AOBPreview originally published online on July 9, 2003
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Annals of Botany 92: 339-347, 2003
© 2003 Annals of Botany Company
Size Structure of Current-year Shoots in Mature Crowns
1 Graduate School of Agriculture, Kyoto University, Kitashirakawa Sakyoku, Kyoto 606-8502, Japan
* For correspondence. E-mail makizoh{at}hitohaku.jp 
Present address: Institute of Natural and Environmental Sciences, Himeji Institute of Technology, Yayoigaoka 6 Sanda Hyogo, 669-1546 Japan.
Received: 11 December 2002; Returned for revision: 8 April 2003; Accepted: 14 May 2003 Published electronically: 9 July 2003
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Characteristics of current-year shoot populations were examined for three mature trees of each of three deciduous broad-leaved species. For first-order branches (branches emerging from the vertical trunk) of the trees examined, lengths or diameters of all current-year shoots were measured. Total leaf mass and total current-year stem mass of first-order branches were estimated using an allometric relationship between leaf or stem mass and length or diameter of current-year stems. For each tree, the number of current-year shoots on a first-order branch was proportional to the basal stem cross-sectional area of the branch. On the other hand, first-order branches had shoot populations with size structures similar to each other. As a result, the leaf mass of a first-order branch was proportional to the basal stem cross-sectional area of the branch, being compatible with the pipe-model relationship. All current-year shoot populations had positively skewed size structures. Because small shoots have a larger ratio of leaf mass to stem mass than large shoots, first-order branches had an extremely large ratio of leaf mass to current-year stem mass. This biased mass allocation will reduce costs for current stem production, respiration and future radial growth, and is beneficial to mature trees with a huge accumulation of non- photosynthetic organs. The allometric relationships between leaf mass and basal stem diameter and that between leaf mass and current-year stem mass of first-order branches were each similar across the trees examined. Characteristics of shoot populations tended to offset inter-species diversity of shoot allometry so that branch allometry shows inter-species convergence.
Key words: Allometry, Acer mono var. mayrii (Schwer.) Koidz., Betula maximowicziana Regel, biomass allocation, current-year shoot population, deciduous broad-leaved trees, first-order branch, mature crown, shoot size structure, pipe-model relationship, Quercus crispula Brume.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
A tree crown contains many current-year shoots of various forms and sizes (Hallé et al., 1978). For deciduous species, the two major functions of the crown, i.e. extension growth and photosynthetic production, are carried out by current-year shoots. To assess their functional importance, the characteristics of current-year shoot populations have often been analysed (e.g. Cannell, 1974; Cochrane and Ford, 1978; Maillette, 1982; Remphrey et al., 1983; Koike, 1989). However, previous researchers have not investigated the relationship between current-year shoot populations and other organs, by which the shoot population is supported mechanically as well as physiologically. Current-year shoots of deciduous trees depend for their early growth on stored resources in older stems and, once current leaves open, they provide photosynthates to other organs (Kozlowski, 1971). Therefore, a close relationship can be expected between the development of the shoot population and the radial growth of older stems.
The pipe-model relationship is a well-known relationship between foliar biomass and the diameter of foliage-supporting stems (Shinozaki et al., 1964). In general, total leaf mass or leaf area tends to be proportional to the basal cross-sectional area of the non-photosynthetic organ, which bears these leaves (Shinozaki et al., 1964; Waring et al., 1980; Chiba, 1990). This trend is explained by the quantitative balance between leaves and supportive stems (Shinozaki et al., 1964; Waring et al., 1980; Whitehead et al., 1984; Long and Smith, 1988). Instead of dealing with the physiological details of the pipe-model theory, the focus here is on the effect of the pipe-model relationship on the characteristics of the current-year shoot population. Suzuki and Hiura (2000) found that large branches of deciduous trees are compatible with the pipe-model relationship: leaf mass of a first-order branch (i.e. large branches that bifurcated directly from the main trunk) was proportional to the basal cross-sectional area of the branch. For each first-order branch, the leaf mass of the branch is the combined mass of leaves on all current-year shoots on the branch. Therefore, leaf mass of each first-order branch should be highly dependent on the number of current-year shoots on the branch. In addition, the size structure of the current-year shoot population will also affect leaf mass of each first-order branch, because leaf mass of each current-year shoot is dependent on shoot size (Takenaka, 1997; Yagi and Kikuzawa, 1999; Suzuki and Hiura, 2000). For these reasons, the number of current-year shoots, size structure of shoot population and basal diameter of first-order branches are expected to correlate with each other, whenever the pipe-model relationship is realized. This hypothesis was tested using well-grown mature trees, whose first-order branches are expected to be compatible with the pipe-model relationship.
Another prediction regarding the size structure of the current-year shoot population in mature trees is provided. As a general trend, large current-year shoots tend to have a smaller ratio of leaf mass to stem mass than do small shoots (Takenaka, 1997; Yagi and Kikuzawa, 1999). This trend results in a functional differentiation between large and small shoots: large shoots form the crown framework, whereas small ones display leaves within the framework. Therefore, the size structure of a shoot population has significant effects on the functional characteristics of their coherent crown or branch (Maillette, 1982; Remphrey et al., 1983; McGraw, 1989). Maillette (1982) found that young trees of Betula pendula had a larger ratio of the number of long shoots to short shoots than mature trees. Young trees produce many long shoots, which should contribute to rapid crown construction and height growth. On the other hand, the positively skewed shoot size structure (many short shoots and a few long shoots) of mature trees has been considered as a negative response of ageing (Maillette, 1982; Wilson, 1991). However, it is expected that the positively skewed size structure of current-year shoot populations has a functional importance for mature trees. As a tree grows, non-photosynthetic organs are accumulated in the tree body more rapidly than the foliar biomass increases. Large trees must reduce biomass allocation to stem production, which has costs not only at present but also in the future for maintenance respiration and radial growth. A positively skewed shoot size structure of mature trees can overcome this problem because a large number of leaves are displayed by a small number of current-year stems. The potential advantage of a positively skewed size structure of the shoot population has not been studied previously. In this study, it is suggested that mature trees have a positively skewed shoot size structure, and that the size structure actually reduces leaf display costs.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
This study was carried out in the Nakagawa Experimental Forest (44°20'N, 144°15'E) of Hokkaido University, Japan, where the vegetation represents the northern mixed forests of Hokkaido Island. Annual precipitation is 1406 mm, of which 40 % falls as snow in winter. Mean annual air temperature is 4·9 °C. Dominant tree species are Abies sachalinensis (Fr. Schm.) Masters, Picea jezoensis (Sieb. et Zucc.) Carr., Acer mono var. mayrii (Schwer.) Koidz., Betula ermanii Cham., Betula maximowicziana Regel, Quercus crispula Brume, Sorbus commixta Hedl. and Tilia japonica Shimonkai (Hiura et al., 1995).
Three species, Betula maximowicziana, Acer mono var. mayrii and Quercus crispula, were examined. B. maximowicziana shows morphological differentiation between long and short shoots. Each long shoot extends sympodially, bearing three to seven leaves with axillary buds in alternate phyllotaxis (Fig. 1A). Each short shoot is monopodial, usually having one terminal bud and two or three leaves in opposite/whorled phyllotaxis (Fig. 1B). Acer mono shows opposite phyllotaxis and monopodial elongation. Each current-year shoot of A. mono has one to four pairs of leaves on a stem (Fig. 1C); moreover, lammas elongation in terminally lateral buds is often observed on flowering current-year shoots (Fig. 1D). Like other Quercus species (Addicott, 1991; Nagy, 1992; Buck-Sorlin and Bell, 1998), Q. crispula abscises young shoots. Each current-year shoot of Q. crispula has one terminal bud, one to five terminally lateral buds and several lateral buds in the lower stem in alternate phyllotaxis (Fig. 1E).
|
In early summer 1997 and 1999, three sets of steel scaffolding were erected. Each set enclosed a tree of each of the target species (enclosed trees are described in Table 1). The enclosed trees were growing naturally on a sunny roadside or in an open space, being unshaded by other trees. For the Q. crispula tree, all first-order branches were examined. For the other two species, only some first-order branches were examined because of time constraints (Table 1). These sample branches were selected randomly from the whole crown. Although compass direction and height in the canopy of a branch can affect the leaf mass of that branch (e.g. Berninger and Nikinmaa, 1994; Dvorak et al., 1996), such effects were not detected in the branches sampled here. The stem diameter of each first-order sample branch at the base of a branch, i.e. at the branching point from the main trunk, was measured. For each first-order branch, lengths of all current-year shoots of A. mono, Q. crispula and those of all current-year long shoots of B. maximowicziana were measured. For short shoots of B. maximowicziana, basal stem diameters instead of shoot lengths were measured, because short shoots were all less than 5 mm long and were poorly correlated with leaf mass (r = –0·29, P > 0·1).
|
The allometric relationship between the number of current-year shoots (N) on a first-order branch and the basal stem diameter of the branch (D, cm) is written as:
ln N = 
+ ß ln D(1)
where and ß are regression parameters. The logarithmic transformations of first-order branches (N and D) were used, and major axis regression for the estimation of parameters and ß was employed. The mean and CV (coefficient of variation) for length or diameter of current-year shoots on each first-order branch was calculated. For each tree, the correlation between mean or CV and basal stem diameter of the first-order branch was tested.
Leaf mass and stem mass of each current-year shoot were estimated from stem length or basal stem diameter of the shoot. For each species examined, 40–120 current-year shoots were sampled from another isolated tree located in a sunny place. Sampled shoots were taken randomly from the whole crown. For each current-year shoot sampled, the dry masses of leaves and stem (F0 and C0, g) were obtained after the length and diameter of the stem (L0 and D0, mm) had been measured. Allometric equations were fitted for log-transformed dimensions:
ln F0 = a + b ln L0(2)
ln C0 = e + f ln L0(3)
where a, b, e and f are regression parameters estimated by least squares regression. In the case of short shoots of B. maximowicziana, regression was carried out for ln F0, ln C0 and log-transformed basal diameter (ln D0) instead of ln L0. Estimates of parameters for eqns (2) and (3) are shown in Tables 2 and 3. Using the above allometric equations and standard errors of the regressions, unbiased estimates of F0 and C0 for each current-year shoot were calculated (Baskerville, 1971). Summing up, all F0 and C0 on each first-order branch, total leaf mass and total current-year stem mass of each branch were estimated. This allowed calculation of the allometric relationship between total leaf mass (F, g) and total current-year stem mass of first-order branches (
C0, g), and that between total leaf mass and basal stem diameter of first-order branches (D, cm):
|
|
ln F =
+ 
ln C0(4)
ln F = 
+ 
ln D(5)
where , , and are regression parameters determined by major axis regression.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Estimates of regression parameters for eqns (1), (4) and (5) are shown in Table 4. The relationship between the number of current-year shoots and basal stem diameter of the first-order branches is illustrated in Fig. 2. Estimates of
and ß were not significantly different across the trees examined (Model-II ANCOVA, P < 0·05). Estimates of ß for Q. crispula and B. maximowicziana were not significantly different from 2·0, whereas that for A. mono was larger than 2·0 (t-test, P < 0·05).
|
|
Figures 3–6 show the frequency distributions of standardized size (Koyama and Kira 1956) of current-year shoot populations on first-order branches. In Q. crispula, current-year shoot populations on first-order branches had an extremely positively skewed frequency distribution of L0 (Fig. 3). In B. maximowicziana, >80 % of all current-year shoots within each first-order branch were short shoots (Fig. 4). When plotted in separate graphs, the frequency distributions of long-shoot length and short-shoot diameter both showed symmetrical or slightly negatively skewed unimodal patterns (Fig. 5). Current-year shoot populations of A. mono showed positively skewed unimodal distributions of L0 (Fig. 6). For long and short shoot populations of B. maximowicziana and for all shoot populations of Q. crispula and A. mono, neither mean nor CV of L0 or D0 was significantly correlated with the basal stem diameter of first-order branches (Fig. 7; P > 0·05). These facts suggest that shoot size structures of first-order branches of the species examined were similar irrespective of branch diameter.
|
|
|
|
|
0 or 
0, solid symbols) or CV (open symbols) of current-year shoot size and basal diameter of first-order branches. For B. maximowicziana, circles show mean and CV of the length of the long shoots and squares show those of the diameter of the short shoots.In Fig. 8, cumulative distribution of leaf mass is plotted against that of stem mass from the smallest to the largest shoot for the current-year shoot population of each first-order branch. First-order branches of the species examined showed a concave pattern in Fig. 8, suggesting that small shoots supported a larger amount of leaves relative to the amount of stems than large shoots. A large contribution of small shoots for leaf display was most clear in B. maximowicziana branches, where approx. 90 % of leaf mass was supported by short shoots. Q. crispula branches tended to show a more concave pattern than A. mono branches, reflecting persistently positive-skewed size structure of shoot populations.
|
In Fig. 9, total leaf mass of each first-order branch is plotted against total current-year stem mass of the branch. Estimates of parameters
and (Table 4) were not signific antly different between the trees examined (MODEL-II ANCOVA, P = 0·59). Estimates of were not significantly different from 1·0 (t-test, P > 0·05), suggesting that leaf mass of first-order branches was proportional to total current-year stem mass of the branch. The ratio of F to C0 ranged from 12·4 to 14·5 in B. maximowicziana, from 9·49 to 30·3 in Q. crispula and from 12·3 to 21·0 in A. mono, showing much larger biomass allocation to leaves than that to current-year stems.
|
Estimated leaf mass of first-order branches is plotted against basal stem diameter of the branch in Fig. 10. Estimates of parameters
and 
(Table 4) were not significantly different across the species examined (MODEL-II ANCOVA, P = 0·17). The estimate of parameter of each species did not differ from 2·0, suggesting that leaf mass of a first-order branch is proportional to basal cross-sectional area of the branch, compatible with the pipe-model relationship. Mean leaf mass per current-year shoot (
0 = F/N) of first-order branches was not significantly correlated with basal stem diameter (D) of the branches, as shown in Fig. 11 (P > 0·05).
|
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Suzuki and Hiura (2000) suggested that the allometric relationship between leaf mass and stem diameter of current-year shoots is different among species, whereas that of first-order branches is similar across species. In the present research, the relationship between leaf mass and current-year stem mass of first-order branches was fairly similar across the species examined (Fig. 9), whereas that of current-year shoots differed among the species examined (Fig. 12). Inter-species variation in shoot allometries should reflect phyllogenic diversity among tree species, whereas inter-species convergence of branch allometries should reflect some functional constraints on branch design. The present results suggest that the characteristics of shoot populations tend to offset the difference in shoot allometries and make branch allometries similar.
|
The pipe-model relationship shown at the scale of first-order branches (Fig. 10) can also be explained by the characteristics of the shoot populations. The pipe-model relationship among first-order branches can be written as:
F 
D2(6)
where F and D are leaf mass and basal stem diameter of a first-order branch, respectively. Using mean leaf mass (F0) of current-year shoots on each first-order branch, eqn (6) can be rewritten as:
NF0 D2(7)
where N is the number of current-year shoots on a first-order branch. Because the leaf mass on each current-year shoot (F0) is dependent on the length of the shoot (L0), as in eqn (2), F0 of each first-order branch depends on the frequency distribution of L0 on the first-order branch. Because current-year shoot populations on first-order branches had similar species-specific size structures irrespective of D (Figs 3–6), F0 was almost constant against D in all the species (Fig. 11). Additionally, the number of current-year shoots on a first-order branch (N) was proportional to the basal cross-sectional area of the branch (Fig. 2). Under these conditions, eqn (6) holds, even if current-year shoots are not compatible with the pipe-model relationship (Fig. 10).
Each first-order branch had a leaf mass 10–30 times as large as the total mass of the current-year stems, irrespective of branch size (Fig. 9). Highly biased biomass allocation to leaves relative to current-year stems was a result of the positively skewed size structure of the current-year shoot population (Fig. 8), which was found in all the species examined (Figs 3–6). Long shoots of B. maximowicziana had a much lower ratio of F0 to C0 than current-year shoots of other species (Fig. 11), reflecting the extremely low frequency of long shoots on first-order branches (Fig. 4), 90 % of whose leaves were supported by short shoots (Fig. 8). A current-year shoot of Q. crispula has less leaf mass than A. mono per unit stem mass (Fig. 12). If crowns of Q. crispula and A. mono had maintained shoot populations with the same size structure, A. mono would have supported a given leaf mass with a lower amount of current-year stems. However, F/C0 of Q. crispula and A. mono did not differ owing to the extremely skewed size structure of current-year shoot populations of Q. crispula (Figs 3 and 6).
Yagi (2000) reported on the relationship between leaf mass and stem mass of current-year shoots and that of a shoot population of open-grown saplings of ten tree species. The ratio of leaf mass to stem mass of current-year shoots (F0/C0) showed inter-species variation, whereas that of shoot populations (F/C0) was similar across the saplings examined. Shoot populations of saplings showed positively skewed size structures and resulted in biased mass allocation as well as mature trees in the present study. However, shoot size structures of saplings were less skewed and the ratio of leaf mass to current-year stem mass of shoot populations (F/C0) was smaller than those observed in the present study. The difference in the ratio F/C0 between that of Yagi (2000) and the present result was much larger than the inter-species variation in each study. The ratio F/C0 is suggested to represent adaptive mass allocation of the current-year shoot population at each life stage. Because saplings have small accumulations of non-photosynthetic organs per unit amount of leaves, they can have a smaller ratio of F/C0 than mature trees. On the other hand, rapid elongation and quick crown construction are the primary requirements for saplings. This might explain why saplings produce shoot populations with fewer skewed size structures than mature trees. Trees must keep up with the changing importance of multiple functional demands throughout their ontogenic stages (Farnsworth and Niklas, 1995), and changing the size structure of shoot populations could be one way of realizing ontogenic adaptation.
Because only three trees from different species were analysed, the present results might not be applicable to other trees. As already suggested, size structures of current-year shoot populations of young trees may differ from those of mature trees. Even current-year shoot populations of shaded mature trees can differ in size structure from those of isolated trees, because demographic processes of shoot populations are sensitive to these conditions (Koike, 1989; Stoll and Schmid, 1998; Takenaka, 2000). In those cases, the relationship among shoot size structure, number of shoots and basal branch diameter might be more complicated than that found in the present research. To what extent then can the present results be generalized?
Wilson (1987) suggested that shoot populations of trees tend to develop positively skewed size structure. He explained that size-dependent demographic processes of the shoot populations, which are common to many tree species, develop shoot populations that are stable in a positive-skewed size structure. According to this scenario, ontogenic change in shoot size structure is a necessary consequence. Positively skewed size structure of the shoot population, which will reduce the supportive cost for leaf display, is necessarily achieved as trees mature. In addition, leaf mass of the first-order branches should be controlled mainly by the number of current-year shoots, not by the size structure of the shoot population, because the latter is a determinant factor. Therefore, the present results might be applicable at least to mature, isolated trees, according to the suggestion of Wilson (1987).
|
ACKNOWLEDGEMENTS |
|---|
I thank Takashi Kohyama, Kihachiro Kikuzawa and Hugh J. Barclay for their helpful discussions. Akio Takenaka, Akihiro Sumida, Douglas G. Sprugel, Hiroaki Ishii, Masato T. Kimura, Shiro Tsuyuzaki and Gaku Kudo gave helpful suggestions on the early drafts. Also appreciated was the support on the field survey given by Atsushi Okuda and all Nakagawa Experimental Forest staff, and Ayako Ikeya, Sanae Tamura, Shin-ichi Tanabe and Hirohumi Hara. I am also grateful to the reviewers who read the manuscript and made meaningful comments on it.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
-
Addicott FT. 1991. Abscission: shedding of parts. In: Raghavendra AS. ed. Physiology of trees. New York: Wiley Interscience, 273–300.
Baskerville GL. 1971. Use of logarithmic regression in the estimation of plant biomass. Canadian Journal of Forest Research 2: 49–53.
Berninger F, Nikinmaa E. 1994. Foliage area–sapwood area relationships of Scots pine (Pinus sylvestris) trees in different climates. Canadian Journal of Forest Research 24: 2263–2268.[CrossRef]
Buck-Sorlin GH, Bell AD. 1998. A quantification of shoot shedding in pedunculate oak (Quercus robur L.). Botanical Journal of the Linnean Society 127: 371–391.[CrossRef]
Cannell MGR. 1974. Production of branches and foliage by young trees of Pinus contorta and Picea sitchensis: provenance differences and their simulation. Journal of Applied Ecology 15: 1091–1115.
Chiba Y. 1990. Plant form based on the pipe model theory. I. A statistical model within the crown. Ecological Research 5: 207–220.[CrossRef]
Cochrane LA, Ford ED. 1978. Growth of a sitka spruce plantation: analysis and stochastic description of the development of the branching architecture. Journal of Applied Ecology 15: 227–244.[CrossRef][Web of Science]
Dvorak V, Oplustilova M, Janous D. 1996. Relation between leaf biomass and annual ring sapwood of Norway spruce according to needle age-class. Canadian Journal of Forest Research 26: 1822–1827.[CrossRef]
Farnsworth KD, Niklas KJ. 1995. Theories of optimization, form and function in branching architecture in plants. Functional Ecology 9: 355–363.[CrossRef][Web of Science]
Hallé F, Oldeman RAA, Tomlinson PB. 1978. Tropical trees and forests. Berlin: Springer-Verlag.
Hiura T, Fujiwara K, Hojo H, Okada J, Udo H, Okuyama S, Morita H, Fukuta H, Fujito E, Fukui T et al. 1995. Stand structure and long-term dynamics of primeval forests in Nakagawa experimental forest, Hokkaido University. Research Bulletin of Hokkaido University Forest 52: 85–94.
Koike F. 1989. Foliage-crown development and interaction in Quercus gilca and Quercus acuta. Journal of Ecology 77: 92–111.[CrossRef]
Koyama H, Kira T. 1956. Intraspecific competition among higher plants. VIII. Frequency distribution of individual plant weight as affected by the interaction between plants. Journal of the Institute of Poly technics, Osaka City University 7: 73–94.
Kozlowski TT. 1971. Growth and development of trees. New York: Academic Press.
Long J, Smith FW. 1988. Leaf area–sapwood area relations of lodgepole pine as influenced by stand density and site index. Canadian Journal of Forest Research 18: 247–250.
McGraw JB. 1989. Effects of age and size on life histories and population growth of Rhododendron maxim shoots. Annals of Botany 76: 113–123.[CrossRef]
Maillette L. 1982. Structural dynamics of silver birch. I. The fates of buds. Journal of Applied Ecology 19: 203–218.[CrossRef][Web of Science]
Nagy M. 1992. Architecture of the shoot system of Quercus petraea (Matt.) LIEBL. Acta Botanica Hungarica 37: 239–249.
Remphrey WR, Steeves TA, Neal BR. 1983. The morphology and growth of Arctostaphylos uva-ursi(bearberry): an architectural analysis. Canadian Journal of Botany 61: 2430–2450.[CrossRef][Web of Science]
Shinozaki K, Yoda K, Hozumi K, Kira T. 1964. A quantitative analysis of plant form – the pipe model theory. I. Basic analyses. Japanese Journal of Ecology 14: 97–105.
Stoll P, Schmid B. 1998. Plant foraging and dynamic competition between branches of Pinus sylvestris in contrasting light environments. Journal of Ecology 86: 934–945.[CrossRef]
Suzuki M, Hiura T. 2000. Allometric difference between current-year shoots and large branches of deciduous broad-leaved tree species. Tree Physiology 20: 203–209.[Abstract]
Takenaka A. 1997. Structural variation in current-year shoots of broad-leaved evergreen tree saplings under forest canopies in warm temperate Japan. Tree Physiology 17: 205–210.[Abstract]
Takenaka A. 2000. Shoot growth responses to light microenvironment and correlative inhibition in tree seedling under a forest canopy. Tree Physiology 20: 987–991.[Abstract]
Waring RH, Thies WG, Muscato D. 1980. Stem growth per unit of leaf area: a measure of tree vigour. Forest Science 26: 112–117.[Web of Science]
Whitehead D, Edwards WRN, Jarvis PG. 1984. Conducting sapwood area, foliage area and permaeability in mature trees of Picea sitchensis and Picea contorta. Canadian Journal of Forest Research 14: 940–947.[CrossRef]
Wilson BF. 1987. Tree branches as population of twigs. Canadian Journal of Botany 67: 434–442.[CrossRef]
Wilson BF. 1991. Shoot-length frequencies in black birch (Betula lenta). Canadian Journal of Forest Research 21: 1475–1480.[CrossRef]
Yagi T. 2000. Morphology and biomass allocation of current-year shoots of ten tall tree species in cool temperate Japan. Journal of Plant Research 113: 171–183.[CrossRef][Web of Science]
Yagi T, Kikuzawa K. 1999. Patterns in size-related variations in current-year shoot structure in eight deciduous tree species. Journal of Plant Research 112: 343–352.[CrossRef][Web of Science]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||