Rationale for growing southern pine seedlings at low seedbed densities

Abstract

Application. Growing bare-root southern yellow pine seedlings at low seedbed densities can improve the morphology of the seedling by increasing diameter and root system volume without increasing seedling height. The outplanting of morphologically improved seedlings can increase the per hectare volume production at age 10 to 20 years by as much as 30 m3/ha per mm increase in root collar diameter (within the range of 2 to 6 mm). However, the economic gains of planting these "morphologically improved" seedlings will depend on proper seedling handling and plantation management.Abstract. Although most bare-root pine seedlings in the Southern United States are grown at seedbed densities near 300/m 2, the density used in other regions of the world is often less than 200/m 2. One rationale for growing seedlings at lower seedbed densities is based on the desire to reduce the time required for successful stand establishment. Achieving a one-to two-year advancement in stand establishment can result in an additional 15 to 30 m3/ha within 15 to 20 years. Although seedling grade studies have demonstrated similar gains in volume production at ages 10 to 30 years, the findings from these studies are not widely known. The rationale in the Southern United States for growing at higher seedbed densities appears to be based on: (1) misinformation regarding the performance of morphologically improved seedlings; (2) a desire to minimize seedling and planting costs; and (3) density recommendations that are not based on volume growth in the field.

Net effect of competing vegetation on selected environmental conditions and performance of four spruce seedling stock sizes after eight years in Qu�bec (Canada)

“…On sites where survival is not uniformly high, seedling size is often positively related to survival [30,32]. On our study sites, average survival rate was greater than 80% and stock size had a minor impact on survival.…”

Chloropicrin as a soil fumigant in forest nurseries

“…However, with some companies, s d g s are assessed a higher value due to a consideration of the net present value of the seedlings with respect to timber production. In other words, genetically improved stock (South 1987) and morphologically improved seedlings (South 1993) have a higher net present value than unimproved seedlings. In some situations, the net present value may be six times higher than the cost of production.…”

Economic returns from enhancing loblolly pine establishment on two upland sites: Effects of seedling grade, fertilization, hexazinone, and intensive soil cultivation

“…Higher RCD seedlings could be obtained by culling 50% of the seedlings (which would double the cost to $50 per thousand) . However, morphologically improved seedlings (South 1993) with a mean RCD of 6 mm can be obtained for $40 per thousand . For this analysis, higher RCD seedlings will be assigned a cost of $40 per thousand and will cost 10% more to plant by hand (Blake and South 1991) .…”

“…Some foresters believe that seedling performance is related to RCD and that with proper planting, seedlings with large diameters tend to survive and grow better than small diameter seedlings (McGrath and Duryea 1994 ;South 1993). In one study with slash pine (Pinus elliottii Englm .…”

“…), a 1 mm increase in RCD resulted in an additional 34 m3/ha by age ten (Bacon 1979) . Although a few studies have shown gains as high as 40 m 3/ha/mm after 19 years growth, gains of 4 to 25 m 3/ha/mm are more common (South 1993) . However, other foresters believe that a 1 mm difference in RCD will "wash out after a few years" and that small nursery induced differences in RCD will not affect long-term growth .…”