Slash Pine

As a rule, natural stands of slash pine grow only within 125 miles of the South's coasts. The species' abundant seed production, rapid growth, relative tolerance to shade (in contrast to longleaf pine), ability to withstand feral hog rooting and fire (after trees grow beyond the sapling stage), and adaptability to a wide range of sites have enlarged its habitation.

Slash pine stands often inhabit creek drainages because seed sources have been available at just the time—during severe drought—when a fire burned over these lower-elevation lands. This coincidental phenomenon occurs perhaps every few decades. For the same reason, slash pine replaces longleaf pine in poorly drained sandy flats. Both species may seed-in together, slash pines overtopping and crowding out the grass-stage longleaf pines in the lower-elevation moist sites while later fires kill young slash pines on the hills, where the longleaf pine seedlings survive, protected from fire injury in their ground-hugging grass stage. Hence, there is an abrupt transition from slash pine to longleaf pine as one traverses a slope from a creek to a knoll. (The same transitional relationship occurs where loblolly pine, rather than slash pine, competes with longleaf pine. This is especially apparent west of the Mississippi where slash pine is not native.)

Slash pine, usually a subclimax, but a climax species when periodic fires keep competitive trees from attaining dominance, allows favorable forage production for livestock and many wildlife animals. Herbaceous ground cover may exceed 1 ton per acre until stands close. The shade of the canopy then causes rapid decline of grasses and forbs.20

Figure 2.13 Loblolly pine-shortleaf pine forest. This 85-year-old stand in the upper Coastal Plain originated from natural seeding on cotton cropland abandoned during the agricultural depression of the 1890s.

Highly successful plantation establishment has favored the spread of the slash pine range. Indeed it was planted into Texas, well west of its natural western extremity—the Mississippi River— and north into the South Carolina Piedmont until plagued by the pathogen discussed below.

Root Rot—Fomes annosus, the causal agent for annosus root rot, infects slash pine more extensively and severely than any other southern tree.21 Windthrow from even mild windstorms is attributed to the decay of tree roots by this fungus. Ironically, intensive management often increases the infection because the fungus spores—always in the atmosphere—come to rest on freshly cut, gummy, resin-soaked stumps where stands have been thinned to improve the vigor of residual stems. Mycelia grow from the germinated spores down the stumps to roots and via root grafts to nearby healthy trees. Death occurs within about two years after infection. As a rule of thumb, the infection is found in thinned stands that have been planted on abandoned farmland. The disease is not occasioned by the establishment of stands off-site, as sometimes claimed.

Certain evidence of the malady is the premature thinning of tree crowns a year before death. The stringy appearance of decayed wood, another symptom, appears where roots have been broken off from trees recently toppled by wind. The brown-topped fruiting bodies of F. annosus are camouflaged by needle litter at the bases of infected trees; the conks also grow on stumps or roots. The careful observer finds them any time of year. Groups of trees dying simultaneously has led to misdiagnosis, death erroneously attributed to bark beetle infestation. Beetles do enter Fomes-weakened stems, there to girdle the boles and to kill the trees as they feed. Other evidence suggests no carryover of root rot hazard on sites where trees had been clear-cut due to serious infection and subsequently planted with slash and other pines (see Chapter 6).

Mycorrhizae—As with all North American pines, mycorrhizal fungi are necessary for survival of slash pines. The minute hair-like growths on roots aid in exchange of cations between soil and plants. Foresters learned this in planting seeds of the species in islands of the West Indies where pines were not native. Newly germinated seedlings succumbed unless the soil was inoculated with the fungus. Transporting seedlings from nurseries in the South to the islands also provided the microbial spores and infected roots. The fungal strands, clinging to the roots, had been abundant in the nursery soils.2223

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