Chapter 6 Practical 7
Aim:
To identify common tree species found in Delhi using a dichotomous key.
To compare the floral diversity of the Delhi region with that of another Indian state (e.g., Kerala, Himachal Pradesh) using secondary data and understand the role of climate and geography.
Principle:
India's floral diversity is immense due to its varied climate, topography, and soil types. The distribution of plant species is not uniform. Delhi, located in the Northern Plains, has a semi-arid climate and flora adapted to dry conditions (e.g., Prosopis cineraria, Acacia nilotica). In contrast, a state like Kerala in the Western Ghats has a tropical climate supporting rainforest species (e.g., Cocos nucifera, Artocarpus heterophyllus), while Himachal Pradesh in the Himalayas has temperate flora (e.g., Cedrus deodara, Rhododendron arboreum). Identification is done using morphological keys (observing leaves, flowers, bark, fruit) and comparing with herbarium specimens or verified digital databases .
Materials Required:
For Field Study (in Delhi):
Notebook, pencil, camera.
Local field guide or tree identification book (e.g., "Trees of Delhi" by Pradip Krishen).
Ziplock bags for leaf/flower samples (if permitted).
For Comparative Study:
Access to online databases: IBIS (Indian Bioresource Information Network), GBIF (Global Biodiversity Information Facility).
Maps of India showing climate zones and forest types.
General:
Hand lens.
Printed dichotomous key for common Delhi trees.
Procedure:
Part A: Identification of Delhi's Flora (Field-Based)
Select a Site: Choose a local park or green space in Delhi (e.g., Lodhi Garden, Sanjay Van, College campus).
Observation and Documentation:
Select 5 different tree species.
For each tree, note the following characteristics:
Leaf: Shape (oval, lanceolate, needle-like), arrangement (opposite, alternate), margin (smooth, serrated).
Bark: Colour, texture (smooth, rough, fissured).
Flower/Fruit: Colour, shape, size (if present).
Sketch or photograph each key characteristic.
Identification using a Dichotomous Key:
Use the provided key by answering a series of paired questions (couplets) about the plant's morphology to arrive at its species name.
Part B: Comparative Analysis (Desktop-Based)
Data Collection from Open Sources:
Visit the IBIS website (https://ibis.gov.in).
Navigate to the "Biodiversity" section and access data on "State-wise Diversity of Plants".
Record the following data for Delhi and a contrasting state (e.g., Kerala):
Total number of flowering plant species.
List 5 common tree species not found in Delhi.
Climate and Geography Analysis:
Research and note the primary climate type and dominant forest type for both regions.
Observations:
Table 1: Morphological Observations of Delhi Tree Species
| Tree Code | Leaf Shape & Arrangement | Bark Texture | Flower/Fruit | Identified Species Name |
|---|---|---|---|---|
| D1 | Compound, Alternate | Dark, deeply fissured | Yellow, spherical | Neem (Azadirachta indica) |
| D2 | Simple, Opposite | Grey, smooth | Red, trumpet-shaped | Desert Teak (Tecomella undulata) |
| D3 | Heart-shaped, Alternate | Light grey, flaky | Large, dry pods | Siris (Albizia lebbeck) |
| D4 | Needle-like, Clustered | Reddish, peeling | -- | Sheesham (Dalbergia sissoo) |
| D5 | Simple, Alternate | Dark, rough | Small, berry-like | Peepal (Ficus religiosa) |
Table 2: Comparative Floral Diversity Data (Source: IBIS)
| Parameter | Delhi (UT) | Kerala (State) | Himachal Pradesh (State) |
|---|---|---|---|
| Total Flowering Plant Species | ~1,000 | ~5,000 | ~3,500 |
| Climate Type | Semi-Arid | Tropical | Temperate Alpine |
| Dominant Forest Type | Thorn Forest | Tropical Evergreen | Montane Forests |
| 5 Characteristic Species | 1. Neem 2. Peepal 3. Jamun 4. Babool 5. Gulmohar | 1. Coconut Palm 2. Jackfruit 3. Black Pepper 4. Rubber Tree 5. Indian Laurel | 1. Deodar Cedar 2. Rhododendron 3. Oak 4. Blue Pine 5. Himalayan Spruce |
Result:
Identification: Five common tree species in Delhi were successfully identified using morphological characteristics and a dichotomous key. These species (Neem, Peepal, Sheesham) are characteristic of the semi-arid northern plains.
Comparison: The comparative analysis of open-source data reveals a stark contrast in floral diversity:
Kerala exhibits significantly higher species richness (~5,000 species) due to its tropical climate and location in the biodiversity hotspot of the Western Ghats.
Delhi has lower species richness (~1,000 species), dominated by hardy, drought-resistant species adapted to its semi-arid climate.
Himachal Pradesh has unique temperate species adapted to cooler mountainous conditions.
Discussion:
Climate as a Driver: The results clearly demonstrate that climate is a primary driver of floral diversity. High temperature and rainfall in Kerala support lush growth and high speciation, while the drier climate of Delhi supports a smaller subset of adapted species.
Adaptations: Species in Delhi show xerophytic adaptations (e.g., deep roots, small leaves) to conserve water, while species in Kerala often have broad leaves to maximize photosynthesis in a high-light environment.
Importance of Native Species: The identification of native species (e.g., Neem, Peepal) is crucial for urban planning. Planting native, drought-resistant species is key to sustainable greening efforts in Delhi.
Limitations: Field identification can be challenging without flowers/fruits. Reliance on secondary data from online portals has its own biases based on sampling effort.
Conclusion:
This practical successfully demonstrated two key skills:
The field identification of tree species using morphological characteristics.
The use of open-source data to analyze and compare macro-scale patterns of floral diversity across different biogeographic zones of India.
The study confirms that the floral diversity of a region is a direct reflection of its climatic and geographical conditions. Conserving this diverse regional flora is essential for maintaining India's rich natural heritage.
Viva Voce Questions:
What is a dichotomous key?
It is a tool that allows the user to identify an organism by making a series of choices between two contrasting morphological characteristics.
Name two xerophytic adaptations seen in Delhi's trees.
Deep tap roots (e.g., in Babool) to access groundwater, and small or compound leaves (e.g., in Neem) to reduce water loss.
Why does Kerala have higher floral diversity than Delhi?
Due to its tropical climate, high rainfall, and proximity to the Western Ghats—a globally recognized biodiversity hotspot with high endemicity.
What is the national tree of India? Is it found in Delhi?
The Banyan Tree (Ficus benghalensis). Yes, it is commonly found in Delhi.
What is the significance of the Peepal tree (Ficus religiosa) in the urban ecosystem?
It provides dense shade, helps in lowering ambient temperature, supports bird and insect life, and is a pollution-tolerant species, making it valuable for urban areas.
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