When trees are dug from the nursery, a portion of the root system may be lost, therefore the trees can struggle because of lack of stored carbohydrates in the intact root system (Khan et al., 1998). If vigor is increased then, in theory, the trees will start production earlier. Both the root system and the shoot system work jointly to satisfy the resource need of the plant and thus promote growth and stimulate development (Puig et al., 2012; Su et al., 2011). The root system ensures the uptake of water and vital minerals while the shoot system accomplishes reproductive functions and manages photosynthetic activities. When one system faces a resource hardship or a disruption of its initial equilibrium, a signal is sent to the other system (Bahrun et al., 2002; Brewer et al., 2013; Kudo et al., 2010), which may react to the new austerity condition. Because roots are typically lost during transplanting, the roots may be unable to support as much stem and shoots as they could before transplanting and so trees are often pruned at planting.
Pecan (Carya illinoinensis) is a multipurpose tree that can be grown at a commercial scale for timber or nuts or as ornamental trees. One unknown is how much pruning at planting is necessary for proper pecan-tree development. Wells (2017) recommends to “prune 1/3 to 1/2 of the top of the tree and remove any branches to compensate for the large percentage of roots lost when the trees are dug.” Wood (1996) found reducing trunk height up to 75% had no effect on tree survival, but did increase growth rate so that there was no difference in the height of pruned and unpruned tress after 3 years; however, Smith and Johnson (1981) found that survival was increased by pruning the tops at planting by 25% or 50%. Like Wood (1996), Smith and Johnson (1981) also found that pruning increased growth. Meadows and Toliver (1987) found that pecan trees clipped to a 10-inch top had recovered to be the same height as unclipped trees after 3 years.
The purpose of this study was to determine if pruning the tops of the single-trunk trees at planting increases vigor of the trees. In the experiment, the tops of bare-root trees were pruned by 50% or 75% at planting. The hypotheses considered are 1) pruning newly established pecan trees increases trunk diameter, 2) pruning of newly established single-trunk tree scions will lead to fewer, but longer shoots, and 3) pruning will lead to higher total shoot growth. The findings generally support the second hypothesis and the third hypothesis only in year 1.
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