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BAD LUCK IN THE NURSERY PRODUCES VALUABLE DATA ON SEEDLING SURVIVAL AND GROWTH

In the spring of 1991, a storm full of rain and hail destroyed some of the slash pine seedlings in beds of an industrial tree nursery, and the extra space available to the remainder allowed some to grow to two or three times the size usually produced for planting. Professors at Auburn University were quick to realize that the storm created a unique opportunity to study early performance of large diameter seedlings. They arranged to have them planted in various test patterns, and Phil Schrock, the graduate student who monitored them, presented the results at the Southern Silvicultural Conference in November 1992. We interviewed Dr. David B. South, one of Shrock's professors and a member of the JMV&CO panel of scientists, to learn implications of the findings, and here's how it went.

JMV:	Tell us what happened after you found the big seedlings.
DBS:	I do not like to use the term "big" because it is too vague and can cause confusion. For example, a "big" seedling could be either tall and spindly or it could be short and fat. However, tall and spindly seedlings do not survive transplanting as well as short and fat seedlings. In fact, what was "big" in 1930 may not be considered as "big" today. In my opinion, it is better to describe the diameter and/or height of a seedling rather than to describe it as just "big". When referring to seedlings grown in the nursery at densities of 20/sq. ft. or less, I prefer the term "morphologically improved." At these densities, loblolly or slash pine seedlings will have larger root collar diameters and will have a better balance between roots and shoots. They will not necessarily be taller than seedlings grown at higher densities, loblolly or slash pine seedlings will have larger root collar diameters and will have a better balance between roots and shoots. They will not necessarily be taller than seedlings grown at higher densities. In fact, the mean height of the 12.5 mm seedlings was about the same as for 6.5 mm seedlings (both average about 32 cm or 12.6 inches).
JMV:	Tell us what happened after you planted the large-diameter seedlings.
DBS:	We selected seedlings that ranged in diameter from 2 mm to 12 mm and had them planted by machine in the normal way by an experienced contractor in October 1991. The site had been prepared by bedding, and half of the plots were later treated with herbicides. Phil Schrock monitored results every three months.
JMV:	What were conditions at time of planting?
DBS:	Soil moisture content was 7%, and the planting machine raised such a cloud of dust that the contractor jokingly said, "We're really dusting these seedlings in." Foresters of the industrial company that supplied the seedlings and planting site thought that we would lose all of them. Then as if to increase the odds against survival, there was no significant rainfall for more than 60 days.
JMV:	So, did they all die?
DBS:	There were two results. 1) Large-diameter seedlings survived much better than small-diameter seedlings. For example, survival of 2.5 mm seedlings was 20%, whereas survival of 9.5-12.5 mm seedlings averaged 85% to 98%. 2) Survival within a diameter class increased with increase in depth of planting i.e, how deep the root collar was buried. For example, survival of a 2.5 mm seedling with the root collar 2.5 cm below groundline was 20%, but survival of the same size with the root collar 17.5 cm deep was almost 40%. Survival of 5.5 mm seedlings planted 2.5 cm deep was about 40%, whereas survival of those planted 22.5 cm deep was 100%. Initial survival was not affected by bedding.
JMV:	What else?
DBS:	In January the industrial company installed an operational plantation adjacent to our experimental plots. Our trees started height growth long before theirs, so it appears that fall planting allows the roots to grow on the site all winter and the seedling to begin vigorous height growth earlier in the spring. We also examined the need for a terminal bud at time of planting. Some researchers have suggested that a terminal bud is necessary to qualify as a high-quality slash pine seedling. However, we found that, when comparing seedlings with equal diameter, there was no difference in survival or early growth. These results are the same as reported by USFS research in 1948. Therefore, for slash pine, the presence of a resinous terminal bud is not necessary to qualify as a high-quality seedling. I do not recommend discarding large-diamater trees just because they do not have a terminal bud.
JMV:	The largest experimental seedlings were 12.5 mm. What do you think will happen if we use even larger ones, maybe ones so large that they must be planted with a post-hole digger?
DBS:	One company successfully transplanted mature seed-orchard trees using a large truck mounted tree spade. Therefore, it is certainly biologically possible to successfully transplant seedlings with diameters that are larger than 13 mm. The real challenge is to identify the system that will optimize the economics of artificial regeneration, i.e., produce the greatest bare-land value. We want to determine if the additional costs associated with growing and planting larger-diameter seedlings can reduce the need for intensive site preparation and can eventually result in a reduction in the per-unit cost of wood production.
JMV:	Didn't you test some applications of herbicides?
DBS:	Yes, with unexpected results. In March the industrial company band-sprayed over both the experimental and the operational trees. The experimental trees had much longer "candles" at that time and absorbed too much of the herbicide, which caused the leaders to be killed. In spite of this, the crown-damaged trees increased in diameter faster than undamaged trees that had not been released with herbicides.
JMV:	Why do you think that double bedding seemed to have little effect?
DBS:	Double bedding is used mainly to improve growth, and we only have preliminary growth data. It may be that, as the seedlings get older, a growth response to double bedding may become more evident. However, the double beds were not substantially higher than the single beds. It appears that the main effect of double bedding was control of woody competitors.
JMV:	We've talked about survival and very early growth. When did you make the last measurements this season, and what were the effects on growth in size?
DBS:	Nine month growth (from October 1991 to June 1992) was positively related to seedling diameter at planting. The average tree volume in June for the 12.5 mm seedlings was much greater than the 4.5 mm seedlings (see the nearby figure). The herbicide treatment (H) reduced height growth in June, but average diameters were not different from the no herbicide (NH) treatment. The double bedding (DB) treatment increased growth slightly over that of the single bedding (SB) treatment.
JMV:	It seems to us that three cultural practices are involved here, large-size seedlings, herbicide treatment, and mechanical cultivation of some type. If all of them were used, maybe each would increase yield, but if you had to choose only one because of limited funds, does your study indicate which would be most effective?
DBS:	The cost of single bedding followed by machine planting of 500 regular (4 mm) seedlings can be $90 per acre. If I only had an additional $15/acre to invest, I would not have enough to spend on a second pass with a bedding plow (about $30/acre). I also would not have enough to apply herbaceous weed control (about $30/acre). However, I could afford to double the price of seedlings (to $60/thousand) in order to get larger diameter seedlings. If you measure the diameter of seedlings on sites one year after planting 3 mm seedlings, many will average less than 8 mm. I therefore believe that we can expect a one- to two-year gain in stand establishment by planting morphologically improved seedlings.