230 This is an attractive ornamental tree when in bloom, with its crown covered with yellow flowers. Samanea saman is an ex- otic large deciduous tree with a wide-spreading crown grow- ing to a height of 25 m. These characteristics make this species an excellent shade tree. This species was brought to Singapore in 1876 from where it spread throughout Peninsular Malaysia. The current study found that about 76.21% of the street trees belong to the Leguminoseae family (Figure 3). This indicates that trees from this family were more hardy and resilient to harsh roadside environment and may also be attributed to the ability of fixing nitrogen. This is followed by Bignoniaceae, which is solely contributed from the species Tabebuai pallida. This species has been planted widely in the city in because it is an attractive and fast growing tree with a spectacular display of flowers after a dry spell. The tree is suitable to provide shade and color along streets. Sreetheran et al.: Street Tree Inventory and Tree Risk Assessment Table 3. Tree species diversity at five major roads in Kuala Lumpur. Species Mangifera caesia Pithecellobium dulce Cratoxylum formosum Artocarpus heterophyllus Fagraea fragrans Artocarpus altilis Lepisanthes rubiginosa Cinnamomum iners Psidium guajava Lagerstroemia speciosa Mangifera indica Plumeria spp. Garcinia atroviridis Delonix regia Casuarina junghuhniana Gliricidia sepium Roystonea regia Morinda citrifolia Casuarina equisetifolia Polyalthia longifolia var. pendula Terminalia catappa Adenanthera pavonina Syzygium campanulatum Elaeis guineensis Mimusops elengi Ficus benjamina Bauhinia spp. Acacia holosericea Calophyllum inophyllum Adonia merrillii Hopea odorata Tabebuia pallida Samanea saman Pelthophorum pterocarpum Pterocarpus indicus Total (Nj) 1 1 1 1 1 1 2 2 2 2 3 3 5 5 5 6 6 7 7 7 9 9 14 19 26 28 28 46 62 88 92 156 414 452 780 2,291 SDI = 5.01 Figure 3. Species composition of street trees graphed by family. Species Diversity Index The analysis of the Species Diversity Index for the street trees in Kuala Lumpur has shown that the SDI was moderately low (SDI = 5.0) when compared to the SDIs for other cities around the world calculated by Sun (1992). Since the SDI is a good indicator for diversity level In comparison with other tropical Asian cities, species diversity is poor. However, the frequencies of the occur- rence of these species are shown in Table 3. Bassuk (1988) pro- posed a 5% criterion for urban street tree planting. She found that many underused tree species could adapt well to the urban envi- ronment and suggested that any species in a street tree population should not be more than 5%. An equivalent SDI to this criterion is 20. To raise the SDI from the current level to 20, the diver- sity of many street tree populations must be more than doubled. The dominance by few species is quite common in urban street tree population both in tropical and temperate cities (Valentine et al. 1978; Jim 1986; Jaenson et al. 1992; Chacalo et al. 1994; Adnan 1995). Miller (1988) and Jaenson et al. (1992) also found the over- planting or the exclusive planting of a single species (Trowbridge and Bassuk 2004). A classic example is from the epidemic of ©2011 International Society of Arboriculture Dutch elm disease in cities of the United States (Grey and Deneke 1986; Philips 1993). Overplanting of a species could also lead to maintenance problems such as weak wood, the tendency to devel- op chlorosis, girdling roots, and messy fruits, but they are manage- able only when planted in moderation (Trowbridge and Bassuk 2004). However, urban environments are particularly stressful and cause low diversity of street trees due to a low survival rate of new- ly planted trees and short life-span for many tree species (Sanders 1981; Richards 1983). Therefore, the SDI for Kuala Lumpur could be enhanced by selecting underused species as proposed by Tho et al. (1985) besides being based on both biological/genetic diver- sity and special characteristic of planting sites. In addition, spe- cies composition can also be influenced by encouraging the plant- ing of certain species through campaigns organized by DBKL. Tree Structure Due to the absence of the information on age or planting date, the surveyed trees were categorized into four main groups, namely newly planted, young, mature, and removed. Figure 4 indicates that there were uneven distributions of the tree status on the five roads surveyed. Overall, mature trees (96%) dominated the road- side. Most of these mature trees were P. indicus, S. saman, and P. pterocarpum. The distribution of trees by DBH classes (Fig- ure 5) shows that majority of the trees are between the young Nj-1 0 0 0 0 0 0 1 1 1 1 2 2 4 4 4 5 5 6 6 6 8 8 13 18 25 27 27 45 61 87 91 155 413 451 779 Nj(Nj-1) 0 0 0 0 0 0 2 2 2 2 6 6 20 20 20 30 30 42 42 42 72 72 182 342 650 756 756 2,070 3,782 7,656 8,372 24,180 170,982 203,852 607,620 2,256 1,031,610
September 2011
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