That’s

Growth!

NATURAL VOLUME 3, NUMBER 1 • USDA FOREST SERVICE

INQUIRER

Swimming

Leaf Me

Some Things

Will

The Trees Are I’ll Huff and I’ll

Puff and I’ll Blow

Your Trees Down!

Page 6

Page 13

O o o o o h !

Page 19

It’s a

Page 25

Please

Page 31

Page 37

Page 43

Page 50

Gas! Always Change

ALONE!

Join Us

for Dinner

Going Batty!

Without a Ladder

Tropical 

Forest 

Edition

Tropical 

Forest 

That’s

Growth!

That’s

Growth!

Upstream pstream

Swimming

Without a Ladder

Please

Always Change
The Natural Inquirer

Volume 3, Number 1

Winter 2001

Tropical Forest Edition

Barbara McDonald

USDA Forest Service,

Research and Development

Washington Office

Wilson Gonzalez Espada

University of Georgia,

Department of Science

Education

Athens, GA

Forest Service scientists highlighted in the journal:

John Francis

Andrew J. R. Gillespie

Michael Keller

Ariel Lugo

John Parrotta

Frederick Scatena

Peter Weaver

Joseph Wunderle

Non-Forest Service scientists

highlighted in the journal:

Jonathan Benstead

Elvira Cuevas

Oliver Henry Knowles

Steven Latta

James March

Sandra Molina

Catherine Pringle

Olga Ramos

Michael Reiners

Linda L. Vélez Rodríguez

Produced by:

USDA Forest Service

Dale Bosworth, Chief

Research and Development,

Washington, DC

Robert Lewis, Deputy Chief

Resource Valuation and Use

Research Staff

Fred Kaiser, Director

State and Private Forestry

Michael Rains, Deputy Chief

Conservation Education Staff

Ann Loose, Director

With thanks to:

USDA Forest Service

Office of Communication

Washington, DC

USDA Forest Service

International Institute of

Tropical Forestry

Rio Piedras, Puerto Rico

USDA Forest Service

International Programs

Washington, DC

Eugene Odum

University of Georgia

Athens, GA

Jessica Tanner

Atlanta City Public Schools

Atlanta, GA

Julie Garrison

Barrow County Schools

Auburn, GA

Karen Murphy

Barrow County Schools

Bethlehem, GA

George Avalos

USDA Design Center

Washington, DC

Katrina Krause

USDA Forest Service

Athens, GA

USDA Forest Service,

Southern Research Station

Athens, GA

Linda Ries

USDA Forest Service

Ogden, UT

Lisa Perez

USDA Forest Service

Salt Lake City, UT
1

Editorial

Review Board

Special

Editorial

Assistants:

Mary Herman, 

Athens, GA

Melissa Hughes,

Marion, NC

Ashley Mead, 

Jefferson, GA

Samantha Mead, 

Jefferson, GA

Hilde Sather-Wickster,

Athens, GA

Mrs. Wilma Zapata’s 5th Grade Class

Academia Presbiteriana

San German, Puerto Rico
2

Teacher’s

Note

As teachers of science, one

of your goals is to teach students the scientific method,

no matter what your area of

focus—life sciences, Earth sciences, etc. The scientific

method can best be taught by

focusing on hands-on and

minds-on inquiry and investigation. This allows the learner to be independent and to

seek answers to questions

throughout the world we live

in. As educators, you are constantly faced with engaging

your students in scientific

inquiry in new and different

ways. Standard teaching

strategies can become monotonous to today’s learners in

an age of abundant technology. The Natural Inquirer gives

a fresh approach to science

and a view of the outside

world bigger than the classroom that can be used while

still in the school setting.

The Natural Inquirer is a

science education resource

journal to be used with learners in Grade 5 and up. The

Natural Inquirer contains

articles describing environmental and natural resource

research conducted by Forest

Service scientists and their

cooperators. These are scientific journal articles that have

been reformatted to meet the

needs of an audience new to

science. The articles are easy

to understand, are aesthetically pleasing to the eye, contain

glossaries, and include handson activities. The goal of The

Natural Inquirer is to stimulate critical reading and thinking about scientific inquiry

and investigation while learning about ecology, the natural

environment, and natural

resources.

Past issues and articles from

The Natural Inquirer are

available by visiting the Web

site at http://www.naturalinquirer.usda.gov.

Science Education

Standards:

In the back of the journal,

you will find a matrix which

allows you to identify articles

by the national science education standards that they

address.

Questions or comments?

Please contact:

Dr. Barbara McDonald

USDA Forest Service

320 Green St.

Athens, GA 30602-2044

706-559-4224

barmac@bigfoot.com

Teacher’s Manual:

Please visit The Natural

Inquirer Web site at

http://www.naturalinquirer.us

da.gov. From this site, you

may read the teacher’s manual

online, download it, or

request a hard copy.

Visit http://www.naturalinquirer.usda.gov for previous issues of the

Natural Inquirer, sample lesson plans, word games, the teacher’s 

manual, information about the Forest Service, and other resources.
3

Page 31

Page 43

Page 50

Contents

Teacher’s Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

About the Natural Inquirer . . . . . . . . . . . . . . . . . . . . . . . .4

What are Scientists? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Welcome to the Natural Inquirer

Tropical Forest Edition . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Features

Swimming Upstream Without a Ladder:

Dams and Pipes and River Shrimp Movements . . . . . . . .6

Leaf Me Alone!

The Movement of Nutrients Between

Trees and the Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Oooh! That’s Growth!

Measuring Trees in Cinnamon Bay Watershed . . . . . . .19

It’s a Gas!

The Exchange of Gases Between the 

Soil and the Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . .25

Please Join Us for Dinner:

Tropical Birds and Their Temporary Guests . . . . . . . . .31

Some Things Will Always Change:

Land Use in a Dry Tropical Forest . . . . . . . . . . . . . . . . .37

The Trees Have Gone Batty!

How Bat Scat Helped Restore a Tropical Forest . . . . . .43

I’ll Huff and I’ll Puff and I’ll Blow Your

Trees Down!

How Wind Speed Affected Trees During 

Hurricane Hugo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Which National Science Education Standards 

Can Be Met by the Natural Inquirer? . . . . . . . . . . . . . . .57

What Is the Forest Service? . . . . . . . . . . . . . . .Back Cover

Web site Connections . . . . . . . . . . . . . . . . . . . .Back Cover

The Natural Inquirer is reproduced on recycled paper with soy-based inks.

Please pass this journal along or recycle it when you have finished using it.
Scientists are people who

collect and evaluate information about a wide range

of topics. Some scientists

study the natural environment. To be a successful

environmental scientist, you

must:

• Be curious—You must be

interested in learning.

• Be enthusiastic—You

must be interested in an

environmental topic.

• Be careful—You must be

accurate in everything

that you do.

• Be open minded—You

must be willing to listen

to new ideas.

• Question everything—

You must think about

what you read and

observe.

What Are Scientists?

Scientists in this issue

at work.

Scientists report their research in journals,

which are special booklets that enable scientists to share information with one another.

This journal, the Natural Inquirer, was created so that scientists can share their research

with you and with other middle school students. Each article tells you about scientific

research conducted by scientists in the Forest

Service. If you want to know more about the

Forest Service, you can read about it on the

back cover of this journal, or you can visit the

Natural Inquirer Web site at http://www.naturalinquirer.usda.gov. 

All of the research in the Natural Inquirer is

concerned with nature, such as trees, forests,

animals, insects, outdoor activities, and water.

First, you will “meet the scientist” who conducted the research. Then you will read something special about science and about the natural environment. You will also read about a

specific research project. This is written in the

format that scientists use when they publish

their research in journals. Then, YOU will

become the scientist when you conduct the

FACTivity associated with each article. Don’t

forget to look at the glossary and the section

called “Thinking About Ecology.” By thinking

about ecology, you will learn about principles

that apply to all life, including yours!

At the end of each section of the article, you

will find a few questions to help you think

about what you have read. These questions

are not a test! They should help you to think

more about the research. Your teacher may

use these questions in a class discussion.

4

About The Natural Inquirer
5

This edition of the Natural

Inquirer describes forest and

environmental research conducted in the tropical region

of the Western Hemisphere

(See Figure 1). The tropics is a

region near the equator,

between 23.5° north latitude,

and 23.5° south latitude.

Natural Inquirer Tropical Forest Edition

Welcome to the

Figure 1. This issue presents research conducted in Puerto

Rico, the U.S. Virgin Islands, Costa Rica, the Dominican

Republic, and Brazil.

Figure 2.

Illustration

of the 

location of

the sun in

relation to

the tropics.

Figure 3. International

Institute of Tropical Forestry.

Latitude is measured by parallel imaginary lines ringing the

Earth. The tropical region gets

a lot of sunshine and is warm

all year around, except in the

high mountain regions (See

Figure 2). The tropics are the

home of a variety of biomes

(bi oms), or regions with different kinds of vegetation and

other life. Tropical biomes are

largely defined by the amount

of rainfall they get. In the tropics, you might find rain forests,

dry forests, shrub lands, tropical plains called savannahs (sä

van uhs), and deserts.

The research in this Natural

Inquirer was conducted by scientists working in the

International (in tür na sha

nul) Institute of Tropical

Forestry, or IITF (Figure 3).

IITF is located in Puerto Rico,

a tropical island in the

Caribbean Sea. The IITF conducts research to help keep

tropical forests healthy now

and into the future, to help

protect the animals that live in

the forests, and to take care of

streams and rivers and the

forests around them. IITF is a

part of the Forest Service. You

can learn about the Forest

Service on the back cover of

the Natural Inquirer, or by

visiting http://www.naturalinquirer.usda.gov and clicking

on “About the Forest Service.”

Gulf of 

Mexico

Atlantic Ocean

Brazil

Costa

Rica

U.S. Virgin Islands

Puerto Rico

Dominican Republic

United States

Caribbean Sea

North

North pole

Equator

South pole

The tropics

SUN }

Glossary:

conserve (kän sürv): To avoid

wasteful or destructive use of

something.

species (spe sez): Groups of

organisms that resemble one another

in appearance, behavior, chemical

processes, and genetic structure.

migrate (mi grat): To move from one

place to another.

larval (lär väl): Relating to the

wormlike feeding form that hatches

from the egg of many insects or

animals that changes form when it

becomes an adult.

tropical (träp i käl): Of, in, or like

the tropics. The tropics is the region

of the earth near the equator.

maturity (muh toor uh te): The state

of being fully grown or developed.

ecosystem (e ko sis tem):

Community of plant and animal

species interacting with one another

and with the nonliving environment.

dependent (duh pen dent): Relying

on.

algae (al je): Simple plants that have

no true root, stem, or leaf and that

usually grow in water or on damp

surfaces.

population (päp yoo la shun): The

whole number of individuals of the

same type occupying an area.

life cycle (lif si kul): Stages in the

development of an organism.

fish ladder (fish lad er): A series of

small dams built in streams or rivers.

These function like steps to enable

animals to swim upstream.

simulate (sim yuh lat): To create the

appearance or effect of something

for purposes of evaluation.

analyze (an uh liz): To study or

examine carefully.

Swimming Upstream

Without a Ladder:

Dams and Pipes

and River Shrimp

Movements

7

Meet Dr. Benstead:

I like being a scientist

because I am excited about the

natural world and want to

help conserve it for future generations to enjoy.

Meet Dr.

Pringle:

I like being

a scientist

because I like

working outside, in the

stream, getting my feet

wet. I also

like doing

research that

will help conserve the 

environment.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

Meet Dr.

March:

I like

being a 

scientist

because I

enjoy 

learning

how natural systems

work. 

Also, for

part of the year my office is a

beautiful stream!

Meet Dr.

Scatena:

I like being

a scientist

because I

like the 

challenge of

trying to

understand

how natural

systems

work so that

we can manage and preserve

them for future generations.

Dr. Benstead

Dr. Pringle

Dr. March Dr. Scatena
8

Thinking About

Science

Although scientists sometimes work

alone, they usually do their

research with other scientists.

Even if they live in different

areas of the Nation or the

world, they find ways to work

together. In this study, scientists from the University of

Georgia worked together with

a Forest Service scientist in

Puerto Rico to study a special

kind of shrimp. In your classroom, you sometimes work

with other students. When

you do this, you are like a scientist who works with other

scientists. Can you name two

reasons why it is a good idea

to work with others when you

are learning something new?

Thinking 

About the

Environment

Many animal

species spend

part of their life

in one location and part of it

in another place. When that

happens, the animal is said to

be migratory. Animals usually

migrate to a place more favorable for reproduction. People

often think of birds when they

think of migratory animals. In

this study, the migratory animal is a river shrimp. When it

is in its larval stage, the

shrimp larvae drift from

streams in high tropical

mountains to areas near the

coast. There they grow

beyond the larval stage. When

they are ready to become

adults and reproduce, the

juvenile shrimp swim back

upstream to where they were

born. When the juveniles

encounter barriers such as

waterfalls, they crawl over

them to continue their

upstream journey. When they

get upstream, they grow into

adult shrimp and reproduce.

Their offspring drift back

downstream with the current,

and the cycle begins again.

Introduction

Tropical streams provide

many benefits to people and

animals. For river shrimp that

spend part of their life in the

mountain streams, the streams

provide a place to reproduce

and develop. River shrimp are

important to the streams as

well. They eat the algae in the

streams and help to turn dead

matter, such as fallen leaves,

into small particles. When

they swim and crawl in the

streams, they stir up the water.

This enables the stream to

wash away any soil and other

things that may have settled

into the stream bed. 

In an area, the

individuals of a

species live in

close relationship

with other living

things and with

the nonliving

environment. This

relationship determines how

many individuals there will be,

how fast they will grow, and

how many individuals of

different ages there will be at

any one time. Living

communities plus the nonliving environment make up

Thinking About Ecology

what we call an ecosystem.

Humans often alter the

nonliving environment. This

alteration can affect a species

by changing their numbers,

changing how fast they grow,

and changing how many

different individuals there will

be of different ages. In this

research, a species of river

shrimp was studied. The

shrimp depend on both

mountain rivers and coastal

wetlands to live and

reproduce. Humans had

altered the river environment

by building a dam and placing

a pipe to carry water from the

river to provide water for

humans. Because all living

individuals have a close

relationship with their

environment, any change in

the environment can cause a

change in the life of the

individual and the group of

individuals. The scientists

wanted to know how the dam

and pipe were affecting the

river shrimp, which must

move up and down the river to

survive.
San Juan

Puerto Rico

Location of

Río Espíritu Santo

North

9

Tropical streams also provide people with the fresh

water they need for drinking,

cooking, and washing.

Because more and more people are living in tropical areas,

more water is needed. To provide water for people, small

dams are often built in tropical streams (Figure 1). This

creates a small pool of water.

The water is diverted from the

small pool into a pipe that carries the water to cities where

people use it. Unfortunately,

the pipe also carries many of

the shrimp larvae out of the

stream. That means fewer larvae are able to get downstream to the coastal zone.

When the juveniles swim back

upstream, the dams can sometimes prevent them from

swimming far enough. When

that happens, the shrimp cannot reproduce. In this way, the

population of shrimp is

reduced more and more over

time. The scientists in this

study wanted to find a way to

protect the shrimp population

while continuing to provide

water for people. 

Reflection

Section

• If the scientists do not find

a way to protect

the shrimp population and still provide

water for people, what do

you think will happen to

the shrimp population in

the future?

• If you were the scientist,

how would you study the

population of migrating

shrimp?

Method

The scientists studied a

mountain stream near a dam

on the Rio (re o) Espiritu (eh

sper eh tu) Santo (sän to) on

the Caribbean (kä rib e un)

National Forest in Puerto

Rico (Figure 2). To find out

how many shrimp larvae were

flowing into the pipe, the scientists put nets into the water.

First, they put nets in the water

above the dam and counted the

total number of larvae floating

downstream. They also put a

net in front of the pipe and

counted the number of larvae in

their net. From this method,

they knew how many larvae

would have flowed into the

pipe and how many would have

floated over the dam. To find

out how many juvenile shrimp

were returning upstream, the

scientists put a net into the

water below the dam. They

counted the number of juveniles

below the dam by counting

how many were caught in the

net. Because shrimp larvae float

downstream in the evening and

at night, the scientists collected

their information in the evening

and at night. They collected

information every third

evening, for a total of 24

evenings.

Reflection

Section

• Instead of collecting their

information on

just one evening,

the scientists counted the

number of shrimp larvae on

24 evenings. Why do you

think it is important to count

the number of larvae on

more than one evening?

• How do you think that the

scientists knew that shrimp

larvae float downstream during the evening and night,

rather than during the daytime?

Figure 1. Dam on the Río Espíritu Santo in Puerto Rico.

Figure 2. Location of the

Rio Espiritu Santo.
10

Results

The scientists discovered

that most shrimp larvae float

downstream between 8:00

p.m. and 12:00 a.m. (Figure

3). The average percentage of

larvae floating into the pipes

was 42 percent of the total

number of larvae floating

downstream (Figure 4). The

scientists also found that the

dam often prevented the juvenile shrimp from swimming

upstream. This meant that

many juvenile shrimp were

trapped below the dam, waiting for a chance to climb over

the dam. With so many waiting below the dam, fish who

feed on the juvenile shrimp

were able to eat larger numbers of the young shrimp than

they normally would have.

Reflection

Section

• In what ways

did the dam and

pipe disrupt the

normal life cycle

of river shrimp? What other

things (animals, plants, or

the stream itself) were

impacted as a result of this?

• How could the scientists’

information be used to help

the river shrimp? What do

you think the scientists recommended?

Implications

The scientists recommended

that the water pipe be closed

every evening between 8:00

p.m. and 12:00 a.m., or at

least for some of the hours

when most of the larvae are

floating downstream. That

way, most of the shrimp larvae

could float downstream to the

wetlands without getting

caught in the pipe. In addition, people would still be able

to use the water from the

streams. The scientists also

recommended that the small

fish ladder that had been built

be repaired so that river

shrimp could use it again

(Figure 5). That way, the juvenile shrimp could climb over

the fish ladder to get back

upstream. If these recommendations are not followed, the

population of fresh water

shrimp will probably continue

to decline in tropical streams

where dams exist.

Amount of larval shrimps going downstream

Average downstream flow of larval shrimps in a typical day. Each column represents 

hourly data beginning at 5:00 pm and ending at 7:00 am of the next day.

Very

Small

Very

Small

Very

Small

Very

Small

Very

Small

Very

Large

Very

Large

Very

Large

Small Average Large Average Small Small Small

6pm 

5pm 

7pm 

8pm 

9pm 

10pm 

11pm 

12am 

1am 2am 

3am 4am 

5am 6am 7am 

Figure 3. The average amount of shrimp larvae floating downstream at different times of the day.

Figure 4. The average percentage of shrimp larvae

floating into the pipe and

down to the wetlands.

42% shrimp larva 

floating into pipe

58% shrimp larva 

floating to wetlands 
11

Reflection

Section

• Although the

scientists’ suggestions may

help protect the

shrimp population and still

allow people to use the

stream water, some people

may not want to follow the

suggestions. Can you think

of reasons why people may

not want to follow these

suggestions? (Hint:

Everything costs money to

build and take care of. Who

would pay for the fish ladders?)

• Do you think that the scientists’ suggestions are a good

compromise between protecting the river shrimp and

providing water for human

use? Why or why not?

Discovery

FACTivity

For this

FACTivity, you

will answer the

question: What

is the difference between having a 50 percent chance of

having something happen,

and having less or more than a

50 percent chance? You will

use marbles to show how

some river shrimp get caught

in the pipes, and other shrimp

are able to drift downstream.

In the study you just read,

each shrimp had just over a 40

percent chance of floating into

the pipe, and almost a 60 percent chance of floating downstream (that means that if 10

shrimp were floating downstream, 4 would go into the

pipe, and 6 would float downstream). Look again at Figure

4. Fortunately for the shrimp,

each one had better than a 50

percent chance of drifting

downstream.

In this FACTivity, each

shrimp will have a 50 percent

chance of floating into a pipe,

and a 50 percent chance of

floating downstream. Each

station that you construct will

simulate a stream with a pipe.

You may make three or four

identical stations, with six to

eight students per station. For

each station, you will need 3

yardsticks, 1 piece of 22- by

28-inch posterboard, 100 marbles, and a coffee can. Cut the

posterboard along its width

into two equal-sized pieces and

fold each piece in half to make

tents. Write “downstream” on

one tent, and “pipe” on the

other. Place the tents side by

side, and lay one yardstick on

each side of the tents. Place the

third yardstick between the

tents, at the back (see diagram

on page 12). 

Three students will be stationed behind the tents. One

student will catch and count

the marbles coming through

one tent, the other will catch

and count the marbles coming

through the other tent. A third

student will record the number

of marbles coming through

each tent. You may use the

chart below as an example to

record your observations.

Place the 100 marbles (simulating 100 shrimp) in the coffee can. Another student,

standing about 6 feet (or 2

meters) back, will gently roll

the marbles toward the tents.

The student should aim for the

center of the tents. Do not roll

them too hard—remember,

they are shrimp floating downstream! The students behind

the tents should catch and

record the number of shrimp

floating “downstream” and

the number floating into the

“pipe.” The shrimp that floated into the pipe will die. The

shrimp that floated downstream should be taken back

upstream and rolled toward

Figure 5. Fish ladder on the Río Espíritu Santo. The fish ladder

is on the far right, below the people. It looks like a ramp in

this photo.
12

Sample form for recording your observations. Begin with 100 marbles

1st roll

2nd roll

3rd roll

4th roll

10th roll

9th roll

8th roll

7th roll

6th roll

5th roll

# through pipe % through pipe # floating

downstream

% floating

downstream

32 (for example) 32 or .32 68 68 or .68

Begin with 68 

marbles – Record #

# through pipe

divided by 68

Subtract number

through pipe from

68

Divide # floating

downstream by 68

Begin with #

floating downstream

the tents again. Every time

you roll the marbles, the marbles represent the offspring of

the shrimp that successfully

returned upstream to reproduce. Continue to roll the

marbles until all of the shrimp

have died (rolled into the

pipe). Now that you have

made and recorded your

observations, you will need to

analyze them. Calculate the

percentage of shrimp going

into the pipe each time. How

many times does it take for all

of the shrimp to drift into the

pipe? Now calculate the average percentage going through

the pipe by adding the numbers in second column and

dividing them by the number

of rolls. This tells you the

overall average percentage of

shrimp drifting through the

pipe.

Record the average percentage of your shrimp drifting

through the pipe. Compare

your percentage to the percentage that the scientists found in

their study (42 percent). Why

do you think your percentage

is different than 42 percent?

What is different about your

experiment and the stream’s

flow? If you rolled your marbles straight down the middle,

your overall percentage should

have been close to 50 percent.

Was it? If not, what may have

caused your percentage to be

different? Why do you think

each shrimp in the Rio Spiritu

Santo had better than a 50 percent chance of drifting past the

pipe?

From Benstead, Jonathan P., March, James G., Pringle, Catherine M. and Scatena, Frederick N. (1999). Effects of a low-head

dam and water abstraction on migratory tropical stream biota. Ecological Applications, 9(2): 656-668.

Marbles rolled toward tents
13

Meet Dr. Cuevas: 

I like being a scientist

because I get to discover new

things about the natural environment.

Meet Dr. Lugo:

I like being a scientist

because it brings me into contact with people who, like me,

are fascinated by the complexity of nature and have an

opportunity to try to figure it

out. Then we can put the

information to work for the

benefit of people.

Glossary:

complexity (käm plek suh te):

The state of being complicated

or having many related parts.

quality (kwôl ä te): Any of the

features that make a thing

what it is. 

quantify (kwän tä fi): To

count or measure; to give the

quantity of. 

nutrient (noo tre ent): Any of

the substances found in food

that are needed for the life and

growth of plants and animals.

organism (ôr gä niz um): Any

living thing. 

decomposer (de käm poz ür):

Organisms that digest parts of

dead organisms and the

wastes from living organisms.

analyze (an ä liz): To study or

examine carefully.

species (spe sez): Groups of

organisms that resemble one

another in appearance, behavior, chemical processes, and

genetic structure.

biomass (bi o mas): All the living things in a particular area.

external (ek stür nul): On the

outside.

manager (ma ni jür): A skilled

person who directs or manages something.

organic (ör ga nik):Related to

or coming from living organisms.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

Leaf Me Alone!

The Movement of Nutrients

Between Trees and the Soil

Dr. Cuevas Dr. Lugo
What is energy?

Energy is the ability to do something. Energy

always behaves in

the same way.

The behavior of

energy is described by what

we call the laws of energy.

Energy can take many forms,

and can be transferred from

Thinking About Ecology

one form to another. When

energy is transferred, its quantity decreases. That means

that the amount of energy

available to do something is

less. The remainder of the

energy becomes scattered or

spread out, usually in the form

of heat. This heat energy is

usually lost to the environment. This means that whenever we use energy, we always

end up with less useable energy than we started with. All

living things need a continual

source of high-quality energy

to survive. As this energy is

used, low-quality heat and

other waste products are

added to the surroundings.

Everything on Earth follows

the laws of energy, including

us! These are laws that no one

can break.

14

Thinking About

Science

Scientists use

many ways to

determine the

quality of a

thing. Most

often, scientists use numbers

to determine the amount of a

particular quality a thing has.

Sometimes, using numbers is

not the best way to determine

something’s quality. For

example, how could you

determine how much better (a

quality) your dinner tastes

after you add salt to it? You

would taste it and make a

judgment. This judgment

would be based on a comparison with how it tasted before

you added salt. This is a way

of determining quality without using numbers. You could

quantify this quality of good

taste by asking everyone in

your neighborhood to taste

your dinner before and after

adding salt. Then, you could

count the number of people

who said it tasted better.

Quality can be judged with or

without numbers. Usually, scientists use numbers because

numbers are less subject to

individual choice or opinion,

as when they measure height

or weight. In this study, the

scientists wanted to know the

quality of leaves that fell from

trees. Quality was determined

by the amount of nutrients

found in the fallen leaves. Do

you think the scientists used

numbers to determine quality

in this case? Why or why not?

Thinking 

About the

Environment

Food chains

describe the

flow of energy

from one organism to another.

A flow of energy occurs when

one organism digests another.

When this happens, some of

the energy is lost to the environment. The food chain

starts with green plants. Green

plants are the only type of

organism that can convert

sunlight into food by photosynthesis (fo to sin thä sis). In

forests, some of the green

plants are consumed by animals such as insects and deer,

but most of them are consumed by decomposers as

dead plant material.

Decomposers include bacteria,

fungi (fun ji), and small animals such as earthworms.

Decomposers move nutrients

from the dead plant material

to the soil. Once in the soil,

plants can use the nutrients

for new growth. The scientists

in this study wanted to know

whether some kinds of fallen

leaves have more nutrients

than other kinds of leaves. If

so, those leaves would provide

more nutrients to the soil,

making more nutrients available to the plants.

Introduction

You probably know that

trees depend on the soil in

which they are rooted. But did

you know that the soil

depends on trees also? By
15

shedding their leaves, trees

provide nutrients to the soil,

which are made available to

the trees once again (Figure 1).

In this study, the scientists

studied trees growing on

Puerto Rico, an island in the

Caribbean (Figure 2). The scientists wanted to know if different trees contribute

different amounts of nutrients

to the soil. By learning if some

kinds of trees contribute more

nutrients to the soil, the scientists could determine if those

kinds of trees should be planted in areas where the soil

needs more nutrients. This is

especially important in the

tropics, where the soil often

has fewer nutrients than in

other forested areas of the

world.

Reflection

Section

• What is one

of the problems

the scientists

were trying to

solve?

• Do you think that it would

be good to plant trees that

contribute more nutrients

to the soil? Why or why

not?

Methods

Trees contribute nutrients to

the soil in many ways. One of

the primary ways they do this

is by shedding their leaves.

When leaves fall to the

ground, bacteria, fungi, and

animals such as earthworms

digest the leaves, moving the

nutrients from the leaves to

the soil. The scientists decided

to collect falling leaves and to

analyze the leaves for nutrient

content. They selected trees

that had been planted 23 to 26

years earlier in the Luquillo

(lu ke o) Experimental Forest

in Puerto Rico (Figure 3).

Puerto Rico is an island in the

Caribbean (See Figure 2 and

locate Puerto Rico on the

map).

The scientists chose to study

10 types of trees that are usually planted to produce wood

products such as lumber, baseball bats, and paper. The scientists randomly (ran dum le)

selected six trees to study from

each species. This means that

the selection of trees was purely by chance, like a drawing in

Gulf of 

Mexico

Atlantic Ocean

Brazil

Costa

Rica

U.S. Virgin Islands

Puerto Rico

Dominican Republic

United States

Caribbean Sea

North

Figure 2. The Caribbean

Leaves fall to ground

Roots take up the 

nutrients from the

soil

Waste products from 

earth worms and bacteria, 

which contain nutrients,

become part of the soil

Earth worms and bacteria

in the soil consume

the leaves

1

4

2

3

Figure 1. The tree nutrient cycle.
16

a lottery. For each type of tree

studied, the scientists hung a

wire basket from the selected

trees (Figure 4). The baskets

caught some of the falling

leaves. Every 2 weeks, the

leaves were collected,

weighed, and a chemical

analysis was done to determine the amount of nutrients

in the fallen leaves. The scientists collected the leaves 29

times over a period of 58

weeks. How many total baskets of leaves did the scientists

analyze? (Multiply 10 tree

species X 6 baskets X 29 collections.) Each time, the scientists weighed the leaves to

determine the quantity of biomass. They analyzed the

leaves for the following nutrients: Nitrogen (N), phosphorous (P), potassium (K),

calcium (Ca), and magnesium

(Mg). The amount of these

nutrients measured in the

leaves helped the scientists to

determine their quality. 

Reflection

Section

• After leaves

fall to the

ground, decomposers, such as

bacteria and fungi, and animals such as earthworms,

help to move the nutrients

from the leaves to the soil.

Do you think that the soil

receives the same amount of

energy as was in the leaves?

Why or why not? (Hint:

Think about the laws of

energy.)

• The scientists collected

leaves over the course of a

little over 1 year. Why do

you think that they wanted

to collect leaves during different times of the year?

Results

The scientists found that the

10 species studied differed in

both the number of fallen

leaves and the quality of the

nutrients. They also found

that there was a relationship

between the number of fallen

leaves and the quality of the

nutrients. For example, if the

nutrient content of individual

leaves was low, there usually

was a high quantity of biomass, or a lot of fallen leaves.

If the nutrient quality of the

leaves was high, not as many

leaves fell. That meant that

the amount of overall nutrients available to the decomposers in the soil was about

the same for most tree species

(Figure 5). 

The scientists also found

that before the trees shed their

leaves, some of the trees took

nutrients back from their

leaves before shedding them.

Those trees kept much of their

nutrients rather than contributing them to the soil

through fallen leaves. The scientists concluded that there

were three groups of trees.

The first group of trees kept

their nutrients within the tree

itself. The second group

cycled most of their nutrients

externally, meaning that the

nutrients were shed with the

leaves and cycled into the soil

for later use by the tree and Figure 4. Wire mesh baskets were used to catch falling leaves.

Figure 3. Luquillo

Experimental Forest.
17

other plants. The third group

used both kinds of nutrient

cycling.

Reflection

Section

• Think about

all of the animals and plants

in the forest.

What do you think might

be the advantages of external nutrient cycling for

other plants and animals?

What might be some advantages for the trees when

they take the nutrients back

from their leaves before

shedding them? 

• In what ways is energy scattered or spread around during external nutrient

cycling?

Implications

Not all trees cycle their

nutrients in exactly the same

way. If forest managers want

to enrich soil with a lot of

organic matter, they should

plant trees that shed a lot of

leaves. If they want to put a

lot of nutrients into the soil

quickly, they should plant

trees that shed leaves with a

high nutrient quality. By

knowing the nutrient quality

of fallen leaves, forest managers can help nature cycle

nutrients from trees to the soil

and back to the trees again.

Reflection

Section

• In the fall,

many people

rake the fallen

leaves from

their yards. What happens

to the nutrient cycle when

people remove the fallen

leaves? How do some people make up for the loss of

nutrients available for plant

growth? (Hint: What do

people usually do in the

spring to encourage tree

and plant growth?)

• When people build a compost bin, they are providing

a special area for leaves and

other organic wastes to

decompose (Figure 6).

What kind of organisms are

causing the organic matter

to decompose in a compost

bin? How is a compost bin

like a forest floor? How is it

different?

Figure 6. Many people use a compost bin to recycle and reuse

their leftover, non-meat foods, fall leaves, and grass clippings.

They then use the compost for their gardens and trees.

Few leaves falling/

High nutrient quality Many leaves falling/

Low nutrient quality

Overall, the amount of nutrients available to

earthworms and decomposers is about the same.

Figure 5. Overall, the amount of nutrients from falling leaves

was equal.
18

FACTivity

In this

FACTivity, you

will explore the

bacteria living

in the soil near

your home or school. The

question you will be answering is: What kind of bacteria

live in different kinds of soil?

It will take 3 to 4 weeks to

complete this FACTivity, so be

patient. Bacteria need time to

grow! You will need:

• 4 clear plastic 2-liter soda

bottles with labels removed

• Enough clear, sturdy plastic

wrap to cover the bottles

• four rubber bands

• marker

• masking tape

• 2-gallon bucket

• a 1-cup measuring cup

• tablespoon

• paint stirrer or other stirring utensil

• 4 small buckets of soil or

mud, each collected from

one of four different

sources (like a pond, garden, stream, forest, yard,

etc.).

• 4 small buckets of water,

one from each place you

collected the soil (use distilled water for soil collected from a dry place). 

• 4 sheets of newspaper

• 1 cup of powdered chalk

(crush several pieces of

chalk or you can buy some

powdered chalk at a hardware store)

Wash your hands before

starting. If you have a cut

on your hand, wear latex

gloves when working with

soil. Divide into four

groups. Each group will prepare one of the experiments.

Be sure to match the bucket

of soil with the bucket of

water from the same source.

Label each bucket with the

source of soil or mud and

water using the masking

tape and marker.

For each experiment:

Cut off the top end of your

plastic bottle. The top end will

be used as a funnel, and the

bottom will hold your experiment. Shred the sheet of newspaper into thin strips and set it

aside. In the 2-gallon bucket,

add 5 or 6 cups of soil or mud.

Pick out all of the sticks,

leaves, and pebbles. While

stirring, slowly add water

(from the same source) until

the mixture becomes like a

thick cream. Add the shredded

newspaper and 1 tablespoon

of powdered chalk. Mix gently, and make sure the mixture

is wet enough to flow through

the funnel. Label your plastic

bottle with the source of the

soil. Then, using the funnel,

pour about 1 centimeter or

1/2 inch of the mixture into

the plastic bottle. With one

hand over the top of the plastic bottle, gently tap the mixture on a hard surface to allow

the mixture to settle evenly.

Continue this process until

you have filled the bottle to

within about 4 centimeters or

2 inches from the top. Cover

the top with plastic wrap and

seal with the rubber band.

Place your bottle in a well-lit

place, but not in direct sunlight. Keep it out of heat and at

room temperature.

For 3 or 4 weeks, observe

the bottles daily. Look for

color changes in the mixtures.

Record your observations,

using the chart below as an

example. You may draw, label,

and color a picture of each of

the jars at the end of each

week.

You should begin to see different colors in the bottles.

What are the colors and where

are they located in the bottle?

What do you think causes the

different colors?

• Red and orange are purple

photosynthetic (fo to sin

theh tik) bacteria

• Green at the surface are

cyanobacteria (si an o bak

ter e uh) and algae

• Olive green in the middle or

lower area are green sulphur

bacteria

• Black patches are iron sulfide, a chemical formed by

certain bacteria

To learn more about these different kinds

of bacteria, visit

www.ucmp.berkeley.edu/bacteria/

bacteriasy.html

This FACTivity was adapted from an activity titled “Biosphere in a Bottle” developed

by the National Association of Biology

Teachers. For more fun activities related to

bacteria, visit http://www.microbe.org.

From: Cuevas, E. & Lugo, A. E. (1998).

Dynamics of organic matter and nutrient

return from litterfall in stands of ten tropical tree plantation species. Forest Ecology

and Management, 112: 263-279.

To learn more about nutrient cycling, visit

http://www.swifty.com/apase/charlotte/soil

7.html
19

Meet Dr. Weaver:

I like being a scientist

because I do a little bit of

everything. My background

has allowed me to travel,

work in different cultures,

learn new languages, and

work with people in developing countries on many practical projects.

Glossary:

watershed (wä tür shed):

Land area with small streams

that deliver water to a larger

stream.

represent (rep re zent): To be

an example of.

diversity (duh vür suh te):

The quality of being different

or varied.

sustainable (suh stan uh bul):

The quality of surviving or

being maintained over a specific time period.

conservation (kän sür va

shun): The care and protection of natural resources such

as forests and water.

sea level (se lev ul): The level

of the surface of the sea.

elevation (el uh va shun):

The height above sea level.

topography (tuh pog ruh fe):

The surface features of a

region, such as rivers, hills,

and valleys.

diameter (di am uh ter): The

distance equal to a straight

line passing through the center of a circle, cylinder, or

sphere.

species (spë sëz): Groups of

organisms that resemble one

another in appearance,

behavior, chemical processes,

and genetic structure.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

Oooh! That’s

Growth!

Measuring Trees in

Cinnamon Bay Watershed

Dr. Weaver
All living

things grow and

develop. Think

about yourself

and your friends.

As a living thing,

you grow and

develop too. Once you stop

growing physically, you will

continue to change and

develop in other ways. When

living systems such as forests

stop growing bigger, they

continue to develop in other

Thinking About Ecology

ways. In this study the scientist wanted to know how the

trees were growing and

developing in a watershed in

the Virgin Islands. By learning how the trees were growing and developing, he would

know about the mixture of

trees in the watershed. With

this information, the scientist

can help managers make better decisions about how to

keep the area healthy and

sustainable.

20

Thinking About

Science

When studying the natural

environment,

scientists sometimes have to

wait many years to discover

new things. The scientist in

this study wanted to know

how the trees were changing

in the Cinnamon Bay watershed, St. John, U.S. Virgin

Islands National Park (Figure

1). He was interested in knowing what kind of new trees

were growing and what kind

of trees were dying. He also

wanted to know how fast the

trees were growing. If people

want to understand the natural environment, they have to

know how to describe it.

Usually, the best way to

describe an environment is to

observe it, and then to record

your observations. When you

know what an environment

looked like one year, you can

compare it with other years to

tell how much it has changed. 

Thinking 

About the

Environment

The Virgin

Islands National

Park is located

in the U.S. Virgin Islands

(Figure 1). In 1976, the United

Nations Educational,

Scientific, and Cultural

Organization (UNESCO, u

nes ko) named the national

park a Biosphere (bi o sfer)

Reserve (re zerv). (The United

Nations is an international

organization that works for

world peace and security.) A

Biosphere Reserve is a special

label given to natural areas

around the world that represent the world’s natural diversity. A biosphere reserve

should be managed so that it

stays healthy into the future.

This is called keeping the area

sustainable. To manage a

Biosphere Reserve for sustainability (suh stan uh bil uh te),

managers have to consider

conservation, research, education, and whether and how to

build structures for human

use. All of these things must

be balanced so that the area

stays healthy into the future.

Introduction

In 1718, Danish settlers

moved to what is now the U.S.

Virgin Islands. They cut down

Gulf of 

Mexico

Atlantic Ocean

Brazil

Costa

Rica

U.S. Virgin Islands

Puerto Rico

Dominican Republic

United States

Caribbean Sea

North

Figure 1. Location of U.S. Virgin Islands in the Caribbean.
21

most of the trees and planted

sugar cane. By 1750, almost

all of the original trees had

been cut down. Over time,

new trees were planted or

began to grow on their own.

In 1917 the United States

bought the Virgin Islands

from Denmark. By then, only

about 10 percent of the island

was being used for crops, and

the rest of it was again a forest. (What percentage was

forested? Subtract 10 percent

from 100 percent.) In 1956,

the United States established a

national park on one of the

islands. The United Nations

named the national park a

Biosphere Reserve in 1976. To

help manage the park as a

Biosphere Reserve, the

National Park Service wanted

to understand how fast the

trees were growing. To do

this, they invited the Forest

Service to do a study of the

trees in the Cinnamon Bay

watershed, one of the areas

within the Biosphere Reserve

(Figures 2 and 3).

Reflection

Section

• If you were

the scientist,

how would you

study how well

the trees were growing in

the Cinnamon Bay watershed?

• Why do you think the

United Nations would like

areas to be managed sustainably?

Method

The Cinnamon Bay watershed covers 1.32 km2 (How

many square miles is that?

Multiply 1.32 X .621), and

rises from sea level to 330

meters in elevation (How

many feet is that? Multiply

330 X 3.28). Because the scientist could not study the

entire area by himself, he

decided to identify 16 smaller

areas within the watershed to

study. Because he wanted

these areas to represent the

whole watershed, he selected

areas at different elevations

and topography. (Figure 4).

How many areas have been

identified in Figure 4?

Compare this number with

the number of areas the scientist studied. You should now

realize that there was one

more area identified by the

scientist that is not shown in

Figure 4. The scientist located

the 16th area near the highest

point of the watershed, at 275

meters in elevation. (How

many feet is that?)

The scientist then measured

the height and diameter of

almost every tree in the 16

areas. When scientists measure the diameter of a tree,

Figures 2 and 3. Cinnamon Bay watershed in the U. S. Virgin

Islands National Park.
22

they always measure it at 1.37

meters (or 4.5 feet) above the

ground. This measurement is

called d.b.h., or diameter at

breast height (Figure 5). If the

d.b.h. of a tree was less than

4.1 centimeters (or 1.61 inches), the scientist did not

include it in his observations.

For every tree measured, the

type of tree was identified and

recorded. The scientist then

left the area to grow for 5

years. When he returned 5

years later, he counted all of

the new trees and the number

of trees that had died, and

measured how much the living

trees had grown.

Reflection

Section

• Why do you

think the scientist studied

areas at different elevations? 

• Why do you think that scientists always measure trees

at d.b.h.? (Hint: What if

one scientist measured a

tree’s diameter at 3 meters

high and another scientist

measured the same tree’s

diameter at 4 meters?

Would their measurements

be the same?)

• What three kinds of information did the scientist

have after he took his measurements 5 years later?

Results

After 5 years, the scientist

counted 206 new trees in the

16 areas. He also found that

161 trees had died. Overall,

would you say that the watershed is gaining trees or losing

trees? Why? The trees grew an

average of 0.07 centimeters a

year when measured at d.b.h.

Most of the trees grew < (less

than) 0.10 centimeters a year

in height (How many inches is

that? Multiply 0.10 X .394)

The scientist found no new

Figure 4. Areas studied in the Cinnamon Bay watershed.

Elevation

Topography

60 meters

(How many

feet?

Multiply 60

X 3.28)

120 meters

(How many

feet?)

10 X 50

meters

10 X 50

meters

10 X 50

meters

10 X 50

meters

Valley

10 X 50

meters

10 X 50

meters

10 X 50

meters

10 X 50

meters

10 X 50

meters

Mountain

Slope

10 X 50

meters

10 X 50

meters

10 X 50

meters

10 X 50

meters 

For example:

This area is

on a mountain ridge at

an elevation

of 120 meters

10 X 50

meters

(How many

feet?)

Mountain

Ridge

240 meters

(How many

feet?)

210 meters

(How many

feet?)

180 meters

(How many

feet?)

10 X 50

meters

Figure 5. Research assistant

measuring d.b.h. in the

Cinnamon Bay watershed.
23

tree species growing in the

study areas.

Reflection

Section

• Think about

the trees where

you live. In the

spring, new

growth appears as new

stems and leaves.

Compared to the trees

where you live, would you

say that the trees in

Cinnamon Bay watershed

were growing faster or

slower?

• Based on the results of this

research, do you think the

watershed is becoming

more diverse in its tree

species? Why or why not?

Implications

This study will help forest

managers in many ways. First,

it tells them how much time

will be needed for the forest to

grow back if, in the future, the

trees are cut down or a hurricane destroys the forest.

Second, it tells scientists what

kind of trees grow at different

elevations in this tropical

watershed. This could be especially helpful if managers

want to plant trees in a similar

area. Finally, this study helps

managers to identify which

trees are common and which

are rare in the tropical watershed. It also tells managers

which trees will grow to maturity, if there is no hurricane or

other disturbance. You can see

that by studying the current

conditions of a natural area,

scientists can help forest managers protect the area into the

future.

Reflection

Section

• Remember

that the

Cinnamon Bay

watershed is

part of the Biosphere

Reserve. Go back to

“Thinking About the

Environment” and look at

what must be balanced in a

Biosphere Reserve. Which

one of those four things are

reported on in this article?

• Do you think the scientist

should go back to

Cinnamon Bay watershed

in 5 more years and take

more measurements? Why

or why not?

FACTivity

For this

FACTivity, you

will answer the

question: What

is the relationship between tree height and

d.b.h.? In other words, when

trees get taller, does the d.b.h.

get smaller, larger, or stay the

same? You might be able to

guess at the answer to this

question based on your existing knowledge. What do you

think the relationship is? Your

guess is a hypothesis (hi paw

thuh sis). A hypothesis is an

assumption that is made for

the time being, so that it can

be tested using planned and

recorded observation. For this

FACTivity, you will need a

cloth (flexible) tape measure. 

The method you will use to

test your hypothesis is this: Go

to an area that has trees of

varying heights. You will first

place the trees into categories,

based on their height. Since

you will not be able to measure the height of most of the

trees, for this FACTivity you

will be placing the trees in

general categories. Find at

least three trees in each of

these categories:

• Short trees (those that are

not much taller than a

human)

• Medium height trees (those

that are much taller than a

human, but not taller than a

two story-building

• Tall trees (those that are

taller than a two story

building

If you cannot find enough

trees in these categories near

your school, you may want to

have your classmates take

measurements of trees at

home or in different places.

The more trees you can measure in each of these categories, the more information

you will have to answer the

question.

To measure each tree’s

diameter at d.b.h., place the

tape measure at ground level.

Measure up the tree’s trunk to

1.37 meters (4.5 feet). Have

your classmate hold a finger at

that height on the trunk. At

that height, measure the circumference of the tree. The

circumference is the distance

around the tree trunk. For
24

each measurement, you will

have to calculate the diameter

from the circumference. To do

this, multiply the circumference by .3183. No matter how

large the circumference, the

diameter is always .3183

times the size of the circumference. Record all of your measurements. You can use the

chart on the right as an example. After you have finished

recording all of your measurements, you will need to determine if there is a relationship

between tree d.b.h. and tree

height.

To determine if there is a

relationship between tree

height and d.b.h., create a histogram (bar chart) from your

recorded information. You

can use the sample on the

right to create your bar chart.

See an example of a bar chart

below the sample.

After you have made your

bar chart, can you see a pattern in the d.b.h. of the trees?

What is the pattern? The pattern is a relationship that you

have discovered between tree

height and d.b.h. Now that

you know this, what is the

answer to the question asked

at the beginning of this

FACTivity? Was your hypothesis correct?

From Weaver, P. L. (1990). Tree diameter

growth rates in Cinnamon Bay watershed,

St. John, U.S. Virgin Islands. Caribbean

Journal of Science, 26(1-2): 1-6.

50

45

40

35

30

d.b.h. 25

20

15

10

5

0

Short trees Medium trees Tall trees

Tree #1 – d.b.h.

Tree #2 – d.b.h.

Tree #3 – d.b.h.

Sample chart for recording measurements

Sample bar chart

Tree #

Tree height Short Medium Tall

1 2 3 1 2 3 1 2 3

50

45

40

35

30

d.b.h. 25

20

15

10

5

0

Example of a bar chart

Tree #

Tree height Short Medium Tall

1 2 3 1 2 3 1 2 3
25

Meet Dr. Keller (with hat):

I like being a scientist

because I get to follow my natural curiosity to learn how the

Earth system works. My work

is split between the field, the

office, and the laboratory and

I have a great deal of independence. I love to learn new

things.

Glossary:

gaseous (gash us): In the

form of gas.

greenhouse effect (gren

howls e fekt): Warming of

the Earth’s surface that

occurs when the sun’s heat is

trapped by the atmosphere.

climate (kli met): The average condition of the weather

at a place.

bacteria (bak ter e uh):

Living things that only have

one cell and can only be seen

using a microscope.

specialization (spesh ul i za

shun): Special study of something or working only in a

special topic or area.

compact (käm pakt): To pack

closely and firmly together.

porous (poor us): Full of

pores or tiny holes through

which water, air, etc., may

pass.

sample (sam pool): A part or

piece that shows what the

whole group or thing is like.

anaerobic (an ä ro bik):

Existing in the absence of

oxygen.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

Thinking About

Science

Chemistry is

the science of

the building

blocks of all

matter. Atoms

are the most basic building

block. Molecules are combinations of two or more atoms

of the same chemical element.

All matter is built from over

100 chemical elements.

Examples of elements are

nitrogen, hydrogen, oxygen,

and carbon. Compounds are

made up of two or more elements. To make it easier to

It’s a Gas!

The Exchange of Gases

Between the Soil and the

Atmosphere

Dr. Keller
26

imagine, think about the

alphabet. Atoms are like different letters. There could be

“A” atoms, “B” atoms, and

“C” atoms, for example.

Elements are like a single letter, such as A, I, or T.

Molecules are like strings of

the same letter (or element),

such as BBB or MMMM.

Compounds are like words,

which are made from different

letters (or elements). When

elements interact and become

compounds, their structure

changes. Elements can form

an almost limitless number of

compounds, just as letters can

form an almost limitless number of words. These compounds can be solid, liquid, or

gas. Some scientists study the

structure and behavior of

gaseous compounds. In this

study, the scientists were interested in studying the gaseous

compounds that go into the

atmosphere as greenhouse

gases. 

Thinking 

About the

Environment

The greenhouse effect is

caused by certain gases that act like glass in

a greenhouse. They reflect

heat in the atmosphere back

down to earth (Figure 1). The

amount of heat trapped in the

atmosphere can vary, depending on the type of gas and how

long it stays in the atmosphere. The major greenhouse

gases are water vapor, carbon

dioxide (kär bun di ox id),

methane (meth an), nitrous (ni

trus) oxide, and chlorofluorocarbons (klôr o flôr o kär

buns), also called CFCs. We

need a certain level of greenhouse gases to maintain a liveable climate on Earth. If we

had too small an amount of

greenhouse gases, the Earth’s

climate would get too cold. If

we get too great an amount of

greenhouse gases, the Earth’s

climate will get too warm.

Human activities, such as

burning fossil fuels like petroleum, can create greenhouse

gases. The scientists in this

study looked at greenhouse

gases from another perspective. They looked at how

human activities have enabled

soil bacteria to increase the

amount of nitrous oxide in the

atmosphere.

Introduction

Tropical forests are sometimes cut down so that

humans can use the trees for

wood and other products.

Then, the cleared land is made

into a pasture so that cattle

can be raised for human consumption. When forest land

becomes pasture, the soil

changes. It becomes more

compacted and less porous.

(Can you think of why this

might happen? Think about

the size and weight of cattle.)

Previous research had shown

SEA LEVEL

7 miles

Thermosphere

Mesosphere

Stratosphere

Troposphere: 

Weather layer—

80% of our

sky “contents”

20 miles

40 miles

30 miles

50 miles

60 miles

70 miles

Figure 1. The Earth’s atmosphere. The troposphere is the section of our atmosphere reaching from sea level up to 7 miles.

Most clouds are contained within the troposphere. When you

fly somewhere in a jet, you are flying through the middle and

upper portions of our troposphere.
27

Figure 2. The nitrogen cycle.

Atmospheric Nitrogen (N2)

Soil bacteria

absorb N2

from the

atmosphere

Plants are

eaten by 

animals

Dead plants, animals, 

and animal wastes

work into the soil 

where bacteria turn

them into 

ammonium ions

Bacteria turn nitrites into 

nitrogen (N2) and nitrates

into nitrogen and 

nitrous oxide (N2O) 

Plants take up

ammonium ions

and create proteins

and other nitrogencontaining nutrients

More bacteria

turn ammonium

ions into nitrites (NO2-)

and nitrates (NO3-)

Bacteria in soil and on plant

roots turn N2 into ammonia

(NH3), then other bacteria

turn ammonia into

ammonia ions (NH4+) 

B B

B

Ammonia

Ammonia ions

B

B

B

B

B

Nitrates

Nitrites

N2O N2 N2

Often, scientists

study one particular event or

object. While

such specialization helps 

scientists to

understand a lot about that

one event or object, it does not

always help them to understand how that event or object

relates to other events or

objects. Ecologists (e käl uh

jists) are scientists who study

how living things relate to

Thinking About Ecology

each other and to nonliving

things. In this study, the ecologists were studying the nitrogen cycle (Figure 2). The

nitrogen cycle explains the

relationship of the element

nitrogen with other elements,

and with plants, animals, and

bacteria. Bacteria are important in the cycle, because they

convert nitrogen from the

atmosphere into forms that

plants can use such as nitrates

and ammonia. These compounds are used by plants to

make other compounds such

as protein. Animals who eat

plants can use the protein

from the plants. Bacteria living in soil convert animal

wastes and dead material

from plants back into nitrogen

compounds. The nitrogen is

released back to the atmosphere, and the cycle begins

again. This is an example of

how life depends on relationships between living and nonliving things. What are some

examples of how your life

depends on living and nonliving things?
28

that pasture soils release more

greenhouse gases than forested land. Sometimes pastures

are abandoned after a while.

This is often because the soil

can no longer produce enough

plants to support the cattle.

When pastures are abandoned, the forest begins to

grow again. No one knew

whether soils from these

young forests would begin to

release less greenhouse gases

as the forest grew again. That

is the question the scientists

wanted to answer.

Reflection

Section

• What is the

question the scientists wanted

to answer?

What is the bigger problem

their research might help to

solve?

• Do you think the scientists

needed to visit and study

young tropical forests, or

could they do all of their

research inside a laboratory? Why or why not?

Method

The scientists selected four

types of areas to study. They

studied old tropical forests,

young tropical forests, pastures that were currently being

used for raising cattle, and

recently abandoned pastures

(Figures 3-5). They selected

three different areas of each

type to study as examples.

(How many total areas did

they study? Multiply 4 types

of areas times 3 examples

each.) Then, they picked eight

spots in each area where they

measured the amount of

nitrous oxide (N2O) in the

Figures 3-5. An old tropical

forest, a current pasture, and

a young tropical forest.
29

soil. (How many total spots

did they measure? Multiply 12

X 8.) The scientists measured

the amount of nitrous oxide at

the top level of the soil at each

spot once a month for 12

months. (How many total

measurements did they collect? Multiply 12 X 8 X 12.

How many measurements did

they collect for each type of

area? Divide the total measurements by the number of

types.) The scientists collected

samples of the gases that were

in the soil by placing an

instrument 2 centimeters into

the soil (Figure 6). (To find out

how many inches that is, multiply 2 X .393.) They took the

gaseous samples back to a laboratory. There they measured

now much nitrous oxide was

in the samples collected from

the top level of the soil.

Reflection

Section

• Why do you

think the scientists studied all

four types of

areas, instead of just studying young tropical forests?

• Do you think that the scientists found that more, the

same, or less nitrous oxide

was in the soil of young

tropical forests compared

with the soil in the pasture

being used by cattle? Why?

Results

The scientists discovered

that the amount of nitrous

oxide near the top of the soil

was different in the four types

of areas (Figure 7). The

amount of nitrous oxide is

low in old tropical forests.

Figure 6. Photograph of

equipment used to collect

nitrous oxide gas.

When forests are cleared and

used for pasture, the amount

of nitrous oxide near the soil’s

surface rises. As pastures are

abandoned and young forests

begin to grow, the amount of

nitrous oxide at the surface

drops to levels even below the

old forest levels. The scientists

think that water is the key to

understanding this pattern.

Because cattle hooves compact the soil, pasture land is

less able to absorb and drain

water. This condition encourages anaerobic bacterial activForest Active

pasture

Abandoned

pasture

Young forest

Trees

cut 

down

0

10

20

30

40

50

60

Nanograms of nitrous oxide

per square centimeter per hour

Figure 7. The amount of nitrous oxide found in the top

layer of the soil over the period of 1 hour in four types of

tropical land.

A nanogram is one-billionth of a gram. That’s not

very much weight! If you

took a frito (Fritos® brand

corn chip) and smashed it

into 1 billion pieces, each

piece would weight about

one nanogram. At the rate of

60 nanograms per hour,

about 60 grams of nitrous

oxide would be released in

an area 1 kilometer (.621

miles) square. In 1 day,

1,440 grams of nitrous oxide

would be released in that

square kilometer. How many

grams would be released in a

month? Although a

nanogram is not much

weight, you can see that over

time, nanograms of nitrous

oxide can add up!
30

ity on plant and animal wastes

near the soil’s surface. This

results in an increased amount

of nitrous oxide near the soil’s

surface, which is then released

into the atmosphere.

Reflection

Section

• What are two

things happening in tropical

pastures that

might be increasing the

amount of nitrous oxide

being released into the

atmosphere?

• The scientists measured the

amount of nitrous oxide 2

centimeters below the surface of the soil. Do you

think that same amount of

nitrous oxide is being

released into the atmosphere? Why or why not?

Implications

The scientists discovered

that nitrous oxide is being

released into the atmosphere

as a part of the nitrogen cycle.

They do not know, however,

what causes bacteria to turn

some ammonium ions into

nitrous oxide and others into

nitrogen. Nitrogen is a necessary gas in the atmosphere,

but nitrous oxide is a greenhouse gas that could cause

harm in great amounts. There

is still a lot to learn about

tropical soils and greenhouse

gases. This research shows

that humans impact the Earth

in ways that we may not be

able to see. By making decisions to manage land in different ways, we affect what

happens now and what will

happen in the future.

Reflection

Section

• What other

things do you

know about the

effect of greenhouse gases?

• Do you think that no matter where they are on the

planet, pastures cause more

nitrous oxide to be released

than would happen if the

land were a forest? Why or

why not?

Discovery

FACTivity

In this

FACTivity, you

will answer the

question: What

are the similarities between a

glass jar with soil and the

Earth’s atmosphere? The

method you will use to answer

this question is this: Get two

thermometers, a large clear

glass jar with a lid (be careful!), and 1 cup of dark soil.

Put the soil into the glass jar to

a depth of about 4 centimeters

(or about 2 inches). Put a thermometer upside down in the

jar, and close the lid. Turn the

glass jar over, so that the soil is

at the lid and the thermometer

is right side up. Place the jar in

the sunlight or under a highintensity bulb for 1 hour. Place

the second thermometer near

the jar.

At the end of the hour,

record the temperature outside of the jar using the second

thermometer. Record the temperature of the air inside of

the glass jar. Compare the two

temperatures. Then consider

the following questions:

• What part of Earth does the

air inside of the jar represent?

• What part of the Earth does

the glass represent?

• What part of the Earth does

the black dirt represent?

You will see that the soil is

heated by the light, which

then radiates the heat back

into the air where it is trapped

by the glass. You have created

a greenhouse effect! Now see

if you can answer the question

posed at the beginning of this

FACTivity.

This FACTivity was adapted from

Rodriguez, N., Kampen, A., and

Dufresne, M. (2000). It’s your planet: A

study of global warming. An interdisciplinary curriculum designed for middle

school students and their exploration of

global warming. Visit this Web site for

more information and activities:

http://www.classtech2000.com/archno2/S

essionB/Jesuit/gwarming.htm

From Keller, M. & Reiners, W. A. (1994).

Soil-atmosphere exchange of nitrous

oxide, nitric oxide, and methane under

secondary succession of pasture to forest

in the Atlantic lowlands of Costa Rica.

Global biogeochemical cycles, 8(4): 399-

409.
31

Meet Dr. Latta 

(Second from left):

I like being a scientist

because of the adventure of

working in wild places and the

challenge of trying to understand the ecology of birds. I

think it is important to protect

the diversity of living things

on the planet. 

Thinking About

Science

When scientists observe

what happens in

nature, they

often must create categories for things that

they observe. Categories help

them to classify their observations. Classifying is a way of

grouping similar things

together. This helps scientists

Glossary:

ecology (e kä luh je): The study of

the interactions of living things

with one another and with their

environment.

diversity (duh vür suh te): The

quality of being different or varied.

classify (klas uh fi): To arrange by

putting into groups according to

some system.

analyze (an uh liz): To study or

examine carefully.

summarize (sum uh riz): To make

a summary or a brief report. 

forage (for ij): Food for animals

usually taken by browsing or

grazing; the act of taking such

food.

adapt (uh dapt): To change so as

to fit new conditions.

mature (muh toor): Fully developed or fully grown.

species (spe sez): Groups of organisms that resemble one another in

appearance, behavior, chemical

processes, and genetic structure.

tropical (träp i käl): Of, in, or like

the tropics. The tropics is the

region of the Earth near the

Equator.

understory (un der stôr e):

Vegetation in a forest that is near

the ground.

migratory (mi gruh tôr e): Having

a characteristic of moving from

one place to another.

perch (purch): A tree branch that

a bird sits on.

population (päp yoo la shun): The

whole number of individuals of

the same type occupying an area.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

Tropical Birds and Their

Temporary Guests

Dr. Latta

Please Join Us

for Dinner:
32

analyze and summarize what

they discover. In this study, the

scientists wanted to understand the foraging behavior of

birds in the Dominican

Republic, which is part of an

island in the Caribbean (kä rib

e un) Sea (Figure 1). By analyzing and summarizing their

observations of bird behavior,

the scientists hoped to better

understand how different

birds find food.

Thinking 

About the

Environment

Even the same

kind of animals

might eat different kinds of foods. Over hundreds or thousands of years,

animals have adapted to different environments where

food is available. In this study,

the scientists wanted to study

the diets of birds. For example, some birds eat insects,

some eat berries, some eat

nectar (the sweet liquid from a

plant), and some eat seeds.

Some birds eat more than one

type of food. When different

kinds of birds eat different

kinds of foods, they can live in

the same area because they do

not have to compete for the

same food source. The same

thing is true for other kinds of

animals. Because of this, many

different kinds of animals can

live in the same area. 

Introduction

Pine forests are common in

the tropical Caribbean.

Usually, these pine forests also

have an understory of broadleafed trees. Broad-leafed trees

are trees with flat leaves. The

pine forests are the home of

many different kinds of birds.

Although scientists had studied the birds living in other

kinds of forests, they had not

studied the birds living in

tropical pine forests. Some

birds live in the pine forests all

year. These birds are called

residents (Figure 2). Other

birds are migratory, living in

Figure 1. Location of the Dominican Republic in the

Caribbean Sea.

Gulf of 

Mexico

Atlantic Ocean

Brazil

Costa

Rica

U.S. Virgin Islands

Puerto Rico

Dominican Republic

United States

Caribbean Sea

North

Diversity is an

important quality

for all mature

communities of

life. In a mature

natural environment, it is important to have a diversity of

species. This means that natural communities usually have

Thinking About Ecology

different kinds of animal and

plant species. It is also important for differences to occur in

the same kinds of animals and

plants. Think about the community that you live in. Your

family is different in many

ways than other families in

your neighborhood, and you

are different in many ways

from other people. In the natural world, there is a diversity

of other animals and plants. In

this study, the scientists were

interested in observing how

different birds eat different

foods. When there is a diversity of animals living in an area,

there is food available for all

of the animals.
33

the pine forests only during

the winter months. Migratory

birds fly from the colder north

to spend the winter in the

tropics, where it is warm. The

scientists in this study wanted

to learn what kind of food the

resident birds and migratory

birds eat during the winter

months.

Reflection

Section

• If you were

the scientist,

how would you

study what

birds eat in the pine forests?

• Do you think that different

birds eat different kinds of

foods in pine forests? Why

or why not?

Methods

First, the scientists selected

12 areas in a large pine forest.

These areas had trees that

were typical of the trees in the

larger pine forest surrounding

the 12 areas. After they selected an area, they drew an imaginary circle 16 meters in diameter (To find out how many

yards this is, multiply 16 by

1.09). Then they identified the

type of trees within the circles.

The scientists observed the

foraging behavior of birds by

walking through different sections of the pine forest each

day. They recorded the type of

bird and the bird behavior

they observed. To record how

each bird was getting its food,

the scientists classified the

birds’ foraging behavior into

five types (Table 1). They also

recorded four more things: 1)

the species of bird, 2) whether

the bird species was a resident

or a migrant, 3) whether the

bird was in the pines, in the

broad leaf area, or in the overlap of the two areas when it

was getting its food, and 4)

how each bird was getting its

food (Table 2 and Figure 3).

Figure 2. Research assistant with resident bird.

Table 1. Classifications of how birds captured their food.

Type of foraging Description of foraging behavior

behavior

Glean (glen) The bird remained on a perch and picked

a food item from another surface

Jump The bird jumped from a perch or any 

surface to get a food item

Probe The bird poked or pecked into a surface 

to get a food item from below the surface

Sally-Air The bird, while in the air, captured its

food item from the air

Sally-Surface The bird, while in the air, captured its 

food item from a surface
34

Reflection

Section

• Why do you

think the scientists selected

smaller areas to

identify trees instead of the

whole pine forest?

• How do you think the scientists knew that the trees

in the 12 areas were similar

to the trees in the larger

pine forest?

Results

Seventy-eight percent of the

birds foraged in an area

between 5 and 10 meters from

the ground (How many yards

is this? See the “Methods”

section above to find out how

to calculate this). This is the

height where the pine needles

and the broad leaves overlap.

Below 5 meters high and closer to the ground, the plants

are mostly broad leafed.

Above 10 meters, the plants

are mostly pine trees. Most of

the birds they observed in the

Caribbean pine forests were

residents and lived there all of

the time. The rest were migratory (Figure 4). Almost half of

all birds ate insects, and the

rest ate other kinds of foods

(Figure 5).

Even though most of the

birds ate insects, the scientists

found that the birds used a lot

of different foraging behaviors

to capture insects. For example, birds gleaned (or picked)

insects from leaf surfaces, they

caught insects while flying in

the air, and they picked insects

from surfaces while they were

flying. Not only did the birds

use different behaviors to capture insects, they usually captured insects from different

surfaces or areas. The scientists found that the pine forest,

with its broad-leafed understory, provided a variety of

food for many different kinds

of birds.

Figure 3. Forest with understory and broadleaf/pine overlap.

Ground R Yes No No Glean

warbler

Palm warbler M No Yes No Glean

Broad-billed R No Yes No Sally-Surface

Tody

Table 2. Example of how the scientists summarized their observations.

Species of

bird

Migrant (M)

or 

Resident (R)

Seen in

broadleafed

area most of

the time?

Seen in the

mixed

broadleaf/

pine area

most of the

time?

Seen in the

pine area

most of the

time?

Most often

used foraging

behavior
35

Figure 4. Percentage of permanent and migratory birds.

Figure 5. Food sources of birds in the Caribbean pine forest.

Reflection

Section

• Name two

examples of

diversity

described in this

article. Think about the

type of birds, the foods they

eat, how they get their food,

and the trees and plants

where they find food.

• In what ways did diversity

help the birds?

Implications

Throughout North

America, the number of songbird species is declining. Many

of those songbirds are

migrants that live in the tropics during the winter. This

study shows how migrant and

resident birds can live in the

same place at one time. With

this information, people can

make sure that resident and

migrant birds have the kinds

of places in the tropics that

they need to survive. By providing and protecting the

forests that different kinds of

birds need, people can help

reduce the declining numbers

of songbirds in the future.

Reflection

Section

• A healthy

food web is balanced between

food sources

and the animals that eat the

food. Think about insecteating birds. What would

happen to the population of

insects if the birds were not

there to eat the insects?

• How might protecting some

tropical forests help reduce

the declining number of

songbirds in North

America?

FACTivity

The scientists

found that birds

ate three kinds

of foods. These

foods were 1)

insects, 2) fruits and seeds,

and 3) nectar. They also found

that birds captured their food

in the air, and they gleaned,

jumped, and probed for their

food (See Table 1). In this

FACTivity, you will answer

the question: What kinds of

physical characteristics might

24%

Migrants

76%

Residents

49%

Insects

24%

Nectar

26%

Fruits 

and seeds
36

different birds have to help

them capture their food? Here

is the method that you will use

to explore the question: You

will need five large pieces of

plain white paper and

crayons. On each piece of

paper, design a bird that captures and eats different kinds

of foods. Pay careful attention

to the kind of beak, wings,

body shape, and legs the bird

should have. You may want to

design your birds in small

groups, discussing how each

part of the bird would help it

capture the right kind of food.

Design a—

• Bird that gleans and eats

seeds and fruit

• Bird that probes into flowers and eats nectar

• Bird that captures insects

while flying

• Bird that captures insects by

probing into trees

• Bird that jumps along the

ground and picks insects off

of the ground

After designing your birds,

you may want to do some

research on different birds to

learn about the shape of their

beaks, the size of their wings,

the shape of their body, and

the length of their legs. You

can explore different birds by

using a bird identification

book. Compare what you

have learned with your own

bird designs. What kind of

physical characteristics do

birds need to capture different

kinds of food? 

From Latta, S. C. and Wunderle, J. M. Jr.

(1998). The assemblage of birds foraging

in native West Indian pine (Pinus occidentalis) forests of the Dominican Republic

during the nonbreeding season.

Biotropica 30(4): 645-656.

Another resource: Bird Beak Buffet:

http://saveourlake.org/lessons/chpt2/act5.

htm.
Glossary:

complexity (käm plek suh te):

The state of being complicated

or having many related parts.

latitude (lat uh tood):

Distance north or south of the

Equator. 

diverse (di vürs): Differing

from one another.

biome (bi om): An area of

Earth with similar plants and

animals because of its climate.

climate (kli met): The average

condition of the weather at a

place.

adapt (uh dapt): To change so

as to fit new conditions.

dense (dens): Having its parts

close together.

land use history (land us hist

ür e): The story of how land

has been used by people over

time.

barren (bear en): Not producing crops, fruit, or many trees.

former (fôr mer): Earlier or in

the past.

native (na tiv): Naturally

occurring in an area.

habitat (ha ba tat):

Environment where a plant or

animal naturally grows and

lives.

consensus (kän sen sus):

Agreement of all or most.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

37

Meet Dr. Lugo:

I like being a scientist

because it brings me into contact with people who, like me,

are fascinated by the complexity of nature and have an

opportunity to try to figure it

out. Then we can put the

information to work for the

benefit of people.

Thinking About

Science

Scientists

observe natural

areas using

many different

techniques. One

way to observe natural areas

is through photographs. In

this article, the scientists wanted to learn about changes in

Some Things Will

Always Change:

Land Use in a Dry 

Tropical Forest

Dr. Lugo
38

an area of land over a long

period of time. They wanted

to know if trees were growing

or had been cut down, or if

roads or buildings had been

built over the years. To do

this, they used photographs of

an area taken between 1936

and 1989. The photographs

were taken from an airplane.

Photographs taken from an

airplane are called aerial (air e

ul) photographs. The aerial

photographs were compared

with each other to show

changes in how the land was

being used. By comparing

these photographs, the scientists were able to see the

changes that had occurred on

the land over a long period of

time.

Thinking 

About the

Environment

Tropical

forests are very

diverse.

Although most people know

about tropical rain forests,

they may not know about

tropical dry forests. Can you

guess what makes dry forests

different than rain forests? A

rain forest receives more rain

than a dry forest (Figure 1). A

rain forest can get up to 400

inches or 1,000 centimeters of

rain each year (What is the

average number of inches or

centimeters possible every

week? What is the average

number possible every day?).

A dry forest receives about 20

inches or 50 centimeters of

Figure 1. The type and amount of vegetation in the tropics is

dependent upon the amount of rainfall received. The amount

of rainfall also affects the type of vegetation growing at any

latitude.

Rain forest Dry forest Scrub

land

Savannah Desert

Wet Decreasing Rainfall Dry

Think about

the natural area

that surrounds

your community. Is it a forest,

a prairie or

grassland, or a

desert? The Earth’s surface is

diverse. Besides having

forests, grasslands, and

deserts, there are also different types of forests, grasslands, and deserts! Have you

ever thought about what

determines these different

types of biomes across the

Earth’s surface? The answer

is that areas of the Earth have

different climates. The climate of an area is determined

mainly by its average temperature and average amount of

Thinking About Ecology

rainfall. The amount of rainfall is the most important factor limiting plant growth in

an area. The plants growing

in drier areas are adapted to

lower rainfall. Drier areas

often have fewer plants, and

the plants do not grow as

densely as plants in areas

with a lot of rain. In this

study, the scientists studied a

dry tropical forest. The dry

tropical forest is the result of

the rain shadow effect

(Figure 2). Over thousands of

years, this forest has adapted

to its dry conditions.

Although it is still a forest, its

trees are shorter and their

leaves are not as large as trees

in the nearby rain forest

(Figure 3).
39

rain each year (What is the

average number of inches or

centimeters possible every

week?). For this reason, the

types of plants and animals

living in dry forests are different from those living in rain

forests. Trees and animals that

are adapted to drier conditions live in tropical dry

forests. In this article, you will

learn about a dry forest in

Puerto Rico. (Just for fun –

What is the average amount of

rainfall your town or area

receives each year?)

Introduction

Guanica (gwa ne kä) Forest

is a tropical dry forest in the

southwest corner of Puerto

Rico (Figure 4). In 1981, the

United Nations recognized it

for being one of the best

examples of a dry tropical forest. Before 1919, Guanica

Forest was used for agriculture and other human activities. In 1919, Guanica Forest

became legally protected from

most human development.

Since 1919, more acres have

been added to Guanica Forest.

Land that had been used in the

past for human activities is

now inside the forest boundaries. It is mostly protected

from development inside the

boundaries. The land in and

around Guanica Forest has

been changing. The scientists

in this study wanted to know

how Guanica Forest and the

land around it has changed

over the years. For example,

they wanted to know whether

the trees have been growing

back where crops used to be.

Figure 2. The rain shadow causes some areas to be drier than

others.

Dry forest

Rain forest

Prevailing

wind

Moist

air

rises

Clouds form and

 release moisture 

as rain

Dry air

Rain shadow

Figure 3. Guanica Forest, a dry forest in Puerto Rico.

San Juan

Dry forest Guanica Forest

Direction of

prevailing

wind 

Caribbean

National 

Forest

Cental Mountains

North

Rain forest

Figure 4 – Location of Guanica Forest in Puerto Rico.
40

They were interested in the

land use history of Guanica

Forest and the surrounding

land. You have probably

learned about the history of

your country, state, or commonwealth. Land use history

is like your country’s, state’s,

or commonwealth’s history,

except that it is a history of

how people used the land. 

Reflection

Section

• Why do you

think it is

important to

learn the land

use history of an area?

• Think about the land that

your home or school was

built on. What do you think

the land was used for, or

what it looked like, before

your home or school was

built there?

Methods

Based on aerial photographs

taken in 1936, 1950, 1963,

1983, and 1989, the scientists

determined how the land was

being used over the years.

They looked at the photographs of land within the

Guanica Forest and outside of

the forest boundaries. They

saw that land had been used

for buildings, roads, and agriculture. They also saw the natural areas of the forest,

including trees, wetlands, and

barren land. The scientists calculated the percentage of the

forest that was in each category. The categories included:

• Urban land (with buildings,

parking lots, roads, and

other structures)

• Agricultural land

• Water

• Forests 

• Wetlands

• Barren land

Reflection

Section

• Why do you

think the scientists created categories of land

use?

• Do you think that the

amount of agricultural land

within Guanica Forest

increased or decreased over

the years? Why?

• Do you think that the

amount of urban land outside Guanica Forest

increased or decreased over

the years? Why?

Results

The scientists found that

land use had changed over the

years. Although the portion of

urban land within the forest

increased much more than

outside of the forest, there

were many more hectares of

urban land outside of the forest (See Figures 5 and 6). The

amount of agricultural land

within the forest decreased

much more than outside of the

forest. Overall, urban land

increased and agricultural

land decreased, while the

amount of forested land

stayed about the same. Figure

7 shows some of the actual

photographs used by the scientists.

Figure 5. Relative amount of change in land use over time

within and outside of Guanica Forest. Percent change in numbers of hectares

Percent of increase

in land use (above the line)

Within

forest

Outside

forest

Within

forest

Outside

forest

Within

forest

Outside

forest

Percent of decrease

in land use (below the line)

 Forested

0 1.5

-2

-40

5

36

Urban Agricultural
41

Figure 6. Actual change in number of hectares by land use type

within and outside of Guanica Forest. A hectare is a metric

measure equal to 2.47 acres. Actual change in numbers of hectares

Within

forest

Outside

forest

 

Within

forest

Outside

forest

Within

forest

Outside

forest

 Forested

136

699

3366

1795

3189 3353

2211

3502

151 .26 9.46 4 0

500

1000

1500

2000

2500

3000

3500

4000

Urban Agricultural

1936 – 1989 

Reflection

Section

• Does the land

around your

home or school

look more like a

forest or is it an urban area?

What land use changes, if

any, are taking place

around your home or

school? 

• Why do you think there is

more urban land outside of

the Guanica Forest boundary compared with inside

the boundary?

Implications

The scientists found that

land use outside of Guanica

Forest was changing quickly.

Urban uses, such as buildings

and roads, were replacing the

native forest. When native

forests are removed, animals

that do not naturally live in

the forest can move into the

area. These non-native animals might gradually move

close to or over the boundary

of Guanica Forest. Once they

do that, they will compete

with the native animals for

food and habitat. An example

in North America is the

European starling, a bird that

competes with native

American songbirds. The scientists suggest that some of

the land surrounding the forest should remain mostly

forested with limited buildings

or other construction (Figure

8). That way, non-native animals will not be as likely to

move into Guanica Forest, Figure 7. Aerial photographs showing land use changes over

time in an area outside of Guanica Forest.
42

and the forest’s native animals

will be protected.

Reflection

Section

• Do you think

it is important

to protect the

native animals

in Guanica Forest? Why or

why not?

• How could the scientists

find out if non-native animals are competing with

native animals for food?

FACTivity

In this

FACTivity, you

will answer the

question:

Should an area

of land outside of the Guanica

Forest boundary be closed to

land development? The

method you will use to answer

this question is by holding

class discussions. Divide your

class into three (or five) equalsized groups of about 6 students each. One or two groups

will take the position that land

outside of the immediate forest boundary can and should

be developed for human uses.

Another group, or two other

groups, will take the position

that an area of land outside of

the forest should be left undeveloped and natural. Each of

these groups will develop

three arguments in support of

their position. You will need

to discuss the issue within

your group before developing

your arguments. Take about

20 minutes to develop your

arguments either for or

against development. You

should consider the advantages of development to people, as well as the

disadvantages of development

to the animals and plants

within the forest. Remember

that Guanica Forest has been

recognized by the United

Nations as one of the best

examples of a dry tropical forest. Once you have developed

your arguments, each group

will present them orally to the

remaining group while the

whole class listens. The

remaining group must decide

whether to allow development

close to the forest boundary,

or whether to create an area

around the forest that is

closed to human development.

The remaining group should

spend time in advance planning how they will make their

decision. Will they vote, or

will they try to reach consensus? Once a decision is made,

the remaining group must

explain to the class how and

why they made their decision.

From Lugo, Ariel E.; Ramos, Olga;

Molina, Sandra; and Scatena, F. N.

(1996). A fifty-three year record of land

use change in the Guanica Forest

Biosphere Reserve and Its vicinity. Rio

Piedras, PR: Institute of Tropical Forestry:

USDA Forest Service

For information on dry tropical forests,

visit www.mobot.org/gradstudents/

olson/drytropics.html

Guanica Forest

Proposed

protected

area

Developed

area outside

of forest

Figure 8. Example of the proposed protected area around

Guanica forest.
Glossary:

scat (skat): Animal fecal dropping; animal waste.

sample (sam pool): A part or

piece that shows what the

whole group or thing is like.

represent (rep re zent): To be

an example of.

mine (min): To take coal, ores,

or other minerals from the

Earth by digging a large hole.

natural resources (na cha rôl

re sôr sez): A supply of something in nature that takes care

of a human need, such as oil.

disperse (di spürs): To scatter

or spread in all directions. 

defecate (def uh kat): To get

rid of waste matter from the

bowels.

infertile (in fürt l): Not able to

produce crops, fruit, or offspring.

complex (käm pleks):

Complicated and having many

different relationships.

native (na tiv): Naturally

occurring in an area.

mammal (mam ul): Any warm

blooded animal with a backbone and glands to produce

milk for feeding their young.

diversity (duh vür suh te): The

quality of being different or

varied.

germination (jür mi na shun):

The act of sprouting or beginning to grow.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

43

Meet Dr. Parrotta: 

I like being a scientist

because I get to explore and

learn about the natural world.

Nature is like a bottomless

treasure chest, full of surprises

and mysteries. It is fun to try

to unravel those mysteries. It

is important for humans to

find ways to use the gifts of

nature without damaging the

environment, and also to

repair the damage that we

have already caused.

The Trees Have

Gone Batty!

How Bat Scat Helped

Restore a Tropical Forest

Dr. Parrotta
44

Thinking About

Science

When scientists want to

learn what is

happening to a

particular piece

of land, they usually go out to

that place to study what is

happening. Because they usually cannot study every inch of

a large piece of land, scientists

select small areas, or samples

of land, to study. They assume

that the samples represent the

rest of the land in which they

are interested. This same idea

is used in most scientific studies. For example, when scientists want to know what the

public thinks about something, they cannot ask everyone. They ask a sample of

people that the scientists

believe can represent everyone. When was the last time

you used a sample? When you

eat a potato chip from a bag,

do you think the rest of the

chips in the bag will taste like

the first one? Is the first potato

chip a sample? Why or why

not?

Thinking 

About the

Environment

Humans use

land for many

things.

Sometimes, they want to use

land temporarily. In this case,

they disturb the land, then

they let it grow naturally

again. An example of this is

when humans mine the land

for minerals and other natural

resources. Can you think of

other examples of using natural resources that cause a temporary disturbance to the

land? Sometimes when the

land is disturbed, it cannot

restore itself back to its original condition without help

from humans and other animals. In this study, the scientists wanted to know whether

humans and other animals

were helping a tropical forest

to restore itself after it had

been disturbed by a mining

operation.

Introduction

The scientists in this study

were interested in knowing

whether humans and other

animals can help disturbed

areas of land to become

healthy ecosystems again. A

mining company in Brazil

(Figure 1) asked the scientists

to restore a tropical forest on

their old mining site. The original tropical forest had been

cut down to mine the area for

Jamaican Fruit bat. 

An ecosystem is

made up of all of

the plants, animals, bacteria,

and nonliving

things that occur

in a particular

environment. When an

ecosystem is healthy, the

plants, animals, and bacteria

depend on each other and on

the nonliving environment to

Thinking About Ecology

live. Some bats, for example,

need to eat the fruit of plants

to live. When bats eat fruit,

they help to disperse the seeds

of plants. Can you think of

how they might do this? When

they eat the fruit, they cannot

digest the seeds. Because they

cannot digest the seeds, they

either defecate or spit out the

seeds. They usually defecate

some time after they have

eaten the fruit. By that time,

they may have flown away

from the tree. The seeds fall

onto the ground and begin to

grow. You can see that the

trees help the bats by providing food, and the bats help the

trees by dispersing seeds. The

bats and the trees depend on

each other. They are part of a

healthy ecosystem.
45

bauxite (bäk sit) or aluminum

ore. Bauxite is the main compound used in making aluminum. 

Mining disturbs the land by

removing the trees and the top

layer of soil, or topsoil (Figure

2). This causes the land to be

infertile. Since there are no

trees left on the land, there is

no source of seeds to help

trees grow again. Although

the scientists could plant some

trees, they would never be

able to create the kind of complex ecosystem that includes

all of the original plants and

animals. The scientists wanted

to know whether they could

set up the conditions so that

plants and animals could

come in from outside the

mined area without further

human help. Then, the new

plants and animals might help

the land to become healthy

again.

Reflection

Section

• If you were

the scientist,

what would you

tell people you

are trying to do through

your research on the old

mining site?

• Although trees are not

mobile, their seeds can

spread to new areas and

grow. Can you think of two

ways that a tree’s seeds can

move from place to place?

Methods

The scientists covered the

bare ground with new topsoil

and planted 70 different kinds

of native trees. Although this

seems like a lot of different

kinds of trees, it is not a lot for

a tropical forest in Brazil.

Brazilian tropical forests can

have thousands of different

kinds of trees! Then, the scientists waited 10 years for the

trees to grow. At the end of 10

years, the scientists selected 32

sample areas to study. The

areas they studied were circles, each 10 meters in diameter (To find out how many

yards this is, multiply 10 times

1.09). 

The scientists went into

these sample areas and identified the kind of trees growing

Mining area

Brazil

Amazon

River

Brazil is 

slightly smaller

than the U.S.

North

Figure 1. Location of the study area in Brazil.

Figure 2. The mining site.
46

in each circle. They also

counted how many of each

kind of tree was growing. The

scientists determined which of

the trees were over 10 years

old. The scientists then knew

that the rest of the trees had

grown on their own over the

last 10 years. The scientists

recorded the number and kind

of birds and mammals they

found within the sample

areas. They collected all of

this information by observing

and carefully recording everything that they saw.

Reflection

Section

• Why did the

scientists want

to identify

which trees they

had planted 10 years ago

and which trees had grown

on their own?

• Why do you think that the

scientists wanted to know

the kind and number of

birds and mammals within

the sample areas?

Results

The scientists found that the

numbers and kinds of new

trees growing in the sample

areas were different, depending on where the sample area

was located. The sample areas

that were close to the outer

edge of the mined area, near

existing tropical forests, had a

greater diversity of tree species

(Figure 3). The scientists

counted 125 different kinds of

trees. They also had more

trees growing in them than the

sample areas near the center

of the mined area. The scientists found 45 different kinds

of birds in the sample areas.

Of these, less than half would

have been able to successfully

disperse seeds. That is because

most of the birds ate insects or

nectar, or would have been

able to digest the seeds.

(Think of parrots and parakeets. They eat and digest

seeds, so they would not be

good at dispersing seeds!) 

Average tree diversity (variety of tree species) in planted

areas at different distances from the existing rain forest

0 100 200 300 400 500 600 700

Distance of study sites from rain forest edge (meters)

Diversity (variety) of tree species

Extremely diverse

Highly diverse

Moderately diverse

Limited in diversity

Very limited in diversity

Figure 3. The amount of tree diversity at different distances

from the rain forest.

Figure 4. The relationship of the planted forest to the existing

rain forest.

Rain Forest

Rain

Forest

Planted Trees

(Old mining

area)

Fewer bats

More bats
47

The scientists found that a

lot of different kinds of mammals lived in the sample areas.

The most numerous kind of

mammal found in the sample

plots was fruit bats. There

were more bats in the sample

areas closer to the edge of the

mined area than in sample

areas closer to the center

(Figure 4). Although there was

not a great diversity of different kinds of bats, there was a

large number of fruit bats living in the sample areas.

Figures 5 and 6 show how

vegetation began growing on

the old mining site.

Reflection

Section

• Where the

scientists found

a diversity of

new kinds of

trees growing, they also

found a large number of

fruit bats. If you were the

scientist, what would you

conclude from this information?

• Why do you think that

there were more bats and

more kinds of new trees

near the edges of the old

mining area, and fewer bats

and fewer kinds of trees

near the center?

Implications

The scientists concluded

that by planting a variety of

trees on an old mining site,

nature can take over and help

the land to become a healthy

ecosystem. The scientists

believe that by planting the

trees, they started a process

that might have taken decades

or centuries to happen on its

own. Once they planted the

trees, animals were able to

move into the young tropical

forest. When bats arrived, they

defecated seeds eaten from

fruit trees outside of the mined

area. The bats helped to make

the young tropical forest more

diverse, which provided more

food for other kinds of animals. After humans have disturbed land, they might have

to help restore the environment to a healthy condition.

Usually if humans lend a helping hand in the beginning,

nature can take over the job.

Reflection

Section

• Do you think

that it is best to

let nature take

over the job of

restoring an ecosystem to a

Figures 5 and 6. The recovering mining site. The roads you can

see throughout the area are for transporting soil and seedlings.

Eventually, these roads will grow naturally with vegetation

and the entire area will become a forest again.
48

Table to be completed weekly. You will create four of these,

one for each week.

Date: Height of

bean 1

Height of

bean 2

Height of

bean 3

Average

height of

the three

beans

School

yard #1

School

yard #2

Manure

#1

Manure

#2

Summary table. Average height of all bean plants over 4 weeks

Date: Average

height of

beans 

Week 1

Average

height of

beans

Week 2

Average

height of

beans

Week 3

Average

height of

beans

Week 4

School

yard #1

School

yard #2

Manure

#1

Manure

#2

healthy condition? Why or

why not?

• Can you think of other

ways that plants and animals depend on each other

in the natural environment?

What do trees and other

plants provide to animals?

What do animals provide to

plants?

FACTivity

In this article,

you learned

how bat scat

helped trees to

reproduce. For

this FACTivity, you will be

answering the question: What

other benefits does animal

scat offer to trees and plants?

To do the FACTivity, you will

need:

• Four 4-inch plant pots with

saucers

• A bucket of soil dug from

your school yard—be sure

to break up any clumps and

remove any grass or plants,

including plant roots and

rocks or pebbles

• An extra bucket for mixing

soil

• A small bag of manure

(may be purchased at a garden shop) or a small bag of

worm castings (may be purchased at a garden shop)

• A bag of bean seeds (may be

purchased at a garden shop)

• A cup or a small shovel

• Masking tape and marker

• Ruler or other type of measuring stick

Before you start, you need

to know what manure and

worm castings are. Can you

guess? Both are animal

wastes. Manure is the waste

from animals like cows and

horses. You should be able to

guess which animal produces

worm castings! 

The method you will use is

this: Fill two of the pots with

the soil from your school yard

to within a few centimeters (or

inches) from the top. Be sure

to wear rubber gloves when

you handle the soil! Label the

pots “school yard” with

masking tape and the marker.

Take a shovelful or cupful of

soil from your school yard

bucket and place it in the

extra bucket. Mix in a shovelful or cupful of manure OR

worm castings and mix well

with the cup or the shovel.

Mix enough schoolyard soil
49

and manure (or worm castings) to fill the next two pots

to within a few centimeters (or

inches) of the top. Label the

pots “manure” or “worm

castings” using the masking

tape and marker. Make three

thumbprints about 2 centimeters deep (or about 1 inch

deep) in each pot. Space the

thumbprints so that they form

a triangle. Place one seed in

each thumbprint. Cover the

seeds with soil from the pot

and gently water. 

Put the pots in a sunny window and keep the soil moist.

Do not over water! Observe

the pots every day for 4

weeks. You can use the chart

on the previous page as an

example. At the end of each

week, measure the growth of

the beans. Keep a weekly

record of your observations.

You will need to calculate the

average height of the beans in

each pot. To calculate the

average, add the height of the

three bean plants and divide

the total height by three. You

can easily compare your data

by creating a bar chart (or histogram). To learn how to create a bar chart, see the

example at the bottom right.

Which kind of soil is best for

seed germination and growth?

Think about what you learned

in this article. Bats helped

trees to reproduce by spreading tree seeds through bat

scat. What other benefits does

animal scat offer to plants?

This experiment should help

you answer this question.

Sample bar chart: Average height of beans over 4 weeks.

(Create this bar chart from the summary table on the

previous page. See the example that follows.)

5

4

3

2

1

0

Average height of beans in centimeters or inches 

Week 1 2 3 4

School yard

#1

1 2 3 4 1 2 3 4 1 2 3 4

School yard

#2

Manure

#1

Manure

#2

Example bar chart: Average height of beans over 4 weeks.

5

4

3

2

1

0

Average height of beans in inches 

Week 1 2 3 4

School yard

#1

1 2 3 4 1 2 3 4 1 2 3 4

School yard

#2

Manure

#1

Manure

#2

From Parrotta, John A., Knowles, Oliver Henry, and Wunderle, Joseph M. Jr. (1997).

Development of floristic diversity in 10-year-old restoration forests on a bauxite mined

site in Amazonia. Forestry Ecology and Management. 99: 21-42.
50

Meet Dr. Francis:

I like being a scientist

because I have an enormous

curiosity about nature, and

science gives me an opportunity to be personally involved in

the unraveling of its mysteries.

Thinking About

Science 

When scientists study something, they

usually like to

plan their

experiments in advance. They

do this so that they have more

control over the experiment.

When scientists study natural

I’ll Huff and I’ll Puff and

I’ll Blow Your Trees Down!

How Wind Speed Affected Trees 

During Hurricane Hugo

Dr. Francis
51

disasters, they cannot always

plan their experiments. This is

because people do not always

know when or where a natural disaster will occur. Natural

disasters include events like

hurricanes, tornadoes, landslides, volcanoes, and floods.

The scientists in this study

wanted to study the effects of

a hurricane. As part of their

research, they needed to know

the wind speed of the hurricane as it blew across different

places. Because they did not

know where or when the hurricane would blow, they had

to rely on measurements made

by other people. You can see

that scientists sometimes have

to use data collected by other

people. Can you think of

examples of when you have to

do the same thing? (Hint:

Think about the weather forecast or about medical information. What other different

kinds of information do you

use that are collected by other

people?)

Thinking 

About the

Environment

In nature,

some events are

cyclical. The

seasons are an example of a

cyclical natural event because

they repeat themselves every

year. Day and night are also

examples of a cyclical event

because they are repeated

daily. Can you think of other

cyclical events that are predictable? Cyclical events happen in nature all of the time.

Some cycles are not as exact as

other cycles. Hurricanes, for

example, are cyclical because

they occur in the tropics every

year between June and

November. However, we do

not know exactly what day a

hurricane will occur during

that time. Can you think of

other cyclical events that are

not as easily predictable?

Glossary:

natural disaster (nach ur ul

di zas tür): A natural happening that causes much damage

or suffering.

data (da tuh): Factual or

measurement information.

cyclical (sik lik ool): Like a

cycle; when events continue

to happen in the same order.

predictable (pre dik tüh bül):

Easy to tell what one thinks

will happen in the future.

feedback (fed bak): A

response, often one that sets

a process in motion. The

response can then also be

affected by the process it set

in motion.

species (spe sez): Groups of

organisms that resemble one

another in appearance,

behavior, chemical processes,

and genetic structure.

compacted (käm pak ted):

Closely and firmly packed

together.

analyze (an ä liz): To study

or examine carefully.

modify (mäd uh fi) To make

a small change in.

Pronunciation Guide

a as in ape

ä as in car

e as in me

i as in ice

o as in go

ô as in for

u as in use

ü as in fur

oo as in tool

ng as in sing

Accented syllables are in bold.

Thinking About Ecology

In the natural

world, feedback and 

control are

important principles to understand.

Feedback is a response to

something that occurs, and

its result is usually some

kind of control on the system. Feedback can be positive as when it accelerates

(ak sel ür ats) a process, or

negative when it slows

down a process. In this

study of hurricane damage,

feedback was provided by

trees. In response to the hurricane’s strong winds, the

trees shed their leaves. Once

the trees lost their leaves,

the hurricane’s winds could

no longer do much more

damage to the trees. This

provided some control by

limiting how much more

damage the wind could do

to the trees. Can you think

of examples of feedback

and control in your own

body?
52

Introduction

When a hurricane occurs, a

lot of damage can be done to

buildings and other structures.

One of the most visible types

of damage occurs to trees.

When hurricanes occur, trees

lose most of their leaves. The

scientists in this study wanted

to know more about the

extent of damage to trees following a tropical hurricane in

Puerto Rico (Figure 1). When

Hurricane Hugo occurred in

September of 1989, the scientists decided to study the damage done to the trees in Puerto

Rico (Figure 2). Hurricane

Hugo was a category 4 hurricane (Table 1). 

Caribbean hurricanes are

formed at the West Africa

coast. Atmospheric conditions

push hurricanes to the islands

in the Caribbean Sea and up

the east coast of the United

States (Figure 3).

Reflection

Section

• The scientists

knew that overall, Hurricane

Hugo had

winds of between 131-155

mph (210-249 kph). Why

do you think they wanted

to measure wind speed at

different places in Puerto

Rico?

• Do you think that hurricane

damage to a tree with leaves

is greater than to a tree without leaves? Why or why not?

Method

The scientists wanted to

understand how much tree

damage was done by the 

North

Gulf of 

Mexico

Atlantic Ocean

Brazil

Costa

Rica

U.S. Virgin Islands

Puerto Rico

Dominican Republic

United States

Caribbean Sea

Figure 1. Location of Puerto Rico

Figure 2. Tree damage following Hurricane Hugo. 

Category Wind speed

1 74-95 mph/

119-153 kph

2 96-110 mph/

154-177 kph

3 111-130 mph/

178-209 kph

4 131-155 mph/

210-249 kph

5 156+ mph/

250+ kph

Table 1. Saffir-Simpson

Hurricane Scale

Note: If you want to convert miles per

hour (mph) to kilometers per hour

(kph), multiply the number of mph X

1.61. To convert from kph to mph,

multiply the number of kph X .621.
53

hurricane at different wind

speeds. To do this, they had to

study the trees in areas where

wind instruments were placed

before Hurricane Hugo

occurred. The scientists

observed 81 different species

of trees in 18 different areas.

They observed damage to

1,226 trees. The scientists put

each of the trees in one of five

categories, based on how

much damage they observed.

They then compared palm

trees with broad-leafed trees,

to determine whether one kind

of tree had more damage than

the other (Figure 4). For the

palms and the broad-leafed

trees, they compared the

amount of damage with the

wind speed.

Reflection

Section

• Why did the

scientists study

trees that were

located near

wind instruments?

• Look at the leaf shapes in

Figure 4. Do you think the

scientists found a difference

in damage to trees with different kinds of leaves? Why

or why not?

Results

The scientists found out

many things about the harm

done to trees during

Hurricane Hugo. First, they

found that larger trees had

more damage than smaller

trees. They also found that

palm trees had less damage

than broad-leafed trees. They

also discovered that after

broad-leafed trees lose their

leaves to the wind, there is less

damage to the trees. Up to a

point, the hurricane’s winds

continued to do more damage

as they blew faster. However,

when the wind blew over 100

kph (multiply 100 by .621 to

find out how fast this is in

miles per hour), it did not do

much more damage (Figure

5). By then, most of the leaves

had blown off of the trees.

Reflection

Section

• Why do you

think the palm

trees had less

damage than

the broad-leafed trees?

Puerto

Rico

...and may become

hurricanes in the

Caribbean and along 

the east coast of North America 

Storms form

off of the

African coast...

Africa

South

America

North

America

Atlantic

Ocean

North

Figure 3. Tropical hurricanes in eastern North America begin

as tropical storms on the west African coast.

Figure 4. Palm and broad-leafed trees.
54

• With your class, discuss

whether anyone has ever

seen a tree that has been

blown over or broken by

the wind. How tall was the

tree? How big was its

trunk? Are there any similarities among the damaged

trees seen by your classmates? What are the similarities? 

Implications

Where hurricanes can occur

often in an area, people must

be careful where they plant

trees or locate their homes and

other buildings. Trees should

only be planted in deep, welldrained soils that are not compacted. If a hurricane is

coming, a broad-leafed tree

might be protected by cutting

off its leaves. Hurricanes are

cyclical natural events in the

Caribbean and the Eastern

United States. Because they

cannot be controlled, people

must learn to live with them. 

Reflection

Section

• Should people who live in

areas where

hurricanes

occur build their homes

next to big broad-leafed

trees? Why or why not?

• Hurricanes might cause

damage to buildings and

some trees. Do you think

there are any natural

advantages to hurricanes?

Why or why not? If you

think there are advantages,

what might they be?

FACTivity:

The scientists

in this study

had to rely on

instruments

Figure 5. Most of the damage to trees happens when winds

blow up to 100 kilometers per hour.

0 50 100 150 200 250 300 350

100

75

50

25

0

Wind speed (kilometers per hour)

Percentage of damaged trees

that were near, but not at, their

study areas. They also had to

rely on instruments that were

maintained by other people. In

this FACTivity, you will

answer the question: Can

weather measurements made

by other people in distant

places be accurate for another

area or situation? We use such

measurements every day, such

as when we hear local reports

of the current temperature.

This FACTivity will help you

think about whether you can

trust weather measurements

that are not made exactly

where you are located. The

method you will use to answer

the question is as follows: Get

an outdoor thermometer and

place it outside in the shade.

Observe and record the temperature every afternoon, for a

week, at the same time of the

day. You can use the example

on the next page as a guide.

Before beginning your observations, find another source

for the current temperature in

your city or town. You may be

able to call a special phone

number, the local airport, a

local radio station, search the

internet, or use a weather

radio. Record the reported

temperature for the same time

(or within 1 hour of the same

time) as your observed temperature, using the chart on the

next page as a guide. To help

you analyze the differences

between observed and reported temperatures, you will create a bar chart from your table

(See an example of a bar chart

at the end of the first

FACTivity). Now compare the
55

Sample chart for recording temperatures.

Observed 

Temperature

(F or C)

Reported 

Temperature

(F or C)

Monday Tuesday Wednesday Thursday Friday

Observed Reported Observed Reported Observed Reported Observed Reported Observed Reported

Sample bar chart (histogram) for analyzing temperatures.

Temperature (Specify F or C) in one degree increments

Monday Tuesday Wednesday Thursday Friday

temperature you observed on

your thermometer with the

reported temperature. Are the

two daily temperatures the

same or different? Do you

think the reported temperature is an adequate measure of

the temperature at your

school? Why or why not?

You may also record the

observed and reported temperature at different times

throughout the day for the

week. The more observations

you have to compare, the

more accurate your findings

will be. If your findings are

more accurate, will you have

more or less confidence in

your answer to the FACTivity

question? Why?

Convert your temperatures

from Centigrade to Fahrenheit

or from Fahrenheit to

Centigrade. Then make a new

bar chart using the converted

measurements. Compare the

bar charts. How are they similar? How are they different?

This is how you do the conversion: 

If you know Fahrenheit:

Subtract 32 from the temperature, then multiply by .55

If you know Centigrade:

Multiply the temperature by

1.8, then add 32

Observed Reported Observed Reported Observed Reported Observed Reported Observed Reported

Example of a bar chart

Temperature in °F

Monday Tuesday Wednesday Thursday Friday

66°

59°

60°

61°

62°

63°

64°

65°
56

Speed in mph Name Common Effects

0-1 Calm Smoke rises straight up

1-3 Light air Smoke drifts

4-7 Light breeze Feel it on your face and see leaves rustle

8-12 Gentle breeze Leaves on the move and flags wave

13-18 Moderate wind Dust, leaves, and paper fly. Branches move

19-24 Fresh wind Small trees sway

25-31 Strong wind Large branches move. Whistles through wires

32-38 Gale Trees sway. Hard to walk

39-46 Fresh gale Twigs snap off trees

47-54 Strong gale Branches break. Shingles blow loose

55-63 Storm Trees break. Buildings damaged

64-72 Violent storm Widespread damage

73-Higher Hurricane Extreme damage

From: Cox, J. D. (2000). Weather for dummies. Foster City, CA: IDG Books, p. 90.

Another

FACTivity!

Want to measure wind speed

the old-fashioned way?

Here’s a modified version of a

scale developed to help British

sailors estimate wind speed in

the days before wind instruments were available. Why do

you think the British sailors

could not have used this scale,

the way it is presented here?

(Hint: Where would British

sailors be when they needed to

estimate wind speed?) What

part of the scale has been

modified?

From Francis, John K. and Gillespie, Andrew J. R. (1993). Relating gust speed to tree damage in Hurricane Hugo, 1989.

Journal of Arboriculture, 19(6): 368-373.
Which National Science Education Standards* Can Be Met by the Natural Inquirer?

Science Education

Standards* 

Science as Inquiry

Abilities Necessary for 

Scientific Inquiry XXXXXXXX

Physical Science

Properties of Matter X

Transfer of Energy XX X

Life Science

Structure & Function of 

Living Systems X XXX

Reproduction & Heredity X X

Regulation & Behavior XX X

Populations & Ecosystems XXXXX XX

Organism Diversity & 

Adaptation X XX

Earth & Space Science

Structure of Earth System X XXX

Earth in the Solar System X X

Science & Technology

Nature of Technological 

Solutions X X

Tradeoffs of Technology X

Benefits and Consequences X X

Science–Personal & 

Social Perspectives

Personal Health X X

Natural Hazards X X

Risks & Benefits XXX

Science & Technology in Society X X

History & Nature of Science

Science as a Human Endeavor XXX

Nature of Science X X Swimming Upstream Without a Ladder Leaf Me Alone! Oooooh! That’s Growth! It’s a Gas! Please Join Us for Dinner

Some Things WillAlways ChangeThe Trees AreGoing Batty!I’ll Huff and I’ll Puffand I’ll Blow YourTrees Down!

*National Research Council, Content Standards, Grades 5-8

Articles
The Forest Service is part of

the Federal Government. It is

made up of thousands of people who care for the Nation’s

forest land. The Forest

Service manages over 150

national forests and almost

20 national grasslands. These

are large areas of trees,

streams, and grasslands.

National forests are similar in

some ways to national parks.

Both national forests and

national parks provide clean

water, homes for animals that

live in the wild, and places for

people to do fun things in the

outdoors. National forests

also provide resources for

people to use, such as trees

for lumber, minerals, and

plants used for medicines.

Some people in the Forest

Service are scientists, whose

work is presented in this journal. Forest Service scientists

work to solve problems and

provide new information

about natural resources so

that we can make sure our

natural environment is

healthy, now and into the

future.

The U.S. Department of

Agriculture (USDA) prohibits discrimination in all its programs and

activities on the basis of race, color,

national origin, sex, religion, age,

disability, political beliefs, sexual

orientation, or marital or family

status. (Not all prohibited bases

apply to all programs.) Persons

with disabilities who require alternative means for communication

of program information (Braille,

large print, audiotape, etc.) should

contact USDA’s TARGET Center

at (202) 720-2600 (voice and

TDD).

To file a complaint of discrimination, write USDA, Director,

Office of Civil Rights, Room 326-

W, Whitten Building, 1400

Independence Avenue, SW,

Washington, D.C. 20250-9410 or

call (202) 720-5964 (voice and

TDD). USDA is an equal opportunity provider and employer.

What Is the Forest Service?

United States Department of Agriculture

Forest Service

Visit these Web sites for more information:

USDA Forest Service:

http://www.fs.fed.us

The Natural Inquirer:

http://www.naturalinquirer.usda.gov

Conservation Education:

http://www.fs.fed.us/outdoors/nrce/

USDA Kid’s Page:

http://www.usda.gov/news/usdakids/index.

html

NatureWatch:

http://www.fs.fed.us/outdoors/naturewatch/

default.htm

Woodsy Owl:

http://www.fs.fed.us/spf/woodsy

Smokey Bear:

http://www.smokeybear.com

National Forest Information:

http://www.fs.fed.us/links/forests/html

National Forest Recreation:

http://www.fs.fed.us/recreation/recreation.

html

International Institute of Tropical Forestry:

http://www.fs.fed.us/global/iitf

FS-726 • December 2001