Prof. Skand Kumar Mishra
Botany Deptt. Govt. New Science College, Rewa (M.P.) 486001
The timing of various phenological activities such as germination, bud break, flowering, fruit dehiscence, and leaf drop is important for survival and reproductive success of many plant species. Abiotic environmental conditions such as rain, change in temperature, presence/absence of pollinators, competitors, and herbivores have been shown to play a significant role in timing of various phenological events. Natural selection has also been considered to play some role in determining the phenological patterns of plant species. Phenological studies are also important in understanding species interrelations and their interaction with the environment. Variations in phenophases among individuals of the same species or different species have been linked to environmental perturbations.
The study of periodically occurring phenomena in plants in relation to the climate and changes of seasons is known as phenology. Leith (1970), Leith and Radford (1971) first discussed the concepts of phenological studies and its significance. The phenology study deals not only the vegetative and reproductive phase corresponding to the climate and seasonal changes of a particular area, but also determines the degree of reproductive synchrony with other plant species (Rathcke, 1988 a, b). Synchrony among species might be advantageous in which the presence of one species facilitates increase in pollinator visitation and enhanced in fruit/seed set in another species (Thomson, 1980, 1982; Rathcke and Lacey, 1985).
Phenological study is important in plant management and combating afforestation, honey analysis, floral biology, estimation of reproductivity and regeneration (Mulik and Bhosale, 1989). The flowering phenology differs from species to species in accordance with the ecosystems they associates and this suggest that specific patterns of flowering phenology may be a characteristic of specific ecosystem types.
Phenological studies reflect the daily occurrence of plants and animals in total response to environment. For plants, this includes both vegetative and reproductive such as bud formation, flowering, fruiting, and seed germination, along with vegetative phase like leaf flushing and shedding. Most phenological studies are based on observation of periodic phenomena occurring at a given location over a period of several years. The microclimatic study with reference to phenological research gains a tremendous attention because it represents the actual conditions that influence plant response. The phenological study helps to understand the adaptative strategies of the plant species in a particular kind of ecosystems T and its management. Therefore, it is important to study the phenological patterns of different taxa for critical analysis of reproductive biology and its implications on scientific study.
Phenology is a branch of science in which we can study the growth of buds, leaf fall, leafing out, fruiting and seed dispersal in relation to months, seasons or years. This study helpful for us on the study of dynamics of plant species within communities. It also help in the study of interaction of plant – animal in a ecosystem.
Leaf fall – Summer Winter
Decomposition – heterotrophic Substatum – Humus
Autotrophic layer – herbivorous
vernal – serotinal – mansoon – p. mansoon
Monsoon – premansoon – winter – summer
-Pollination and fruits (seeds) dispersal agents
Foliage Dynamics :
The foliation and defoliation of trees and shrubs form events which are significant from the point of view of ecosystem function. Formation of foliage help in the formation of cover within communities it also acts as a food resources of herbivores, whereas defoliation creates an annual heterotrophic stratum in which most nutrients and moisture content remain tagged, they help in the early establishment of seedlings. Leaf fall in tropical forests may be continuous or seasonal, even seasonal, at least two types of leaf fall pattern have been observed (1) Winter defoliation: (eg. Salmalia malabarica, Sterculia Urens etc.) (2) Summer defoliation : (eg. Cassia fistula, Holoptelia, integrifolia etc.)
Maximum number of trees of Central Indian Forest are summer defoliators. Some sps. Show new flushing just after the completion of leaf fall, whereas other show time gap between leaf fall and new leaf flushing.
Flowering phonologies as shown to have evolved as a result of selective role of pollinators on flowering time. There are four patterns of flowering have been observed for the tropical forest: (1) Vernal (spring) (eg. Azadirachta indica, Dalbergia sissoo etc.) (2) Serotinal (summer) (eg. Acacia catechu, Annona squamosa etc.) (3) Monsoon (eg. Tamarindus indica, Tectona grandis etc.) (4) Post monsoon (eg. Zizyphus sps., Smilex chinensis etc.).
Maximum number of trees of Central Indian Forest show vernal pattern of flowering.
The fruiting of trees also play an important role for the maintain of food chain in any ecosystem. There are different types of plants are found in tropical forest and gave their fruit in different seasons like monsoon, Post monsoon, summer and winter. There are two patterns of fruiting have been observed:
(1) Bradyspory: Sps. Shows delayed fruit maturation (eg. Aegle marmelos, Cassia fistula, Feronia lemonia etc.)
(2) Trachyspory: Sps. Shows quick maturation of fruits. (eg. Azadirachta indica, Buchanania lanzan etc.)
Seed dispersal is a critical event in plant life history for the survival of populations, and the survival must link to various biotic and abiotic factors (Vanschaik et al., 1993). The diasporas of many plant species have characteristic morphological structures and traits that enhance their probability of being dispersed away from the mother plant (Griz and Machado, 2001). Among these traits are fruit color, seed size and shape, and time of fruit ripening. The most commonly used classification system of dispersal syndromes is based on the agent or vector of dispersal, typically inferred from seed morphology (Levin et al., 2003). The principal agents of dispersal are either abiotic or biotic, and the dispersal syndromes are termed, respectively, anemochory, ballistic, and zoochory. The proportion of dispersal modes in a particular vegetation type is defined as the dispersal spectrum, which is influenced by community attributes, environmental circumstances and floristic composition. Although dispersal syndromes have many exceptions and are moderately predictive about dispersal mechanisms (Fleming et al., 1993), knowledge on dispersal spectra of plant communities is helpful for interpreting local ecology and for understanding factors that control composition and structure of communities (Arbelaez and Parrado-Rosselli, 2005). Seed dispersal by animals predominates tropical forest plant species (Willson et al., 1989), and involves a tremendous diversity of animal species and behaviors. Animals may consume fruit and drop, spit or defecate the seeds, carry seeds in their coats or scatterhoard seeds for later consumption. Abiotic strategies such as wind, water and ballistic dispersal form the main mode of seed movement for the remaining 10–30% of tropical tree species (Willson et al., 1989). However, little research studies the seed dispersal syndromes in subtropical tree species. Seasonality exposes plants to periodic changes in the quality and abundance of resources and almost all subtropical environments vary seasonally in temperature, rainfall, wind speed and daylength. All of these factors would play a role in triggering phenological changes in subtropical plants. A seasonal climate also brings about fluctuations in pollinators, seed dispersal agents, predators, and competitors (Griz and Machado, 2001). The activity of pollinators and seed dispersers, and breeding periods of animals depend on the seasonal production of flowers and fruits in the community. Phenological patterns are of great importance in determining the temporal changes, which constrain the physiological and morphological adaptations in plant community for utilization of resources (Selwyn and Parthasarathy, 2006) by fauna. However, phenological patterns of seed dispersal in subtropical broad-leaved forests are little known.
The movement of seeds away from the parent known as dispersal of seed. Due to dispersal of seed they get suitable environment for the growth and reproduction. This process complete in two successive stage: (1) Removal of seeds from the parent plant by dispersal agents (2) Final deposition of seeds.
The are two hypothesis have been advanced to explain the advantage of dispersal (1) Escape Hypothesis (2) Colonization Hypothesis. Both hypothesis predict that seedling recruitment occurs at some distance from the parent and that the seedling distribution will be discordant with the distribution of dispersed seed.
Fruit Traits and Seed Dispersal:
Plants provide food to dispersal agents in the form of nutritions structure (fruit). Traits of individual fruits have been shown to influence forgiving preference of animal in the field in same cases, but such effects varies among sites, seasons or years, shifted in response to other factors.
Piji consideds bird fruit to be (1) gaudy (2) absence of odour (3) bright coloured (4) absence of tough pericarp (5) diasporas easier to swallow. Mammal fruits are characterised by (1) dull colour (2) unfresh odour (3) tough pericarp (4) hangling on long stalk (5) attached to the main stem or branch.
Seed Dispersal by Birds:
Fleshy fruits are eaten by birds, which obtain a reward as a result of digesting the pulp and take the seeds away from the parent plant to be later discarded in conditions suitable for germination.
Seed dispersal is a one way movement in which the dispersers activity delivering seed to safe sites for the plants is of core plants. Frugivorous birds swallowed the whole fruit mass (including seeds) during feeding. At the end of foregoing bouts they fly to perching trees and shrubs of the area where they are wid swallowed seed intacted either by regurgitation or by defection. Thus birds remove seeds or diaspores from the parent plant where there is possibility of their mortality on account of predation or competition to safer areas.
Seed Dispersal by Mammals:
Inspite of high cost of seed predation, mamalion dispersal has some advantage, (1) If seed is buried, it has a high chance of survival than if it remains above soil. (2) Seed that are scattered by animals feeding on the fruits have a greater chance of survival than those remain in high densities near the parent.
In addition to providing mobility of seeds, frugivores can sometimes affect the germination probabilities of seed they defaecate. When seeds passed through the digestive tract of animals, germination is improved by such passage, since the hard seed coat is partly digested. Thus seed are not only hyper dispersed and the strategy reduces dominance of single species in the community, but also mammalian dispersal improves the chances of seed germination by breaking hard seed coat dormancy.
Yanjun Du et al., (2009) described the dispersal phenology and syndromes in Gutianshan 24 ha plot in a subtropical broad-leaved forest of China. The 130 0.5 m2 seed traps collected 69,115 mature seeds, representing 27 species (belonging to 24 genera, and 15 families) in 12 months. One marked peak in the number of seeds and species during the year was found in dry season (November). Zoochory was the most common dispersal syndrome (70.4%), followed by anemochory (18.5%), ballistic dispersal (11.1%). Among fruit types, berry (33%), capsule (22%), nut (18%), and drupe (11%) were common in the subtropical evergreen forest. In fruit color, brown was the commonest (40%), followed by dark brown (30%), black (15%), red (11%), and yellow (4%). Overall, the community level seed rain study revealed that one marked peak in seed number occurred in the middle of dry season; zoochory was the principal dispersal mode of woody plants in subtropical forest, and dry seasons favor seed dispersal by animal and wind.
Lokho and Kumar (2012) studied sixteen species of Indian Dendrobium Sw. from the Northeastern regions which are economically important from aesthetic value related industry. The detailed morphological characterization and the reproductive phenology are discussed. Vegetative characters reveal sizeable variations among the species which can be differentiated from one another. The height of the psuedobulb stem with nodes and internodes ranges from 15 cm to 130 cm, the maximum height was recorded in D. moschatum. The sessile lanceolate leaves with a maximum length were recorded in D. moschatum. The longest inflorescence was found in D. clavatum, interestingly in Dendrobium the longer the inflorescence the more the numbers of flower bearing. The flowers were exquisite and showy which exhibit different shapes and colours, the largest flower was recorded in D. formosum. Most of the species began to sprout new shoots during spring season. The low temperature, rainfall and humidity promote the flower bud initiation except in D. nobile, and D. heterocarpum favoured by moderate temperature and high humidity. The longevity of the flower ranges from 5 to 23 days with a maximum recorded in D. formosum. Post fertilization phenophase is the longest period exhibited by all the species under study, for instance seedpod initiation to maturity ranges from 56 to 120 days.
According to Kaur et al., (2013) the timing of seasonal biological activities of plants is very important to know about plant’s survival and its reproductive success. The variation in the phenological activities is due to change in different abiotic conditions. Paper deals with the study of phenological activities like bud formation, flowering time, fruiting time, and seed formation for some leguminous plants of Amritsar, Punjab (India).
According to Solomon et al.. (2014) Syzygium alternifolium is a semi-evergreen mass-flowering tree species of dry deciduous forest in the southern Eastern Ghats of India. It is a mass bloomer with flowering during dry season. The floral traits suggest a mixed pollination syndrome involving entomophily and anemophily together called as ambophily. Further, the floral traits suggest generalist pollination system adapted for a guild of pollinating insects. The plant is self-incompatible and obligate out-crosser. The flowers are many-ovuled but only a single ovule forms seed and hence, fruit and seed set rates are the same. Natural fruit set stands at 11%. Bud infestation by a moth, flower predation by the beetle, Popillia impressipyga and bud and flower mounds significantly limit fruit set rate. The ability of the plant to repopulate itself is limited by the collection of fruits by locals due to their edible nature, short viability of seeds, high seedling mortality due to water stress, nutrient deficiency and erratic rainfall or interval of drought within the rainy season. Therefore, S. alternifolium is struggling to populate itself under various intrinsic and extrinsic factors. Further studies should focus on how to assist the plant to increase its population size in its natural area taking into account the information provided in this study.
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Received on 10.08.2018 Modified on 22.09.2018
Accepted on 14.10.2018 ©A&V Publications All right reserved