Five-year survival and growth of northern red oak (Quercus rubra L) seedlings in upland hardwood stands in south central Iowa
A major concern in the management of Quercus rubra is the the difficulty in regenerating stands that have developed dense understories of shade tolerant species. A study was conducted at two locations in south central Iowa to determine the impact over a five year period of using root graded seedlings, understory control, tree shelters, and overstory reduction on establishing underplanted, 1-0, Quercus rubra bare root stock. Relationships between growth or mortality, and photosynthetically active radiation, red to far red light ratio, basal area, average stand diameter, number of trees/hectare, percent stocking, and various combinations of these variables were tested. Shelters and root grading had the greatest impact on survival and growth of the underplanted seedlings. Annual survival and growth of non-sheltered seedlings was greater than sheltered seedlings after three growing seasons. However, By the end of the fifth growing season non-sheltered seedlings had averaged 221 percent greater growth and 75 percent greater survival than sheltered seedlings. Underplanted seedlings with five or more permanent, first-order, lateral roots had 93 percent greater growth at the McNay site and 407 percent at the Stephens sites, respectively, compared to seedlings with fewer, first-order lateral roots. R-square relationships between growth or mortality, and photosynthetically active radiation, red to far red light ratio, basal area, average stand diameter, number of trees/hectare, percent stocking, and various combinations ranged from 0.00 to 0.66. Spraying and mechanical clearing of the understory prior to underplanting helped underplanted seedlings maintaining a competitive position in the understory. Based on the literature and the results of this study resource managers should: (i) reduce overstory stocking to approximately 60 percent; (ii) use herbicide or mechanical methods to reduce understory competition; (iii) plant bare root stock with five or more permanent, first-order, lateral roots; and (iv) remove the remaining overstory when the underplanted Quercus rubra seedlings are 1.5 m in height in order to aid in the regeneration of Quercus rubra in south central Iowa.