Arboriculture & Urban Forestry 36(6): November 2010 Arboriculture & Urban Forestry 2010. 36(6): 261-271 261 Habitat Studies Identifying Potential Trees for Urban Paved Environments: A Case Study from Qinling Mt., China Henrik Sjöman, Anders Busse Nielsen, Stephan Pauleit, and Mats Olsson Abstract. Trees in urban paved environments are highly exposed to heat, low air humidity, periods of critical water stress, high soil lime content and soil pH, limited soil volume, pollutants, and de-icing salts. Combined with the challenges of climate change and the threat of disease and pest infesta- tions, this has led to considerable and persistent arguments for using a more varied range of trees, including stress-tolerant species, at urban paved sites. Extensive fieldwork was carried out in the Qinling Mountains, China, in a search for tree species suitable for urban paved sites in northern parts of central Europe and in adjoining milder parts of northern Europe (CNE-region), where tree species are exposed to seasonally dry and harsh condi- tions. The study identified habitats in the Qinling Mountain range that are similar to those at sites in paved environments, and analyzed the growth and performance of different tree species in these habitats. A total of 25 tree species representing 21 genera were found, of which 14 species were identified as specialist colonizers of warm, dry south-facing slopes where site conditions are similar to those in paved environments of the CNE-region. Key Words: Habitat Studies; Selection; Site-Adapted Species Use; Urban Paved Sites; Woody Species. Traditionally, a limited number of species and genera dominate the tree stock in city streets and other urban paved sites (in the following simply referred to as urban paved sites). Urban paved sites are defined here as sites where the surface is sealed with hard materials such as concrete, asphalt, paving slabs, or other substances. Recent surveys in European and North American cities show that a few species/genera continue to dominate in these habitats (Pauleit et al. 2002; Raupp et al. 2006; Bühler et al. 2007). Over recent decades, a growing proportion of these commonly used species have shown increasing difficulties in coping with the conditions at urban paved sites. Overall, trees in these environments tend to be greatly exposed to heat, low air humidity, periods of critical water stress, high lime content and high soil pH, limited soil volume, pollutants and de-icing salts (Pauleit 2003; Sieghardt et al. 2005). These negative condi- tions, combined with the challenges of climate change and the threat of diseases and pest infestations (e.g., Sun 1992; Tello et al. 2005; Raupp et al. 2006), have led to considerable and per- sistent argumentation for the use of a more varied range of trees, including species selected for stress tolerance, at urban paved sites (Richards 1983; Duhme and Pauleit 2000; Pauleit 2003). A number of selection programs with the focus on trees for urban sites are underway in different countries (Sæbø et al. 2005). However, the majority of these are concentrating on the genetic aspect of species in current use, with the aim of select- ing suitable varieties and genotypes (Santamour 1990; Miller and Miller 1991; Saebø et al. 2005). In the case of northern Europe, the majority of species used in cities originate from the native dendroflora, representing cool and moist site condi- tions. Therefore, limitations in terms of drought and pest toler- ance continue to constitute the main problems, despite efforts to select suitable genotypes of existing tree species (Sæbø et al. 2005). To succeed in these selection programs, new tree spe- cies must be identified and tested (Duhme and Pauleit 2000). From the perspective of northern parts of central Europe and adjoining milder parts of northern Europe (in the fol- lowing abbreviated to the CNE-region), it is unlikely that the species-poor native dendroflora can contribute a large range of tree species with extended tolerance of the environmental stresses characterizing paved sites within urban areas of the re- gion (Duhme and Pauleit 2000). However, other regions with a comparable climate but with a rich dendroflora may have the potential to contribute new tree species and genera well adapt- ed to the growing conditions in urban paved sites in the CNE- region (Takhtajan 1986; Breckle 2002; Roloff et al. 2009). Water stress is argued to be the main constraint for tree growth and health in the urban environment (e.g., Whitlow and Bassuk 1987; Craul 1999). Research on the drought tolerance of trees has classically focused on physiological reactions in the water balance/water use in terms of transpiration rates, sap flow mea- surements, and the hydraulic architecture of the tree (e.g., Ko- zlowski et al. 1991; Sperry et al. 1998; Breda et al. 2006; David et al. 2007; West et al. 2007) These investigations give valu- able information at the tree level but are limited in their prac- tical everyday use for urban tree planners and arborists (Roloff et al. 2009). Dendroecological studies, such as that presented in this paper, contribute ecological knowledge that can help evalu- ate the reaction and tolerance of different trees species to dif- ferent stressors, and can be a first step in the selection process for ‘new’ tree species for urban paved sites (Roloff et al. 2009). In natural habitats, trees have been stress-tested and se- lected over evolutionary periods of time. Some species have ©2010 International Society of Arboriculture
November 2010
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