266 Sjöman et al.: Habitat Studies Identifying Potential Trees for Urban Paved Environments ping were used, with 62% water runoff (Lin et al. 2007). Mean annual precipitation in Yangping exceeds that in Qinling by 215 mm, but the runoff data were considered suitable as the distribu- tion and intensity of rain were closely correlated in both areas. Estimates of water runoff data for park environ- ments and urban paved areas of Copenhagen were based on P90 (2004), including 10% runoff from park environ- ments and an expected 70% water runoff from paved areas. RESULTS Study Plots: Soil and Surface Conditions In all plots except three (plots 3, 5, and 11), soil depth was at least 50 cm, indicating that tree roots can penetrate into deep- er soil (Table 2). However, shallow bedrock and rock out- crops partly limited the soil depth in the majority of the plots (Table 2). The soil texture was similar for all plots, with high to very high levels of silt (mean 53%) and low con- tents of clay (mean 2.3%) (Table 2). The organic matter con- tent was also low across the plots (mean 36.3 g/kg) (Table 2). Study Plots: Cumulative Water Net and Surface Runoff With regard to the present situation in Copenhagen, the negative water status for urban paved areas gradually increases from April onwards, while there is an increase in surface runoff in the au- tumn and winter. Park environments in Copenhagen experience partial water stress from June, with a less dramatic trend through- out the season (Figure 3). Under current conditions on steep south-facing slopes in the Qinling Mountains at 1000–1500 m asl., the plots experienced partial water stress in April and June, and more severe water stress in July and the remainder of the growing season (Figure 3). Hence, there is a clear discrepancy be- tween the water stress status in Qinling and that in paved sites of Copenhagen today. This is mainly due to the higher precipitation Plot no. 1 2 3 4 5 6 7 8 9 Altitude (m asl.) 1490 1500 1160 1190 1220 1400 1320 1350 1590 10 1560 11 1280 12 1290 13 1280 14 1260 15 1370 16 1400 17 1410 18 1350 19 1390 20 1360 Mean ©2010 International Society of Arboriculture Slope aspect South Southeast Southwest Slope steepness (degree) 64 49 53 South/Southwest 50 South/Southeast 51 Southwest Southwest Southwest South 43 53 43 40 South/Southeast 43 South South 20 44 South/Southwest 35 South South 45 44 South/Southwest 38 South/Southwest 49 South/Southwest 44 Southeast South 43 45 No. soil samples pH (30–50 cm) 7 10 rate in Qinling, as the area receives an additional 287 mm rain in the summer season (May–September) compared with Copen- hagen. However, temperatures during the corresponding period are 4.7°C higher at the study site in China, which leads to much more efficient evapotranspiration compared with Copenhagen. Study Plots Species Composition and Performance A total 306 trees divided between 25 species representing 21 genera were found in the study plots (Table 3). Combining the plot data with general observations on species occurrence across the woodland systems revealed that a large proportion of the 25 species mainly or exclusively grow on steep, south-facing slopes, while other species occur both on south-facing slopes and in valleys and slopes with different orientations (Table 1). Acer davidii, Kalopanax pictus, Pinus armandii, Quercus spi- nosa, Rhus potaninii, and Tilia paucicostata were present in great numbers in river valleys and north-facing slopes, where they de- velop into large canopy trees (Table 1), while their occurrence on hot and dry south-facing slopes was more scattered. On the latter, their growth is slow and/or underdeveloped, primarily occurring in the understory (Table 3). In contrast, Ailanthus altissima, Car- pinus turczaninowii, Celtis bungeana, Cercis chinensis, Fraxinus chinensis, Koelreuteria paniculata, Morus mongolica, Ostrya ja- ponica, Quercus aliena var. acuteserrata, Q. baronii, Q. wutaishan- ica, Sorbus folgneri, Syringa pekinensis, Ulmus glausescens, and Ulmus pumila were mainly found on steeper parts of south-facing slopes, where they develop into tall, old trees (Table 1; Table 3). Based on the numbers of individual trees, age and growth (height and DBH) (Table 3), it is possible to divide the 25 tree species into two groups. Group 1 includes the species which have their main presence in river valleys or on north-facing slopes, whereas on steep south-facing slopes they are small and/or slow-growing individuals. Group 2 includes species which de- velop into tall, old trees on steep south-facing slopes at altitudes between 1000 and 1500 m asl. The exceptions to this grouping Table 2. Compilation of plot data. Rock outcrops in the plots were classified as N (None 0%), V (Very Few 0%–2%), F (Few 2%–5%), C (Common 5%–15%), M (Many 15%–40%), A (Abundant 40%–80%), or D (Dominant >80%). Rock outcrops 6.7 F 6.8 N 0 (max 25 cm) 6.5 C 9 0 (max 25 cm) 6.0 A 10 5 5 6.6 F 6.4 F 10 10 0 (max 20 cm) 7.3 A 6 6 2 6 5 2 6 7 5 6.7 Field layer cover (%) 20 20 20 30 30 10 6.9 M 40 6.0 C 7.2 V 7.6 N 50 20 20 20 6.8 M 30 6.9 M 40 6.4 C 6.9 V 7.0 C 6.8 A 6.5 C 5.8 F 6.5 A 30 40 30 10 40 30 10 27 Plot size (m) 10x10 10x10 10x10 10x10 10x10 10x10 10x10 10x10 10x10 10x10 10x10 30x30 10x10 10x10 10x10 10x10 10x10 10x10 10x10 10x10 Organic matter (g/kg) 17.4 25.9 65.6 29.3 89.6 18.8 41.0 21.8 41.3 23.0 59.4 39.3 48.0 51.1 31.0 44.5 54.8 22.6 16.8 44.8 36.3 Clay content (%) 3.0 2.3 2.2 2.7 2.2 2.0 2.5 3.0 2.7 2.5 1.3 2.6 1.4 1.6 2.5 1.8 1.6 3.0 3.0 1.9 2.3 Silt content (%) 63.0 53.1 56.8 56.7 47.0 48.2 59.2 61.9 59.4 52.7 33.6 54.5 41.7 45.7 53.8 44.3 44.0 60.2 58.6 47.5 53.0
November 2010
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