Effects of pine straw harvesting on quantity and quality of surface runoff

ABSTRACT:

Pine needles (straw) are an attractive landscape mulching material that protects the soil surface against erosion, conserves soil moisture, moderates soil temperature, and inhibits weed growth; yet it retains a loose, open structure that allows air, fertilizer, and water to easily penetrate the soil surface. Such characteristics have made pine straw a valuable commodity, but the loss of those mulching benefits from pine forests has raised concerns about effects on watersheds where pine straw is harvested. For example, pine straw absorbs the impact of raindrops and slows the speed of runoff, so its removal may increase soil erosion and nutrient losses, and decrease water-holding capacity of the forest floor. To test this hypothesis, three pine-straw harvesting practices and a control treatment (no straw harvest) were compared to determine harvesting effects on water, soil, and nutrient losses in runoff. The 24 plots (six replications of each treatment) were constructed in an established (16 yrs) loblolly pine (Pinus taeda L.) stand that had tree spacing of 3.0 m by 1.5 m (10 ft by 5 ft), and basal area of 41.3 m² ha⁻¹ (180 ft² ac⁻¹). Each plot (2 m by 1 m or 6.6 ft by 3.3 ft) had four percent slope, aluminum borders, and a runoff collector. Simulated rainfall was applied [5 cm h⁻¹ (2 in h⁻¹)] to produce 20 minutes of runoff from each plot. Annual pine straw harvesting clearly increased runoff, soil erosion from 0.5 to 91.6 kg ha⁻¹ (0.4 to 81.7 Ib ac⁻¹), and losses of phosphorus (P), carbon (C), and total Kjeldahl nitrogen (N) in runoff; but these losses were partially controlled by less-frequent harvesting, and declined to control levels when pine straw had accumulated for two years.