In the present study, we investigated the effect of hillslope gradient on vegetation recovery on abandoned land of shifting cultivation In Hainan Island, south China, by measuring community composition and structure o...In the present study, we investigated the effect of hillslope gradient on vegetation recovery on abandoned land of shifting cultivation In Hainan Island, south China, by measuring community composition and structure of 25-year-old secondary forest fallows along a hillslope gradient （up-, middle-, and down-slope position）. A total of 49 733 free-standing woody plant stems higher than 10 cm and belonging to 170 species, 112 genera, and 57 families was found in the three l-hm2 investigation plots. Stem density was highest in the down-slope stand and lowest in the up-slope stand. Species richness and the Shannon-Wiener Index were both highest in the middle-slope stand, and lower In the down-slope and up-slope stands. The recovery forest fallows on different hiUslope positions were all dominated by a few species. The five most abundant species accounted for 70.1%, 58.8%, and 72.9% of total stem densities in stands in the up-, middle-, and down-slope positions, respectively. The five species with the greatest basal areas accounted for 74.5%, 84.3%, and 74.7% of total stem basal area for the up-, middle-, and down-slope positions, respectively. The number of low-density species （stem abundance less than five） Increased from the up-slope position downward. Of the nine local common species among three different functional groups, the short-lived pioneer species dominated the up-slope position, but long-lived pioneer species dominated the middle- and down-slope positions. The climax species of primary tropical lowland rain forest was found in the downslope position. Both the mean diameter at breast height （DBH） and mean height of the trees Increased with decreasing hillslope gradient. The stem density and basal area in different size classes were significantly different in stands In different slope positions. Our results indicated that the rate of secondary succession varies, even over small spatial scales caused by the hlllslope gradient, in early vegetation recovery.展开更多
The spatially controllable shape-shifting behaviors of a planar two-dimensional(2D)film to three-dimensional(3D)shapes upon external stimuli are of paramount significance for the development of smart materials.Herein,...The spatially controllable shape-shifting behaviors of a planar two-dimensional(2D)film to three-dimensional(3D)shapes upon external stimuli are of paramount significance for the development of smart materials.Herein,the present work focuses on fabricating plain film whose shape can be remotely and spatially transformed into various 3D configurations via the formation of a laser-induced temperature gradient;when subjected to laser irradiation,the prestretched hybrid films exhibit out-of-plane bending behavior owing to anisotropic chain relaxation and strain energy release.On this basis,various sophisticated shape transformations can be achieved by site-specific irradiations of laser with a controllable magnitude.Meanwhile,shape morphing involving reversible bending transformations can also be realized by employing the laser on the corresponding opposite side of the hybrid films.Remarkably,under a 160 mW/cm^(2) simulated sunlight illumination,the transformation of flat 2D film into 3D chiral actuators is driven by material anisotropy and geometrical heterogeneity of a bilayer strip design,and it yields right and left-handed helix,the morphologies of the helix shape can be precisely tailored by the strip angles and strain values.展开更多
基金Supported by the National Natural Science Foundation of China(30340047 and 30430570)
文摘In the present study, we investigated the effect of hillslope gradient on vegetation recovery on abandoned land of shifting cultivation In Hainan Island, south China, by measuring community composition and structure of 25-year-old secondary forest fallows along a hillslope gradient （up-, middle-, and down-slope position）. A total of 49 733 free-standing woody plant stems higher than 10 cm and belonging to 170 species, 112 genera, and 57 families was found in the three l-hm2 investigation plots. Stem density was highest in the down-slope stand and lowest in the up-slope stand. Species richness and the Shannon-Wiener Index were both highest in the middle-slope stand, and lower In the down-slope and up-slope stands. The recovery forest fallows on different hiUslope positions were all dominated by a few species. The five most abundant species accounted for 70.1%, 58.8%, and 72.9% of total stem densities in stands in the up-, middle-, and down-slope positions, respectively. The five species with the greatest basal areas accounted for 74.5%, 84.3%, and 74.7% of total stem basal area for the up-, middle-, and down-slope positions, respectively. The number of low-density species （stem abundance less than five） Increased from the up-slope position downward. Of the nine local common species among three different functional groups, the short-lived pioneer species dominated the up-slope position, but long-lived pioneer species dominated the middle- and down-slope positions. The climax species of primary tropical lowland rain forest was found in the downslope position. Both the mean diameter at breast height （DBH） and mean height of the trees Increased with decreasing hillslope gradient. The stem density and basal area in different size classes were significantly different in stands In different slope positions. Our results indicated that the rate of secondary succession varies, even over small spatial scales caused by the hlllslope gradient, in early vegetation recovery.
基金supported by the National Natural Science Foundation of China (Grant No.22105152)。
文摘The spatially controllable shape-shifting behaviors of a planar two-dimensional(2D)film to three-dimensional(3D)shapes upon external stimuli are of paramount significance for the development of smart materials.Herein,the present work focuses on fabricating plain film whose shape can be remotely and spatially transformed into various 3D configurations via the formation of a laser-induced temperature gradient;when subjected to laser irradiation,the prestretched hybrid films exhibit out-of-plane bending behavior owing to anisotropic chain relaxation and strain energy release.On this basis,various sophisticated shape transformations can be achieved by site-specific irradiations of laser with a controllable magnitude.Meanwhile,shape morphing involving reversible bending transformations can also be realized by employing the laser on the corresponding opposite side of the hybrid films.Remarkably,under a 160 mW/cm^(2) simulated sunlight illumination,the transformation of flat 2D film into 3D chiral actuators is driven by material anisotropy and geometrical heterogeneity of a bilayer strip design,and it yields right and left-handed helix,the morphologies of the helix shape can be precisely tailored by the strip angles and strain values.
