Arboriculture & Urban Forestry 38(6): November 2012 Collection of Infrared Images Infrared images were collected using a Thermoteknix VisIR 640 IR camera (Cambridge, UK) calibrated using ambient tempera- ture and emissivity values appropriate for tree bark prior to evalu- ation. The emissivity setting was held constant at 0.95, an average of six bark emissivity values for temperate species reported by Salisbury and D’Aria (1992), and the ambient temperature was adjusted for each image to correspond with conditions at the time of collection. The camera was consistently positioned 1.2 m above the ground at a distance of 10 m from the trunk base and oriented to measure the surface temperature on each tree’s western aspect (270°C). The images were collected for all 48 trees between 2:00 and 4:00 pm on March 5, 2011. The camera orientation and time of image collection were selected to ensure each tree received the maximum solar heating. During this process, the marking tape was removed from each tree immediately before measure- ment and afterwards replaced. Climate data for the immediate area during the same period was obtained from the Meteorologi- cal Services Division, National Environment Agency, Singapore. Destructive Harvesting and Measurement After measurement, the trees were felled and the lowest 3 m of the trunk was removed and retained for dissection. These 3 m trunk sec- tions were cut with a chainsaw into 15, 20 cm thick cross sections. Each cross section was examined for bark color and texture, cavita- tions, reaction zones, sapwood, and heartwood. Each cross section was photographed for visual reference within a 1 m × 1 m square frame, containing a metric scale on two opposing axes (Figure 2). The presence of decayed wood was confirmed by measuring the axial compressive strength of fungal lesions using a method mod- ified from Watson (2008). A Penetrometer® (Lang Penetrometer, Gulf Shores, Alabama, U.S.) fitted with a blunt dissecting probe was used to exert 83 N of force axially onto the cut wood surface, and the depth of holes created by the probe was measured using a Digimatic Caliper (Mitutoyo Corporation, Kawasaki, Japan). Us- ing this method, fungal lesions permitting impressions at least 1 mm greater than proximal healthy tissue was considered decayed. The stem perimeter and outline of internal defects (e.g., decay, discoloration, cavitation) were traced manually onto a clear plas- tic transparency sheet from the superior cut surface of each cross section. In addition, tracings were also made from the remaining flush cut stumps in situ, yielding the lowest measurement from 16 total cross-sectional tracings spaced equidistantly along the 3 m section. The tracings were digitized using a flatbed scanner and the CSA of each feature was determined using the image analy- sis toolset in Photoshop® CS3 Extended (Adobe Systems, San Jose, California, U.S.). These values were subsequently used to determine the relative defect CSA (%) for six defect categories, including 1) undamaged, 2) discolored, 3) decayed, 4) decayed + discolored, 5) cavitated, and 6) cavitated + discolored (Figure 3). Data Analysis The collected data were analyzed using a concurrent mixed-meth- ods approach to corroborate findings obtained from both qualita- tive and quantitative strategies. IR images were processed using the TherMonitor® Reporter System (Thermoteknix 2001). The temperature span rendered in each image was set between 25°C and 35°C, and the captured images were compared visually for Figure 2. Each cross section was photographed in a 1 m × 1 m frame for visual reference. Among the sampled trees, sections were excised containing: (a) termite-induced cavitations with irregular, smooth-walled voids; (b) decay with irregular color changes, host reaction zones, and dark fungal interaction lines; (c) discoloration with irregular wood color changes and dark fun- gal interaction lines; and (d) no measurable defects with substan- tially healthy tissue. 279 Figure 3. The relative amount of cross-sectional area occupied by a defect (relative defect CSA), represented as a percentage, was determined by dividing the surface area of the defect by that of the entire stem. In order to determine cross-sectional area, the perimeter of the stem and defect(s) were manually transferred onto a clear PVC transparency sheet, digitized, and analyzed us- ing image processing software. qualitative differences in trunk surface temperature distributions. The consistent temporal and spatial appearance of temperature anomalies was recorded, and these areas were compared with the observed external and measured internal stem characteristics. Quantitative temperature readings were extracted from the im- ages using two separate techniques. First, temperature data was extracted from the trunk surface within two rectangular transects positioned immediately above and below each other at the base ©2012 International Society of Arboriculture
November 2012
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
