Capacity of Quercus robur L. and Tilia cordata Mill. trees in providing urban ecosystem services in boreal climate

<p>Trees play an important role in urban ecosystem functioning and providing many ecosystem services, in particular, water and energy balance regulation. Consequently, trees can be a tool to mitigate to run-off and heat island effect in urban areas. We quantified the possibility of urban trees to provide these ecosystem services in the northernmost city with a million population – St. Petersburg (59°57′ N / 30°19′ E; Russia). Two diffuse-porous tree species – Quercus robur L. (n=2) and Tilia cordata Mill. (n=4) – were chosen for the research. These tree species are the most common in the green infrastructure of the city despite they are not typical for this biome, i.e. south taiga. During two growing season (July-Oct. 2019, April-Oct. 2020), tree sap flux was measured by thermal dissipation method using TreeTalker device (Nature 4.0 Corp., Italy). Sap flux density (Js) was calculated with modified Granier’s empirical calibration equation. Energy loss through tree transpiration was estimated from sap flux per tree (Js × sap wood area) and latent heat of vaporization. For the entire observed period, average daily<strong> </strong>Js (24 h) of Q. robur trees were almost two times higher than T. cordata trees (3.46 vs. 1.91 g cm<sup>-2</sup> h<sup>-1</sup>). Importantly, for Q. robur Js significantly decreased with increasing tree age (from 3.75 to 1.99 g cm<sup>-2</sup> h<sup>-1</sup> with age alteration from 145 to 350 yrs.), while for T. cordata it did not change (1.74 and 1.69 g cm<sup>-2</sup> h<sup>-1</sup> for 60-80 and 100-115 yrs.). Q. robur showed a significant higher daily energy loss through tree transpiration compared to T. cordata (618 and 396 W tree<sup>-1</sup> with 100-108 diameter at breast high) for the studying period. Thus, Q. robur compared to T. cordata was more effective in providing water regulation services, especially in shallow groundwater table typical for St. Petersburg. Moreover, this tree species also has a higher capacity in mitigate to urban heat island effect.</p><p>Current research was financially supported by Russian Science Foundation, No 19-77-30012.</p>