Natural Vegetation--1

·        Climate, soil and topography are the major factors that influence Natural Vegetation of a place.

·        The main climatic factors are rainfall and temperature. The amount of annual rainfall has a great bearing on the type of vegetation.

Annual Rainfall	Type of Vegetation
200 cm or more	Evergreen Rain Forests
100 to 200 cm	Monsoon Deciduous Forests
50 to 100 cm	Drier Deciduous or Tropical Savanna
25 to 50 cm	Dry Thorny Scrub (Semi-arid)
Below 25 cm	Desert (Arid)

·        While rainfall is the major factor in most of the regions, temperature is the major factor in Himalayas and other hilly regions with an elevation of more than 900 metres.

·        As the temperature falls with altitude in the Himalayan region the vegetal cover changes with altitude from tropical to sub-tropical, temperate and finally alpine.

·        Soil is an equally determining factor in few regions. Mangrove forests, swamp forests are some of the examples where soil is the major factor.

·        Topography is responsible for certain minor types e.g. alpine flora, tidal forests, etc..

Classification Of Natural Vegetation

·        Classification of Natural Vegetation is primarily based on spatial and annual variations in rainfall. Temperature, soil and topography are also considered.

·        India's vegetation can be divided into 5 main types and 16 sub-types as given below.

A. Moist Tropical Forests

1.  Tropical Wet Evergreen

2.  Tropical Semi-Evergreen

3.  Tropical Moist Deciduous

4.  Littoral and Swamp

B. Dry Tropical Forest

1.  Tropical Dry Evergreen

2.  Tropical Dry Deciduous

3.  Tropical Thorn

C. Montane Sub-tropical Forests

1.  Sub-tropical broad leaved hill

2.  Sub-tropical moist hill (pine)

3.  Sub-tropical dry evergreen

D. Montane Temperate Forests

1.  Montane Wet Temperate

2.  Himalayan Moist Temperate

3.  Himalayan Dry Temperate

E. Alpine Forests

1.  Sub-Alpine

2.  Moist Alpine scrub

3.  Dry Alpine scrub

A. Moist Tropical Forests

Tropical Wet Evergreen Forests or Rain Forests

Climatic Conditions

1.  Annual rainfall exceeds 250 cm

2.  The annual temperature is about 25°-27°C

3.  The average annual humidity exceeds 77 per cent and

4.  The dry season is distinctly short.

Characteristics

·        Evergreen: Due to high heat and high humidity, the trees of these forests do not shed their leaves together.

·        Mesosphytic:

What are mesophytes? ·        Unlike hydrophytic plants, such as water lily or pondweed, that grow in saturated soil or water, or xerophytic plants, such as cactus, that grow in extremely dry soil, mesophytes are ordinary plants that exist between the two extremes. ·        Mesophytic environments are marked by average to hot temperatures and soil that is neither too dry nor too wet.

·        Lofty: The trees often reach 45 – 60 metres in height.

·        Thick Canopy: From the air, the tropical rain forest appears like a thick canopy of foliage, broken only where it is crossed by large rivers or cleared for cultivation.

·        All plants struggle upwards (most ephiphytes) for sunlight resulting in a peculiar layer arrangement. The entire morphology looks like a green carpet when viewed from above.

·        Less undergrowth: The sun light cannot reach the ground due to thick canopy. The undergrowth is formed mainly of bamboos, ferns, climbers, orchids, etc.

Distribution

1.  Western side of the Western Ghats (500 to 1370 metres above sea level).

2.  Some regions in the Purvanchal hills.

3.  In the Andaman and Nicobar Islands.

Timber

·        Hardwood: The timber of these forests is fine-grained, hard and durable.

·        It has high commercial value but it is highly challenging to exploit due to dense undergrowth, absence of pure stands and lack of transport facilities [Read previous posts on Climatic regions to understand how lumbering industry works in Equatorial Rainforests (hardwood) and Taiga Climatic (softwood) conditions].

·        The important species of these forests are mahogany, mesua, white cedar, jamun, canes, bamboo etc.

Tropical Semi-Evergreen Forests

·        They are transitional forests between tropical wet evergreen forests and tropical deciduous forests.

·        They are comparatively drier areas compared to tropical wet evergreen forests.

Climatic Conditions

·        Annual rainfall is 200-250 cm

·        Mean annual temperature varies from 24°C to 27°C

·        The relative humidity is about 75 per cent

·        The dry season is not short like in tropical evergreen forests.

Distribution

·        Western coast

·        Assam

·        Lower slopes of the Eastern Himalayas

·        Odisha and

·        Andamans.

Characteristics

·        The semi-evergreen forests are less dense.

·        They are more gregarious [living in flocks or colonies – more pure strands] than the wet evergreen forests.

·        These forests are characterized by many species.

·        Trees usually have buttressed trunks with abundant epiphytes.

·        The important species are laurel, rosewood, mesua, thorny bamboo – Western Ghats, white cedar, Indian chestnut, champa, mango, etc. – Himalayan   region.

Timber

·        Hardwood: Similar to that in tropical evergreen forests except that these forests are less dense with more pure strands (timber industry here is better than in evergreen forests).

Tropical Moist Deciduous Forests

Climatic Conditions

·        Annual rainfall 100 to 200 cm.

·        Mean annual temperature of about 27°C

·        The average annual relative humidity of 60 to 75 per cent.

·        Spring (between winter and summer) and summer are dry.

Characteristics

·        The trees drop their leaves during the spring and early summer when sufficient moisture is not available.

·        The general appearance is bare in extreme summers (April-May).

·        Tropical moist deciduous forests present irregular top storey [25 to 60 m].

·        Heavily buttressed trees and fairly complete undergrowth.

·        These forests occupy a much larger area than the evergreen forests but large tracts under these forests have been cleared for cultivation.

Distribution

·        Belt running along the Western Ghats surrounding the belt of evergreen forests.

·        A strip along the Shiwalik range including terai and bhabar from 77° E to 88° E.

·        Manipur and Mizoram.

·        Hills of eastern Madhya Pradesh and Chhattisgarh.

·        Chota Nagpur Plateau.

·        Most of Odisha.

·        Parts of West Bengal and

·        Andaman and Nicobar islands.

Timber

·        These provide valuable timer like Teak.

·        The main species found in these forests are teak, sal, laurel, rosewood, amla, jamun, bamboo, etc.

·        It is comparatively easy to exploit these forests due to their high degree of gregariousness (pure strands).

Littoral and Swamp Forests

·        They can survive and grow both in fresh as well as brackish water(The mixture of seawater and fresh water in estuaries is called brackish water and its salinity can range from 0.5 to 35 ppt).

·        Occur in and around the deltas, estuaries and creeks prone to tidal influences (delta or tidal forests).

·        Littoral (relating to or on the shore of the sea or a lake) forests occur at several places along the coast.

·        Swamp forests are confined to the deltas of the Ganga, the Mahanadi, the Godavari, the Krishna and the Cauvery.

·        Dense mangroves occur all along the coastline in sheltered estuaries, tidal creeks, backwaters, salt marshes and mudflats. It provides useful fuel wood.

·        The most pronounced and the densest is the Sunderban in the Ganga delta where the predominant species is Sundri (Heriteera).

Timber

·        It provides hard and durable timber which is used for construction, building purposes and making boats.

·        The important species found in these forests are Sundri, agar, rhizophora, screw pines, canes and palms, etc.