A technique to determine critical years in evaluating important environmental factors affecting tree growth in forest ecosystem

KIM, Eun-Shik and Young-sun Kim

Kookmin University

Department of Forest Resources

Seoul 136-702 Korea

Tel. : + (82 2) 910-4814

Fax. : + (82 2) 910-4809

e-mail address : kimeuns@kmu.kookmin.ac.kr

Abstract

As tree-rings are end-products of tree growth affected by many environmental factors, synchronous growth patterns represent the existence of large-scale environmental factors affecting tree growth simultaneously. In this study, the potentials of crossdating tree-rings are examined by the determination of critical years to detect some of the large-scale environmental factors affecting tree growth simultaneously. Tree-rings of tree species growing in the pine (Pinus densiflora Sieb. et Zucc.; Japanese red pine) forest on Mt. Namsan in central Seoul were used to determine the critical years and to examine the potentials to crossdate tree-rings to evaluate changes of tree growth in forest ecosystem affected by environmental changes. In order to quantify the magnitude of changes in radial increment in tree-rings, a computational way of indexing technique was applied, which is used to determine critical years for annual growth of tree species in relation to environmental changes. The synchronous patterns of tree growth observed in the tree-rings represent the existence of large-scale environmental factors affecting the growth of trees simultaneously, at least in the local scale. Studied results provide us with new explanation on the relationships between environmental factors and tree growth in Korea as well as in this region.

Key Words: tree-rings, secondary growth, ecological variables, critical years, crossdating, environmental factors

INTRODUCTION

In temperate forests, tree-rings are formed annually as end-products of tree growth affected by many environmental factors. As the tree growth is affected by so many environmental factors, it is very difficult to differentiate the effects of single environmental factor to tree growth and forest growth. It is especially difficult to analyze the effects of such factors as global warming and climate change to forest growth because those factors are not so much variable as the other environmental factors. Tree rings, the end-products of secondary growth of trees formulated in response to seasonal changes of environment, contain information on year-to-year amount of annual growth as well as growth history (Kim, 1988). Their absolute and relative width as well as the quantity of the cells that makes up tree-rings provides us with a measure of the effects of succession, biotic and abiotic disturbances, climate and weather, and many other environmental factors which have influenced the growth. Among many methodologies applied to tree-ring studies, crossdating of tree-rings, which allows the identification of the exact year in which each ring was formed (Fritts, 1976), is one of the most important premises for tree-ring related studies. Crossdated tree-ring series show high cross-correlation among them. If the growth of trees in a region fluctuates synchronously with each other for many years, this may not only indicates the existence of some environmental factors that affect tree growth broadly, but also provides us with a reasonable basis for subsequent study to find the factor that affects the synchronous fluctuation of tree growth. Consideration on the selection of tree cores and the site as well as correct reading of them is important for better crossdating. Therefore, the rejection of obviously useless cores is needed before the crossdating. Cores are crossdated by the comparison of tree growth information using naked eyes, graphics of growth patterns, and/or computer programs.

The most important premises for applying the tree-ring studies to forest dynamics are 1) to find out the existence of critically good and bad years for tree growth, 2) to define them objectively and quantitatively, and 3) to find out the common factors that are responsible for the growth fluctuation. Here, critically good and bad years for tree growth are defined as critical years. Conventionally in tree-ring studies, critically bad years were evaluated from the skeleton-plot method, which researchers subjectively record the year that is characteristically narrow in tree-ring width on strips of paper with 2 mm divisions. Usually this skeleton-plot method is useful to cross-date tree-rings in the area where tree growth is limited by a few factors and tree-ring width has low variability. In the region where tree growth is limited by many factors and tree-ring width has high variability, it is difficult to apply this simple method to cross-date tree-rings, however. Therefore, it is strongly needed to develop a objective and quantitative method to cross-date tree-rings in such areas as this region of temperate monsoon overcoming this problem.

This study was carried out to crossdate tree-rings using a relatively simple computer program and to determine critical years to crossdate tree-rings better, which ultimately provide potentials to better interpret tree growth and to ultimately evaluate the change of forest dynamics and biodiversity related to such environmental changes as global warming and climate change.

MATERIALS AND METHODS

Tree-rings of pine trees (Pinus densiflora Sieb. et Zucc.; Japanese red pine) and some hardwood trees including Mongolian oak (Quercus mongolica Fischer) collected from Mt. Namsan, central Seoul, Korea, were used to determine the critical years and to crossdate the tree-rings (Kim, 1993).

To describe the current conditions of tree growth, tree cores sampled from 40 trees at 3 sites were taken using the point-sampling methods on Mt. Namsan, central Seoul, Korea. The sites were randomly selected considering the representativeness and the difference of the vegetation types which are closely related to the aspects (Kim, 1993). While the stands of northern and western slopes, where pine trees are growing as isolated islands on the ridges of the mountain, are mainly dominated by the deciduous tree species, southern slopes are mainly dominated by the pine trees. On the eastern slopes, pine trees are showing a generally suppressed growth by the other taller trees. Sampled tree-rings were carefully prepared and precisely examined using a computer-aided Tree-Ring Measuring System at Kookmin University.

Critical years that trees showed synchronously good or bad growth were determined using the SAS program (SAS Institute, Inc., 1990). In the SAS program, the ratios of good and bad growth were calculated using the equations,

yi = (xi-xi-1)*100/xi-1, (when xi >= xi-1),

yi = (xi-xi-1)*100/xi, (when xi < xi-1),

where, xi : tree-ring increment of the i-th year,

xi-1 : tree-ring increment of the (i-1)-th year, and

yi : ratio of the i-th year's growth evaluated

The ratios of the growth were categorized as follows:

GGG : increased growth with the ratio, yi >= 300%

GG : increased growth with the ratio, 200% <= yi < 300%,

G : increased growth with the ratio, 100% <= yi < 200%,

+ : increased growth with the ratio, 50% <= yi < 100%,

- : decreased growth with the ratio, -50% >= yi > -100%,

B : decreased growth with the ratio, -100% >= yi > -200%,

BB : decreased growth with the ratio, -200% >= yi > -300%,

BBB : decreased growth with the ratio, yi,<= -300,

here, no sign was allocated with the ratio, -50% < yi < 50%.

Here, critical year is defined as the year when the tree-ring width was critically increased or decreased compared to that of previous year. Although there is no quantitative criterion to determine the critical years, the increasing rates of more than 100%, 200%, and 300% in growth were used as the criteria to evaluate critical years of good growth, and the decreased rates of decreased increment compared to actual increment in the current year of less than 100%, 200%, and 300% in growth were used as the criteria to evaluate critical years of bad growth in this study. Critical years provide dendroecologists with the potential to crossdate the tree-rings.

The author simulated daily soil moisture contents using daily inputs of temperature and precipitation data for the last 82 years (Kim, 1992). Computer simulation model, BROOK, developed by Federer and Lash (1978), made it possible to simulate the daily soil moisture deficit in this region.

RESULTS AND DISCUSSION

Determination of critical years

When the author checked the fluctuating growth patterns, it was interesting to observe that the trees on Mt. Namsan showed a rather synchronous growth patterns, which indicates that

Table 1. Determination of critical years for tree growth

Name

of Qm01 Qm02 Qm03 Qm04 Qm05 Qm06 Qm07 Qm08 Qm09 Qm10 Qm1 Tree

Year

1944 +

1945

1946 +

1947

1948 -

1949

1950 - +

1951 -

1952

1953

1954 B

1955 +

1956 -

1957 + B

1958 G - -

1959 GG

1960 G

1961 - BB + +

1962 - + -

1963 B + G - +

1964 -

1965 + BBB B -

1966 + + + B +

1967 +

1968 -

1969 G - - +

1970 B +

1971

1972

1973 - + -

1974 +

1975 - - G

1976 B B B

1977 + - -

1978 B - B -

1979 G + G G -

1980 + + G + +

1981 -

1982 -

1983 - +

1984 B + +

1985 + -

1986

1987 + - B -

1988 - -

1989 + + G +

1990 + G +

1991 - -

1992 -

Note: The first two characters in the name of tree, i.e., Qm, Pd, Fr, Sa, Kp, and Rs stand for Quercus mongolica, Pinus densiflora, Fraxinus rhynchophylla, Sorbus alnifolia, and Robinia pseudoacacia, respectively.
Table 1. Determination of critical years for tree growth (continued)

Name

of Pd01 Pd02 Pd03 Pd04 Pd05 Pd06 Pd07 Fr01 Sa01 Kp01 Rs01

Year Tree

1944

1945

1946 +

1947 - +

1948 GG -

1949 +

1950 B B -

1951 - BBB BB B +

1952 + GGG

1953 -

1954 GG + B +

1955 B BBB G + G

1956 - - -

1957 B -

1958 + + B +

1959 G GG - B

1960 + + + -

1961 - + + GGG

1962 + BB BBB +

1963 G BB GG

1964 G G G

1965 BB BB B BBB

1966 GGG GGG G GG

1967 G G + G

1968 - - BBB +

1969 BB B - G BBB -

1970 + - G G G +

1971 + BB - +

1972 + B BB B -

1973 GGG GGG GG -

1974 + GG - + G

1975 -

1976 BBB BBB BB BBB +

1977 B - GG G + - -

1978 + + G - GG

1979 + G + GG GGG +

1980 - BB B GG

1981 - B B

1982 G + + G GGG B

1983 G G G G GG + B

1984 B BBB

1985 G - B + +

1986 B - - BB +

1987 + + GG G - -

1988 - - BB BBB +

1989 -

1990 G G +

1991 - B GGG +

1992 G + G + G + GGG +

Note: The first two characters in the name of tree, i.e., Qm, Pd, Fr, Sa, Kp, and Rs stand for Quercus mongolica, Pinus densiflora, Fraxinus rhynchophylla, Sorbus alnifolia, and Robinia pseudoacacia, respectively.

there are some factors that affect the growth of trees simultaneously (Kim, 1988). Another thing to point out is that there are certain years that trees showed very good or bad growth synchronously, which is the critical year. By examining the environmental factors in these years, we can interpret which are the major environmental factors that affect the growth of tree species significantly. Based on the records of tree growth, Kim (1994) selected critical years as was shown in the rightmost column of the Table 1. The year that more number of trees are apparent in the Table indicates that the trees have shown either better or worse growth in the year.

In this study, absolute ratios evaluating tree growth of the current year in relation to that of the previous year were calculated and the ratios were compared with each other. When tree growth ratios were examined, many trees showed abrupt growth changes in radial increment, which was indicated by 'GG', 'GGG', 'BB', and 'BBB' signs in the Figures. Using the years when tree showed abrupt growth change, crossdating can be carried out. Although, at this point, it is difficult to mention the range to crossdate tree-rings in species and in geographical location, this study clearly shows that it is possible to crossdate tree-rings of the trees on Mt. Namsan in central Seoul, Korea. Based on the results, it is possible to mention that the years of 1974, 1979, and 1989 are evaluated as good years for tree growth, while the years of 1988, 1976, and 1986 are evaluated as bad years for tree growth. Among the years, the year of 1992 can be evaluated as the best year, while the year of 1976 can be evaluated as the worst year.

It was interesting to check that, among the 40 samples of tree-rings, the growth patterns of some trees were different from those of the other trees, which can be ascribed to false reading of tree-rings, possibly based on the missing rings or false rings. This procedure can be used as a good device to check the correctness of the reading of tree-rings. While the potentials using this index are promising to check the validity of the reading, further studies on the year-to-year indices are needed to interpret them ecologically meaningfully.

Drought conditions and their effects

Based on the results of the simulation of the BROOK model, summary table for the occurrence and the period of drought in each year since 1961 is presented in Table 2. When the occurrences of the drought and the critical year were compared with each other, there were several years that tree growth was negatively related. For example, the years of 1988, 1982, 1979, 1965, and 1977 can be categorized as very dry years. Except in the year of 1979, trees showed negative growth in those years when droughts occurred. It is also worthwhile to note that the trees grew well in the years of 1970, 1967, 1974, and 1992, when no drought occurred. Ten years among the 32 year period have shown either positive or negative growth synchrony with the fluctuation of soil moisture conditions. These conclusively indicate that tree growth is strongly affected by the occurrence of drought. In other words, drought is one of the major factors that give strong and negative impacts upon the growth of trees on Mt. Namsan (Kim, 1994).

When the relationships between the drought and tree growth were examined statistically, generally, trees showed negative correlations to the length of drought of the current year and the previous year (Kim, 1994). However, the mountain cherries on Mt. Namsan showed a positive correlation to the length of drought of the previous year. In addition, trees showed high correlations to the lowest moisture condition of the current year and the previous year.

Here, it is worthwhile to note that the correlation coefficients between the growth of trees and the drought vary by species. While some of these differences can be explained by the difference of the growth strategy of the tree species, some of them can be attributed to the mere chances. These should be explained by the ecophysiological studies on the growth of tree species. In this paper, it is suffice to point out that soil moisture stress is one of the major factors that should be explained prior to describe any effects or damages that are caused by the air pollutants in natural conditions. On the effects of air pollutants to tree growth, the readers are referred to Kim(1994) for more details.

Table 2. Relationship between drought and critical years for tree growth

Year	Number of Days for Severe Drought	The Lowest Moisture Condition of the Year (mm)	Year That Tree Growth May Have Been Negatively Affected
1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992	0 4 5 0 35 0 0 1 9 0 0 3 0 0 0 0 27 10 68 1 0 56 2 0 0 0 8 107 0 0 0 0	B(-)* B(-)* B(++)** B(-)* D(+) D(-) B(++)** D(+) P(+)D(-) B(---)*** D(--) B(+)* B(+++)*** P(-)D(+) D(---) B(++)** B(--)** D(+++) B(---)*** B(+)* B(---)*** D(++++) P(+) B(--)** P(++++)***	ㅇ ㅇ no drought no drought no drought ㅇ ㅇ no drought ㅇ no drought

Note : Notation of the tree symbol using an alphabet

P: Pine trees; D: Deciduous trees; and B: Both categories of the trees.

CONCLUSIONS

Tree-rings are end-products of tree growth affected by many environmental factors. Synchronous growth patterns represent the existence of large-scale environmental factors affecting the growth of trees similarly. In this study, the potentials of crossdating tree-rings are examined by the determination of critical years. Tree-rings of tree species including pine trees growing on Mt. Namsan in central Seoul were used to determine the critical years and to examine the potential to crossdate tree-rings. These results provide us with new explanation on the relationships between the environmental factors and the growth of trees growing on Mt. Namsan in central Seoul, Korea.

REFERENCES

Agerter, S.R. and W.S. Glock. 1965. An annotated bibliography of tree growth and growth rings 1950-1962. The Univ. of Arizona Press, Tucson. 180pp.

Baillie, M.G.L. and J.R. Pilcher. 1973. A simple crossdating program for tree-ring research. Tree-Ring Bulletin 33:7-14.

Botkin, D.B. 1993. Forest Dynamics: an ecological model. Oxford University Press, Oxford. 309 pp.

Cleaveland, M.K. 1980. Dating tree rings in the eastern United States, pp:110-124, In: P.P. Feret and T.L. Sharik (eds.), Proceedings of dendrology in the eastern deciduous forest biome. Publication No. FWS-2-80, Virginia Polytechnic Inst. and Sate Univ.

Cook, E.R. 1980. A dendrochronological study of drought in the Hudson Valley, New York, pp:133-141. In: P.P. Foret and T.L. Sharik(eds.), Proceedings of dendrology in the eastern deciduous forest biome. Publication No. FWS-2-80, Virginia Polytechnic Inst. and State Univ.

Cook, E.R. and G.C. Jacoby. 1983. Potomac River streamflow since 1730 as reconstructed by tree rings. Journal of Climate and Applied Meteorology 22(10):1659-1672.

Creber, G.T. 1977. Tree rings: a natural data-storage system. Biol. Review 52:49-384

Cropper, J.P. 1979. Tree-ring skeleton plotting by computer. Tree-Ring Bulletin 39:47-59.

Federer, C.A. and D. Lash. 1978. BROOK: a hydrologic simulation model for eastern forests. Research Report, 19. Water Resource Research Center, University of New Hampshire, U.S.A. 84 pp.

Fritts, H.C. 1976. Tree Rings and Climate. Academic Press, New York. 567 pp.

Fritts, H.C. 1987. Principles and practices of dendroecology, pp, 6-17. In: G.C. Jacoby and J.W. Hornbeck (eds.), Proceedings of the International Symposium on Ecological Aspects of Tree-Ring Analysis. U.S. Dept. of Energy Publ., Tarrytown, New York, U.S.A.; August 18-21, 1986. CONF-8608144.

Goldthwait, L. and C.J. Lyon. 1937. Secondary growth of white pine in relation to its water supply. Ecology 18(3):406-415.

Holmes, R.L. 1983. Computer-assisted quality control in tree-ring dating and measurement. Tree-Ring Bulletin 43:69-78.

Hughes, M.K., F.H. Schweingruber, D. Cartwright, and P.M. Kelly. 1984. July-August temperature at Edinburgh Between 1721 and 1975 from tree-ring density and width data. Nature 308:341-344.

Hughes, M.K., P.M. Kelly, J.R. Pilcher, and V.C. LaMarche, Jr. (eds) 1982. Climate from tree rings. Cambridge, England. 223pp.

Jacoby, G.C. and J.W. Hornbeck. 1987. Proceedings of the International Symposium on Ecological Aspects of Tree-Ring Analysis. U.S. Dept. of Energy Publ., Tarrytown, N.Y., U.S.A.;18-21 August 1986. CONF-8608144. 726p.

Kim, E. 1988. Radial growth patterns of tree species in relation to environmental factors. Ph.D. Dissertation, Yale University, New Haven, Connecticut. 293 pp.

Kim, E.S. 1992. Dynamics of climate and soil moisture content in forests of Seoul Area. Forest and Humanity, 5, 47-62. Institute of Forest Science, Kookmin University, Seoul, Korea.

Kim, E.S. 1993. Distribution and radial growth patterns of Japanese red pine trees (Pinus densiflora Sieb. et Zucc.) growing on Mt. Namsan in central Seoul, Korea. Forest and Humanity, 6, 31-67. Institute of Forest Science, Kookmin University, Seoul, Korea. (written in Korean with an English abstract)

Kim, E.S. 1994. Ecological examinations of the radial growth of pine trees (Pinus densiflora S. et Z.) on Mt. Namsan and the potential effects of current level of air pollutants to the growth of the trees in central Seoul, Korea. J. Korea Air Pollution Research Association, 10(E):371-386.

Kim, Eun Shik. 1994a. Decline of Tree Growth and the Changes of Environmental Factors on High Altitude Mountains. Unpublished Research Report. Korea Science and Engineering Foundation (Project Number: KOSEF 921-1500-018-2). 89 pp. (written in Korean with an English abstract)

Kim, E.-S. and Young Sun Kim. 1997. Determination of critical years and crossdating in dendroecological studies: Tree growth of pine forest on Mt. Namsan in central Seoul, Korea. Forest and Humanity 9:47-65. Institute of Forest Science, Kookmin University, Seoul, Korea.

Kim, Eun-Shik. 1997. Radial growth patterns of Korean fir trees (Abies koreana Wilson) and related environmental factors on Mt. Hallasan in Korea, pp:47-58. In: Won-Kyu Park (ed.), Proceedings of the East Asia Workshop on Tree-Ring Analysis. Agricultural Science and Technology Institute of Chungbuk National University and Korean Forestry Society Division 5. Cheongju, Korea; November 6-7, 1997.

Kimmins, J.P. 1987. Forest Ecology. Macmillan Pub. Co. New York, New York. 531 pp.

LaMarche, V.C., Jr. and H.C. Fritts. 1972. Tree-rings and sunspot numbers. Tree-Ring Bulletin 32:19-33.

LaMarche, V.C., Jr. and K.K. Hirschboeck. 1984. Frost rings in trees as records of major volcanic eruptions. Nature 307:121-126.

Lyon, C.J. 1936. Tree ring width as an index of physiological dryness in New England. Ecology 17(3):457-478.

Manion, P.D. 1981. Tree Disease Concepts. Prentice-Hall. Englewood Cliffs, New Jersey. 399 pp.

Meko, D.M., C.W. Stockton, and T.J. Blasing. 1985. Periodicity in tree rings from the corn belt. Science 229:381-384.

Munro, M.A.R. 1984. An improved algorithm for crossdating tree-ring series. Tree-Ring Bulletin 44:17-27.

Phipps, R.L. 1972. Tree rings, stream runoff, and precipitation in central New York- a reevaluation. Professional Paper 800:B259-264.

Puckett, L.J. 1982. Acid rain, air pollution, and tree growth in southeastern New York. J. Environ. Quality 11(3):376-381.

Robinson, W.J. and R. Evans. 1980. A microcomputer-based tree-ring measuring system. Tree-Ring Bulletin 40:59-64.

SAS Institute, Inc. 1990. SAS user's guide: statistics (1982 ed.) Cary, N.C. 584 pp.

Schweingruber, F.H. 1987. Tree Rings: basics and applications of dendrochronology. CIP. 276 pp.

Smith, W.H. 1990. Air Pollution and Forests : Interaction between air contaminants and forest ecosystems. (2nd ed.) Springer-Verlag, New York. 618 pp.

Stockton, C.W. and D.M. Meko. 1975. A long term history of drought occurrence in western United States as inferred from tree rings. Weatherwise 28(6):244-249.

Tesche, M., O. Wienhaus, St. Godzik, and J. Materna, 1993. Stress and decline in air-polluted forest ecosystems of some countries situated in the eastern parts of central Europe, p, 59. In, Abstracts of the XV International Botanical Congress. Yokohama, Japan; August 28 - September 3, 1993.

Weimann, J., V. Mitchell, and M. Nay 1965. A partially automatic tree ring interval counter and key punch: (Patrick). Tree-Ring Bulletin 27(3-4):12-15.

Wendland, W.M. 1975. An objective method to identify missing or false rings. Tree-Ring Bulletin 35:41-47.