David B. South

Transplant Stress Index: A proposed method of quantifying planting check

This paper demonstrates a simple way of estimating the intensity and duration of planting check by examining height growth patterns. A “transplant stress index” is determined by the relationship between initial seedling height and subsequent height growth. This index is defined as the slope of a linear relationship between initial height and height increment. If the slope is negative, the plants (as a population) are said to be experiencing planting check. When the slope is approximately zero, the stock is said to be recovering from planting check. A steep positive slope suggests the stock has recovered from planting check. TSI values were determined for several conifers including Pinus elliottii Engelm. var. elliottii, Pinus taeda L., Pinus radiata D. Don, Picea sitchensis (Bongard) Carrière, and Larix× eurolepis Henry.

Rationale for growing southern pine seedlings at low seedbed densities

Although most bare-root pine seedlings in the Southern United States are grown at seedbed densities near 300/m2, the density used in other regions of the world is often less than 200/m2. 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.

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

On two well drained Coastal Plain sites, early (4-year) and mid-rotation (12-year) performance of loblolly pine (Pinus taeda L.) was examined in relation to mechanical site preparation, herbaceous weed control, and fertilization with diammonium phosphate (DAP). In addition, seedling grade as determined by groundline diameter (GLD) was a fourth factor evaluated. Of the four factors examined, seedling grade was the only factor to consistently improve fourth-year survival. In Alabama, seedlings with a 2.5 mm GLD averaged 62% survival while 5.1 mm seedlings averaged 83% survival. In Virginia, 1.3 mm seedlings had 73% survival and 5.1 mm seedlings had 79% survival. Calculated volume gains from increasing seedling grade suggest that a 1 mm increase in GLD could amount to an additional 7 to 12 m3/ha at age 12. Seedling size and mechanical site preparation were partly exchangeable in influencing survival and growth. Use of hexazinone on late planted seedlings increased mortality at both sites. Applications of hexazinone increased volume/ha when combined with DAP fertilization. Fertilization with DAP increased 12-year volume/ha only when weeds were controlled with hexazinone or disking.

Relative Growth Rates: a Critique

SYNOPSIS Forest researchers frequently use mean relative growth rates to compare growth of seedlings that differ in initial size. Reasons for using the technique include: 1) to eliminate any size-related growth differences, and 2) to determine which seedlings are inherently more “efficient.” Although this technique is based on the theory that tree growth occurs as a constant percentage of initial size (the compound interest law), researchers apply this technique even when the percentage increase changes with increasing size (the variable interest law). However, such use may lead to faulty conclusions. Several alternative methods of analysis have been proposed to overcome the problems inherent when comparing mean relative growth rates. One potential alternative is the incremental growth analysis method that changes the basis of comparison from trees of equal age to trees of equal size. This method involves plotting the absolute growth rate (e.g. current annual increment) as a function of size at the beginn...

Herbicides and planting date affect early performance of container-grown and bare-root loblolly pine seedlings in Alabama

The survival of bare-root and container-grown loblolly pine (Pinus taeda L.) seedlings exceeded 90% when outplanted in March at two sites in Lee County, Alabama. At both sites, soil moisture and seedling survival were greater in March than in May. A March herbicide application reduced weed biomass by 75–80% at both sites. At the moist site, herbicide application did not affect survival. However, at the drier site, a reduction in weed biomass increased both the percent soil moisture and the survival of May-planted bare-root seedlings. When soil moisture at planting time was less than 13% on a dry weight basis container-grown seedlings survived better than bare-root seedlings. At both sites, reduced weed competition resulted in greater seedling heights and diameters.

Early growth responses from weed control and planting larger stock of Pinus radiata are greater than that obtained from mechanical soil cultivation

Early growth of two grades ofbare-root Pinus radiata D.Don seedlingswere studied in response to four soilcultivation treatments and two weed controltreatments.Soil cultivation treatments included (i) pitsmade by hand, (ii) pits made with an auger,(iii) ripping alone, and (iv) ripping plusdisking. Weed treatments included (i) manualrelease 1 year after planting or (ii) totalweed control for 1 year involving the use ofherbicides and additional hoeing. Bare-rootseedlings were separated into either medium(4.1-mm average root-collar diameter; height25–31 cm) or small (2.8-mm average root-collardiameter; height 14–20 cm) size classes.Growth on this site was excellent and 7 yearsafter treatment, trees in the least expensivetreatment averaged 12.8 m in height. Use ofmedium seedlings and extra weed controlincreased merchantable volume by20 m3 haminus 1 and 19 m3 haminus 1,respectively. When combined, the increase was39 m3 haminus 1. However, none of the soilcultivation treatments caused a significantincrease in merchantable volume. Disking onthis site proved to be of no benefit. Aboundary-line analysis was used to examine themarginal returns from investing in intensivesilviculture.

How can we feign sustainability with an increasing population

Attitudes of human societies toward tree plantations can be a critical factor in determining the source of wood supply in the future. Because human populations will expand substantially in the next century, considerable increases in the demands on native forests will occur. Currently, only a limited amount of tree plantations have been established specifically to provide firewood in developing countries. This may be the result, in part, of a world society that has evolved a general preference for pastures, but an aversion to tree plantations. In total, pastureland and tree plantations amount to 26 percent and 1 percent of the worlds land base, respectively. Nevertheless, our actions today will determine whether children in the future collect firewood from natural stands or from tree plantations. It is estimated that a substantial afforestation program could increase the amount of tree plantations to equal 5 percent of the worlds land base by the year 2050. Ten billion dollars (United States) is a rough estimate of the annual costs for such a program (assuming no overhead or administrative costs). Most of the wood needs could be met from tree plantations. However, if the worlds society wants most of its wood in 2050 to come from natural stands (>80 percent), then tree plantations can be limited to just 1 percent of the land base.

A root-bound index for evaluating planting stock quality of container-grown pines

Pot-binding can adversely affect the performance of container-grown stock. One factor that affects pot-binding is the size of the root system in relation to the size of the container. The aim of this study was to determine if an objective root-bound index (RBI) would be useful when evaluating the quality of pines grown in various types of containers. A RBIdia was determined by dividing the root-collar diameter (RCD) by the cavity diameter (i.e. the distance from one container wall to the opposite container wall, measured at the top of the container cavity and passing over the centre of the cavity) and a RBIvol was determined by dividing the RCD (mm) by the container volume (ml). Field assessments of seedlings produced in six container types in the United States indicate that both RBI methods produced similar results for survival of Pinus palustris (stock with the highest RBI values exhibited the lowest survival). However, the RBIvol method did a better job of separating the performance of two types of peat pots. Both indices were also related to outplanting performance of P. patula cuttings grown in South Africa. When sorting container stock, P. elliottii × caribaea cuttings with RBIvol values greater than 7 might be culled while P. palustris seedlings might be culled when the RBIvol index exceeds 11. Therefore, the target RBIvol value will vary with species and plant type. When tree planting guides cover a range of container types, listing a maximum RBIvol value would provide some indication of when root-binding might reduce plant quality. In addition to RBI, the age of the roots also appears to affect field performance of pot-bound stock. We rejected the hypothesis that age is not related to post-planting survival of Pinus elliottii × caribaea cuttings.

Effect of planting depth on growth of open-rooted Pinus elliottii and Pinus taeda seedlings in the United States

Synopsis Three studies in the Coastal Plain of Georgia were remeasured 7 or 8 years after planting to determine the effects of planting depth on field performance of open-rooted seedlings [root-collar diameter (RCD) ≤ 5 mm]. Average planting depth (i.e, shoot height before planting minus shoot height above ground after planting) for machine planted P. elliottii was 14 cm while hand-planted P. taeda seedlings averaged 9-11 em deep. P. taeda showed no adverse effects on growth when planting seedlings up to 15 em deep. Data for machine planted P. elliottii indicated that seedlings were planted 9 mm deeper on double-beds than on single-beds. Small-diameter pine seedlings < 5mm RCD) were not planted as deeply as seedlings with large diameters (RCD ≥ 5 mm). For P. elliottii planted on double-beds, seedlings planted more than 15 em deep had slightly smaller diameters at breast height than seedlings planted 10 em deep. Although most tree planting guides recommend planting seedlings 7,5 em deep or less, many company plantations have been established by planting at greater depths.

Integrated Pest Management Practices in Southern Pine Nurseries

Integrated Pest Management is a system that combines cultural, biological and chemical technologies to reduce insect, fungal and weed populations to levels below those that result in economic damage. Nursery managers in the southern United States currently use many practices to control pests of southern pine seedlings. Over the last three decades, improvements in chemical, cultural, and biological pest control practices have increased seed efficiency (defined as the number of plantable seedlings produced divided by the number of pure live seed sown) and reduced the percentage of production costs associated with pest control. As crop values increase, the economic thresholds for applying control measures decrease. However, since the statistical power of most trials in bareroot nurseries is low, the likelihood of experiments that detect “real” treatment difference (e.g. those that consistently increase seed efficiency to the point where economic returns are affected) will be low. This paper describes some current practices in southern pine nurseries and provides some economic injury levels for various pest control treatments.