The Identification of Criteria and Indicators to Evaluate Hazardous ...

urban & community forestry

The Identification of Criteria and Indicators to Evaluate Hazardous Street Trees of Kuala Lumpur, Malaysia: A Delphi Study ABSTRACT

Sreetheran Maruthaveeran and Amat Ramsa Yaman Trees have been playing important roles in our lives for centuries; however, too often, city councils in Malaysia are unaware about the consequences of a tree failure such as property damage and personal injury. Identifying hazardous trees and taking appropriate corrective actions can protect property and save lives. A study was conducted to identify the criteria and indicators needed to identify hazardous street trees in Kuala Lumpur, Malaysia. The Delphi method was used in this study to solicit the opinion from the experts through a series of questionnaires. This study generated and identified 6 criteria and 38 indicators that arborist need to evaluate to identify hazardous street trees in Kuala Lumpur. Hopefully the generated criteria and indicators will be an initial step for Malaysian park managers as they implement their hazard tree management programs. Keywords: hazard tree management, structural defects, property damage, personal injury

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n 1997, the prime minister launched a nationwide treeplanting campaign, with the aim of making Malaysia a “garden nation” by 2005. However, proper tree maintenance was not implemented with the greening program. Consequently, this has created problems for Kuala Lumpur in the management of hazardous trees. As trees age, they grow larger and eventually decline. Some may become hazardous to the public and properties because of weak structure, decay of trunk and branches, and

root loss or root decay (Harris et al. 1999). These potentially hazardous trees are often overlooked and maybe noticed only after a failure. According to Smiley et al. (2000), for a tree to be considered hazardous to the public, it must meet the following criteria: it must possess some type of structural defect(s) that predisposes it to failure and it must be associated with a target such as a building, road, or walkway. A tree may also be considered hazardous if it limits the routine activities of people such as tree branches

obstructing motorists’ vision or tree roots raising sidewalks. Trees can not be neatly separated into hazardous and nonhazardous groups, because nearly every tree has some potential to fail (Harris et al. 1999). Although the city managers of Kuala Lumpur are enthusiastic about planting more trees to beautify the city and environment, tree maintenance and management has been neglected. In addition, the lack of relevant information on urban trees is lacking (Murad 2000). Many cities know about failures either by public complaint or by the city’s inspection (Anderson and Eaton 1986). In today’s society, more people and institutions are being sued for negligence caused by tree failures on public and private properties. Malaysians have to realize that the soul of a garden nation will not materialize just by planting trees. Malaysians need to ensure that trees and parks that have been established are well cared for and maintained to minimize personal injury and property damage. Identifying potentially hazardous trees

Received January 14, 2009; accepted January 4, 2010. Sreetheran Maruthaveeran ([email protected]), Forest Research Institute Malaysia (FRIM), 52109 Kepong, Kuala Lumpur, Malaysia. Amat Ramsa Yaman ([email protected]), Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia. The authors acknowledge the useful guidance of an anonymous review in the preparation of this article. Copyright © 2010 by the Society of American Foresters. 360

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by using proper guidelines and taking appropriate actions can protect property and save lives. A proactive approach is essential to provide a safe environment for the public and property. At present, there are few standard methods to evaluate hazardous street trees in Malaysia, but such information is fundamental to the development of management guidelines in urban areas. Similarly, only few studies have been in Malaysia, such as studies by Murad (2000), Sreetheran (2002), and Noor Syakila (2002). This article aims to develop a set of criteria and indicators to identify hazardous street trees by using the Delphi method. The Delphi method was originally developed in the 1950s by Olaf Helmer and Norman Dalkey, both scientists at the Rand Corporation, as an iterative, consensus building process for forecasting futures (Sackman 1975). Later, the US government enhanced it as a group decisionmaking tool with the results of Project HINDSIGHT, which established a factual basis for the workability of Delphi. That project produced a tool in which a group of experts could come to some consensus if factors were subjective and not knowledge based. This technique initially was been designed to forecast technological innovations for the Rand Corporation and attempts to forecast developments. The Delphi method is used to obtain a reliable consensus of opinion for a group of experts (Dalkey and Helmer 1962). It attempts to achieve this by a series of intensive questionnaires interspersed with controlled opinion feedback (Dalkey and Helmer 1962). Because Delphi studies at Rand were primarily concerned with scientific and technological forecasting, they were viewed as experiments with interesting and possibly useful new techniques (Sachman 1975). This method has spread rapidly and has been used in many studies in a number of other countries (Sackman 1975).

Table 1. Field of experts of the 30 Delphi respondents. Kuala Lumpur City Hall (5 respondents) Agriculture Landscape design Landscape architect

Subang Jaya Municipal Council (2 respondents)

FRIM (13 respondents)

UPM (10 respondents)

Agriculture

Pathology Landscape Urban forestry Landscape design Pest management Landscape architect Town planning

Conservation biology Agriculture Landscape design Landscape architect Risk management

FRIM, Forest Research Institute Malaysia; UPM, Universiti Putra Malaysia

ing assisted in developing the questionnaire for this study. Selection of Delphi Experts In this study, the process of developing criteria and indicators involved a panel of 30 experts (including the respondents from the pretest, n ⫽ 20) from local universities and government agencies. Among these 30 respondents for the Delphi process, 10 were university lecturers and 20 were government officials (Table 1). The respondents selected were those involved directly with tree care such as tree pest management, urban soils, landscape, tree physiology, tree ecology, risk management, and others. This was done to ensure that the panel contained a balance of expertise in the field of hazard tree management.

Method

Ranking Process The identification of criteria and indicators of hazardous trees involved pretesting for the experts (n ⫽ 20). After pretesting, questions were made shorter and simpler. Respondents were asked to rank the criteria and indicators that they would use to measure each criterion following the five-point Likert scale ranging from 1 (least important) to 5 (most important) through a series of questionnaires in round 1 (Figure 1). In round 2 the respondents were asked to use a four-point Likert scale (1, extremely unimportant; 2, unimportant; 3, important; and 4, extremely important) to reprioritize the criteria from round 1 to avoid the neutral value.

Study Design The Delphi method is a process to obtain the most reliable consensus of opinion from a group of experts. This process is achieved through a series of intensive questionnaires interspersed with controlled opinion feedback. A pretest was conducted among 20 respondents from local universities and government agencies. The pretest-

Round 1 In round 1, the questionnaire consists of two sections: section A and section B. In section A, the respondents are asked to rank five most important criteria to identify and evaluate hazardous trees. In section B, the respondents were asked to list what are the most important indicators that they would use to measure each criterion.

Round 2 In round 2 the respondents were asked to review the summarized information obtained from the first-round questionnaire. They were asked to reprioritize or rank the criteria that were selected in the first round. The summary included the criteria that were selected by the respondents in round 1. The mean rank for each of the criterion and the number of respondents selecting each criterion were given. Reprioritizing the criteria reduces the number of criteria under consideration focusing on those thought to be most important by the experts (Zaaba 1999). In the second round each respondent has the opportunity to make changes (if necessary) to their earlier selection. Round 3 Finally, in the third or last round, the criteria selected in rounds 1 and 2 and indicators selected were analyzed and were made known to the panel of experts for prioritization as needed. In this round of the Delphi process, the criteria and indicators that were ranked by the experts during round 1 were matched together. In this round the sum frequency and rank were also included in the round 3 questionnaire. Indicators with the mean rank of 3.0 and above were identified and considered as the primary indicators for a particular criterion to evaluate and identify hazardous street trees. The value 3.0 and above was chosen because it was considered important and extremely important criteria.

Results and Discussions Round 1 Seven categories of criteria were identified (Table 2) by the experts through round 1. The result shows that the Delphi experts identified and ranked all the seven criteria that were identified by the researcher from the literature review. Out of these seven criteria, branch defect, trunk defect, root de-


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fect, root defect, trunk shape, and crown defect were considered most important criteria in identifying and evaluating hazardous street trees. Rounds 1 and 2 identified six criteria.

Figure 1. Flow chart of the Delphi process.

fect, location, trunk shape, and crown defect were ranked high by more than 70% of the participants. Only physical damage (60%) was ranked less highly. There were no new criteria found in the first round. The Delphi experts also identified and ranked 53 indicators that best describe the criteria. As the results for the criteria, most of the indicators were also ranked high (more than 2.5 mean rank; Table 3). Round 2 Out of the seven original criteria that were obtained from round 1, six emerged

from round 2 with a mean rating of 2.5 and above (Table 4). From Table 4, branch defect was rated the highest (3.9), followed by location and root defect at 3.6. Trunk shape (3.0) and crown defect (2.8) followed the six criteria from the second round–identified tree defects: branch attachment, stem defects, reaction wood, and canopy development as suggested by Matheny and Clark (1994). Many of the criteria that were ranked high in round 1 were also rated high in round 2. This shows, clearly, that the branch defect, location of the tree, trunk de-

Table 2. A summary of criteria that were suggested by 20 Delphi experts during round 1 for evaluating and identifying hazardous street trees.

No. 1 2 3 4 5 6 7 a

Category of criteria

Mean ranka

No. of Respondents (n ⫽ 20)

Percent

Branch defect Trunk defect Root defect Location Trunk shape Crown defect Physical damage

4.10 3.22 3.27 4.25 3.24 2.86 2.00

18 18 17 17 16 14 12

90 90 85 85 80 70 60

Rating of criteria importance: 1(least important) to 5 (most important).

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Round 3 In round 3, only the criteria that were selected in round 2 were included in the final set of criteria. Physical damage was eliminated in round 2. A number of important indicators have been identified for each of the seven criteria that had been identified during round 1. Only those indicators with a mean rank of 2.5 or above were selected to represent priority indicators that best measure and provide information on the criteria to evaluate and identify hazardous street trees (Table 5). Identified criteria have the indicators with the mean 2.5 and above, except for trunk defect (lean, 1.8, and epiphytes, 1.4) and trunk shape (single with taper, 1.5). Only those indicators with overall mean of 2.5 and above were selected to represent priority indicators that best measure and provide information on each criterion to evaluate and identify hazardous street trees. Five indicators for root defect recorded overall mean of 2.5 and above. Basal rot scored 4.0, and root decay and exposed root scored of 3.8, respectively. These three indicators are considered as critical indicators of hazard. According to Smiley et al. (2000) one-third of all tree failures are related to the root system. This finding can be supported by Murad (2000) where 49% of the street trees population has an exposed root while another 45% of the population had root wounds. Other indicators such as soil mounding can also predispose root failure. Trees growing on raised mounds may have been affected by a grade cut and thus predispose the tree to windthrow (Smiley et al. 2000). High traffic, sidewalks interference, power lines conflict, road edge damage, and shallow soils are priority indicators (more than a 2.5 mean) for the location criterion, which scored 3.6 in the second round of the Delphi process. Location (site factors) has a significant influence on the development of hazards (Harris et al. 1999). Many failures occur during storm events with high winds and saturated soils. Knowledge of regional and local climate, soils, and topography is invaluable in assessing failure potential (Matheny and Clark 1994). Moreover, trees in areas of high vehicular or pedestrian traffic

Table 3. A summary of indicators for seven that were identified by 20 Delphi experts during round 1 for evaluating and identifying hazardous street trees. Criteria Branch defect

Root defect

Trunk shape

Physical damage

Trunk defect

Crown defect

Location

a

Indicators Narrow attachment of branches Multiple branches Multiple branches with included bark Hangers Dead/weak attached branches Loose/dead barks Dead leaves Fungus fruiting bodies Basal rot Decay roots A tree is leaning with recent root exposure. More than one-half of the roots of the tree’s crown have been cut or crushed Fungus fruiting structures “Mounded trees” Abnormal flare Cavity Root girdling Exposed roots Multiple attachment Multiple attachment with included bark Codominant attachment Codominant with included bark Single with taper Power line conflict Road damage Drainage damage Fence lifted View obstructions Accumulation of litter Cracks to building Sidewalk interference Hangers Dead/weak attachment branches Imbalance crown Defoliated branches Dead leaves Fungal structures Fungal fruiting bodies Cankers Epicormic shoots Decayed parts Sign of cracks v-Shaped crotches Leaning trees Abnormal root flare Epiphytes Branch stubs Cavity Termites Shallow soils Sidewalk interference High-traffic areas Power line conflict Road edge damage

Mean ranka 4.6 4.4 4.9 4.0 4.7 4.0 3.7 2.8 3.6 3.2 4.7 3.2 3.0 2.9 3.2 3.3 2.8 3.2 3.5 4.7 3.2 4.0 2.3 2.7 3.5 3.2 2.3 2.5 0.1 2.0 3.2 4.1 4.5 4.1 3.6 3.3 3.0 2.8 3.2 3.3 4.1 2.8 3.4 2.0 3.2 2.2 3.2 3.1 2.9 3.2 4.4 4.2 3.5 1.6

Rating of criteria importance: 1 (least important) to 5 (most important).

are more likely to experience soil compaction as well as root damage (Smiley et al. 2000). Trunk defect indicators include decayed parts, cracks, cavities, cankers, v-shaped crotch, epicormic shoots, fungal bodies, termites, branch stubs, and abnormal flare. For these, indicators were scored high (2.5– 4.0). Defects in the stem or

Table 4. Mean rating of criteria by panel of experts (n ⴝ 30) for round 2 of the Delphi process.

branch would reduce the overall strength of the tree and include external deformities such as cankers, galls, girdling, wound, and cracks (Matheny and Clark 1994). Murad (2000) observed that the majority of street trees in Kuala Lumpur had v-shaped crotches (68%). The presence of a v-shaped crotch is a predictor for codominants and multiple attachments in Kuala Lumpur.

Category of criteria (selection by the experts in round 1) Branch defect Location Root defect Trunk defect Trunk shape Crown defect Physical damage

Meana 3.9 3.6 3.6 3.2 3.0 2.8 1.4

a

Rating of criteria importance: 1, extremely unimportant; 2, unimportant; 3, important; and 4, extremely important. Bolded items indicate selected criteria.

Indicators such as multiple attachments, included bark and codominant, are important details to look for during trunk shape assessment. From Table 3, codominant attachments with included bark, multiple attachments, and codominant attachments are considered as critical indicators of hazard. Murad (2000) also noted that the majority of the trees surveyed (98%) had codominant or multiple attachments. Additionally, multiple attachments trunks and codominant leads were thought to cause more frequent crown breakage (Murad 2000). Trees with a single trunk with a desirable taper scored very low (1.5) as a risk factor. Murad’s study showed that less than 2% (1.7%) of the street tree population had the preferred single trunk with good taper. Closely spaced trees have poor taper compared with trees grown in the open (Matheny and Clark 1994). Branch defects are the most common type of tree defect where small branches can cause serious injury when they fall on a person (Shigo 1983). Narrow angles of branch attachment emerged as the top indicator for branch defect, followed by multiple attachments: multiple attachments with included bark, dead/weak attached branches, defoliated branches, hangers, fungal bodies, and dead leaves. According to Murad (2000), the majority of the street trees in Kuala Lumpur had v-shaped crotches (68%). A factor here may be early pruning practice in the nursery where tree stock is headed back to force trees to develop a compacted crown (Murad 2000). Heading back or topping, which involves cutting back the branches to stubs, tends to produce more vigorous shoots that grow close and tend to form a v-shaped crotch. Crown defects are characterized as hangers, dead and weak in attached


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Table 5. Final set of criteria and indicators. Criteria

Indicators

1. Root defect 2. Location 3. Trunk defect 4. Crown defect 5. Trunk shape 6. Branch defect

Basal rot, decayed roots, a tree is leaning with recent root exposure, mounded trees, and abnormal flair High traffic, sidewalks interference, power line conflict, road edge damage, and shallow soils Decayed parts, sign of cracks, cavity, cankers, v-shaped crotch, epicormic shots, fungal bodies, termites, branch stubs, and abnormal flair Hangers, dead/weakly attached branches, imbalanced crown, defoliated branches, and fungal structures Multiple attachment with included bark, codominant attachment with included bark, multiple attachment, codominant attachment Narrow attachment of branches, multiple attachments, multiple attachment with included bark, dead/weak attached branches, defoliated branches, hangers, fungal bodies, and dead leaves

branches, imbalanced crowns, defoliated branches, dead leaves, and fungal bodies. The means for these indicators ranges from 2.7 to 3.7. The criterion for imbalanced crown scored a value of 3.4, making it a critical indicator for hazard. Trees with unbalanced or asymmetrical crowns may have poorly distributed weight over the stem. These trees are prone to failure when combined with other defects such as decay and root disease (Smiley et al. 2000). On the other hand, from this study it shows that the majority of the trees in the study area exhibit no major foliage problems or defects. This shows from the criterion dead leaves which scored the lowest value (2.7). This same result was even obtained by Murad (2000), where only 2.6% suffered from chlorosis and necrosis.

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Conclusions This study identified 6 criteria and 34 indicators that might be used to evaluate and identify hazardous street trees. The criteria and indicators developed here could be used to evaluate and identify hazardous trees In Kuala Lumpur, the tropics, or other regions. Future studies could identify additional criteria because there will be changes in the expert’s preferences and new findings in the area of hazard tree evaluation.

Literature Cited ANDERSON, L.M., AND T.A. EATON. 1986. Liability for damages caused by hazardous trees. J. Arboricult. 12:189 –195. DALKEY, N., AND O. HELMER. 1962. An experimental application of the Delphi method to the use of experts. Manag. Sci. 9(3):458 – 467.


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