Survival and growth of planted and seeded oak (Quercus robur L.) seedlings with and without shelters on field afforestation sites in Finland

The study focused on the initial development of oak (Quercus robur L.) seedlings on former agricultural fields with or without treeshelters. Additionally, planting and direct seeding were preliminary compared in terms of a parallel small-scale seeding trial. The influence of treeshelters was examined using 120-cm-high polypropylene tubes. Initial success was assessed in terms of average survival rate and seedling height during a 5-year-period after establishment. The study was based on 8 experimental plots, with 3 sheltering treatments (100, 50 and 0% of the seedlings sheltered). A set of seeding plots were established adjacent to the planting experiments. The average survival rate for the planted seedlings was 75–83%. Sheltering had accelerated the height growth of the planted oaks substantially (average height was 60 cm for 0% sheltered, 82 cm with 50%, and 101 cm for 100% sheltered). The sheltered and unsheltered seedlings in the 50% treatment exhibited growth and mortality similar to the 100 and 0% treatments, respectively. The seeded seedlings were much smaller (average 34 cm) and their combined emergence and survival rate (average 56%) was lower than the survival rate in planting. Since the seeding plots did not belong to the same block design as the planting treatments, differences between seeded and planted seedlings were not statistically tested. The seedlings in all treatments were subjected to rapidly increasing competition by the remarkably proliferating weed vegetation, resulting in poor growth and vigor, and high mortality rate in direct seeding but much less so in planting. With an unexpectedly low incidence of herbivory in the study stands, the survival rate of unsheltered seedlings was not significantly lower than that of sheltered seedlings.