Effect of Soil Humus Cover on the Establishment and Development of Mycorrhiza on Containerised Pinus sylvestris L. and Pinus contorta ssp latifolia Engelm. after Outplanting

The presence of humus was evaluated as a factor affecting the establishment and development of mycorrhiza in Scots pine (Pinus sylvestris L.) and lodgepole pine (Pinus contorta ssp. latifolia Engelm.) during the first growing season after outplanting on two clear-cut sites. Humus proved to be of minor importance for the formation of mycorrhizae. Instead, the colonisation showed a patchy pattern, indicating spatial variation in the amounts of active inoculum. This variation may reflect differences in soil microhabitat and perhaps the mycorrhizal distribution in the logged stands. Total mycorrhizal short-root frequency increased from 10% at outplanting in June to 40-65% in October. The nursery mycorrhiza accounted for 80-95% of the total mycorrhiza at the end of the investigation. However, by this time 60-90% of the seedlings had, to some extent, indigenous mycorrhiza with fungi from the clear-cut sites. Piloderma croceum tended to be formed at a higher rate in the presence of humus than in its absence while another mycorrhizal type increased faster in the mineral soil.