Planting Depth at Onset of Container Production and Subsequent Root Ball Remediation at Transplanting Affects Pin Oak and Littleleaf Linden

Abstract

<jats:p>Root flares of landscape trees are increasingly found to be much deeper than their forest counterparts, indicating that their root systems have been situated deeper in the soil. Planting deeply in production containers contributes to this phenomenon, yet the consequences of deep planting in production containers or the consequences of any adjustments made to planting depth at the time of transplant on growth in the landscape have not been reported for many species. Container-grown (11.4 L) liners of <jats:italic>Tilia cordata</jats:italic> Mill. (littleleaf linden) and <jats:italic>Quercus palustris</jats:italic> Münchh. (pin oak) were planted in 50-L containers with the first main lateral roots (structural roots) at substrate-surface grade or 10 cm or 20 cm below grade (deep planting). Trees were grown in the 50-L containers for two growing seasons and in a simulated landscape for three additional seasons after transplanting with the top of the container substrate at soil level or with some roots and substrate removed such that the original structural roots were just below the soil surface (remediated). Deep planting pin oak, but not littleleaf linden, slowed growth during container production; however, the effect did not persist after transplanting. Remediation of the 20-cm-deep pin oaks slowed growth during all three post-transplant years. Littleleaf linden remediation slowed growth for the first season after transplanting to a simulated landscape for 10-cm-deep trees and for the first two seasons for 20-cm-deep trees. Evaluation of pin oak root systems 3 years after transplanting revealed vigorous growth of non-deflected adventitious roots that had formed on the trunks of deep trees, and these roots appeared to be developing into main structural roots. No adventitious roots were present on littleleaf linden; instead, deflected roots grew and produced deformed root systems. Deep planting of linden reduced suckering; however, we conclude that remediation of deep-planted littleleaf linden is warranted as a result of potential hazards from trunk-girdling roots. In some species such as pin oak, non-deflected, strong adventitious root systems may assume the role of structural roots and diminish the effect of deflected and circling roots systems formed during container production. Remediation of these trees is likely not as critical as for species without abundant adventitious roots.</jats:p>

Development of a Mixed-Effects Individual-Tree Basal Area Increment Model for Oaks (Quercus spp.) Considering Forest Structural Diversity

“…Oak-dominated forests are of great ecological and economical importance [3,4]. For instance, oaks are extensively used in soil and water conservation and restoration efforts since they have strong, adventitious root systems and exhibit a high tolerance to waterlogging [5][6][7]. Additionally, oaks are well adapted to fire and hence are frequently used for constructing forest fire belts [8].…”

Effect of Liner Container Size, Root Ball Slicing, and Season of Root Pruning in a Field Nursery on Quercus virginiana Mill. Growth and Anchorage After Transplanting

“…Root remediation by slicing root balls and removing potentially girdling roots on the top of the liner root ball had little influence on post-transplanting xylem potential, trunk diameter, or tree height; this was also found in other taxa planted from nursery containers (Gilman and Masters 2010;Harris and Day 2010). However, root pruning by slicing the root ball when planting containers into the field nursery increased root system quality in the current study and others (Gilman et al 2009); despite this increase, 66% of trees at the end of the field production period graded as culls, and an average of 43% of trunk circumference remained circled on trees receiving the slicing treatment (Table 2).…”

Nursery Planting Depth, Mulch Application, and Root Pruning at Landscape Planting Affect Tree Health and Anchorage

“…There is growing evidence that planting deeply when installing certain taxa into a landscape reduces survival or growth rates (Arnold et al 2007). However, Bryan et al (2010) and Harris and Day (2010) showed that height and trunk diameter growth after landscape planting was little affected by root collar depth in nursery containers. There is little published on the impact of root collar depth in a container root ball on root attributes and anchorage in the landscape.…”

“…In recognition of the potential problems of planting the root collar too deeply in the root ball, the ANSI Z60 American nursery stock standard (Anonymous 2004) does not consider soil above the root collar as part of root ball depth. There is good evidence for reduced as well as for equal growth rate in the nursery when the root collar is installed deeply in container substrate depending on study location, planting depth, and taxa (Browne and Tilt 1992;Fare 2005;Gilbin et al 2005;Byran et al 2010;Harris and Day 2010). Gilman and Harchick (2008) and Harris and Day (2010) showed that certain taxa generate adventitious roots from the buried stem in the nursery container or after landscape planting from small containers.…”

“…There is good evidence for reduced as well as for equal growth rate in the nursery when the root collar is installed deeply in container substrate depending on study location, planting depth, and taxa (Browne and Tilt 1992;Fare 2005;Gilbin et al 2005;Byran et al 2010;Harris and Day 2010). Gilman and Harchick (2008) and Harris and Day (2010) showed that certain taxa generate adventitious roots from the buried stem in the nursery container or after landscape planting from small containers. They agree that adventitious roots may function to aid in establishment of certain deeply planted young trees, although some taxa do not appear to have the capacity to grow new roots from the buried stem.…”