Arboriculture & Urban Forestry 38(5): September 2012 tive species. These patterns are indicative of a shift in the over- all makeup of the Chicago urban forest from a complex mixture of remnant, emergent, and planted stands, to one more heavily dominated by the latter two categories and lacking in large, old trees (Figure 9). Much effort has been expended attempting to reverse the trend from oak to mesic species dominance in natu- ral areas in the region, but the necessary resources to influence this trend at a landscape-level generally do not exist. Even where resources do exist, the problem of mesophication (replacement of fire-adapted species by mesic site species) has proven to be a difficult one (Nowacki and Abrams 2008), and may be espe- cially complicated in an urban setting because of the difficulty of implementing high intensity prescribed fire and canopy removal treatments. Planting of oaks into urban settings could alleviate the trend away from oak dominance to some extent, and main- tain oak canopy in some areas. Such activities are likely reflected in the relatively large number of oak stems in small size classes (as these are mostly absent in natural areas; Bowles et al. 2005). However, a wholesale switch to oak-dominated urban plantings is unlikely and may be unwarranted because of the need to main- tain species diversity and landscape resilience in the urban forest (Santamour 2004). A shift in dominance away from oaks and to- ward short-lived, smaller-statured opportunistic species (whether native or exotic) would probably result in an urban forest that has a much lower potential to provide the ecosystem services that are increasingly being touted as the reason to plant and maintain the urban forest (Nowak et al. 2001a). For example, the high cor- relation in this analysis between basal area and canopy structure characteristics suggests that the loss of large trees (which has an exponential effect on basal area), and the reduction in dominance of species with the potential to become large, will likely result in decreased overall canopy cover and structural complexity. The resilience of the urban forest to climatic changes and the introduction of exotic pests may also be affected by the patterns in composition and structure observed in this study. One exotic pest that has recently been introduced and will likely have im- portant impacts on composition and structure is the emerald ash borer. Developed areas with high levels of planted ash trees will be especially hard hit by this pest, but the emerald ash borer will also likely further the shift away from native species dominance across the urban continuum (Poland and McCullough 2006). The Asian longhorned beetle, another potentially devastating forest pest, was detected in Chicago in 1998 and eventually eradicat- ed, but has since become a problem in other urban areas in the U.S. (Haack et al. 2009). The Asian longhorned beetle attacks a wide variety of hosts, including maples and other native spe- cies found in both the natural areas and plantings in the Chi- cago urban forest. An outbreak of this pest would strongly af- fect the urban forest (Nowak et al. 2001b), especially given the ongoing transition from oak to maple dominance in the region. These and other forest pests could exacerbate the expected loss in ecosystem service potential related to decline in oak domi- nance. Forecasted changes in regional climate are also likely to impact the urban forest, but the high species richness of the current landscape could help provide resiliency to these changes (Elmqvist et al. 2003). For example, the inclusion of many spe- cies with southern ranges and high drought tolerance in urban plantings could help the regional forest respond to predicted cli- matic changes (Woodall et al. 2010). However, the transitions in 191 composition and structure indicated in this analysis could reduce the species and age diversity of the urban forest and result in re- duced overall resiliency to both climate change and exotic pests. Acknowledgments. Funding for the Urban Tree Census was provided by The Morton Arboretum and USDA Forest Service Northeastern Area State and Private Forestry and for PLS analysis by Chicago Wilderness, USDA Forest Service, U.S. Fish & Wildlife Service, and Illinois Conser- vation Foundation. The authors wish to thank all of those involved in co- ordination and data collection for the Urban Tree Census, and especially Veta Bonnewell for assistance with accessing and manipulating the data. For comments on the manuscript we thank two anonymous reviewers. LITERATURE CITED Angel, J.R. 2011. Illinois Climate Normals (updated to 1981–2010). Il- linois State Water Survey, Champaign, IL. Boone, C.G., M.L. Cadenasso, J.M. Grove, K. Schwarz, and G.L. Buck- ley. 2010. Landscape, vegetation characteristics, and group identity in an urban and suburban watershed: Why the 60s matter. Urban Eco- systems 1–17. Borchert, J.R. 1950. The climate of the central North American grass- land. Annals of the Association of American Geographers 40:1–39. Bowles, M., M. Hutchison, and J. McBride. 1994. Landscape pattern and structure of oak savanna, woodland, and barrens in northeastern Il- linois at the time of European settlement. pp. 65–74 in Proceedings of the North American Conference on Savannas and Barrens., Illinois State University, Normal, Illinois, U.S. Bowles, M., M. Jones, J. McBride, T. Bell, and C. Dunn. 2005. Temporal instability in Chicago’s upland old growth forests. Chicago Wilder- ness Journal 3:5–16. Bowles, M.L., and M.D. Jones. 2008. Chronological Change in Old Growth Forests of the Chicago Region. Report to the Illinois Depart- ment of Natural Resources and the Chicago Wilderness. The Morton Arboretum, Lisle, Illinois, U.S. Buckley, D.S., J. Isebrands, and T.L. Sharik. 1999. Practical field meth- ods of estimating canopy cover, PAR, and LAI in Michigan oak and pine stands. Northern Journal of Applied Forestry 16:25–32. Cadenasso, M.L., S.T.A. Pickett, and K. Schwarz. 2007. Spatial het- erogeneity in urban ecosystems: reconceptualizing land cover and a framework for classification. Frontiers in Ecology and the Environ- ment 5:80–88. Elmqvist, T., C. Folke, M. Nyström, G. Peterson, J. Bengtsson, B. Walk- er, and J. Norberg. 2003. Response diversity, ecosystem change, and resilience. Frontiers in Ecology and the Environment 1:488–494. Fehrenbacher, J.B., D. Alexander, I.J. Jansen, R.G. Darmody, R.A. Pope, M.A. Flock, E.E. Voss, J.W. Scott, W.F. Andrews, and L.J. Bushue. 1984. Soils of Illinois. Bulletin 778. Urbana-Champaign, Illinois: University of Illinois at Urbana Champaign College of Agriculture Experiment Station and Soil Conservation Service, S.S. Department of Agriculture. Grove, J.M., M.L. Cadenasso, W.R. Burch, S.T.A. Pickett, K. Schwarz, J. O’Neil-Dunne, M. Wilson, A. Troy, and C. Boone. 2006. Data and methods comparing social structure and vegetation structure of urban neighborhoods in Baltimore, Maryland. Society and Natural Resources 19:117. Haack, R.A., F. Hérard, J. Sun, and J.J. Turgeon. 2009. Managing inva- sive populations of Asian longhorned beetle and citrus longhorned beetle: a worldwide perspective. Annual Review of Entomology 55:521. ©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
