Results from a thinning experiment in a Scots pine (Pinus sylvestris L.) natural regeneration stand in the Sistema Iberico Mountain Range (Spain)

In this paper, we present data and results about a thinning experiment in a natural regeneration stand of Pinus sylvestris L. in Burgos (Spain). The stand has a site index of 29 m at the age of 100 years, according to the site curves given by Rojo and Montero [El pino silvestre en la Sierra de Guadarrama. MAPA, Madrid, 1996, p. 293]. The experiment began in 1972, when the stand was 41 years old. It is now 66 years old. The statistical design of the experiment was a randomised complete block with three blocks and three treatments. Low thinning was carried out with varying intensities in a 10-year rotation (1972, 1982, 1992). The treatments were control, light and moderate thinning. The thinning intensity was measured by using the residual basal area (%) as parameter. Since the first inventory (1972) we have made four more. Effects of these treatments on stand yield, mean tree and stand structure are studied. Results showed that with the heaviest thinning the total yield of the stand was a bit lower than in control treatment. According to these results the heaviest treatment of the trial is near the lower density limit for this species (critical basal area of Assmann). On the other hand, mean tree and stand structure characteristics become more suitable for crop stability increment when thinning were heavier. The greater the intensity of thinning, the lesser the h/d ratio and the larger the square mean diameter too. As conclusion, we recommend low heavy thinning in early ages, reducing the intensity with age. Specially in stands of middle and high quality, the first thinning should be early, at 20-25 years old, despite the lack of economic profit at this stage. (C) 2001 Elsevier Science B.V. All rights reserved.