Consequences of rapid urbanization on plant diversity in a western siberian city

Plant communities respond sensitively to urban sprawl and are therefore considered as indicators for human-induced changes in habitats and landscapes. Ecological effects of urbanization on local plant diversity have been studied in various regions. However, these processes are poorly understood in rapidly growing cities in Western Siberia. In the city of Pavlodar in Kazakhstan, Western Siberia, recent anthropogenic degradation of the original ecosystems occurred as a result of enforced land-use changes (Virgin Land Campaign by the former Soviet Union) and expanding urbanization (from a few thousands to 355,000 inhabitants in 2015). The impacts of these changes on plant diversity may differ between the city core, the suburban zone and rural surroundings. One effect is the spread of alien plant species, which in turn profoundly influence native vegetation. This thesis consists of three studies conducted to investigate the consequences of urbanization for local plant communities in the region of Pavlodar. I considered species richness of native and alien plants, species composition and plant species characteristics (mainly frequencies of different plant life forms) in relation to different urban impacts.
The aim of the first study was to examine changes in plant species composition and abundance along an urban-rural gradient. Plant diversity and abundance as well as the percentage of alien species were recorded in plots on four 20-km long transect lines running from the city centre to the rural surroundings. Various habitat and landscape characteristics were assessed along the transect lines to describe the urban-rural gradient. The results showed that plant diversity increased with increasing distance to the city centre, which contrasts diversity patterns reported from European cities. The percentage of alien species decreased from 45% in the city centre to 23% in the rural surroundings. Local plant species richness, community structure and plant traits were partly influenced by habitat and landscape characteristics, which in turn were altered by recent land-use change.
Vehicles are an important vector for the dispersal of alien plants. Roads with high traffic densities in urban regions may facilitate the invasion of alien plants. The aim of the second project was to examine the effects of road type and distance to the city centre on native and alien plant species in both the aboveground vegetation and soil seed bank of road verges in the surroundings of Pavlodar. I investigated roadside vegetation at 12 sites along roads with two different traffic densities (national and local roads) and at two distances to the city centre (city edge and rural surrounding). At the same sites, the soil seed bank was also examined using the seedling-emergency method. I demonstrated that the type of road and distance to the city centre influence the proportion of alien species in the aboveground vegetation. In the soil seed bank, seed species richness was affected by the distance to the city, while measures of alien seed diversity were affected by both the type of road and distance to the city. The increase of alien plant species along national roads and at the edge of the city could be explained by the propagule transportation through vehicles as well as by specific conditions in the roadside verges. Analysis of plant species composition indicates a delayed response of the soil seed bank to the establishment of alien species. Furthermore, the frequencies of different plant life forms differed between the two road types and were influenced by the distance to the city.
Within the expanding area of the city, new forests were planted for wind protection and to damp extreme climatic conditions between 1960 and 1970. Nowadays, urban forests no longer properly managed, and the increasing needs of people for recreation have to be fulfilled by visiting floodplain forests in the suburban zone. The third study aimed to assess the frequency of forest visitors, their characteristics and activities, and to quantify the effects of recreation disturbance (trampling, damage to ground vegetation and damage to trees and shrubs) and other human-mediated disturbance (waste deposits, soil disturbance, removal of leaf litter layer and ground fire) on the vegetation and plant characteristics of urban and suburban forests in Pavlodar. In urban forests, total plant species richness was reduced by recreation disturbance. In suburban forests, recreation disturbance and other human-mediated disturbance enhanced the colonization success of alien plants. Plant life forms were affected to a different extent by recreation disturbance and other human-mediated disturbances in urban and suburban forests.
To my knowledge, the results of this thesis provide the first evidence on effects of urbanization processes on the biodiversity in Western Siberia. Adequate management actions are required to prevent further degradation of original ecosystems in this Western Siberian city. These findings may contribute that aspects of human well-being and nature are better considered in future planning processes in this region.