212 Etemadi et al.: Post-transplant Shoot Growth is Affected by Site and Species disadvantage of bare root trees is that having lost the protective soil cover, roots are exposed to desiccation (Anella et al. 2008). Findings of some studies directly comparing bare root and B&B trees have shown higher mortality in bare root trees (Cool 1975; Sather et al. 2004), while other studies have sug- gested that if bare root trees transplanted with proper care (roots be dipped in a hydrophilic gel immediately after harvesting and wrapped in a plastic bag to keep the roots mois- ture), no significant difference could be observed between two methods (Buckstrup and Bassuk 2000; Anella et al. 2008; Jack-Scott 2012). However, B&B trees had higher growth indices in some studies (Vanstone and Ronald 1981; Ross 2008). Although transplanting and re-establishment of urban trees in arid and semiarid regions, such as Isfahan province, Iran, is a costly process, the value of returned benefits is great enough to justify the expenses. Furthermore, obtaining information regard- ing growth and vitality of urban trees in these regions is critically required for maximizing transplanting success and minimizing public expenditure. The objective of the present study was to examine the effect of two different transplanting method (BR versus B&B) as well as transplanting date on growth and sur- vival of three popular urban trees, including eldarica pine (Pinus eldarica Medw.), white mulberry (Morus alba L.), and smooth- leaf elm (Ulmus carpinifolia Gled.) in arid and semiarid climate. MATERIAL AND METHODS Study Area and Climatic Conditions The experiment was carried out in a two hectare, open field agricultural research center, located at eastern Isfahan, Iran (latitude 32°37’26”N, longitude 51°44’23”E, altitude 1,566.6 m). According to the climatic information obtained from Iran Meteorological Organization, the study area was classified as cold-arid, with mean monthly temperature ranging from 3.2°C in winter to 29.1°C in summer. Mean daily temperature may exceed 40°C during summer. During the experimental period, mean annual evaporation and rainfall were 1,923 mm and 125 mm, respectively. Rainfall was not seasonally well distrib- uted and mostly concentrated in the November to May period. Planting Description and Cultural Practices A total of 144 trees of three dominant urban species in Isfahan landscape, including eldarica pine, white mulberry, and smooth- leaf elm were selected from streets and boulevards that con- flict with roads and subways developing projects and randomly assigned for transplant as BR or B&B. All trees (48 trees per species) were 7–12 years old, with average trunk diameter of ~9 cm (measured 10 cm above the ground). These trees had been first installed along the streets as container-grown nursery stocks at the age of 2–3 years old. Selected trees were harvested and transplanted from January to June 2010, when daily mean air temperatures were: 1) less than 10°C (early winter, when de- ciduous trees were leafless), 2) between 10°C and 20°C (early spring, before budbreak), and 3) more than 20°C (late spring, during active shoot growth). These periods of time were con- current with construction activities in Isfahan city. The number of trees for each date of transplanting was not equal but at least eight trees were assigned to each date. Due to the lack of suffi- ©2013 International Society of Arboriculture cient number of trees in late spring, transplanting of smoothleaf elm trees was performed only in early winter and early spring. Based on the distance from pavements and neighboring struc- tures, trees were dug manually or using a backhoe, with root ball width about 10 times of trunk diameter (~1 m). Three to four days before harvesting, trees were irrigated in order to facilitate digging operations. Twenty-four trees of each species were bare rooted; their roots were sprayed with a stream of water and then slipped into black plastic bags and kept in shade to maintain mois- ture. The root balls of 24 remaining trees of each species were wrapped in burlap and tightly laced with wire, so that the root ball was prevented from disintegrating. B&B and BR trees were stacked gently in the bed of a dump truck and transported to the experiment site. Transporting distance to the destination site was between 5 and 15 kilometers and all trees were planted the same day they were harvested, without delay or hardening-off process. Planting holes were dug twice the width and the same depth (about 1 m) of root balls, on 4 m × 4 m rows spacing. After instal- lation, the planting holes were refilled with original, unamended soil (silt loam texture with pH 7.9, EC 2.6 dS/m, and SAR 4.2) and trees were watered immediately. Thereafter, each tree was irri- gated via surface irrigation with 150 L of water every 5 to 10 days, according to the air temperature and seasonal weather conditions. This amount of irrigation water was greater than that of used for trees in the Isfahan landscape but continued until trees established. Trees were in full sun during the day and there was no prevailing wind direction at the site. Weeds were controlled mechanically dur- ing the trial. No supplemental fertilization was applied to the trees. Data Collection Percent survival of each species in October of 2010 and 2011 was calculated as the total number of survived trees in each year divided by the initial number of trees. At the same time, four one-year shoots from different cardinal directions were select- ed at mid-canopy of each tree and average number and length of current-season shoots (shoots that grow during the growing season and are green, flexible, easy to bend, and can be distin- guished from last growing season’s shoots from the place of bud scales drop), as well as dieback of terminal shoots (dried part of shoots tip) were measured on them. In October of the third year (2012), current-season shoot length of untransplanted trees that was of almost equal size of transplanted trees, were also mea- sured in order to examine trees establishment. Untransplanted trees were in an adjacent field and were in a similar situation to transplanted trees in terms of soil condition and irrigation. No supplemental fertilization was applied to untransplanted trees except in the case of observation of deficiency symptoms. For broadleaf trees, mean leaf chlorophyll content was mea- sured by averaging SPAD meter (Hansatech Instruments, CL-01, UK) readings from four randomly selected leaves per tree. Leaf chlorophyll content of eldarica pine trees was determined by measuring the absorbance at 663 mm and 645 nm, after extraction with 80% v/v aqueous acetone (Lichtenthaler 1987). Relative growth rate for trunk diameter 10 cm above the soil surface (RGRD) was calculated from June to RGR D = loge D2 t2 – loge –t1 D1 October 2010 and from June to October 2011, using the conventional formula (Hoffman and Poorter 2002):
September 2013
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