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Dendrochronological analysis of debris flow disturbance on Rishiri Island
GEOMORPHOLOGY ELSEVIER
Geomorphology 20 (1997) 135 145
Dendrochronological analysis of debris flow disturbance on Rishiri Island Keiji Yoshida
a Shun-ich Kikuchi a,* Futoshi Nakamura a Masato Noda b
a Department of Forest Science, Faculty of Agriculture, Hokkaido University, Sapporo, 060, Japan b Uryu Experimental Forest, Faculty of Agriculture, Hokkaido University, Nayoro, 096, Japan
Received 13 June 1996; accepted 25 January 1997
Abstract Abies sachalinensis dominates the alluvial fan head of the Ochiushinai Gully on Rishiri Island, Japan. This species is able to adapt to frequent disturbances by debris flows. Even-aged stands composed of A. sachalinensis or Alnus maximowiczii were found along the channel, and standing dead trees buried by debris flows were discovered at the alluvial fan head. We used dendrochronological data in order to analyse the geomorphic history of the fan head. We determined the master ring-width chronology by synchronizing ring-width variations in living trees. This master chronology was used to cross-date the establishment and death of the buried trees. Results indicated that most of the buried trees were established in the 1870s and died in the early 1950s. Fuxther, debris flow was estimated to have occurred in the 1890s and the late 1960s based upon the distribution of even-aged stands seen in aerial photos. The ring-width variations of the trees adjacent to the channel indicate a low correlation for synchronization, while those located on the hillslope have a high correlation. A low correlation in the riparian trees can be attributed to the instability of geomorphic surfaces caused by debris flow disturbances. Keywords." dendrochronology; debris flows; alluvial fan; disturbance; Rishiri Island (Japan)
1. Introduction Tree ring-width variations contain chronological and environmental information, which can be used for spatial and temporal analysis of geomorphic processes. For example, La Marche (1966) employed a cross-dating method for dating trees killed b y bank erosion and analyzed an 800-year history of river sedimentation. Higashi et al. (1971) used the forma-
* Corresponding author. Phone: + 81-11-706-2809. Fax: + 8111-706-4935. E-mail: Idk3,[email protected]
tion of reaction wood in tree rings in order to analyze the chronological movement of landslides. Yamaguchi and Hoblitt (1995) estimated age of death of trees buried in pyroclastic flows or lahar sediments and discussed their disturbances. In a river floodplain, riparian forests with uniform heights are frequently observed. They are generally composed of pioneer species such as Salix, Populus and Alnus spp. and are even-aged (Everitt, 1968; Araya, 1971; Nakamura, 1986). The seeds of pioneer trees are disseminated widely b y wind. They invade bare lands soon after the sediment is stabilized and germinate within a year (Araya, 1971). Everitt (1968)
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K. Yoshida et aL / Geomorphology 20 (1997) 135 145
used the ages of cottonwood established on a floodplain to explain a recent history of flood disturbance on a valley floor. Nakamura et al. (1995) used the age distribution of even-aged stands to determine the sediment budget and routing in a river basin in Japan. Even-aged stands can be found on the deposits of debris flow. Further, trees damaged by geomorphic processes preserve much temporal information (Sigafoos, 1964). For example, trees buried by debris flows show suppressed growth and may survive by sprouting adventitious roots, or eventually die. Scars remain in their trunks if they are wounded (Alestalo, 1971; Shroder, 1978). The geomorphic processes on an alluvial fan have been inferred based on using dendrochronological data such as the age of even-aged stands, trunk scars, and the period of growth suppression (Sasa, 1978; Strunk, 1991). Debris flows frequently occur in small tributaries in Japan and they disturb alluvial fans, particularly at the fan head (Higashi, 1979). We found a number of standing dead trees at the fan
head of a gully cut in volcanic rocks on Rishiri Island, and could date the occurrence of debris flows by dendrochronological analysis. The main objectives of this study are to clarify the geomorphic history of debris flows by cross-dating the ring series of buried dead trees and by investigating the age structure and distribution of even-aged stands, and also to examine the effects of debris flow disturbances on tree ring-width variations.
2. Study site Rishiri Island is located northwest of Hokkaido, in extreme northern Japan (Fig. 1). The circumference and area of the island are about 60 km and 183 km 2, respectively. Rishiri is a round volcanic island approximately 16 km in diameter. Rishiri Volcano (1721 m) lies at the center of the island, and is a Quaternary stratovolcano having deep gullies seeding active alluvial fans (Kobayashi, 1987). Abies
Sea i
ully
Kutsug~ ~futoromanai ;ully
Risiri Is
I
1
Teshio E x p e r i m e n t a l
I Forest of H o k k a i d o Univ.
Fig. 1. Location of the study site.
0
I
2
3
I
I
I
I km
137
K. Yoshida et al. / Geomorphology 20 (1997) 135 145 sachalinensis and Picea jezoensis predominate on the alluvial fans, although Alnus maximowiczii, Salix sachalinensis, and Populus maximowiczii are dis-
at. (1993). This asymmetric pattern of rainfall may contribute to the concentration of debris torrents on the eastern side of the island.
tributed along the stream channel (Tatewaki, 1941). The study site is the fan head of the Ochiushinai Gully, where even-aged stands (about 102 to 10 4 m 2) established immediately after debris flow disturbances are prominent and where many trees buried by debris flows are found. The watershed area is 6.5 km 2 and the average channel gradient is 12.1%. A. maximowiczii is widely distributed over the low, terraced deposits. Major debris flow disasters at the Ochiushinai Gully which destroyed property were recorded in 1897, 1923, 1947, 1972 and 1989 (Kikuchi et at., 1993). The average annual precipitation over the 12-year period from 1979-1990 is 935.8 mm, recorded in the Kutsugata, on the western side of the island (Sapporo District Meteorological Observatory, 1993). However, the intense, heavy rainfalls tend to fall on the eastern side of the island, as reported by Kikuchi et
The OchiushinaiGully k N~.3 checkdam ...."
3. M e t h o d s
3.1. Collection o f tree ring data
We found a group of standing buried trees exposed beside the channel bank. They appeared in debris flow deposits along the channel (Figs. 2 and 3). Of these, cross-sectional disks of four trees (No. 1, No. 2, No. 3 and No. 4) being not severely damaged, were obtained near the original root flare of a tree in order to estimate the date of the establishment period. The debris flow deposits burying these tree trunks were about 3 m thick, consisting of massive, matrix-supported gravel, and no humus layers were included. The sediment, where original root flares of buried trees were situated, was composed of
,,) ',,-q ~ '
J
Line~l~/
Tree ring sampling site © : in stable area © : in semi-active area • : in active area • : Location of buried t r e e s
2 ~
.-..~, ~ = =
~j
250m
semi-active
active Abandoned channel
~% :~ Present channel
Briefsketchof the Line-1
/0 N
stable I
.d.;o
,L~: .~.:C .~
/ 1 2m lm
Fig. 2. Map of the fan head of the Ochiushinai Gully and tree-ring samplingsites.
200m
I
100
I
138
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
coarse sand including few gravel fragments. This stratigraphy indicates that these deposits were formed by a single, high-magnitude debris flow event. Moreover, two other buried trees (No. 5, No. 6) were uncovered in the same deposits of the debris flow during the construction of check dams. A master ring-width chronology maximizing common variance in the area is required to conduct
reliable cross-dating (Schweingruber, 1986). There is no master ring-width chronology covering the Rishiri Island. Thus, we collected living 34 samples of A. sachalinensis in 1994 to create the master ring-width chronology containing average width variation at the fan head of Ochiushinai Gully (Fig. 2). We classified geomorphic surfaces into stable, semi-active and active areas, based upon the distance and height from
Fig. 3. Photoof buriedtrees.
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
the channel bed, and samples were collected from the three areas. The stable area is furthest away from the channel bed at highest elevation, while the active area is close to the channel on the lower floodplain surfaces. The semi-active area is situated between the two. We used an increment borer (~b 5 mm) and took one core sample per tree at breast height (1.3 m above ground). We obtained disks from stumps which had been cut during construction of check dams. Of 34 samples, 30 were core samples and 4 were disks. 3.2. Standardization ofring-width variation and establishment o f the master ring-width chronology
Tree ring-widths were measured in units of 0.01 mm. We cross-checked each ring-width variation statistically using the COFECHA program (Holmes, 1983). This program detects missing rings or errors due to artifacts and improves the reliability of the ring-width chronology. Removing non-climatic factors (@) from the measured ring-width series (R t) is referred to as 'standardization' and the standardized ring-width series ( I t ) can be expressed as: (l)
It = R J @
The measured ring-width series should be standardized to create the master ring-width chronology. Deterministic methods represented by the exponential and polynomial models and stochastic methods such as low-pass digital filtering are available for estimating @ (Cook, 1990). In the present study, we used one of the stochastic methods named 'lowpass filter' (Holloway, 1958; Fritts, 1976; Cook, 1990; Yasue et al., 1994; Noda, 1996). This filter is able to select any cut-off frequency and remove a long time scale variation by keeping medium and short time scales (Noda, 1996). Debris flows, a major geomorphic disturbance over the alluvial fans of the Rishiri Island, will leave short-frequency signals such as suppression in radial growth. Thus we used 5-year filter length to include short-frequency signals. The equation of Gt was derived as follows: i
Gt=
~
wkRt+k
k i ( i = 2 ; t = 1,2,3 . . . . . n)
(2)
where wk is the filter weight value and R t is the
139
Table 1 Filter weight values of low-pass filter for wave lengths greater than five years Weight number (i)
Weight values
2 1 0 - 1 - 2
0.0269 0.2335 0.4792 0.2335 0.0269
(Wi)
width of tree rings; filter weight values are shown in Table 1 (Holloway, 1958; Noda, 1996). After standardizing all samples, we calculated the cross-correlation among the samples. Because of a difference in the number of annual rings among the samples, degrees of freedom of coefficients differ and therefore cannot be compared directly. Instead, we calculated Student t-values (Fritts, 1976) by modifying the r-value in the following equation to take the degrees of freedom into account: t o = r~/( N - 2 ) / ( 1 - r 2)
(3)
where t o is the t-value, r is the correlation coefficient, N is the number of overlapping data between two chronologies, and ( N - 2 ) are the degrees of freedom. This t-value can be used as an index reflecting degrees of correlation. Finally, the master ring-width chronology was derived by averaging the ring-width chronologies showing high coefficients ( P < 0.01). 3.3. Cross-dating ofundated trees
There are two methods used to cross-date the tree ring samples. One is statistical cross-dating and the other is visual cross-dating using 'signature year' comparison (Douglass, 1941; Huber, 1941). In this study, first we cross-dated buried trees' lifespans by the statistical method, and then confirmed these data using signature years. Statistical cross-dating was conducted by calculating the correlation coefficients between an undated chronology and the master chronology, followed by conversion to the t-value. Thereafter the overlapping period is shifted one year forward or backward, and the t-value is calculated again. This procedure is repeated until the final overlap is calculated. The overlapping period having the highest t-value is the synchronizing period between the two chronologies.
K. Yoshida et aL / Geomorphology 20 (1997) 135 145
140
The signature year is defined as a specific year where almost all samples indicate the same positive or negative growth in ring-width increments compared with the previous year. If agreement in positive or negative growth is greater than 80% of the samples, it was determined as the signature year. The pattern of signature years obtained from the dated trees should coincide with that of undated trees if the undated trees' lifespans are correctly cross-dated. This cross-dating method can be employed for selecting one synchronizing period out of several periods indicating similar high t-values.
(A. sachalinensis and P. jezoensis) collected at breast height to create the master ring-width chronology were also used to estimate tree age. Tree ages were adjusted by adding years calculated from the initial growth rate of conifers. In addition, the latest aerial photos taken in 1991 were used to delineate bare lands and even-aged stands. We also used other air-photo sets taken in 1955, 1963, 1972, 1977 and 1984 to identify old debris flow deposits and the spatial and chronological changes in the even-aged stands. The spatial pattern of debris flow disturbances could be estimated chronologically by interpreting these age and spatial distributions of even-aged stands.
3.4. Other data used in estimating debris flow disturbances
4. Results and discussion
Even-aged stands on deposits of debris flows were found along the Ochiushinai Gully. Thus the disturbance year by debris flow can be estimated according to the age of even-aged stands. Tree rings were counted on stumps. The age information of P. maximowiczii and A. maximowiczii established along the channel was also collected in 1994. Core samples
4.1. The master ring-width chronology of the Ochiushinai Gully in comparison with other sites Thirty-four individual ring-width chronologies were produced from living A. sachalinensis in the Ochiushinai Gully. Of these samples, 28 individual
Master
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03
Fig. 4. The master chronology of the Ochiushinai Gully and cross-dated chronology of the six buried trees. The thick solid lines indicate the ring series for which we cannot measure the widths because of their substantial decay, although they could be counted.
K. Yoshida et al. / Geomorphology 20 (1997) 135 145 Table 2 Correlation of ring-width chronologies among the different sites and species Sampling sites
Species
O.P.
A.A.
T.P.
Ochiushinai
Abies sachalinensis r 0.495 0.604 0.296 N 121 76 120 t 6.22 * 5.83 * 3.38 *
Ochiushinai
Piceajezoensis
r N t
0.528 0.332 76 135 5.35 * 4.06 *
Afutoromanai Abiessachalinensis r N t
0.295 75 2.65 *
Teshio Exp. For.
Picea glehnii
r: correlation coefficient. N: number of overlapping, t: t-value. * P < 0.01.
series having high cross-correlations were chosen and averaged after standardizing each individual series to create the master ring-width chronology for the period from 1871 to 1991 (Fig. 4). This master chronology was compared with other ring-width variations in northern Hokkaido in order to verify that the chronology reflects the regional climate. Noda (1993) indicated that there is a high correlation between the two chronologies of Chamaecyparis obtusa in the western region of Japan which are 450 km apart. In this study, correlations were calculated between the master chronology of the Ochiushinai Gully and (1) P. jezoensis in the Ochiushinai Gully, (2) A. sachalinensis of the Afutoromanai Gully adjacent to the Ochiushinai Gully, and (3) Picea glehnii in the Teshio Experimental Forest of Hokkaido University, which is 70 km southeast of Rishiri Island (Yasue et at., 1994). The master chronology for A. sachalinensis in the Ochiushinai Gully indicates statistically significant correlations with those of the above three chronologies (Table 2). However, the t-value decreases with increasing distance. Thus, the master chronology is assumed to reflect the regional climate.
4.2. Influence of debris flow disturbances on tree ring-width variations Climatic factors greatly influence ring-width variations as indicated previously. However, geomorphic
141
disturbances, such as debris flow, may also have a significant impact on ring-width variation (Atestato, 1971; Shroder, 1978) in association with shear of rootwood or burial of stemwood. We determined the presence or absence of geomorphic effects by analyzing ring-width variations at the Ochiushinai Gully, where frequent debris flows were observed (Kikuchi et at., 1993). The ring-width chronology produced at the Teshio Experimental Forest was used as a reference because this site has not been disturbed by debris flows. Each individual ring-width series in stable, semi-active and active areas was correlated with this referential chronology and the t-values were averaged in every area (Table 3). Mean t-values were compared by one-way ANOVA and multiple comparison tests performed with the statistical package SPSS (Norusis, 1993). The mean t-values were significantly different for the three areas ( F = 9.10, P < 0.001); the stable area had the highest t-value (Tukey-HSD test, P < 0.05). A low t-value, indicating a high variation in ring-widths of the samples in the active and semi-active areas, can be attributed to frequent debris flows, because these areas are characterized by proximity to the channel and lower floodplain surfaces. Therefore, trees in the active area suffer frequent damage or burial by debris flows, resulting in a high variation in tree growth.
4. 3. Cross-dating of establishment and death of the buried trees It is interesting to note that some trunks of buried trees were broken on the present geomorphic surface (Fig. 3). These trees may possibly have been buried in the last 100 years because their decay was not severe. The bark is important in dating their death, Table 3 Mean t-values between the ring-width chronology produced at the Teshio Experimental Forest and those at stable, semi-active and active areas in the Ochiushinai Gully Area
No. of samples
Mean t-value a
Stable Semi-active Active
9 16 9
3.14 _+0.30 c~ 1.72 _+0.26/3 0.97 _+0.46/3
a Means followed by the same letter are not significantly different from each other according to ANOVA, followed by the TukeyHSD test ( P < 0.05).
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
142
Table 4 Disk conditions of the six buried trees Sample No.
Diameter (cm)
Species
Bark
Unearthed situation
Pith
Terminal ring
Number of tings
No. 1 No. 2
30.8 32.2
A.s. A.s.
A A
S S
P A
A A
73 102
No. 3 No. 4
19.5 30.6
A.s. A.s.
A A
S S
P P
A A
62 79
No. 5 No. 6
36.0
A.s. A.s.
A A
O O
P A
A A
87 75
A.s.: Abies sachalinensis. P: present. A: absent. S: standing. O: Other situation.
but unfortunately it was absent on all six samples (Table 4). Anatomical observations with a microscope showed that the six samples belonged to the genus Abies; we determined the species to be as A. sachalinensis from current flora. Buried trees, lifespans were determined by finding the highest t-value through shifting overlaps between the master chronology and each buried tree chronology year by year (Fig. 4). All these t-values of cross-dating were significant at the level of 1%. These results were verified by the signature years comparison. There were six signature years for the living trees between 1902 and 1945. Four of the six years coincided with the signature years of buried trees (Table 5). The positive or negative trends coincided in the living trees and buried trees, for these four years. This result suggests that the dating of buried trees by the statistical test was appropriate. However, the death year may include a minor error introduced by the absence of bark in the sample disks. We believe that the estimated death year is fairly accurate because these samples were not severely decayed and the edge rings were not weathered away. Most of the buried trees were established in the 1870s and died in the 1950s (Fig. 4). Only No. 5 tree survived until 1979, but it showed extremely narrow rings, such as suppression growth, in the middle 1950s (Fig. 5). This suppression period of radial growth was probably caused by sediment burial by a debris flow (Alestalo, 1971) in early 1950s. Thus, we suppose that a large debris flow destroyed the original forest stands on the alluvial fan and provided the regeneration site for A. sachalinensis to invade simultaneously in the 1870s. In the early 1950s, another large debris flow disturbed these
regenerated forests, and some stands adjacent to the channel were buried, killed by thick deposits of sediment. The debris flow disturbance in early 1950s was confirmed by aerial photos taken in 1955. The bare lands and young forests (20-120 m in width) were identified where debris flows had spread, although elongated islands of old stands remained. Table 5 Comparison of the signature years between the living trees and buried dead trees between 1902 and 1945 Year
1902 1903 1904 1905 b 1906 1907 1908 1909 1910 1911 1912 1913 1914 b
Living Buried Year tree tree signature a signature a
_ +
+
+
1924 1925 1926 1927
--
1928 1929 1930 1931 1932 1933 b
+ -+
1934 1935 1936
--
1937 1938 1939 1940 1941 1942 b
+
1915 1916 1917 1918 1919 1920 1921 1922 1923
+ _
Living Buried tree tree signature signature
+
+
1943 1944 1945
a Increase ( + ) and decrease ( - ) in annual increment in compari-
son with the previous year. b The signature year coincided between the living tree and buried dead tree.
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
4.4. 5~atial and temporal pattern of debris flow disturbances The even-aged stands were distributed over the alluvial fan head in the Ochiushinai Gully. These forests were observed in aerial photos and verified by field observations in 1994. Based upon the age distribution, the even-aged stands along the channel were classified into three age categories: 100 (97 _+ 4.1; mean _+ SD), 40 (36 _+ 1.1), and 25 (24 _+ 0.5) years old. Most of these stands are distributed at the left side (looking downstream) of the present channel, forming elongated narrow patches (Fig. 6). The forests mainly composed of A. sachalinensis over the entire fan head were dated at 97 _+ 3.5 years from collected core samples, which were used to develop the master ring chronology. These A. sachalinensis forests were estimated at about 120 years old because age determination from 20 samples in the field indicated that seedlings of A. sachalinensis took about 20 years to reach to breast height, where core samples were taken. Based on the aerial photos, the channel course in 1955 was at the left side of the
143
alluvial fan head and it shifted from the left to the fight side where the present channel is situated during 1963-1972. These lateral migrations cause destruction and regeneration of the forests at this fan head of the Ochiushinai Gully. The results of dating the buried trees and the distribution of these even-aged stands are discussed here together. First, most of the buried trees were established in the 1870s. The living trees on the same geomorphic surface were 120 years old. We believed that pre-existing forests on the entire fan head were once cleared by a high-magnitude debris flow in the 1870s and replaced by the present regenerated forests mainly composed of A. sachalinensis. Second, the ring growth of the buried trees ended in the early 1950s and 40 year-old forests were distributed in the vicinity. This debris flow, in the early 1950s, killed trees along the channel by depositing a 3 m thick body of sediment. These sites were simultaneously invaded by A. maximowiczii. Further, small patches aged about 100 and 25 year-old, respectively, indicated partial disturbances by small debris flows in the 1890s and the late 1960s. According to
Fig. 5. The extreme narrow tings of the mid-1950s.
K. Yoshida et aL / Geomorphology 20 (1997) 135 145
144
i!i"ii'i!i4 ....
iii=
J i'ili 50m
Forest stand map About 120 years old
About 100 years old i
Present channel
spreading area of
the debris flow
bout 40 years old About 25 years old
1870 S
1890 s
early 1950 s
0i late 1 9 6 0 s
100 R (rn)
Fig. 6. Forest stand map and the extent of the debris flows.
the aerial photos in 1972, uniform stands established after the early 1950s debris flow remained in the middle of bare lands and young stands (20-50 m in width) which presumably were created by the late 1960s debris flow. This disturbance occurred along the abandoned channel. The extents of the sequential debris flow disturbances are shown on Fig. 6. The debris flow disturbed the entire fan head in the 1870s, and the left side of the present channel in the 1890s. The disturbance areas in the 1890s and the early 1950s nearly overlap, but the intensity of the early 1950s flow is probably greater than the 1890s, as shown by the 3 m thick deposits. The late 1960s flow exhibited a narrow strip of disturbance which follows an abandoned channel course. Dendrochronological analysis of trees buried by debris flows and spatial distribution of even-aged stands were used to clarify the recent history of geomorphic disturbances. An advantage of cross-dating is the ability to date the occurrence of event on a yearly basis. Unfortunately, all buried trees we sampled had no bark and could not be determined when they died. It is not clear, however, whether trees may be killed instantly by the deposition of debris flows or wether they may survive for a certain period. This
should be dependent on the depth of the buried sediment and tolerance of the responding species to the deposition. Strunk (1991) reported that the critical burial depth which withered spruces by a debris flow was between 1.6 and 1.8 m, but did not define the period taken for the trees to die completely. Thus, estimation of debris flow occurrence always includes some errors derived from the physiological responses of tree species, even though their death year was accurately cross-dated.
Acknowledgements We would like to thank Dr. R. Funada, Dr. O. Kobayashi and Mr. K. Yasue (Laboratory of Wood Biology, Hokkaido University) for their technical assistance on dendrochronological procedures and identification of buried trees. We are also grateful to the staff of the Wakkanai Public Works Office and Mr. T. Takagai (Taka Kikakaku-Consultant) for their assistance in the field during our investigation. Moreover, we thank Professors T. Araya and O. Shimizu for their kind advice throughout this study. Dr. D.K. Yamaguchi gave us productive comments on the method of cross-dating and introduced many
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
references. The earlier drafts of this manuscript was substantially improved by the critical comments made by Drs. B.H. Luckman and A. Rapp. This research was supported in part by Grant-in Aid for Scientific Research (07456065, 07308066, 08760141, 08456072, 08556022) from the Ministry of Education, Science and Culture.
References Alestalo, J., 1971. Dendrochronological interpretation of geomorphic processes. Fennia 105, 1 140. Araya, T., 1971. Morphological study of bed load movement in torrential rivers. Res. Bull. Exp. For. Hokkaido Univ. 28, 193 258 (in Japanese with English abstract). Cook, E.R., 1990. A conceptual linear aggregate model for tree rings. In: E.R. Cook and L.A. Kairiukstis (Editors), Methods of Dendrochronology. Kluwer, Dordrecht, pp. 98 104. Douglass, A.E., 1941. Crossdating in dendrochronology. J. For. 39, 825 831. Everitt, B.L., 1968. Use of the cottonwood in an investigation of the recent history of a flood plain. Am. J. Sci. 266, 417 439. Fritts, H.C., 1976. Tree Rings and Climate. Academic Press, London, 567 pp. Higashi, S., 1979. Earth-surface movement (Chihyou-HendouRon). Hokkaido Univ. PUN., Sapporo, 280 pp. (in Japanese). Higashi, S., Fujiwara, K., Araya, T., Murai, N., 1971. Dendrochronological studies on the transition of the creeping land. Res. Bull. Exp. For. Hokkaido Univ. 28, 339 419 (in Japanese with English abstract). Holloway, J.L., 1958. Smoothing and filtering of time series and space. Adv. Geophys. 4, 351 389. Holmes, R.L., 1983. Computer-assisted quality control in tree-ring dating and measurement. Tree-Ring Bull. 43, 69 78. Huber, B., 1941. Aufbau einer mitteleuropiiischen Jahrring-chronologie. Mitt. Akad. Dtsch. Forstwiss. 1, 110 120. Kikuchi, S., Araya, T., Maldno, T., Takagai, T., 1993. Debris flow disasters on the east coast of Rishiri island in recent years. Trans. Meet. Hokkaido. Br. Jpn. For. Soc. 41, 139 141 (in Japanese). Kobayashi, T., 1987. Geology of Rishiri Volcano. J. Geol. Soc. Jpn. 93, 749 760 (in Japanese with English abstract).
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La Marche, V.C., 1966. An 800-year history of stream erosion as indicated by botanical evidence. U.S. Geol. Surv. Prof. Pap. 550-D, 83 86. Nakamura, F., 1986. Analysis of storage and transport processes based on age distribution of sediment. Trans. Jpn. Geomorph. Union 7, 165 184. Nakamura, F., Maita, H., Araya, T., 1995. Sediment routing analyses based on chronological changes in hillslope and riverbed morphologies. Earth Surf. Process. Landforms 20, 333 346. Noda, M., 1993. Method for calculating common variations in time series of annual growth rings, L On the Chamaecyparis obtusa and Cryptomeria japonica in western Japan. Trans. Jpn. For. Soc. 104, 335 337 (in Japanese). Noda, M., 1996. Analysis of time-series variation of tree-ring width. Res. Bull. Exp. For. Hokkaido Univ. 53, 97 146 (in Japanese with English abstract). Norusis, M.J., 1993. SPSS for Windows: Base System User's Guide. SPSS Inc., Chicago (Translated into Japanese by SPSS Japan Inc., Tokyo). Sapporo District Meteorological Observatory, 1993. The Statistics of Automated Meteorological Data Acquisition Systems in Hokkaido. Hokkaido Branch of the Japan Weather Association, Sapporo, 417 pp. (in Japanese). Sasa, K., 1978. Debris flow on the Horaizawa and Aoldnosawa fan. J. Jpn. Erosion. Control Eng. 107, 1 8 (in Japanese). Schweingruber, F.H., 1986. Tree Rings-Basics and Applications of Dendrochronology. Kluwer, Dordrecht, 276 pp. Shroder, J.F., 1978. Dendrogeomorphological analysis of mass movement on Table Cliffs Plateau, Utah. Quat. Res. 9, 168 185. Sigafoos, R.S., 1964. Botanical evidence of floods and flood-plain deposition. U.S. Geol. Surv. Prof. Pap. 485-A, 1 35. Strunk, H., 1991. Frequency distribution of debris flows in the Alps since the 'Little ice age'. Z. Geomorphol. Suppl. 83, 71 81. Tatewald, M., 1941. The vegetation of the Island of Rishiri. J. Sapporo Soc. Agric. For. 34, 70 102 (in Japanese). Yamaguchi, D.K., Hoblitt, R.P., 1995. Tree-ring dating ofpre-1980 volcanic flowage deposits at Mount St. Helens, Washington. Geol. Soc. Am. Bull. Yasue, K., Funada, R., Noda, M., Fukazawa, K., 1994. Dendroclimatological study of Picea glehnii growing in the Teshio Exp. For., Hokkaido Univ.. Res. Bull. Exp. For. Hokkaido Univ. 51,243 266 (in Japanese with English abstract).
Geomorphology 20 (1997) 135 145
Dendrochronological analysis of debris flow disturbance on Rishiri Island Keiji Yoshida
a Shun-ich Kikuchi a,* Futoshi Nakamura a Masato Noda b
a Department of Forest Science, Faculty of Agriculture, Hokkaido University, Sapporo, 060, Japan b Uryu Experimental Forest, Faculty of Agriculture, Hokkaido University, Nayoro, 096, Japan
Received 13 June 1996; accepted 25 January 1997
Abstract Abies sachalinensis dominates the alluvial fan head of the Ochiushinai Gully on Rishiri Island, Japan. This species is able to adapt to frequent disturbances by debris flows. Even-aged stands composed of A. sachalinensis or Alnus maximowiczii were found along the channel, and standing dead trees buried by debris flows were discovered at the alluvial fan head. We used dendrochronological data in order to analyse the geomorphic history of the fan head. We determined the master ring-width chronology by synchronizing ring-width variations in living trees. This master chronology was used to cross-date the establishment and death of the buried trees. Results indicated that most of the buried trees were established in the 1870s and died in the early 1950s. Fuxther, debris flow was estimated to have occurred in the 1890s and the late 1960s based upon the distribution of even-aged stands seen in aerial photos. The ring-width variations of the trees adjacent to the channel indicate a low correlation for synchronization, while those located on the hillslope have a high correlation. A low correlation in the riparian trees can be attributed to the instability of geomorphic surfaces caused by debris flow disturbances. Keywords." dendrochronology; debris flows; alluvial fan; disturbance; Rishiri Island (Japan)
1. Introduction Tree ring-width variations contain chronological and environmental information, which can be used for spatial and temporal analysis of geomorphic processes. For example, La Marche (1966) employed a cross-dating method for dating trees killed b y bank erosion and analyzed an 800-year history of river sedimentation. Higashi et al. (1971) used the forma-
* Corresponding author. Phone: + 81-11-706-2809. Fax: + 8111-706-4935. E-mail: Idk3,[email protected]
tion of reaction wood in tree rings in order to analyze the chronological movement of landslides. Yamaguchi and Hoblitt (1995) estimated age of death of trees buried in pyroclastic flows or lahar sediments and discussed their disturbances. In a river floodplain, riparian forests with uniform heights are frequently observed. They are generally composed of pioneer species such as Salix, Populus and Alnus spp. and are even-aged (Everitt, 1968; Araya, 1971; Nakamura, 1986). The seeds of pioneer trees are disseminated widely b y wind. They invade bare lands soon after the sediment is stabilized and germinate within a year (Araya, 1971). Everitt (1968)
0169-555X/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0 1 69-555X(97)000 10-X
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K. Yoshida et aL / Geomorphology 20 (1997) 135 145
used the ages of cottonwood established on a floodplain to explain a recent history of flood disturbance on a valley floor. Nakamura et al. (1995) used the age distribution of even-aged stands to determine the sediment budget and routing in a river basin in Japan. Even-aged stands can be found on the deposits of debris flow. Further, trees damaged by geomorphic processes preserve much temporal information (Sigafoos, 1964). For example, trees buried by debris flows show suppressed growth and may survive by sprouting adventitious roots, or eventually die. Scars remain in their trunks if they are wounded (Alestalo, 1971; Shroder, 1978). The geomorphic processes on an alluvial fan have been inferred based on using dendrochronological data such as the age of even-aged stands, trunk scars, and the period of growth suppression (Sasa, 1978; Strunk, 1991). Debris flows frequently occur in small tributaries in Japan and they disturb alluvial fans, particularly at the fan head (Higashi, 1979). We found a number of standing dead trees at the fan
head of a gully cut in volcanic rocks on Rishiri Island, and could date the occurrence of debris flows by dendrochronological analysis. The main objectives of this study are to clarify the geomorphic history of debris flows by cross-dating the ring series of buried dead trees and by investigating the age structure and distribution of even-aged stands, and also to examine the effects of debris flow disturbances on tree ring-width variations.
2. Study site Rishiri Island is located northwest of Hokkaido, in extreme northern Japan (Fig. 1). The circumference and area of the island are about 60 km and 183 km 2, respectively. Rishiri is a round volcanic island approximately 16 km in diameter. Rishiri Volcano (1721 m) lies at the center of the island, and is a Quaternary stratovolcano having deep gullies seeding active alluvial fans (Kobayashi, 1987). Abies
Sea i
ully
Kutsug~ ~futoromanai ;ully
Risiri Is
I
1
Teshio E x p e r i m e n t a l
I Forest of H o k k a i d o Univ.
Fig. 1. Location of the study site.
0
I
2
3
I
I
I
I km
137
K. Yoshida et al. / Geomorphology 20 (1997) 135 145 sachalinensis and Picea jezoensis predominate on the alluvial fans, although Alnus maximowiczii, Salix sachalinensis, and Populus maximowiczii are dis-
at. (1993). This asymmetric pattern of rainfall may contribute to the concentration of debris torrents on the eastern side of the island.
tributed along the stream channel (Tatewaki, 1941). The study site is the fan head of the Ochiushinai Gully, where even-aged stands (about 102 to 10 4 m 2) established immediately after debris flow disturbances are prominent and where many trees buried by debris flows are found. The watershed area is 6.5 km 2 and the average channel gradient is 12.1%. A. maximowiczii is widely distributed over the low, terraced deposits. Major debris flow disasters at the Ochiushinai Gully which destroyed property were recorded in 1897, 1923, 1947, 1972 and 1989 (Kikuchi et at., 1993). The average annual precipitation over the 12-year period from 1979-1990 is 935.8 mm, recorded in the Kutsugata, on the western side of the island (Sapporo District Meteorological Observatory, 1993). However, the intense, heavy rainfalls tend to fall on the eastern side of the island, as reported by Kikuchi et
The OchiushinaiGully k N~.3 checkdam ...."
3. M e t h o d s
3.1. Collection o f tree ring data
We found a group of standing buried trees exposed beside the channel bank. They appeared in debris flow deposits along the channel (Figs. 2 and 3). Of these, cross-sectional disks of four trees (No. 1, No. 2, No. 3 and No. 4) being not severely damaged, were obtained near the original root flare of a tree in order to estimate the date of the establishment period. The debris flow deposits burying these tree trunks were about 3 m thick, consisting of massive, matrix-supported gravel, and no humus layers were included. The sediment, where original root flares of buried trees were situated, was composed of
,,) ',,-q ~ '
J
Line~l~/
Tree ring sampling site © : in stable area © : in semi-active area • : in active area • : Location of buried t r e e s
2 ~
.-..~, ~ = =
~j
250m
semi-active
active Abandoned channel
~% :~ Present channel
Briefsketchof the Line-1
/0 N
stable I
.d.;o
,L~: .~.:C .~
/ 1 2m lm
Fig. 2. Map of the fan head of the Ochiushinai Gully and tree-ring samplingsites.
200m
I
100
I
138
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
coarse sand including few gravel fragments. This stratigraphy indicates that these deposits were formed by a single, high-magnitude debris flow event. Moreover, two other buried trees (No. 5, No. 6) were uncovered in the same deposits of the debris flow during the construction of check dams. A master ring-width chronology maximizing common variance in the area is required to conduct
reliable cross-dating (Schweingruber, 1986). There is no master ring-width chronology covering the Rishiri Island. Thus, we collected living 34 samples of A. sachalinensis in 1994 to create the master ring-width chronology containing average width variation at the fan head of Ochiushinai Gully (Fig. 2). We classified geomorphic surfaces into stable, semi-active and active areas, based upon the distance and height from
Fig. 3. Photoof buriedtrees.
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
the channel bed, and samples were collected from the three areas. The stable area is furthest away from the channel bed at highest elevation, while the active area is close to the channel on the lower floodplain surfaces. The semi-active area is situated between the two. We used an increment borer (~b 5 mm) and took one core sample per tree at breast height (1.3 m above ground). We obtained disks from stumps which had been cut during construction of check dams. Of 34 samples, 30 were core samples and 4 were disks. 3.2. Standardization ofring-width variation and establishment o f the master ring-width chronology
Tree ring-widths were measured in units of 0.01 mm. We cross-checked each ring-width variation statistically using the COFECHA program (Holmes, 1983). This program detects missing rings or errors due to artifacts and improves the reliability of the ring-width chronology. Removing non-climatic factors (@) from the measured ring-width series (R t) is referred to as 'standardization' and the standardized ring-width series ( I t ) can be expressed as: (l)
It = R J @
The measured ring-width series should be standardized to create the master ring-width chronology. Deterministic methods represented by the exponential and polynomial models and stochastic methods such as low-pass digital filtering are available for estimating @ (Cook, 1990). In the present study, we used one of the stochastic methods named 'lowpass filter' (Holloway, 1958; Fritts, 1976; Cook, 1990; Yasue et al., 1994; Noda, 1996). This filter is able to select any cut-off frequency and remove a long time scale variation by keeping medium and short time scales (Noda, 1996). Debris flows, a major geomorphic disturbance over the alluvial fans of the Rishiri Island, will leave short-frequency signals such as suppression in radial growth. Thus we used 5-year filter length to include short-frequency signals. The equation of Gt was derived as follows: i
Gt=
~
wkRt+k
k i ( i = 2 ; t = 1,2,3 . . . . . n)
(2)
where wk is the filter weight value and R t is the
139
Table 1 Filter weight values of low-pass filter for wave lengths greater than five years Weight number (i)
Weight values
2 1 0 - 1 - 2
0.0269 0.2335 0.4792 0.2335 0.0269
(Wi)
width of tree rings; filter weight values are shown in Table 1 (Holloway, 1958; Noda, 1996). After standardizing all samples, we calculated the cross-correlation among the samples. Because of a difference in the number of annual rings among the samples, degrees of freedom of coefficients differ and therefore cannot be compared directly. Instead, we calculated Student t-values (Fritts, 1976) by modifying the r-value in the following equation to take the degrees of freedom into account: t o = r~/( N - 2 ) / ( 1 - r 2)
(3)
where t o is the t-value, r is the correlation coefficient, N is the number of overlapping data between two chronologies, and ( N - 2 ) are the degrees of freedom. This t-value can be used as an index reflecting degrees of correlation. Finally, the master ring-width chronology was derived by averaging the ring-width chronologies showing high coefficients ( P < 0.01). 3.3. Cross-dating ofundated trees
There are two methods used to cross-date the tree ring samples. One is statistical cross-dating and the other is visual cross-dating using 'signature year' comparison (Douglass, 1941; Huber, 1941). In this study, first we cross-dated buried trees' lifespans by the statistical method, and then confirmed these data using signature years. Statistical cross-dating was conducted by calculating the correlation coefficients between an undated chronology and the master chronology, followed by conversion to the t-value. Thereafter the overlapping period is shifted one year forward or backward, and the t-value is calculated again. This procedure is repeated until the final overlap is calculated. The overlapping period having the highest t-value is the synchronizing period between the two chronologies.
K. Yoshida et aL / Geomorphology 20 (1997) 135 145
140
The signature year is defined as a specific year where almost all samples indicate the same positive or negative growth in ring-width increments compared with the previous year. If agreement in positive or negative growth is greater than 80% of the samples, it was determined as the signature year. The pattern of signature years obtained from the dated trees should coincide with that of undated trees if the undated trees' lifespans are correctly cross-dated. This cross-dating method can be employed for selecting one synchronizing period out of several periods indicating similar high t-values.
(A. sachalinensis and P. jezoensis) collected at breast height to create the master ring-width chronology were also used to estimate tree age. Tree ages were adjusted by adding years calculated from the initial growth rate of conifers. In addition, the latest aerial photos taken in 1991 were used to delineate bare lands and even-aged stands. We also used other air-photo sets taken in 1955, 1963, 1972, 1977 and 1984 to identify old debris flow deposits and the spatial and chronological changes in the even-aged stands. The spatial pattern of debris flow disturbances could be estimated chronologically by interpreting these age and spatial distributions of even-aged stands.
3.4. Other data used in estimating debris flow disturbances
4. Results and discussion
Even-aged stands on deposits of debris flows were found along the Ochiushinai Gully. Thus the disturbance year by debris flow can be estimated according to the age of even-aged stands. Tree rings were counted on stumps. The age information of P. maximowiczii and A. maximowiczii established along the channel was also collected in 1994. Core samples
4.1. The master ring-width chronology of the Ochiushinai Gully in comparison with other sites Thirty-four individual ring-width chronologies were produced from living A. sachalinensis in the Ochiushinai Gully. Of these samples, 28 individual
Master
.~ /'X./~/~.J"%~AP~./~
chronology
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- V ~'
~'V f
.
.
.
.
.
.
.
.
.
A^AA^AAMI t-value
V
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~ .
.
.
.
.
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~V'~
v v
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-V
l
'
.
.............................................................................
.............................................................................
Sp 3
1881
1943
Sp 4
Sp. 6
:
957
~
5.63
ii
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4.37
3.02
i iiiiiiii
CO
O3
i
CO
i
,i
~J
CO
CO
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CO
O0
!iil
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CO
I
I llll
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I
I I I I
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I
I
~
llllllll
~
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ILl
~
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~
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~
I!lll
Ob
IIII1'1
Ob
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i
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IIIIIIIII
Ob
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i
Ob
, IIIIIIII
Ob
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03
Fig. 4. The master chronology of the Ochiushinai Gully and cross-dated chronology of the six buried trees. The thick solid lines indicate the ring series for which we cannot measure the widths because of their substantial decay, although they could be counted.
K. Yoshida et al. / Geomorphology 20 (1997) 135 145 Table 2 Correlation of ring-width chronologies among the different sites and species Sampling sites
Species
O.P.
A.A.
T.P.
Ochiushinai
Abies sachalinensis r 0.495 0.604 0.296 N 121 76 120 t 6.22 * 5.83 * 3.38 *
Ochiushinai
Piceajezoensis
r N t
0.528 0.332 76 135 5.35 * 4.06 *
Afutoromanai Abiessachalinensis r N t
0.295 75 2.65 *
Teshio Exp. For.
Picea glehnii
r: correlation coefficient. N: number of overlapping, t: t-value. * P < 0.01.
series having high cross-correlations were chosen and averaged after standardizing each individual series to create the master ring-width chronology for the period from 1871 to 1991 (Fig. 4). This master chronology was compared with other ring-width variations in northern Hokkaido in order to verify that the chronology reflects the regional climate. Noda (1993) indicated that there is a high correlation between the two chronologies of Chamaecyparis obtusa in the western region of Japan which are 450 km apart. In this study, correlations were calculated between the master chronology of the Ochiushinai Gully and (1) P. jezoensis in the Ochiushinai Gully, (2) A. sachalinensis of the Afutoromanai Gully adjacent to the Ochiushinai Gully, and (3) Picea glehnii in the Teshio Experimental Forest of Hokkaido University, which is 70 km southeast of Rishiri Island (Yasue et at., 1994). The master chronology for A. sachalinensis in the Ochiushinai Gully indicates statistically significant correlations with those of the above three chronologies (Table 2). However, the t-value decreases with increasing distance. Thus, the master chronology is assumed to reflect the regional climate.
4.2. Influence of debris flow disturbances on tree ring-width variations Climatic factors greatly influence ring-width variations as indicated previously. However, geomorphic
141
disturbances, such as debris flow, may also have a significant impact on ring-width variation (Atestato, 1971; Shroder, 1978) in association with shear of rootwood or burial of stemwood. We determined the presence or absence of geomorphic effects by analyzing ring-width variations at the Ochiushinai Gully, where frequent debris flows were observed (Kikuchi et at., 1993). The ring-width chronology produced at the Teshio Experimental Forest was used as a reference because this site has not been disturbed by debris flows. Each individual ring-width series in stable, semi-active and active areas was correlated with this referential chronology and the t-values were averaged in every area (Table 3). Mean t-values were compared by one-way ANOVA and multiple comparison tests performed with the statistical package SPSS (Norusis, 1993). The mean t-values were significantly different for the three areas ( F = 9.10, P < 0.001); the stable area had the highest t-value (Tukey-HSD test, P < 0.05). A low t-value, indicating a high variation in ring-widths of the samples in the active and semi-active areas, can be attributed to frequent debris flows, because these areas are characterized by proximity to the channel and lower floodplain surfaces. Therefore, trees in the active area suffer frequent damage or burial by debris flows, resulting in a high variation in tree growth.
4. 3. Cross-dating of establishment and death of the buried trees It is interesting to note that some trunks of buried trees were broken on the present geomorphic surface (Fig. 3). These trees may possibly have been buried in the last 100 years because their decay was not severe. The bark is important in dating their death, Table 3 Mean t-values between the ring-width chronology produced at the Teshio Experimental Forest and those at stable, semi-active and active areas in the Ochiushinai Gully Area
No. of samples
Mean t-value a
Stable Semi-active Active
9 16 9
3.14 _+0.30 c~ 1.72 _+0.26/3 0.97 _+0.46/3
a Means followed by the same letter are not significantly different from each other according to ANOVA, followed by the TukeyHSD test ( P < 0.05).
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
142
Table 4 Disk conditions of the six buried trees Sample No.
Diameter (cm)
Species
Bark
Unearthed situation
Pith
Terminal ring
Number of tings
No. 1 No. 2
30.8 32.2
A.s. A.s.
A A
S S
P A
A A
73 102
No. 3 No. 4
19.5 30.6
A.s. A.s.
A A
S S
P P
A A
62 79
No. 5 No. 6
36.0
A.s. A.s.
A A
O O
P A
A A
87 75
A.s.: Abies sachalinensis. P: present. A: absent. S: standing. O: Other situation.
but unfortunately it was absent on all six samples (Table 4). Anatomical observations with a microscope showed that the six samples belonged to the genus Abies; we determined the species to be as A. sachalinensis from current flora. Buried trees, lifespans were determined by finding the highest t-value through shifting overlaps between the master chronology and each buried tree chronology year by year (Fig. 4). All these t-values of cross-dating were significant at the level of 1%. These results were verified by the signature years comparison. There were six signature years for the living trees between 1902 and 1945. Four of the six years coincided with the signature years of buried trees (Table 5). The positive or negative trends coincided in the living trees and buried trees, for these four years. This result suggests that the dating of buried trees by the statistical test was appropriate. However, the death year may include a minor error introduced by the absence of bark in the sample disks. We believe that the estimated death year is fairly accurate because these samples were not severely decayed and the edge rings were not weathered away. Most of the buried trees were established in the 1870s and died in the 1950s (Fig. 4). Only No. 5 tree survived until 1979, but it showed extremely narrow rings, such as suppression growth, in the middle 1950s (Fig. 5). This suppression period of radial growth was probably caused by sediment burial by a debris flow (Alestalo, 1971) in early 1950s. Thus, we suppose that a large debris flow destroyed the original forest stands on the alluvial fan and provided the regeneration site for A. sachalinensis to invade simultaneously in the 1870s. In the early 1950s, another large debris flow disturbed these
regenerated forests, and some stands adjacent to the channel were buried, killed by thick deposits of sediment. The debris flow disturbance in early 1950s was confirmed by aerial photos taken in 1955. The bare lands and young forests (20-120 m in width) were identified where debris flows had spread, although elongated islands of old stands remained. Table 5 Comparison of the signature years between the living trees and buried dead trees between 1902 and 1945 Year
1902 1903 1904 1905 b 1906 1907 1908 1909 1910 1911 1912 1913 1914 b
Living Buried Year tree tree signature a signature a
_ +
+
+
1924 1925 1926 1927
--
1928 1929 1930 1931 1932 1933 b
+ -+
1934 1935 1936
--
1937 1938 1939 1940 1941 1942 b
+
1915 1916 1917 1918 1919 1920 1921 1922 1923
+ _
Living Buried tree tree signature signature
+
+
1943 1944 1945
a Increase ( + ) and decrease ( - ) in annual increment in compari-
son with the previous year. b The signature year coincided between the living tree and buried dead tree.
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
4.4. 5~atial and temporal pattern of debris flow disturbances The even-aged stands were distributed over the alluvial fan head in the Ochiushinai Gully. These forests were observed in aerial photos and verified by field observations in 1994. Based upon the age distribution, the even-aged stands along the channel were classified into three age categories: 100 (97 _+ 4.1; mean _+ SD), 40 (36 _+ 1.1), and 25 (24 _+ 0.5) years old. Most of these stands are distributed at the left side (looking downstream) of the present channel, forming elongated narrow patches (Fig. 6). The forests mainly composed of A. sachalinensis over the entire fan head were dated at 97 _+ 3.5 years from collected core samples, which were used to develop the master ring chronology. These A. sachalinensis forests were estimated at about 120 years old because age determination from 20 samples in the field indicated that seedlings of A. sachalinensis took about 20 years to reach to breast height, where core samples were taken. Based on the aerial photos, the channel course in 1955 was at the left side of the
143
alluvial fan head and it shifted from the left to the fight side where the present channel is situated during 1963-1972. These lateral migrations cause destruction and regeneration of the forests at this fan head of the Ochiushinai Gully. The results of dating the buried trees and the distribution of these even-aged stands are discussed here together. First, most of the buried trees were established in the 1870s. The living trees on the same geomorphic surface were 120 years old. We believed that pre-existing forests on the entire fan head were once cleared by a high-magnitude debris flow in the 1870s and replaced by the present regenerated forests mainly composed of A. sachalinensis. Second, the ring growth of the buried trees ended in the early 1950s and 40 year-old forests were distributed in the vicinity. This debris flow, in the early 1950s, killed trees along the channel by depositing a 3 m thick body of sediment. These sites were simultaneously invaded by A. maximowiczii. Further, small patches aged about 100 and 25 year-old, respectively, indicated partial disturbances by small debris flows in the 1890s and the late 1960s. According to
Fig. 5. The extreme narrow tings of the mid-1950s.
K. Yoshida et aL / Geomorphology 20 (1997) 135 145
144
i!i"ii'i!i4 ....
iii=
J i'ili 50m
Forest stand map About 120 years old
About 100 years old i
Present channel
spreading area of
the debris flow
bout 40 years old About 25 years old
1870 S
1890 s
early 1950 s
0i late 1 9 6 0 s
100 R (rn)
Fig. 6. Forest stand map and the extent of the debris flows.
the aerial photos in 1972, uniform stands established after the early 1950s debris flow remained in the middle of bare lands and young stands (20-50 m in width) which presumably were created by the late 1960s debris flow. This disturbance occurred along the abandoned channel. The extents of the sequential debris flow disturbances are shown on Fig. 6. The debris flow disturbed the entire fan head in the 1870s, and the left side of the present channel in the 1890s. The disturbance areas in the 1890s and the early 1950s nearly overlap, but the intensity of the early 1950s flow is probably greater than the 1890s, as shown by the 3 m thick deposits. The late 1960s flow exhibited a narrow strip of disturbance which follows an abandoned channel course. Dendrochronological analysis of trees buried by debris flows and spatial distribution of even-aged stands were used to clarify the recent history of geomorphic disturbances. An advantage of cross-dating is the ability to date the occurrence of event on a yearly basis. Unfortunately, all buried trees we sampled had no bark and could not be determined when they died. It is not clear, however, whether trees may be killed instantly by the deposition of debris flows or wether they may survive for a certain period. This
should be dependent on the depth of the buried sediment and tolerance of the responding species to the deposition. Strunk (1991) reported that the critical burial depth which withered spruces by a debris flow was between 1.6 and 1.8 m, but did not define the period taken for the trees to die completely. Thus, estimation of debris flow occurrence always includes some errors derived from the physiological responses of tree species, even though their death year was accurately cross-dated.
Acknowledgements We would like to thank Dr. R. Funada, Dr. O. Kobayashi and Mr. K. Yasue (Laboratory of Wood Biology, Hokkaido University) for their technical assistance on dendrochronological procedures and identification of buried trees. We are also grateful to the staff of the Wakkanai Public Works Office and Mr. T. Takagai (Taka Kikakaku-Consultant) for their assistance in the field during our investigation. Moreover, we thank Professors T. Araya and O. Shimizu for their kind advice throughout this study. Dr. D.K. Yamaguchi gave us productive comments on the method of cross-dating and introduced many
K. Yoshida et al. / Geomorphology 20 (1997) 135 145
references. The earlier drafts of this manuscript was substantially improved by the critical comments made by Drs. B.H. Luckman and A. Rapp. This research was supported in part by Grant-in Aid for Scientific Research (07456065, 07308066, 08760141, 08456072, 08556022) from the Ministry of Education, Science and Culture.
References Alestalo, J., 1971. Dendrochronological interpretation of geomorphic processes. Fennia 105, 1 140. Araya, T., 1971. Morphological study of bed load movement in torrential rivers. Res. Bull. Exp. For. Hokkaido Univ. 28, 193 258 (in Japanese with English abstract). Cook, E.R., 1990. A conceptual linear aggregate model for tree rings. In: E.R. Cook and L.A. Kairiukstis (Editors), Methods of Dendrochronology. Kluwer, Dordrecht, pp. 98 104. Douglass, A.E., 1941. Crossdating in dendrochronology. J. For. 39, 825 831. Everitt, B.L., 1968. Use of the cottonwood in an investigation of the recent history of a flood plain. Am. J. Sci. 266, 417 439. Fritts, H.C., 1976. Tree Rings and Climate. Academic Press, London, 567 pp. Higashi, S., 1979. Earth-surface movement (Chihyou-HendouRon). Hokkaido Univ. PUN., Sapporo, 280 pp. (in Japanese). Higashi, S., Fujiwara, K., Araya, T., Murai, N., 1971. Dendrochronological studies on the transition of the creeping land. Res. Bull. Exp. For. Hokkaido Univ. 28, 339 419 (in Japanese with English abstract). Holloway, J.L., 1958. Smoothing and filtering of time series and space. Adv. Geophys. 4, 351 389. Holmes, R.L., 1983. Computer-assisted quality control in tree-ring dating and measurement. Tree-Ring Bull. 43, 69 78. Huber, B., 1941. Aufbau einer mitteleuropiiischen Jahrring-chronologie. Mitt. Akad. Dtsch. Forstwiss. 1, 110 120. Kikuchi, S., Araya, T., Maldno, T., Takagai, T., 1993. Debris flow disasters on the east coast of Rishiri island in recent years. Trans. Meet. Hokkaido. Br. Jpn. For. Soc. 41, 139 141 (in Japanese). Kobayashi, T., 1987. Geology of Rishiri Volcano. J. Geol. Soc. Jpn. 93, 749 760 (in Japanese with English abstract).
145
La Marche, V.C., 1966. An 800-year history of stream erosion as indicated by botanical evidence. U.S. Geol. Surv. Prof. Pap. 550-D, 83 86. Nakamura, F., 1986. Analysis of storage and transport processes based on age distribution of sediment. Trans. Jpn. Geomorph. Union 7, 165 184. Nakamura, F., Maita, H., Araya, T., 1995. Sediment routing analyses based on chronological changes in hillslope and riverbed morphologies. Earth Surf. Process. Landforms 20, 333 346. Noda, M., 1993. Method for calculating common variations in time series of annual growth rings, L On the Chamaecyparis obtusa and Cryptomeria japonica in western Japan. Trans. Jpn. For. Soc. 104, 335 337 (in Japanese). Noda, M., 1996. Analysis of time-series variation of tree-ring width. Res. Bull. Exp. For. Hokkaido Univ. 53, 97 146 (in Japanese with English abstract). Norusis, M.J., 1993. SPSS for Windows: Base System User's Guide. SPSS Inc., Chicago (Translated into Japanese by SPSS Japan Inc., Tokyo). Sapporo District Meteorological Observatory, 1993. The Statistics of Automated Meteorological Data Acquisition Systems in Hokkaido. Hokkaido Branch of the Japan Weather Association, Sapporo, 417 pp. (in Japanese). Sasa, K., 1978. Debris flow on the Horaizawa and Aoldnosawa fan. J. Jpn. Erosion. Control Eng. 107, 1 8 (in Japanese). Schweingruber, F.H., 1986. Tree Rings-Basics and Applications of Dendrochronology. Kluwer, Dordrecht, 276 pp. Shroder, J.F., 1978. Dendrogeomorphological analysis of mass movement on Table Cliffs Plateau, Utah. Quat. Res. 9, 168 185. Sigafoos, R.S., 1964. Botanical evidence of floods and flood-plain deposition. U.S. Geol. Surv. Prof. Pap. 485-A, 1 35. Strunk, H., 1991. Frequency distribution of debris flows in the Alps since the 'Little ice age'. Z. Geomorphol. Suppl. 83, 71 81. Tatewald, M., 1941. The vegetation of the Island of Rishiri. J. Sapporo Soc. Agric. For. 34, 70 102 (in Japanese). Yamaguchi, D.K., Hoblitt, R.P., 1995. Tree-ring dating ofpre-1980 volcanic flowage deposits at Mount St. Helens, Washington. Geol. Soc. Am. Bull. Yasue, K., Funada, R., Noda, M., Fukazawa, K., 1994. Dendroclimatological study of Picea glehnii growing in the Teshio Exp. For., Hokkaido Univ.. Res. Bull. Exp. For. Hokkaido Univ. 51,243 266 (in Japanese with English abstract).