BEHIND THE BARKA Quick Reference to Tree Physiology

Read the tree’s life Story

Growth RingsLook at a cross section or “cookie” from atree to see its layers. The soft center is the pith.Heartwood is the darker inactive wood. Thelighter active wood, Xylem, carries the sapfrom the roots to the leaves. Phloem is theinner bark that carries the sugar from theleaves to other parts of the tree. The livingsection just inside the bark is cambium. Theoutermost layer, bark, protects the tree.There are two rings for every year. The darkcolored thin ring is the summer growth whenconditions are dry. The lighter colored, biggerring is spring wood from the spring rains. Tofind out the tree’s age, count either set of rings.

Drought or insect damage Broken/dead branch Forest fire

Phloem(inner bark)

Xylem(sapwood)

Outer bark

CambiumHeartwood

(inactivesapwood)

Look at the cross section of a tree to to tell if it survived fire, or diedfrom drought. Each tree has a different story.

Growing on slope orfallen tree leaning

against tree

Trees help create soil, and need soil to survive. Trees’ leaves fall to the ground as leaf litter anddecompose into humus. Soil is a mixture of organic ingredients (living organisms and humus); mineralingredients (rock, clay, silt, and sand);moisture, and air space. Soil does more thananchor a tree, it gives a tree nutrients, water,and air it needs. Not all plants need the sameamounts. Some prefer wet soils, and othersneed more air space. These individual treerequirements reduce competition.

Soil

Sand Silt Clay

Pith(center)

TERMS TO KNOWcambium - single layer of living cells between the xylemand phloem layers in the tree’s trunk that produces newwood and barkcarbon cycle - natural cycle of carbon dioxide convertedto carbohydrates by photosynthesis and its return to theatmosphere by animal metabolism and decompositionchlorophyll - green plant pigment that absorbs thesunlight for photosynthesiscompetition - interaction between two or more organismsliving in the same space; each tries to dominate the otherby taking in the most food, water, and sunlightdecomposition - process of breaking down organic matterinto its basic elements including nutrients needed for plantgrowthdendrology - the study of treesforestry - the science of managing forestsheartwood - dead inner core of a tree that was sapwoodbut now provides support for the treehumus - decomposed plant and animal material thatbecomes part of the soilhydrologic cycle - continuous circulation of water from theatmosphere to the earth, and back to the atmospherethrough condensation, precipitation, evaporation, andtranspirationlateral roots - roots that extend horizontally from the rootcollarleaf litter - collection of dead leaves and vegetation on theforest floornitrogen cycle - natural cycle where nitrogen is used by aliving organism, transformed upon death and decomposi-tion of the organism, and converted to its original state ofoxidationouter bark - outermost part of the tree that protects it fromanimals, insects, cold, heat, and drynessphloem - inner bark of a tree that carries sugar made in theleaves to other parts of the treephotosynthesis - process by which plants use the sun’senergy to convert carbon dioxide and water into sugar andoxygenrootlets - finer roots extending from lateral roots .root hairs - very thin, hair like extensions of a rootletwhich soak up most of the water and minerals the treeneedsstomata - small pores in a tree’s leaves and stems thatopen to absorb carbon dioxide and release oxygentap root - primary root that grows vertically and gives offsmall lateral rootstranspiration - process by which a tree loses waterthrough stomata on its leaves and stemsxylem - active wood in the tree that carries sap from theroots to the leaves where sugar is madePhotosynthesis creates food for the tree, takes in carbon

dioxide, and releases water vapor and oxygen.

Chemical Energy + Carbon Dioxide = Sugar

Water enters leaf

Chloroplasts trap light energy

Water + Light = Chemical Energy

Carbon dioxide entersleaf through stomata

Sugar leaves leaf

RootsAs the underground branches of the tree, roots anchor thetree to the ground. Most roots are located less than 18 inchesbelow the soil surface. Trees have lateral roots, whichspread out from the tree, and a tap root, which growsstraight into the ground. As the lateral roots and tap rootgrow away from the tree they develop smaller roots calledrootlets. The rootlets grow root hairs which absorb most ofthe nutrients and water from the soil. The nutrients and waterare sent up to the leavesthrough the xylem layer ofthe tree. Tree roots needoxygen, water, nutrients,and soil to grow.

Forest Resource Education Center 370 East Veterans Hwy Jackson, NJ 08527 (732) 928-2360 njfsfrec@bellatlantic.net

“FORESTS ARE THE ‘LUNGS’OF OUR L AND, PURIFYING THEAIR AND GIVING FRESHS TRENG TH TO OUR PEOPLE.”- FRANKLIN D. ROOSEVELT

Photosynthesis

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