Species diversity patterns in managed Scots pine stands in ancient forest sites

Abstract

Continuity in forest habitats is crucial for species diversity and richness. Ancient Scots pine forests are usually under forest management, which disturbs vegetation and causes differentiation in terms of tree stand age. To date, vegetation variability in ancient Scots pine forests has not been examined based on tree stand age classes. In the present study the continuity of a large Scots pine forest complex was investigated, and a system of sampling plots established in five tree stand age classes: initiation stands (4-10 years), young stands (20-35 years), middle-aged stands (45-60 years), pre-mature stands (70-85 years) and mature stands (95-110 years). Species composition, including vascular plants, bryophytes and lichens, on soil, tree trunks, and coarse woody debris, was analyzed. Based on existing classifications systems, forest species and ancient forest species groups were distinguished. In the studied ancient Scots pine forests the species pool and richness were relatively low, and the vegetation consisted mostly of generalist species. Cryptogams, which can grow on diverse substrates, were the most abundant species. Moreover, most species could tolerate both forest and non-forest conditions. Age class forests provided different environmental niches for species. Initiation stands were optimal for terrestrial light-demanding species, and in terms of species composition, initiation stands were most specific. Young stands were most preferred by species on coarse woody debris, and at this stage of stand maturation epiphytic species re-appeared. The oldest stands were not rich in forest specialists, i.e. species of closed forest and ancient forest species. Cryptogams of closed forests inhabited different substrates, and they were not associated only with the oldest stands. The low number of forest specialists in the oldest stands may be a general feature of acidophilus pine forests. However, it may also be a result of the lack of species sources in the vicinity of maturing pine stands. In managed forests a frequent diversity pattern is an increase in a species pool and richness after clear-cut logging. In the present study we obtained higher species pools in initiation and young stands, but richness was similar in all tree stand age classes. This resulted from taking into account species of different substrates (terrestrial, epixylous and epiphytic species) which changed their participation in the vegetation of subsequent stages of tree stand development.

Fig 1

Location of the study area in Poland (a) and distribution of sampling plots (b). Stand age classes: 1 –initiation stands (4–10 years), 2 –young stands (20–35 years), 3 –middle-aged stands (45–60 years), 4 –pre-mature stands (70–85 years), 5 –mature stands (95–110 years).

Fig 2

Proportion of cryptogam species observed on one (I), two (II) and three (III) substrates (soil, coarse woody debris and trunks) dividing in lichens (l) and bryophytes (b).

Fig 3. Ordination plot of floristic relations between stand age classes.

Supplementary variables: CovT1 –cover of high tree layer, CovT2 –cover of low tree layer, CovS1 –cover of high shrub layer, CovS2 –cover of low shrub layer; CovCWD–cover of coarse woody debris, LEIV–light index, FEIV–moisture index, REIV–reaction index, NEIV–nitrogen index, based on ecological indicator values for species.

Fig 4

Distribution of species in the studied forests a) vascular plants, b) terrestrial lichens and bryophytes, c) lichens and bryophytes on coarse woody debris, d) lichens and bryophytes on tree trunks. a) black boxes: trees and shrubs of herb layer, grey boxes: non-tree vascular plants; b-d) black triangles: bryophytes, grey triangles: lichens; d) numbers after species codes–trunks as substrates for epiphytes: 1 –Pinus, 2 –Quercus, 3 –Picea; supplementary variables: see Fig 3; species codes–abbreviation of the species name consists of three letters of the genus name and three letters of the species name (see S2 Table). Only species observed more than once were included. Tree and shrub species of the T and S layers were excluded from the species list and their cover was included into the analysis as supplementary variables CovT1, CovT2, CovS1, CovS2.

Fig 5. Richness of species restricted to closed forests (1.1).

Means followed by the same letter are not significantly different according the Kruskal-Wallis test and multiple comparisons of average ranks as post-hoc test (p = 0.05).

Fig 6

Richness (a) and cover (b) of ancient forest species (AFS) in stand age classes. Means followed by the same letter are not significantly different according the Kruskal-Wallis test and multiple comparisons of average ranks as post-hoc test (p = 0.05).

Fig 7. Quantitative changes of ancient forest species along time gradient.

Model of species response was generated with the linear degree and Gaussian distribution as analysis options. Black dashed line–species of increasing cover; grey solid line–species of decreasing cover; species codes–abbreviation of the species name consists of three letters of the genus name and three letters of the species name (see S2 Table).