ECOLOGICAL FACTORS (Forces)
These innumerable factors are, grouped into the following five classes:-
(A) CLIMATIC FACTORS e.g.
Light, Temperature, Humidity, and precipitation etc.
(B) EDAPHIC FACTORS e.g.
Soil depth, Texture, Structure, Drainage available nutrients etc.
(C) PHYSIOGRAPHIC/TOPOGRAPHIC FACTORS e.g.
Slope, Aspect, Altitude, Latitude etc.
(D) BIOTIC FACTORS e.g.
Trees, Crops, Animals, insects, Man etc.
(E) PYRIC OR FIRE FACTORS
Wildfire, Controlled Pruning.
1. Like every other living organisms trees are also sternly influenced by the environmental factor (Forces).
2. Each one of these factors has 3 levels:
i. The maximum level is one above which trees cannot survive.
ii. The minimum level is one below which trees cannot survive.
iii. The optimum level is an ideal one and at this level tree growth is maximum.
3. The extreme values are important for the survival of species where average values are important for their productivity.
4. These environmental Factors are not of equal importance all the time.
5. Their importance is variable and is determined by the magnitude up to the difference between their available level and their optimum level.
6. The Relative importance of these factors keeps changing and depends on tree species, their age or growth stage and season of the year etc.
7. The trees also in return influence these factors.
8. These factors also influence each other and are influenced by each other. In many cases, these make up the deficiency of each other i.e. This supplement each other.
9. Some of them exhibit instant influence on trees whereas others exhibit delayed influence. (Factors having lagged effects).
(A) CLIMATIC FACTORS
1. These factors comprise of solar Radiation (light), Temperature, Humidity, Precipitation and Atmosphere etc. These factors are undoubtedly most important of all other factors.
2. Precipitation is perhaps most important in tropical/subtropical regions and temperature, as well as light, is most important in Temperate and Alpine Regions.
3. Solar Radiation is essentially required for photosynthesis.
It affects forest growth in different aspects i.e. Quality, intensity, day length and cumulative total per annum.
4. Forest trees are generally of two types:-
i. Shade bearers.
ii. Light demanders
5. Light can be manipulated through thinning and regeneration fellings.
6. Solar Radiation is never a limiting factor for tree growth in Pakistan. It is in fact frequently in excess. Sunburn of tender leaves/shoots is a common observation during summers.
7. Soil and air temperature affect all life processes.
8. Trees are more sensitive to temperature extreme in their early growth stages.
9. Un-expected and sudden fluctuation is more damaging than gradual seasonal changes.
10. Temperature extremes are more severe near the ground surface.
11. Provision of shelter, mulch and moisture can ameliorate temperature extremes on the soil surface.
12. Areas of high precipitation are always s areas of tall dense forest vegetation.
13. Out of numerous components of Atmosphere, relative, humidity, Co2 concentration and wind velocity are relatively more important for tree growth.
14. Hot, dry strong winds are quite killing to young seedlings and suppresses the growth of grown-ups.
15. Presence of harmful gases in the atmosphere is fast assuming alarming proportions in the vicinity of Industrial areas.
(B) EDAPHIC FACTORS
1. Soil is also an equally important factor for tree growth.
2. Tree roots are generally deeper and extensive than crops, roots and these explore a much larger volume of soil in search of water and nutrients.
3. Compact and shallow soils cause numerous problems such as Erosion, Lack of moisture, Nutrients and Fluctuations of soil temperature.
4. Waterlogging is a very serious local problem in many of soil. This is due to:-
i. Increased and continuous input of irrigation;
ii. Lack of natural drainage due to the little natural slope of our soils, and iii. absence of drains.
Trees suffer from waterlogging (lack of Co2 in soils) but later in their life, these adjustments to the situation and transpire large amounts of soil water, these thus make the soil suitable for cultivation and for other uses. e.g. Eucalyptus plantation in saline & waterlogged area.
5. Trees also ameliorate salinity by increasing soil porosity, lowering water-table and leading to rapid down of salts by a drastic reduction of upward movement of salts through the formation of a dense litter layer and canopy simultaneously.
(C) PHYSIOGRAPHIC FACTORS
1. Altitude, slope gradient, slope length, slope nature (CONVEX CONCAVE PLANE) and Aspect are an important component of land configuration have a strong indirect influence on tree growth.
2. These landform features have a very strong modifying effect on temperature, soil moisture, duration of growing season and precipitation etc.
(D) BIOTIC FACTORS
1. Biotic factors include Fire, Grazing and browsing, felling and lopping of trees, Torchwood extraction, Grass cutting, Encroachment and injuries caused by animals, insect, plants (Parasites) and chemical warfare of plants (Releasing toxic materials).
2. Trees are continuously affected by other trees, crops, weeds, fungi, insects, animals and man.
3. Young trees are more exposed to trampling and browsing by livestock, nibbling by rodents and rabbits, uprooting by children and to damage by a careless performance of forest farms operation.
4. The harmful effect of shade on desirable trees can be reduced by judicious thinning and pruning of unwanted trees.
5. Biotic factors have beneficial effects on trees as well e.g.
i. Earthworms, Beetles, Reptiles and Rodents loosen the soil.
ii. Grazing livestock adds nutrients to the soil through their urine & dung.
iii. Mycorrhizae (fungi) efficiently absorb mineral nutrients and water and supply these to trees.
iv. Bacteria fix atmospheric nitrogen and exchange it with trees for sugars.
(E) PYRIC FACTORS
1. Both Natural wildfires, as well as Artificial controlled burnings, have a significant effect on plant growth.
2. Burning also releases the nutrients that are tied up in a litter and make them available for new plant growth.
3. Keep the balance between Woody vegetation and Grasses.
Details of Each Factor is given separately. Please check out in Locality Factors.
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