Soil Scarification Shortly before a Rich Seed Fall Improves Seedling Establishment in Seed Tree Stands of Pinus sylvestris
The effect of timing of soil scarification on establishment of Scots pine (Pinus sylvestris L.) in relation to amount of seed fall was studied in two seed-tree stands in central Sweden. The seed trees were released in autumn 1989. The treatments were: (i) scarification the autumn following cutting and before a seed fall expected to be poor; (ii) scarification in autumn 2 yrs after release, before a seed fall expected to be rich; and (iii) no soil preparation (control). Seedling establishment, mortality and height growth were monitored for 7 yrs from the start of the experiment. After 7 yrs, the seedling density was highest (c. 69 000 ha-1) in the area where soil scarification preceded a rich seed fall, whereas scarification immediately after cutting resulted in 34000 seedlings ha-1. The frequency of plots (size 3.14 m2) without seedlings was 5 and 7.5% where scarification was made before the rich seed fall and before the poor seed fall, respectively. Unscarified plots showed the poorest result according to number of seedlings (6000 ha-1) and number of plots without seedlings (52.5%). There was no significant difference in mortality of germinated seedlings between treatments. Height growth was significantly improved by scarification. The time elapsed since scarification clearly affected seed germination: The germination percentage of viable seeds dispersed on exposed mineral soil varied from 28.6% in the first year following scarification to 0.8% in the 7th year. The mean germination percentage in unprepared humus (control) was only 0.9% during the monitored period.