ercenta by Dr. Kim D. Coder, Professor of Tree Biology & Health Care Warnell School of Forestry & Natural Resources, University of Georgia

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1 Tree Growth Rate Table: Absolute Area Increase & Annual Per ercenta centage e Growth by Dr. Kim D. Coder, Professor of Tree Biology & Health Care Warnell School of Forestry & Natural Resources, University of Georgia Trees grow in diameter every year. From the farthest reach of woody roots to tips of twigs, trees expand in girth. This annual growth increment allows trees to respond to changing environmental conditions and react to injuries. The ability of a tree to resist strong winds, ice storms, and major losses of woody materials, while remaining alive and erect, is a direct consequence of annual diameter growth. A New Annual Sheath Trees produce a sheath of living cells, more exterior to last year s wood, every growing season. Much of the new growth increment is composed of longitudinal transport cells. These cells quickly die and only then become functional in transporting water, essential elements, and growth regulators. These functional but dead cells are held within a matrix of living cells which regulate water pressure, help correlate growth in the rest of a tree, store food, and react to injury or attack. Only the outer few annual increments (visible as rings in a cross-section) are reactive to short term changes inside and outside a tree. As you examine a tree stem farther to the inside, living cells become fewer and less active. Depending upon environmental conditions, tree health, and usable food reserves, at some position inside a tree an inner core of living tissues are systematically shut-down. During senescence of this inner core of wood (xylem), valuable materials still needed for tree life are moved outward to living cells, and waste materials are stored or manufactured within each cell as it dies. These waste materials can make the inner dead core resistant to decay. This dead inner core is called heartwood. Leaf Crown Production The amount of woody increment produced each year is dependent upon proper functioning and productivity of leaves. All leaves together make up the living crown of a tree. Food and growth substances ultimately generated by photosynthesis and metabolic processes in leaves determine the amount of materials available for generating annual increments. An annual

2 increment of xylem produced throughout a tree is a result of crown production crown production is a direct result of annual increment transport efficiency and volume. A growth increment also mechanically supports the crown against dynamic forces of gravity, wind, precipitation and the tree s own size, shape and mass. Because the tree s crown of leaves is provided with raw materials and growth substances collected and generated by roots, and roots are provided with food and growth substances generated by the crown, the physical pathway and shear distance between living crown and absorbing root is critical to tree survival. All the cells between leaf and rootlet must store, defend, support, transport, prevent waste, and conserve precious resources needed for tree life and survival. Trees invest heavily in woody materials applied as an annual layer of cells over the outside of last year s structure. Ecological Growth Summary The annual addition of tree growth represents an approximation of specific crown vigor, general tree health, relative whole tree growth rates, and crown volume. The more net food (CHO) and growth substances generated by the crown of leaves, the larger a tree grows at a faster annual pace. Each year the total annual growth increment is an ecological integration of all genetic, environmental, and chance occurrence factors influencing whole tree survival and growth. Cross-Sectional Area of Growth One measure of annual growth increments in trees can be estimated by circular crosssections showing annual radial growth (as measured with an increment core, for example). Annual increment values in square inches using Table 1 can be determined by first estimating tree diameter in inches at four-and-one-half feet above the ground (DBH) as measured along the main stem on the uphill side. For this table, an estimate of generalized annual growth rate is determined based upon the number of annual increments present in the last (outside or most exterior) inch of wood (xylem). This measure estimates a growth rate by diameter (DBH) class. Table 1 provides the annual xylem increment area increase based upon growth rate per tree diameter class in square inches. Note, DBH should be estimated inside the bark. For example if an increment core of a 20 inch DBH tree reveals 3 annual increments (rings) per inch, the tree is growing an estimated 21 square inches of cross section (wood) per year. Table 1. Percent Area Growth A second annual growth rate percent can be estimated for a tree by measuring annual growth increment circular cross-sections and annual radial growth. Relative annual increment values (as a percent of last year s increment) can be determined by first estimating tree diameter in inches at four-and-one-half feet above the ground (DBH) as measured along the main stem on the uphill side. Table 2 provides an estimate of annual growth rate based upon the number of annual increments present within the last (outside or most exterior) inch of wood (xylem) generated. This percent measure estimates a growth rate by tree diameter (DBH) class. Table 2 provides a percent (in decimal form) increase per year in xylem increment area based upon growth rate per diameter class. Note, DBH should be estimated inside the bark. For example if an increment core of a 20 inch DBH tree reveals 3 annual increments (rings) per inch, the tree is growing at an annual rate of roughly 7%. Table 2. Dr. Kim D. Coder, Warnell School, University of Georgia 2

3 Table 1: Tree area increase measured in cross-sectional inches (square inches) for each single growth increment by tree diameter. Growth rate estimator ranges from 1.0 growth increment (ring) per inch (R1) to 20 growth increments (rings) per inch (R20). Diameter (D) ranges from 6 inches DBH to 100 inches DBH. (D = DBH = diameter of tree in inches at 4.5 feet above ground). 6in 16in Dr. Kim D. Coder, Warnell School, University of Georgia 3

4 Table 1 (CONTINUED): Tree area increase measured in cross-sectional inches (square inches) for each single growth increment by tree diameter. 21in 63in Dr. Kim D. Coder, Warnell School, University of Georgia 4

5 Table 1 (CONTINUED): Tree area increase measured in cross-sectional inches (square inches) for each single growth increment by tree diameter. 36in 110in Dr. Kim D. Coder, Warnell School, University of Georgia 5

6 Table 2: Decimal percent (0.12 decimal percent = 12%) increase in tree cross-sectional area for a single growth increment by tree diameter. Growth rate estimator ranges from 1.0 growth increment (ring) per inch (R1) to 20 growth increments (rings) per inch (R20). Tree diameter (D) ranges from 6 inches DBH to 100 inches DBH. (D = DBH = tree diameter in inches at 4.5 feet above ground). 6in Dr. Kim D. Coder, Warnell School, University of Georgia 6

7 Table 2 (CONTINUED): Decimal percent (0.12 decimal percent = 12%) increase in tree cross-sectional area for a single growth increment by tree diameter. 21in Dr. Kim D. Coder, Warnell School, University of Georgia 7

8 Table 2 (CONTINUED): Decimal percent (0.12 decimal percent = 12%) increase in tree cross-sectional area for a single growth increment by tree diameter. 36in Dr. Kim D. Coder, Warnell School, University of Georgia 8

9 Citation: Coder, Kim D Tree growth rate table: Absolute area increase & annual percentage growth. Warnell School of Forestry & Natural Resources, University of Georgia, Outreach Publication WSFNR-17-WML. Pp.9. Publication WSFNR-17-WML DECEMBER 2017 The University of Georgia Warnell School of Forestry and Natural Resources offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, gender or disability The University of Georgia is committed to principles of equal opportunity and affirmative action.