Monsoon Deciduous Biome

  • Normally, tropical deciduous forests are found in regions of monsoon climate. 
  • Three major areas of tropical deciduous forest biome:
    • Neotropics mainly West Indies.
    • Indo-Malaysian Zone (mainly in south and south-east Asia except equatorial evergreen rainforest areas).
    • Eastern Africa and northern Australia.
  • Besides these major areas, some discontinuous localities of tropical deciduous forest biomes are also found in South Africa, Southern Brazil, South-Eastern U.S.A., Formosa (Taiwan), southern China and Japan.

Climate:

  • This tropical deciduous forest biome is characterized by two distinct seasons viz. moist season and dry season.
  • Three main seasons in a year in Indian subcontinent: 
    • Dry warm summer season (March to June),
    • Warm humid summer season (July to October), and
    • Dry winter season (November to February).
  • Average temperature of warm dry summer season ranges between 27°C and 32°C but the maximum temperature ranges between 38°C and 48°C during May and June.
  • The length of dry season is more important than the total amount of precipitation in affecting vegetation in the tropical deciduous forest biome.
  • On an average, the mean annual rainfall is around 1500mm but there are many variations in temporal and spatial distribution of rainfall. For e.g. 80% of the mean annual rainfall is received within 3 wet months of summer season. 
  • Sometimes a few areas receive even less than 500 mm of mean annual rainfall.
  • This seasonal regime of annual monsoonal rainfall gives deciduous character to the vegetations which shed their leaves (mostly trees and shrubs) during the transitional period between winter and summer season.
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Natural Vegetation:

  • The number of plant species and density is less in the tropical deciduous forest biome than the tropical evergreen rainforest biome and hence there is comparatively less competition among the plants for getting sunlight.
  • The height of most of the trees ranges between 12m and 30m.
  • There are four strata or layers in the vertical structure of the tropical deciduous forests. The uppermost and the second strata consist of trees; the third stratum is formed by shrubs whereas the last and the fourth stratum or the ground stratum represents herbaceous plants.
  • The trees are characterized by thick girth of stems, thick, rough and coarse bark and large hydromorphic leaves or small, hard xeromorphic leaves.
  • The large hydromorphic leaves enable the trees to trap more and more rainfall during wet seasons, but these large leaves are shed in dry periods to conserve moisture whereas small and hard xeromorphic leaves enable the trees to withstand dry weather and water deficiencies.
  • Though there are numerous climbers mainly lianas and epiphytes, but their numbers are far less in the tropical deciduous forest biome than the tropical evergreen rainforest biome.

Animal Life:

  • It is a significant ecological principle that more is the development of stratification of the vertical structure of the vegetation community of a biome and greater the number of plant species, the more will be the number of animal species, their total population and species diversity. This ecological principle holds good in the case of tropical evergreen rainforest biome.
  • There are comparatively lesser number of animals species in the monsoon deciduous forest biome than the rainforest biome because of comparatively less developed vertical strata and hence less diversification of animal species.
  • The seasonal character has affected and determined the seasonal behaviour of animal communities particularly breeding and migrating behaviour.
  • For example, birds in east Africa breed twice during the two different seasons of a year. Indian dogs generally breed once a year mainly at the end of wet monsoon season (during October-November).
  • The animals of the tropical and sub-tropical dry deciduous forest biome range from very small animals (micro-organisms) to very large-bodied animals like elephants, horses, hippopotamus, rhinos, lions, forest buffalo together with a large population of birds of several species.
  • This biome represents the largest number of domesticated mammals because of the development of agriculture.
  • This biome carries the largest human population of the world.
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