Tree Rings of Cedrus Libani at the Northern Boundary of Its

IAWA Journal, Vol. 24 (1), 2003: 63–73

TREE RINGS OF CEDRUS LIBANI AT THE NORTHERN BOUNDARY OF ITS NATURAL DISTRIBUTION by Ünal Akkemik Istanbul University, Faculty of Forestry, Department of Forest Botany, 80895 Bahçeköy-Istanbul, Turkey [E-mail: [email protected]]

SUMMARY

The present study was carried out taking a total of 41 increment cores from three sites located in the northern boundary of Cedrus libani and three site chronologies were constructed. Three response functions were computed and a higher correlation with climate was found in the trees on the steep slopes. The low precipitation was an important limiting factor for growth. At the valley bottom site, neither precipitation, except for December, nor temperature, except for February were a limiting factor. The radial diameters of tracheids were measured, and the tracheid numbers representing the last seven years, from 1994 to 2000, were counted. Although the radial diameters were almost similar in all sites, the numbers of tracheids were greatest at the valley bottom site and lowest at the steep slope site. Key words: Cedrus libani, tree ring, tracheid, dendroclimatology, Tur- key.

INTRODUCTION

Cedrus libani A.Rich. has its largest natural distribution area in the Mediterranean region of Turkey. It is an important forest tree species of this region between 1000–2300 m above sea level, and there are pure and mixed forests in the Taurus orogenic belt. The species has also two relic stands in the Kelkit Basin in the Middle Black Sea region of Turkey. These relic stands are located in the villages Erbaa-Çatalan and Niksar-Akıncı, and cover an area of 31.5 ha and 21 ha, respectively (Atalay 1990). Anșin and Küçük (1990) stated that Taurus cedar in the Middle Black Sea region should be considered as an old Mediterranean relic tree due to its close association with characteristic Mediterranean species. Kalay (1990) explained that the limiting soil factors for growth of cedar trees in these stands are the physiological soil depth, absolute soil depth, and skeleton contents of the A2 horizon of the soil. Long-term Cedar chronologies were constructed by Kuniholm (1996), Kuniholm and Striker (1976, 1983), and Kuniholm et al. (1996) for dating purposes. Selik et al. (1990) and Hughes et al. (2001) concluded that precipitation is the most important limiting factor for the growth of Taurus Cedar in the Mediterranean region of Turkey. The most comprehensive tree-ring research on Cedar species was carried out by Till and Guiot

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(1990), and Till (1987). They reconstructed the precipitation in Morocco since 1100 A.D. Borgaonkar et al. (1999) pointed out that spring temperature and precipitation are limiting factors for the growth of Cedar in the Himalayas.

The aim of the present study is: • to construct a local tree-ring chronology, • to determine the relationships between climate and tree-ring widths of trees growing on different soils and slopes, • to investigate and discuss the differences in tracheid formation of trees growing on different soils and slopes.

STUDY AREA The most appropriate regions for dendroclimatological investigations are those where trees grow at their climatic distribution boundary and where climatic factors greatly affect tree-ring variability such as northern, southern, upper and lower distribution areas (Schweingruber et al. 1989). The sites selected for the present study are located in the northern boundary of the distribution area of the species. For more detailed in- formation see Atalay (1990). Climate — The mean annual temperature, dominated by the Black Sea mild and rainy climate, ranges from 6 to 15 °C. The mean temperature in January is over 4 °C, the absolute minimum is -15 °C in the Kelkit Basin; the mean temperature in July is over 20 °C, and its absolute maximum is more than 40 °C. The average annual precipitation is in excess of 450 mm and this value is more than 600 mm towards the upper part. The rainy seasons are winter and spring, but the region receives a small amount of precipitation in summer as well. Soil — Non-calcareous acidic soils have been developed on the flysch and volcanic flysch. The soil is very shallow (less than 30 cm) at steep slopes and very deep (over 120 cm) at the valley bottoms. Vegetation — Several Mediterranean species occur, such as Pinus brutia, Vitex agnus-castus, Fontanesia phillyreoides, Phillyrea latifolia, Olea europaea var. oleaster, Jasminum fruticans, Ruscus aculeatus, Salvia officinalis. Furthermore, the relic stands contain Euxine flora which is composed of broad-leaved deciduous species in the lowland of the Black Sea region in Turkey, such as Quercus cerris, Carpinus orientalis, Sorbus torminalis, Acer campestre, Acer monspessulanum, Fagus orientalis, Tilia rubra, Paliurus spina-christi, etc. The local characteristics of the sampled sites — Cedrus libani grows between 570–920 m in Niksar-Akıncı and between 800–1250 m in Erbaa-Çatalan (Atalay 1987). Two sites, very close to each other and having different topographic conditions, were selected in Niksar (Fig. 1). The slope is around 75–80% and the soil is very shallow on the steep slopes. In contrast, in the valley bottoms the slope is around 10–20% and the soil is very deep. The samples were taken from the valley bottoms and the steep slopes with elevations of 600 m and 800 m, respectively. Trees on the steep slope and in the valley bottom sites reached 12–14 m and 18–23 m heights, respectively. Another site was selected in Erbaa-Çatalan (Fig. 1): the slope is around 25–30%, the soil is deep and the altitude is 1200 m (Table 1).

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B L A C K S E A 42

T U R K E Y 40 Sampled sites

36 0 100 200 300 km MEDITERRANEAN SEA | | | |

26 28 30 32 34 36 38 40 42 44 Fig. 1. Distribution of Cedrus libani in Turkey. The species grows throughout the Mediterranean region, but it has a relic area in the Black Sea region (arrow).

Table 1. Several characteristics of the three sites, Erbaa region (CELIERB), steep slope site (CELINIU) and valley bottom site (CELINIA), and the numbers of cores studied.

Sites Lat. / Long. Altitude Soil Slope Aspect Cores / (m) (%) trees

Erbaa region 40° 48' N / 1200 deep 25–30 East 22 /17 (CELIERB) 36° 33' E

Steep slope site 40° 27' N / 800 very 75–80 South-west 11/10 (CELINIU) 37° 05' E shallow

Valley bottom site 40° 27' N / 600 very deep 10–20 South-west 8 / 8 (CELINIA) 37° 05' E

MATERIAL AND METHODS Chronology development A total of 41 cores from 35 trees in the three different sites (see Table 1) were extract- ed using a Swedish Increment Borer. The sampled sites were coded as CELIERB for Erbaa, CELINIA for the valley bottom site, and CELINIU for the steep slope site in Niksar. The transverse surfaces of all cores were smoothed and an Eclund Measuring Ma- chine was used for measuring the tree-ring widths. An individual chronology for each tree was constructed and then correlations between all trees were calculated. The mean sensitivity and first order autocorrelation were calculated as well (Fritts 1976), and DPL and ARSTAN programs (Grissino-Mayer et al. 1996) were used for the chronology

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Tree-ring–climate relationships For the response function calculations (Fritts 1976) the mean monthly temperature and total monthly precipitation for the period from October of the year before growth through September of the year of growth were used in the program PRECON as predictor, and the residual versions of the site chronologies were used. The climatic data from 1961 to 2000 were obtained from the Tokat Meteorology Station near the sampled sites.

Tracheid measurements The radial tracheid diameter was measured and the number of tracheids counted to ascertain the influence of the different soil conditions. Since the trees were young and the early rings were complacent and very wide, the last seven years (1994–2000) of the trees were measured in radial direction. The trees very rarely formed false rings (Akkemik 2000; Akkemik & Dagdeviren 2000). However, the formation of a false ring in the year 2000 was seen on all cores. To discern the reason for this formation, mean monthly temperatures and total monthly precipitation of the year 2000 and the average of the whole record period were com- pared.

RESULTS AND DISCUSSION Chronology development A local tree-ring chronology called CELITRBS was constructed covering the years 1937–2000 (Fig. 2), the statistical characteristics of its standard, residual and arstan versions are given in Table 2. The local chronology including 64 years has little im- portance for dating purposes. However, it can be useful in climatic and ecological as well as forestry studies.

 CELIERB CELINIA CELINIU CELITRBS 2000 1600

1600 1200

1200 800 (CELITRBS) 800 400 Indices of the site chronologies 400 0 Indices of the mean chronology 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 Years Fig. 2. Site chronologies for the three sampled sites and their mean, the local chronology. The upper one is the local chronology. The chronologies are residual versions obtained by using the detrending method in the program ARSTAN.

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Table 2. ARSTAN statistics of the three versions of the local mean chronology based on speci- mens from all sites. The statistics of the residual chronology are more significant than those of the standard chronology.

Chronology type Standard Residual ARSTAN

Mean 1.000 1.000 0.9998 Median 0.9833 1.0109 0.9696 Skewness 0.0153 -0.2299 0.2090 Kurtosis -0.1468 0.4886 -0.5140 Autocorrelation order 1 0.5061 -0.1541 0.5562 order 2 0.1213 0.0277 0.1558 order 3 0.0053 0.0378 0.0057 Variance due to autoregression 26.7% — 32.8% Error variance 0.009135 0.008689 Ratio of error variance of chronologies (ARSTAN / STNDRD) 0.9512

Common interval time span 1948 to 2000 53 years 3 site chronologies Mean correlations Detrended series Residuals between trees 0.256 0.360 radii vs mean 0.629 0.709 Signal-to-noise ratio 1.035 1.690 Agreement with population chronology 0.509 0.628 Variance in first eigenvestor 52.24% 57.81% Chron common interval mean 1.024 1.008 Chron common interval std dev. 0.160 0.133

Table 3. Correlation coefficients (upper part of diagonal) and percentages of parallel variations (lower part of diagonal) between the site chronologies and their mean, and sensitivity and mean tree-ring widths of the site chronologies.

CELINIU CELINIA CELIERB CELITRBS CELINIU — 0.24* 0.53*** 0.87*** CELINIA 0.67* — 0.06 ns 0.45*** CELIERB 0.69* 0.65* — 0.65*** CELITRBS 0.83*** 0.85*** 0.76*** —

Mean correlation coefficient with individual chronologies 0.85*** 0.80*** 0.82*** Sensitivity 0.211 0.169 0.170 Mean tree-ring widths (mm) 2.77 4.11 2.45 *, ** and *** indicate the 0.95, 0.99 and 0.999 confidence levels, respectively.

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The percentage of parallel variation and correlation coefficients between the site chronologies and with the local chronology CELITRBS are presented in Table 3. The similarities can be seen in Figure 2. In Table 3 mean sensitivities, mean correlation coefficients between individual and mean chronologies and mean tree-ring widths can also be seen. Figure 3 shows cumulative tree-ring widths. In the first 15 years, growth rates were similar to each other in all sites. Due to rather favourable growing conditions at the valley bottom, the growth rate here appeared to be much higher than in the other two sites after the 15th year. It is suggested that this species can be cultivated in this region when soil conditions are favourable.

CELINIU CELIERB CELINIA 25

5 Cumulative tree-ring width (cm)

0 1 6 11 16 21 26 31 36 41 46 51 56 61 Years Fig. 3. Cumulative tree-ring widths in the site chronologies. In the first 15 years, growth is similar in all sites, after that it is much higher in the valley bottom than in the other two sites.

Tree-ring–climate relationships The response functions are given in Figures 4a–c. For CELIERB (Fig. 4a) the RSQ value of climate is 0.555, and thus explains 55.5% of the total variance in tree-ring width. Precipitation from April to September, except for June, has a positive influence on the tree-ring width. Its negative effect in January is statistically significant. High temperatures in November, December and January have a positive effect on the tree-ring width, whereas high temperatures in April of the current year have a significantly negative effect. In CELINIA (Fig. 4b) the RSQ value of climate (0.699) explains 69.9% of the total variance. At this site, due to favourable soil conditions, the influence of climate during spring and summer is small. Two climatic variables, precipitation in December of the previous year and temperature in February of the current year are statistically significant and they have a positive effect on the radial increment in the current year. Winter temperature has a positive effect on the tree-ring width, and high temperatures have a negative effect during late spring and summer months. We can conclude that

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0.5 0.4 0.3 0.2 Precip 0.1 sig 0.95 0 Temp -0.1 sig 0.95 -0.2 -0.3 Precip -0.4 a -0.5 Temp O N D J F M A M J J A S 0.5 0.4 0.3 0.2 Precip 0.1 sig 0.95 0 Temp -0.1 sig 0.95 -0.2 -0.3 Precip -0.4 b -0.5 Temp O N D J F M A M J J A S 0.5 0.4 0.3 0.2 Precip 0.1 sig 0.95 0 Temp -0.1 sig 0.95 -0.2 -0.3 Precip -0.4 c -0.5 Temp O N D J F M A M J J A S Fig. 4. Response function (Rf) results. – a: Rf for CELIERB. – b: Rf for CELINIA. – c: Rf for CELINIU.

Downloaded from Brill.com09/29/2021 08:32:36AM via free access 70 IAWA Journal, Vol. 24 (1), 2003 temperature and precipitation in winter are the most important limiting factors on the growth of tree rings in valley bottom conditions. In CELINIU (Fig. 4c), due to the steep slopes and shallow soil conditions, tree-ring widths are more sensitive. The RSQ value of climate is 0.639 (total variance 63.9%). Due to unfavourable topographic conditions, the water economy of the soil is too poor, and therefore precipitation has generally a positive effect except for rainfall in November of the previous year and August. It was statistically significant in December and April. Whereas temperatures in October of the previous year, March, April and September of the current year negatively affect the width of tree rings, its impact is positive in December, January and July, and it was statistically significant in December and July. In general, high precipitation creates a very important optimum condition on the growth of tree rings on the steep slopes. Depending on different soil and slope conditions, the climatic impacts vary remark- ably. While water deficiency begins in early spring at the steep slope site, an important water deficiency does not occur throughout the year at the valley bottoms, and it begins in late spring in Erbaa. In the year 1994, precipitation was very low (355.1 mm), and the total precipitation in July and August was only 0.2 mm. This is a pointer year in this region. Similar results were found by Akkemik and Dagdeviren (2000) in this latitudinal zone. In addition, there is a decrease in the growth of trees between the years of 1967–1987 (Fig. 2). Tolunay (1993) concluded that a drought problem occurred during the 1980’s at the same latitude. In addition to climatic impact, it can be concluded that another most important limiting factor is the soil depth. The results show that low precipitation has a greater negative effect on tree rings of the trees growing on the shallow soils. The year 1961 is explained as pointer year for the Aegean region by Hughes et al. (2001). This year also shows up in our local mean chronology (Fig. 2). Other pointer years for our region are 1989 and 1994.

Tracheid measurements Radial diameters, numbers and cell wall thickness of tracheids were measured and counted in radial direction of the last seven tree rings (1994–2000) of all trees at the three sites (Fig. 5). The numbers of tracheids vary widely depending on the width of the tree rings. Total tracheid numbers in the last seven years are 583 cells at the valley bottom site, 307 cells in Erbaa and 194 cells at the steep slope site in Niksar. As expect- ed, the numbers of tracheids are lowest on the steep slopes. Radial diameters are almost the same at all sites. In earlywood, diameters of tracheids vary between 20–50 µm depending on the daily and weekly climatic conditions. In the transition zone they are 10–20 µm, and in the latewood tracheid diameters they are around 10 µm or mostly less. In wide rings, the transition zone from earlywood to latewood is very wide, and in narrow rings it is very narrow. The tree rings of the trees on the steep slope site usually do not show a transition zone. Based on these results, we can conclude that limiting conditions such as low temperature in early spring, water stress and high temperature in summer reduced division of the cambia initials more than their differentiation and expansion in Taurus cedar wood.

Downloaded from Brill.com09/29/2021 08:32:36AM via free access Akkemik — Tree rings of Cedrus libani 71 ). ). CELIERB , thin line) CWT ). for the trees on the valley CELINIU CWT CWT and RD for the trees in the Erbaa region ( region Erbaa the in trees the for CWT CWT and and , bold line) and cell wall thickness ( RD RD RD ). – b: b: – ). for the trees on steep slope site ( CWT CWT CELINIA Number of tracheids and RD Fig. 5. Radial diameters ( of tracheids for the years 1994–2000. – a: ( site bottom – c: Number of tracheids

Number of tracheids

(µm) (µm) (µm)

Diameter of tracheids of Diameter tracheids of Diameter tracheids of Diameter a b c

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Replenishment of soil moisture and consequent reduction in water stress during the growing season may be accompanied by a resurgence of shoot and radial growth, causing unlignified tracheids to expand in size. This increase in size of maturing cells can produce a band of earlywood between layers of latewood, forming a false ring (Fritts 1976). Figure 5a–c illustrate such a false ring in the year 2000. Just after the radial diameter of tracheids decreases and their cell wall thickness increases, thin- walled tracheids with wide lumina are formed similar to those of the earlywood. The numbers of the last forming tracheids differ depending on the different conditions, that is, their numbers increase depending on the soil depth. The cause of this formation can be the high temperatures and extremely low precipitation in July. The highest July temperature in the entire period occurred in the year 2000, and the precipitation in June and especially in July is also very low. Mean July temperature in the entire period and in July of the year 2000 are 22.07 °C and 24.6 °C, respectively. Average July precipitation in the whole period is 11.5 mm, and 2 mm in July of the year 2000. As seen, the precipitation is extremely low and the temperature is highest. Precipitation in August of the year 2000 is 6.1 mm, which is virtually the same as the mean August precipitation of the entire period: 6.0 mm. Consequently, we can conclude that a very high temperature and low precipitation in mid-summer in this region can induce the false ring formation.

ACKNOWLEDGEMENT

I am very grateful to Dr. Ramzi Touchan (Laboratory of Tree-ring Research, Tucson, Arizona, USA) for his helpful suggestions and comments on this manuscript.

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