198 exhibited Sjöman et al.: Selection Approach of Urban Trees for Inner-city Environments the data are therefore combined. In contrast, the study sites in Romania and Moldavia large climatological and site-related differences and are hence presented separately. In order to detect site matching between the study sites and the CNE-region, the site-related data are compared with two dif- ferent site situations in the inner-city environment of Copen- hagen, Denmark: 1) urban paved sites; and 2) urban park en- vironments. Copenhagen is used as an example to illustrate growing conditions in a large city in the northern CNE-region. The mean annual temperature of Copenhagen is 8°C–12°C (an additional 1°C–3°C when UHI is included) (US EPA 2009; DMI 2011). Mean annual precipitation in Copenhagen is 525 mm (DMI 2011). When calculating potential water stress (net water difference) for the sites in Copenhagen, park environments were assumed to have 10% water runoff and paved areas 70% water runoff (P90 2004). Case study 1: Qinling Mountains, China China is considered the most species-rich region of the world (Körner and Spehn 2002; Tang et al. 2006). The Qinling Moun- tain range is situated in the central, temperate part of the coun- try and forms a botanic border between the southern and north- ern regions of China, consequently hosting a species-rich flora (Ying and Boufford 1998). Shaanxi province, where the Qinling Mountains are situated, is reported to have 1224 indigenous woody species (Kang, pers. comm. 2009), compared with only 166 in the Nordic countries (Mossberg and Stenberg 2003). The relatively northern location of the mountain range combined with its high altitudes means that plants are exposed to cold winters and warm summer months with periods of intense drought lo- cally (Takhtajan 1986; Breckle 2002) – conditions thar are com- parable to the climate in urban sites of the CNE-region. Field studies were carried out within three different areas in the north of the Qinling Mountain range, located between 1150 and 1590 meters a.s.l. (Sjöman et al. 2010). At the study site, the mean annual temperature in the area ranges from 9°C to 12°C. The mean annual precipitation is 830 mm where 50% of the pre- cipitation occurs predominantly from May to July, mainly as heavy rainstorms (Liu and Zhang 2003; Tang and Fang 2006). The sites for the field studies were located based on climate data, literature, guiding by local botanists, and field inventories. In total, 20 study plots were inventoried, with a total area of 2,800 m2 including a total number of 306 trees divided between 25 species. and Evaluation of site conditions and tree growth The direct exposure to sunlight on the steep slopes creates low air humidity and rapid drying of the soil, which is comparable to the situation at many urban paved sites (Sieghardt et al. 2005). The low organic matter content (mean 3.6%) and neutral pH (mean 6.7) are similar to values reported for urban sites (Craul 1999; Table 1). The Area Qinling Mt. (China) Codri (Moldavia) Rădeşti (Romania) Repedea Hill (Romania) Roşcani (Romania) Bădeana (Romania) Bursucani (Romania) Mean clay (%) 2.3 27.3 16.5 26.8 33.0 17.8 16.4 ©2012 International Society of Arboriculture soil texture was similar for all plots, with high to very high levels of silt (mean 53%) and low levels of clay (mean 2.3%; Table 1). In calculation of potential water net difference, based on Thornthwaite (1948), the study plots experienced partial water stress in April and June, with more severe water stress in July and the remainder of the growing season (Figure 3). In com- parison with urban sites in Copenhagen, the study plots expe- rienced higher levels of water stress than park environments but less stress than paved environments. This discrepancy in water stress status is mainly due to higher precipitation rates in Qinling (Table 2). However, temperatures during the study period were 4.7°C higher at the site in China, leading to much higher evapotranspiration when compared with Copenhagen. A large proportion of the 25 species in the study plots were growing mainly or exclusively on steep, south-facing slopes, while other species occurred both on south-facing slopes and in valleys and slopes with different orientation. The growth pattern of the species in the latter group was slow and/or un- derdeveloped, primarily occurring in the understory (Sjöman et al. 2010). In contrast, Ailanthus altissima, Carpinus turcza- ninowii, Celtis bungeana, Fraxinus chinensis, Koelreuteria pa- niculata, Morus mongolica, Ostrya japonica, Quercus aliena var. acuteserrata, Q. baronii, Q. wutaishanica, Sorbus folgn- eri, Syringa pekinensis, Ulmus glauescens, and U. pumila were mainly found on steeper parts of south-facing slopes. Here, the species had developed into tall, old trees and were present in the canopy as well as in the understory layer (Table 3). Among the species cited, six, A. altissima, K. paniculata, Q. aliena var. acuteserrata, Q. wutaishanica, S. folgneri, and S. pekinensis, had an annual mean height growth of 20 cm or more (Table 3). Case Study 2: Northeast Romania and Moldavia Northeast Romania and the Republic of Moldavia have a tem- perate continental climate, with hot summers, long, cold winters, and distinct seasons. Due to the higher summer temperatures and lower rainfall compared with Western Europe, large forest steppe systems have developed in this area (Breckle 2002). The field studies were carried out in six semi-natural forest reserves. Climate data for the field study areas (Table 2) were obtained from the nearby meteorological stations (Sjöman et al. 2012). In Romania and Moldavia the microclimate had less influence on the study sites due to topographical differences being small. In total, 30 study plots where inventoried, with an allocated area of 1.2 ha, including 1159 trees representing 23 species (Sjöman et al. 2012). Evaluation of site conditions and tree growth The climate of the area, with cold winters and warm, dry sum- mers, has clear similarities to inner-city environments in the CNE-region (Breckle 2002; Sieghardt et al. 2005). Based Table 1. Selected properties of the soil in the study sites. Values shown are the mean of three different sampling depths (after Sjöman et al. 2010 and Sjöman et al. 2012). Mean silt (%) 53.0 54.1 35.8 58.0 58.1 28.7 33.8 Mean humus (%) 3.6 4.4 4.0 2.3 2.7 2.4 1.8 Mean pH 6.7 6.1 5.4 6.7 5.0 5.9 4.8
September 2012
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