Architecture, cover and light interception by bramble (Rubus fruticosus): a common understorey weed in temperate forests

Bramble (Rubus fruticosus L.) is a common weed in temperate forest and also in other world ecosystems where it is recorded as an invasive plant. Although it has been described to efficiently compete for water and nutrients, little is known on its competitive ability for light. We described bramble canopy architecture, cover relative to light availability and light interception ability in 60 areas of bramble thicket at 17 sites in France and 1 in England with contrasting soils and climates. The leaf area and leaf number can be predicted by the cane (shoot) length. The leaf inclination distribution was planophile (i.e. leaf laminas distributed in the horizontal plane). There was a good relationship between light interception and leaf area index (LAI) of the different bramble thickets, with no significant site influence, meaning that a single model can be used to predict light interception by bramble in different conditions. Bramble LAI and cover rapidly increased with light availability in the understorey to reach almost 20 cover at only 57 light availability above the thicket. Consequently, bramble is able to tolerate deep shade, which is not in accordance with its reputed moderate to high light requirement reported in the literature and suggests that it is difficult to control this species by manipulating tree canopy. This would have adverse consequences on tree regeneration.