Simulation and analysis

Based on the results of the simulations, the management regime for mixed, uneven-aged, well stocked stands applied in this paper can be recommended for practical purposes in Galicia. If this harvest pattern were to continue the forest would remain in a balanced situation. The sustainable harvest levels obtained with this regime are lower than those for even-aged stands of pure maritime pine. MAI values of 12 to 15 m³ ha^-1 yr^-1 can be obtained on medium to good quality sites (Rodríguez, 1995), i.e. in areas where the productivity is comparable to the forest analysed in this study. Nevertheless it is important to point out the potential for high-value timber production under uneven-aged selective management. For example, the proportion of grade I timber - a valuable class that is in high demand by the local sawmilling and veneer industry - reaches 40%, which is much higher than the 16% obtained for an even-aged saw timber regime (Rodríguez et al., 2000). Also, the high degree of competition and the lack of light may favour selfpruning and reduce the low-quality juvenile core in the pines.

A fully stocked stand may be managed in the selection system producing timber every 5 years. This is not possible in an understocked stand where a decision has to be taken whether to rehabilitate the existing forest or prepare the site and regenerate the forest to obtain a

satisfactory stocking (Baker, 1989). A forest with a basal area before harvest of 11 m² ha^-1 could be considered as understocked.

Simulation results show the need of improvement cuts, concentrated on broadleaved species, and removing only a small part of the annual growth, these results are comparable with those obtained by Baker (1986) in the South-Eastern United States who could show rapid rehabilitation of an uneven-aged pine-hardwood forest with an average growth of 6.2 m³ ha^-1 yr^-1 during the first 14 years of rehabilitation management.

If the no-harvesting management option were to continue, the stand structure would change to a prevalence of broadleaved species with virtually no pine ingrowth. This prediction proves that model performance is consistent with the expected natural evolution observed in Galicia. Similar results were also obtained for the Italian Alps by Volin et al.

(1996) and from the French Jura by Buongiorno et al. (1995).

In conclusion, a selection silviculture aiming to maintain an adequate proportion of broadleaved species in the stand, thus allowing sufficient regeneration and ingrowth of pines and controlling undesirable eucalypts, may be a practical alternative in Galicia, if the aim is to establish a mixed continuous cover forest. The presence of eucalyptus trees makes the management of the stands very difficult, since the growth patterns, reproduction methods and usual harvest ages are very different in this species. Normally pine and oak are dominated by the Eucalypts, with poor growth of the suppressed trees. The continuous cover forest management has also other indirect benefits, such as the protection against soil erosion, the improvement of landscape aesthetics, the reduction of negative impacts associated with forest fragmentation, the improvement of wildlife habitat or the protection against natural disturbances (Matthews, 1989; Baker et al., 1991; Schulte and Buongiorno, 1998). However, the cost of tree selection and logging are generally higher, more technical expertise is required to regulate harvests and greater damage to residual trees can be expected. In the future, more information should be collected from permanent plots representing a variety of silvicultural treatment options.

Acknowledgements

The research reported in this study was supported by “Fundación Pedro Barrie de la Maza”

and by the Spanish Education Ministry within the program of grants for stays of spanish

110

researchers in foreign institutions. We thank Prof. Dr. Klaus von Gadow and Prof. Dr.

Andres Kiviste for their advice and valuable comments.

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Veröffentlichung V

Optimal residual growing stock and cutting cycle in mixed uneven-aged maritime pine stands in northwestern Spain

SÁNCHEZ OROIS,S.,CHANG,S.J. UND GADOW,K. V.

Angenommen (im Druck):

Forest Policy and Economics

Optimal residual growing stock and cutting cycle in mixed