Arboriculture & Urban Forestry 37(2): March 2011 CONCLUSION From 1992 to 2000, forest land cover types declined by 17% and the Texas Forest Service (2005) reports that this equated to a loss of more than 10 million trees per year. As such, it is assumed that the current findings measured the changes due to urbanization, and hurricanes to a lesser degree, that have affected tree growth and mortality in Houston. Land cover was shown to significantly affect mortality, in-growth, and growth rates, as exemplified by growth rates being higher in urban developed areas as opposed to non-urban land covers with more natural forest structure. This might explain the discrepancy between the current findings and those of Jo and McPherson (1995) and Smith and Shifley (1984) mentioned in the literature review. Plots with a structure resem- bling more natural, closed canopy-like, forest conditions (e.g., woody wetland) had the lowest growth rates and were similar to those reported in Smith and Shifley (1984). Mortality and in- growth were influenced by land cover, with significantly higher rates in more intensive developed land cover (DH) versus those of low development (DO). Mortality also had a significant relation- ship with tree density, increasing as trees per hectare increased. Growth decreased as crown condition deteriorated (crown width decreased as dieback increased) highlighting the effect of spacing on urban tree growth. In general, hurricane mortality increased with increasing rates of development and might indicate increased urban forest damage and debris in urban areas characterized by open-grown, single trees and urban land covers with low tree den- sity, which corroborates findings from Escobedo et al. (2009). Currently, most urban forest and hurricane literature focus- es on tree species characteristics’ resistance to hurricane force winds (Duryea et al. 2007a; Escobedo et al. 2009) and urban forest structure change in temperate urban forests (Nowak et al. 2004). It is hoped that results from this study can be used to better assess changes in structural characteristics in urban forests of the U.S. Gulf Coast region and to better understand landscape level effects of hurricanes on urban forests and debris generation. A concurrent study is using this data to analyze hurricane effects on tree debris generation and urban forest structure effects on hurri- cane winds and building damage. Using this approach of re-mea- surement permanent plots could be useful in future research to measure actual change in urban tree biomass, generation of green waste from pruning and tree removal activities, and to explore the effects of socioeconomics, urban morphology, and land use change on urban forest structure, function, and ecosystem servic- es. Urban forest structure and function models, such as the i-Tree UFORE/ECO and STREETS models, are being used throughout the southeastern U.S. (i-Tree 2009). However, many of the algo- rithms used are from natural forest and urban tree growth studies from northern or western U.S. regions (Nowak 1994; Nowak and Crane 2002). Results from this study could be used to verify and better adjust growth and mortality algorithms in these models. Acknowledgments. We thank the USDA Forest Service Centers for Ur- ban and Interface Forestry for funding this project. We thank Sebastian Varela, Erick Smith, and Eric Kuehler for field work as well as Ed Macie, The Texas Forest Service, and David Nowak for project support and use of their data in this analysis. LITERATURE CITED Avery, T.E., and H.E. Burkhart. 1983. Forest Measurements 3rd ed. McGraw-Hill Companies, NY. 290 pp. Bechtold, W.A. 2003. Crown position and light exposure classification- An alternative to field assigned crown class. Northern Journal of Ap- plied Forestry 20:154–160. Berg, R. 2009. Tropical Cyclone Report, Hurricane Ike. National Hur- ricane Center. January 23, 2009. AL092008. Burnham, K.P., and D.R. Anderson. 2002. Model Selection and Multi- model Inference: A Practical Information-Theoretic Approach, 2nd Ed. Springer-Verlag, NY. 496 pp. deVries, R.E. 1987. A Preliminary Investigation of the Growth and Longevity of Trees in Central Park. New Brunswick, NJ: Rutgers University. MS thesis. 95 pp. Duryea, M.L., E. Kampf, and R.C. Littell. 2007a. Hurricanes and the Urban Forest: I. Effects on Southeastern U.S. Coastal Plain Tree Species. Arboriculture & Urban Forestry 33(2):83–97. Duryea, M.L., E. Kampf, R.C. Littell, and C.D. Rodríguez-Pedraza. 2007b. Hurricanes and the Urban Forest: II. Effects on Tropical and Subtropi- cal Tree Species. Arboriculture & Urban Forestry 33(2):98–112. Escobedo, F.J., C. Luley, J. Bond, C.L. Staudhammer, C. Bartel. 2009. A hurricane debris and damage assessment for Florida urban forests. Arboriculture & Urban Forestry 35:100–106. Escobedo, F.J., S. Varela, M. Zhao, J. Wagner, and W. Zipperer. 2010. Analyzing the efficacy of subtropical urban forests in offsetting carbon emissions from cities. Environmental Science and Policy 13:362–372. Foster, R.S., and J. Blaine. 1978. Urban tree survival trees in the side- walk. Journal of Arboriculture 4(1):14–17. Gilbertson, P., and A.D. Bradshaw. 1985. Tree survival in cities: the ex- tent and nature of the problem. Arboriculture Journal (9):131–142. Grabosky, J., and E.F. Gilman. 2004. Measurement and prediction of tree growth reduction from tree planting space design in established park- ing lots. Journal of Arboriculture 30:154–159. i-Tree. 2009. i-Tree Software Suite v2.1 User’s Manual. Accessed 10/15/2010. Jo, H., and E.G. McPherson. 1995. Carbon storage and flux in urban residential greenspace. Journal of Environmental Management 45, 109–133. Kuo, F.E. 2003. The role of arboriculture in a healthy social ecology. Journal of Arboriculture 29(3):148–155. Littell, R.C., G.A. Milliken, W.W. Stroup, R.D. Wolfinger, and O. Scha- benberger. 2006. SAS for Mixed Models, 2nd ed. SAS Institute Inc., Cary, NC. McNulty, S.G. 2002. Hurricane impacts on US forest carbon sequestra- tion. Environmental Pollution 116:S17–S24. Nowak, D.J. 1986. Silvics of an urban tree species: Norway maple (Acer plantanoides L.). State University of New York, College of Environ- mental Science and Forestry. Unpublished MS thesis. Syracuse, NY. Nowak, D.J., J.R. McBride, and R.A. Beatty. 1990. Newly planted street tree growth and mortality. Journal of Arboriculture 16(5):124–129. Nowak, D.J. 1994. Atmospheric carbon dioxide reduction by Chicago’s urban forest. In: E.G. McPherson, D.J. Nowak, R.A. Rowntree (Eds.). Chicago’s urban forest ecosystem: results of the Chicago Urban Forest Climate Project. Gen. Tech. Rep. NE-186, Radnor, PA: US. Department of Agriculture, Forest Service, Northeastern Forest Ex- periment Station. pp. 63–81. Nowak, D.J., and D.E. Crane. 1998. The Urban Forest Effects (UFORE) Model: quantifying urban forest structure and functions. In: M. Han- sen and T. Burk (Eds.). Integrated tools for natural resources invento- ©2011 International Society of Arboriculture 65
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