Tropical Deciduous Biome (Monsoon Climate) – UPSC Environment Notes

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• Monsoons encompass expansive land and sea breezes, presenting on a grander scale. 
• Divergent from equatorial wet climates, the monsoon climate displays explicit wet and dry seasons marked by the seasonal reversal of winds. 
• Common occurrences during these periods include floods in the wet season and droughts in the dry season. 
• Typically, the monsoon climate unfolds across three distinct seasons: summer, winter, and the rainy season.

DISTRIBUTION

• Found within the latitudinal belt of 5° to 30° N and S of the equator, tropical monsoons exhibit on-shore movements from sea to land during the summer and off-shore patterns from land to sea in the winter. 
• This climatic phenomenon is most prominently observed and well-developed in regions such as the Indian subcontinent, Burma, Thailand, Laos, Cambodia, parts of Vietnam, southern China, and northern Australia.

CLIMATE

The tropical deciduous forest biome is characterized by distinct moist and dry seasons, with three main seasons prevailing in the Indian subcontinent:

Dry Warm Summer Season (March to June):

• This season is marked by elevated temperatures.
• The average temperature during the warm, dry summer season ranges between 27°C and 32°C.
• Maximum temperatures can soar between 38°C and 48°C, particularly in May and June.

Warm Humid Summer Season (July to October):

• This period experiences warm and humid conditions.
• It spans from July to October.

Dry Winter Season (November to February):

• The winter season, lasting from November to February, is characterized by dryness.

Temperature and Rainfall:

• The critical dry season is more impactful on vegetation than the overall precipitation amount.
• The mean annual rainfall averages around 1500mm, but significant variations exist in the temporal and spatial distribution of rainfall.
• Approximately 80% of the mean annual rainfall occurs within the three wet months of the summer season.
• Some areas receive less than 500 mm of mean annual rainfall.

Deciduous Character:

• The deciduous character of the vegetation is influenced by the seasonal regime of annual monsoonal rainfall.
• Trees and shrubs, comprising a significant portion of the vegetation, shed their leaves during the transitional period between winter and summer seasons.
• This distinct seasonal pattern shapes the ecological dynamics of the tropical deciduous forest biome, creating a habitat that adapts to the alternating conditions of moisture and dryness.

NATURAL VEGETATION

The tropical deciduous forest biome exhibits a lower number of plant species and reduced density compared to the tropical evergreen rainforest biome, leading to less competition among plants for sunlight. 

Key features of the tropical deciduous forest biome include:

Tree Height:

• Most trees in this biome have heights ranging from 12m to 30m.

Vertical Structure:

• The vertical structure consists of four strata or layers.
• The uppermost and second strata are composed of trees.
• The third stratum is formed by shrubs.
• The fourth stratum, or ground stratum, is characterized by herbaceous plants.

Tree Characteristics:

• Trees in the tropical deciduous forest biome are recognized by:
• Thick girth of stems,
• Thick, rough, and coarse bark,
• Large hydromorphic leaves or small, hard xeromorphic leaves.

Adaptations to Moisture Variation:

• Large hydromorphic leaves aid in trapping more rainfall during wet seasons.
• These large leaves are shed during dry periods to conserve moisture.
• Small and hard xeromorphic leaves enable trees to withstand dry weather and water deficiencies.

Climbers and Epiphytes:

• While numerous climbers, mainly lianas and epiphytes, exist, their numbers are relatively lower compared to the tropical evergreen rainforest biome.
• The distinctive characteristics of the tropical deciduous forest biome reflect adaptations to the pronounced seasonal variations, where periods of wetness are followed by dry intervals. 
• This biome showcases a unique ecosystem where plants have evolved strategies to thrive in the dynamic conditions of moisture availability.

ANIMAL LIFE

• The ecological principle that emphasizes the development of stratification in the vertical structure of a biome’s vegetation community correlates with an increased number of animal species, total population, and species diversity. 
• This principle is particularly evident in the tropical evergreen rainforest biome. 
• In contrast, the monsoon deciduous forest biome exhibits a relatively lower number of animal species due to less developed vertical strata, resulting in reduced diversification of animal species.
• The seasonal character of the monsoon deciduous forest biome significantly influences the behavior of animal communities, particularly in terms of breeding and migration. 
• Examples include birds in East Africa breeding twice a year during different seasons, and Indian dogs typically breeding once a year, mainly at the conclusion of the wet monsoon season (October-November).
• The animal inhabitants of the tropical and sub-tropical dry deciduous forest biome encompass a diverse range, from micro-organisms to large-bodied species such as elephants, horses, hippopotamuses, rhinos, lions, and forest buffalo. 
• The biome also sustains a substantial population of various bird species.
• Notably, the tropical and sub-tropical dry deciduous forest biome harbors the largest number of domesticated mammals, a phenomenon attributed to the development of agriculture within this biome. 
• Additionally, this biome is home to the world’s largest human population, further underscoring its ecological and anthropological significance.

FAQs – Monsoon Climate and Tropical Deciduous Forest Biome

Q1: What defines the Monsoon Climate?

A: Monsoons encompass expansive land and sea breezes, presenting on a grander scale. Divergent from equatorial wet climates, the monsoon climate displays explicit wet and dry seasons marked by the seasonal reversal of winds. Common occurrences during these periods include floods in the wet season and droughts in the dry season. Typically, the monsoon climate unfolds across three distinct seasons: summer, winter, and the rainy season.

Q2: Where are Tropical Monsoons Found?

A: Found within the latitudinal belt of 5° to 30° N and S of the equator, tropical monsoons exhibit on-shore movements from sea to land during the summer and off-shore patterns from land to sea in the winter. This climatic phenomenon is most prominently observed and well-developed in regions such as the Indian subcontinent, Burma, Thailand, Laos, Cambodia, parts of Vietnam, southern China, and northern Australia.

Q3: What are the Main Seasons in the Indian Subcontinent’s Deciduous Forest Biome?

A: The Indian subcontinent’s tropical deciduous forest biome experiences three main seasons: a dry warm summer season (March to June), a warm humid summer season (July to October), and a dry winter season (November to February).

Q4: What are the Characteristics of the Warm Dry Summer Season?

A: During the warm dry summer season, temperatures range between 27°C and 32°C, with maximum temperatures soaring between 38°C and 48°C in May and June.

Q5: How does Rainfall Affect Vegetation in the Deciduous Forest Biome?

A: The length of the critical dry season is more impactful on vegetation than the overall precipitation amount. The mean annual rainfall averages around 1500mm, with approximately 80% occurring within the three wet months of the summer season. Some areas receive less than 500 mm of mean annual rainfall, shaping the deciduous character of the vegetation.

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