Silvicultural and pathological evaluation of Scots pine afforestations mixed with deciduous trees to reduce the infections by Heterobasidion annosum s.s.

One possible option to avoid infections of the root rot fungus Heterobasidion annosum s.s. in plantations of Pinus sylvestris is to thin as few times and as late as possible. For this purpose, experimental plantations of P. sylvestris were established on former agricultural land in central Lithuania, where pine seedlings had been sparsely planted in different mixture schemes with the deciduous species Robinia pseudoacacia, Amorpha fruticosa and Betula pendula. As a control, two plantations of pure P. sylvestris were established at the same site in different densities. We estimated tree and stand characteristics in the experimental plantations at the age of 25 years and identified the community of wood-inhabiting fungi. No infection of H. annosum s.s. was found. The results showed that intercropping allows delayed thinnings and a better economical result could be obtained in mixed than in pure pine stands. Crown width and stem taper of the individual trees, however, were negatively affected by the wide spacing, but still remaining acceptable from a silvicultural point of view. The fungal flora differed between externally healthy and declining pines within a forest site. Higher mycodiversity was revealed in wood of declining trees.