Riparian buffer growth and soil nitrate supply are affected by tree species selection and black plastic mulching.
Truax, B., Gagnon, D., Lambert, F., & Fortier, J. . 2017.
Abstract
Tree species selection in the design of agricultural riparian buffers is important to optimize particular ecosystem services, while vegetation management (weed treatment) is often critical in obtaining first-rate tree growth and survival. This farm-scale study took place along a 1 km section of a headwater stream in southern Québec (southeastern Canada). Five tree species with contrasted ecological characteristics were planted (Populus × canadensis, Fraxinus pennsylvanica, Quercus macrocarpa, Quercus rubra and Pinus strobus), with black plastic (polyethylene) mulches as the vegetation management method, as well as a control with no vegetation management, all within a fenced herbaceous riparian buffer. Tree growth and survival were measured along with soil nutrient supply. Significant Species × Vegetation treatment interactions where observed for all growth variables (p < 0.001), but also for soil nitrate (NO3) supply (p < 0.01). All species benefited from the plastic mulch treatment, but varied greatly in their responses. After 5 years, mulched hybrid poplar produced 774 times more stem volume than red oak without mulch. Across all species/vegetation treatment combinations, a 13-fold variation in soil NO3 supply rate was observed during the 4th growing season. Compared to the other species, NO3 supply rate in hybrid poplar plots was 39-87% lower in the plastic mulch treatment and 48-62% lower in the control treatment. Significantly higher soil NO3 supply rates were observed beneath the mulches of non nitrophilous species (white pine and red oak). Red oak growth was negatively correlated with NO3 supply (R2 = 0.57, p < 0.05) in the mulch treatment. Early-successional nitrophilous species (hybrid poplar and red ash) planted with the plastic mulch led to the lowest increase in soil NO3 and the greatest gains in buffer structural attributes (stem volume, diameter and height). Hybrid poplar growth was positively correlated with soil NO3 supply (R2 = 0.86, p < 0.001) in the control treatment. Natural abandoned field/grassland invaders (white pine and bur oak) grew well without black plastic mulch, while the growth of non-mulched red oaks was marginal. In the control treatment, stem volume was a strong negative predictor (across all species) of soil NO3 supply (R2 = 0.91, p < 0.05), indicating that under herbaceous vegetation competition larger trees have a greater ability to reduce soil NO3. This study provides evidence that particular tree species/vegetation management treatment combinations strongly influence early riparian buffer structural development and soil NO3 dynamics in agricultural riparian zones.
Key Words
Hybrid poplar Red and bur oak Red (green) ash White pine Riparian forest restoration Agroforestry
