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Hardwood Conversion to Planted Pine

Swank and Vose (1994) summarized over 40 years of research on changes in water yield and timing of streamflow and over 20 years of stream chemistry data after conversion from hardwood forests to eastern white pine plantations. Significant decreases in water yield (up to 25 percent) were attributed to greater leaf area index throughout the year and, consequently, greater interception loss in the dormant season, plus greater transpiration loss in the early spring and late fall and on warm winter days. The magnitudes of high and low flows were reduced by 33 to 60 percent. Streamwater solute concentrations remained similar on the pine and hardwood watersheds. Net accumulations of calcium, magnesium, potassium, and sodium increased by 1.1 to 3.9 pounds per acre on the pine watershed. Decreases in water yield resulting from extensive hardwood conversion to planted pine could potentially impact the availability of future water yields for municipal water supplies.

In a series of papers on timber harvesting in a Carolina Bay, Askew and Williams (Askew and Williams 1984, 1986; Williams and Askew 1988) concluded that pine plantations could be established without harming water quality. Askew and Williams (1984) quantified suspended sediment in drainage waters from active logging sites, site-prepared areas, 3- to 15-year-old plantations, and main ditches in a 2,388-ha Carolina Bay in South Carolina. Suspended sediment in new secondary ditches was significantly greater than in native streams draining an undisturbed hardwood stand. Water in the main ditch near the discharge point averaged 16.4 mg per L, compared to 2.5 mg per L in the undisturbed hardwood forest. Ditch contributions to suspended sediment concentrations were transient, culminating within 2 years of installation.