Root Grafts

Although natural root grafts between white pine trees stimulate growth of residual stems following thinning, the prevalence of such grafts is unknown. As roots of harvested stems continue to absorb soil moisture and nutrients and to compete with pioneer vegetation endeavoring to become established, growth improves for residual stems grafted to a harvested tree. Thus, water consumption by residual trees adjacent to openings in a canopy made by thinning keeps such clearings relatively barren of vegetation for years.

Both intraspecific grafting and unions of the roots of a single tree have been noted for both wet and dry sites and in stands ranging from 15 to 70 years of age. During periods of moisture stress, water supplied through root unions permits survival of trees some distance from streams. Apparently the phenomenon occurs mostly among stems in a cluster of trees.2

Flowers and Seeds

Flowering of white pine in its southern range extends from May to mid-June, when yellow staminate cone-like blossoms appear on new shoots of lower branches and small, pink ovulate flowers with purple scale margins occur on the ends of upper shoots. The green conelets, an inch long at the end of the first season, grow to maturity during the second summer. Elevational distinction within the tree precludes selfing and the consequent production of hollow seeds the staminate strobili are carried by wind from these low branches to the female flowers high among the foliage of neighboring stems. Natural crossing among trees within the species follows.

Watershed Protection

As forests of white pines in the South are generally indigenous to mountainous areas, they often clothe lands dedicated to the production of clean, clear water. Even where timber is an important commodity, white pines aid in maintaining favorable watershed conditions. The depth of litter and unincorporated humus tends to be greater for a longer period of the year than in broadleaf forests, as most of the litter layers of fallen leaves and twigs of hardwoods decompose in early summer. With litter depth constant throughout the year, white-pine forests continuously provide favorable rates of rainwater infiltration into the soil surface.

Figure 3.2 A second-growth white pine stand in the northern reaches of the Southern Appalachian Mountains. These pioneer species seed-in on abandoned agricultural land and almost always occur in even-aged stands. While the crowns at a distance give the appearance of an even-sized woodland, dominance expresses itself early; stems of many sizes are in the understory. (USDA Forest Service photo by E. Shipp, 1936)

Figure 3.2 A second-growth white pine stand in the northern reaches of the Southern Appalachian Mountains. These pioneer species seed-in on abandoned agricultural land and almost always occur in even-aged stands. While the crowns at a distance give the appearance of an even-sized woodland, dominance expresses itself early; stems of many sizes are in the understory. (USDA Forest Service photo by E. Shipp, 1936)

White pines may, however, over several rotations, alter crumb-mull humus layers in once-deciduous woodlands to a less-porous mull and mor humus—the latter with minimal organic matter mixed with the mineral component of the surface horizon. Infiltration through mor humus layers is generally slower than for crumb-mull types. For example, 7 inches of rain seeps into the soil in a cove-hardwood stand within a minute, while 5 minutes are required under a 30-year-old stand of white pine. The thick mat of needles under the conifers also absorbs water from light storms, holding it like a sponge until evaporation removes it. This rainwater is neither used by plants nor percolated into streams for later consumption.3

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