Total and by species estimated volume increment in mixed stands over species composition (expressed as proportion by area of oak): (a) Scots pine is natural, the stocking degree (S) is 0.5 and the dominant heights (H_dom) of Scots pine and oak are 13 and 8 m respectively; (b) similar to (a) but with S = 1; and (c) Scots pine was planted, S = 0.5. and H_dom of Scots pine and oak are 7.5 and 7 m respectively. Dashed lines reflect the expected volume increment (total and by species) if there were not reduction of competition in mixed stands, that is the volume increment of each species is proportional to the species proportion by area.