Oak Underplanting Success Program

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Study

Results of an 11-year study of the growth and survival of planted northern red oak (Quercus rubra L.) seedlings (2-0 bare-root) in the Boston Mountains of Northern Arkansas are presented. More than 4,000 seedlings were planted under shelterwood overstories that were harvested 3 years after planting. Results are expressed as planted-tree dominance probabilities.

Dominance probability is the probability that a planted tree will live to attain a favorable competitive position (i.e., at least 80 percent of the mean height of dominant competitors) at a specified year. We interpret the resulting probability as a measure of the competitive capacity of an individual seedling, i.e., its potential of attaining dominance in a specified environment.

Based on our logistic regression analysis, we found that dominance probabilities increase with time after shelterwood overstory removal for any given environment and initial seedling characteristics. At any specified time, dominance probabilities depend on initial seedling stem caliper before planting, site quality, intensity of competition control, and shelterwood percent stocking. Dominance probabilities increase with decreasing shelterwood stocking, increasing initial stem caliper, and increasing intensity of competition control. Other factors being equal, top clipped seedlings have higher dominance probabilities than unclipped seedlings. The reciprocals of the dominance probabilities provide silviculturally useful estimates of the numbers of trees that would need to be planted to obtain, on the average, one competitively successful tree.

For example, if clipped seedlings averaging 1/4 in. in stem caliper were planted where oak site index was 79 ft, shelterwood stocking was 80 percent, and the site was given no competition control before or after planting, obtaining one competitively successful tree 11 years after planting (8 years after shelterwood removal) would require planting 144 seedlings. April 28, 2006aliper to 7/8 inch would require planting only 5 trees to obtain one competitively successful tree. For the same size (7/8 inch) and type of seedling planted on site index 60 ft under a shelterwood at 40 to 60% stocking and given two competition control treatments, only 1.4 trees would need to be planted. Results emphasize the sensitivity of competitive capacity, and thus the silvicultural potential, of planted northern red oaks in the Interior Highlands to the joint effects of field environment and initial seedling characteristics.

Through the use of logistic regression, we examined the struggle between planted seedlings and their competitors, and evaluated the importance of seedling size, site quality and intensity of competition control to seedling success in order to develop planting recommendations that could help breathe new life into these forests. When planting northern red oaks in the Boston Mountains one can maximize the likelihood of their attaining dominance or codominance 11 years after planting (8 years after overstory removal) by: (1) planting large (e.g. > ½ in. stem caliper), shoot-clipped seedlings, (2) planting under shelterwoods thinned to 40 to 60 percent stocking, and (3) controlling competing woody vegetation, including stump sprouts during early establishment similar to methods applied in this study. Competition control treatments are more important on high site index/quality sites due to increased competition.

Note that in this study competition control treatments consisted of applying an herbicide to cut stem surfaces of woody competition > 1 foot tall and £ 1.5 inches in diameter at breast height (d.b.h.). Cut stems of harvested trees were also treated. In this study all woody stems were considered to be competitors. However, in application, desirable species would not be treated in order to further encourage development of the future forest. Oaks would not be planted near these existing trees. See Planting Recommendations.

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