Optimum seedling productivity in cottonwoods: A function of neighbor distance

In most wind-dispersed species, young seedlings usually grow in clusters. Dense stands of seedlings are however not often recommended for most restoration sites due to poor stand growths. We evaluate the effect of varying neighbor distances on biomass (above ground) and survival of Cottonwood (Populus deltoides) seedlings. We used four different neighbor distances (5, 15, 25, and 35 cm) as treatments and planted seedlings in the field in hexagonal arrays. Each array had 31 equidistant seedlings. Bases on the position, seedlings were categorized as growing in the ‘core’ or the ‘edge’ in the array. Morphometric measurements of seedling, seedling biomass and survival were recorded. Seedling biomass was lower in treatments where neighbor distances were large, 35 cm or small, 5 cm. There was an optimum neighbor distance (15 cm) where seedlings had the greatest biomass accumulation. Morphometric comparisons of plants growing in different treatments showed that, seedlings had greater stem diameter and more leaves at the neighbor distance of 15 cm than at other distances. Seedling survival did not differ among the four treatment types but was significantly different based on the position of the seedling within an array, with greater survival in the core region than the edge.