The results from this report are not suitable for further use and publication without agreement from the author

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1 COST Action FP1204 Green infrastructure approach: linking environmental with social aspects in studying and managing urban forests The results from this report are not suitable for further use and publication without agreement from the author STSM reference: COST-STSM-FP Title: Transpiration of urban forests in response to environmental conditions implications for climate change Applicant: SrĎan Stojnić, University of Novi Sad, Institute of Lowland Forestry and Environment, Novi Sad, Serbia. Host: Dr. Josef Urban, Mendel University, Faculty of Forestry and Wood Technology, Brno, Czech Republic. Period: 4 th May th May 2015

2 Background Urban forests have a great importance in improvement of urban environment quality. The previous researches showed that these forests are a significant source of water vapour, which is generated through the processes of transpiration and evaporation. Climate change is expected to decrease summer rainfalls in parts of Central and Southern Europe, leading to increases of number and intensity of summer droughts. Drought results in the reduction of soil water availability which can further lead to the reduction of tree transpiration and, finally, disturbance of water balance in the entire urban area. Sap flow is a key indicator reflecting tree water status and plays a central role in plant drought research. Within the present STSM, we processed and analyzed the data on tree sap flow from two Sessile oak (Quercus petraea (Mattuschka) Liebl.) urban forests Sobesice and Fruska Gora. The forests are situated close to the cities of Brno (Czech Republic) and Novi Sad (Serbia). The aim of the study was to quantify tree transpiration during summer period and examine an impact of summer drought on transpiration. We found that sap flow rates were low in the both forest during the entire observation periods. The preliminary results evidenced that soil water deficit during mid-summer notably affected tree transpiration in Sobesice. In contrast, short periods of soil water deficit in the soil at Fruska Gora did not have large impact on transpiration. Likewise, we found that relationship between sap flow and potential evapotranspiration was slight but significant at the both sites. Introduction Urban forests provide a wide range of benefits to the urban environment (Smith, 1990; Heisler et al. 1995; Yang et al. 2005). Among other things, vegetation has the potential to moderate air temperature not only through shading and the reduction of surface temperatures, but also through evaporative cooling (Shashua-Bar et al. 2009). The water released by the trees has an important role in increasing of the air humidity, thus improving the quality of the urban environment (Orlovic et al. 2005). Climate change will negatively affect forest ecosystems, because the long life-span of trees does not allow for rapid adaptation to environmental changes (Lindner et al. 2010). A very important issue in this context could be a possibly drastic restriction in the water supply of the trees. In natural communities, the frequency and severity of these deficits play a major role in determining the structure and species composition of the vegetation occupying a particular site (Whitlow et al., 1992). Drought events may cause rapid decrease of ground water table that can result in a lack of available soil water in the tree root zone, root mortality and finally in significant decrease of root water uptake, transpiration and photosynthesis rates (Oltchev et al. 2002). Transpiration in plants is mainly determined by meteorological factors, leaf water status, stomatal conductance and soil water potential. Drought results in the reduction of soil water availability and hence in reduction of sap flow (transpiration) rate. Furthermore, reduction in tree sap flow may 2

3 substantially affect water balance in the entire urban area (Sitkova et al. 2014). For that reason, continuous sap flow measurements on trees provide a valuable background for the analysis of physiological processes and of the water balance (Nadezhdina, 1999). Sap flow measurements give reliable, direct estimates of plant water loss, which might be related to plant water use and water status (Escalona et al. 2002). The objective of STSM was to process and analyze the data on tree sap flow, obtained in two urban forests, in order to quantify tree transpiration during summer period and evaluate summer drought impact on transpiration. The altitude of the area is 485 m a.s.l. The climate is temperate continental with a mean annual temperature of 11.1 C and annual precipitation sum of 624 mm (Figure 2). Figure 1. Experimental plots Sobesice (CZ) and Fruska Gora (RS). Material and methods Measurements of sap flow were obtained from two mixed Sessile oak (Quercus petraea (Mattuschka) Liebl.) urban forests Sobesice and Fruska Gora. The forests are located nearby cities of Brno (Czech Republic) and Novi Sad (Serbia) (Figure1). With the populations of 385,000 and 250,000 citizens, Brno and Novi Sad are the second largest cities in Czech Republic and Serbia, respectively. Urban forest Sobesice is located in a mixed Carpineto-Quercetum forest, at the altitude of 360 m above sea level. The longterm mean annual temperature is 7.5 C and the mean annual precipitation is 550 mm. The study site in Serbia is situated at the territory of National Park Fruska Gora. NP Fruska Gora is the oldest national park in Serbia (established in 1960) and today it is favorite place for rest and recreation. It belongs to the association Quercetum montanum typicum. In Sobesice, sap flow was measured at nine trees, from May till October 2014, while in Fruska Gora it was measured at six trees from the beginning of June till October The trees were selected as being representative of the entire stand on the basis of diameter at the breast height (DBH). The measuring principle of sap flow was based on THB (tissue heat balance) method with internal heating and variable power. Besides of sap flow measurements, meteorological observations (air temperature ( C), relative air humidity (%) and global radiation (W m -2 )) and monitoring of the soil water content were performed. 3

4 All measured raw data were processed in Mini32 software (EMS Brno, CZ).The scalingup procedure from the tree to the stand level was performed in Microsoft Excel 2007, based on sap flow distribution in DBH classes at the selected experimental plots (Čermák et al. 2004). Figure 2. Climate diagrams for experimental plots Sobesice (upper plot) and Fruska Gora (lower plot). function we calculated mean sap flow rate per diameter classes. The step of diameter classes amounted to 2 cm. Furthermore, total sap flow per diameter class was calculated by multiplying mean sap flow rate per class and number of trees per class. In order to compare the amount of sap flow and meteorological data, reference evapotranspiration (PET) was calculated. PET was calculated by the FAO Penman-Monteith equation (Allen et al. 1998). Preliminary results Source: Transpiration of single trees was plotted against tree diameter in order to get scaling curves. The scaling curves were calculated for the parts of growing season with constant soil water supply, using power function. Based on mean diameter per class and the obtained We found that daily courses of sap flow were low in the both forests during the entire period of observation. In Sobesice, daily values ranged between mm day -1, whereas in Fruska Gora it ranged from mm day -1. Totally, trees in Sobesice transpired mm of water for 161 days of observation, while in Fruska Gora it transpired mm for 130 days. It was 19.4% and 21.2% of the reference evapotranspiration for the studied period in Sobesice and Fruska Gora, respectively. Also, our results showed that soil water deficit during mid-summer notably affected tree transpiration in Sobesice (Figure 3). In contrast, short periods of soil water deficit in the soil at Fruska Gora did not have large impact on transpiration (Figure4). Observed stand transpiration ranged from 1 to 59% of potential evapotranspiration (PET) for Sobesice and from 2 to 60% of PET for Fruska Gora (Figure 5). We revealed significant dependency of tree transpiration and potential evapotranspiration (PET) in both urban forests (r 2 SOB=0.26; p= and r 2 FG=0.34; p=0.0000, respectively) (Figure 6). 4

5 Figure 3. Seasonal observations of sap flow rate [mm day -1 ] and soil water potential [MPa] (at the depth of 50 cm) in urban forest Sobesice (Czech Republic). 5

6 Figure 4. Seasonal observations of sap flow rate [mm day -1 ] and soil water potential [MPa] (at the depth of 50 cm) in urban forest Fruska Gora (Serbia). 6

7 Figure 5. The ratio between sap flow rate and PET in Sobesice (blue line) and Fruska Gora (red line). 7

8 Figure 6. Linear regression between daily sap flow values (mm day -1 ) and potential evapotranspiration (mm day -1 ) in: Sobesice (upper figure) and Fruska Gora (lower figure). References Allen, R.G., Pereira, L.S., Raes, D., Smith, M. (1998). Crop Evapotranpiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage Paper No 56. Food and Agriculture Organisation, Land and Water. Rome, Italy. Čermák, J., Kučera, J., Nadezhdina, N. (2004). Sap flow measurements with some thermodynamic methods, flow integration within trees and scaling up from sample trees to entire forest stands. Trees - Struct. Funct. 18: Escalona, J., Flexas, J., Medrano, H. (2002). Drought effects on water flow, photosynthesis and growth of potted grapevines. Vitis 41: Heisler, G.M., Grant, R.H., Grimmond, S., and Souch, C. (1995). Urban forests cooling our communities? Proceedings of the Seventh National Urban Forestry Conference (C. Kollin, and M. Barratt, eds.), American Forests, Washington, DC, pp Lindner, M., Maroschek, M., Netherer, S., Kremer, A., Barbati, A., Garcia-Gonzalo, J., Seidl, R., Delzon, S., Corona, P., Kolstrom, M., Lexer, M., Marchetti, M. (2010). Climate change impacts, adaptive capacity, and vulnerability of European forest ecosystems. Forest. Ecol. Manag. 259: Nadezhdina, N. (1999). Sap flow index as an indicator of plant water status. Tree Physiol. 19: Oltchev, A., Cermak, J., Gurtz, J., Kiely, G., Nadezhdina, N., Tishenko, A., Zappa, M., Lebedeva, N., Vitvar, T., Albertson, J.D., Tatarinov, F., Tishenko, D., Nadezhdin, V., Kozlov, B., Ibrom, A., Vygodskaya, N., Gravenhorst, G. (2002). The response of the water fluxes of the boreal forest region at the Volga s source area to climatic and land-use changes, J. Phys. Chem. Earth. 27: Orlovic, S., Klasnja, B., Galic, Z., Pilipovic, A. (2005). Transpiration of poplar clones as a factor of improvement environment quality. Annals of the Faculty of Engineering Hunedoara. Tome III, Fascicole 1: Shashua-Bar, L., Pearlmutter, D., Erell, E. (2009). The cooling efficiency of urban landscape strategies in a hot dry 8

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