An overview of the basic concepts and principles of tree biology, including tree structure, growth patterns, and physiological processes.
Introduction to Tree Biology – Study Notes
| Aspect | Description |
|---|---|
| Definition | A perennial woody plant with a single main stem (the trunk) that supports a crown of branches and leaves. |
| Key Features | • Height ≥ 3 m (most definitions) • Secondary growth (wood formation) • Long‑lived (decades to millennia) |
| Ecological Role | • Primary producers (photosynthesis) • Habitat & food for wildlife • Soil stabilizers & carbon sinks |
| Part | Function | Main Tissues |
|---|---|---|
| Root System | Anchors tree, absorbs water & nutrients | Taproot ↔ Lateral roots; root hairs |
| Trunk (Stem) | Supports crown, conducts water & sugars | Xylem (water), Phloem (photosynthates), Cambium (growth) |
| Branches | Extend photosynthetic surface, bear reproductive structures | Same tissue organization as trunk, but smaller diameter |
| Leaves | Photosynthesis, transpiration, gas exchange | Epidermis, Mesophyll (palisade & spongy), Stomata |
| Reproductive Organs | Produce seeds & spores | Flowers, cones, fruits, seeds (species‑specific) |
| Process | Description | Key Hormones/Factors |
|---|---|---|
| Primary Growth | Lengthening of shoots & roots via apical meristems | Auxin, cytokinin |
| Secondary Growth | Increase in girth (wood formation) via vascular cambium | Auxin (maintains cambium activity) |
| Dormancy | Seasonal pause in growth (often winter) | Abscisic acid, low temperature, photoperiod |
| Phenology | Timing of life‑cycle events (bud burst, leaf fall) | Day length, temperature cues |
| System | Direction | Main Pathway | Driving Forces |
|---|---|---|---|
| Xylem | Roots → Leaves | Vessels & tracheids (water, minerals) | • Root pressure • Cohesion‑tension (transpiration pull) |
| Phloem | Leaves ↔ Roots & other sinks | Sieve‑tube elements (photosynthates) | Pressure‑flow hypothesis – osmotic loading/unloading creates a bulk flow |
Factors influencing rate
| Stage | Description | Typical Structures |
|---|---|---|
| Flowering / Cone Production | Sexual organs develop (spring‑summer) | Flowers (angiosperms) or cones (gymnosperms) |
| Pollination | Transfer of pollen to stigma (wind, insects, birds) | Pollen grains |