202 Levinsson: Post-transplant Shoot Growth is Affected by Site and Species of field-grown trees in nurseries and the ensuing transplanting inevitably affect the root systems, disrupt the root:shoot bal- ance, and impair the absorptive capacity of the tree. This means that not only water availability at the transplanting site, but also the tree’s ability to take up water is a crucial factor for shoot growth after transplant (i.e., there must be a sufficient amount of vital roots for sustained water uptake and root regeneration). Field-grown trees have been shown to lose 32% of their total dry root weight at harvest, while the loss of fine-root length is as high as 88% (Gilman and Beeson 1996a). Regeneration of fine roots after transplanting is therefore crucial for the tree’s ability to take up water and thus retain vigorous growth. Con- tainer-grown seedlings of red oak (Quercus rubra) have shown higher new root initiation on lateral roots than bare-rooted red oaks in a forestry study (Johnson et al. 1984) indicating that production systems may modify the root regeneration capacity. Studies of the effect of production method on shoot growth have shown differing results. In a comparison between field-grown B&B and BR Celtis occidentalis (L.), Ostrya virginiana (Mill.), and Quercus bicolor (Willd.), only B&B Q. bicolor showed high- er shoot growth than BR cultivated trees two years after planting (Buckstrup and Bassuk 2000). When field-grown B&B were com- pared with plastic-container- and FC-grown plants, the production method was found to have no influence on growth rates 18 months after transplanting for either of the species Quercus laurifolia (Michx.) and Ilex × attenuata ‘East Palatka’ (Gilman and Beeson 1996b). No differences were found between production methods in a study of post-transplant growth of Acer rubrum (L.) produced in seven different container types (Marshall and Gilman 1998). The extent to which a tree is influenced by production method after transplanting has also been shown to depend on the water availability (Gilman and Beeson 1996b). Under limited irrigation conditions, RP Quercus virginiana (Mill.) trees showed better survival and post-transplant growth than trees cultivated in various containers, while under well-irrigated conditions no differences were seen (Gilman 2001). Previous studies have led scientists to formulate the hypothesis that the response of trees to production method is dependent on species and the conditions at the transplant- ing site (Struve 1993; Gilman 2001; Ferrini and Baietto 2006; Ferrini and Nicese 2006). It has also been hypothesized that root structure affects the response of the tree to the production method (Schuch et al. 2000). In general, trees with a coarse root system are considered more difficult to transplant than species with fibrous root systems because of their lower root regenera- tion potential (Struve 2009). A previous study on two species with different types of root structure indicated that fibrous- rooted plants are more adaptable to growth in various types of container than coarse-rooted species (Schuch et al. 2000). In this study, two tree species common in urban areas in northern Europe were compared: the fibrous-rooted sweet cherry (Prunus avium) and the coarse-rooted red oak. The objectives of the study were: 1) to determine the effect of produc- tion method on shoot growth in sweet cherry trees and red oak trees during one year in the nurseries and for four consecutive years after transplanting, 2) to compare how sweet cherry and red oak produced in different production methods responded to transplanting at an urban site and a controlled landscape site, 3) to study the influence of different production methods on root growth in the nursery for the two species with different root ©2013 International Society of Arboriculture structures and to analyze if such differences might correspond to post-transplant shoot growth, 4) to evaluate the effect of the production method on the accumulated shoot growth for the two species during the period of the experiment, and 5) to study the time required for sweet cherry and red oak trees produced in dif- ferent production systems to restore nursery shoot growth rates. MATERIALS AND METHODS Plant Material and Experimental Conditions Sixty specimens of each species were included in the study. The trees of both species had a stem circumference of 14–17 cm, 1 meter above the root collar when the study started. Sweet cher- ry is a fibrous-rooted species with a determinate shoot growth pattern under natural Swedish growth conditions. All sweet cherry trees had the same provenance and had reached adult phase before the experiment started. Red oak is a coarse-rooted species with a semi-determinate shoot growth habit (Hanson et al. 1986; Struve 2009). Red oaks can have one or more shoot flushes per season, depending on how favorable the condi- tions are. None of the red oak trees had reached adult phase or set any fruit before transplanting. During the study, a few oak trees sporadically produced acorns. Most of the trees, how- ever, stayed in the juvenile phase throughout the study. There was no detectable connection between fruit setting and produc- tion method, and it had no detectable effect on shoot growth. No red oak trees were therefore excluded due to fruit setting. The study was carried out over five growing seasons, from 2007 to 2011. The trees were selected at two Swedish nurseries before the growing season of 2007. All plants within each spe- cies were produced at the same nursery (location of sweet cherry nursery: 56°13’40”N 12°40’19”E, location of red oak nursery: 58°39’21”N 16°0’58”E). All trees had been field grown until the selection in 2007. The selection was based on stem circum- ference and visual appearance, aiming at as high uniformity in visual appearance as possible. The size of stem circumference was determined based on the goal to deliver trees of the size of 16–18 cm the following spring. Within each species, the trees were then randomly categorized into five groups of twelve, each group submitted to a different production method: BR, B&B, RP, AP, and FC, and were cultivated for one more season in the nurseries. The AP and the FC trees were moved to one of two other nurseries (depending on treatment) before the growth period of 2007. Each nursery specialized in the relevant production system. All four nurseries in the study are located in south- ern Sweden and have similar climatic prerequisites. All trees were then treated according to Swedish standard procedures for each production method (LRF 2012). BR and B&B trees were left undisturbed in the fields. RP trees were root pruned before the growth season started and left in-ground, together with the BR and B&B trees. The AP trees were transport- ed as B&B trees and were installed in air-pots (Superoots® , The Caledonian Tree Company, Edinburgh, UK) filled with a peat-sand mixture and placed on a polypropylene ground cloth. The FC trees were transported to the new nursery as BR trees. They were root-pruned and installed in a peat- filled fabric container (Smart Pot® , High Caliper, Oklahoma, U.S.) and placed in-field. All trees were drip-irrigated and AP trees also had crown-irrigation installed. The trees were
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