Like the Phoenix of Egyptian mythology, pitch pines often depend on fire for their continuation, as seedings rise from the ashes. Although killed by heat, these pines quickly seed-in following a holocaust on burned-over lands of shallow, dry, charred, and scarred soils. Competing hardwoods also succumb in the fire. That only some pitch pine trees are serotinous suggests this to be an inherited characteristic.29
The tree has fantastic restorative ability following fire. Even when heat kills all the foliage, crowns sprout new needles. New terminal shoots replace charred ones and sprouts at tree bases join with newly germinated seedlings to promptly replace fire-killed stems. Basal sprouting, however, depends on the existence of a basal crook where dormant buds are protected by thick bark. New stems on 90-year-old stumps rejuvenate root systems.
Pitch pine, of course, is not limited to the scalp-locks mentioned earlier. In every locale, regeneration must take place at least every 80 years, for the stands of pine mysteriously break up, apparently not for any pathogenic reason. For this rapid-growing tree, diameters of 20 inches may be exceeded in that time period, even on the relatively sterile sites of the higher elevations. In time, and in the absence of fire, more tolerant hardwoods or shortleaf pines replace the ecologically temporary pitch pine forest. Here, shortleaf pine endures, for its deeper taproot penetrates crevices of crystalline rocks that lie under shallow mountain soils. Stability against strong winds that whip across the ridges is thereby enhanced. Windthrow for pitch pines is attributed to the species' shallower roots in these soils. On the typically warmer, drier, south- or west-facing slope on which this tree grows, only low-value stems of any kind persist, and on damper lands given over to pitch pine, even trees of high-value species are likely to be poorly formed. The species' presence is an indicator of a poor site.
Flowering of pitch pines in the mountain climes extends from late April to mid-May. The trees produce seeds at an early age, occasionally as young as 4 years. Dispersion of seeds, even where fire is an aid to cone opening, is usually limited to about 300 feet. This limitation continues the scalp-lock appearance of stands in hilly country.
Openings of cones of pitch pine are subject to changes in humidity as well as to changes in temperature. A crude barometer can be made from a cone by gluing a stiff wire to a cone scale and mounting the cone on a board to which has also been affixed a paper chart with lines indicating humidity. The wire moves as the cone scale responds to changes in atmospheric moisture, the wire's free end pointing to the forecast weather conditions on the chart.
Ring-counts are especially undependable in aging pitch pine trees. False rings develop from mid-seasonal growth flushes, while enduring drought prevents the formation of true rings.
Copper Basin—An unusual site for pitch pine includes the Copper Basin of southeastern Tennessee and north-central Georgia. There the species has been planted to effectively reforest the eroded hills. It is the choice tree for reclamation here because of its extensive and fast-growing lateral root system for absorbing moisture and nutrients in xeric infertile situations. The 23,000-acre "desert" was created a century past when smelter fume effluent from copper-refining stacks formed sulfuric acid as it poured from industrial flues into the atmosphere. The descent to the ground of this liquid particulate matter in the form of acid rain lowered soil pH by several units. Vegetation was destroyed, exposing the land to such severe sheet and gully erosion that one authority claimed that by 1954 the soil had been washed away in places to a depth of 16 feet. The smelter fumes are now largely controlled.
Influence of a forest upon air and ground temperature is demonstrated by the appreciably higher summer and lower winter readings in the denuded area than in the forest that surrounds the Basin. Harsh microclimate due to the absence of ground cover makes plant establishment difficult. Throughout the year, loss of water from the soil to the atmosphere is greater within the treeless zone than in the nearby forest. While seeding fume-resistant grasses offers the most promise for amelioration of the worst sites, pitch pine holds its own once grasses control erosion.30
The Barrens of New Jersey31—The Barrens of southern New Jersey, the northernmost subregion of the southern forest, illustrate a unique situation for pitch pine. Stands there have been an ecological entity for study since at least the early days of this century. The interrelationships of the various kinds of vegetation to the nonliving components of the environment fascinate the imaginative mind. Fire has played an important role.
In the vast barrens, pitch pine occurs pure, in mixtures with scrub oaks like bear and blackjack, and commingled with other oak trees such as black, white, scarlet, and chestnut. Shortleaf pine stems are sometimes woven into the canopy. Often true podzol soils, exhibiting ash-white leached horizons, extend to depths of 14 inches. If fires could be excluded for a generation in order to accurately measure site index, the site SI might be between 50 and 65, at best an indication of low land productivity.
Within the barrens are pitch pine plains of even poorer site quality. Here the average tree height at 65 years of age tallies less than 11 feet, and normally developed trees are absent. The virgin forests probably were never lush, but acceptable stands of both pitch and shortleaf pines likely occurred. The place of these pines in ecological succession is temporary, giving way in the absence of fire to deciduous broadleaf trees.
Fires, however, periodically burn the woods, killing non-serotinous shortleaf pine and oaks (white, black, scarlet, and chestnut) in the plains. The inability of broadleaf trees to produce seeds at an early age hinders hardwood reproduction in the oft-burned areas. Even shortleaf pine and hardwood sprouts, both originating in massive clumps, cannot be maintained in such a fire situation. Forest ecologists attribute the stunted growth in the plains solely to burning, with wildfires occurring on average every 8 years—twice as frequently as in the surrounding barrens. No marked differences are apparent between soils of the plains and those immediately beyond their boundaries.
Repeated wildfires took place prior to fire protection by the state, keeping the vegetation at a low level. Shoots from the stumps of fire-killed stems quickly sprouted. Stools from which new shoots arise are 80 or more years of age, each stump producing as many as 200 sprouts. While sprouts from young, small stools exhibit good form, shoots from old or large stumps are likely to be of poor form and rot-infected within a few years of sprouting.
Roots of pitch pine, even though heavily infected with favorable nutrient- and moisture-absorbing mycorrhizae, apparently are little better adapted for the dry soils of the barrens than are
those of more drought-hardy species. Root tips die during periods of moisture stress. Yet, roots of the predominantly taprooted seedlings of the species grow to depths of 3 to 12 inches the first year. Even for a tree's first decade in this xeric situation, taproot depth equals lateral root length—about 2 feet. Shortly thereafter, laterals take over as the most pronounced feature of the root system, eventually extending as far as 35 feet from the stems. Taproots measure as much as 9 feet deep.
Natural root grafts between trees in a stand are not uncommon. Where rock-bound, the roots join, eventually able to translocate moisture, nutrients, and carbohydrates from one stem to another. Interspecific root grafts between pitch and shortleaf pines also have been noted.32
Hardwood trees growing on sandy soils in other situations favorably improve the structure and nutrient levels in the soil. Apparently, this does not hold for the barrens. Even frequent fires there have little adverse effect on soil organic matter, for the warm, humid climate just as assuredly rapidly oxidizes dead tissues in the absence of fire. The dry sands are so sterile that earthworms and myriapods are scarce, due, no doubt, to the low pH of 3.4 to 5, but also to the unavailability of nutritious deciduous tree leaf tissues. However, if the site remains unburned for several years, litter accumulates in places to a depth of 4 inches; the organic matter is then attacked by fungi to bring about its decay and incorporation into the mineral soil.
In addition to fire that encourages sprouting from basal crooks of pine seedlings, burning prepares a seedbed favorable for pine seed germination. Thus seedlings begin to grow, are killed back to the ground by fire, and resprout from dormant buds; the cycle is repeated. Some trees survive each of the fires, giving the appearance of a many-aged forest. Silvical history of the oaks in the Barrens is similar. Hence, 16000 stems per acre (25 in a square yard) occur, yet fewer than a 10th of these may be larger than one-half inch in diameter at breast height when 25 years old.
When farmers abandon cultivated fields in the Barrens, pines and oaks quickly invade the land. Panicums and umbrella sedges also encroach and, within a year, over 100 species of seed-bearing plants arise on a typical acre. The relative number of tree stems on the old fields relates directly to the availability of seeds, both in time and place. Dense covers of herbs especially restrain pine reforestation. The coarseness of the soil, its consequent low colloidal content, minimal moisture-holding capacity, and the lack of organic matter contribute to poor tree growth.
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