- Institutionen för sydsvensk skogsvetenskap, Sveriges lantbruksuniversitet
In southern Scandinavia there is a general desire to increase the amount of broadleaved forest using, for example, beech and oak, in order to preserve biodiversity and spread risk in the face of climate change. In order to realise this goal cheaper regeneration methods are needed. Although there are a number of uncertainties at present, direct seeding has the potential to fulfill this role. Two of the greatest obstacles to successful regeneration of beech and oak using direct seeding are seed removal by granivorous rodents and competition from ground vegetation. These issues need to be addressed before direct seeding can become a reliable regeneration method. The work described in papers I, II and IV in this thesis investigated the influence of site, sowing dates, rodent population densities, site preparation and repellents on rodent damage to sown beech nuts and acorns. Paper III describes a study which examined the effect of different mechanical site preparation methods, and different sowing dates, on the growth of young oak seedlings. Seedling establishment was more successful at large sites surrounded by mixed forests, compared to smaller areas surrounded by broadleaved forest (I, II). Oak seedling establishment was more successful than that of beech. Fewer acorns were lost and seedling establishment was better following spring sowing compared with summer sowing. In all years, more rodents were captured in the summer/autumn period than the spring. However, no clear correlation between rodent numbers and the success of direct seeding could be established. More rodents were captured in traps close to features providing cover, for example slash piles and the remains of stone walls. There were no clear relationships between the various mechanical site preparation treatments and rodent distribution and seed removal. In a laboratory study, mink excrement was found to have potential as a bank vole repellent, since it reduced consumption of beech nuts to half that of water soaked seeds, and reduced consumption of acorns was also indicated. No decrease in the germination of acorns treated with mink excrement was found, and there was only a minor negative effect on beech nuts (IV). The growth of young oak seedlings was better following sowing in spring than in summer, and mounding was the mechanical site preparation treatment most beneficial for oak seedling growth (III). The results indicate that successful direct seeding of oak on clear-cuts is most likely when acorns are sown at large sites situated in areas surrounded by coniferous forest, in spring rather than summer. In addition, more successful regeneration could be achieved through preparing sites by mounding, removing slash and sowing seeds treated with mink excrement. The data collected in this study indicate it is more difficult to achieve successful direct seeding of beech, than of oak.
quercus; fagus; sowing; seedlings; site preparation; site factors; rodents; population density
Acta Universitatis Agriculturae Sueciae
2010, nummer: 2010:13
Utgivare: Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences