Origins of the Chicago Urban Forest: Composition and Structure in Relation to Presettlement Vegetation and Modern Land Use

Urban forests provide important ecosystem services, but species composition and canopy structure influence provisioning of these services and long-term stability of the urban canopy. Two landscape-scale data sets (presettlement land surveys and an urban tree census) were used to explore relationships among modern land use, presettlement vegetation, and urban forest canopy structure, size structure, and composition in the Chicago, Illinois, U.S., metropolitan region. Presettlement vegetation and modern land use combined to influence urban forest composition and structure. Modern forested areas with high native species dominance, canopy cover, and structural complexity were associated with forest (rather than prairie) vegetation in the presettlement landscape. Oaks (Quercus spp.), which dominated presettlement forests and provide high ecosystem service value because of their large stature and wildlife value, were strongly associated with presettlement forest areas and modern natural areas. The Chicago region is in a transitional state where composition and structure of larger size classes is heavily tied to pre-urban vegetation. In the future, this landscape is likely to experience a shift in dominance from oaks to smaller-statured, shorter-lived non-native and opportunistic species. This shift, along with climatic change and introduction of exotic pests, may result in an urban forest with reduced potential to provide important ecosystem services.

Presettlement land survey records of vegetation: geographic characteristics, quality and modes of analysis

Presettlement land survey records (PLSRs) of North America provide insights into the landscape before European disturbance and have been used in various ecological studies. The usefulness of the data, however, varies with their characteristics and qualities. The purpose of this paper is to examine the geographic characteristics of PLSRs, to review PLSR studies in the last five decades and trends in these studies based on the geographic characteristics that have been analysed, and to investigate data quality issues concerning the PLSRs. The framework used in this examination is that of Geographic Information Science (GIScience), including geographic characteristics of space, theme and time, and data quality components of lineage, positional accuracy, attribute accuracy, logical consistency and completeness. The results show that different types of PLSRs have distinct geographic characteristics, especially regarding the spatial characteristics of shape and size/resolution. Prior studies have used PLSRs in six modes of analysis, with presettlement vegetation patterns and compositions analysed most often. Data quality investigations suggest that whether the potential quality issues will influence an analysis depends on the study purpose and the spatial extent of interest. In cases of studying vegetation dynamics of small areas, the positional accuracy of landscape features is essential, while this issue may not impede large area reconstruction. Finally, thoughts concerning future research avenues are presented. This study uses a GIScience framework to provide a more systematic and comprehensive examination of the usefulness and limitations of PLSRs than previous studies, and can assist future research to employ the data most appropriately.