258 Rahman et al.: Effect of Pit Design and Soil Composistion on Performance of Street Trees Table 1. Design of three types of planting pit used in the experiment. Type 1 Type 2 Pit dimension (m) 1.2 × 1.2 × 1.0 Soil composition Topsoil Irrigation setup Root barrier Paving material none 1.2 × 1.2 × 1.0 Urban soilz An irrigation pipe of 895 mm × 3 m length, outside of the root barrier at 200–300 mm depth was installed. Only re-root 300 linear root barriers were With linear root barrier a terram 3000 permeable wrapped around top of root ball. geotextile layer was laid to stop upward root growth. Finished off with 100 mm depth of composting mulch. 50 mm laying course of 6 mm washed graded aggregate was laid. Finally Marshall ‘Priora’x concrete block paving was used to seal the pit. z Urban soil is a mix of 50% sand and 50% topsoil; overall texture is 10%–12% clay, 10%–12% silt, and 75%–80 % sand content. y , each cell weighs 0.38 kg and has 92% empty space inside. Root cell system (Green-tech Ltd, York, UK): Each cell is 250 mm × 250 mm × 90 mm in size, made of recycled high-density polyethylene (HDPE) and has a load- bearing capacity of 80 tonnes per m2 x Marshall ‘Priora’ concrete block: These are special zigzag bordered blocks with approximately 6 mm of gap between each block which allows 1.8 L S-1 Tree Growth and Phenology To compare the growth increment of trees, the total height of each tree was measured using a Suunto Clinometer, and bole height, DBH, and canopy spreads in four directions measured biannu- ally using a measuring tape between April 2010 and October 2012. The leaf area index (LAI) of trees was measured in May 2010 and another eight times over the summers between 11:30 am and 4:30 pm on warm sunny days at monthly intervals us- ing an AccuPAR model LP-80 PAR/LAI Ceptometer (Decagon Devices, Washington, U.S.) along with other leaf physiological measurements. Bud break autumn coloration, and leaf fall were recorded according to Close et al. (1996) at the initiation of bud break, initiation of color change, peak color, and 100% leaf fall. Autumn coloration and leaf fall were recorded in 2010, 2011, and 2012; but bud break was recorded in 2011 and 2012 only. Leaf Physiology Physiological and meteorological measurements were made to investigate the water status and cooling potential of trees. Predawn leaf water potential between 2:00 and 4:00 am, midday leaf water potential, and stomatal conductance between 12:00 noon and 4:00 pm, were measured on the same warm sunny days on eleven dates over the three growing seasons. Leaf water potential was measured using a pressure chamber tech- nique (Digital Plant Water Potential Apparatus EL540-300 and EL540-305, ELE International, Hertfordshire, UK) and stomatal conductance was measured using a leaf porometer (model SC-1, Decagon Devices, Washington, U.S.). For each measurement, three sunlit leaves were used from the mid crown of each tree. At the same time, meteorological measurements were also made that would enable researchers to calculate evapotranspi- ration. Air temperature and relative humidity were simultane- ously measured in the tree shade, to reduce the radiation effect, 1.5 m above the ground using a Temperature and Humidity Datalogger - CEM DT-172 (accuracy +1%) (Digital meter, Dar- wen, Lancashire, UK). Measurements were logged every five seconds and averaged over two minutes period for each record of air temperature and relative humidity. Leaf temperatures were also recorded using the porometer at the time of measur- ©2013 International Society of Arboriculture m-2 water through them. ing the stomatal conductance. Atmospheric pressure data for each measurement day were recorded from published data of the meteorological station, Manchester Airport, UK. To check whether there was any significant difference in wind speed among the streets, wind speed at 1.5 m above ground was also measured (averaged over five minutes) using a handheld digi- tal anemometer (Omega digital anemometer, model HHF92A). The transpiration rates (E, mmol m-2 s-1 ) of leaves were finally calculated from the stomatal conductance and me- teorological data using Fick’s law (Lambers et al. 1998): [1] E = gv total × (eleaf – ea ) / Pa where gv total is the total conductance to water vapor (mmol m-2 s-1), eleaf sumed to be the saturation vapor pressure at leaf temperature, and ea and multiplied by the latent heat of vaporization, which is 2.45 kJ g-1 Energy loss per tree was then calculated according to Equation 2: [2] Energy loss per tree = Energy loss per unit leaf area × LAI × A where LAI is the leaf area index of the tree and A is the crown area of the tree calculated from its crown diameter. Leaf Chlorophyll Fluorescence (Fv/Fm) Chlorophyll fluorescence has been used to provide a rapid and non-destructive diagnostic method for detecting and quanti- fying damage to the leaf photosynthetic apparatus in a variety of tree species in response to environmental stress (Percival 2004; Resco et al. 2008). Researchers measured chlorophyll fluorescence four times each over the growing seasons of 2011 and 2012 between May and September (due to technical difficulties, the study authors could not measure chlorophyll multiplying the saturation vapor pressure at air temperature by the relative humidity of the air. Pa From Equation 1, the transpiration rate was converted to g m-2 s-1 , to calculate the energy loss per unit leaf area (W m-2 ). is the vapor pressure inside the leaf, which was as- is the vapor pressure of the atmosphere, calculated by is atmospheric pressure. Same as Type 2. Same as Type 2. Type 3 1.2 × 2.8 × 1.0 Special interlocking root cell systemy with topsoil. Same as Type 2. filled
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