The extra space allows the seedlings to develop superior root systems for higher resistance to drought and almost immediate growth once planted. Other seedlings can spend much of the first growing season establishing a root system before growth above ground occurs. Second Generation Seedlings are the offspring of a genetically selected seed orchard that has already produced one crop of genetically improved seedlings and the parent trees of poorest performers have been removed. These seedlings must also exhibit minimum length and diameter requirements in addition to origin. SI25 and SI50 are abbreviations for Site Index at age 25 or 50.
Site index is a measure of the productivity of forest soils for a particular species.
It is given as the total height in feet that the dominant trees will reach at the given age. For instance, if a site has a SI25 of 60 for loblolly pine, then at age 25 the dominant loblolly pines in the stand will be 60 feet tall. All PPICs contain nothing but planted loblolly pines, a minimum of 40 acres and must have access to public roads on sites that can be logged at all times. It locates the land, appraises its productivity, negotiates its purchase, prepares its management plan, and arranges tree planting if necessary. Its foresters inspect the tract each December and send reports to both parties.