UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre Effects of urban environment on budburst and leaf development on Tilia europaea trees in Gothenburg, Sweden Katarina Bergman Lyck ISSN 1400-3821 B1023 Bachelor of Science thesis Göteborg 2018 Mailing address Address Telephone Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN I. Abstract In cities there is a well-documented phenomenon called urban heat island (UHI), this means that the temperature inside the city is higher than the surrounding countryside. Today the artificial surface in the city consisting of buildings, pavements, cars and traffic, contributes to a temperature rise within the city. Trees and vegetation however, lower surface and air temperatures through evapotranspiration and by providing shade. The modern city generally only have vegetation in parks and a few trees for sun and wind coverage along the streets. Trees provide benefits such as emitting oxygen, screening out particulates and other air pollutants, minimize erosion by intercepting precipitation and modify the surface temperature by shading the ground. An important factor for these benefits is the timing of budburst and leaf development. This study aims to get a better understanding about how the intra-urban air temperatures affects the phenology of Tilia europaea (common lime). T. europaea is the most common street tree in Gothenburg, which is why it is chosen for observation in this study. The study was done through air temperature measurements and observations of budburst at eight sites within the city. Hourly, daily, day-time and night-time average temperatures all shows an increase in temperature during the investigated period. The sites closer to the centre are generally warmer and shows a stronger UHI effect during night than the sites further out. When it comes to budburst and leaf development there is no statistical significance between intra-urban air temperatures and onset of budburst and leaf development.. A possible factor influencing phenology is the growing conditions for the trees at the sites. Vegetation covered ground is favourable over paved ground for tree growth. Also the area the trees can grow in can influence the phenology. Keywords: Phenology · Tilia europaea · Urban heat island · Gothenburg · Sweden I II. Sammanfattning I städer finns ett väl dokumenterat fenomen som kallas stadens värmeö (UHI), vilket innebär att temperaturen i staden är högre än den omgivande landsbygden. I dag bidrar den konstgjorda ytan i staden som består av byggnader, trottoarer, vägar, bilar och trafik, till en temperaturökning inom staden. Träd och vegetation, sänker lufttemperaturer genom evapotranspiration och genom att ge skugga. Den moderna staden har i allmänhet bara vegetation i parker och några träd för sol och vindskydd längs gatorna. Träd ger fördelar som utsläpp av syre, filtrering av partiklar och andra luftföroreningar, minimerar erosion genom att hejda nederbörd och modifiera yttemperaturen genom att skugga marken. En viktig faktor för dessa fördelar är tidpunkten för knoppsprickning och lövutveckling. Denna studie syftar till att få en bättre förståelse om hur intra-urbana temperaturer påverkar fenologin av Tilia europaea (park lind) i Göteborg. T. europaea är det vanligaste trädet i städer vilket gjorde att det blev valt för denna studie. Studien genomfördes genom lufttemperaturmätningar och observationer av knoppsprickning vid åtta platser i Göteborg. Dygns-, tim-, dagtids- och nattids medeltemperaturer visar alla en temperatur ökning under undersökningsperioden. Platserna närmare centrum är vanligtvis varmare och visar en starkare UHI-effekt under nattetid än de längre bort från centrum. När det gäller knoppsprickning och lövutveckling finns det ingen statistisk signifikans mellan intra-urbana lufttemperaturer och tiden för knoppsprickning. En möjlig faktor som kan påverkar fenologin är växt förhållandena för träden. Mark täkt av vegetation är gynnsamt över asfalterad mark för trädtillväxt. Även storleken på ytan som träden kan växa i kan påverka fenologin. Nyckelord: Fenologi · Tilia europaea · Stadens värmeö · Göteborg · Sverige II Table of content I. Abstract ....................................................................................................................................... I II. Sammanfattning ........................................................................................................................ II 1 Introduction ............................................................................................................................... 4 1.1 Urban Heat Island .................................................................................................................... 4 1.2 Urban vegetation ..................................................................................................................... 5 1.3 Plant phenology and temperature ............................................................................................ 6 1.4 Aim .......................................................................................................................................... 6 2 Method ........................................................................................................................................ 7 2.1 Study Area ............................................................................................................................... 7 2.1.1 Gothenburg climate and its UHI ..................................................................................... 7 2.1.2 Gothenburg vegetation and Tilia euopaea ...................................................................... 7 2.1.3 Site location ..................................................................................................................... 8 2.2 Observations .......................................................................................................................... 11 2.3 Analysis ................................................................................................................................. 12 3 Results....................................................................................................................................... 13 3.1 Air temperature differences ................................................................................................... 13 3.1.1 Average air temperature ................................................................................................ 13 3.1.2 Average day-time and night-time air temperature ........................................................ 14 3.1.3 Hourly average air temperature .................................................................................... 16 3.2 Budburst and leaf development ............................................................................................. 17 3.3 Regression analysis ............................................................................................................... 18 4 Discussion ................................................................................................................................. 19 4.1 Limitations............................................................................................................................. 20 5 Conclusion ................................................................................................................................ 20 Acknowledgements .............................................................................................................................. 21 References ............................................................................................................................................ 22 Appendix .............................................................................................................................................. 25 III 1 Introduction 1.1 Urban Heat Island In every city we have a phenomenon called Urban Heat Island (UHI), this means that the temperature inside the city is higher than the surrounding countryside (Oke, 1972, 1982, 1988). This well-documented phenomenon was discovered in 1818 by meteorologist Luke Howard. Intra-urban thermal variations within a neighbourhood depend on sky view factor (SVF) or amount of greenery. SVF is the proportion of visible sky at the investigated site (Svensson, 2006). Cooling during the night has two modes. The first mode is site dependent cooling during night-time – dense canyons cool less than open spaces. During this time the wind speeds are still relatively high which allows sensible heat flux to dominate. Also the radiative divergence is an important process in this mode. The geometry of the site determines the heat flux. In the second mode, which begins three to four hours after sunset, all places have the same cooling rate. In this mode the wind cease and develops an elevated inversion. During this mode the determining factor becomes the air layer above the rooftops (Holmer et al., 2007). Geometry is one of the most important factors affecting intra-urban sand urban-rural air temperature differences. SVF strongly controls differences of intra-urban surface temperature. SVF relationship with air temperature is, however, less evident (Holmer et al., 2007; Konarska et al., 2016a). Night-time air temperatures is strongly affected by SVF. Anthropogenic heat flux and