Arboriculture & Urban Forestry 38(5): September 2012 Arboriculture & Urban Forestry 2012. 38(5): 181–193 181 Origins of the Chicago Urban Forest: Composition and Structure in Relation to Presettlement Vegetation and Modern Land Use Robert T. Fahey, Marlin L. Bowles, and Jeanette L. McBride Abstract. 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 ex- plore relationships among modern land use, presettlement vegetation, and urban forest canopy structure, size structure, and composition in the Chi- cago, Illinois, U.S., metropolitan region. Presettlement vegetation and modern land use combined to influence urban forest composition and struc- ture. 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 land- scape 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. Key Words. Canopy Structure; Chicago; Ecosystem Services; Land Use; Oak; Presettlement; Quercus; Urban Forest. Urban forests are increasingly being recognized for their abil- ity to provide ecosystem services, such as mitigation of urban heat island effects, water retention/filtration, and carbon seques- tration (Zipperer et al. 1997; Nowak et al. 2001a; Pickett et al. 2008). The composition and structure of the urban forest have a very strong influence on its potential to provide ecosystem services (Nowak and Crane 2000). For example, long-lived, large trees have an especially high potential to sequester carbon and to reduce heat exchange and moderate high temperatures through shading and evapotranspirational cooling (McPher- son et al. 1997). The makeup of the urban forest likely varies quite strongly across the patchwork of land use types that com- pose a metropolitan region, which include traditionally defined urban forests in residential and commercial/industrial areas, as well as protected natural areas and parks (Zipperer et al. 1997). Across this mosaic, the composition and structure of the urban forest are related to a variety of drivers, including patterns of pre-urban vegetation, historic, post-settlement and modern land use, underlying geomorphology, and climate (Rowntree 1984a; Rowntree 1986). However, exactly how and why composition and structure vary across the wide range of forest types that make up a metropolitan urban landscape is often not well understood. Naturally occurring vegetation is an important driver of com- position and structure in urban forests (Nowak 1994). However, the degree to which the urban forest is related to historic vegeta- tion patterns depends on the environment and the nature of the pre-urban landscape (McBride and Jacobs 1986; Nowak 1993). For example, urban tree cover is greater in cities that developed in naturally forested areas (Nowak et al. 1996). In such regions, ur- ban areas have remnant, transitional, and emergent stands as sig- nificant components of the urban forest (Zipperer 2002). In desert regions, urban forests are largely a product of planting patterns because of the lack of emergent forest development (Walker et al. 2009). The vegetation of the Chicago, Illinois, U.S., metropolitan region (referred to hereafter as the “Chicago region”) was histori- cally controlled by an interaction between landscape fire breaks and fire processes related largely to American Indian activity (McBride and Bowles 2001). In this region, frequent fire main- tained prairie and oak savanna in much of the landscape, but more closed-canopy forests dominated by oak (Quercus spp.), maple (Acer spp.), and ash (Fraxinus spp.) developed where fire had less impact, such as on the east side of waterways (Bowles et al. 1994). Therefore, the urban forest of the Chicago region is superimposed on a dynamic landscape, which although having a complex pre- urban vegetation pattern, is generally amenable to the development of closed-canopy forests in the absence of frequent disturbance. In addition to pre-urban vegetation, patterns of historic settlement and modern urban development are likely to have a strong impact on the composition and structure of the ur- ban forest. Timing of settlement and development affect forest structure (Nowak 1993; Boone et al. 2010) and pattern of de- velopment may also be important. For example, one would ©2012 International Society of Arboriculture
September 2012
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
