Arboriculture & Urban Forestry 43(4): July 2017 al. 2004; Etemadi et al. 2013), while other studies have suggested that if BR trees transplanted with proper care (roots dipped in a hydrophilic gel immediately aſter harvesting and wrapped in a plastic bag to keep the roots moisture), no significant difference could be observed between two methods (Buckstrup and Bassuk 2000; Anella et al. 2008; Jack-Scott 2012). CG trees have become favored over FG trees in many cases for transplanting projects because a much higher proportion of the root system is retained within the root ball, which allows for the trees to be transplanted with an entirely intact and undisturbed root system. Also, less effort is needed for digging CG trees, and they can be successfully planted during a greater portion of the year (Clewell and Lea 1990; Harris and Gilman 1993). However, increased production costs and the formation of circling roots along the outside or bottom of the root ball, which results in poor establishment of CG trees in the landscape, are limiting factors for large-scale use of CG trees (Amoroso et al. 2010). Intact root density within the root ball of CG trees has resulted in the assumption that CG trees may tolerate transplant stress better than FG trees. However, there is some evidence demonstrating that there are no significant differences in estab- lishment of various production methods. Gilman (1994) states that trees from a variety of production systems perform almost equally well if regularly irrigated. Blessing and Dana (1987) reported that root spread and new root dry weight of FG Chinese juniper (Juniperus chinensis) was slightly greater than CG trees 16 weeks aſter transplant- ing, whereas their shoot growth was not sta- tistically different. In a prolonged experiment, Laiche et al. (1983) showed that five years fol- lowing transplant, height, caliper, and number of roots were not different between CG and BR trees for Carya illinoensis (Wangenh.) K. Koch. Biostimulant application at planting is also among the methods that have been used to increase post-transplant survival and encourage rapid establishment (Ferrini and Nicese 2002). Humate-based matters (humic acids, humin, fulvic acids) are formed from the biological and chemi- cal degradation of soil organic matter and are very resistant to further biodegradation (Baigorri et al. 2009). Russo and Berlyn (1990) described these biostimulant as “non-nutritional products 145 that may reduce fertilizer use and increase yield and resistance to water and temperature stress.” Humic acids (HAs) are the main active com- ponents among humate-based products (Ferrara and Brunetti 2010). These complex materials may contain vitamins (e.g., thiamine) or other organic materials (e.g., seaweed extracts) and have the potential to directly and indirectly affect different cellular mechanisms, including cell respiration, photosynthesis, protein synthesis, enzyme activi- ties, water, and nutrient uptake (Muscolo et al. 1999; Nardi et al. 2002; Chen et al. 2004; Nikbakht et al. 2008; Khattab et al. 2012). Several studies have also shown that HAs stimulate plant growth and yield by hormone-like activities, in particular auxin/cytokinin effects (Ferrara and Brunetti 2010; Trevisan et al. 2010). Hormone-like activity of HAs has been demonstrated to be dose-dependent, with optimal concentrations in the range of 50–300 mg kg-1 , but positive effects have also been exerted by lower concentrations (Chen et al. 2004). However, research on the effects of HAs is mostly reported for vegetable and fruit species (Nikbakht et al. 2008; Hagagg et al. 2013; Mustafa and El-Shazly 2013), and little is known about their efficacy on woody species in landscapes (Ferrini et al. 2005) In most developing countries with arid climates, freshly dug trees and shrubs are usually used for planting projects, such as afforestation. These trees, depending on species, are highly susceptible to death if not irrigated appropriately. Digging trees and holding them in ground or containers for several weeks or months prior to planting (which is commonly known as hardening-off process) help trees adapt to the new site environment and restore their damaged root system (Gilman 2001). However, hardening-off processes will increase expenses associated with digging, handling, and maintenance of trees, which is in contrast with the goals of large-scale planting projects (i.e., speed and minimum unit cost). Considering the key impor- tance of trees and shrubs and their valuable benefits in arid areas, it is crucial to determine the best transplanting method and practice for each species, as well as treatments that improve transplant suc- cess. Therefore, the present study was conducted to 1) determine the impact of production method on hardening-off process of oriental thuja (Platy- cladus orientalis) trees, 2) compare survival and ©2017 International Society of Arboriculture
July 2017
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