To understand the natural regeneration of manchurian ash and the seed banks under various secondary stands, we have investigated the seed quantity and vitality of major trees in the ground floor of the stands. In natu...To understand the natural regeneration of manchurian ash and the seed banks under various secondary stands, we have investigated the seed quantity and vitality of major trees in the ground floor of the stands. In natural secondary stands and dahurian larch plantations with seed source of manchurian ash around them, the vital seed numbers of valuable trees (mono maple, manchurian ash, amur linden, manchurian linden, manchurian walnut) are 20933/ha and 18000/ha respectively. The numbers of manchurian ash seeds arc 11000/ha and 12133/ha respectively. It has been found that litter affects the seedling recruitment of manchurian ash. When the seeds were sown on the litter and under the litter respectively, the final seedling recruitment rates were 17.9 and 28.9% respectively. The peak of seedling recruitment in the former case occurred one year later.展开更多
Samaras or winged seeds spread themselves by wind. Ash seed, unlike other samaras, has a high aspect ratio wing which can generate enough lift force to slow down descent by rotating about the vertical axis and spinnin...Samaras or winged seeds spread themselves by wind. Ash seed, unlike other samaras, has a high aspect ratio wing which can generate enough lift force to slow down descent by rotating about the vertical axis and spinning around its wing span axis simultaneously. This unique kinematics and inherent fluid mechanism are definitely of great interest. Detailed kinematics of free falling ash seeds were measured using high-speed cameras, then corresponding aerodynamic forces and moments were calculated employing computational fluid dynamics. The results show that both rotating and spinning directions are in the same side and the spinning angular velocity is about 6 times of rotating speed. The terminal descending velocity and cone angles are similar to other samaras. Analysis of the forces and moments shows that the lift is enough to balance the weight and the vertical rotation results from a processional motion of total angular moment because the spin-cycle-averaged aer-odynamic moment is perpendicular to the total angular moment and can only change its direction but maintain its magnitude, which is very similar to a spinning top in processional motion except that the total angular moment of ash seed is not along the spin axis but almost normal to it. The flow structures show that both leading and trailing edge vortices contribute to lift generation and the spanwise spinning results in an augmentation of the lift, implying that ash seeds with high aspect ratio wing may evolve in a different way in utilizing fluid mechanisms to facilitate dispersal.展开更多
文摘To understand the natural regeneration of manchurian ash and the seed banks under various secondary stands, we have investigated the seed quantity and vitality of major trees in the ground floor of the stands. In natural secondary stands and dahurian larch plantations with seed source of manchurian ash around them, the vital seed numbers of valuable trees (mono maple, manchurian ash, amur linden, manchurian linden, manchurian walnut) are 20933/ha and 18000/ha respectively. The numbers of manchurian ash seeds arc 11000/ha and 12133/ha respectively. It has been found that litter affects the seedling recruitment of manchurian ash. When the seeds were sown on the litter and under the litter respectively, the final seedling recruitment rates were 17.9 and 28.9% respectively. The peak of seedling recruitment in the former case occurred one year later.
文摘Samaras or winged seeds spread themselves by wind. Ash seed, unlike other samaras, has a high aspect ratio wing which can generate enough lift force to slow down descent by rotating about the vertical axis and spinning around its wing span axis simultaneously. This unique kinematics and inherent fluid mechanism are definitely of great interest. Detailed kinematics of free falling ash seeds were measured using high-speed cameras, then corresponding aerodynamic forces and moments were calculated employing computational fluid dynamics. The results show that both rotating and spinning directions are in the same side and the spinning angular velocity is about 6 times of rotating speed. The terminal descending velocity and cone angles are similar to other samaras. Analysis of the forces and moments shows that the lift is enough to balance the weight and the vertical rotation results from a processional motion of total angular moment because the spin-cycle-averaged aer-odynamic moment is perpendicular to the total angular moment and can only change its direction but maintain its magnitude, which is very similar to a spinning top in processional motion except that the total angular moment of ash seed is not along the spin axis but almost normal to it. The flow structures show that both leading and trailing edge vortices contribute to lift generation and the spanwise spinning results in an augmentation of the lift, implying that ash seeds with high aspect ratio wing may evolve in a different way in utilizing fluid mechanisms to facilitate dispersal.
