Yearly changes in the growth of overstory and understory vegetation in a young Pinus brutia plantation with different tree spacing

The yearly changes in the growth of the overstory and understory vegetation in a young Pinus brutia plantation were studied for 12 years (1983-1995) in a semi-arid Mediterranean environment with cold winters in northern Greece. The plantation was established in 1970 at three spacings: 2×2 m, 3×3 m and 4×4 m or 2500, 1250 and 625 plants ha-1, respectively. Two understory treatments were applied: 1) herbaceous vegetation cut at the end of the growing season to simulate grazing and 2) no cutting (control). Herbage production and tree diameter were measured every year. Spacing and cutting treatments produced significant differences in herbage production in the first years of the experiment, but later disappeared. The same course was followed by the old dry matter and the branches and needles, that fell on the ground. Cutting treatments produce significant differences in tree diameter only in medium and low spacing during the 12 years of the experiment.