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 70Â ft (21.36Â m) | 2 (Maximum) | ||
Canopy structure | Sparse, irregular, globular | 0 | |
Spreading crown, open, semi dense | 1 | ||
Spreading dense | 2 (Maximum) | ||
Laminar structure | Â | ||
 (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) | ||