Arboriculture & Urban Forestry 39(5): September 2013 influenced the duration of the transplanting stress, as has been stated in the definition of transplanting stress (Rietveld 1989). The reduced growth rates for sweet cherry trees, observed for most of the production methods at Alnarp in 2011, compared to 2010, may be the result of increased complexity of the crown associated with the vigorous lateral shoot growth in 2010 (Borchert 1976). Previous studies have shown that water availability is the main limiting resource in vegetative growth, and that nutrient supply is less important during the establishment phase (Day and Harris 2007; Liu et al. 2012). The frequent irrigation at Alnarp could be one explanation of the more rapid recovery of shoot growth in sweet cherry trees at that site, but comparison of the two sites showed that the shoot growth was not higher at Alnarp during the first two post-transplant years, when the trees were irrigated. This indicates that the ability of the root system to take up water was limited during the first year, regardless of the water availability and the method used for cultivation. Even though the more frequent irrigation at Alnarp had no initial posi- tive effect on shoot growth, it might have had a positive effect on root regeneration. Studies have shown that even minor soil moisture stress reduces root regeneration (Larson and Whit- more 1970), thereby prolonging the time for a transplanted tree to restore a balance between root and crown, roots to explore the new soil and to obtain the necessary contact with the growth medium. Soil moisture stress might have slowed the process of recovery from transplanting stress for the Malmö-situated trees to a greater extent than for the Alnarp-planted trees. Shoot growth patterns differed between the species, with seem- ingly better acclimation of the fibrous-rooted sweet cherry. These results support a previous hypothesis on species-specific responses to nursery production methods (Struve 1993; Schuch et al. 2000; Ferrini and Baietto 2006). Differences in time for recovery of pre- transplant growth rates between the species might also be a result of the species root:shoot ratio. Red oak is generally considered to be a species with a high root:shoot ratio, which could prolong the time required for the species to return to the pre-transplant root:shoot ratio to a greater extent than for a species with a lower ratio, and higher root regeneration potential, as sweet cherry. The trees in this study were planted before budbreak in spring, and one of the advantages of modern production methods is the greater flexibility in transplanting period (Ferrini et al. 2000). The results of this study might have been different for red oak if the trees had been planted at another time of year, when plant- ing of field-grown red oak trees is normally not recommended. Earlier studies on the effect of transplanting time for estab- lishment, however, have not shown any clear results regarding which time of year is most beneficial for transplanting in gen- eral (Solfjeld and Hansen 2004; Richardson-Calfee et al. 2007). It has been argued that for a tree to exhibit significant above- ground growth there must be a balance between the root and the crown (Borchert 1973; Brouwer 1983). The functional balance hypothesis describes the continuous modification of roots and shoots to obtain a ratio that is favorable in a certain develop- ment phase under a great variety of environmental conditions (Brouwer 1983). Although the observed differences between the root systems were large, the differences in shoot growth be- tween the different production systems were not as pronounced. There was no clear relation between the amount of fine roots at delivery from the nurseries and post-transplant shoot growth in the trees in the current study. The AP and RP sweet cherry trees 207 that were examined had the highest amount of small-diameter roots, but the possible advantage of this was only detectable in AP trees during the first post-transplant year. RP sweet cherry trees instead showed poor initial shoot growth. If the higher shoot growth shown by RP trees at both sites later in the experiment (three and four years after transplanting) was related to the high amount of fine roots at transplant, this positive effect was not evident in the AP trees, which initially had the same amount of fine roots. One explanation for this may be that the different production methods create roots of different quality, or with dif- ferent regeneration capacity. A previous study on red oak has shown that container-grown seedlings produced more first-order lateral roots than bare-rooted red oak seedlings, suggesting that the root architecture developed in the container is more favor- able for root regeneration (Wilson et al. 2007). No data on root regeneration after transplanting was collected in this study, but the differences in shoot growth between RP and AP sweet cherry trees in 2010 might be an indication that root pruning had a more positive effect on root regeneration, ensuring long-term survival. Considerable visual differences were noted in the root systems of the trees in this study, and some of these different appearances may have been more favorable for root regeneration. The lack of a relationship between total fine-root length and shoot growth might also be due to the different medium surrounding the roots. It has previously been shown that there is a risk that container- grown trees will have very dry soil after transplanting, since the porous medium often used has a lower water-holding capacity than the surrounding soil (Nelms and Spomer 1983; Hanson et al. 2004). The water may be drawn out of the root ball, leading to a water deficit, despite irrigation and vigorous root systems (Harris 2007). Similar observations were made during this study. The root balls of the AP trees at Alnarp dried out faster than the other root balls with the nursery’s natural soil (data not shown), something that was probably due to structural differences between the peat-filled root ball and the surrounding soil in the experimen- tal field. This could explain why AP sweet cherry trees did not benefit more from the larger root ball and higher amount of fine roots. Sweet cherry and red oak reacted very differently to root pruning in the nursery: the WinRhizo-analysis and the visual observations showed that pruning seemed to stimulate root growth in sweet cherry but not in red oak. No differences were noted between the production methods in the accumulated shoot growth of the sweet cherry trees at Alnarp when all the years were included, since the initially high- performing production methods were the lower-performing ones during the second half of the experiment. Shoot growth was thus evened out over the years, resulting in trees of equal size four years after transplanting, for all production methods. Assuming that growth continues at the current rate, the trees will remain equal in size. The production method would, in such a case, have little long-term effect on the size of the tree. The effect of the pro- duction methods in a longer perspective was not studied here and production method may affect long-term mechanical stability due to potential differences in root system regeneration and devel- opment. Such differences could affect survival and growth, and are complicating forecasts on future canopy sizes. To make long- term studies on production methods influence on shoot growth and canopy size would therefore be highly relevant. The accu- mulated shoot growth-results for the sweet cherry trees planted in Malmö differed from the Alnarp-results. The post-transplant ©2013 International Society of Arboriculture
September 2013
| Title Name |
Pages |
Delete |
Url |
| Empty |
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. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
