228 size and form in bole and crown commonly associated with the mature form of the species. The status “removed” is noted for those trees which were removed due to tree structural defects, because they died, or for the purposes of land development. Tree condition was derived from a general observation from ground level from several directions in order to categorize the street trees as Good or Poor. Good trees referred to trees that were healthy, with trunk, branches, and the entire crown not displaying any impaired form and typical of the species. Poor trees should show symptoms of crown ill-health, such as yel- lowing of leaves or crown dieback or mechanical injuries that had affected the tree stability and longevity. Other aspects of tree condition under consideration were foliage color and density. Apart from tree dimensions, data on the hazard status of the street trees was also taken. A tree is considered hazardous if it possesses some type of structural defect associated with a tar- get, such as buildings, vehicles, pavements, or picnic areas where people and property are present. These identified hazardous street trees would have their hazard status determined following the method developed by Matheny and Clark (1994) as follows: [1] Hazard Rating = Failure Potential + Size of Part + Target Rating where Failure Potential = the most likely failure that the structural defect(s) will result in failure within the inspection period (Scale: 1–5). Size of Part = rating of the size of the part most likely to fail. The larger the part that fails, the greater the potential damage (Scale: 1–5). Target Rating = rating of the use and occupancy of the area that would be struck by the defective parts (Scale: 1–4). Hazard Rating will be assigned according to the total rat- ing given, with 3 to 5 points as the minimum value and 12 to 14 points being the maximum (Table 1). This rating will indi- cate the level of hazard and the extent of potential danger of the tree to potential targets. Using this rating system, the fol- lowing hazard status has been assigned. In addition, the loca- tion of each species was also recorded by using DGPS (Dif- ferential Global Positioning System). This data will be used to develop a tree inventory system for DBKL. However the system will be developed in the second phase of the study. Table 1. Hazard rating. Hazard Status 12–14 9–11 6–8 3–5 Species Diversity The biological and genetic diversity level is a major factor in determining the stability and catastrophic tolerance of the roadside tree population (Richards 1983; Sun 1992). There- fore, it is pertinent to examine the current diversity level of the street trees in Kuala Lumpur to develop effective planning and management strategies for the street tree planting program. Diversity index is defined as a measure of the number of spe- cies in a community and their relative abundances (Lincoln et Hazard Rating Very High High Moderate Low Sreetheran et al.: Street Tree Inventory and Tree Risk Assessment al. 1982). For the purpose of quantifying the species diversity in Kuala Lumpur, a simple measure of the inverse of Simpson’s Diversity Index (SDI) was employed as derived by Sun (1992): [2] SDI = Inverse of Simpson’s Index = Σ Nj * (Σ Nj Σ Nj (Nj – 1) where Nj = number of individuals in the jth (j = 1, 2, 3... n) group (species or genus), and n = the total number of groups in a particular population. The Inverse of Simpson’s Index can be interpreted as the ex- pected number of samples with two randomly selected trees, of which one sample could have two trees belonging to the same species. The greater the SDI, the higher the diversity level. This SDI can be considered as the adjusted number of species in a street population based on species composition. This is because SDI equals the number of species if all the species are evenly represented in a population. Any street population with a SDI + X is diverse as much as an evenly-distributed population with X species. The SDI permits linear comparisons of species di- versity levels between any street tree populations (Sun 1992). Analysis The collected data were compiled and analyzed using SPSS sta- tistical software. For this study, the data were analyzed using descriptive statistics, such as means and frequency tabulation. RESULTS AND DISCUSSION Species Composition A total of 2,291 trees comprising 35 species from 16 families were enumerated from five major roads in Kuala Lumpur. The highest number of trees were recorded along Jalan Kuching (646 trees) and Jalan Cheras (613 trees) (Figure 1). However, the most diverse tree species composition was found along Jalan Ampang (24 species) (Figure 2). The survey shows that 68.6% of the spe- cies were indigenous and 31.4% were exotic species, reflecting the trend towards planting more indigenous tree species in street planting by DBKL. When compared to the list of plants proposed by Chee and Ridwan (1984), the tree species composition can be considered rich, but when compared to the proposed list by Tho et al. (1983) the species composition was considered to be very poor. Another street tree survey, conducted by Adnan (1995) on 11 streets in Kuala Lumpur, only identifies 29 species, where 51% were indigenous and 49% were exotic. This reflects the trend toward planting more indigenous tree species by DBKL. It is interesting to note that there are many more potentially suitable indigenous tree species that are underused for street tree planting. The frequencies of individual tree species (Table 2) showed an overwhelming dominance by three main species which make up 72% of the total tree population. The three species were P. indicus (34%), P. pterocarpum (20%), and S. saman (18%). The findings were similar to the results of urban tree studies by Jim (1985), Kunick (1987), and Gilbertson (1987), which indicate only a few major and popular species dominated in urban areas. How- ever, study by Siti Rubiah (2008) in Kuching, Sarawak, indicated species such as Michellia sp. and C. iners dominated the roads. – 1) / ©2011 International Society of Arboriculture
September 2011
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