Current issue: 55(5)
Under compilation: 56(1)
The resilience of closed-crown coniferous stands within the boreal forest of North America is highly dependent on successful re-establishment of tree species following fire. A shift from closed-crown forest to open lichen woodland is possible following poor natural regeneration during the initial establishment phase, followed by the development of extensive lichen cover, which may hinder ongoing recruitment. We examined the development of the crustose lichen Trapeliopsis granulosa (Hoffm.) 18 to 21 years following fire within six sites in the boreal forest of northwestern Quebec, and explored its potential to affect ongoing recruitment during early successional stages of stand development. Germination and survivorship trials were conducted within the laboratory to determine the establishment rate of Pinus banksiana Lamb. (jack pine) on T. granulosa, mineral soil, and burnt duff under two separate watering frequencies (observed and drought). Survival and establishment rates of jack pine were highest on burnt duff, and poor on both T. granulosa and mineral soil. Under the drought treatment, no seedlings survived on any substrates. In the field, T. granulosa cover had a positive relationship with mineral soil cover, and negative relationships with duff cover, ericaceous shrub cover, organic layer depth, other lichen cover, and Sphagnum moss cover. No discernable relationship was found between T. granulosa and tree density, rock cover, dead wood cover or other moss cover. The development of extensive T. granulosa cover in fire-initiated stands can impede ongoing recruitment of conifer species due to its poor seedbed quality, thereby maintaining open forests.
The article includes observations on forest site types in Canada and the United States, with special emphasis on forests of lodgepole pine (Pinus murrayana, now Pinus contorta Douglas ex Loudon) which the author considers a species that can become a favourite exotic tree species in Finland. Some notes are made also about Jack pine (Pinus banksiana Lamb.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. The author was not able to make a systematic forest type investigation, because the journey was made on another purpose. The article describes the vegetation and climate of the visited areas, and divides the forest site types in three groups: Dry forest site types, moist forest site types and grass-herb site types. The vegetation and plant species on several subtypes are described in detail.
The volume 34 of Acta Forestalia Fennica is a jubileum publication of professor Aimo Kaarlo Cajander.