188 49,046 54,929Unknown 0 1 11,400 12,290 29,999 32,342Unknown 1 1 142,004 153,093Unknown, other 2 330,374 324,801

Total 89,749,736 13,954,793 34,927,848 8,386,049
9

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Figure 4—In areas where limestone 

has been eroded to expose the underlying volcanic core, volcanic soils have 

developed that support ravine forest. 

Repeated burning and loss of forest 

cover have led to soil erosion and 

slumping in these areas. Foresters in

the Commonwealth of the Northern 

Mariana Islands are working to revegetate these areas and stabilize soils.

Pisonia grandis, Morinda citrifolia, Aglaia mariannensis, Pandanus dubius, Aidia 

cochinchinensis, Musa spp., Spathodea campanulata, Acacia confusa, Neisosperma 

oppositifolia, Erythrina variegata, Cocos nucifera, Adenanthera pavonina, 

Guettarda speciosa, Casuarina equisetifolia, Intsia bijuga, Bruguiera gymnorrhiza, 

Pithecellobium dulce, Cassia fistula, Heterospathe elata, and Pouteria obovata.

Tangantangan (Leucaena leucocephala)—

Widely planted, Leucaena forests have become widespread, self-perpetuating 

stands. Dominant species within this type are Leucaena leucocephala, Cynometra 

ramiflora, Carica papaya, Delonix regia, Albizia lebbeck, Annona spp., Guamia 

mariannae, Melanolepis multiglandulosa, Psychotria mariniana, Premna obtusifolia, Pithecellobium dulce, Intsia bijuga, Cerbera dilatata, and Ficus prolixa.

Other shrub and grass—

Some of the most common grasses, vines, and shrubs found in this type included 

Pennisetum polystachyon, Mikania micrantha, P. purpureum, Urochloa maximum, 

Chromolaena odorata, Lantana camara, Macroptilium lathyroides, Antigonon

leptopus, Nephrolepis hirsutula, and Solanum torvum. Scattered among the shrubs Joseph Donnegan
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RESOURCE BULLETIN PNW-RB-261

and grasses were trees including Leucaena leucocephala, Eugenia

stelechantha, Guamia mariannae, Intsia bijuga, Citrus ×aurantifolia, Ficus

prolixa, Morus alba, Pipturus argenteus, Premna obtusifolia, and Neisosperma

oppositifolia.

Savanna complex—

The dominant tree species distributed within the savanna complex were Morinda 

citrifolia, Leucaena leucocephala, and Neisosperma oppositifolia. Dominant grasses include Miscanthus floridulus, and Pennisetum spp.

Urban and built-up areas—

Urban areas were dominated by Albizia lebbeck, and Leucaena leucocephala.

Casuarina thicket—

Casuarina equisetifolia forms monospecific stands in this type.

Inventory Methods

The CNMI inventory was based on the FIA inventory design that was implemented 

across the mainland United States beginning in 2000. We adapted the national 

design to include additional branching and rooting forms (fig. 5), additional tree 

crown measurements, and special-interest species ranging from invasive plants to 

Figure 5—Forest Inventory and Analysis protocols have been modified to capture rooting and 

branching forms unique to tropical tree species.

All photos Joseph Donnegan
11

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

pathogens to culturally or economically important species of various life forms. 

Additionally, we used topography to define site productivity or drought resilience 

(for perhumid climates). In the mainland FIA program, plots are spaced within 

forest land on a 3.3-mile grid. With the assistance of the government of the CNMI, 

Department of Land and Natural Resources (CNMI-DLNR), plots were spaced 

across all vegetation types at about 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. 6). 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 is 120 feet.

Figure 6—The plot design used for the continental U.S. Forest Inventory and Analysis program was adopted with slight 

simplification for the inventory in the Pacific Islands.
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RESOURCE BULLETIN PNW-RB-261

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

(USDA FS 2004). 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, 

damage, branching and rooting forms, decay, epiphytic loadings, crown characteristics, tree locations, and regeneration information. The fieldwork for this inventory 

was performed February to April 2004.

Analysis Methods

The FIA estimates derived for forest land are based on a system that uses aerial 

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

landscape. 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. Because boundaries and research questions often change through time, FIA generally chooses to post-stratify the plot 

sample by using a consistent spatial distribution of plots across forested landscapes.

The CNMI stratification for estimating numbers of trees, volume, biomass, 

and carbon was conducted via a classification of 2003 IKONOS satellite data. The 

initial land cover classification divided the landscape into forest, urban, nonforest 

vegetation, barren, and water land types. At least 10 percent tree cover 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 tree cover. A geographic information system was used to sum acreage 

for each type. The acreage each field plot represents was derived by dividing the 

total acreage of forest by the number of field plots. Adjustments were made for plots 

that could not be visited owing to hazardous conditions or denial of access. Average 

stand size (mean diameters of trees) was expanded from the plots to the landscape 

level by using the same expansion factors.

Wood volume was estimated for individual trees by approximating the centroid 

method (Wood et al. 1990, Yavuz 1999) 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 damage and rotten defects 

from gross stem volume. Biomass for individual tree stems was estimated by using 

the specific gravity for known species (7 out of 57 species on the CNMI had known 

specific gravities). For species where specific gravity was not known, an average 
13

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

specific gravity of 0.5 gram per cubic centimeter 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.

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 examined as a proxy for site productivity. The TRMI used a weighted, 

additive combination of slope steepness, slope shape, and slope position to assess 

the potential moisture retention in a forested stand. Remeasurement data from 

these plots at the next inventory cycle will provide a better estimate of productivity 

than TRMI. In very wet environments, TRMI may be best considered a droughtresilience proxy, predicting where soil and water accumulates, owing to topography, 

across a landscape. We also recognize moisture is not likely to be the only factor 

limiting tree growth and that a prolonged excess of moisture can be detrimental to 

the growth of many tree species. In highly porous limestone-derived soils and karst 

topography, drainage may occur very rapidly, making substrate water retention a 

limiting factor in plant growth.

Forest-type mapping was conducted independently by the Pacific Southwest 

Region’s Remote Sensing Lab (S&PF-RSL) with support from FIA. Land cover 

polygons were generated from IKONOS and QuickBird imagery and labeled via 

low-elevation flights combined with ground survey through the cooperation of the 

CNMI-DLNR (Liu and Fischer 2007). Both the 2003 IKONOS and 2005 QuickBird 

satellite imagery were used for the detailed mapping and served as the basis for 

land cover estimates.

Reliability of FIA Data

The area of forested land cover types classified from the IKONOS and QuickBird 

satellite imagery was assumed to be accurate and used as the basis for the expansion of the numbers of trees, tree volume, and tree biomass from the plot 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 errors for the expansion of our estimates from field 

plots to the forested landscape were calculated according to the proportion of area 

occupied by forest. 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 for trees >5 inches in diameter on the CNMI lies between 26.5 
14

RESOURCE BULLETIN PNW-RB-261

and 43.3 million cubic feet. There is a 68-percent chance that the true number of 

trees (>1 inch diameter) on the CNMI lies within the range of 75.8 to 103.7 million. 

Readers are cautioned to examine the standard errors associated with species-level 

estimates for the number of individuals and volume by tree species in table 1.

Resource Highlights

Land Cover

The CNMI is currently about 67 percent forested, which includes agroforest and 

Leucaena forest that had been classificed as secondary forest in the prior inventory 

(fig. 7, table 2). About 12 percent of the landscape was classified as urban land 

including roads, and about 20 percent was classified as nonforest vegetation including savanna and agricultural lands. The area used for land cover estimates totaled 

75,407 acres.

A prior vegetation survey (Falanruw et al. 1989) delineated vegetation types by 

using 1976 aerial photography, and estimated forest cover to be 71 percent of total 

land, including secondary forest and agroforest (fig. 7, table 2). About 3 percent 

of the land area was classified as urban. Nonforest vegetation was estimated to 

be about 24 percent of the total land cover. Total acreage from the Falanruw et al. 

(1989) maps was 75,487 acres, calculated from the original maps that FIA scanned 

and digitized with support from S&PF-RSL.

The methodology and the area sampled for land cover estimates differ from 

those used for prior estimates. Falanruw et al. (1989) defined forested lands on the 

basis of a canopy cover of approximately ≥ 30 percent. The recent effort used a 

forest-land canopy threshold of ≥ 10 percent to remain consistent with the recent 

FIA work in American Samoa, Guam, and Palau. The current survey mapped roads 

as urban land.

Although the differences in interpretation methods and canopy cover thresholds 

between 1989 and 2005 must be considered, trends suggest conversions of forest 

and nonforest vegetation to urban land, especially on Saipan where urban land more 

than tripled.

Productivity and Drought Resilience

Site productivity estimates are difficult to obtain in tropical environments because 

of a lack of consistent annual tree rings. The standard premise for site productivity 

hinges on determining how height or diameter changes with respect to tree age 

under particular site conditions; depending on site quality, a given tree species is 

expected to grow to a certain diameter or height given a certain age. Remeasurement of individual trees at the next inventory cycle will provide better estimates 
15

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Figure 7—Forest land and nonforest vegetation appear to be losing area to urbanization, especially on Saipan. The population of the 

Commonwealth of the Northern Mariana Islands grew from an estimated 15,316 people in 1976 to 51,484 in 2009 (U.S. Census

Bureau 2009).
16

RESOURCE BULLETIN PNW-RB-261 Table 2—Estimated area by land cover by island in the Commonwealth of the Northern Mariana Islands, 1976a and 2005b 1976 2005

Rota Saipan Tinian Total Rota Saipan Tinian Total

Acres Acres

Land cover typec Land cover typec

Limestone forest 12,196 1,181 1,710 15,087 Native limestone forest 10,943 255 1,355 12,553Mangrove forest 18 18 Ravine forest 204 204

Atoll forest 81 11 92 Mixed introduced forest 1,833 12,801 7,002 21,635

Introduced forest 289 7,880 2,513 10,682 Casuarina thicket 76 359 434Casuarina thicket 454 1,125 1,810 3,389 Agroforest 240 89 42 371

Agroforest 35 94 4 133 Agroforest—coconut 574 312 56 942

Coconut 1,057 3,015 282 4,355 Leucaena leucocephala 330 5,221 8,528 14,078Secondary vegetation, forest 344 8,399 11,130 19,873

Nonforest vegetation Nonforest vegetation

Savanna 3,121 3,352 2,957 9,430 Savanna 1,278 1,278Secondary vegetation 2,374 456 2,428 5,257 Other shrub and grass 4,814 2,314 4,966 12,094Strand 674 1,084 1,127 2,885 Strand 250 205 551 1,006Cropland 128 222 474 824 Cropland 353 234 332 918Urban 210 1,844 204 2,259 Urban and built-up 629 2,511 991 4,131Unknown 35 2 12 49 Urban vegetation 761 3,745 530 5,036Barren 41 300 363 704 Barren, beach, rocks 74 257 200 531Marsh 360 42 402 Wetland 29 65 94

Water 45 5 50 Water 6 96 103

Forested subtotals 14,456 21,722 17,449 53,627 Forested subtotals 14,124 18,753 17,341 50,218

Total 21,040 29,386 25,061 75,487 Total 21,011 29,421 24,976 75,407a Figures for maps derived from 1976 aerial photography differ slightly from those published by Falanruw et. al (1989). Figures here were derived by scanning the historical maps and aggregating 

area totals with a geographic information system.

b Figures for 2005 were summarized from the work of Liu and Fischer (2005), aggregating area totals with a geographic information system.c Note that classification schemes differ slightly from the 1989 to 2005 map summaries.
17

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

of site productivity by using growth over the specific period. For the present work, 

we estimated productivity as an additive index based on a site’s potential moisture 

accumulation owing to local topography (TRMI) (Parker 1982). The topographic 

relative moisture index may have utility in very wet environments as a predictor 

of resilience to occasional drought, because TRMI predicts moisture accumulation 

(and likely sediment/soil accumulation as well) based on topography. By using 

TRMI in this context, we classified nearly 60 percent of the forested lands in the 

CNMI as highly drought resilient (fig. 8). This high percentage demonstrates that 

the topography of the three southern islands is characterized by a relatively flat 

series of benches separated by narrow cliffs. However, owing to the porosity of the 

dominant limestone soils and geology, drought resilience is likely overestimated 

because of rapid infiltration and low moisture holding capacity.

In a region of moderately high precipitation, such as the CNMI, the TRMI estimate of productivity may be much less reliable than productivity estimates based on

detailed soil mapping. For example, differences among forest and savanna soils are

dramatic with respect to soil organic matter, cation exchange capacity, and potential

aluminum toxicity for plant growth. In volcanic landscapes, a succession of soil 

Figure 8—A topographic relative moisture index was used to predict drought resilience in the 

perhumid climate of the Commonwealth of the Northern Mariana Islands. Owing to the series of 

plateaus and escarpments that characterize Rota, Tinian, and Saipan, the degree of drought resilience 

estimated is higher than would be expected for porous limestone soils and karst topography.
18

RESOURCE BULLETIN PNW-RB-261

degradation can occur from forest soils to savanna and badland soils through 

processes of land clearing, repeated burning, and subsequent erosion and leaching 

of topsoil nutrients (e.g., see Smith and Babik 1988). Aluminum toxicity to plants 

may be an issue in the limited extent of volcanic soils on the CNMI, but it is not 

a problem on limestone-derived soils where the soil pH is high enough to prevent 

aluminum from becoming soluble.

Forest Structure

For this inventory, we estimated stand size class on forested field plots to capture 

the predominant diameter of live trees in forest stands. In the CNMI, the dominant 

size class tends to be small, in the less-than-5-inch diameter category (fig. 9, table 

3). About 45 percent of acreage in the CNMI is made up of stands in the 5- to 

10.9-inch category, and only about 2 percent of acreage is dominated by larger trees 

in the 11- to 19.9-inch category. No plots were sampled that included stands in the 

largest diameter category of 20 inches and greater.

Forest stands on the CNMI are dominated by small-diameter trees (fig. 10). 

This “reverse-J” distribution of tree diameter is typical where regeneration is abundant, especially following frequent disturbance. Through time, many small trees die 

before they grow into the larger diameter classes. For trees at least 5 inches in diameter, tree heights are predominantly in the 20- to 29-foot height classes (fig. 11). The 

tallest tree on an FIA plot, an Albizia lebbeck, measured 12.6 inches in diameter 

Figure 9—The stands that characterize the Commonwealth of the Northern Mariana Islands’ 

forests tend to be somewhat small, primarily in the less than 11-inch diameter category.
19

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 3—Estimated number of live trees on forest land by species and diameter class

Diameter class (inches)

5.0– 7.0– 9.0– 11.0– 13.0– 15.0- 17.0– 19.0– 21.0– 23.0– 25.0– 27.0– All

Species < 5.0 6.9 8.9 10.9 12.9 14.9 16.9 18.9 20.9 22.9 24.9 26.9 28.9 29.0+ classes

Number of trees

Acacia confusa 132,241 132,241Adenanthera pavonina 22,800 11,400 34,199Aglaia mariannensis 998,839 12,769 1,011,607Aidia cochinchinensis 142,004 142,004Albizia lebbeck 1,582,323 138,575 37,573 11,400 11,400 11,400 1,792,671Allophylus timorensis 132,241 132,241Annona spp. 142,004 142,004Artocarpus altilis 10,616 21,232 31,848Barringtonia asiatica 10,616 10,616 10,616 31,848Barringtonia racemosa 132,241 10,616 142,857Bruguiera gymnorrhiza 11,400 11,400 22,800Carica papaya 2,460,268 49,240 12,769 2,522,276Cassia fistula 11,400 11,400Casuarina equisetifolia 13,087 47,406 36,790 52,347 52,347 13,087 215,063Cerbera dilatata 11,400 11,400Citrus ×aurantifolia 330,374 330,374Citrus hystrix 6,215,306 6,215,306Claoxylon marianum 132,241 132,241Cocos nucifera 22,016 87,279 44,815 22,800 176,910Cynometra ramiflora 6,566,153 251,369 44,032 12,769 12,769 12,769 6,899,858Delonix regia 710,022 11,400 11,400 732,821Discocalyx ponapensis 1,906,823 1,906,823Drypetes spp. 528,962 528,962Elaeocarpus joga 31,848 21,232 53,080Erythrina variegata 22,800 34,199 22,800 11,400 22,800 113,998Eugenia palumbis 1,586,887 1,586,887Eugenia stelechantha 1,651,872 1,651,872Ficus prolixa 3,327,541 298,336 126,369 22,016 12,769 11,400 11,400 3,809,830Ficus spp. 21,232 21,232Ficus tinctoria 710,022 11,400 10,616 732,038Guamia mariannae 5,051,697 47,553 5,099,250Guettarda speciosa 44,032 21,232 10,616 75,879Hernandia sonora 132,241 74,312 74,312 10,616 31,848 10,616 21,232 10,616 365,792Heterospathe elata 11,400 11,400Hibiscus tiliaceus 945,212 79,015 22,800 11,400 1,058,426Intsia bijuga 330,374 125,608 47,406 55,551 13,087 572,025Leucaena leucocephala 38,193,490 609,455 12,769 38,815,714Mammea odorata 12,769 12,769Mangifera indica 10,616 10,616
20

RESOURCE BULLETIN PNW-RB-261Table 3—Estimated number of live trees on forest land by species and diameter class (continued)

Diameter class (inches)

5.0– 7.0– 9.0– 11.0– 13.0– 15.0– 17.0– 19.0– 21.0– 23.0– 25.0– 27.0– All

Species < 5.0 6.9 8.9 10.9 12.9 14.9 16.9 18.9 20.9 22.9 24.9 26.9 28.9 29.0+ classes

Number of trees

Melanolepis multiglandulosa 1,255,384 167,809 25,537 1,448,730Morinda citrifolia 813,670 25,537 11,400 850,607Morus alba 330,374 330,374Musa spp. 79,799 56,999 136,798Neisosperma oppositifolia 132,241 36,790 23,703 192,733Pandanus dubius 259,844 66,831 326,675Pandanus tectorius 3,702,736 881,126 42,464 4,626,326Pipturus argenteus 297,428 297,428Pisonia grandis 284,009 56,999 22,800 363,807Pithecellobium dulce 35,568 11,400 46,968Pouteria obovata 11,400 11,400Premna obtusifolia 460,113 382,532 158,853 23,385 10,616 12,769 12,769 12,769 1,073,804Psychotria mariana 301,059 76,611 25,537 403,207Spathodea campanulata 56,999 56,999 11,400 11,400 136,798Unknown 1,719,127 10,616 1,729,743Unknown 0 11,400 11,400Unknown 1 142,004 142,004Unknown, other 330,374 330,374

Total 83,809,894 3,958,4431,059,266 360,835 257,265 153,963 34,319 34,000 24,168 24,168 11,400 22,016 89,749,736
21

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Figure 10—Small trees are very common in the Commonwealth of the Northern Mariana Islands, 

indicating disturbance and regeneration are abundant.

Figure 11—For trees greater than or equal to 5 inches in diameter, the most common heights attained 

range from 20 to 29 feet tall.
22

RESOURCE BULLETIN PNW-RB-261

and about 67 feet tall. The largest diameter tree was a Ficus prolixa measuring 28 

inches in diameter and 54 feet tall.

Wood volume (fig. 12, tables 1, 4, and 5), biomass (fig. 13, table 6), and carbon 

storage (table 7) follow a similar distribution as the “reverse-J” seen for the number 

of trees according to diameter (fig. 10). Most of the volume, biomass, and carbon is 

accounted for in the smaller diameter classes owing to the relatively high number of 

trees in those size classes.

Number of Canopy and Understory Species

In addition to counting and measuring overstory trees, understory vegetation cover 

and layer heights were estimated for shrubs, forbs, vines, and grasses on FIA 

subplots where a species occupied at least 3 percent cover on that subplot (table 8). 

Tree seedlings that are less than or equal to 1 inch in diameter are also estimated 

Figure 12—As with numbers of trees, gross volume of wood tends to be concentrated in the smaller 

diameter classes. However, some larger diameter trees contribute to the volume in those size classes.

Table 4—Estimated volume of live trees on forest land by diameter class

Diameter class (inches)

< 5 5–9.9 10–14.9 15–19.9 ≥ 20 All sizes

Cubic feet

Gross volume 31,592,041 18,641,936 7,893,647 3,349,492 5,042,772 66,519,888

Net volume (≥ 5 in) 18,612,869 7,862,086 3,301,640 4,922,072 34,698,667
23

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 5—Estimated gross volume of live trees ≥ 5 inches diameter at breast height on forest land by species and diameter class

Diameter class (inches)

5.0– 7.0– 9.0– 11.0– 13.0– 15.0– 17.0– 19.0– 21.0– 23.0– 25.0– 27.0– All

Species 6.9 8.9 10.9 12.9 14.9 16.9 18.9 20.9 22.9 24.9 26.9 28.9 29.0+ classes

Cubic feet

Adenanthera pavonina 264,650 844,086 1,108,736

Aglaia mariannensis 27,663 27,663Albizia lebbeck 389,256 208,802 114,238 262,499 712,926 1,687,721Artocarpus altilis 239,435 821,178 1,060,613Barringtonia asiatica 18,116 35,328 123,158 176,601Barringtonia racemosa 14,185 14,185Bruguiera gymnorrhiza 66,024 96,400 162,424Carica papaya 157,309 66,858 224,167Cassia fistula 45,838 45,838Casuarina equisetifolia 39,970 285,899 386,706 670,989 1,029,251 409,357 2,822,173Cerbera dilatata 21,138 21,138Cocos nucifera 147,509 922,527 528,819 614,373 2,213,227Cynometra ramiflora 579,828 250,209 83,969 109,287 226,955 1,250,248Delonix regia 172,230 250,356 422,586Elaeocarpus joga 78,719 96,134 174,853Erythrina variegata 66,838 162,168 215,931 191,269 631,314 1,267,520Ficus prolixa 932,736 650,919 204,278 166,345 1,042,417 2,358,489 5,355,185Ficus spp. 48,825 48,825Ficus tinctoria 36,336 76,442 112,779Guamia mariannae 97,072 97,072Guettarda speciosa 113,040 87,547 54,504 255,091Hernandia sonora 186,616 315,740 68,701 346,541 152,119 530,365 696,527 2,296,609Heterospathe elata 34,661 34,661Hibiscus tiliaceus 221,806 97,321 82,222 401,349Intsia bijuga 311,158 198,619 373,450 114,490 997,715Leucaena leucocephala 1,684,029 43,571 1,727,600Mammea odorata 25,099 25,099Mangifera indica 91,305 91,305Melanolepis multiglandulosa 434,952 114,201 549,154Morinda citrifolia 66,405 86,016 152,420Neisosperma oppositifolia 114,139 113,425 227,565Pandanus dubius 1,070,765 428,649 1,499,415Pandanus tectorius 2,859,948 219,280 3,079,227Pisonia grandis 181,121 277,054 458,175Pithecellobium dulce 80,287 55,989 136,276Pouteria obovata 75,945 75,945Premna obtusifolia 1,379,089 834,140 154,791 112,364 174,571 319,220 430,743 3,404,918Psychotria mariana 195,168 117,067 312,235Spathodea campanulata 197,427 345,790 137,943 149,326 830,487Unknown 49,046 49,046Unknown 0 29,999 29,999 Total 11,693,701 5,198,035 3,251,615 3,177,655 3,214,576 1,230,535 757,320 1,361,637 1,143,670 844,086 3,055,016 34,927,848
24

RESOURCE BULLETIN PNW-RB-261

Figure 13—Biomass is also concentrated in the smaller size classes.
25

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 6—Estimated aboveground dry stem weight of live trees ≥ 5 inches diameter at breast height on forest land by species and diameter class

Diameter class (inches)

5.0 7.0– 9.0– 11.0– 13.0– 15.0– 17.0– 19.0– 21.0– 23.0– 25.0– 27.0– All

Species 6.9 8.9 10.9 12.9 14.9 16.9 18.9 20.9 22.9 24.9 26.9 28.9 29.0+ classes

Tons

Adenanthera pavonina 4,131 13,174 17,305

Aglaia mariannensis 432 432Albizia lebbeck 6,075 3,259 1,783 4,097 11,127 26,341Artocarpus altilis 3,737 12,817 16,554Barringtonia asiatica 283 551 1,922 2,756Barringtonia racemosa 221 221Bruguiera gymnorrhiza 1,030 1,505 2,535Carica papaya 2,455 1,043 3,499Cassia fistula 715 715Casuarina equisetifolia 1,036 7,407 10,019 17,384 26,666 10,606 73,118Cerbera dilatata 330 330Cocos nucifera 2,302 14,398 8,254 9,589 34,543Cynometra ramiflora 9,050 3,905 1,311 1,706 3,542 19,513Delonix regia 2,688 3,907 6,596Elaeocarpus joga 1,229 1,500 2,729Erythrina variegata 1,043 2,531 3,370 2,985 9,853 19,783Ficus prolixa 14,558 10,159 3,188 2,596 16,270 36,810 83,581Ficus spp. 488 488Ficus tinctoria 442 931 1,373Guamia mariannae 1,515 1,515Guettarda speciosa 1,764 1,366 851 3,981Hernandia sonora 1,689 2,858 622 3,137 1,377 4,801 6,305 20,790Heterospathe elata 541 541Hibiscus tiliaceus 3,946 1,732 1,463 7,141Intsia bijuga 5,925 3,782 7,111 2,180 18,998Leucaena leucocephala 26,283 680 26,964Mammea odorata 392 392Mangifera indica 1,425 1,425Melanolepis multiglandulosa 6,789 1,782 8,571Morinda citrifolia 1,036 1,342 2,379Neisosperma oppositifolia 1,781 1,770 3,552Pandanus dubius 16,712 6,690 23,402Pandanus tectorius 44,637 3,422 48,059Pisonia grandis 2,827 4,324 7,151Pithecellobium dulce 1,253 874 2,127Pouteria obovata 1,185 1,185Premna obtusifolia 21,524 13,019 2,416 1,754 2,725 4,982 6,723 53,142Psychotria mariana 3,046 1,827 4,873Spathodea campanulata 3,081 5,397 2,153 2,331 12,962Unknown 765 765Unknown 0 468 468Total 182,852 82,898 55,745 54,366 59,777 23,422 8,343 21,252 17,850 13,174 43,115 562,794
26

RESOURCE BULLETIN PNW-RB-261 Table 7—Estimated carbon mass of live trees ≥ 5 inches diameter at breast height on forest land by species and diameter class Diameter class (inches) 5.0– 7.0– 9.0– 11.0– 13.0– 15.0– 17.0– 19.0– 21.0– 23.0– 25.0– 27.0– All Species 6.9 8.9 10.9 12.9 14.9 16.9 18.9 20.9 22.9 24.9 26.9 28.9 29.0+ classes Tons Adenanthera pavonina 2,065 6,587 8,652 Aglaia mariannensis 216 216 Albizia lebbeck 3,038 1,629 891 2,048 5,563 13,171 Artocarpus altilis 1,868 6,408 8,277 Barringtonia asiatica 141 276 961 1,378 Barringtonia racemosa 111 111 Bruguiera gymnorrhiza 515 752 1,268 

Carica papaya 1,228 522 1,749 Cassia fistula 358 358 Casuarina equisetifolia 518 3,704 5,009 8,692 13,333 5,303 36,559 Cerbera dilatata 165 165 Cocos nucifera 1,151 7,199 4,127 4,794 17,271 Cynometra ramiflora 4,525 1,953 655 853 1,771 9,757 Delonix regia 1,344 1,954 3,298 Elaeocarpus joga 614 750 1,365 Erythrina variegata 522 1,266 1,685 1,493 4,927 9,891 Ficus prolixa 7,279 5,080 1,594 1,298 8,135 18,405 41,791 Ficus spp. 244 244 Ficus tinctoria 221 465 686 Guamia mariannae 758 758 Guettarda speciosa 882 683 425 1,991 Hernandia sonora 845 1,429 311 1,569 689 2,401 3,153 10,395 Heterospathe elata 270 270 Hibiscus tiliaceus 1,973 866 731 3,571 Intsia bijuga 2,962 1,891 3,555 1,090 9,499 Leucaena leucocephala 13,142 340 13,482 Mammea odorata 196 196 Mangifera indica 713 713 Melanolepis multiglandulosa 3,394 891 4,285 Morinda citrifolia 518 671 1,189 Neisosperma oppositifolia 891 885 1,776 Pandanus dubius 8,356 3,345 11,701 Pandanus tectorius 22,318 1,711 24,030 Pisonia grandis 1,413 2,162 3,575 Pithecellobium dulce 627 437 1,063 Pouteria obovata 593 593 Premna obtusifolia 10,762 6,509 1,208 877 1,362 2,491 3,361 26,571 Psychotria mariana 1,523 914 2,437 Spathodea campanulata 1,541 2,698 1,076 1,165 6,481 Unknown 383 383 Unknown 0 234 234  Total 91,426 41,449 27,872 27,183 29,888 11,711 4,172 10,626 8,925 6,587 21,558 281,397
27

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 8—Average understory vegetation covera on Forest Inventory and Analysis field 

subplots by species 

 Standard deviation

 across subplots

Number of where species

Scientific name Cover subplots was found

Percent

Abrus precatorius L. 3.8 17 3.6

Achyranthes aspera L. 1.7 3 1.2

Alocasia cucullata (Lour.) G. Don 1.0 1

Aloe sp. L. 1.0 1

Antigonon leptopus Hook. & Arn. 15.7 3 21.2

Antrophyum plantagineum (Cav.) Kaulf. 2.0 1

Asplenium nidus L. 1.9 16 1.4

Asplenium pellucidum Lam. 1.0 2 0.0

Asplenium polyodon G. Forst. 1.7 3 0.6

Axonopus compressus (Sw.) Beauv. 3.3 3 1.5

Bidens alba (L.) DC. 21.3 14 29.0

Bikka mariannensis Brongniart 6.3 3 6.1

Bixa orellana L. 6.0 1

Blechum pyramidatum (Lam.) Urb. 9.2 16 8.0

Bougainvillea sp. Comm. ex Juss 1.0 1

Brachiarai mutica (Forsk.) Stapf 28.0 1

Brassica sp. L. 30.0 1

Bulbophyllum longiflorum Thouars 1.0 5 0.0

Callicarpa candicans (Burm. f.) Hochr. 2.7 3 2.1

Calopogonium mucunoides Desv. 3.0 1

Capparis cordifolia Lam. 1.0 1

Capsicum annuum var. annuum L. 3.0 38 2.1

Cayratia trifolia (L.) Domin 1.0 1

Centrosema pubescens Benth. 9.3 8 9.2

Cheilanthes tenuifolia (Burmann) Swartz 2.0 3 1.0

Chromolaena odorata (L.) King & H.E. Robins. 5.8 40 7.0

Coccinia grandis (L.) Voigt 22.4 10 23.9

Coelogyne guamensis Ames 1.0 1

Colocasia sp. Schott 6.0 1

Colubrina asiatica (L.) Brongn. 1.9 13 0.8

Combined ferns 3.0 1

Commelina benghalensis L. 24.0 2 29.7

Commelina diffusa Burm. f. 1.0 2 0.0

Cyperus compressus L. 4.0 1

Cyperus polystachyos var. polystachyos

(Rottb.) Beauv. 1.0 2 0.0

Davallia solida (Forster fil.) Swartz. Schrad 5.8 6 10.4

Dichanthium bladhii (Retz.) S.T. Blake 35.0 2 0.0

Digitaria ciliaris (Retz.) Koel. 2.0 1

Digitaria insularis (L.) Mez ex Ekman 26.0 4 29.6

Euphorbia heterophylla L. 12.0 1
28

RESOURCE BULLETIN PNW-RB-261

Table 8—Average understory vegetation covera on Forest Inventory and Analysis field 

subplots by species (continued)

 Standard deviation

 across subplots

Number of where species

Scientific name Cover subplots was found

Percent

Flagellaria indica L. 3.6 27 3.4

Freycinetia mariannensis Merrill 3.7 6 2.1

Freycinetia sp. Gaud. 1.0 1

Gleichenia linearis (Luers.) Fosberg 14.0 2 8.5

Heterogonium pinnatum (Copel.) Holtt. 20.0 1

Ipomea obscura (L.) Ker-Gawl 6.0 1

Ipomoea indica (Burm.f.) Merr. 1.0 1

Ipomoea littoralis Blume 6.0 1

Justicia procumbens L. 20.1 7 30.7

Lantana camara L. 8.7 34 16.1

Macroptilium lathyroides (L.) Urban 11.6 7 8.5

Merremia peltata (L.) Merrill 9.0 22 9.4

Microsorum scolopendria (Burm. f.) 5.5 37 5.7

Mikania micrantha Kunth 13.5 47 14.1

Mimosa diplotricha C. Wright ex Sauvalle

Mart., non Mart. ex Colla 1.3 4 0.5

Mimosa pudica L. 1.8 4 1.0

Mimosa sp. L. 2.3 6 1.6

Momordica charantia L. 4.1 19 3.0

Nephrolepis biserrata (Sw.) Schott 38.5 2 30.4

Nephrolepis hirsutula (J.R. Forst.) K. Presl 8.3 13 7.0

Nephrolepis sp. Schott 3.0 4 1.6

Nerium oleander L. 1.0 1

Nesogenes sp. A. DC. 1.0 2 0.0

Operculina turpethum (L.) Silva Manso 12.4 5 21.1

Oplismenus hirtellus (L.) Beauv. var.

setarius (Lam.) F.M. Bailey 11.4 7 19.3

Paspalum conjugatum Berg. 4.0 3 3.5

Passiflora foetida L. 4.0 3 2.7

Passiflora suberosa L. 7.1 16 6.5

Pennisetum polystachyon (L.) J.A. Schultes 29.8 14 37.1

Pennisetum purpureum Schumacher 22.9 17 27.4

Pennisetum setaceum (Forsk.) Chiov. 8.0 2 9.9

Physalis angulata L. 1.0 1

Piper betel L. 2.0 1

Piper guahamense C. DC. 5.5 10 5.2

Poaceae unknown 13.0 2 17.0

Polygala paniculata L. 1.0 1

Polypodium cyathoides Sw. 12.0 2 11.3

Polypodium punctatum Thunb. ex Murray 4.0 2 4.2

Psychotria mariniana Bartling ex DC 2.5 4 1.9
29

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 8—Average understory vegetation covera on Forest Inventory and Analysis field 

subplots by species (continued)

 Standard deviation

 across subplots

Number of where species

Scientific name Cover subplots was found

Percent

Pteris tripartita Sw. 4.0 1

Pueraria montana (Lour.) Merr. 3.0 1

Rivina humilis L. 14.3 4 17.2

Ruellia prostrata Poir. 16.0 5 19.5

Scaevola sericea Vahl var. taccada (Gaertn.)

Thieret & B. Lipscomb 34.0 4 43.8

Sida rhombifolia L. 4.0 2 2.8

Solanum americanum P. Mill 2.7 3 0.6

Solanum melongena L. 1.0 1

Solanum torvum Sw. 5.3 7 6.7

Spathoglottis plicata Blume 1.0 1

Stachytarpheta jamaicensis (L.) Vahl 8.0 1

Stachytarpheta sp. Vahl 1.0 1

Stachytarpheta urticifolia Sims 20.8 9 24.9

Stictocardia tiliifolia (Desr.) Hallier f. 11.0 2 12.7

Tectaria crenata Cav. 2.7 3 1.5

Thelypteris gretheri (W. Wagner) Stone 1.0 2 0.0

Thelypteris truncata (Poir.) K. Iwats. 3.0 1

Urochloa maxima (Jacq.) R. Webster 17.3 9 19.7

Verbena litoralis Kunth 1.0 2 0.0

Unknown fern 1 10.0 1

Unknown fern 3 2.0 1

Unknown forb 3.2 26 2.4

Unknown grass 1 2.0 2 1.4

Unknown perrenial grass 1 5.3 9 5.2

Unknown perrenial grass 2 2.0 4 2.0

Unknown shrub 6.0 31 5.2

Unknown sp. 3.0 1

Unknown vine 6.3 24 6.9

a Percentage cover of “1” indicates cover less than or equal to 1 percent. Cover estimates are averaged among 

subplots where each species was found. A total of 138 subplots were surveyed for vegetation cover. The number 

of subplots where a species was found and the standard deviation for cover estimates provide an idea of spatial 

variability for each species across the island group.
30

RESOURCE BULLETIN PNW-RB-261

as understory vegetation cover (table 9). Special interest species (e.g., rare, endangered, medicinal, or invasive) identified by island foresters were also noted when 

found. However, if a species covered less than 3 percent of a subplot and was not 

listed as special interest, it was not enumerated.

For the 2004 inventory, 57 tree species and 107 understory species were measured on FIA plots. On a per-plot basis (approximately one-sixth acre), the mean 

number of tree species found was five (fig. 14).

Tree Damage and Mortality

We estimated about 32 percent of the individual trees on the CNMI show some sign 

of damage (table 10). The most prevalent damage types are vines in crowns, lost 

apical dominance (damage to the primary growing leader), and conks (shelf-fungus 

indicating rot) (fig. 15). Vines in tree crowns are common (44 percent of damaged trees), although their effect on their supporting tree hosts was not quantified. 

Effects ranged from some additional weight to instances of strangulation, smothering (especially Antigonon leptopus, Coccinia grandis, and Mikania micrantha), 

and breaking of branches. For the identifiable damaging agents, damage by other 

vegetation, weather, and insects ranked as the most prevalent primary damage 

agents (fig. 16).

Less than one half of 1 percent of the trees sampled during the inventory were 

dead. The most prevalent, identifiable dead trees were Premna obtusifolia (27.9 percent of total dead), Pandanus tectorius (15.2 percent), Intsia bijuga (14.5 percent), 

and Albizia lebbeck (9.4 percent) (fig. 17).

Epiphytes

In the moist environment of the tropics, many plant species are found growing on 

longer lived trees. These epiphytes use the trees primarily for support, but they also 

use space, moisture, and nutrients that might otherwise be used by the tree. When 

the epiphytes accumulate over many years, their weight can be excessive, leading 

to the breakage of branches and occasionally snapping the stems of trees. In the 

CNMI, we rated epiphytic loading on trees as a summation of loading on the bole, 

branches, and canopy. We estimate that about 59 percent of the trees in the CNMI 

had few to no epiphytes, and 41 percent of the trees had moderate to high amounts 

of epiphytes (table 11).

Forest Dynamics

Forest structure and species composition change through time as a result of forest 

succession and disturbance dynamics. The forests of the CNMI have been strongly 
31

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 9—Average understory tree covera on Forest Inventory and Analysis field subplots 

by species

 Standard deviation

 across subplots

Number of where species

Scientific name Cover subplots was found

Percent

Acacia confusa 2.0 2 1.4

Adenanthera pavonina 15.0 1

Aglaia mariannensis 1.6 16 1.0

Aidia cochinchinensis 1.7 3 1.2

Albizia lebbeck 3.6 10 4.3

Annona sp. 1.0 1

Annona squamosa L. 13.0 1

Areca catechu L. 5.0 1

Artocarpus altilis 4.0 2 1.4

Carica papaya 1.6 16 0.9

Casuarina equisetifolia 2.0 2 1.4

Citrus hystrix 14.7 7 13.0

Citrus sp. 9.0 1

Claoxylon marianum 1.7 3 1.2

Cocos nucifera 5.9 14 5.0

Coffea arabica L. 1.0 1

Commersonia bartramia (L.) Merr. 1.0 1

Cynometra ramiflora 8.4 16 7.5

Delonix regia 3.0 1

Discocalyx ponapensis 1.0 2 0.0

Elaeocarpus joga 1.0 1

Eugenia palumbis 2.9 15 3.1

Eugenia reinwardtiana (Blume) DC. 2.0 1

Eugenia stelechantha Merr. 2.2 5 1.6

Eugenia thompsonii 1.0 1

Ficus prolixa 1.8 16 0.8

Ficus sp. 1.0 1

Ficus tinctoria 2.0 4 0.8

Guamia mariannae 3.6 31 3.6

Guettarda speciosa 3.0 1

Hernandia sonora 2.3 4 1.3

Hibiscus tiliaceus 2.5 2 2.1

Leucaena leucocephala 4.2 65 7.1

Macaranga thompsonii Merr. 1.0 1

Mammea odorata 1.5 2 0.7

Melanolepis multiglandulosa 1.6 22 0.9

Morinda citrifolia 1.7 19 1.6

Neisosperma oppositifolia 1.8 5 1.3

Pandanus dubius 7.7 13 10.6
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Table 9—Average understory tree covera on Forest Inventory and Analysis field subplots 

by species (continued)

 Standard deviation

 across subplots

Number of where species

Scientific name Cover subplots was found

Percent

Pandanus tectorius 12.7 24 16.4

Pemphis acidula J.R. Forst. & G. Forst. 59.3 3 9.0

Pipturus argenteus 3.3 3 2.5

Pithecellobium dulce 1.0 1

Pouteria obovata 1.8 6 1.0

Premna obtusifolia 1.3 6 0.5

Psidium guajava L. 1.3 3 0.6

Psychotria mariniana 3.0 17 3.0

Spathodea campanulata 2.5 2 0.7

Streblus pendulinus (Endl.) F. Muell. 1.0 1

Thespesia populnea (L.) Sol. ex Correa 1.0 1

Unknown 1.0 1

Unknown 0 1.0 2 0.0

Unknown 1 1.0 1

Unknown 30 2.7 3 2.9

Unknown 50 1.0 1

Unknown, other 2.0 1

a Percentage cover of “1” indicates cover less than or equal to 1 percent. Cover estimates are averaged among 

subplots where each species was found. A total of 138 subplots were surveyed for vegetation cover. The number 

of subplots where a species was found and the standard deviation for cover estimates provide an idea of spatial 

variability for each species across the island group.

Figure 14—The mean number of tree species found per one-sixth-acre plot was five.
33

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 10—Number of trees by primary damage type and species for all trees (

≥1 inch diameter at breast height; includes dead trees)

Broken Damaged Loss of

Broken or dead Broken Cracks/ foliage/ apical Open

Vines in All

Species No damage bole branches roots Brooms Conks seams shoots dominance wounds Other crown damages

Number of trees

Acacia confusa 132,241Adenanthera pavonina 22,800 11,400 11,400Aglaia mariannensis 747,126 264,481 264,481Aidia cochinchinensis 142,004Albizia lebbeck 558,224 165,187 26,174 307,192 735,895 1,234,448Allophylus timorensis 132,241 132,241Annona spp. 142,004Artocarpus altilis 31,848Barringtonia asiatica 31,848 31,848Barringtonia racemosa 132,241 10,616 142,857Bruguiera gymnorrhiza 11,400 11,400 11,400Carica papaya 2,511,660 10,616 10,616Cassia fistula 11,400Casuarina equisetifolia 149,629 39,260 13,087 13,087 65,434Cerbera dilatata 11,400Citrus ×aurantifolia 330,374Citrus hystrix 2,777,052 132,241 1,057,925 2,248,090 3,438,255Claoxylon marianum 132,241 132,241Cocos nucifera 143,494 10,616 22,800 33,416Cynometra ramiflora 5,671,455 12,769 602,802 294,625 318,208 1,228,403Delonix regia 732,821Discocalyx ponapensis 1,774,582 132,241 132,241Drypetes spp. 528,962Elaeocarpus joga 21,232 31,848 31,848Erythrina variegata 91,198 22,800 22,800Eugenia palumbis 793,443 132,241 132,241 132,241 396,722 793,443Eugenia stelechantha 991,123 165,187 495,562 660,749Ficus prolixa 2,741,736 142,004 31,848 596,559 152,620 145,062 1,068,094Ficus spp. 21,232Ficus tinctoria 579,417 142,004 10,616 152,620Guamia mariannae 3,294,003 132,241 694,149 978,857 1,805,247Guettarda speciosa 22,800 31,848 10,616 10,616 53,080Hernandia sonora 106,160 10,616 84,928 164,088 259,632Heterospathe elata 11,400Hibiscus tiliaceus 914,785 11,400 132,241 143,640Intsia bijuga 408,577 58,021 39,260 66,167 163,449Leucaena leucocephala 26,172,949 159,054 852,478 4,080,479 2,785,711 668,688 4,096,355 12,642,765
34

RESOURCE BULLETIN PNW-RB-261Table 10—Number of trees by primary damage type and species for all trees (≥1 inch diameter at breast height; includes dead trees) (continued)

Broken Damaged Loss of

Broken or dead Broken Cracks/ foliage/ apical Open Vines in All

Species No damage bole branches roots Brooms Conks seams shoots dominance wounds Other crown damages

Number of trees

Mammea odorata 12,769Mangifera indica 10,616 10,616Melanolepis multiglandulosa 325,227 11,400 1,112,104 1,123,503Morinda citrifolia 839,207 11,400 11,400Morus alba 330,374Musa spp. 136,798Neisosperma oppositifolia 182,117 10,616 10,616Pandanus dubius 272,811 10,616 21,232 10,616 11,400 53,864Pandanus tectorius 4,313,614 31,848 164,088 10,616 31,848 53,080 21,232 312,712Pipturus argenteus 132,241 165,187 165,187Pisonia grandis 221,803 142,004 142,004Pithecellobium dulce 46,968Pouteria obovata 11,400Premna obtusifolia 197,823 10,616 205,037 97,696 10,616 11,400 540,616 875,981Psychotria mariana 231,384 12,769 159,054 171,823Spathodea campanulata 91,198 11,400 11,400 22,800 45,599Unknown 1,057,925 264,481 142,857 264,481 671,819Unknown 0 11,400 11,400Unknown 1 142,004 142,004Unknown, other 330,374 330,374 Total 61,004,189 743,249 1,740,860 42,464 10,616 5,426,032 132,241 10,616 7,057,938 878,427 11,400 12,691,706 28,745,547
35

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Figure 15—Vines in the crowns of trees are very common in the Commonwealth of the Northern Mariana 

Islands. Damage from vines was recorded when the vines occupied 20 percent or more of the crown. Lost 

apical dominance, and conks (fruiting shelf fungi indicating rot), were also common damages.

Figure 16—Disturbance from other vegetation and weather were the most common identifiable damaging 

agents for trees.
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Table 11—Estimated number of live trees (≥ 5 inches diameter at breast height) on forest 

land by epiphyte loading (amounts of nontree vegetation in the canopy and branches) and 

species

Epiphyte loadings

 All

Species None Low Moderate High loadings

Number of trees

Adenanthera pavonina 22,800 11,400 34,199

Aglaia mariannensis 12,769 12,769

Albizia lebbeck 48,973 73,460 50,342 37,573 210,348

Artocarpus altilis 31,848 31,848

Barringtonia asiatica 31,848 31,848

Barringtonia racemosa 10,616 10,616

Bruguiera gymnorrhiza 11,400 11,400 22,800

Carica papaya 36,471 25,537 62,008

Cassia fistula 11,400 11,400

Casuarina equisetifolia 143,955 60,492 10,616 215,063

Cerbera dilatata 11,400 11,400

Cocos nucifera 44,815 97,895 22,800 11,400 176,910

Cynometra ramiflora 85,273 79,600 120,496 48,337 333,706

Delonix regia 22,800 22,800

Elaeocarpus joga 10,616 10,616 31,848 53,080

Erythrina variegata 22,800 68,399 22,800 113,998

Ficus prolixa 48,337 107,289 259,048 67,615 482,289

Ficus spp. 21,232 21,232

Ficus tinctoria 11,400 10,616 22,016

Guamia mariannae 36,937 10,616 47,553

Figure 17—Dead trees were not abundant in the Commonwealth of the Northern Mariana Islands. 

Premna obtusifolia, Pandanus tectorius, and Intsia bijuga were the most common dead trees of those 

identified.
37

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Table 11—Estimated number of live trees (≥ 5 inches diameter at breast height) on forest 

land by epiphyte loading (amounts of nontree vegetation in the canopy and branches) and 

species (continued)

Epiphyte loadings

 All

Species None Low Moderate High loadings

Number of trees

Guettarda speciosa 22,800 53,080 75,879

Hernandia sonora 84,928 138,008 10,616 233,552

Heterospathe elata 11,400 11,400

Hibiscus tiliaceus 45,599 56,215 11,400 113,214

Intsia bijuga 12,769 52,347 116,043 60,492 241,651

Leucaena leucocephala 109,760 184,588 136,348 191,528 622,224

Mammea odorata 12,769 12,769

Mangifera indica 10,616 10,616

Melanolepis multiglandulosa 11,400 11,400 25,537 145,010 193,346

Morinda citrifolia 12,769 24,168 36,937

Musa spp. 113,998 22,800 136,798

Neisosperma oppositifolia 21,232 26,174 13,087 60,492

Pandanus dubius 67,615 236,260 22,800 326,675

Pandanus tectorius 106,160 552,031 201,704 63,696 923,590

Pisonia grandis 11,400 56,999 11,400 79,799

Pithecellobium dulce 34,199 12,769 46,968

Pouteria obovata 11,400 11,400

Premna obtusifolia 88,011 214,165 198,261 113,254 613,691

Psychotria mariana 12,769 63,843 12,769 12,769 102,148

Spathodea campanulata 22,800 79,799 11,400 22,800 136,798

Unknown 10,616 10,616

Unknown 0 11,400 11,400

 Total 1,207,023 2,324,819 1,493,952 914,048 5,939,842

influenced by a long history of disturbance, both human-caused and climatic 

disturbance. Human populations and land use on the CNMI have changed, resulting in differing influences on forest vegetation. Within the last century, the most 

important land use changes have involved the conversion of forests to agriculture 

and urban uses. The changes have been rapid. In addition to loss of forest to urbanization, invasive weeds have also become a threat to forests in the CNMI. Some of 

the most prevalent understory species recorded were weedy vines that smother the 

forest canopy (fig. 18). Foresters in the CNMI have developed and implemented 

strong invasive species programs to educate the public, assess threats and current 

status, and to eradicate several plants threatening forest sustainability. As a result 

of continuing efforts to eradicate invasive species, reforest degraded lands, and 

conserve existing forests, we expect to see concomitant increases in wood volume 

per acre and the basal area covered by trees (table 12).
38

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Figure 18—Smothering invasive vines have become widespread throughout the Pacific Islands. 

Foresters on the Commonwealth of the Northern Mariana Islands have implemented several 

education and eradication programs.

Acknowledgments

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

number of groups and agencies. Foremost, the help and expertise of local island 

foresters and ecologists made the data collection and plant identification efforts 

possible; sincere thanks to James Babauta, Felix Calvo, M. Camacho, Ben Cepeda, 

Victor dl. Guerrero, Falaniko Mika, James Monglona, David Palacios, Manny Pangelinan, Mike Saures, Jeff Vance, and Erik Waguk. 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 Imagery Consortium partners for sharing costs on imagery and interpretation. Thanks to Lynn Raulerson at University of Guam for species identification 

and training; Lisa Fischer and Zhafeng Liu (Leo) at the Remote Sensing Lab in the 

Table 12—Estimated number of trees per acre, basal area 

per acre, net volume per acre, and standard errors (SE) for 

trees ≥ 5 inches diameter, 2004

Estimate SE

Trees per acre 100 15

Basal area (square feet per acre) 33 6

Volume (cubic feet per acre) 582 133

Joseph Donnegan
39

Commonwealth of the Northern Mariana Islands’ Forest Resources, 2004

Pacific Southwest Region. We also thank Dale Weyermann, John Chase, and Chuck 

Veneklase with FIA for their work with geographic information systems, programming, and technical support. Dave Azuma and Tom Brandeis U.S. Forest Service, 

and David Clausnitzer and Bob Gavenda Natural Resources Conservation Service 

offered very helpful comments on prior drafts.

Metric Equivalents

When you know: Multiply by: To find:

Inches 2.54 Centimeters

Feet .305 Meters

Miles 1.609 Kilometers

Acres .405 Hectares

Square miles 2.59 Square kilometers

Cubic feet .028 Cubic meters

Tons 907 Kilograms

Tons per acre 2.24 Tonnes or megagrams per hectare

Cubic feet per acre .07 Cubic meters per hectare

Trees per acre 2.471 Trees per hectare

Degrees Fahrenheit ( ̊F - 32) / 1.8 Degrees Celsius

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