Ülo Niinemets1,2, Ivika Ostonen3. 1. Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 1, 51006 Tartu, Estonia. 2. Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia. 3. Department of Geography, Institute of Ecology and Earth Sciences University of Tartu, Vanemuise 46, Tartu, Estonia 51014.