| Sorbus pohuashanensis is deciduous tree in the genus Sorbus of Rosaceae native to northern China. It is an endemic accompanying broad-leaved species in boreal coniferous forest and mountain dark coniferous forest distributed in single-scattered or contagious patterns. As an important non-timber tree species in Northeast China, S. pohuashanensis has been over-developed recently and its population declined or even disappeared in some areas. In the paper, we investigated the wild seedlings establishment, population age structure, seed natural dispersal, soil seed bank and seedling emergence for the purpose of understanding the natural regeneration characteristics of this species and its influencing factors. The research results can provide scientific support for the rational protection and silviculture of the wild resources of Sorbus pohuashanensis.The results are as follows:S. pohuashanensis in eastern forest region of Northeast China regenerated by seed, stump sprouting and root sprouting. The line method of sampling indicated that roughly a third of the population was established by each regeneration method in S. pohuashanensis forests; in fact, there was no significant difference (P>0.05) among tree proportions established by these propagation methods whether in intact natural forests or in natural forests on stony sites. In secondary forests formed after damage, the frequency of stump sprouts (16.5%) was lower than in natural forests. Establishment ratio of seedling and root sprouts were no significant difference (P>0.05) among secondary formed forests after damage, intact natural forests and natural forests on stony sites; but significant difference (P<0.05) was detected for establishment ratio of stump sprouts between secondary forests formed after damage and intact natural forests or natural forests on stony sites.There was 76.0% of S. pohuashanensis whose diameter is less than 2.9 cm in secondary forests formed after damage; the result was 68.9% and 75.8% in natural forests on stony sites and intact natural forests respectively. The transfer rate from diameter classⅡ(1.0-2.9 cm) to diameter classⅢ(3.0-4.9 cm) was 25.6% in secondary forests formed after damage,45.3% in natural forests on stony sites and 15.9% in intact natural forests.The fruit ripening and natural dispersal of S. pohuashanensis last about 40 days that began in early September and ended in mid or late October. There was no significant correlation between the fruit dispersal of S. pohuashanensis and wind speed, air temperature, precipitation and air moisture content. Field tests found that there were 96.1% naturally dispersed seeds of S. pohuashanensis distributed within the range of 2 m around the stock tree.97.0% seeds in soil seed bank of S. pohuashanensis were distributed in the litter layer and 2 cm deep surface soil with a discontinuous temporal pattern, i.e., soil seed bank of S. pohuashanensis reached its maximum with 257.7±69.2 seeds per square meter in early November in current year of seed dispersal, and decreased to its minimum with less than 2.9±2.9 seeds per square meter in next July.Temperature had no obvious direct limitation effect on seedling emergence process of S. pohuashanensis, and seedling emergence can occurred at 0～5℃with (67.5±6.6)% seedling emergence percentage, the highest seedling emergence (81.5±1.9)% occurred at 20℃. But temperature strongly regulated seedling emergence rate and height growth of S. pohuashanensis. Maximum height of seedlings of S. pohuashanensis occurred under 25℃at the 7th day and the 21st day of germination tests with the seedling height of 2.5±0.1 cm and 3.1±0.1 cm respectively; and minimum height of seedlings of S. pohuashanensis occurred under 0～5℃at the 7th day and the 21st day of germination tests with the seedling height of 0.6±0.1 cm and 1.8±0.2 cm respectively. Soil moisture content not only affected seedling emergence percentage of S. pohuashanensis, but also adjusted the seedling mortality. The most proper soil moisture content for seedling emergence was 50%, seedling emergence percentage could reach (74.7±4.2)% in this situation; when soil moisture content was up to 60%, and seedling mortality was lowest to (32.7±0.6)%. Besides, the seed buried depth had a highly significant differences effect on seedling emergence (P<0.01). Seedling emergence of S. pohuashanensis decreased from (70.3±3.3)% to 0 with increasing soil depth from 0 to 1.5 cm.We conclude that habitats have certain effect on seedlings establishment types of S. pohuashanensis, and human disturbance could significantly reduce the establishment ratio of root sprouts. Adequate seedling bank was not a limiting factor of S. pohuashanensis natural regeneration, but the transfer rate from diameter class II to diameter class III was very lower and was the key limit factor for S. pohuashanensis natural regeneration. Seed dispersal process had no significant effect but the temporal and spatial pattern of soil seed bank had significant effect on S. pohuashanensis natural regeneration. Temperature may be a limiting factor for S. pohuashanensis natural regeneration through density-dependent effects on seedling emergence and survival, rather than by limiting individual seedling germination process effect natural regeneration. Soil moisture and burial depth were the crucial factor in S. pohuashanensis natural regeneration. |
PDF Full Text Request