Studies on the regeneration of Pinus sylvestris and Betula pendula
This research involved three years of field work in Glen Tanar, NNR, in northeast of Scotland. The role and seedbed preparation on regeneration of native pinewood and birchwood has been studied. The ground disturbance effects on soil seed bank, soil nutrient dynamics and ground vegetation recovery have been investigated in detail. Effect of light and burning of soil or fertiliser on Scots pine and silver birch seedling survival and growth were monitored in the laboratory to provide some information for the field observations. Germination of pine and birch seeds began about 3 weeks after experimental sowing at the end of July, 1988. However, the number of germinants in 1989 and 1990 was much lower than in 1988. 90% of Scots pine viable seeds died or failed to germinate and more than 95% of birch viable seeds failed to germinate. The germination of pine and birch seedlings was greatly increased when the moss and litter layers were completely removed by the `Burning' and `Pull' treatments. With treatments in which no humus was removed, the treatments `Control' and `Cut', little or no germination of pine and birch seeds occurred. Mortality of both pine and birch seedlings established in 1988 is significantly less on all sub-plots of ground treatments than seedlings established in 1989. Seedlings which were established after light burning are suffering the highest mortality in most cases, possibly because of competition from unburnt Calluna shoots and the rapid recovery of the ground flora in this treatment. Birch seedlings established in 1989 are suffering higher mortalities than pine seedlings established in 1989 on most of the ground treatments. Scots pine and birch seedlings were significantly depressed in relation to increasing shade in terms of height growth, biomass production and relative growth rates, which might suggest that birch and pine are both shade-avoider and light-demanding species. Scots pine seedlings demonstrate a much lower compensation point (3% RLI, relative light intensity) than birch (12% RLI) seedlings. Scots pine would thus have better survival than birch under shaded conditions of 10% RLI or less. The laboratory experiment showed that birch and pine seedling height growth was enhanced by burning or PK fertiliser treatments. Burning plus PK fertiliser is better than burning alone. Growth of Scots pine and silver birch seedlings in the absence of PK fertiliser additions was enhanced by burning but not by ash additions. Seedling height, relative growth rate, biomass and nutrient assimilation were greater on burned soil. Birch seedling demonstrates higher growth rate, higher height growth and more sensitive response to burning or fertiliser addition than pine seedling. However, the field study showed that height growth of pine and birch was not significantly increased by burning. The field enumeration surveys at Glen Tanar showed that some forms of soil disturbance (mechanical or burning) might be necessary and beneficial to Scots pine and birch regeneration. However, in the longer term, fencing (or some forms of protection from browsing) is very important to secure tree regeneration since the significant effect of initial soil disturbance was eliminated 12 years after the disturbance.