Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This ...Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This study investigates the effects of patchy vegetation on solitary wave run-up by using a numerical simulation.A numerical model based on fully nonlinear Boussinesq equations is established to simulate the wave propagation on a slope with patchy vegetation.By using the model,the process of solitary wave run-up attenuation due to patchy vegetation is numerically analysed.The numerical results reveal that patchy vegetation can considerably attenuate the wave run-up in an effective manner.In addition,high-density patched vegetation can attenuate the solitary wave run-up more effectively than low-density patched vegetation can.For the same density,patchy vegetation with a uniform distribution has a better attenuation effect on wave run-up compared to that of patchy vegetation with a non-uniform distribution.展开更多
In drylands,biocrusts play crucial roles in regulating ecosystem functions.The study was conducted in the hilly rangelands of the semi-arid northern Negev of Israel,where we assessed the visual,morphological,spectral,...In drylands,biocrusts play crucial roles in regulating ecosystem functions.The study was conducted in the hilly rangelands of the semi-arid northern Negev of Israel,where we assessed the visual,morphological,spectral,and soil properties of livestock trampling routes and inter-route spaces in northern and southern facing hillslopes.Overall,both hillslope aspects were visually similar,whereas the ground surface of the routes was brighter(74.4%were characterized as having a'light'color)than the inter-route spaces(86.8%were characterized as having a'dark'color).These observations were supported by morphological identification of biocrust composition,which was dominated by cyanobacteria(67%)in the routes,and by mixed cyanobacteria/moss(56%)in the inter-routes.Mean Normalized Difference Vegetation Index(NDVI)was 24%higher in the inter-routes,while the mean Brightness Index(BI)was 12%higher in the routes.At the same time,the mean Crust Index(CI)was identical in the two microhabitats.Soil quality index(SQI),calculated based on the(pedoderm)soil properties of the two microhabitats,was 6%greater in the inter-routes than in the routes.This study suggests that recurrent trampling exacerbates soil compaction and shearing along the routes,thus preventing the successional development of complex biocrust compositions.展开更多
A long-term drought has led to the mass mortality of shrubs in the semi-arid Israeli Negev.The most impacted shrub species is the Noaea mucronata(Forssk.)Asch.and Schweinf.In a four-year study,we found that herbaceous...A long-term drought has led to the mass mortality of shrubs in the semi-arid Israeli Negev.The most impacted shrub species is the Noaea mucronata(Forssk.)Asch.and Schweinf.In a four-year study,we found that herbaceous vegetation growth was greater in the dead shrub patches than in the surrounding inter-patch biocrusted spaces,suggesting that the dead shrub patches encompass improved micro-habitats.However,unexpectedly,the soil moisture in the dead shrub patches was consistently lower than that of the inter-patch biocrusted spaces.At the same time,soil quality in the dead shrub patches was higher than that in the inter-patch spaces.Therefore,it seems that the overall better soil conditions in the dead patches overcome the scarcity of soil-water,supporting increased herbaceous productivity.For explaining the discrepancy between herbaceous vegetation and soil-water,we formulated a conceptual framework,which highlights the key factors that regulate soil-water dynamics in this dryland ecosystem.We demonstrate that herbaceous vegetation is facilitated in the dead shrub patches by a legacy effect that takes place long after the shrubs have died.The dead shrub patches encompass a unique form of ecosystem engineering.The study highlights the complex and unpredicted impacts of prolonged droughts on dryland ecosystems.展开更多
Aims Grasslands are globally threatened by climate changes and unsustainable land-use,which often cause transitions among alternative stable states,and even catastrophic transition to desertification.Spatial vegetatio...Aims Grasslands are globally threatened by climate changes and unsustainable land-use,which often cause transitions among alternative stable states,and even catastrophic transition to desertification.Spatial vegetation patch configurations have been shown to signify such transitions at large spatial scale.Here,we demonstrate how small-scale patch configurations can also indicate state transitions.Methods The whole spatial series of degradation successions were chosen in alpine grasslands characterized as seven typical communities.Patch numbers,and perimeter and cover of each patch were recorded using adjacent quadrats along transects in each type of the communities.Species abundance within each patch was measured.Important Findings Across seven grazing-induced degradation stages in the world’s largest expanse of grassland,from dense ungrazed turf to bare black-soil crust,patch numbers and perimeters first increased as patch cover decreased.Numbers and perimeters then decreased rapidly beyond an intersection point at 68%of initial continuous vegetation cover.Around this point,the vegetation fluctuated back and forth between the sedge-dominated grassland breaking-up phase and the forb-dominated phase,suggesting impending shift of grassland state.This study thus demonstrates how ground-based small-scale vegetation surveys can provide a quantitative,easy-to-use signals for vegetation degradation,with promise for detecting the catastrophic transition to desertification.展开更多
基金The National Natural Science Foundation of China under contract Nos 51579036 and 51779039the Fundamental Research Funds for the Central Universities of China under contract No.DUT19LAB13。
文摘Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This study investigates the effects of patchy vegetation on solitary wave run-up by using a numerical simulation.A numerical model based on fully nonlinear Boussinesq equations is established to simulate the wave propagation on a slope with patchy vegetation.By using the model,the process of solitary wave run-up attenuation due to patchy vegetation is numerically analysed.The numerical results reveal that patchy vegetation can considerably attenuate the wave run-up in an effective manner.In addition,high-density patched vegetation can attenuate the solitary wave run-up more effectively than low-density patched vegetation can.For the same density,patchy vegetation with a uniform distribution has a better attenuation effect on wave run-up compared to that of patchy vegetation with a non-uniform distribution.
文摘In drylands,biocrusts play crucial roles in regulating ecosystem functions.The study was conducted in the hilly rangelands of the semi-arid northern Negev of Israel,where we assessed the visual,morphological,spectral,and soil properties of livestock trampling routes and inter-route spaces in northern and southern facing hillslopes.Overall,both hillslope aspects were visually similar,whereas the ground surface of the routes was brighter(74.4%were characterized as having a'light'color)than the inter-route spaces(86.8%were characterized as having a'dark'color).These observations were supported by morphological identification of biocrust composition,which was dominated by cyanobacteria(67%)in the routes,and by mixed cyanobacteria/moss(56%)in the inter-routes.Mean Normalized Difference Vegetation Index(NDVI)was 24%higher in the inter-routes,while the mean Brightness Index(BI)was 12%higher in the routes.At the same time,the mean Crust Index(CI)was identical in the two microhabitats.Soil quality index(SQI),calculated based on the(pedoderm)soil properties of the two microhabitats,was 6%greater in the inter-routes than in the routes.This study suggests that recurrent trampling exacerbates soil compaction and shearing along the routes,thus preventing the successional development of complex biocrust compositions.
基金funded by the Israel Science Foundation(ISF),grant number 1260/15。
文摘A long-term drought has led to the mass mortality of shrubs in the semi-arid Israeli Negev.The most impacted shrub species is the Noaea mucronata(Forssk.)Asch.and Schweinf.In a four-year study,we found that herbaceous vegetation growth was greater in the dead shrub patches than in the surrounding inter-patch biocrusted spaces,suggesting that the dead shrub patches encompass improved micro-habitats.However,unexpectedly,the soil moisture in the dead shrub patches was consistently lower than that of the inter-patch biocrusted spaces.At the same time,soil quality in the dead shrub patches was higher than that in the inter-patch spaces.Therefore,it seems that the overall better soil conditions in the dead patches overcome the scarcity of soil-water,supporting increased herbaceous productivity.For explaining the discrepancy between herbaceous vegetation and soil-water,we formulated a conceptual framework,which highlights the key factors that regulate soil-water dynamics in this dryland ecosystem.We demonstrate that herbaceous vegetation is facilitated in the dead shrub patches by a legacy effect that takes place long after the shrubs have died.The dead shrub patches encompass a unique form of ecosystem engineering.The study highlights the complex and unpredicted impacts of prolonged droughts on dryland ecosystems.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)(grant no.2019QZKK0302)the National Key Research and Development Program(2016YFC0501802,2016YFC0501803)the National Natural Science Foundation of China(41671263,41730752).
文摘Aims Grasslands are globally threatened by climate changes and unsustainable land-use,which often cause transitions among alternative stable states,and even catastrophic transition to desertification.Spatial vegetation patch configurations have been shown to signify such transitions at large spatial scale.Here,we demonstrate how small-scale patch configurations can also indicate state transitions.Methods The whole spatial series of degradation successions were chosen in alpine grasslands characterized as seven typical communities.Patch numbers,and perimeter and cover of each patch were recorded using adjacent quadrats along transects in each type of the communities.Species abundance within each patch was measured.Important Findings Across seven grazing-induced degradation stages in the world’s largest expanse of grassland,from dense ungrazed turf to bare black-soil crust,patch numbers and perimeters first increased as patch cover decreased.Numbers and perimeters then decreased rapidly beyond an intersection point at 68%of initial continuous vegetation cover.Around this point,the vegetation fluctuated back and forth between the sedge-dominated grassland breaking-up phase and the forb-dominated phase,suggesting impending shift of grassland state.This study thus demonstrates how ground-based small-scale vegetation surveys can provide a quantitative,easy-to-use signals for vegetation degradation,with promise for detecting the catastrophic transition to desertification.
