Natural Regeneration

Natural regeneration of the hard southern yellow pines requires three criteria. In addition to the availability of seeds carried with the wind by hymenous-like wings, mineral seedbeds are necessary. Where mineral soil is exposed, seeds promptly germinate and seedlings become established; where covered with grass, pine needles (called straw when accumulated on the ground) or dead leaves, germination and seedling establishment often fails. Too little starch, protein, and nutrients are stored in the tiny seeds to provide sustenance while the root grows through the dry litter toward the soil. Some seeds germinate where the ground is covered with grass or debris or the "rough" of a longleaf pine stand, those seeds falling in crevices that provide contact with mineral soil. Finally, adequate sunlight is necessary. While some seeds germinate under canopies of brush and large trees, these seedlings succumb within several years if the overtopping foliage or water-competing stems are not removed.

Hence, under normal undisturbed and natural conditions, stands of the southern pines sometimes do not naturally regenerate to the same species. Rather, under large old pines, one finds oaks and hickories or other broadleaf trees. These hardwoods compose the climax forest, that assortment of species that continues to be found on the land ad infinitum if nature is left alone and neither wildfire nor hurricane-strength storms occur. These broadleaf plants, in contrast to the southern pines, are shade tolerant. They endure and fare well in undisturbed forests. Eventually, as the shade-intolerant conifers die, broadleaf hardwoods capture the site.

While yellow pines in the South are unable to compete successfully for light with the oaks and hickories, they grow aggressively in other situations. Adaptability as an initial plant in ecological succession on abandoned lands relates to abundance and frequency of seed production, seed mobility, and tolerance to droughty conditions. Loblolly pine has replaced longleaf pine over much of the lower Coastal Plain because of the latter's sensitivity to the timing of fire and to its uniquely sporadic seed production as well as the shorter rotation required by loblolly pine to reach pulpwood-size boles. Fires control a seedling needle blight attacking longleaf pine while a large number of seeds of the species fall only at 10-year average intervals. Ten-year averages may tally abundant seedfall two years in a row and then a 20-year lapse occur until the next crop of seeds matures.

Natural occurrences damage many seedlings. Evidence of injury to young seedlings by cottontail rabbits shortly after seed germination are the mammals' droppings and the trees' nipped stems. The harvest mouse cuts off the small tops of seedlings. Cotton rats remove the edges of seed coats before germination, and fox squirrels chew open the seed coats. Shrews and white-footed mice cut seed hulls. The short-tailed cricket joins in the raid, clipping cotyledon-stage seedlings 1/8-inch from the ground and depositing small fragments of seed leaves in their galleries in mounds nearby. Feral hogs, raccoons, opossums, skunks, pocket gophers, and town ants also hustle their share of southern pine seeds and seedlings.

Figure 2.6 Often it appears that natural regeneration of loblolly and shortleaf pines is readily obtained in dense stands or following partial harvests, like the selection and shelterwood systems. However, these 3-year old seedlings will be dead in another 2 or 3 years, their photosynthetic ability diminishing with age in the early years where a canopy provides shade.

Figure 2.6 Often it appears that natural regeneration of loblolly and shortleaf pines is readily obtained in dense stands or following partial harvests, like the selection and shelterwood systems. However, these 3-year old seedlings will be dead in another 2 or 3 years, their photosynthetic ability diminishing with age in the early years where a canopy provides shade.

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