forestry

Solar radiation and its effects on vegetation

The energy which is responsible for the growth of vegetation and all life depending on it, in this earth comes directly or indirectly from the sun. Thus the nature and amount of solar radiation received on the surface of the earth is a factor of great importance. The energy radiated by sun reaches the earth in the form of electromagnetic waves of varying length, ranging nearly from 290 millimicrons to 5300 millimicrons.
The maximum energy of solar radiation occurs in the green and yellow regions of the visible spectrum (400mµ to 720mµ). Since the heat produced by the radiation is independent, in its effect, of the wavelength, the intensity of radiation is generally measured by the heart generated by it. The solar radiation reaching the earth is further is affected by latitude, altitude, season of the year and time of the day. As latitude increases, the intensity of solar radiation decreases. With increase in altitude, the radiation increases. The most important effect of solar radiation is that it provides both light and heat (temperature).
Importance of Light

1. Chlorophyll formation: Light is one of the important and essential factors responsible for chlorophyll in plants. Without light plants become pale yellow and have long thin internodes, a condition known as 'etiolating.' Chlorophyll decomposes in bright sun light; thus formation and decomposition both go on simultaneously when the plant is exposed to light.
2. Functioning of stomata: Light is an important factor influencing the daily opening and closing of stomata, which in turn, affect respiration and photosynthesis.
3. Photosynthesis: Light is the most important factor of locality for photosynthesis as it can not take place in darkness. Out of the seven colors in visible part of the spectrum, only red and blue are effective in photosynthesis. It has been estimated that light used in photosynthesis is less than 2 percent of the light energy incident on well-illuminated leaves.
4. Growth: Light influence the growth of plants and trees through its effect on photosynthesis. The influence of light varies with its quality, duration and intensity. Quality of light refers to colors. Plant growth in blue light is small. Red light on other hand results in elongation of cells giving the appearance of etiolated plants. Violet and ultraviolet light bring about dwarfing effect.
5. Form and quality of trees: The elongation of the growing axes of tree in the forest occurs mainly between sunset and sunrise because the low intensities of light and infrared radiation tend to stimulate height growth. Even the form of trees growing in shade is very dissimilar to that of trees growing in the open.
6. Species stratification and size and structure of leaves: The intensity of light in the forest varies from place to place and from time to time between wide limits.
Light requirement:

1. Light demander is a species that requires abundant light for its best development.

2. Shade bearer is a species capable of persisting and developing under shade.

3. Shade demander is species requiring, at least in its early stages, some degree of shade for its normal development.