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Life cycle (生活環)·life history (生活史)

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

Life history stage (growth stage)

Life history

≈ life cycle (on ecology)
A system of interrelated adaptive traits forming a set of reproductive tactics
There are various definitions on each life history stage, depnding on research objectives. This page is for terrestrial seed-plant community ecology.


Growth stages on terrestrial seed plants. Note that the definitions of seedling and junenile are totally fuzzy.
  • Seed: a structure that encapsulates the embryo. The seeds are often in dormant and makes a seedbank
  • Seedling (実生): a young plant reproduced by means of seeds (not by sprouts). On forestry, seedling often means young trees less than the defined height, 1.0-1.3 m. For monitoring tree growth on Mount Koma, we define trees less than 30 cm high for trees.
  • Sapling
    1. young tree, that does not produce any flowers and fruits even if the environmental conditions are appropriate
    2. in the case of the researches on Mount Koma, the height of saplings ranges from 0.3 m to 1.3 m (= DBH). A sapling of Magnolica kobus
    3. plants having a DBH greater than 0 and less than the minimum adult DBH defined in the tree parameters
  • Juvenile: an immature (non-flowering) individual resembling an adult except reproductive activity, i.e., seedlings and saplings
    ↓ growth / competition
  • Adult: the mature stage. In the case of terrestrial plants, it is recognized by theproduction of reproductive organs, such as flowers and fruits. See an adult Robinia pseudoacacia
    seed dispersal
    Time has passed …
  • Dead: an individual makes neither photosynthesis nor respiration
seedling seedling [Left] A Picea mariana seedling emerged on a petri dish with three-layered filter paper in an incubator. The length is about 2 cm. [Right] A P. mariana seedling on burned ground surface after the 2004 wildfire (森林火災) at Poker Flat near Fairbanks, Alaska, on July 30 2007 (by Narita K).


  1. From seed dispersal to seedling emergence
  2. Seedling establishment
  3. Seedling development
  4. Sapling, or juvenile
  5. Pole development
  6. Maturation
Perennials (based on age)
  1. Viable seeds in soil
  2. Seedlings
  3. Juvenile plants
  4. Immature plants
  5. Mature virginile plants
  6. Plants in the initial phase of generative period
  7. Plants in the period of life culmination
  8. Senescing plants
  9. Senile plants
  10. Plants in the dormant state

(DeGasperis & Motzkin 2007)

Windows of opportunity
Timing for establishing the life-history stage

Grime's triangle (グライムの三角形)

The combination of three strategies of plants:

                   Low                    High

Disturbance  High  -                      Ruderals (R)
             Low   Stress tolerators (S)  Competitors (C)

Competitors (C)
Plants have high competition ability when low stress and disturbance are given. The high competition ability is evaluated by fast growth rate and high productivity.
Stress tolerators (S)
Plants adapt to high stress and low disturbance, by slow growth rates, long-lived leaves, and high nutrient retention rate. These are represented by species growing in alpine, arid, or sprpentine habitats.
Ruderals (R)
Species favor disturbance with low stress, and are fast-growing. Plants that have adapted this strategy are often found colonizing recently disturbed land, and are often annuals.
⇒ Application to Succession (遷移)

Phenology (フェノロジー)

periodic plant and animal life cycle events

Ex. seedd germination, leaf flushing, flower production, defoliation

Spring ephemeral (春植物)

Producing flowers immediately after snowmelt and completing the life-cycle by early summer

be perennial that can reproduce by underground organs in each spring soon after snow melting
be able to utlize excess light before the leaf flushing of canopy trees →
be distributed in deciduous forests

Spring ephemerals
Fig. Seasonal changes in light intensity on the forest floor of deciduous and evergreen forests
Representative species
Adonis ramosa (フクジュソウ), Adoxa moschatellina (レンプクソウ), Allium monanthum (ヒメニラ), Amana edulis (アマナ), A. erythronioides (ヒロハノアマナ), Anemone debilis (ヒメイチゲ), A. flaccida (ニリンソウ), A. nikoensis (イチリンソウ), A. pseudoaltaica (キクザキイチゲ), A. soyensis (エゾイチゲ), Erythronium japonicum (カタクリ), Trillium smallii (コジマエンレイソウ), Soldanella alpina L. (イワカガミダマシ, alpine snowball)
Five species often shown in my lectures for international students

Trillium kamtschaticum (オオバナノエンレイソウ)
Anemone raddeana (アズマイチゲ)
Corydalis ambigua (エゾエンゴサク)
Scopolia japonica (ハシリドコロ)
Gagea lutea (キバナノアマナ)

Sex ()

vegetative stage = often immature stage ↔ reproductive stage = mature stage, anyway
sex ratio: polygamy (多系), vegetative propagation, monogamy

Sexual form

Case. Plants
Hermaphrodite and monoecy (synoecious)

protandry (adj. protandrous)
protogyny (adj. protogynous)

hermaphrodite flower, bisexual flower

adichogamous flower
dichogamous flower

monoecism, or monoecy
Dioecism, dioecy

androgynodioecious, triecious: (♂)/(♀)/(♂♀)
androdioecious: (♂)/(♂♀)
gynodioecious: (♀)/(♂♀)

Case. Animals
Hermaphrodite, or monoecy (monoecious)
Agamospermy (無融合種子形成)
Gametophytic apomixis: more in tropical regions

Adventitious embryony: northern elements
antipod → antipodal embryo

synerig → [agamospermy] → synerigid embryo

synerigid embryo Ex. Taraxacum, Alnus, Poa
antipodal embryo Ex. Elatostema, Allium → false vivipary

Agamic complex (無融合性複合体)

agamosperms, related sexual species
A. Normal sexual cycle
Sporophyte 2nSpore nGametophyte n → [Fertilization]

Zygote 2nSeed with embryo 2n

B. Cagetophytic apmixis
___[Diplospory]_________________[Diploid parthenogenesis]
___Embyro-sac mother cell 2n__Egg cell 2n____
Sprophyte 2n____Gametophyte 2n____Seed with embryo 2n
___Sotamtic cell of ovule 2n____Sotamtic cell 2n
C. Adventitious embryony
Sprophyte 2nSotamtic cell of ovule 2nSeed with embryo 2n
Fig. 31.1. Modes of agamospermous reproduction. A normal sexual life cicle is shown for comparison.

zygote (接合子): the cellular product of gametic union

Apomixis (無配偶生殖)
Reproduction is achieved without fertilisation, the sexual process being wholly or partly lost (the term and its definition are according to Winkler 1908). Two types of system are found: vegetative apomixis and agamospermy.
1) Vegetative apomixis
While for a time plants are usually rooted to the precise spot where germination and establishment has occurred, radial growth by means of rhizomes, stolons, runners, etc., is characteristic of many perennial species. Bulbils (small, readily detachable propagules, often borne on aerial structures, (Figure) are found in some species. Plants arising from such propagules will, of course, have the same genotype as the parent plant. Certain crop-plant varieties, e.g. potatoes, and such familiar garden plants as Pelargonium (the gardener's 'Geranium') are regularly propagated by vegetative means.
2) Agamospermy
In certain plants normal seed is set but no sexual fusion has occurred in its production. Offspring have the genetic constitution of the plant which produces them. A plant reproducing by seed apomixis or agamosperrny has all the advantages of the seed habit (dispersal of propagules and a potential means of survival through unfavourable seasons) without the risks which may be associated with pollination. As there is no essential genetic difference between simple agamospermy and asexual reproduction, Winkler grouped these two types of reproduction under the common term of apomixis.
apomixis Fig. 7.6. Bulbils. (a) Saxifraga cernua: 1. (× 1); 2. a cluster of bulbils; 3, bulbils in various stages of development (From Kerner 1895) (b) Poa alpina:1. P. olpina with bulbils replacing its flowers (× 1); 2. a portion of the inflorescence; 3. a miniature grass-plant developed between the glumes of a spikelet of P. alpina.

Apospory (無胞子生殖)

Figure 31.2. Apospory in Crepis occidentalis. (A) Embryo-sac (胚嚢) mother cell dividing (ESMC) and below it an enlarging somatic cell (SC). (B) Linear tetrad above and somatic cell below developing into aposporic embryo-sac (AES). (C) Embryo-sac mother cell degenerating in first division and below it a one-celled aposporic embryo-sac (AES). (Stebbins & Jenkins 1939). (D-G) Diplospory in Antennaria porsildil. Embryo-sac mother cell developing into unreduced embryo-sac. (Urbanska 1974)

Recombination system, res (組み換えシステム)

Maximum res: open res (開放型組み換え), restricted res (制限型組み換え), colsed res (閉鎖型組み換え)
Maximum replication

Open res: wide allogamy
Restricted res: predominant autogamy
Closed res: agamospermy

Table 1.1. Components of the recombination system in plants
1. Factors controlling the amount of recombination per gernerations; control operative at meiosis

a. chromosome number
b. frequency of corssing-over
c. hybrid sterility

2. Factors controlling the amount of recmbination per generation; controlling operative at fertilization

d. brdding system
e. pollination system
f. dispersal potential
g. seed number and germination behavior
h. population size
i. crossability barriers and external mechanisms

3. factor controlling the amount of recombination per mechanisms

j. length of generation

[ cytogenetics ]

Reproduction (生殖)

Sex determination

Sex chromosome