Unit 1: Diversity, Distribution and Growth Behaviour

1. Global Distribution of Bamboos

Bamboos are a subfamily of grasses (Poaceae). They are found on every continent except Europe and Antarctica. They grow in a wide range of climates, from cold mountains to hot tropical regions.

Major Regions: The highest diversity of bamboo is found in the Asia-Pacific region, followed by South America.
Asia: Countries like China, India, Japan, and Indonesia have a vast diversity and long history of bamboo use.
South America: Home to large tracts of bamboo forests, especially in Brazil and Colombia.
Africa: Has native bamboo species, though less diverse than Asia or South America.
North America: Has a few native species, such as the "river cane" (Arundinaria).

2. Distribution of Bamboos in Northeast India

Northeast India is recognized as one of the largest centers of bamboo diversity in the world. It is often called the "Bamboo Capital" of India.

Significance: The region accounts for over 50% of India's total bamboo resources.
States: Bamboo is an integral part of the culture, economy, and landscape in all the "Seven Sisters" states (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura) and Sikkim.
Rich Diversity: The region's unique topography and climate (ranging from tropical lowlands to alpine hills) support a vast number of bamboo species.
Common Genera: Important and common genera found here include Bambusa, Dendrocalamus, Melocanna, and Chimonobambusa.
Example: Melocanna baccifera ("Muli" bamboo) is famous for its gregarious flowering and its dominant presence in states like Mizoram.

3. Rhizome Types

The rhizome is the underground stem system of the bamboo. It is the "brain" of the plant, storing food and determining its growth pattern. The type of rhizome determines whether the bamboo is a "clumper" or a "runner."

Crucial Exam Topic: You must be able to differentiate the rhizome types. This is also a practical topic.

Diagram: A side-by-side comparison.
Left (Sympodial): Shows a "U" shaped rhizome with a bud at the end turning upwards to form a culm, and another bud at the side forming the next rhizome. All culms are close together in a "clump."
Right (Monopodial): Shows a long, horizontal, spear-like rhizome running underground, with individual culms popping up at intervals, far apart.

Feature	Sympodial (Clumping)	Monopodial (Running)	Amphipodial
Growth Habit	Grows in dense, discrete clumps. "Clumpers."	Spreads rapidly and invasively. "Runners."	A combination, with both running and clumping characteristics. (Less common).
Rhizome Shape	Short, thick, U-shaped. Grows upwards to form a culm.	Long, thin, horizontal. Grows parallel to the ground.	Shows both types of development.
Culm Position	New culms emerge close to the parent clump.	New culms emerge from nodes along the running rhizome, often far apart.	Variable.
Climate	Typically found in tropical and subtropical regions.	Typically found in temperate regions.	Found in both.
Example Genera	Bambusa, Dendrocalamus	Phyllostachys, Sasa	Chimonobambusa

4. Clump Expansion and Culm Growth

Clump Expansion

This applies to sympodial (clumping) bamboos. The clump expands outward as new rhizomes are produced from the buds of existing rhizomes. The pattern of expansion can be:

Pachymorph: The rhizomes are short and thick, resulting in a very dense, tight clump (e.g., Bambusa vulgaris).
Leptomorph: While still clumping, the rhizomes have slightly longer "necks," leading to a more open, scattered clump (e.g., Melocanna).

Culm Growth

The growth of a bamboo culm (the above-ground stalk) is one of the most remarkable events in the plant kingdom.

Rapid Growth: New bamboo shoots emerge from the ground (from rhizome buds) and grow to their full height in a single growing season (typically 2-4 months).
No Secondary Growth: Once the culm reaches its full height, it never grows taller or thicker in the following years. It only adds branches and leaves.
Telescopic Growth: The culm grows by elongating its pre-formed sections (internodes), like extending a telescope. The elongation starts from the bottom internodes and proceeds upwards.
Speed: Some species have been recorded to grow over 90 cm (3 feet) in a single 24-hour period.

5. Culm Sheath

The culm sheath is the protective, leaf-like covering found on a new, growing bamboo culm. It is a vital and temporary organ.

Functions:

Protection: It protects the tender, growing tip (apical meristem) and the soft internodes from insects, animals, and mechanical damage.
Support: It provides structural support to the soft, rapidly elongating culm.
Photosynthesis: In some species, the sheaths are green and can perform photosynthesis.

Identification:

Culm sheaths fall off as the culm matures, but they are a primary tool for bamboo species identification. Taxonomists look at the sheath's size, shape, color, hairs, and the shape of its parts (like the auricle and ligule).

Diagram: A detailed drawing of a flattened bamboo culm sheath, labeling its key parts: Sheath proper (main body), Blade (the leaf-like tip), Auricles (ear-like appendages at the base of the blade), and Ligule (a small flap at the junction of the sheath and blade).

6. Culm Structure

The bamboo culm is what is harvested and used.

Node: The solid, jointed part of the culm where the culm sheaths, branches, and leaves emerge. This is a solid, woody diaphragm.
Internode: The hollow, cylindrical section of the culm *between* the nodes.
Wall: The woody wall of the internode. Its thickness is a key property for utilization.
Vascular Bundles: The "veins" of the bamboo, composed of fibers and vessels, run vertically through the culm wall. They are more densely packed near the outer wall, making the outside of the culm the strongest and densest part.

7. Gregarious and Sporadic Flowering

Bamboo flowering is a mysterious and often dramatic event. Unlike most plants, many bamboo species flower at very long, fixed intervals and then die.

Gregarious Flowering ("Masting")

What it is: A phenomenon where all individuals of a single bamboo species in a large geographical region flower at the exact same time.
Interval: This is a genetically pre-set cycle, which can be as long as 40, 60, or even 120 years.
Consequence: After flowering and setting seed, the entire bamboo population dies off.
Ecological Impact: This event (called "Mautam" or "Bautam" in Northeast India, especially for Melocanna baccifera) produces a massive amount of seed (fruit). This leads to a sudden explosion in the rat population, which, after eating all the seeds, moves on to devastate agricultural crops, causing widespread famine.

Sporadic Flowering

What it is: The flowering of individual bamboo clumps or a few clumps in a small area.
Timing: It does not follow a predictable mass cycle. It may be triggered by environmental stress (like drought or cutting).
Consequence: The individual clump may or may not die after flowering. It does not cause the widespread ecological problems of gregarious flowering.