Anthropogenic transformation of vegetation in urban pine forests

Abstract

In the paper, we discuss anthropogenic transformation of forest plant communities in Novosibirsk Akademgorodok. The aim of this study was to evaluate the anthropogenic impact on the floristic composition and to identify forest plant communities resistant to invasions. The explored area is about 2500 hectares, it is located in the western part of Novosibirsk Akademgorodok, which is dissected by streets and roads into several fragments (See Fig. 1). The basis of this work is 232 geobotanical descriptions, carried out during 2015-2016. Descriptions of forest vegetation are made at the sites of 25×25 m (625 m2) and 10×10 m (100 m2) of sparse forest areas between buildings (wood layer was taken into account in the area of 250-400 m2). We took into account all vascular plants. We used the dominant approach to classify vegetation. We identified the composition of native, adventive and ruderal species. The degree of anthropogenic stress was considered on the basis of distances from the center of the site to nearby buildings. The geographical coordinates of the center of geobotanical descriptions were determined using GPS/GLONASS. We identified three degrees of anthropogenic stress (See Fig. 3): 1) the highest is the center of Novosibirsk Academgorodok with the lowest remoteness of plant communities from residential buildings (up to 100 m); 2) the average is 500 m from the Akademgorodok center, and the remoteness from residential buildings at the distance of 120-130 m; 3) low degree of stress is the maximum distance from the center of Novosibirsk Akademgorodok and residential buildings (over 400 m). Vegetation was classified by clustering (DIANA), the matrix of dimension was 232×354. We used Spearman's correlation coefficient to assess the relationship between the total number of species, the number of natural flora species, the number of ruderal and adventive species and the area occupied by each community type. The parameters are statistically significant (p<0.05). The similarity between the objects was computed using the Bray- Curtis similarity measure. All calculations are performed using the software R. We identified the types of plant communities within the studied area (See Fig. 2). 1. Anthropogenic birch-pine forests. The closeness to the forest is 30%: Betula pendula, Populus tremula and Pinus sylvestris. The shrub layer cover is 30%: Sorbus sibirica, Syringa josikaea, Syringa vulgaris, Acer negundo and Acer ginnala. In the same layer are Tilia cordata and Quercus robur. The herb layer cover is 60-70%. Among these common ruderal and adventive species are Taraxacum officinale, Plantago major, Poa annua and Amoria repens. Species richness is 12-41 species per 100 m2. We found 195 species, 56 of which are weed (Elytrigia repens, Berteroa incana, Convolvulus arvensis, etc.) and 40 are adventive (Cichorium intybus). 2. Birch-pine forests in the residential area. The closeness to the forest is 75%: Betula pendula is up to 40% and Pinus sylvestris is up to 8%, Populus tremula is also encountered. The cover shrub layer is 20%: Padus avium, Sorbus sibirica, Acer ginnala and Syringa josikaea. This layer is composed of Tilia cordata and Quercus robur. The grass layer is dominated by adventive and ruderal species: Urtica dioica, Plantago major, Geranium sibiricum, Chelidonium majus, Impatiens glandulifera, Aegopodium podagraria and Arctium lappa. Species richness is from 13 to 52 species per 100 m2. The number of species is 285, the number of weed species is 49 and 23 alien species. 3. Birch-pine and pine sedge forests. The closeness to the forest is 70-75%: Pinus sylvestris, often Betula pendula, and there are plantations of Picea obovata. The cover shrub layer is 20%: Sorbus sibirica and Caragana arborescens. The grass layer is dominated by Rubus saxatilis Carex macroura, there are Brachypodium pinnatum and Calamagrostis arundinacea. The moss and lichen layer is represented by Pleurozium schreberi. It forms clumps on old fallen trees. Coniferous litter is found in communities with a capacity of 3-5cm. Species richness is, on average, 32 to 47 species per 625 m2. We identified 144 species, including 6 weed and 24 adventive ones. 4. Birch-pine and pine tor-grass forests. The closeness to the forest is 65-70%; the undergrowth is less than 5%. The cover shrub layer is 10-15%: Caragana arborescens, Sorbus sibirica and Rosa majalis. The vegetation shrub layer is up to 30%: Salix caprea, Viburnum opulus and Frangula alnus. The grass layer is dominated by Brachypodium pinnatum 20-40%, Carex macroura - 10-25%, Rubus saxatilis - 5-10% and Calamagrostis arundinacea - 3-5%. The moss and lichen layer forms specimens on the fallen trees. Its projective cover is 1-5%. Species richness is 18-54 species per 625 m2. In total, 151 species were discovered, including 9 weed and 24adventive ones. 5. Birch-pine and pine grass forests. The forest cover is 60-75%: Pinus sylvestris and Betula pendula (less than 10%). The cover of the undergrowth is 5%. The cover shrub layer is 1%: Caragana arborescens and Sorbus sibirica. The herb layer covers 50-60%, and in some plant communities up to 80%. It is represented by Carex macroura and Calamagrostis arundinacea. The layer of mosses is located in tree trunks and fallen trees; its projective cover reaches 40%. Species richness is 24-57 species per 625 m2. We found 132 species, of them 6 are weed species and 21 are alien species. 6. Birch-pine bracken forests. The forest cover is 65-70%: Pinus sylvestris is 40% and Betula pendula is 20-25%, in depressions Betula pubescens is encountered. The undergrowth is less than 1%. The cover shrub layer is 20-30%, in some plant communities it is up to 50%. It is represented by Sorbus sibirica and Caragana arborescens. The herbaceous layer cover is 80-85%. It is dominated by Pteridium pinetorum, its projective cover reaches 70%. There is a significant proportion of Carex macroura and Brachypodium pinnatum. Species richness is 13-58 species per 625 m2. In this group, 154 species were identified, 5 of them are ruderal and 24 are adventive, the lowest result among the identified groups. A low proportion of weed and adventive species in the composition of grass allows us to characterize this group of vegetation as more resistant to anthropogenic pressures due to competitive abilities of Pteridium pinetorum. We should note correlation between the total number of all species, the number of natural flora species (0.87), and the number of ruderal species (0.81). This indicates that with a decrease in the total number of species, the number of natural flora species decreases. Within the studied area, we determined 342 species of higher vascular plants: 66 ruderal species, 72 alien species, and 9 musci species. There was an increased degradation of vegetation closer to residential areas. On the territories of residential areas, we identified anthropogenically modified vegetation of birch-pine and pinebirch forests with a total area of 61 hectares, in which the proportion of natural flora species is 58%. We established that with a moderate anthropogenic load on birch-pine grass forests located in the development zone, the proportion of synanthropic species increases to 30%, which leads to an increase in the total number of species. Natural forests (birch-pine and pine sedge forests and birch-pine and pine tor-grass forests) with low anthropogenic influence are less susceptible to degradation. In the three groups (birch-pine and pine sedge forests, birch-pine and pine tor-grass forests and birch-pine and pine grass forests) the proportion of natural flora species is 87-89%. In birch-pine bracken forests, the proportion of natural flora species is 94%. Thus, forest vegetation, which is represented over large areas and less fragmented, is more resistant to invasions, and an increase in the number of ruderal species increases the total number of vegetation. Birch-pine bracken forests are most resistant to invasions.