Local neighbourhood effects on sapling growth in a young experimental forest

Abstract

Mixing different tree species in forest plantations might increase stand productivity and resilience compared to monocultures, but mixing effects in the early stage of mixed forest plantations are still poorly understood. In general, sapling growth is affected by environmental factors, sapling species identity, direct and indirect interactions with neighbouring saplings, and competition with the ground layer vegetation. We assessed the diameter increment, height increment, and height to diameter ratio of ca. 5500 permanently marked saplings growing in local neighbourhoods that differ in number and identity of the sapling species present. We found that sapling growth was related to the sapling’s species identity and the characteristics of its local neighbourhood (notably phylogenetic diversity, relative size asymmetry, and ground vegetation cover). The identity of the neighbours only mattered when target and neighbour tree species differed in, for instance, light requirements. The growth of the young saplings was positively affected by tall neighbours and ground vegetation cover. This suggests that careful species selection when designing mixed forest plantations is important and that ground vegetation can be favourable for sapling growth in the first years of a new plantation.