Study On The Soil Seed Bank And Biodiversity In Eucalyptus Grandis Plantation With A Range Of Forest Ages

The large area development of commercial plantations affects the native biodiversity. Understanding of the biodiversity pattern can provide an important scientific basis for plantation management. All viable seeds present on and in the soil and/or associated litters constitute the soil seed bank. As one of the important life history stages for a given plant population, soil seed bank is called subpopulation stage. Soil seed bank play important role in vegetation resevation, natural regeneration, the maintance of biodiversity. However, previsou studies mostly focused on the soil seed bank of croplands and natural forests, little information was given in the soil seed bank of plantation. Mover, the characteristics of soil seed bank would change with the increasing plantation age, however, seldom studies have taken the plantation age into consideration. Therefore, soil seed bank dynamics and diverisyt in the eucalypt plantations with a range of forest ages (1-10 years) converted from cropland, therefore, were measured in order to obtain an understanding of eucalypt effects on biodiversity. The present results showed1) A total of 58 species from 38 families with shrub and herbaceous species dominated were recorded across 1-10 year old E. grandis plantations (Rostellularia, affine D. Don, Viola diffusa, Eragrostis pilosa, auriculata (Thunb.) Druce, japonicum Thunb. ex Murray, urinaria Linn., media (Linn.) Cyr, orthostachyus Franch. et Savat, Cyperus szechuanensis, plicata (Lam.) T. Cooke, corniculata Linn., saxatilis Buch.-Ham, philippica Cav, Plantago asiatica L, nudiflora (Linn.) Brenan, Kyllinga Rottb., verticillatum Reinw., indica (Andr.) Focke hirta (Bl.) Wedd., thunbergii Kunth ex Steud.)2) The species number of soil seed bank fluctuated in the first five years, and reached the minimum in the 5-year-old stands, the species number of soil seed bank in 10 year-old stands was 1.9 times than in 1 year-old-plantations. Herb species dominated the various Eucalyptus plantations and the seed density increased with the plantation age. It was highest in the 1th year-plantation (3090 ind m-2), and then decreased from 1-to 6-year-old plantations, thereafter increased from 6-to 10-year-old stands. The soil density was 2098.ind m-2. The changeable trend of herb species was similar to that of the soil seed bank.The soil seed bank of shrub species was lowest in the first year of afforestation and increased from 1-to 3-year-old stands, decreased from 3-to 6-year-old plantations and increased along with plantation age, the seed bank in 10-year-old stands was 202 ind m-2.3) The density of soil seed bank decreased with soil depths. A large amout of seeds occurred in 0-5 layers. The average mean density of soil seed bank in litters was 20-21% that of all the whole seed density. The average mean density was 79-80%. It implied that the there are a considerable seeds in litters, however, far lower than that in soil layers.4) Across a range of 10 year-old plantations, the Shannon-wiener index of shrub species decreased from 1 to 3-year-old stands and then decreased from 3 to 6-year-old stands, thereafter increased significantly along with plantation age. Pielou index decreased from 1 to 3-year-old plantations and then increased from 3 to 6-year-old stands, thereafter increased along with plantation age; however, the variations did not reach the significant level. Simpson index increased from 1 to 2-year-old plantations and decreased from 2-to 3-year-old stands, increased from 3 to 6-years-old stands and then increased significantly along with plantation age, however, the variations did not reach the significant level. The Shannon-wiener index of herb species decreased from 1-to 5-year-old stands and then increased with plantation age. Pielou index represent no significant variations along with plantation age. Simpson index increased from 1-to 5-year-old stands and then decreased along with plantation age. At e community level, the Shannon-wiener index decreased from 1-to 5-year-old stands and increased along with plantation age; Simpson index increased from 1-to 5-year-old stands and thereafter decreased along with plantation age; Pielou index decreased from 1-to 5-year-plantation and thereafter increased along with plantation age and did not reach the significant level.5) Compared with that in crop lands, the Tuckey test indicated that the variations of biodiverisy indices in 1-year-old stands were not significant, that in 2-to 4-year-old stands were significant, that in 9,10-year-old stands were not significant,and significant in other stands.6) The species richness and abundance of understory plants decreased in the first 5 years however, those indices thereafter increased by 5.09 and 5.83 times in the 10-year plantation compared to 1-year stands, respectively. The species richness and diversity indices of herb species were significantly higher (p< 0.05) than shrub layer in younger stands (1 to 4 years), thereafter lower than shrub species in middle aged stands (5 years old) and paralleled with shrub layer in older E. grandis. Simpson index and Shannon-weiner index increased from 1-to 3-year-old stands and decreased in the following 2 years and then increased along with plantation ages. Pielou index fluctuated along with plantation ages.7) The Jaccard coefficient index indicated that the value of it was lower across the range of Eucalyptus ages.