Received 28 August 2015. Accepted 28 August 2015. A. Niglas, M. Alber, K. Suur, P. Kupper, and A. Sellin. Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia. A.K. Jasinska. Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia; Institute of Dendrology, Polish Academy of Sciences, Parkowa 5, 62-035 Kornik, Poland. Corresponding author: Aigar Niglas (e-mail: aigar.niglas@ut.ee). Fig. 3. Stomatal conductance (gS) versus leaf-to-air vapour pressure difference (VPDL) in leaves showing increasing response (IR) of stomatal conductance with rising VPDL. The IR data were divided into seven groups by VPDL; the data points represent means of the groups. 709