Fire: An Ecological Factor

FIRE: AN ECOLOGICAL FACTOR: Fire is an important ecological factor. Fire ecology is concerned with natural processes involving fire in an ecosystem and ecological effects, interaction of ecosystem and role of fire as an ecosystem process. → Fire is an integral component in the function and biodiversity of many natural habitats. → Fires are generally classified into 3 types: i) ground fires ii) surface fires iii) crown fires Ground fires: → These develop in such conditions where organic matter accumulates richly as heaps and they catch fire. → These fires are flameless and subterranean. → These fires kill almost all plants rooted in burning material except some woody species. Surface fires: → These fires sweep over the ground surface rapidly and their flames consume the living herbaceous vegetation and shrubs. Crown fires: → These are the most destructive fires. → It can burn forest canopy, surface debris even if causes vegetational destruction at a large scale. EFFECTS OF FIRE: In addition to its direct lethal effects on plants, fire also affects them indirectly in following ways: → Due to injury by fire, some trees have large scars on their stems. Such scars may serve as a suitable place of entry of parasitic fungi. And insects (EX: Epilobium angustifolium) and some grasses (Ex: Cynodon dactylon) are stimulated to growth by fires. → Some fungi, mainly some ascomycetes, grow in soils of burnt areas. Such fungi are known as pyrophilous (ex: Pyronema confluens). Fire has important effects on abiotic components, also particularly soil. → It affects soil by removing overhead vegetation, which leads to increased solar radiation on soil. → It causes changes in soil nutrients. → It reduces plant transpiration rate, allowing the soil to retain more moisture. → Fire makes the soil more basic (higher pH). → Fire also alters the texture and structure of soil by affecting the clay content and soil porosity. ADAPTATION OF PLANTS TO FIRE: Plants have evolved many adaptations to cope with fire. The adaptive features are as follows: → Some shrubs produce seeds in large number and whose seed coats are very hard. → Some wood plants develop fire-resistant seeds or fruits. → In some plants, leaves are fire-resistant due to poor contents of some compounds like resin or oil, and may check surface fires. → Some plants have adventitious or latent axillary buds, which may develop into new branches even if after fire kills the older ones Some shrubs develop special structures called lignotubers which may produce new shoots after damage. A no. of conifers produce serotinous cones, cones remaining on trees with viable seeds for several years, to resist from fire. If fire damage caused it can only cause the opening of these cones. On the basis of fire resistivity to fire, plant species are of 2 types: i) Fire tolerant ii) Fire intolerant iii) Fire resistant Fire tolerant: These plants are able to withstand fire up to a certain degree. These plants are 'resprouters' which store extra energy in their roots to aid recovery and regrowth. Ex: Mountain Grey-Gum tree (Eucalyptus cypellocarpa) Fire intolerant: These plant species are highly flammable and are destroyed completely by fire. Fire resistant: These plants suffer little damage during fire damage. These includes large trees whose flammable parts are high above the surface fires. Ex: Ponderosa Pine (Pinus Ponderosa) WATER FACTOR: Water occupies a central position in the life of organisms. It is an universal solvent for all the minerals present in soil. In some plants, water plays an important role in fertilization, pollination, and dissemination. Water also affects seed germination, transpiration, photosynthesis, respiration, translocation, and some biochemical processes. Water is an ideal solvent of life. It has various physical properties described as follows: (1) Melting Point: The melting point of water is 0°C, which is higher than most other common liquids like methanol, ethanol, acetone, chloroform, etc. (2) Boiling Point: The boiling point of water is 100°C, which is highest in comparison to all other solvents. This property is due to hydrogen bonding among water molecules. (3) Specific heat capacity: Specific heat capacity of water is 1.0, which is highest among most of natural solvents. (4) Heat of fusion: It may be defined as the no. of calories of heat energy required to convert a gram of substance from solid state to liquid state at its melting point. Heat of fusion of water is 80 cal/g. (5) Heat of vaporization: The latent heat of vaporization is defined as the no. of calories per gram required to overcome the attractive forces between adjacent molecules in a liquid. Heat of vaporization of water is 540 cal/g. Water has the highest density at 4°C. This property of water has much biological significance. IMPORTANCE: Water plays an important role in the world economy. Water covers 71% of Earth's surface. Water is an excellent solvent for a wide variety of chemical substances for which it is widely used in industrial processes and in cooking and washing. Water is a transparent and nearly colorless chemical substance. That's the main constituent of Earth's streams, lakes, and oceans etc. It is also present in nature as snow, glaciers, clouds, fog, dew, and atmospheric humidity. STATES OF WATER IN THE ENVIRONMENT: Water exists in 3 states: (1) Liquid state (2) Solid state (3) Gaseous state Liquid state: → It is the normal water, present in liquid state at standard temperature and pressure. → The temperature range is 0°C - 100°C. → Liquid water is present in rivers, ponds, seas, lakes, and oceans. Solid state: Ice is the solid state of water, present below 0°C. Water is converted to ice at the melting point when it gives off 80 cal of heat energy per gram. Other forms of solid state of water are icebergs, glaciers, snow, hailstone, etc. Gaseous State: → Steam and water vapor present in atmosphere are gaseous state of water present normally above 100°C. → Water is converted to gaseous state of heat energy per gm. ATMOSPHERIC HUMIDITY OR; ATMOSPHERIC MOISTURE: In the atmosphere, water is present in the gaseous state in the form of water vapor or moisture, which is called atmospheric moisture or atmospheric humidity. → It is an important climatic factor which directly affects the vegetation. The most important environmental factor that affects atmospheric humidity is temperature. Evaporation of water from earth's surface, particularly from open water bodies like oceans, rivers, lakes, ponds etc. and transpiration from plants are the main cause of atmospheric humidity. Atmospheric moisture or humidity can be measured in various ways as follows: (1) Absolute Humidity: Absolute humidity is the total mass of water vapor present in a given volume of air. AH = mH2O / Vnet where, mH2O = Mass of the water vapor Vnet = volume of air → Absolute humidity changes as air temperature or pressure changes. Mass of water per unit volume is also defined as volumetric humidity. → The field concerned with the study of physical and thermodynamic properties of gas vapor mixture is named as psychrometrics. (2) Relative Humidity: The invisible vapor or humidity of the air is usually expressed as relative humidity. Relative humidity (RH or Φ) of an mixture is also defined as the ratio of the partial pressure of water vapor (PH2O) to the vapor pressure of pure water (PH2O) over a flat surface of pure water at a given temperature. Φ = PH2O / PH2O Relative humidity is measured by the instrument called Psychrometer or by paper strip hygrometer or a thermo-hydrograph.   Relative humidity is an important metric used in weather forecasts & reports as it is an indicator of the likelihood of precipitation, dew, or fog. (3) Specific humidity: Specific humidity is the ratio of the mass of water vapor to the total mass of the moist or humid air. (4) Vapor Pressure: Vapor Pressure of water vapor is known as the pressure exerted by vapor in the thermodynamic equilibrium with its condensed phase. (5) Saturation deficit: It is the difference between the vapor pressure at saturation at a given location and actual vapor pressure at the same spot. (6) Dew Point: Dew Point is the atmospheric temperature below which water droplets begin to condense and dew can form. PRECIPITATION: Precipitation (rainfall) is actually the chief source of soil moisture. Precipitation is the chief source of soil water, which is available to plants & animals. Precipitation can also fall in either liquid or solid phases or transition between them. Liquid forms of precipitation include rain and drizzle.   Frozen forms of precipitation include snow, ice needles, sleet, hail, and snow pellets etc. TYPES OF PRECIPITATION: Precipitation is of 2 types: (1) orographic precipitation (2) convectional precipitation (3) cyclonic precipitation (1) Orographic Precipitation: It results when warm moist air moving across the ocean is forced to rise by large mountains. (2) Convectional Precipitation: → This type can be observed in mountain side termed as windward side & leeward side of mountain. → It results from the heating of earth's surface. → It falls over a certain area for a relatively short time as convective clouds have limited horizontal extent. → This type of precipitation is common in the prairies and ontario, and in tropics. (3) Cyclonic Precipitation: Cyclonic or frontal precipitation results when the leading edge of a warm, moist air mass (warm front) meets   a cool and dry air mass (cold front).   → This precipitation is common in Atlantic Canada. In addition to these 3 types, there is another type of precipitation called as stratiform precipitation which occurs when large air masses rise diagonally as large scale atmospheric dynamics force them to move over each other. It results from stratiform clouds. VARIOUS FORMS OF PRECIPITATION: Precipitation can occur in various forms. (1) Rain: Rain is the liquid form of water, occurs as droplets on earth. It is a major component of water cycle and is responsible for depositing most of fresh water on earth. The major cause of rain production is moisture moving along certain zonal temperature and moisture contrast known as weather fronts. (1) Rain: → Droplets smaller than half a millimeter are classified as drizzle. → Raindrops are often formed when small cloud particles collide and stick together, forming bigger drops. → Sometimes rain evaporates before reaching the ground, resulting in virga. → Acid rain occurs when rain becomes mixed with pollutants such as sulfur oxides and nitrous oxide. → It kills plants and pollutes water sources. pH of acid rain is ≤ 5.6. → Global warming is also causing changes in the precipitation. → Rain and drizzle are generally beneficial to plants and crops. However, excessive rain can cause significant runoff and erosion that can damage the fields of without plants or drown their roots. (2) Snow: → Snow refers to the ice crystals that precipitate from the atmosphere and undergo changes on the earth's surface. → Under suitable conditions, snowstorms and snowflakes are formed. → Snow affects human activities such as transportation, agriculture, warfare, etc. (3) Hail: → Hail is a form of solid precipitation. → Hail consists of balls or irregular lumps of ice, each of which is called a hailstone. → Hail is produced by clouds associated with thunderstorms. → There are methods available to detect hail-producing thunderstorms using weather satellites. → Hail is nicknamed as the "white plague." → Hail can cause a lot of damage to trees and crush young plants.