Aerial photographs and 3-D laser scans of a 90-m high star dune at the Crescent Moon Spring scenic spot in Dunhuang,China,are used to investigate the changes in dune morphology on timescales from months to decades.The...Aerial photographs and 3-D laser scans of a 90-m high star dune at the Crescent Moon Spring scenic spot in Dunhuang,China,are used to investigate the changes in dune morphology on timescales from months to decades.The result revealed that relative-equilibrium airflow strength in three wind directions of northeast,west and south was an important condition for the stability of star dunes with limited migration.Transverse and longitudinal airflows exerted a crucial impact on variation processes of star dune morphology.Controlled by transverse airflows,the easterly winds,the east side was dominated by wind erosion;and strong deposition occurred on the south-south-east arm with a maximum deposition rate of 0.44 m/a in the 46-a monitoring period,causing the east side becoming steep and high.Controlled by longitudinal airflows,the westerly winds,the west-north-west side was mainly eroded and the north arm migrated from west to east with a rate of 0.30 m/a,causing the dune slope becoming gentle and elongate.The local air circulation(southerly winds)exerted a significant impact on the development process of the star dune.Due to the influence of human activities,the south side present surface processes from a concave profile to a convex profile in 46 a,which is a potential threat to the Crescent Moon Spring.The results indicate that rehabilitating the airflow field at most is a crucial strategy to the protection of Crescent Moon Spring from burial.Opening up the passage of easterly,westerly and southerly winds through intermediately cutting the protection forest,demolishing the enclosed wall and changing the pavilion into a porous pattern have been suggested to protect the Crescent Moon Spring from burial.展开更多
Seed germination is a key transitional stage in plant life cycle and is strongly regulated by temperature and light.Therefore, research on the effects of temperature and light on seed germination is extremely meaningf...Seed germination is a key transitional stage in plant life cycle and is strongly regulated by temperature and light.Therefore, research on the effects of temperature and light on seed germination is extremely meaningful for vegetation restoration, especially in desert ecosystems.Seeds of 28 ephemeral plants collected from the Gurbantunggut Desert of China were incubated at different temperatures(5℃/1℃, 15℃/5℃, 20℃/5℃, 25℃/10℃ and 30℃/15℃) in 12-h light/12-h darkness or continuous darkness regimes, and the responses of seed germination to temperature and light and the germination speed were studied in 2016.Results showed that seed germination percentage of the 28 ephemeral plants significantly differed to temperature and light.We classified the studied plants as the following groups based on their responses to temperature: 1 low temperature responsed plants, 12 moderate temperature responsed plants, 7 high temperature responsed plants, 4 non-responsed plants and 5 plants of no germination.It should be noted that Corispermum lehmannianum Bunge is sensitive to both moderate and high temperatures.There were 4 groups of plant in response to light, i.e., 7 light responsed plants, 10 dark responsed plants, 6 light non-responsed plants and 5 plants of no germination.Based on seed germination speed of the 28 ephemeral plants, we divided them into 4 patterns of germination, i.e., very rapid, moderately rapid, moderate and slow.Combining variations of temperature, precipitation and sand dune types in the study area, we suggested that very rapid and moderately rapid germinated plants could be used to moving sand dunes in early spring during vegetation restoration, moderate germinated plants could be used to semi-fixed sand dunes in late autumn, and slow germinated plants could be used to sand plain in summer.Thus, seedling establishment and vegetation restoration would be improved by considering seed germination characteristics of these ephemeral plants in the Gurbantunggut Desert, China.展开更多
Background: For migrating birds, stopover requires spending time and energy that otherwise could be allocated to flying. Thus, birds optimally refuel their subsequent migratory flight by reducing stopover duration or ...Background: For migrating birds, stopover requires spending time and energy that otherwise could be allocated to flying. Thus, birds optimally refuel their subsequent migratory flight by reducing stopover duration or foraging activ-ity in food-rich environments. In coastal habitats, birds may forego refueling and take short stopovers irrespective of local food availability. Given the paucity of studies exploring how migrants adjust stopover behavior in response to temporal variation in food availability, especially in the Neotropics, we fixed radio tags to 51 Red-eyed Vireos(Vireo olivaceous) over two years at two sites on the coast of Mexico's Yucatan Peninsula.Methods: We applied VHF radio tags during the fall of 2016 and 2017, and tracked birds using automatic and manual receiving units. We estimated stopover duration and activity levels(one site only) for between six and fifteen birds,depending on site and year. We measured fruit availability weekly along the net lanes where we captured birds. We used a generalized linear model to estimate the relationships between stopover duration/activity level and fruit den-sity, bird body mass and year. We interpreted relationships for the model with the lowest AICc value.Results: We found that approximately half of the birds departed on the same day they were captured. For the birds that stayed longer, we could not discern whether they did so because they were light, or fruit density was high. On the other hand, lighter birds were more active than heavier birds but only in one of the two years.Conclusions: Given our results, it is unlikely that Red-eyed Vireos refuel along the Yucatan coast. However, they still likely need to recuperate from crossing the Gulf of Mexico, which may necessitate foraging more often if in poor body condition. If the birds then move inland then stopover should be thought of as a large-scale phenomenon, where habitats with different functions may be spread out over a broad landscape.展开更多
Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dun...Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dune chronologies and the complexity of paleo-dune deposits as paleoenvironmental records. This paper addresses questions on the paleoenvi- ronmental implications of dune chronostratigraphies that have been raised by those reviews, in the specific case of crescentic dunes, using a case study from the Mu Us dune field, north-central China. The processes of turn-over and stabilization of relatively small crescentic dunes are first investigated by observational evidence. In combination with the analysis of a simplified sand preservation model and stratigraphic records, the effect of dune morphody- namics on sand preservation is demonstrated. It is especially evident that thick, nearly in- stantaneously deposited sand units record dune stabilization near the very end of a dune activity episode, while thin sand units may signal the preservation of sand deposited earlier in episodes of activity. Interpreting the distribution of luminescence ages that indicate sand deposition over time is not as simple as assumed in some previous work. Low frequency of sand ages could indicate an interval of either dune field stabilization or extensive dune activity but poor sand preservation. A peak of sand age frequency likely represents a shift in dune field activity towards stabilization, not a peak of active dune extent, especially if it partially overlaps with an independently identified interval of stabilization （e.g. one recorded by pa- leosols）. The nature and magnitude of these biases in the distribution of sand ages over time are strongly affected by the magnitude of net sand accumulation, which is in turn related to sand supply, transport capacity and sand availability, and ultimately climate change. Rela- tively short dune stabilization and turn-over time （101 to 102 yrs） indicate that dune geomor- phic processes can quickly respond to short-term disturbance, but the chronology of that response must be interpreted in light of how those processes influence age distributions.展开更多
基金funded by the National Natural Science Foundation of China(41271023)
文摘Aerial photographs and 3-D laser scans of a 90-m high star dune at the Crescent Moon Spring scenic spot in Dunhuang,China,are used to investigate the changes in dune morphology on timescales from months to decades.The result revealed that relative-equilibrium airflow strength in three wind directions of northeast,west and south was an important condition for the stability of star dunes with limited migration.Transverse and longitudinal airflows exerted a crucial impact on variation processes of star dune morphology.Controlled by transverse airflows,the easterly winds,the east side was dominated by wind erosion;and strong deposition occurred on the south-south-east arm with a maximum deposition rate of 0.44 m/a in the 46-a monitoring period,causing the east side becoming steep and high.Controlled by longitudinal airflows,the westerly winds,the west-north-west side was mainly eroded and the north arm migrated from west to east with a rate of 0.30 m/a,causing the dune slope becoming gentle and elongate.The local air circulation(southerly winds)exerted a significant impact on the development process of the star dune.Due to the influence of human activities,the south side present surface processes from a concave profile to a convex profile in 46 a,which is a potential threat to the Crescent Moon Spring.The results indicate that rehabilitating the airflow field at most is a crucial strategy to the protection of Crescent Moon Spring from burial.Opening up the passage of easterly,westerly and southerly winds through intermediately cutting the protection forest,demolishing the enclosed wall and changing the pavilion into a porous pattern have been suggested to protect the Crescent Moon Spring from burial.
基金funded by the Science and Technology Plan Project of Xinjiang Uygur Autonomous Region (2016B03040)the National Natural Science Foundation of China (31570529, 31660162, 31971428, 31770638)the Youth Innovation Promotion Association of Chinese Academy of Sciences (2018477)
文摘Seed germination is a key transitional stage in plant life cycle and is strongly regulated by temperature and light.Therefore, research on the effects of temperature and light on seed germination is extremely meaningful for vegetation restoration, especially in desert ecosystems.Seeds of 28 ephemeral plants collected from the Gurbantunggut Desert of China were incubated at different temperatures(5℃/1℃, 15℃/5℃, 20℃/5℃, 25℃/10℃ and 30℃/15℃) in 12-h light/12-h darkness or continuous darkness regimes, and the responses of seed germination to temperature and light and the germination speed were studied in 2016.Results showed that seed germination percentage of the 28 ephemeral plants significantly differed to temperature and light.We classified the studied plants as the following groups based on their responses to temperature: 1 low temperature responsed plants, 12 moderate temperature responsed plants, 7 high temperature responsed plants, 4 non-responsed plants and 5 plants of no germination.It should be noted that Corispermum lehmannianum Bunge is sensitive to both moderate and high temperatures.There were 4 groups of plant in response to light, i.e., 7 light responsed plants, 10 dark responsed plants, 6 light non-responsed plants and 5 plants of no germination.Based on seed germination speed of the 28 ephemeral plants, we divided them into 4 patterns of germination, i.e., very rapid, moderately rapid, moderate and slow.Combining variations of temperature, precipitation and sand dune types in the study area, we suggested that very rapid and moderately rapid germinated plants could be used to moving sand dunes in early spring during vegetation restoration, moderate germinated plants could be used to semi-fixed sand dunes in late autumn, and slow germinated plants could be used to sand plain in summer.Thus, seedling establishment and vegetation restoration would be improved by considering seed germination characteristics of these ephemeral plants in the Gurbantunggut Desert, China.
基金supported by a joint grant from the Secretaria de Medio Ambiente y Recursos Naturales of Mexico and the Consejo Nacional de Ciencia y Tecnología of Mexico (#262986)。
文摘Background: For migrating birds, stopover requires spending time and energy that otherwise could be allocated to flying. Thus, birds optimally refuel their subsequent migratory flight by reducing stopover duration or foraging activ-ity in food-rich environments. In coastal habitats, birds may forego refueling and take short stopovers irrespective of local food availability. Given the paucity of studies exploring how migrants adjust stopover behavior in response to temporal variation in food availability, especially in the Neotropics, we fixed radio tags to 51 Red-eyed Vireos(Vireo olivaceous) over two years at two sites on the coast of Mexico's Yucatan Peninsula.Methods: We applied VHF radio tags during the fall of 2016 and 2017, and tracked birds using automatic and manual receiving units. We estimated stopover duration and activity levels(one site only) for between six and fifteen birds,depending on site and year. We measured fruit availability weekly along the net lanes where we captured birds. We used a generalized linear model to estimate the relationships between stopover duration/activity level and fruit den-sity, bird body mass and year. We interpreted relationships for the model with the lowest AICc value.Results: We found that approximately half of the birds departed on the same day they were captured. For the birds that stayed longer, we could not discern whether they did so because they were light, or fruit density was high. On the other hand, lighter birds were more active than heavier birds but only in one of the two years.Conclusions: Given our results, it is unlikely that Red-eyed Vireos refuel along the Yucatan coast. However, they still likely need to recuperate from crossing the Gulf of Mexico, which may necessitate foraging more often if in poor body condition. If the birds then move inland then stopover should be thought of as a large-scale phenomenon, where habitats with different functions may be spread out over a broad landscape.
基金Foundation： National Natural Science Foundation of China, No.41501208 The Global Change Program of Ministry of Science and Technology of China, No.2016YFA0600503 The U.S. National Science Foundation, No.ATM-0502489
文摘Paleo-dune deposits have been widely used as a proxy indicator of past dune ac- tivity, which is further used to reconstruct paleoclimates. However, recent studies have criti- cally examined the reproducibility of dune chronologies and the complexity of paleo-dune deposits as paleoenvironmental records. This paper addresses questions on the paleoenvi- ronmental implications of dune chronostratigraphies that have been raised by those reviews, in the specific case of crescentic dunes, using a case study from the Mu Us dune field, north-central China. The processes of turn-over and stabilization of relatively small crescentic dunes are first investigated by observational evidence. In combination with the analysis of a simplified sand preservation model and stratigraphic records, the effect of dune morphody- namics on sand preservation is demonstrated. It is especially evident that thick, nearly in- stantaneously deposited sand units record dune stabilization near the very end of a dune activity episode, while thin sand units may signal the preservation of sand deposited earlier in episodes of activity. Interpreting the distribution of luminescence ages that indicate sand deposition over time is not as simple as assumed in some previous work. Low frequency of sand ages could indicate an interval of either dune field stabilization or extensive dune activity but poor sand preservation. A peak of sand age frequency likely represents a shift in dune field activity towards stabilization, not a peak of active dune extent, especially if it partially overlaps with an independently identified interval of stabilization （e.g. one recorded by pa- leosols）. The nature and magnitude of these biases in the distribution of sand ages over time are strongly affected by the magnitude of net sand accumulation, which is in turn related to sand supply, transport capacity and sand availability, and ultimately climate change. Rela- tively short dune stabilization and turn-over time （101 to 102 yrs） indicate that dune geomor- phic processes can quickly respond to short-term disturbance, but the chronology of that response must be interpreted in light of how those processes influence age distributions.
