Fig. 3. Average annual elongation of the shoots (bars) of (a) Arctostaphylos uva-ursi and (b) Empetrum nigrum. The data consist of 3 plots x 5 plants for the two treatments (mulch-covered and uncovered plots). The reference represents 10-yr (1996–2005) average elongation measured on five natural clones per species. Standard deviation is marked. Statistically significant differences between the treatments: *p < 0.05; **p < 0.01; ***p < 0.001 (t test). Average July temperature is marked with a line in (a).