Influence of soil compaction on Quercus robur seedlings establishment

Compaction of forest soil due to the increasing use of heavy machinery in forest management can affect seedling survival and establishment. Our study was aimed at assessing the effect of forest operations on soil physical parameters as well as on growth and physiology of Quercus robur seedlings during the first growing season since germination. The study was based on two experiments: one in field, where compaction was simulated by tractor passes, and one in nursery, where compaction was obtained by direct compression of the soil surface on the top of containers using a compression machine in laboratory. In the first experiment two levels of soil compaction were simulated (i.e. 10 vs. 25 tractor passes) and physiological and morphological attributes of the seedlings were measured during and at the end of the first year in field. The higher compaction level has affected the shoot system biomass, the number of growth flushes and leaves, the shoot/root ratio and the main root length. These aspects were accompanied by lower photosynthetic rate and leaf nitrogen content. In the second experiment we investigated the effect on soil compaction on above and below ground morphological traits of seedlings grown in plastic containers during the first month after germination. Three compaction levels were considered. The results showed significant differences between the compaction treatments and highlighted a constraint effect of increasing levels of compaction on root system development during the first growth stages after germination. Especially in Mediterranean forests, as the photosynthetic rate differed greatly between the compaction treatments in late summer, the shorter main-roots developed due to the soil compaction may limit the availability of water and nutrients to seedlings for more favorable climatic conditions after the summer drought.