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We review a series of papers based on Kikuzawa’s (1991) cost-benefit model for leaf longevity, including its extension to whole plants and entire communities in seasonal environments. This simple model of net carbon gain over the life of a leaf can explain relationships among key foliar traits such as the positive correlation between leaf longevity (L) and leaf mass per area (LMA) and the negative correlations between photosynthetic rate (A) and both L and LMA. The extension of the model to seasonal environments can explain and reproduce various biogeographical trends including bimodality in the distribution of evergreen species across latitude, increase and decrease in L of evergreen and deciduous species with shortening of the period favorable for photosynthesis (f), modulation of L-LMA relationships with f, and decrease in functional type richness in terms of phenology patterns towards higher latitudes and altitudes. Finally, the model suggests the possibility that the lifetime carbon gain by a single leaf can be extended by analogy to predict the productivity of forest ecosystems.

Aim At a global scale, the relationship of leaf longevity (LL) to mean annual temperature (MAT) is positive for deciduous species but negative for evergreen species. The aim of this paper is to understand the mechanisms underlying these contrasting patterns of leaf longevity, from a cost–benefit perspective. Location Global. Methods We tested our hypothesis that contrasting LL–MAT relationships in evergreen and deciduous species result from differing adaptations to variation in the length of the annual favourable period. We defined f as the portion of the year when monthly temperature and water availability were favourable. We examined whether the contrasting LL patterns with MAT can be also seen with f. Next, we calculated the optimal LL that maximizes carbon gain per unit time across a range of f. Results The contrasting LL patterns across MAT were also found across f. Our optimization model successfully reproduced the contrasting LL patterns across f for the evergreen (LL longer than 1 year) and deciduous plants. The model shows that longer LL is required to maximize carbon gain for evergreen plants in shorter f, while LL of deciduous plants decreases with decreasing f. Without any a priori trait association, the model reproduced the well-known LL–leaf mass per area (LMA) relationship. The model also reproduced observed shifts in LL–LMA relationships across MAT or f. Evergreen leaves in long f need greater LMA to maintain LL than those in shorter f. Main conclusions Observed contrasting LL–MAT patterns in deciduous and evergreen species can be reproduced via the simple rule of maximizing carbon gain across different lengths of favourable periods. Our model provides a mechanistic explanation for the empirical global patterns of several key leaf traits and their relationships.

Starting from an axiom that sunlight is the fundamental energy source for green plants, we derived some theorems in plant ecology. We began by reviewing the Monsi-Saeki model, which was the first to relate the structure of canopy and productivity. Optimum leaf area (and thus leaf biomass) were predicted from the Monsi-Saeki model, which also introduced the concept of constant final yield per unit land area. A relationship between total biomass (y) and plant number (n) per unit land area was derived by combining the principles of constant final yield and logistic plant growth, which is based upon the diminishing return of total individual photosynthesis due to self-shading, An analogous equation was obtained in the analysis of cumulative plant biomass (Y) against cumulative plant number (N) within a stand. Mass-number relationships among stands (y-n) and within a stand (Y-N) were revealed to be the same under one-sided competition for light. The self-thinning line is the point where individual plant’s growth becomes zero on the translocation of a Y-N relationship through time. Self-thinning is expected to occur due to the death of the smallest plants shaded by larger plants. The Monsi-Saeki modeling framework was reoriented considering leaf longevity, which is the optimal timing to replace individual leaves to maximize carbon gain of the plant. Under canopy ergodic hypothesis, which supposes space-time equivalence in the performance of leaves, leaf longevity can be used to circumvent the difficulties in the scaling from leaf to canopy. Gross primary production then can be estimated using functional leaf longevity together with the mean labor time of a leaf, two measures of the time during the leaf span when it can be photosynthetically active. Finally, if leaf longevity is used in a species-specific normalization constant, plant productivity can be described as an allometric function of plant mass. In that case, the relative growth rate of plants can be shown to have an inverse relationship to leaf longevity.

To explain why the composition of evergreen and deciduous forests changes along air temperature gradients, we measured several traits of single leaves from temperate deciduous and evergreen broadleaf trees with simultaneous and successive leaf emergence growing at different altitudes in the field. The parameters included seasonal net photosynthetic rate, longevity, mass per area, nitrogen content, and photosynthetic nitrogen-use efficiency. With decreasing altitude, the leaf longevity of deciduous broadleaf trees increased, whereas the maximum net photosynthetic rate decreased. In contrast, leaf longevity of evergreen broadleaf trees decreased, whereas the minimum net photosynthetic rate in winter increased. Along the air temperature gradient, the annual production of deciduous trees with simultaneous leaf emergence may be constant, because the integrated lifetime net photosynthetic rate (ILNPR) of a single leaf changed little. In comparison, deciduous trees with successive leaf emergence may show enhanced annual production with increasing air temperature, by increasing the total leaf number per branch and tree under an extended growing season. Temperate evergreen broadleaf tree species may also show increased annual production with increasing air temperature by sufficiently raising the number of the first-year leaves to the total leaves of branch and tree, which is accelerated by raising the integrated first-year net photosynthetic rate of the single leaf, despite little change in the ILNPR. With increasing air temperature from cool-temperate to warm-temperate zones, evergreen broadleaf tree species gain an advantage of the annual production over deciduous broadleaf tree species with simultaneous leaf emergence.

Leafing pattern has long been considered as an important element characterizing the growth strategy of tree species; however, the consequences of leafing pattern for tree-crown formation have not been fully understood. To address this issue, the dynamic events (growth, birth, and death) of current-year shoots and leaves were investigated together with their location in saplings of a pioneer tree, Alnus sieboldiana. The leafing pattern was characterized by successive emergence and shedding of short-lived leaves. The combination of successive leafing and within-crown variation in leaf production brought about characteristic outcomes in crown morphology. In the outer crown, because of continuous leaf production, the shoots achieved great extension and enormous daughter shoot production, resulting in rapid expansion of the crown. In contrast, in the inner crown, due to early termination of leaf production, the shoots completely lost their leaves early in the growing season and consequently themselves died and were shed within the season. Such quick shedding of shoots caused “crown hollowing”, i.e., the interior crown consisted of primary branches with little secondary development or foliage. These dynamic features are an effective adaptive strategy in early succession but also may be a disadvantage to maintaining foliage for longer period. Crown maintenance associated with the longevity of structural components is thought to play an important role in survival strategy of tree species.

The light environment and growth traits of the pioneer tree species Litsea citriodora in a recently clear-cut plantation were investigated in order to reveal the establishment process and growth of this species under annual weeding after clear-cutting. We investigated the light environments and the morphology, physiology and aboveground architecture of L. citriodora saplings in a plot that included both clear-cut open areas and forest floor under a conifer canopy. Dense populations of L. citriodora saplings were found in the open sites but few were observed on the forest floor. Saplings that originated from old stumps (sprout-saplings) were tall in height and dense, but seedlings were sparse and lower in height than the competitive tall herbaceous species Solidago altissima. Saplings of L. citriodora showed a higher leaf area per aboveground mass and greater area-based photosynthetic capacity than saplings of the co-occurring pioneer tree species Mallotus japonicus and Clerodendron trichotomum. Moreover, the L. citriodora saplings had a main stem with a larger length per mass ratio and more efficiently elongated per unit aboveground mass than M. japonicus and C. trichotomum. Sprout-saplings of L. citriodora attained rapid vertical elongation with rapid biomass acquisition as a result of their aboveground shoot architecture, allowing competition with S. altissima. Clear-cutting and subsequent weeding not only created open sites favorable for this pioneer tree, but also promoted the formation of sprouts, allowing sprout-saplings with rapid vertical growth to successfully establish in the clear-cut zone by inhibiting complete coverage by other pioneer trees.

The assimilation of carbon by plant communities (gross primary production [GPP]) is a central concern in plant ecology as well as for our understanding of global climate change. As an alternative to traditional methods involving destructive harvests or time-consuming measurements, we present a simple, general model for GPP as the product of the lifetime carbon gain by a single leaf, the daily leaf production rate, and the length of the favorable period for photosynthesis. To test the model, we estimated leaf lifetime carbon gain for 26 species using the concept of mean labor time for leaves (the part of each day the leaf functions to full capacity), average potential photosynthetic capacity over the leaf lifetime, and functional leaf longevity (leaf longevity discounted for periods within a year wholly unfavorable for photosynthesis). We found that the lifetime carbon gain of leaves was rather constant across species. Moreover, when foliar biomass was regressed against functional leaf longevity, aseasonal and seasonal forests fell on a single line, suggesting that the leaf production rate during favorable periods is not substantially different among forests in the world. The gross production of forest ecosystems then can be predicted to a first approximation simply by the annual duration of the period favorable for photosynthetic activity in any given region.

We have investigated stem turnover strategy for Lindera umbellata, an understory shrub that sprouts from its rootstock under natural conditions to replace constituent stems, on the basis of the hypothesis that the multiple-stemmed form of woody species is an adaptation enabling efficient reproduction in high-stress environments. We tested the hypothesis that the timing of stem replacement maximizes sexual reproduction for the shrub. We developed a model for the time of optimum replacement of a stem by a daughter stem which maximizes the sexual reproduction of a shrub and tested the model using L. umbellata growing in the field. From the model, the optimum time of replacement of a stem with a daughter stem is when cumulative sexual reproduction per unit time for the stem is maximum. In practice, this will be the last age (t opt) at which annual sexual reproduction in a stem can potentially exceed cumulative sexual reproduction per unit time for the stem. Half of the stems died at almost t opt and had sexually mature daughter stems at that time. Other stems, however, died at times more remote from t opt when daughter stems were sexually immature. It is thought that normal replacement of the latter stems was prevented by accidents such as breakage. We conclude that clumps of L. umbellata achieve efficient sexual reproduction by stem replacement at the optimum time, although accidents can, to some extent, determine when the stem actually dies.

We tested whether the difference in shoot production patterns of reproductive and vegetative shoots is only due to resource or meristem availability or also due to species-specific factors. Rates of shoot production by four shoot types (reproductive long shoots, vegetative long shoots, reproductive short shoots, and vegetative short shoots) in Betula platyphylla Sukatchev var. japonica (Miq.) Hara, Betula davurica Pall., Betula ermanii Cham., Betula grossa Sieb. et Zucc., and Betula maximowicziana Regel were compared. In the first three species, each shoot type produced all four shoot types. However, in the latter species, limited shoot production pathways were found both in reproductive shoots and in vegetative shoots, which do not carry any costs associated with reproduction. Furthermore, shoot production by reproductive shoots was not always diminished, but rather was enhanced compared with that by vegetative shoots in B. maximowicziana. These results suggest the importance of species-specific patterns in shoot production, in addition to previously suggested explanations involving resource or meristem limitation.Key words: species specificity, cost of reproduction, Betula, reproductive shoots, vegetative shoots.

The sex expression of Tilia japonica is functional andromonoecy (an andromonoecious system with abortion of perfect flowers). Some of protandrous flowers are aborted after shedding pollen grains and thus are functionally male flowers (FMF). When both male and female organs are retained in a flower, the plants can more flexibly regulate sex allocation, or resource allocation to male and female functions than true andromonoecious plants, which is considered as an adaptive significance of functional andromonoecy. However, the plants have to pay some costs of female organ in FMF. For functional andromonoecious plants, there is a conflict between flexibility and cost in determining the timing of flower abortion, or arrest investing in female functions in a flower. We clarified that (i) differentiation of the timing of flower abortion caused two types of FMF: short-style (SS) and normal-style (NS) flowers; (ii) SS can be produced at a lower cost than NS, and (iii) plants having NS can flexibly regulate sex allocation following a sudden change in conditions. Hence, we concluded that differentiation of the timing of flower abortion makes a compromise of the conflict. We also found that NS is more frequent than SS, and we discuss the adaptive significance of keeping potential fertility.

The cost–benefit model of leaf life span is extended by incorporating the cost of construction and maintenance of supporting structures, such as shoots and roots. Published data on leaf longevities were reviewed, and they support qualitative predictions of optimal leaf life span based on the present model. In relation to life form, leaf life span increases in the following sequence, due to increasing costs of support structures: floating leaves of aquatic plants < annual herbs < perennial herbs < deciduous trees. Within species, leaf life span increases with plant size as support costs per unit of leaf increase. This prediction is supported by comparisons of seedlings and adults of temperate trees. These results suggest that the construction and maintenance costs of supporting structures significantly influence life span of individual leaves. Leaf longevity, in turn, connects the ecophysiology of the individual leaf to growth of the individual plant and energy and matter cycling at the ecosystem level.

As yet there is no comprehensive theory in plant population ecology to explain relationships between mean plant size, size distribution and self-thinning. In this paper, a new synthesis of plant monocultures is proposed. If the reciprocal relationship between plant biomass and plant population density among various stands of even-aged plant populations holds, the same reciprocal relationship must exist between cumulative mass and cumulative number of plants from the largest individual within a population, assuming strict one-sided competition (which is an extreme condition for competition for light among plants). The two parameters of the relationship between cumulative mass and cumulative number within a stand both correlate with maximum plant height in the stand. One parameter equals the reciprocal of the potential maximum plant mass per area, which is expressed by the product of maximum plant height and dry-matter density. The other parameter correlates with the potential maximum individual plant mass, which is allometrically related to maximum plant height. As a stand develops, the growth rate of the smallest individuals will become zero due to suppression from larger individuals, and they will die; i.e. self-thinning will occur. The slope of the self-thinning line is expressed through the coefficients of allometry between height and mass and between dry matter density and height. When the former coefficient is 3 and the latter is 0, the gradient exactly corresponds to the value expected from the 3/2 power rule, but it can take various values depending on the values of the two coefficients. Competition among individuals determines size-density relationships among stands, which in turn determine the size structure of the stand. The size structure constrains the growth of individuals and results in self-thinning within the stand.

We developed a game-theoretic model for wind-dispersed seed production to examine the seed mass–dispersal ability relationship and the evolutionarily stable distance of seed dispersal in terms of exploitation of safe sites. We assumed trade-offs between masses of the embryo (including albumen) and the wind-dispersal structures per seed, and also between seed mass and number of seeds per parent. We showed that ESS wing-loading is independent of embryo mass; that is, heavy seeds are not poor dispersers if the cost of producing wind-dispersal structures per unit area is constant. The ESS embryo mass per seed depends only on the factors which determine the probability of a seedling being established from a seed. However, wing-loading was found to increase with embryo mass when the change in length was isometric and there was a negative correlation between seed mass and dispersal ability. Thus, the area–mass relationship in wind-dispersal structures may have large effects on the ESS production of wind-dispersed seeds. On the other hand, given that only a limited number of adults can be established at a safe site, the ESS seed dispersal distance depends on the relative degree of sib to non-sib competition. A parent disperses its seeds over a wide area to exploit many safe sites if sib competition is strong. However, it disperses its seeds within a narrow area if the mean number of parents per unit area is large, or if non-sib competition is strong. Thus, in addition to an upper limit on the number of adults per safe site, the degree of sib and non-sib competition may be important for the ESS dispersal distance in wind-dispersed seeds.

In metabolic scaling theory the size-dependence of plant processes is described by a power function of form Y=Y o M (θ) where Y is a characteristic such as plant productivity that changes with plant size (M) raised to the θ (th) power and Y o is a normalization constant that adjusts the general relationship across environments and species. In essence, the theory considers that the value of θ arises in the size-dependent relationship between leaf area and vascular architecture that influences plant function and that Y o modulates this general relationship to account for ecological and evolutionary effects on the exchange of resources between plant and environment. Enquist and colleagues have shown from first principles that Y o is a function of carbon use efficiency, the carbon fraction of a plant, the area-specific carbon assimilation rate of a leaf, the laminar area of a leaf, and the mass of a leaf. We show that leaf longevity provides a functional integration of these traits that can serve as a simpler normalization in scaling plant productivity for individual species and potentially for mixed-species communities as well.

Two-year-old seedlings of Alnus japonica Steud. and Betula platyphylla var. japonica Hara were flooded from mid-June to early November, to study the effects of flooding on seedling survival and growth, morphological changes in stems and roots, leaf emergence, leaf fall, and leaf longevity. In A. japonica, growth was not affected by flooding, except for a slight decrease in height growth, but some morphological changes of stems and roots were observed, i.e., stem base hypertrophy, hypertrophied lenticels, formation of adventitious roots and development of new roots. In B. platyphylla var. japonica, growth was severely reduced by flooding and all seedlings died by the 20th week of flooding, without showing any adaptive morphological changes in stems or roots. Flooding induced rapid depression of leaf emergence, promoted leaf abscission, and reduced leaf longevity in B. platyphylla var. japonica. In contrast, in A. japonica, basal leaf senescence was delayed in flooded seedlings, thereby extending leaf longevity compared with unflooded seedlings.

Leaf longevity and “leaf lifespan” are sometimes used as equivalent terms, and at other times “leaf longevity” designates the potential longevity of leaves and “leaf lifespan” their realized longevity. To keep things simple, we here consistently refer only to leaf longevity, qualifying the context as may be necessary. With an emphasis on times when a leaf can carry out its photosynthetic function, we define leaf longevity as the period from the emergence to the fall of a leaf. Because leaf development is a continuous process, a reasonably consistent operational definition of leaf appearance and leaffall is necessary. It is impractical to include the period of leaf initiation and early development before budburst in estimations of leaf longevity, and in any case these earliest stages in leaf development are not directly relevant to photosynthetic function (Vincent 2006). The onset of full photosynthetic function would be the most logical starting point from which to estimate leaf longevity, but this is not ­practical in broad comparative studies because of species-specific variation in the relation between foliar development and foliar function (Niinemets and Sack 2004). We generally resort to recording a phenophase consistent with records in phenological networks (Koch et al. 2007; Morisette et al. 2009) that is associated with a late stage of foliar development, such as expansion and flattening of the leaf blade in broadleaf deciduous trees (Kikuzawa 1978). Similar uncertainties are involved in scoring the timing of leaffall. Senescence of fully formed leaves is generally more drawn out than budburst and early leaf development and hence is less amenable to timing precisely (Worrall 1999).

The normal value of leaf longevity for a species reflects functional relationships at the foliar and whole-plant level, but longevity can be both prolonged and shortened by environmental conditions. From first principles, leaf longevity is expected to increase in environments where critical resources are scarce. This generalization is rooted in a cost–benefit analysis of leaf longevity arguing that the nature of leaves in resource-limited environments imposes a long payback period on the cost of their construction (Chabot and Hicks 1982; Kikuzawa 1991). In this view, selection pressure is expected to act to prolong leaf longevity in light-, water-, or nutrient-limited environments. This expectation is consistent with observations among species and plants in differing resource environments, but not within individual plants. The expectation applies to conditions of resource limitation, not stress conditions that near or exceed the limits to a species’ survival and reproduction. Stress events such as deep drought, unseasonal frost and freezing, lengthy flooding, salinity, air pollutants, and attack by herbivores or pathogens each impose qualitatively different challenges to leaf function (Kozlowski and Pallardy 2002), which we also address in this chapter.

Leaf longevity is an integral part of a quintet of highly intercorrelated and functionally interdependent traits that organize the function of leaves as photosynthetic organs: photosynthetic capacity, A max; leaf mass per unit area, LMA; foliar nitrogen content, N; and leaf dry matter content, LDMC (Wright et al. 2004; Shipley et al. 2006). Photosynthetic capacity, a direct measure of foliar function, is the natural focal element in the quintet. Leaf longevity, LMA, and foliar N initially drew attention as correlates of photosynthetic capacity and only later were recognized as part of a unified set of traits characterizing overall variation in leaf function: the “leaf economic spectrum” (Wright et al. 2004). Leaf dry matter content subsequently was identified as a little-studied trait that in fact underpinned the relationships among A max, LMA, foliar N, and leaf longevity (Shipley et al. 2006). Considering the innumerable characteristics of leaves, including some that figure in theories of leaf longevity, what makes these the cardinal traits central in defining trends in variation of leaf function? There are basically two reasons these five traits have primacy. First, all these characteristics bear on the costs of leaf construction and the photosynthetic functions that repay those costs over the life of the leaf. Second, these traits show a wider and ecologically more consistent range of interspecific variation than other characteristics of leaves.

There is, apparently, no general restriction on variation in leaf longevity per se along local and regional spatial gradients. Leaf longevity is only part of a suite of foliar traits that act in concert to ensure effective photosynthetic function in a given environmental regime (Wright et al. 2004; Shipley et al. 2006). Coordinated quantitative variation among the set of foliar traits can underpin equivalently effective photosynthetic function despite considerable variation in leaf longevity (Marks and Lechowicz 2006). As a consequence, leaf longevity typically varies substantially among species even in a single locality, a point made forcefully in earlier chapters but worth reinforcing here with another example. A careful study of 100 species representing four growth forms in the understory of a tropical montane forest (Fig. 9.1) shows the high variability in leaf survivorship curves among co-occurring species; survivorship, in turn, is consistently correlated with elements in the leaf economic spectrum (Wright et al. 2004) as well as with aspects of foliar defense such as condensed tannin content and leaf toughness (Shiodera et al. 2008).

As an integral part of the adaptive strategy for productivity at the level of individual plants, leaf longevity should scale up to impact flows of energy and materials at the ecosystem level. Consequently, leaf longevity and foliar habit consistently appear in enumerations of traits relevant to ecosystem function (Weiher et al. 1999; Lavorel and Garnier 2002; Cornelissen et al. 2003; Kleyer et al. 2008). The past decade has seen a flood of papers discussing linkages between various traits and ecosystem function: useful entry points to this literature include Lavorel and Garnier (2002), Diaz et al. (2004), Wright et al. (2005b), Quetier et al. (2007), and Suding and Goldstein (2008). Although leaf longevity and its foliar correlates clearly influence ecosystem processes (Thomas and Sadras 2001; Wright et al. 2005b; Cornwell et al. 2008), scaling up the effects of leaf longevity at the level of individual plants or species to the aggregate influence of species assembled in diverse communities across the landscape is not at all straightforward (Suding et al. 2008). Zhang and colleagues (Zhang et al. 2009) provide perhaps the best example of what is possible if one is willing to invest the effort. They followed leaf longevity on individual species in ten evergreen forests in eastern China for 5 years, calculating frequency-weighted mean leaf longevity for each forest, which was negatively correlated with mean annual temperature and positively correlated with mean annual precipitation. Very few ecosystem studies focus to this degree on leaf longevity per se at the level of individual species, or for that matter on any other species-specific traits. Some models of forest productivity incorporate an impressive amount of detail on individual species at the population level in the forest community (cf. Medvigy et al. 2009), but the focus typically remains on the forest as a whole, not the detailed analysis of individual trees and species that in aggregate decide the functional characteristics of the forest. It clearly is no easy task to assess how leaf longevity and associated traits at the species level scale up to affect ecosystem function.

There are broad patterns of variation in leaf longevity associated with plant growth form (Fig. 5.1), and leaf longevity spans more than two orders of magnitude (Fig. 5.2). Longevities as little as a few weeks are recorded for some herbaceous species and 20 years or more for some woody species (Wright et al. 2004). Lusk (2001) reported leaf longevities for a conifer in south-central Chile as long as 26.2 years in shaded sites and 21.5 years in open sites. The extensive compilation of leaf longevities by Wright et al. (2004) is primarily for woody species (79%), mostly shrubs and trees, with only a few vines; the herbaceous plants in this compilation include graminoids as well as forbs. The median value of leaf longevity in this data set is 8.5 months. Biologically noteworthy longevities are illustrated by the temporary flattening of the rank-order diagram (see Fig. 5.2) at about 3.5 months and again at 6 months. Although there is in general a highly regular and continuous variation in longevity across species, these clusters of species with similar longevities suggest the existence of some sort of limiting factor on leaf viability associated with ­longevities of these durations. We can speculate that the 6-month longevity reflects the typical length of the growing season in temperate regions where many of the compiled data were taken, but what might account for the 3.5-month longevity? This cluster of species with rather rapid leaf turnover includes many fast-growing herbaceous and woody species from temperate regions, which reflects a dichotomy between deciduous species that produce only one set of leaves per season and others which produce leaves throughout the season. Even within a single climatic regime there are alternative evolutionary outcomes in the organization of foliar phenology that involve distinct differences in leaf longevity.

To maximize net gain of a tree, leaves must be replaced when net gain of a leaf per unit time over the leaf's life span is maximum. A model in which leaf longevity is determined to maximize the net gain of a leaf per unit time is constructed. The model predicts that leaf longevity is short when initial net photosynthetic rate of the leaf is large, long when the construction cost of the leaf is large, and short when the decrease in net photosynthetic rate with time is large. The model describes leaf habit (deciduousness and evergreenness) with the length of the favorable period for photosynthesis within a year and simulates distributional pattern of leaf habit along latitudes. The percentages of evergreenness decrease with decreasing favorable-period length and reach the minimum at an intermediate length of the favorable period but increase again with a decrease in the length of the favorable period. A bimodal distributional pattern with two peaks, one at lower and the other at higher latitudes, is observe...

Publisher Summary This chapter reviews longevity of leaves of higher plants by considering the replacement of leaves to be an adaptive strategy of plants. The life span of floating leaves of aquatic floating plants ranges from 13 to 40 days, while that of emergent leaves of the same species is 35–57 days. The short life span of floating leaves is closely related to the fact that old leaves are submerged, lose their photosynthetic function quickly, and are replaced by new leaves early. Some patterns and trends are observed concerning leaf longevities of various plant species in relation to their physiological traits, architectures, and habitat conditions. Differences in leaf longevities among different life forms or architectures are attributed to the differences in the costs of supporting tissues. Leaf longevities of tree seedlings are shorter than those of tall trees of the same species, reflecting the difference in the amount of supporting tissues.

Any theory of leaf phenology must predict leaf longevity, leaf habit, leaf expansion and its timing among other variables. These phenological traits may be important keys to understand the response of trees to climatic change. Here I concentrate on and review two of these critical phenological traits, leaf longevity and leaf habit. Theories of leaf longevity were re-evaluated and leaf longevity is concluded to be optimized to maximize plant carbon gain. From this perspective, three points are predicted. Leaf longevity is short when the photosynthetic rate of the leaf is high, when the photosynthetic rate decreases rapidly through time, or when the construction cost of the leaf is small. These predictions are well supported by empirical as well as experimental results on various plant species. The theory, which is extended to seasonal environments, is general and applicable to seasonal as well as aseasonal environments. The theory simulated the bimodal geographic distribution of evergreenness.

Leaf longevities of three woody dwarf-shrub species were investigated in relation to the length of the snow-free period in a mountain area in Hokkaido, northern Japan. Leaf longevity of a deciduous species, Sieversia pentapetala, slightly increased with increasing length of the snow free period. In contrast, the leaf life-span of two evergreen species, Phyllodoce aleutica and Rhododendron aureum, decreased with increasing snow-free period. These trends are consistent with a cost-benefit model for leaf longevity as a function of the changing length of the yearly period favorable for photosynthesis. Hence the plastic changes in leaf longevity with varying snow-free periods were concluded to be adaptive traits for maximizing photosynthetic gain for the plants

SUMMARY (1) The growth patterns of tree height and stem diameter in crowded Abies veitchii, A. mariesii and Betula ermanii populations were investigated based on the diffusion model for growth dynamics in size-structured populations. (2) Size-dependent growth was found in each species, but the pattern was different between the species. Small, suppressed individuals of Abies spp. showed little growth in tree height but grew in stem diameter. In small, suppressed individuals of B. ermanii, the converse was found. (3) The diffusion model revealed that stem diameter growth of Abies spp. and tree height growth of B. ermanii are affected only a little by competition between individuals even under crowded conditions, and thus that growth in these dimensions is determined in a genetically strict manner for each species. These growth patterns correspond to the life-history traits and the successional status of Abies spp. (shade-tolerant late-successional species) and B. ermanii (a shade-intolerant early-successional species). (4) This study indicates the quantitative differences of assimilate partitioning between tree height growth and stem diameter growth in size-structured plant populations in relation to the characteristics and successional status of species.