Wind not only causes extensive damages to trees in many parts of the world, it also has more subtle effects on the growth and morphology of trees and forest ecology as well. Wind damage to trees has historically been ...Wind not only causes extensive damages to trees in many parts of the world, it also has more subtle effects on the growth and morphology of trees and forest ecology as well. Wind damage to trees has historically been the field of silviculture, but increasing recognition of the importance and complexity of the subject has recently got people involved from many other disciplines. Due to the global climate changes, it is believed that the risk of further and stronger storms is increasing. In order to better understand the effects of wind on individual trees, forest stand and forest ecosystem, and further to practice the management of forests, it is necessary to summarize the research results related to this subject. This review was mostly based on the references from recent researches in the field, especially from the symposium volumes of some international conferences on this subject. The results indicated that there have been significant progresses in the following aspects: 1) the aerodynamic interaction between wind and trees, 2) the mechanics of trees under wind loading and adaptive growth, 3) the tree's physiological responses to wind, and 4) the risk assessment of wind damage to forest. However, there are some aspects which may need further studies: 1) wind damage to natural forests, 2) wind-driven gap formation and forest dynamics, 3) the effects of changes resulted from wind disturbances on ecological processes of forest ecosystem, and 4) management for the wind-damaged forests. Key words Wind - Wind effect - Trees/forest - Forest ecology - Disturbance CLC number S718 Document code B Foundation item: This research was supported by “the 100-Young-Researcher Project” of Chinese Academy of Sciences (BR0301) and National Natural Science Foundation (30371149).Biography: ZHU Jiao-jun (1965-), male, Ph. Doctor, Professor of Institute of Applied Ecology, Chinese Academy of Sciences, Professor of Graduate School of Chinese Academy of Sciences. China. Scholar researcher of Faculty of Agriculture, Niigata University, JapanResponsible editor: Song Funan展开更多
Aim To study the chemical constituents from the stems of Xylosma controversum Clos. Methods The constituents were isolated by solvent extraction, repeated chromatography with silica gel, Sephadex LH-20, and RP-18 colu...Aim To study the chemical constituents from the stems of Xylosma controversum Clos. Methods The constituents were isolated by solvent extraction, repeated chromatography with silica gel, Sephadex LH-20, and RP-18 columns. The structures were elucidated by spectral analysis. Results Thirteen compounds were isolated and their structures were identified as （-）-syringaresinol （1）, syringaresinol-4-O-β-D-glucopyranoside （2）, syringaresinol-4,4′-bis-O-β-D-glucopyranoside （3）, （±）-catechin （4）, catechin-3-O- β-D-glucopyranoside （5）, catechin-5-O-β-D-glucopyranoside （6）, 1,3-bis-（4-hydroxy-3,5-dimethoxyphenyl）-1,3-propanediol （7）, （R）-（＋）-chaulmoogric acid （8）, friedelin （9）, uracile （10）, benzoic acid （11）, vaniUic acid （12）, and 4-hydroxybenzoic acid （13）. Conclusion All the compounds described above were isolated from this genus for the first time.展开更多
The Qinghai-Tibet Railway(QTR) passes through 281 km of sandy land, 11.07 km of which causes serious sand damage to the railway and thus, the control of blown sand is important for the safe operation of the railway. C...The Qinghai-Tibet Railway(QTR) passes through 281 km of sandy land, 11.07 km of which causes serious sand damage to the railway and thus, the control of blown sand is important for the safe operation of the railway. Construction of the railway and sand prevention system greatly changed the blown sand transport of the primary surface. Effective and feasible sand-control measures include stone checkerboard barriers(SCBs), sand fences(SFs), and gravel coverings. This study simulated the embankments, SCBs and SFs of the QTR in a wind tunnel, and analyzed their respective wind profile, sand deposition, and sand-blocking rate(SBR) in conjunction with field data, aiming at studying the influence of Golmud-Lhasa section of the QTR and sand prevention system on blown sand transport. The results of wind tunnel experiments showed that wind speed increased by 67.7%–77.3% at the upwind shoulder of the embankment and decreased by 50.0%–83.3% at upwind foot of embankment. Wind speed decreased by 50.0%–100.0% after passing through the first SF, and 72.2%–100.0% after the first row of stones within the first SCB grid. In the experiment of sand deposition, the higher the wind speed, the lower the SBR of SCB and SF. From field investigation, the amount of sand blocked by the four SFs decreased exponentially and its SBR was about 50.0%. By contrast, SCB could only block lower amounts of sand, but had a higher SBR(96.7%) than SF. Although, results show that SFs and SCBs along the Golmud-Lhasa section of the QTR provide an obvious sand blocking effect, they lead to the deposition of a large amount of sand, which forms artificial dunes and becomes a new source of sand damage.展开更多
The oasis-desert ecotone is a fragile ecological zone that is affected both by oasis and desert conditions. To understand the impact of the differences in wind power, and the influence of wind erosion and deposition o...The oasis-desert ecotone is a fragile ecological zone that is affected both by oasis and desert conditions. To understand the impact of the differences in wind power, and the influence of wind erosion and deposition on the ecotone, meteorological data and con- temporaneous wind erosion and deposition data were collected on the southern margin of Tarim Basin with serious sand-blown hazards. The wind velocity, average wind velocity, sand drift potential （DP）, resultant sand drift potential （RDP）, and sand transportation rate decrease significantly and successively across four landscape types with increasing vegetation coverage （VC）. Flat surfaces and areas of shifting sandy ground experience intense wind erosion with fast movement of mobile sand dunes; semi-fixed sand areas experience ex- tensive wind deposition but only slight wind erosion; and fixed sand areas experience only slight wind erosion and deposition. Volume of wind erosion on bare newly reclaimed farmland is up to 6.96 times that of bare shifting sandy ground. Wind erosion volume per unit area and VC follow an exponential function relationship in natural conditions, while wind deposition volume per unit area does not conform to any functions which has close relationship with vary topography and arrangement patterns of vegetation besides for VC. The results indicate that the volume of wind erosion has a close correlation with VC, and different types and distribution patterns of topog- raphy and vegetation also profoundly influence the wind deposition volume in the field, and underground water tables in different land- scape types control the plant community distribution. Keywords： wind erosion; wind deposition; oasis-desert ecotone; vegetation coverage （VC）; topography; Cele County展开更多
The distribution characteristics of heavy metals in soil-root systems have great significance for the research into soil pollution risk assessment and the phytoremediation effect. This paper takes ligustrum lucidum as...The distribution characteristics of heavy metals in soil-root systems have great significance for the research into soil pollution risk assessment and the phytoremediation effect. This paper takes ligustrum lucidum as an example, based on the characteristics of adsorption of heavy metals in soil by woody plants, lays out sampling points, and using software Surer for the Kiging interpolation analysis, and the horizontal migration law of heavy metal cadmium in the soil-root interface system is simulated. Through multi-model statistical regression trend analysis, the horizontal migration mechanism of cadmium in different sections is discussed. The results show that： （1） under horizontal migration law： the migration ability of Cd is weaker near the Ligustrum lucidum root （0 30 cm）; with the root extension, the migration ability of Cd gradually is strengthened, and the main range of the migration ability is 60-90 cm. In addition, its migration law follows the cubic curve mode. （2） under longitudinal migration law： based on the Kriging method, migration models Z（hi） of heavy metal Cd in any depth of hi are constructed and fit the correlation coefficient R^2〉0.95.展开更多
Timber bridges can provide an economical alternative to concrete and steel structures, particularly in rural areas where vehicle traffic is light to moderate. The wooden components of bridges have historically been pr...Timber bridges can provide an economical alternative to concrete and steel structures, particularly in rural areas where vehicle traffic is light to moderate. The wooden components of bridges have historically been preserved with either an oil type or waterborne preservative system to protect the wood from decay in order to maintain required performance standards for an extended period of time. The focus of this paper is to describe some of the key preservatives, research and case studies that support use of preserved wood, and some important steps to follow for the appropriate and safe use of preserved wood when the planned application will be in or over aquatic and wetland environments. A wealth of scientific information has been collected and analyzed that clearly suggests the use of preserved wood does not present a significant adverse effect on aquatic and wetland environments. This conclusion is based on two decades of empirical research and case study evaluating the environmental fate and effects of preserved wood, level of migration of contaminates into aquatic and marine environments, and the preserved wood environment. This is particularly true when risks are properly assessed on a project site, the appropriate preservative is selected and the wood is preserved to the Western Wood Preservers Institute＇s BMPs （best management practices）, along with properly installing and maintaining the preserved material. To assist with the assessment process, peer-reviewed risk assessment models for 11 commonly used preservatives have been developed that provide for streamlined data entry by users and allow for evaluation of a structure above and below water. A companion preliminary screening level assessment tool is also available. When these measures are properly utilized engineers, biologists and other responsible officials can be confident that the service life of the preserved wood components will more than likely meet the required performance standards in an environmentally safe manner for up to 50 or more years on a majority of timber bridge projects.展开更多
This paper analyzed time-series variation and spatial distribution characteristics of wind resources at the eastern edge of Qaidam Basin based on the wind resources gradient automatic observation system. Wind resource...This paper analyzed time-series variation and spatial distribution characteristics of wind resources at the eastern edge of Qaidam Basin based on the wind resources gradient automatic observation system. Wind resources are relatively abundant in the study area, the cumulative number of hours of wind speed between 3–25m s -1 are more than 6600, equal to 275 days, exceeding 75% of total annual hours. Advantage wind velocity spectrum was in the scope of 3–9m s -1 at all gradients and the peak value of wind speed was 4–6m s -1 . Differences in the wind speed frequency distribution at other gradients were not apparent except for the 10m gradient. Compared with other layers, the occurrence frequency of small wind at the level of 10m was higher, while the occurrence frequency of wind speed between 6 and 12m s -1 was higher at other layers. The advantage wind direction in this area was northwest and the wind speed difference was not obvious. Wind speed and wind power density gradually increased with the increasing height, and differences among sites were apparent. The average wind turbulence intensity was 0.199 at each layer and the average shear index was 0.075; turbulence intensity and shear index gradually reduced from over a 10–70m gradient. Turbulence intensity had the same variation tendency as local temperature, whereby a high temperature corresponded to high turbulence and low temperature to low turbulence. The variation tendency of shear index was opposite to that for turbulence intensity; turbulence intensity gradually decreased from lower layers to top layers and shear index was most obvious between 10–30m. Turbulence intensity at each site at each level was between 0.10–0.25, and of medium intensity. These data will provide a technical gist for the layout of wind farms and the utilization of wind power resource at ground level throughout the study region.展开更多
By means of solvent extraction and repeated chromatography on silica gel, Sephadex LH-20, HPLC, and preparative TLC, the ethanol extract of the stems of Homalium ceylanicum（Flacourtiaceae/Salicaceae sensu lato） was ...By means of solvent extraction and repeated chromatography on silica gel, Sephadex LH-20, HPLC, and preparative TLC, the ethanol extract of the stems of Homalium ceylanicum（Flacourtiaceae/Salicaceae sensu lato） was chemically investigated, which led to the isolation of 13 constituents, including five lignans（1–5） and three isocoumarins（6–8）. Based on the spectroscopic analysis and comparison of its 1H NMR and 13C NMR data with those in literatures, their structures were identified as（–）-5＇-methoxyisolariciresinol 3α-O-β-D-glucopyranoside（1）,（＋）-lyoniresinol 3α-O-β-D-glucopyranoside（2）,（＋）-isolarisiresinol 3α-O-β-Dglucopyranoside（3）,（–）-isolarisiresinol 3α-O-β-D-glucopyranoside（4）, icariside E5（5）, 3-phenylisocoumarin（6）, homalicine（7）,（–）-dihydrohomalicine（8）, friedelin（9）, 4-hydroxybenzoic acid（10）, catechol（11）, methyl-α-arabinofuranoside（12）, and uridine（13）. All isolates except compounds 6–8 were described from this genus for the first time. Compound 6 was isolated from this species for the first time.展开更多
During January–February 2008, a severe ice storm caused significant damages to forests in southern China, creating canopy gaps and changing soil nutrient availability and enzyme activity. To understand the relationsh...During January–February 2008, a severe ice storm caused significant damages to forests in southern China, creating canopy gaps and changing soil nutrient availability and enzyme activity. To understand the relationships between gap size, changes in the soil environment and the effects that these changes have on soil processes, we investigated the effects of gap size on soil chemical and biological properties in the forest gaps in a Cunninghamia lanceolata stand in northern Guangdong Province, southern China. Ten naturally created gaps, five large(80–100 m^2) and five small(30–40 m^2), were selected in the stand of C.lanceolata. The large gaps showed a significant increase in light transmission ratio and air and soil temperatures and a decline in soil moisture, organic matter,N and P compared with the small gaps and the adjacent canopy-covered plots in the 0–10 cm soil. The differences in organic matter and nutrient levels found between the large and small gaps and the canopy-covered plots may be related to changes in environmental conditions. This indicated rapid litter decomposition and increased nutrient leaching in the large gaps. Moreover, the lowest levels of catalase, acid phosphatase and urease activities occurred in large gaps because of the decline in their soil fertility. Large forest gaps may have a region of poor fertility, reducing soil nutrient availability and enzyme activity within the C.lanceolata stand.展开更多
基金This research was supported by the 100-Young-Researcher Project of Chinese Academy of Sciences (BR0301) and National Natural Science Foundation (30371149).
文摘Wind not only causes extensive damages to trees in many parts of the world, it also has more subtle effects on the growth and morphology of trees and forest ecology as well. Wind damage to trees has historically been the field of silviculture, but increasing recognition of the importance and complexity of the subject has recently got people involved from many other disciplines. Due to the global climate changes, it is believed that the risk of further and stronger storms is increasing. In order to better understand the effects of wind on individual trees, forest stand and forest ecosystem, and further to practice the management of forests, it is necessary to summarize the research results related to this subject. This review was mostly based on the references from recent researches in the field, especially from the symposium volumes of some international conferences on this subject. The results indicated that there have been significant progresses in the following aspects: 1) the aerodynamic interaction between wind and trees, 2) the mechanics of trees under wind loading and adaptive growth, 3) the tree's physiological responses to wind, and 4) the risk assessment of wind damage to forest. However, there are some aspects which may need further studies: 1) wind damage to natural forests, 2) wind-driven gap formation and forest dynamics, 3) the effects of changes resulted from wind disturbances on ecological processes of forest ecosystem, and 4) management for the wind-damaged forests. Key words Wind - Wind effect - Trees/forest - Forest ecology - Disturbance CLC number S718 Document code B Foundation item: This research was supported by “the 100-Young-Researcher Project” of Chinese Academy of Sciences (BR0301) and National Natural Science Foundation (30371149).Biography: ZHU Jiao-jun (1965-), male, Ph. Doctor, Professor of Institute of Applied Ecology, Chinese Academy of Sciences, Professor of Graduate School of Chinese Academy of Sciences. China. Scholar researcher of Faculty of Agriculture, Niigata University, JapanResponsible editor: Song Funan
基金Program for Changjiang Scholar and InnovativeTeam in Peking University (Grant number: 985-2-063-112).
文摘Aim To study the chemical constituents from the stems of Xylosma controversum Clos. Methods The constituents were isolated by solvent extraction, repeated chromatography with silica gel, Sephadex LH-20, and RP-18 columns. The structures were elucidated by spectral analysis. Results Thirteen compounds were isolated and their structures were identified as （-）-syringaresinol （1）, syringaresinol-4-O-β-D-glucopyranoside （2）, syringaresinol-4,4′-bis-O-β-D-glucopyranoside （3）, （±）-catechin （4）, catechin-3-O- β-D-glucopyranoside （5）, catechin-5-O-β-D-glucopyranoside （6）, 1,3-bis-（4-hydroxy-3,5-dimethoxyphenyl）-1,3-propanediol （7）, （R）-（＋）-chaulmoogric acid （8）, friedelin （9）, uracile （10）, benzoic acid （11）, vaniUic acid （12）, and 4-hydroxybenzoic acid （13）. Conclusion All the compounds described above were isolated from this genus for the first time.
基金Under the auspices of National Natural Science Foundation of China(No.40930741)National Basic Research Program of China(No.2012CB026105)
文摘The Qinghai-Tibet Railway(QTR) passes through 281 km of sandy land, 11.07 km of which causes serious sand damage to the railway and thus, the control of blown sand is important for the safe operation of the railway. Construction of the railway and sand prevention system greatly changed the blown sand transport of the primary surface. Effective and feasible sand-control measures include stone checkerboard barriers(SCBs), sand fences(SFs), and gravel coverings. This study simulated the embankments, SCBs and SFs of the QTR in a wind tunnel, and analyzed their respective wind profile, sand deposition, and sand-blocking rate(SBR) in conjunction with field data, aiming at studying the influence of Golmud-Lhasa section of the QTR and sand prevention system on blown sand transport. The results of wind tunnel experiments showed that wind speed increased by 67.7%–77.3% at the upwind shoulder of the embankment and decreased by 50.0%–83.3% at upwind foot of embankment. Wind speed decreased by 50.0%–100.0% after passing through the first SF, and 72.2%–100.0% after the first row of stones within the first SCB grid. In the experiment of sand deposition, the higher the wind speed, the lower the SBR of SCB and SF. From field investigation, the amount of sand blocked by the four SFs decreased exponentially and its SBR was about 50.0%. By contrast, SCB could only block lower amounts of sand, but had a higher SBR(96.7%) than SF. Although, results show that SFs and SCBs along the Golmud-Lhasa section of the QTR provide an obvious sand blocking effect, they lead to the deposition of a large amount of sand, which forms artificial dunes and becomes a new source of sand damage.
基金Under the auspices of Special Major Science and Technology Projects in Xinjiang Uygur Autonomous Region(No.201130106-1)Public Sector(Meteorology)Research Project(No.GYHY201106025)Doctoral Station Supporting Foundation for Geography of Xinjiang Normal University and Open Project of Xinjiang Lake Environment and Resources Key Laboratory of Arid Zone(No.XJDX0909-2013-08)
文摘The oasis-desert ecotone is a fragile ecological zone that is affected both by oasis and desert conditions. To understand the impact of the differences in wind power, and the influence of wind erosion and deposition on the ecotone, meteorological data and con- temporaneous wind erosion and deposition data were collected on the southern margin of Tarim Basin with serious sand-blown hazards. The wind velocity, average wind velocity, sand drift potential （DP）, resultant sand drift potential （RDP）, and sand transportation rate decrease significantly and successively across four landscape types with increasing vegetation coverage （VC）. Flat surfaces and areas of shifting sandy ground experience intense wind erosion with fast movement of mobile sand dunes; semi-fixed sand areas experience ex- tensive wind deposition but only slight wind erosion; and fixed sand areas experience only slight wind erosion and deposition. Volume of wind erosion on bare newly reclaimed farmland is up to 6.96 times that of bare shifting sandy ground. Wind erosion volume per unit area and VC follow an exponential function relationship in natural conditions, while wind deposition volume per unit area does not conform to any functions which has close relationship with vary topography and arrangement patterns of vegetation besides for VC. The results indicate that the volume of wind erosion has a close correlation with VC, and different types and distribution patterns of topog- raphy and vegetation also profoundly influence the wind deposition volume in the field, and underground water tables in different land- scape types control the plant community distribution. Keywords： wind erosion; wind deposition; oasis-desert ecotone; vegetation coverage （VC）; topography; Cele County
文摘The distribution characteristics of heavy metals in soil-root systems have great significance for the research into soil pollution risk assessment and the phytoremediation effect. This paper takes ligustrum lucidum as an example, based on the characteristics of adsorption of heavy metals in soil by woody plants, lays out sampling points, and using software Surer for the Kiging interpolation analysis, and the horizontal migration law of heavy metal cadmium in the soil-root interface system is simulated. Through multi-model statistical regression trend analysis, the horizontal migration mechanism of cadmium in different sections is discussed. The results show that： （1） under horizontal migration law： the migration ability of Cd is weaker near the Ligustrum lucidum root （0 30 cm）; with the root extension, the migration ability of Cd gradually is strengthened, and the main range of the migration ability is 60-90 cm. In addition, its migration law follows the cubic curve mode. （2） under longitudinal migration law： based on the Kriging method, migration models Z（hi） of heavy metal Cd in any depth of hi are constructed and fit the correlation coefficient R^2〉0.95.
文摘Timber bridges can provide an economical alternative to concrete and steel structures, particularly in rural areas where vehicle traffic is light to moderate. The wooden components of bridges have historically been preserved with either an oil type or waterborne preservative system to protect the wood from decay in order to maintain required performance standards for an extended period of time. The focus of this paper is to describe some of the key preservatives, research and case studies that support use of preserved wood, and some important steps to follow for the appropriate and safe use of preserved wood when the planned application will be in or over aquatic and wetland environments. A wealth of scientific information has been collected and analyzed that clearly suggests the use of preserved wood does not present a significant adverse effect on aquatic and wetland environments. This conclusion is based on two decades of empirical research and case study evaluating the environmental fate and effects of preserved wood, level of migration of contaminates into aquatic and marine environments, and the preserved wood environment. This is particularly true when risks are properly assessed on a project site, the appropriate preservative is selected and the wood is preserved to the Western Wood Preservers Institute＇s BMPs （best management practices）, along with properly installing and maintaining the preserved material. To assist with the assessment process, peer-reviewed risk assessment models for 11 commonly used preservatives have been developed that provide for streamlined data entry by users and allow for evaluation of a structure above and below water. A companion preliminary screening level assessment tool is also available. When these measures are properly utilized engineers, biologists and other responsible officials can be confident that the service life of the preserved wood components will more than likely meet the required performance standards in an environmentally safe manner for up to 50 or more years on a majority of timber bridge projects.
基金Public welfare meteorological industry specific "China’s wind power exploration evaluation and safety operation of meteorological guarantee technology research" (GYHY200806016)
文摘This paper analyzed time-series variation and spatial distribution characteristics of wind resources at the eastern edge of Qaidam Basin based on the wind resources gradient automatic observation system. Wind resources are relatively abundant in the study area, the cumulative number of hours of wind speed between 3–25m s -1 are more than 6600, equal to 275 days, exceeding 75% of total annual hours. Advantage wind velocity spectrum was in the scope of 3–9m s -1 at all gradients and the peak value of wind speed was 4–6m s -1 . Differences in the wind speed frequency distribution at other gradients were not apparent except for the 10m gradient. Compared with other layers, the occurrence frequency of small wind at the level of 10m was higher, while the occurrence frequency of wind speed between 6 and 12m s -1 was higher at other layers. The advantage wind direction in this area was northwest and the wind speed difference was not obvious. Wind speed and wind power density gradually increased with the increasing height, and differences among sites were apparent. The average wind turbulence intensity was 0.199 at each layer and the average shear index was 0.075; turbulence intensity and shear index gradually reduced from over a 10–70m gradient. Turbulence intensity had the same variation tendency as local temperature, whereby a high temperature corresponded to high turbulence and low temperature to low turbulence. The variation tendency of shear index was opposite to that for turbulence intensity; turbulence intensity gradually decreased from lower layers to top layers and shear index was most obvious between 10–30m. Turbulence intensity at each site at each level was between 0.10–0.25, and of medium intensity. These data will provide a technical gist for the layout of wind farms and the utilization of wind power resource at ground level throughout the study region.
基金Program for Changjiang Scholar and Innovative Tea m in University(Grant No.985-2-063-112)
文摘By means of solvent extraction and repeated chromatography on silica gel, Sephadex LH-20, HPLC, and preparative TLC, the ethanol extract of the stems of Homalium ceylanicum（Flacourtiaceae/Salicaceae sensu lato） was chemically investigated, which led to the isolation of 13 constituents, including five lignans（1–5） and three isocoumarins（6–8）. Based on the spectroscopic analysis and comparison of its 1H NMR and 13C NMR data with those in literatures, their structures were identified as（–）-5＇-methoxyisolariciresinol 3α-O-β-D-glucopyranoside（1）,（＋）-lyoniresinol 3α-O-β-D-glucopyranoside（2）,（＋）-isolarisiresinol 3α-O-β-Dglucopyranoside（3）,（–）-isolarisiresinol 3α-O-β-D-glucopyranoside（4）, icariside E5（5）, 3-phenylisocoumarin（6）, homalicine（7）,（–）-dihydrohomalicine（8）, friedelin（9）, 4-hydroxybenzoic acid（10）, catechol（11）, methyl-α-arabinofuranoside（12）, and uridine（13）. All isolates except compounds 6–8 were described from this genus for the first time. Compound 6 was isolated from this species for the first time.
基金supported by the Foundation of Guangdong Forestry Bureau of China(Nos.F11031 and F15141)
文摘During January–February 2008, a severe ice storm caused significant damages to forests in southern China, creating canopy gaps and changing soil nutrient availability and enzyme activity. To understand the relationships between gap size, changes in the soil environment and the effects that these changes have on soil processes, we investigated the effects of gap size on soil chemical and biological properties in the forest gaps in a Cunninghamia lanceolata stand in northern Guangdong Province, southern China. Ten naturally created gaps, five large(80–100 m^2) and five small(30–40 m^2), were selected in the stand of C.lanceolata. The large gaps showed a significant increase in light transmission ratio and air and soil temperatures and a decline in soil moisture, organic matter,N and P compared with the small gaps and the adjacent canopy-covered plots in the 0–10 cm soil. The differences in organic matter and nutrient levels found between the large and small gaps and the canopy-covered plots may be related to changes in environmental conditions. This indicated rapid litter decomposition and increased nutrient leaching in the large gaps. Moreover, the lowest levels of catalase, acid phosphatase and urease activities occurred in large gaps because of the decline in their soil fertility. Large forest gaps may have a region of poor fertility, reducing soil nutrient availability and enzyme activity within the C.lanceolata stand.
