Table 1 Tree species gradation based on air pollution tolerance index, morphological parameters and socio-economic importance
From: Roadside air pollution in a tropical city: physiological and biochemical response from trees
| Grading character | Parameters | Pattern of assessment | Grade allotment (point) |
|---|---|---|---|
| Tolerance | Air Pollution Tolerance Index | Less than 12 | 1 |
| Between 10 and 16 | 2 | ||
| Above 17 | 3 (Maximum) | ||
| Morphological | Type of tree | Deciduous, Semideciduous | 0 |
| Evergreen | 1 (Maximum) | ||
| Tree size (height) | Small: less than 30 ft (< 9.14 m) | 0 | |
| Medium: 30–70 ft (9.17–21.34 m) | 1 | ||
| Large: above 70 ft (21.36 m) | 2 (Maximum) | ||
| Canopy structure | Sparse, irregular, globular | 0 | |
| Spreading crown, open, semi dense | 1 | ||
| Spreading dense | 2 (Maximum) | ||
| Laminar structure | |||
| (a) Leaf size | Less than 225 mm2 | 1 | |
| 225–2025 mm2 | 2 | ||
| 2025–4500 mm2 | 3 | ||
| 4500–18,225 mm2 | 4 (Maximum) | ||
| (b) Texture | Smooth | 0 | |
| Rough, coriaceous, leathery | 1 (Maximum) | ||
| (c) Hardness | Soft, delicate, fragile | 0 | |
| Hardy, robust, sturdy | 1 (Maximum) | ||
| Socio-economic value | Food, fodder, timber, medicinal, raw material, erosion control, shade/shelter, ornamental, reclamation | Less than three uses | 0 |
| Three or more uses | 1 | ||
| Five or more uses | 2 (Maximum) | ||