Air pollution tolerance index and anticipated performance index of ...

Urban Forestry & Urban Greening 14 (2015) 866–871

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Air pollution tolerance index and anticipated performance index of some plant species for development of urban forest Ashutosh Kumar Pandey a , Mayank Pandey a , Ashutosh Mishra a , Ssiddhant Mohan Tiwary b , B.D. Tripathi b,∗ a b

Institute of Environment & Sustainable Development, Banaras Hindu University, Varanasi 221005, India Department of Botany, Banaras Hindu University, Varanasi 221005, India

a r t i c l e

i n f o

Article history: Received 2 January 2015 Received in revised form 31 July 2015 Accepted 1 August 2015 Keywords: Air pollution Greenbelt Green ways Peri-urban green space Urban forest Urban heat island

a b s t r a c t Urban forest is a collection of trees growing in urban area. Green plants are well known for their abilities to reduce air and noise pollution. It is important that plants used for the development of urban forest must be tolerant to air pollutants. There must be some criteria to select tolerant plants for urban forest and for that two indices viz. air pollution tolerance index (APTI) and anticipated performance index (API) can be a good tool. In the present study, 29 plant species commonly found in urban area of Varanasi, India, has been evaluated for their APTI and API. Based on these two indices, the most suitable plant species were identified and recommended for development of urban forest in Varanasi for long-term air pollution abatement. It was revealed that Ficus benghalensis L. and Ficus religiosa would be excellent performers. Similarly Polyalthia longifolia, Ficus glomerata (Roxb.), Anthocephalus indicus and Mangifera indica were estimated to be very good performers. In the similar fashion Cassia fistula L., Drypetes roxburghii, Terminalia arjuna, Psidium guajava L., Millingtonia hortensis and Dalbergia sissoo were estimated to be good performers with respect to anticipated performance index. © 2015 Elsevier GmbH. All rights reserved.

1. Introduction Enhanced intensity of air pollution in the cities has become a worldwide issue. Increasing pace of urbanization has resulted in loss of vegetation cover. Tall buildings and narrow roads in urban areas form street canyon like conditions. It hinders dispersal of air pollutants in cities (Wong et al., 2010). During the past few decades, urban areas have experienced increasing environmental stress, especially in the form of poor air quality, excessive noise and traffic congestion (Sanesi and Chiarello, 2006). Climate change impact has also added more stress. Road traffic is considered as one of the most important sources of air and noise pollution with adverse effects on human health. Urban air often contains high levels of pollutants that are harmful to human health and well being (Kanakidou et al., 2011). The main cause of increase in the level of air pollution is increasing population, urbanization and industrialization. Green plants play an important role in air pollution attenuation (Cavanagh et al., 2009) thus, they can be utilized

∗ Corresponding author. E-mail addresses: [email protected] (A.K. Pandey), [email protected] (M. Pandey), [email protected] (A. Mishra), [email protected] (S.M. Tiwary), [email protected] (B.D. Tripathi). http://dx.doi.org/10.1016/j.ufug.2015.08.001 1618-8667/© 2015 Elsevier GmbH. All rights reserved.

for the same. The ever increasing pace of urbanization is replacing huge quantities of vegetation with concrete buildings and low albedo surfaces (Singh and Grover, 2015). This has become a big issue in densely populated cities of developing nations like India. These resulting changes in the thermal properties of surface materials and the lack of proper evapotranspiration in urban areas may lead to the urban heat island (UHI) effect (Wong et al., 2010). It is thus essential that greenery should be reintroduced in such urban areas. This aim can be achieved by collaboration of nature and city. An urban forest is a collection of trees that grow within a city, town or a suburb. It includes woody plants growing in and around human settlements. Urban forests not only help in attenuation of air pollution but also in noise pollution reduction, controlling soil erosion and enhancing the aesthetic beauty of the area (Yang et al., 2005). Urban forests can be developed around rivers banks, roads and railways, parks, gardens, playgrounds, cemeteries, roadside, etc. Some plants are comparatively more tolerant to air pollutants. An index to identify the tolerance of air pollutants was developed which is known as air pollution tolerance index (APTI). It is mainly based on four major properties of leaves namely ascorbic acid content, relative water content, total chlorophyll content and leaf extract pH (Singh and Rao, 1983). Plant’s tolerance to air pollutants generally varies with these parameters.

A.K. Pandey et al. / Urban Forestry & Urban Greening 14 (2015) 866–871

The urban area of the Varanasi is expanding and the sub-urban areas are also facing loss of green spaces due to urban sprawl. This has resulted in dense settlements in the core areas of the city. These areas are subjected to dense exacerbated urban settlement patterns with little green space (Kumar et al., 2010). Increasing vehicular population and decreasing green space has created an imbalance in the air quality and thus it is necessary to develop urban forest in and around this concrete jungle to reduce the loss of natural vegetation in the process of urbanization. Previous workers have done extensive work on various selection criteria for plants to be used in urban forestry (Ng et al., 2015; Sæbø et al., 2003; Sjöman and Busse Nielsen, 2010). APTI of various tree species in Varanasi was evaluated by previous researchers (Prajapati and Tripathi, 2008; Singh et al., 1991). Anticipated performance index based on APTI for green belt development was also analyzed for noise pollution reduction and air pollution attenuation (Pathak et al., 2011; Prajapati and Tripathi, 2008; Rai et al., 2014). Mitigation of air pollutants with the high vegetation cover is the economic solution for air pollution. However, lack of knowledge pertaining to the suitable plant species for the development of urban forest is the major hurdle. Henceforth, present study deals with the use of two indices to select most tolerant and best suited plants for development of urban forest. This study however, done on pilot scale but similar studies can be performed in any part of the world for selecting best plants for air pollution mitigation in urban areas. Aim of the present study was to evaluate APTI and API of selected plant species and to recommend tolerant plants for the development of urban forest. 2. Materials and methods 2.1. Study sites This study was performed during period of July 2013–June 2014 in Varanasi, India. The city of Varanasi (82◦ 15 E–83◦ 30 E and 24◦ 35 N–25◦ 30 N, area 79.79 km2 , India) is said to be the oldest living city in the world and regarded as religious and cultural capital of India. Varanasi is a densely populated city having a population density of 2399 inhabitants per square kilometre (Census of India, 2011). Varanasi city is comprised congested residential colonies, commercial areas and traffic intersections. These areas are not well defined and thus overlap with each other. This city is known for its tall buildings and narrow lanes and thus street canyon like features are common in the urban areas (Prajapati et al., 2009). This results in limited air circulations, thereby, acting as a hindrance to the dispersal of pollution load.

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digital pH metre. Finally APTI was calculated by following mathematical expression (Singh and Rao, 1983). APTI =

[A(T + P) + R] 10

(1)

where A is the ascorbic acid content in mg g−1 of fresh weight; T is the total chlorophyll in mg g−1 of fresh weight; P is the pH of leaf extract and R is the relative content of water in percentage. 2.3. Anticipated performance index (API) API is based on various factors influencing the performance of a certain species of plant. Most suitable plants species for development of urban forest can be determined by obtaining their API values. Higher is the API, higher will be the performance of the species in the urban forest. API (Table 5) is calculated by evaluating various socioeconomic, biochemical, and biological characteristics of the plant such as APTI, canopy structure, plant habit and economic value, and then API score is given to each species according to the criteria described in Table 2. 3. Results and discussion Green trees act as sink and living filters to minimize air pollution by various processes like absorption, adsorption, accumulation detoxification, etc. without undergoing any serious foliar damage (Garbisu et al., 2002; Jim and Chen, 2008). They also improve the air quality by releasing oxygen into the atmosphere (Beckett et al., 1998; Hill, 1971). Particulate and gaseous pollutants are generally removed by the phenomena of dry deposition and wet deposition. In dry deposition, pollutants are absorbed or adsorbed on plant surfaces (McPherson et al., 1998; Moreira et al., 2010; Smith, 1981). SO2 could be absorbed into plant tissues through the stomata and react with water on inner-leaf cell walls to form sulphurous and sulphuric acids (Legge and Krupa, 2002). Similarly NO2 also forms nitrous and nitric acids. These acids further react with other compounds and ultimately transported to different parts of the plant (Nowak, 1994). 3.1. Assessment of ambient air quality The monitoring of ambient air quality revealed that NO2 and PM10 concentrations exceeded the standard annual mean prescribed by Central Pollution Control Board, India (CPCB, 2009) (recorded concentrations of SO2 , NO2 , and PM10 in the year 2013 the city were 35.83, 43.70 and 141.29 ␮g m−3 respectively).

2.2. Air pollution tolerance index (APTI)

3.2. Air pollution tolerance index (APTI)

Twenty-nine commonly found plant species were identified and selected for assessment of APTI. Sampling was done thrice a year i.e. in winter (November–February), summer (March–June) and rainy (July–October) seasons. At least three mature individual plants were identified and samples in triplicate were taken from each plant. Seasonal mean values of all parameters were used to calculate final APTI. Sampling was done in morning hours between 07:00 am and 9:00 am. Proper care was taken to ensure that all plant species tend to have the comparable ecological conditions with respect to soil, water, light and exposure to the pollutants. For evaluating the APTI, four parameters viz. chlorophylls ‘a’ and ‘b’ content (Bell and Mudd, 1976), ascorbic acid content of leaf samples (Keller and Schwager, 1977), and relative water content (Sen and Bhandari, 1978) and leaf extract pH were determined. To calculate leaf extract pH, 0.5 g of leaf sample was crushed and homogenized in 50 ml de-ionized water, then the mixture was centrifuged and supernatant was collected for detection of pH by a

The results of the present investigation revealed that the APTI values of 29 selected plant species ranged from 11.01 to 26.01 (Table 1). Highest value was recorded for Ficus benghalensis (26.01) followed by Cassia fistula (24.52), Ficus religiosa (23.35), Polyalthia longifolia (22.88), Drypetes roxburghii (22.88) and Zizyphus jujuba (22.11) while lowest APTI was recorded for Madhuca indica (11.01). APTI can also be used alone as a criterion to select air pollution tolerant plants (Singh et al., 1991). However, API will add more value to the selection criteria and thus it is recommended to use both of these indices together. Some previous researchers have also used some other properties of plants such as their potential to act as nat˜ ural carbon sinks (Munoz-Vallés et al., 2013), their role in carbon sequestration (Liu and Li, 2012) and their dust capturing potential. Among four parameters of APTI, ascorbic acid content (in mg g−1 fresh wt) was found to be highest in F. benghalensis (10.54 ± 0.25). Ascorbic acid is an antioxidant and thus it influences the resistance to air pollution in plants (Agbaire and Esiefarienrhe, 2009; Keller

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Table 1 APTI of plants commonly found at study site. S.no.

Plant species

A

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Ficus benghalensis Cassia fistula L. Ficus religiosa Polyalthia longifolia Drypetes roxburghii Zizyphus jujuba Lamk. Delonix regia Terminalia arjuna Psidium guajava L. Albizia lebbeck Linn. Kigelia pinnata Ficus glomerata (Roxb.) Millingtonia hortensis Anthocephalus indicus Mangifera indica Dalbergia sissoo Nerium indicum Azadirachta indica Juss Artocarpus heterophyllus Bauhinia purpurea Alstonia scholaris Tectona grandis Bauhinia variegata Holoptelea integrifolia Cassia siamea Terminalia bellirica Murraya peniculata Syzygium cumini Madhuca indica

10.54 10.25 9.45 9.21 9.21 9.4 8.65 8.54 8.25 9.54 7.32 8.25 7.52 7.56 6.35 6.84 6.54 7.35 6.54 6.21 5.05 4.34 5.11 5.21 4.21 4.51 7.44 3.12 4.24

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.25 1.24 0.85 0.71 0.78 0.82 0.18 0.47 0.48 0.14 0.45 0.85 0.54 0.36 0.47 0.14 0.85 0.58 0.47 0.88 0.61 0.74 0.48 0.65 0.45 0.44 0.99 0.48 0.65

P

T

7.24 7.01 6.15 6.14 7.01 6.25 6.21 7.14 5.56 6.54 7.89 6.83 6.54 7.14 6.87 5.64 5.87 6.87 5.79 5.78 6.87 6.87 5.65 5.24 5.75 5.12 6.32 5.36 5.10

9.75 9.18 10.53 10.65 8.83 8.45 8.65 9.12 9.54 8.21 8.56 6.99 7.32 5.47 7.38 7.67 4.65 3.54 5.87 4.54 6.54 7.12 4.12 5.17 3.54 3.17 5.36 5.85 1.89

APTI*

R ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.85 0.81 1.05 0.41 0.84 0.79 0.68 0.58 0.91 0.54 0.85 0.18 0.47 0.49 0.88 0.75 0.71 0.73 0.48 0.73 0.49 0.58 0.68 0.67 0.82 0.14 0.74 0.49 0.08

81 79.21 75.83 74.21 75.21 75.21 77.25 66.54 79.25 59.25 78.25 78.21 72.14 78.25 78.38 68.5 82.1 74.31 69.23 76.12 71.32 72.21 71.21 63 77.21 78.64 24.76 75.89 80.5

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

3.89 2.12 1.77 1.32 1.71 1.14 2.17 1.11 1.32 0.95 1.57 1.65 1.54 1.14 1.13 0.85 1.15 2.74 1.77 2.18 1.86 1.48 1.76 1.05 1.54 1.75 1.71 1.77 3.12

26.01 24.52 23.35 22.88 22.11 21.37 20.58 20.54 20.38 20.00 19.87 19.22 17.64 17.36 16.89 15.95 15.09 15.08 14.55 14.02 13.90 13.29 12.11 11.72 11.63 11.60 11.17 11.09 11.01

A, ascorbic acid content; P, leaf extract pH; T, total chlorophyll content; R, relative water content.

and Schwager, 1977; Pathak et al., 2011). An increased level of ascorbic acid in leaves is known to increase air pollution tolerance in plants (Chaudhary and Rao, 1977; Mittler, 2002). The production of reactive oxygen species (ROS) in the chloroplast under water stress decreases the chlorophyll content in the leaves (Apel and Hirt, 2004). The presence of higher ascorbic acid content in leaves might be a strategy to protect thylakoid membranes from oxidative Table 2 Gradation of plant species based on air pollution tolerance index (APTI) as well as biological parameters and socioeconomic importance. Grading character (a) Tolerance APTI

Pattern of assessment

Gradea allotted

11.0–14.0 14.1–17.0 17.1–20.0 20.1–23.0 23.1–26.0

+ ++ +++ ++++ +++++

(b) Biological and socioeconomic Small Plant habit Medium Large Sparse/irregular/globular Canopy structure Spreading crown/open/semi-dense Spreading dense Deciduous Type of plant Evergreen

− + ++ − + ++ − +

(c) Laminar structure Small Size Medium Large Texture Smooth Curvaceous Delineate Hardiness Hardy Less than three uses Economic value Three or four uses Five or more uses

− + ++ − + − + − + ++

a

Maximum grades that can be scored by a plant = 16.

damage under such water stress conditions (Tambussi et al., 2000). This may be due to the fact that ascorbic acid is involved in the defence against ROS produced by the photosynthetic apparatus (He and Häder, 2002). Similar findings on ascorbic acid content of leaves have been reported by previous researchers in different regions of world (Kaur and Nayyar, 2014; Krishnaveni, 2013; Mächler et al., 1995). Similarly, higher chlorophyll content might favour tolerance to air pollutants in plants (Prajapati and Tripathi, 2008; Rai and Panda, 2014; Shannigrahi et al., 2003). Its highest value (in mg g−1 ) was found in P. longifolia (10.65 ± 0.41). Similarly, it has been reported that higher leaf extract pH in plants, especially in polluted conditions may tend to increase their tolerance level to acidic air pollutants (Agbaire and Esiefarienrhe, 2009; Singh et al., 1991). Relative water content (in percentage) was found highest in Nerium indicum (82.1 ± 1.15) followed by F. benghalensis (81 ± 3.89). Relative water content of leaf is associated with protoplasmic permeability, thus plants with its higher values are probably more tolerant to air pollutants (Singh et al., 1991). High relative water content within plant leaf helps to maintain its physiological balance under stress conditions such as exposure to air pollution when the transpiration rates usually remain high. It also serves as an indicator of drought resistance in plants (Chaves et al., 2003; Ritchie et al., 1990). 3.3. Anticipated performance index The grading pattern (Table 3) of 29 plant species evaluated (Table 4) and plant species which fit into the grading pattern with respect to their anticipated performance index (API) were recommended (Table 5) for the development of urban forest in Varanasi city. F. benghalensis L. and F. religiosa are expected to be excellent performers. Comparable results were reported by previous workers also (Pathak et al., 2011; Prajapati and Tripathi, 2008; Rai and Panda, 2014). On the other hand, P. longifolia, Ficus glomerata (Roxb.), Anthocephalus indicus and Mangifera indica are predicted to be very good performers. In the same manner C. fistula L., D.

A.K. Pandey et al. / Urban Forestry & Urban Greening 14 (2015) 866–871 Table 3 Anticipated performance index (API) of plant species.

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Table 5 Assessment based on anticipated performance index of different tree species.

Grade

Score (%)

Assessment category

0 1 2 3 4 5 6 7

Up to 30 31–40 41–50 51–60 61–70 71–80 81–90 91–100

Not recommended Very poor Poor Moderate Good Very good Excellent Best

Plant species

Grade

Ficus benghalensis L. Ficus religiosa Polyalthia longifolia Ficus glomerata (Roxb.) Anthocephalus indicus Mangifera indica Cassia fistula L. Drypetes roxburghii Terminalia arjuna Psidium guajava L. Millingtonia hortensis Dalbergia sissoo Artocarpus heterophyllus Alstonia scholaris Delonix regia Kigelia pinnata Azadirachta indica Juss Terminalia bellirica Murraya peniculata Syzygium cumini Zizyphus jujuba Lamk. Albizia lebbeck Linn. Nerium indicum Bauhinia purpurea Holoptelea integrifolia Cassia siamea Madhuca indica Tectona grandis Bauhinia variegata

roxburghii, Terminalia arjuna, Psidium guajava L., Millingtonia hortensis and Dalbergia sissoo are likely to be good performers. Six plant species were recognized as moderate performers while seven plant species as poor performers. The remaining two plant species either were very poor performers or not recommended for plantation. Many other researchers estimated the APTI and API of various plant species for green belt development and found similar results (Govindaraju et al., 2012; Shannigrahi et al., 2003; Thambavani and Maheswari, 2012). Tolerance of plant towards air pollutants is specific to a site and depends on the type and level of pollution (Noor et al., 2014). The significance of micro-morphological leaf surface characters of various species of plants in indication and mitigation of auto-exhaust air pollution was performed by Pal et al. (2002) in Kolkata, India. In this study it was revealed that changes in morphology of leaf surface was significant; however, the phenology of these plants remained unchanged by auto-exhaust pollution and thus these plants can be grown along road sides for development of urban forest. Performance evaluation studies have revealed that green belts are effective measure for mitigation of ambient air pollution (Rao et al., 2004). Many previous workers have demonstrated that urban forests play an important role in mitigation of air pollution (Cavanagh et al., 2009; Islam et al., 2012; Vailshery et al., 2013; Yang et al., 2005). APTI and API is

Total+

%

14 14 12 12 12 12 10 11 11 11 11 11 10 10 9 9 9 9 9 9 8 7 8 7 8 8 8 6 6

87.5 87.5 75 75 75 75 62.5 68.8 68.8 68.8 68.8 68.8 62.5 62.5 56.3 56.3 56.3 56.3 56.3 56.3 50 43.8 50 43.8 50 50 50 37.5 37.5

API value

Assessment

6 6 5 5 5 5 4 4 4 4 4 4 4 4 3 3 3 3 3 3 2 2 2 2 2 2 2 1 1

Excellent Excellent Very good Very good Very good Very good Good Good Good Good Good Good Good Good Moderate Moderate Moderate Moderate Moderate Moderate Poor Poor Poor Poor Poor Poor Poor Not recommended Not recommended

important combination of measuring significance of green plants in air pollution mitigation (Govindaraju et al., 2012; Prajapati and Tripathi, 2008). Henceforth, plants falling under API category of excellent, very good, good and moderate performers can be recommended for the development of urban forest. Similar studies

Table 4 Evaluation of API of plant species based on their APTI values and some other biological and socio-economic characters. S.no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Name of the plant

Ficus benghalensis L. Cassia fistula L. Ficus religiosa Polyalthia longifolia Drypetes roxburghii Zizyphus jujuba Lamk. Delonix regia Terminalia arjuna Psidium guajava L. Albizia lebbeck Linn. Kigelia pinnata Ficus glomerata (Roxb.) Millingtonia hortensis Anthocephalus indicus Mangifera indica Dalbergia sissoo Nerium indicum Azadirachta indica Juss Artocarpus heterophyllus Bauhinia purpurea Alstonia scholaris Tectona grandis Bauhinia variegata Holoptelea integrifolia Cassia siamea Terminalia bellirica Murraya peniculata Syzygium cumini Madhuca indica

APTI

+++++ +++++ +++++ ++++ ++++ ++++ ++++ ++++ ++++ +++ +++ +++ +++ +++ ++ ++ ++ ++ ++ + + + + + + + + + +

Tree habit

++ + ++ ++ + + + ++ + + + ++ ++ ++ ++ ++ + ++ ++ + ++ + + ++ + ++ + ++ ++

Canopy structure

+ + + ++ + + + ++ + + + + + + ++ ++ + + ++ + ++ − + + + ++ ++ ++ ++

Type of tree

+ − + + + − + − + − − + + + + + + + + − + − − − + − + + −

Laminar

Size

Texture

++ + ++ + + − + + + + + ++ + ++ + + + − + + + + + + + + + + +

+ − + + + + − − + − + + + + + + − − − + + + + + + − + − −

Economic Importance

Hardiness

Grade allotted

Total plus (+) + + + + + + + + + + + + + + ++ + + ++ + + + + − + + ++ + + +

+ + + − + − − + + − + + + + + + + + + + + + + + + + + + +

14 10 14 12 11 8 9 11 11 7 9 12 11 12 12 11 8 9 10 7 10 6 6 8 8 9 9 9 8

API grade

% scoring 87.5 62.5 87.5 75 68.75 50 56.25 68.75 68.75 43.75 56.25 75 68.75 75 75 68.75 50 56.25 62.5 43.75 62.5 37.5 37.5 50 50 56.25 56.25 56.25 50

6 4 6 5 4 2 3 4 4 2 3 5 4 5 5 4 2 3 4 2 4 1 1 2 2 3 3 3 2

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can also be performed in any part of the world with local flora to recommend air pollutant tolerant plants for development of urban forest. Many previous researchers have investigated various aspects of urban vegetation. One such study conducted in Bangalore, India revealed that older street trees with large canopy are being cut in the process of urbanization, this study also explained that older trees have a more diverse distribution with several large sized species, while young trees come from a less diverse species set, largely dominated by small statured species with narrow canopies, which have a lower capacity to absorb atmospheric pollutants, mitigate urban heat island effects, stabilize soil, prevent ground water runoff, and sequester carbon (Nagendra and Gopal, 2010). A survey conducted in Pakistan revealed that presence of various plants with medicinal properties in urban area may provide low cost health care to local communities (Kayani et al., 2014). Moreover, essential oils produced from some plants can be used as green pesticides (Ashraf et al., 2014). Similarly, sawdust produced from woods of some trees can be utilized as sorbent for the removal of pollutants form aqueous systems (Qureshi et al., 2015). Thus, APTI and API, along with other properties of plants can be used in the selection of best trees for urban forest. In a study conducted in Nagpur, India, it was revealed that presence of diversified vegetation cover in the city results in better air quality (Chaturvedi et al., 2013). Similar results were obtained in Chennai also (Muthulingam and Thangavel, 2012). Studies based on APTI and API has also been done by some of the previous workers in tropical and sub-tropical climatic zones such as India (Gupta et al., 2011; Pathak et al., 2011). However, proper investigations based on APTI and API has not been done vastly in other climatic zones of the world and very few studies are available from other countries such as Nigeria (Ogunkunle et al., 2015) and Iran (Esfahani et al., 2013). Thus it is recommended that these two indices should be applied to select best suited plants for plantation in urban forestry from the available flora of that particular locality. 4. Conclusion and implications Air pollution in urban areas of Varanasi can be mitigated by developing urban forest in the city by choosing air pollution tolerant plants. To fulfil this aim air pollution tolerance index (APTI) and anticipated performance index (API) of 29 commonly found plant species were estimated. APTI was found highest for F. benghalensis followed by C. fistula and Ficus relegiosa and lowest for M. indica. Further, API was estimated for the same set of plants to estimate their performance in an urban forest which is based on grading characters such as tolerance to air pollution along with other socioeconomic and biological characters of plants such as plant habit, canopy, size and economic value. Present study revealed that F. benghalensis L. and F. religiosa would be excellent performers in urban forest. Similarly P. longifolia, F. glomerata (Roxb.), A. indicus and M. indica were estimated to be very good performers in the marble industrial areas of Potwar region. In the similar fashion C. fistula L., D. roxburghii, T. arjuna, P. guajava L., M. hortensis and D. sissoo were estimated to be good performers in urban forest with respect to their API. This study is relevant as this experiment can be performed with locally available green vegetation in any part of the world to select best suited plants for development of urban forest. Acknowledgements The authors are thankful to Department of Botany and Institute of Environment and Sustainable Development, Banaras Hindu University for providing facilities for study and University Grants

Commission for providing financial assistance (R/Dev/IX Sch. BHU Res. Sch. 2010-11/22627).

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