Influence of Tree Root Competition on Growth Response of Four Cool Season Turfgrasses 1

Trees and turf are important elements in most landscaped and recreational areas. However, must turf research has been conducted in full sun far removed from trees. This study was initiated to determine the competitive ability of four cool season grasses subjected to three competition treatments beneath tree shade: (1) silver maple ( Acer saccharinum L.) roots, (2) honeylocust ( Gleditsia triacanthos L.) roots and (3) no tree roots. A connecting pot technique was used to maintain light intensity nearly uniform over tree shaded pots with and without tree roots. A fourth competition treatment was located in full sun separate from all trees. Kentucky bluegrass ( Poa pratensis L.) clipping yields were more affected by tree roots than the other three grasses. Effect of tree roots on perennial ryegrass was intermediate. Red fescue ( Festuca rubra L.) and Poa trivialis responded similarly with or without tree roots suggesting a strong competitive ability. However, all Poa trivialis treatments with tree roots later became diseased. Tree roots in some way reduced growth and vigor of most grasses even when water and nutrients were maintained at optimum levels. In addition to direct competition, biochemical inhibition (allelopathy) may be involved.