Development of forests in the former heathland landscape: changes in the habitat quality, structure of undergrowth, syntaxonomy of phytocoenoses and modern pollen deposition

This study presents changes in the quality of habitats between 1926 and 2013 in permanent units of forest division restored in the 19th century as a result of afforestation carried out in the landscape dominated by heaths and xerothermic grasslands. The research was conducted in the Zaborski Landscape Park, located in the north-western part of the Tuchola Forest - one of the largest forest complexes in Poland. Changes in the habitat quality were determined based on data included in seven consecutive inventory books. Assessment according to the 5-point quality scale was performed on the basis of average height reached by a pine forest stand of a certain age occurring in particular forest subsections. It has been found that the quality of habitat increased over 87 years by two classes, on average from IV to II. The number of species, especially deciduous trees and shrubs listed in inventory books, was an additional parameter expressing the habitat quality. The extent of habitat changes was also determined based on the types of syntaxa, which are represented by releves forming the time series and made more or lass at the same sites by different authors in 1961, 2002 and 2013, i.e. over the period of 52 years. Temporal changes in the structure of phytocoenoses and their syntaxonomic affiliation were determined using the classification and ordination methods. It has been found that in the study area and within the studied time horizon, there was a recession of dry coniferous forest which developed towards mesic (fresh) pine forests. Whereas within the fresh coniferous forest, there were transitions from the poor cladonietosum variant to the mesotrophic typicum variant, or from the typicum variant towards the fertile variant with a large contribution of Fagus sylvatica in the main tree layer and undergrowth. A change in the forest type from a pine monoculture to mixed pine-beech forest was also reflected in the spectrum of modern pollen deposition collected after annual exposures of Tauber traps. In this case, the observations were performed by the same research team over 15 years.