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On the natural regeneration of dry heath forests in Finnish Lapland: a review of V. T. Aaltonen (1919)

Abstract This paper reviews the doctoral thesis of Viktor Toivo Aaltonen, published in 1919. The study was the first, and to this date the only detailed ecological description of the structure and regeneration of natural Pinus sylvestris-dominated dry heath forests in northern Finland. The average density of Pinus seedlings was 8766 ha–1. In general, Calluna sites had the most seedlings, followed by Cladina sites, postfire areas and Empetrum sites. Seedling abundance and quality declined with decreasing site fertility and increasing canopy cover. The main limiting factor for regeneration was regarded to be not canopy cover (shading), but its correlate, the intensity of below-ground competition. The mostly small understorey seedlings (10–30 cm) were considered to be unable to grow into the dominant tree layer unless a gap had formed in this layer. Several examples of the asymmetric competition between large trees and seedlings were provided. These included the distance-dependent adverse influence of isolated trees as well as gap and forest edge environments on seedling number and size. Special microhabitats, such as logs and their surroundings as well as uprooting spots, were found to be favourable regeneration sites. A special regeneration microsite effect was demonstrated by groups of seedlings around isolated large canopy trees, termed Tapio's gardens by local people. The study illustrates how the small-scale spatial heterogeneity observed in unmanaged dry pine forests influences tree population dynamics, leading to a wide range of variability in stand structures and successional stages. The value of Aaltonen's study perhaps especially lies in the description of a relatively intact ecosystem type, whose ecological quality has recently declined to the extent of becoming classified as a nationally threatened habitat type.