The number of times a semi-mature tree has been transplanted and/or undercut during cultivation has a huge influence on the tree's ability to survive when it is planted into your landscape scheme.
Few semi-mature trees found growing naturally in the landscape would survive being lifted and transplanted. This is because the only parts of a root system which can absorb water are the very tips of the youngest roots. The thick, woody roots function only as anchorage and ‘pipes' for transporting the water absorbed at the root tips to the base of the trunk.
Trees left to grow naturally in the landscape have root systems which have extended far underground for anchorage and in the search for water. Reducing the root ball to a manageable size for transplanting would mean essentially ‘amputating' the water absorbing part of the root system. Obviously, this would cripple a mature tree, which would be unable to regenerate small roots quickly enough to meet the massive water requirements of its crown.
Commercial nurseries specializing in the production of semi-mature trees overcome this problem by regularly transplanting (lifting and replanting, usually at increased spacing) and undercutting (pruning back the roots underground whilst in situ) their trees as they develop. Doing this at regular intervals curtails the lateral extension of the root system and forces out a mass of fibrous roots close to the base of the stem. The more times this procedure has been performed, the more robust the root system, and the more likely it is to establish when ultimately planted out in the landscape.
Of course, the procedure does require additional investment in labour and machinery, and because the added-value is hidden beneath the soil, an unscrupulous grower can easily increase his profit margin by skimping on undercutting and transplanting. We always check a tree's transplanting history prior to purchasing, and you should too!