- Email: [email protected]
Age and size distribution in a long-term forest dynamics
Fores;~~logy Management Forest Ecology and Management 92 (1997) 39-44
Age and size distribution in a long-term forest dynamics Junji Sano ’ Fact&
of Agriculture,
Tottori
University.
4-101 Koyama-minami,
Tottori
680, Japan
Accepted 22 October 1996
Abstract To examine regenerational patterns in a long-term forestdynamics,ageandsizedistributionwasstudiedin an old-growth deciduousoak (Quercus mongolica var. grosseserrata) forest in northernHokkaido,Japan.The frequencydistributionof size classes(diameterat breastheightand tree height) showedcontinuoussize structureswith a largenumberof smaller treesanda smallnumberof largerones.The distributionof diametersshoweda reversed-Jshape,andthat of heightshad smallpeaksshowingvertical strata.The frequency distributionof ages,on the other hand, showeddiscontinuousand periodicpatternswith an interval of approximately100yearsbetweenthe peaksof ageconcentration.This periodwould be relatedto the stemexclusionand understoryreinitiation stagesin forest standdynamics.Although the age distribution showeda discontinuous pattern,therelationshipbetweenagesandsizeswaswell fitted to logarithmicregressions. The curve fitting wasbetterfor diameterthanfor height,andthe agedistributionalsodemonstrated the existenceof severalcohortsin a stand.The cohortsrangedwidely in size in the old-growth forest and demonstrated a gradualdecreasein regeneration following the most concentratedperiod. Theseresultssuggestthat the concentratedregenerations would be established several times in long-term forest development showing multicohort structure and cyclic forest dynamics. Forest management should be planned with the recognition of such results and decisions made concerning long-term forest dynamics. Keywords:
Cyclic
forest dynamics;
Deciduous
oak; Forest
development;
1. Introduction The deciduous oak, Quercus mongolica var. is distributed widely in Japan and is the most common speciesof broadleaf and mixed natural forests in flat and montane regions of Hokkaido, northern Japan (Tatewaki, 1958). The old-growth mixed forest dominated by Q. mongolica var. grosseserrata and Abies sachalinensis in cen-
grosseserrata,
Tel.:+ (faculty);
81 857 31 5377 (dial-in); e-mail: [email protected].
0378-l 127/97/$17.00 Copyright PII SO378-1127(96)03958-S
fax:
+ 81 857 31 5347
0 1997 Elsevier
Multicoht;
Old-gro~h;
Quercus
tral Hokkaido was maintained by lessfrequent large disturbances and more frequent smaller ones. The age distribution of almost all of the species was intermittent (Ishikawa and Ito, 1989). The secondary forests of Q. mongolica var. grosseserrata affected by cuttings showed age distributions with single or few cohort structuresin Hokkaido (Kikuzawa, 1983) and other regions in Japan (Komiyama, 1989; Higo and Teramoto, 1989). Age distribution results have been obtained from some old-growth coniferous forests in Hokkaido (Suzuki et al., 1987; Hiura et al., 1996). However, little is known about the age distribution and dynamics of old-growth Q. mongolica var. grosseserrata forests.
Science B.V. All rights reserved.
40
J. Sane/
Forest Ecology
and Management
Oliver and Larson (1990) stated that the oldgrowth stage of forest stand dynamics demonstrated a multicohort structure created by several disturbances. Koop (1989) also reported that an old-growth forest showed long-term cyclic forest dynamics. It has not been determined whether the old-growth Q. mongolica var. grosseserrata forests, including those dominated by trees with a long life span (exceeding 500 years), have a multicohort structure and longterm cyclic dynamics. The objective of the current study was to assess the age and size distribution in a long-term forest dynamics in relation to regenerational patterns of an old-growth Q. mongolica var. grosseserrata forest.
3. Methods Today there are only a few primeval forests including old-growth Q. mongolica var. grosseserrata forests, even in northern Hokkaido, compared with the number of primeval forests a century ago when the first settlement appeared in this region. I set up a plot to examine the age distribution in an old-growth Q. mongolica var. grosseseratta forest in the Uryu Experiment Forest of Hokkaido University. The stand was dominated by Q. mongolica var. grosseserrata in the overstory, Acer mono var. mayrii. Abies sachalinensis, and the other broadleaf species in the midstory and understory, and was primarily covered with Susa senanensis, a dwarf bamboo, on the forest floor. A 0.25-ha square plot (50 m X 50 m) was accepted for this study. It had relatively flat topography, gently sloping under 5” on a well-drained hillside, and there was no evidence of fire or artificial trace in the records, forest floors, or cross-sections within the plot. There was a wood yard used for
The study area was located in the Uryu Experiment Forest of Hokkaido University (21600 ha), which lies at 44”N and 142“E, in northern Hokkaido of northern Japan. Here, many gentle ridges and valleys surround an artificial lake, Shumarinai-ko. The natural and semi-natural broadleaf, coniferous, and mixed forests are located in the pan-mixed forest zone (Tatewaki, 1958), with dense dwarf bamboos (Susu spp.) on the forest floors. Dominant tree species include oak (Quercus morzgolica var. grosseserrata), maple ( Acer mono), fir ( Abies sachalinensis), and birch (Bet&a spp.).
Species
Density
2 2 m) in an old-growth (ha-’
)
312 216 56 52 48 40 28 20 20 8 4
deciduous
DBH (cm) Mean
Quercus mongolica var. grosseserrata Acer motto var. mayrii Magnolia obouata Abies sachalinensis Acanthopanax sciadophylloides Phellodendron amurense Betula ermanii Kalopanax pictus Sorbus americana subsp. japonica Ulmus laciniata Fraxinus mandrhurica var. japonica
24.7 8.6 12.0 6.9 13.8 15.0 10.9 28.6 9.9 9.3 4.5
39-44
The climate of the area is characterized by cold snowy winters and short warm summers. Mean daily temperature is 3.l”C, and mean yearly precipitation is 1652 mm. The precipitation is usually well-distributed throughout the year. The average snow-covered season extends over half the year, and the maximum yearly snow depth is 2750 mm (Ujiie. 1986).
2. Study area
Table 1 Stem density, DBH, height, and age of trees (height in northern Hokkaido, Japan
92 (I9971
+ k * rt + + * f f f *
oak (Quercus Height
mongolicu
(ml
var. grosseserrata)
forest
Age (years)
+ SD
Max.
Mean f SD
Max.
Mean f SD
Max.
24.2 7.7 14.0 5.6 12.6 4.4 9.0 22.5 12.2 1.1 0.0
123 32 44 23 39 21 25 60 SI 10 5
14.6 6.9 8.3 4.3 8.1 14.1 8.2 15.5 1.2 5.1 4.9
28.2 16.3 21.2 12.3 16.7 18.5 18.7 27.1 12.4 7.3 4.9
109.9 70.2 61.0 62.6 70.3 74.6 59.2 138.3 40.3 68.8 62.0
so.5 168 19s 101 14s 79 76 295 63 72 62
5 f 5 f f f f f + * f
6.3 4.4 6.2 3.0 5.2 4.2 6.1 8.5 4.5 3.2 0.0
f rt & f * 5 + * + f It
%.8 25.5 65.8 17.4 25.1 3.6 10.2 101.3 19.6 3.9 0.0
J. Sano / Forest Ecology
and Management
92 (1997)
41
39-44
4. Results 4.1. Size distribution
of trees
80
20 30 40 50 60 70 80 60100110120130
4
6
Eleven tree species occurred in the 0.25-ha plot (Table 1). The density of the trees was 804 ha-’ and Quercus mongolica var. grosseserrata comprised 38.8% of all species. The mean dimensions of Q. mongolica var. grosseserrata and Kalopanax pictus were higher than other species. The frequency distribution of DBH class (at lo-cm intervals) showed a continuous reversed-J shape, with many smaller trees and a few larger ones (Fig. l(a)). The frequency distribution of height class (at 2-m intervals) showed small peaks at the 24-26-m, 1214-m, and 2-4-m classes (Fig. l(b)). Three strata of crown layer (height over ca. 20 m), midstory (ca. lo-20 m), and understory (under ca. 10 m> were recognized. Q. mongolica var. grosseserrata, the most dominant species, was found predominantly in larger size classes, and the other species, mainly Acer mono var. mayrii, were found primarily in smaller size classes.
8 10 12 14 16 18 20 22 24 26 28 30
Height class (m) Fig. 1. Frequency distribution of tree sizes. (a) Diameter at 1.3 m (DBH) in IO-cm classes. (b) Tree height in 2-m classes.
selective cuttings of a primeval forest in this region after the clear cutting of all the trees in the plot. All living trees (height 2 2 m) in the plot were identified and numbered. The diameter at breast height (DBH) and height of each tree were measured. After clear cutting, the ages of all trees were estimated by counting their annual rings using stereoscopic microscopes in the laboratory.
0
100
200
300
400
500
Age class (years) Fig. 2. Frequency classes.
distribution
of tree ages, shown in 20-year
age
J. Sam /Forest
32
4.2. Age distribution
Ecology
and Management
qf trees
92 f 199713944
4.3. Relationship between age and si,-e
The frequency distribution of age class (at 20-year intervals) included many younger trees with a few older ones (Fig. 2). However, the age-class distribution demonstrated discontinuous patterns compared with size distribution. Trees were found primarily around five age classes: 60-80, 200-220, 280-300. 420-440, and 500-520 years. The distribution seemed to be discontinuous with an interval of approximately 100 years between the peaks. The age classes of 60-80 and 200-220 years, with a relatively large number of trees in each, showed similar patterns, namely a gradual decrease in trees following the peaks toward the younger age classes.
(a)
Relationships between tree ages and sizes (in log scale) with logarithmic regression curves are represented in Fig. 3. The curve fittings to logarithmic regressions are as follows: Log( D) = 61.492 Log( A) - 97.844 (r’=0.641.
P
Log( H ) = 19.73 I Log( A) -- 26.095 (r~=O.SOS_
P
where A represents the tree age (years), I> is the DBH (cm) and H is the tree height (m). The fittings of DBH were shown to be better than for height, mainly becausethe DBH distribution showed a continuous reversed-J shape, and the height distribution showed three small peaks with vertical strata (see also Fig. 1). The size distribution within each cohort showed wide variation. especially in the cohort of 60-80 years.
5. Discussion
! 100
200
I
I
I
300
400
500
400
I 500
Age (years)
II' 0
I 100
I 300
200 Age
Fig. 3. Relationships between DBH. (b) Age vs height.
I 600
Wars)
ages and sizes of trees. (a) Age vs
The old-growth Quercus mongolicu var. ~~a.~eserruta forest showed different patterns in age and size distribution. The distribution was continuous for sizes (Fig. 1). and discontinuous for ages (Fig. 21. The continuous patterns of size distribution was affected by growth differences among trees in each cohort, becauseof the wide variation in size, even in a given age class, and especially in younger trees (Fig. 31. In the sameway, it is possiblethat any tree in a given size class tnay have quite a different age. Therefore, except in the casewhere significant linear relationships between age and size were obtained as in Abrams (1985) and Ishikawa and Ito (19891, extrapolating from tree size distribution to age distribution can be misleading(Oliver and Larson, f990). Some coniferous forests showed periodic patterns of age distribution (H&t and Loucks, 1936), similar to the overlap of wave regenerations@rugel. 1976: Kohyama and Fujita, 1981). In old-growth coniferous forests in Hokkaido, the distributional-patterns of sizes were continuous and age structures were allaged (Suzuki et al., 1987; Hiura et al.. 1996). On the other hand, in natural broadleaf forests, the distribu-
J. Sano / Forest Ecology and Management 92 (1997) 39-44
tional patterns appeared relatively discontinuous (Falinski, 1986; Koop, 1989). Similarly, the age structuresof e. mongolica var. grosseserrata forests were revealed as having discontinuous patterns (Kikuzawa, 1983; Komiyama, 1989; Higo and Teramoto, 1989). Secondary forests dominated by another deciduous oak
43
lower shade tolerance of oak than that of beech (Nomoto, 1956; Koike, 1988). Understory reinitiation occurs soonest in stands of intolerant species since much sunlight reachesthe forest floor at that point (Oliver and Larson, 1990). In the old-growth Q. mongolica var. grosseserrata forest, the regeneration patterns should be evaluated for forest managementby spatial and temporal distribution of trees becausethe multicohort structure showing the wide variation in sizes was constructed in a long-term forest development. At the sametime, even if there is little advanced and/or new regeneration on the forest floor at a given time, it does not always correspond to a new safe site (Silvertown, 1982) even in the future, especially for Q. mongolica var. grosseserrata with a long life span; it may be just before the understory reinitiation stage in longterm cyclic forest dynamics. Implications for forest managementof old-growth forests regarding natural regenerationsshould be considered to preserve the cyclic forest structure and the density of cohorts, especially in advanced and/or new regenerations, needsto be controlled when the overstory trees are removed. Future studies should examine the results of the old-growth Q. mongolica var. grosseserrata forest in the context of other forests in relation to the intra/inter-cohort speciesperformances.
Acknowledgements The author wishes to sincerely thank the staff of the Uryu Experiment Forest for their offering of the sampling plot and the many membersof the Department of Forestry of Hokkaido University for their field assistanceand their patient and reliable laboratory measurementsof the annual rings. The author also thanks the two anonymousreviewers for helpful commentson the manuscript.
References Abrams, M.D., 1985. Age-diameter relationships of Quercus species in relation to edaphic factors in Gallery forests in northeast Kansas. For. Ecol. Manage., 13: 181-193. Day. R.J., 1972. Stand structure, succession, and use of southern Alberta’s Rocky Mountain forest. Ecology. 53: 472-478. Falinski, J.B., 1986. Vegetation Dynamics in Temperate Lowland Primeval Forest. Dr. Junk, Dordrecht, 537 pp.
44
J. Sane / Forest Ecology
and Management
Hashizume, H., 1991. Studies on the regeneration process of secondary stands (II) - on the stand structure and tree age structure of deciduous broad-leaved forests. Hardwood Res., 6: 17-30 (in Japanese with English summary). Hett, J.M. and Loucks, O.L., 1976. Age structure models of balsam fir and eastern hemlock. J. Ecol., 64: 1029-1044. Higo, M. and Teramoto, T., 1989. Stand structure and dynamics of cool temperate broad-leaved forest dominated by Quercus mongolica var. grosseserrata. Res. Bull. Fat. Agric. Gifu Univ., 54: 51-58 (in Japanese with English summary). Hiura, T., Sano, J. and Konno, Y., 1996. Age structure and response to ftne-scale disturbances of Abies sacknlinensis. Picea jezoensis, Picea gleknii, and Betula ermmii growing under the influence of a dwarf bamboo understory in northern Japan. Can. J. For. Res., 26: 289-297. Horn, H.S., 1974. The ecology of secondary succession. Ann. Rev. Ecol. Syst., 5: 25-37. Ishikawa, Y. and ho, K., 1989. The regeneration process in a mixed forest in central Hokkaido, Japan. Vegetatio, 79: 75-84. Kikuzawa, K., 1983. Broadleaved Forests of Hokkaido. Hokkaido Zorin Shinko Kyokai, Sapporo, 152 pp. (in Japanese). Kohyama. T. and Fujita, N.. 1981. Studies on the Abies population of Mt. Shimagarc. I. Survivorship curve. Bot. Mag. Tokyo, 94: 55-68. Koike, T., 1988. Leaf structure and photosynthetic performance as related to the forest succession of deciduous broad-leaved trees. PI. Sp. Biol., 3: 77-87.
Y2 (1997)
39-44
Komiyama, A., 1989. Tree age composition and the regeneration process of a secondary deciduous broad-leaved forest. J. Jpn. For. Sot., 71: 374-379 (in Japanese). Koop. H., 1989. Forest Dynamics. Springer-Verlag, Berlin. 229 PP. Monk, C.D. and Day, F.P., Jr.. 1985. Vegetation analysis, primary production and selected nutrient budgets for a southern Appalachian oak forest: a synthesis of IBP studies at Coweeta. For. Ecol. Manage., 10: 87- 113. Nomoto, N.. 1956. Analysis of the succession process on the beech-oak forest. Jpn. J. Ecol., 6: 102-107. Oliver. CD. and Larson, B.C.. 1990. Forest Stand Dynamics. McGraw-Hill, New York, 467 pp. Silvettown. J.W., 1982. Introduction to Plant Population Ecology. Longman, London, 209 pp. Spmgel. D.G.. 1976. Dynamic structure of wave-generated Abies balsamea forests in the north-eastern United States. J. Ecol.. 64: 889-911. Suzuki. E.. Ota, K., Igarashi, T. and Fujiwara. K., 1987. Regeneration process of coniferous forests in notthern Hokkaido. 1. A&es suckulinensis forest and Picea gleknii forest. Ecol. Reb.. 2: 61-75. Tatewaki, M., 1958. Forest ecology of the islands of the North Pacific Ocean. 3. Fat. Agric. Hokkaido Univ., 50: 371-486. Ujiie, M., 1986. Outlines of College Experiment Forests, Hokkaido University. College Experiment Forest. Hokkaido University. Sapporo. 47 pp.
Age and size distribution in a long-term forest dynamics Junji Sano ’ Fact&
of Agriculture,
Tottori
University.
4-101 Koyama-minami,
Tottori
680, Japan
Accepted 22 October 1996
Abstract To examine regenerational patterns in a long-term forestdynamics,ageandsizedistributionwasstudiedin an old-growth deciduousoak (Quercus mongolica var. grosseserrata) forest in northernHokkaido,Japan.The frequencydistributionof size classes(diameterat breastheightand tree height) showedcontinuoussize structureswith a largenumberof smaller treesanda smallnumberof largerones.The distributionof diametersshoweda reversed-Jshape,andthat of heightshad smallpeaksshowingvertical strata.The frequency distributionof ages,on the other hand, showeddiscontinuousand periodicpatternswith an interval of approximately100yearsbetweenthe peaksof ageconcentration.This periodwould be relatedto the stemexclusionand understoryreinitiation stagesin forest standdynamics.Although the age distribution showeda discontinuous pattern,therelationshipbetweenagesandsizeswaswell fitted to logarithmicregressions. The curve fitting wasbetterfor diameterthanfor height,andthe agedistributionalsodemonstrated the existenceof severalcohortsin a stand.The cohortsrangedwidely in size in the old-growth forest and demonstrated a gradualdecreasein regeneration following the most concentratedperiod. Theseresultssuggestthat the concentratedregenerations would be established several times in long-term forest development showing multicohort structure and cyclic forest dynamics. Forest management should be planned with the recognition of such results and decisions made concerning long-term forest dynamics. Keywords:
Cyclic
forest dynamics;
Deciduous
oak; Forest
development;
1. Introduction The deciduous oak, Quercus mongolica var. is distributed widely in Japan and is the most common speciesof broadleaf and mixed natural forests in flat and montane regions of Hokkaido, northern Japan (Tatewaki, 1958). The old-growth mixed forest dominated by Q. mongolica var. grosseserrata and Abies sachalinensis in cen-
grosseserrata,
Tel.:+ (faculty);
81 857 31 5377 (dial-in); e-mail: [email protected].
0378-l 127/97/$17.00 Copyright PII SO378-1127(96)03958-S
fax:
+ 81 857 31 5347
0 1997 Elsevier
Multicoht;
Old-gro~h;
Quercus
tral Hokkaido was maintained by lessfrequent large disturbances and more frequent smaller ones. The age distribution of almost all of the species was intermittent (Ishikawa and Ito, 1989). The secondary forests of Q. mongolica var. grosseserrata affected by cuttings showed age distributions with single or few cohort structuresin Hokkaido (Kikuzawa, 1983) and other regions in Japan (Komiyama, 1989; Higo and Teramoto, 1989). Age distribution results have been obtained from some old-growth coniferous forests in Hokkaido (Suzuki et al., 1987; Hiura et al., 1996). However, little is known about the age distribution and dynamics of old-growth Q. mongolica var. grosseserrata forests.
Science B.V. All rights reserved.
40
J. Sane/
Forest Ecology
and Management
Oliver and Larson (1990) stated that the oldgrowth stage of forest stand dynamics demonstrated a multicohort structure created by several disturbances. Koop (1989) also reported that an old-growth forest showed long-term cyclic forest dynamics. It has not been determined whether the old-growth Q. mongolica var. grosseserrata forests, including those dominated by trees with a long life span (exceeding 500 years), have a multicohort structure and longterm cyclic dynamics. The objective of the current study was to assess the age and size distribution in a long-term forest dynamics in relation to regenerational patterns of an old-growth Q. mongolica var. grosseserrata forest.
3. Methods Today there are only a few primeval forests including old-growth Q. mongolica var. grosseserrata forests, even in northern Hokkaido, compared with the number of primeval forests a century ago when the first settlement appeared in this region. I set up a plot to examine the age distribution in an old-growth Q. mongolica var. grosseseratta forest in the Uryu Experiment Forest of Hokkaido University. The stand was dominated by Q. mongolica var. grosseserrata in the overstory, Acer mono var. mayrii. Abies sachalinensis, and the other broadleaf species in the midstory and understory, and was primarily covered with Susa senanensis, a dwarf bamboo, on the forest floor. A 0.25-ha square plot (50 m X 50 m) was accepted for this study. It had relatively flat topography, gently sloping under 5” on a well-drained hillside, and there was no evidence of fire or artificial trace in the records, forest floors, or cross-sections within the plot. There was a wood yard used for
The study area was located in the Uryu Experiment Forest of Hokkaido University (21600 ha), which lies at 44”N and 142“E, in northern Hokkaido of northern Japan. Here, many gentle ridges and valleys surround an artificial lake, Shumarinai-ko. The natural and semi-natural broadleaf, coniferous, and mixed forests are located in the pan-mixed forest zone (Tatewaki, 1958), with dense dwarf bamboos (Susu spp.) on the forest floors. Dominant tree species include oak (Quercus morzgolica var. grosseserrata), maple ( Acer mono), fir ( Abies sachalinensis), and birch (Bet&a spp.).
Species
Density
2 2 m) in an old-growth (ha-’
)
312 216 56 52 48 40 28 20 20 8 4
deciduous
DBH (cm) Mean
Quercus mongolica var. grosseserrata Acer motto var. mayrii Magnolia obouata Abies sachalinensis Acanthopanax sciadophylloides Phellodendron amurense Betula ermanii Kalopanax pictus Sorbus americana subsp. japonica Ulmus laciniata Fraxinus mandrhurica var. japonica
24.7 8.6 12.0 6.9 13.8 15.0 10.9 28.6 9.9 9.3 4.5
39-44
The climate of the area is characterized by cold snowy winters and short warm summers. Mean daily temperature is 3.l”C, and mean yearly precipitation is 1652 mm. The precipitation is usually well-distributed throughout the year. The average snow-covered season extends over half the year, and the maximum yearly snow depth is 2750 mm (Ujiie. 1986).
2. Study area
Table 1 Stem density, DBH, height, and age of trees (height in northern Hokkaido, Japan
92 (I9971
+ k * rt + + * f f f *
oak (Quercus Height
mongolicu
(ml
var. grosseserrata)
forest
Age (years)
+ SD
Max.
Mean f SD
Max.
Mean f SD
Max.
24.2 7.7 14.0 5.6 12.6 4.4 9.0 22.5 12.2 1.1 0.0
123 32 44 23 39 21 25 60 SI 10 5
14.6 6.9 8.3 4.3 8.1 14.1 8.2 15.5 1.2 5.1 4.9
28.2 16.3 21.2 12.3 16.7 18.5 18.7 27.1 12.4 7.3 4.9
109.9 70.2 61.0 62.6 70.3 74.6 59.2 138.3 40.3 68.8 62.0
so.5 168 19s 101 14s 79 76 295 63 72 62
5 f 5 f f f f f + * f
6.3 4.4 6.2 3.0 5.2 4.2 6.1 8.5 4.5 3.2 0.0
f rt & f * 5 + * + f It
%.8 25.5 65.8 17.4 25.1 3.6 10.2 101.3 19.6 3.9 0.0
J. Sano / Forest Ecology
and Management
92 (1997)
41
39-44
4. Results 4.1. Size distribution
of trees
80
20 30 40 50 60 70 80 60100110120130
4
6
Eleven tree species occurred in the 0.25-ha plot (Table 1). The density of the trees was 804 ha-’ and Quercus mongolica var. grosseserrata comprised 38.8% of all species. The mean dimensions of Q. mongolica var. grosseserrata and Kalopanax pictus were higher than other species. The frequency distribution of DBH class (at lo-cm intervals) showed a continuous reversed-J shape, with many smaller trees and a few larger ones (Fig. l(a)). The frequency distribution of height class (at 2-m intervals) showed small peaks at the 24-26-m, 1214-m, and 2-4-m classes (Fig. l(b)). Three strata of crown layer (height over ca. 20 m), midstory (ca. lo-20 m), and understory (under ca. 10 m> were recognized. Q. mongolica var. grosseserrata, the most dominant species, was found predominantly in larger size classes, and the other species, mainly Acer mono var. mayrii, were found primarily in smaller size classes.
8 10 12 14 16 18 20 22 24 26 28 30
Height class (m) Fig. 1. Frequency distribution of tree sizes. (a) Diameter at 1.3 m (DBH) in IO-cm classes. (b) Tree height in 2-m classes.
selective cuttings of a primeval forest in this region after the clear cutting of all the trees in the plot. All living trees (height 2 2 m) in the plot were identified and numbered. The diameter at breast height (DBH) and height of each tree were measured. After clear cutting, the ages of all trees were estimated by counting their annual rings using stereoscopic microscopes in the laboratory.
0
100
200
300
400
500
Age class (years) Fig. 2. Frequency classes.
distribution
of tree ages, shown in 20-year
age
J. Sam /Forest
32
4.2. Age distribution
Ecology
and Management
qf trees
92 f 199713944
4.3. Relationship between age and si,-e
The frequency distribution of age class (at 20-year intervals) included many younger trees with a few older ones (Fig. 2). However, the age-class distribution demonstrated discontinuous patterns compared with size distribution. Trees were found primarily around five age classes: 60-80, 200-220, 280-300. 420-440, and 500-520 years. The distribution seemed to be discontinuous with an interval of approximately 100 years between the peaks. The age classes of 60-80 and 200-220 years, with a relatively large number of trees in each, showed similar patterns, namely a gradual decrease in trees following the peaks toward the younger age classes.
(a)
Relationships between tree ages and sizes (in log scale) with logarithmic regression curves are represented in Fig. 3. The curve fittings to logarithmic regressions are as follows: Log( D) = 61.492 Log( A) - 97.844 (r’=0.641.
P
Log( H ) = 19.73 I Log( A) -- 26.095 (r~=O.SOS_
P
where A represents the tree age (years), I> is the DBH (cm) and H is the tree height (m). The fittings of DBH were shown to be better than for height, mainly becausethe DBH distribution showed a continuous reversed-J shape, and the height distribution showed three small peaks with vertical strata (see also Fig. 1). The size distribution within each cohort showed wide variation. especially in the cohort of 60-80 years.
5. Discussion
! 100
200
I
I
I
300
400
500
400
I 500
Age (years)
II' 0
I 100
I 300
200 Age
Fig. 3. Relationships between DBH. (b) Age vs height.
I 600
Wars)
ages and sizes of trees. (a) Age vs
The old-growth Quercus mongolicu var. ~~a.~eserruta forest showed different patterns in age and size distribution. The distribution was continuous for sizes (Fig. 1). and discontinuous for ages (Fig. 21. The continuous patterns of size distribution was affected by growth differences among trees in each cohort, becauseof the wide variation in size, even in a given age class, and especially in younger trees (Fig. 31. In the sameway, it is possiblethat any tree in a given size class tnay have quite a different age. Therefore, except in the casewhere significant linear relationships between age and size were obtained as in Abrams (1985) and Ishikawa and Ito (19891, extrapolating from tree size distribution to age distribution can be misleading(Oliver and Larson, f990). Some coniferous forests showed periodic patterns of age distribution (H&t and Loucks, 1936), similar to the overlap of wave regenerations@rugel. 1976: Kohyama and Fujita, 1981). In old-growth coniferous forests in Hokkaido, the distributional-patterns of sizes were continuous and age structures were allaged (Suzuki et al., 1987; Hiura et al.. 1996). On the other hand, in natural broadleaf forests, the distribu-
J. Sano / Forest Ecology and Management 92 (1997) 39-44
tional patterns appeared relatively discontinuous (Falinski, 1986; Koop, 1989). Similarly, the age structuresof e. mongolica var. grosseserrata forests were revealed as having discontinuous patterns (Kikuzawa, 1983; Komiyama, 1989; Higo and Teramoto, 1989). Secondary forests dominated by another deciduous oak
43
lower shade tolerance of oak than that of beech (Nomoto, 1956; Koike, 1988). Understory reinitiation occurs soonest in stands of intolerant species since much sunlight reachesthe forest floor at that point (Oliver and Larson, 1990). In the old-growth Q. mongolica var. grosseserrata forest, the regeneration patterns should be evaluated for forest managementby spatial and temporal distribution of trees becausethe multicohort structure showing the wide variation in sizes was constructed in a long-term forest development. At the sametime, even if there is little advanced and/or new regeneration on the forest floor at a given time, it does not always correspond to a new safe site (Silvertown, 1982) even in the future, especially for Q. mongolica var. grosseserrata with a long life span; it may be just before the understory reinitiation stage in longterm cyclic forest dynamics. Implications for forest managementof old-growth forests regarding natural regenerationsshould be considered to preserve the cyclic forest structure and the density of cohorts, especially in advanced and/or new regenerations, needsto be controlled when the overstory trees are removed. Future studies should examine the results of the old-growth Q. mongolica var. grosseserrata forest in the context of other forests in relation to the intra/inter-cohort speciesperformances.
Acknowledgements The author wishes to sincerely thank the staff of the Uryu Experiment Forest for their offering of the sampling plot and the many membersof the Department of Forestry of Hokkaido University for their field assistanceand their patient and reliable laboratory measurementsof the annual rings. The author also thanks the two anonymousreviewers for helpful commentson the manuscript.
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