Growth dynamics and water uptake of two forest grasses differing in their growth strategy and potentially competing with forest seedlings

Growth characteristics and water uptake were compared on two forest grass species (Agrostis stolonifera L. and Deschampsia cespirosa (L.) Beauv.) to evaluate their potential competitive effects on young forest seedlings. The two grass species were grown in large containers under two watering regimes (regular irrigation that maintained the soil at field capacity or seasonal water stress). Spring regrowth occurred earlier in Deschampsia than in Agrostis. During the summer, under irrigated conditions, Agrostis had higher values of leaf and tiller appearance rates than Deschampsia. Under water-stressed conditions, leaf and tiller appearance rates decreased sharply for both species during the desiccation period, and regrowth was much more pronounced in Agrostis than in Deschampsia after rewatering. Observations of the root systems indicated that Deschampsia developed deeper roots than Agrostis. Despite these differences, evapotranspiration in the irrigated and in the dry treatments were similar for both grasses. In the water-stressed treatments, soil water potential decreased rapidly under both grasses and was slightly lower in Agrostis than in Deschampsia. Although the two grasses had similar soil water uptake, differences in the overall competitive effect of the two grasses on forest tree seedlings might appear because of differences in their phenology, their recovery from drought, and the development of their root system.