7-56

7-56 is a loblolly pine Pinus taeda selection, frequently occurring in seed orchards in southeastern US, either the clone itself or its offspring. It is still deployed to new orchards (2003).

There are 35 initial 2^nd generation selections, which have this tree as a parent. In the initial mating designs, it was chosen as one of four fathers in a common father testing design. That is a contributing reason that it is a common second generation selection. It is much used in research, which further increases the probability that it will have an appeal even in future mass-multiplication.

There exists no reliable estimate of the extent to which 7-56 is used. I’ll try to make an “educated” guess. The total loblolly pine plant production is 1.2 million seedlings (McKeand et al 2003). From a provenance point of view 7-56 can be considered non adapted for half of the use of loblolly pine. I conclude that 7-56 is in seed orchards meant to serve half the seedlings produced. Seed orchards of loblolly pine on an average have 24 clones (McKeand et al 2003). The “effective” average (the average per deployed seedling) can be expected to be lower from purely mathematical reasons. The figure is not weighted with age, and 7-56 can be expected to remain after thinning in mature seed orchards, which are expected to have fewer clones. The clone can be expected to be among those harvested also from seed orchards where all clones are not harvested. 7-56 is a rather abundant pollen producer. There is a 40-50 percent pollen contamination (where 7-56 soon may have a share worth an evaluation of its impact), but I consider contamination. I conclude that 10 percent of the seed orchard crops have 7-56 as either father or mother. Thus I conclude that the annual plantation rate (2003) of offspring to 7-56 is 60 million seedlings. But there are other able to make an educated guess who believes it may by 100 million!

If 50 million is multiplied by a rotation time of 25 years, we get above one billion trees, but as an estimate of the number of living offspring 1 billion may do at the moment.

The total output of NZ 55 was something like 50 million living children, it seems like the annual output of 7-56, thus NZ 55 (or the Swedish contender W4009) do not deserve the title of the worlds most reproductively successful tree.

In seed orchards established the coming decade, I predict it will be common to have one or two offspring to 7-56.

In spite of that 7-56 is the tree in the World which gets its offspring most used and is one of the most known trees and most tested, the breeding value of 7-56 is still an issue of debate where estimates vary by a factor two. From that we learn that even the most fundamental concepts of tree breeding, like breeding value, is far from simple to estimate.

The first digit (7-) indicates that it is a selection of International Paper Company. A permission to use it must formally origin from this “owner” (but that does not concern its offspring).

McKeand S, Mullin T, Byram T, and White T. 2003. Deployment of Genetically-Improved Loblolly and Slash Pines in the South. Journal of Forestry. April/May: 32-37.

Last edit Dag Lindgren 03-05-19