Effects of polyethylene mulch in a short-rotation, poplar plantation vary with weed-control strategies, site quality and clone

Abstract

The utility of mulching in various forestry applications remains unclear due to mixed results in field trials. Additionally, few studies have attempted to assess the utility of mulching across a range of conditions, to determine the circumstances that maximize the degree and longevity of mulching-related enhancements. The objective of this study was to gauge the effect of black polyethylene mulch (poly mulch) across a range of site conditions, weed-control treatments and genotypes in a short-rotation, poplar plantation, to describe the circumstances that maximize the benefits of mulching on early growth and survival. Poplar plantations composed of one native clone ( Populus deltoides Bartr. [D105]) and one hybrid clone ( P. nigra L.×P. maximowiczii A. Henry [NM6]) were established in a randomized complete-block design ( 2.4 m×3 m spacing) during May, 1999, under intensive and minimal weed-control strategies at two sites of different soil quality. Nested within each weed-control treatment was an assessment of tree performance using poly mulch vs. no mulch. Stem volume increments (SVI, dm 3) were measured on trees in all treatments during the 1999 and 2000 growing seasons. During establishment (1999), poly mulch enhanced SVI in all treatment combinations. In the second year, the benefit of mulching was restricted to conditions of higher vegetative competition and lower site quality. The relative benefit of poly mulch (i.e., the ratio of SVI under mulched vs. non-mulched conditions) increased in the second year in conditions of high vegetative competition at both sites, while it decreased in the intensively managed plots at both the sites. Tree survival exceeded 90% for both the clones in all treatment combinations, except under the greatest vegetative competition (i.e., high-quality site with minimal weed control), where survival for D105 fell below 40% in both mulched and non-mulched conditions. While poly mulch may improve early growth in short-rotation, woody crop plantations under a wide range of conditions, its practical utility appears to be restricted to specific applications. At the high-quality site in this study, mulching showed little potential as an economically feasible tool under either intensive weed control (due to the rapid attrition of mulching benefits) or minimal weed control (due to low survival and slow growth). Conversely, on marginal sites poly mulch may provide a more attractive management option in both intensive and minimal weed-control applications, particularly for certain clones.