Africa is covered with extensive woodlands,savannas and rainforests.The tree cover of these biomes has been undergoing substantial changes in recent decades.However,the dynamics of forests in Africa are currently uncl...Africa is covered with extensive woodlands,savannas and rainforests.The tree cover of these biomes has been undergoing substantial changes in recent decades.However,the dynamics of forests in Africa are currently unclear,particularly in the woodlands and savanna areas covered by sparse trees.Here,we assessed the spatio-temporal trend of African forests from 2000 to 2020,using a 250-m resolution fractional tree cover product that can capture the variation of forest density in the widespread mixed vegetation landscapes of the continent.The tree cover trends,interannual change and hotspots of forest gain and loss were evaluated.Results showed that the African forest area increased at a rate of 3.59 million ha/year over the study period,reaching 589 million ha in 2020.Considerable forest gain and loss both occurred in Africa.The net change rate in woodlands’forest area was the fastest(2.28 million ha/year),followed by rainforests(0.80 million ha/year)and savannas(0.34 million ha/year).Hotspots of forest gain were concentrated in the north belt of woodlands and savannas,while forest loss primarily clustered in East and South Africa.This work would help African countries to monitor forest change and promote forest management to achieve the Sustainable Development Goals.展开更多
We developed a global,30-m resolution dataset of percent tree cover by rescaling the 250-m MOderate-resolution Imaging Spectroradiometer(MODIS)Vegetation Continuous Fields(VCF)Tree Cover layer using circa-2000 and 200...We developed a global,30-m resolution dataset of percent tree cover by rescaling the 250-m MOderate-resolution Imaging Spectroradiometer(MODIS)Vegetation Continuous Fields(VCF)Tree Cover layer using circa-2000 and 2005 Landsat images,incorporating the MODIS Cropland Layer to improve accuracy in agricultural areas.Resulting Landsat-based estimates maintained consistency with the MODIS VCF in both epochs(RMSE=8.6%in 2000 and 11.9%in 2005),but showed improved accuracy in agricultural areas and increased discrimination of small forest patches.Against lidar measurements,the Landsat-based estimates exhibited accuracy slightly less than that of the MODIS VCF(RMSE=16.8%for MODIS-based vs.17.4%for Landsat-based estimates),but RMSE of Landsat estimates was 3.3 percentage points lower than that of the MODIS data in an agricultural region.The Landsat data retained the saturation artifact of the MODIS VCF at greater than or equal to 80%tree cover but showed greater potential for removal of errors through calibration to lidar,with post-calibration RMSE of 9.4%compared to 13.5%in MODIS estimates.Provided for free download at the Global Land Cover Facility(GLCF)website(www.landcover.org),the 30-m resolution GLCF tree cover dataset is the highest-resolution multi=temporal depiction of Earth’s tree cover available to the Earth science community.展开更多
In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest a...In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest access. Urban Heat Island Effects are measurable phenomenon that are being experienced by the world’s most urbanized areas, including increased summer high temperatures and lower evapotranspiration from having impervious surfaces instead of vegetation and trees. Tree canopy cover is our natural mitigation tool that absorbs sunlight for photosynthesis, protects humans from incoming radiation, and releases cooling moisture into the air. Unfortunately, urban areas typically have low levels of vegetation. Vulnerable urban communities are lower-income areas of inner cities with less access to heat protection like air conditioners. This study uses mean evapotranspiration levels to assess the variability of urban heat island effects across the state of Tennessee. Results show that increased developed land surface cover in Tennessee creates measurable changes in atmospheric evapotranspiration. As a result, the mean evapotranspiration levels in areas with less tree vegetation are significantly lower than the surrounding forested areas. Central areas of urban cities in Tennessee had lower mean evapotranspiration recordings than surrounding areas with less development. This work demonstrates the need for increased tree canopy coverage.展开更多
The main objective of this research is to determine the capacity of land cover classification combining spec- tral and textural features of Landsat TM imagery with ancillary geographical data in wetlands of the Sanjia...The main objective of this research is to determine the capacity of land cover classification combining spec- tral and textural features of Landsat TM imagery with ancillary geographical data in wetlands of the Sanjiang Plain, Heilongjiang Province, China. Semi-variograms and Z-test value were calculated to assess the separability of grey-level co-occurrence texture measures to maximize the difference between land cover types. The degree of spatial autocorrelation showed that window sizes of 3×3 pixels and 11×11 pixels were most appropriate for Landsat TM im- age texture calculations. The texture analysis showed that co-occurrence entropy, dissimilarity, and variance texture measures, derived from the Landsat TM spectrum bands and vegetation indices provided the most significant statistical differentiation between land cover types. Subsequently, a Classification and Regression Tree (CART) algorithm was applied to three different combinations of predictors: 1) TM imagery alone (TM-only); 2) TM imagery plus image texture (TM+TXT model); and 3) all predictors including TM imagery, image texture and additional ancillary GIS in- formation (TM+TXT+GIS model). Compared with traditional Maximum Likelihood Classification (MLC) supervised classification, three classification trees predictive models reduced the overall error rate significantly. Image texture measures and ancillary geographical variables depressed the speckle noise effectively and reduced classification error rate of marsh obviously. For classification trees model making use of all available predictors, omission error rate was 12.90% and commission error rate was 10.99% for marsh. The developed method is portable, relatively easy to im- plement and should be applicable in other settings and over larger extents.展开更多
The dynamics of snow cover differs greatly from basin to basin in the Songhua River of Northeast China, which is attributable to the differences in the topographic shift as well as changes in the vegetation and climat...The dynamics of snow cover differs greatly from basin to basin in the Songhua River of Northeast China, which is attributable to the differences in the topographic shift as well as changes in the vegetation and climate since the hydrological year(HY) 2003. Daily and flexible multi-day combinations from the HY 2003 to 2014 were produced using Moderate Resolution Imaging Spectroradiometer(MODIS) from Terra and Aqua remote sensing satellites for the snow cover products in the three basins including the Nenjiang River Basin(NJ), Downstream Songhua River Basin(SD) and Upstream Songhua River Basin(SU). Snow cover duration(SCD) was derived from flexible multiday combination each year. The results showed that SCD was significantly associated with elevation, and higher SCD values were found out in the mountainous areas. Further, the average SCDs of NJ, SU and SD basins were 69.43, 98.14 and 88.84 d with an annual growth of 1.36, 2.04 and 2.71 d, respectively. Binary decision tree was used to analyze the nonlinear relationships between SCD and six impact factors, which were successfully applied to simulate the spatial distribution of depth and water equivalent of snow. The impact factors included three topographic factors(elevation, aspect and slope), two climatic factors(precipitation and air temperature) and one vegetation index(Normalized Difference Vegetation Index, NDVI). By treating yearly SCD values as dependent variables and six climatic factors as independent variables, six binary decision trees were built through the combination classification and regression tree(CART) with and without the consideration of climate effect. The results from the model show that elevation, precipitation and air temperature are the three most influential factors, among which air temperature is the most important and ranks first in two of the three studied basins. It is suggested that SCD in the mountainous areas might be more sensitive to climate warming, since precipitation and air temperature are the major factors controlling the persistence of snow cover in the mountainous areas.展开更多
The aim of this study was to develop and test a new basal area growth model in mixed species continuous cover forests in northern Iran.Weanalyzed 421 core samples from 6 main species in the forest area to develop our ...The aim of this study was to develop and test a new basal area growth model in mixed species continuous cover forests in northern Iran.Weanalyzed 421 core samples from 6 main species in the forest area to develop our growth model.In each plot,we measured variables such as total tree height(m),diameter at breast height(DBH)(cm)and basal area of larger trees as cumulative basal areas of trees(GCUM)ofDBH[5 cm.The empirical data were analyzed using regression analysis.There was a statistically significant nonlinear function between the annual basal area increment,as the dependent variable,and the basal area of the individual trees and competition as explanatory variables.Reference area from the largest trees,was circular plot with area of 0.1 ha.GCUM was estimated for trees of DBH>5 cm.Furthermore,we investigated the dependencies of diameter growth of different species on stand density at different levels of competition,and diameter development of individual trees through time.The results indicate that competition caused by larger neighborhood trees has a negative effect on growth.In addition,the maximum diameter increment is affected by competition level.Therefore,the maximum diameter increment of species occurs when the trees are about 35–40 cm in dense-forest(40 to 0 m^2 per ha)and when the trees are about 60 to 70 cm in very dense forest(60 to 0 m^2 per ha)which is more likely to Caspian natural forests with high level density due to uneven-aged composition of stands.展开更多
为解决均值漂移聚类算法聚类效果依赖于带宽参数的主观选取,以及处理密度变化大的数据集时聚类结果精确度问题,提出一种基于覆盖树的自适应均值漂移聚类算法MSCT(MeanShift based on Cover-Tree)。构建一个覆盖树数据集,在计算漂移向量...为解决均值漂移聚类算法聚类效果依赖于带宽参数的主观选取,以及处理密度变化大的数据集时聚类结果精确度问题,提出一种基于覆盖树的自适应均值漂移聚类算法MSCT(MeanShift based on Cover-Tree)。构建一个覆盖树数据集,在计算漂移向量过程中结合覆盖树数据集获得新的漂移向量结果KnnShift,在不同数据密度分布的数据集上都能自适应产生带宽参数,所有数据点完成漂移过程后获得聚类结果。实验结果表明,MSCT算法的聚类效果整体上优于MS、DBSCAN等算法。展开更多
We investigated the effect of tree cover,forest patch and disturbances on tree species richness in a highly diverse conservation area of northeast Bangladesh.A systematic sampling protocol was adopted and 80 sub-plots...We investigated the effect of tree cover,forest patch and disturbances on tree species richness in a highly diverse conservation area of northeast Bangladesh.A systematic sampling protocol was adopted and 80 sub-plots from twenty five 1 ha plots were used for the vegetation survey.Linear regression analysis was performed to understand the effect of patch area,disturbances and tree cover on tree species richness.Ordination using Redundancy analysis(RDA) and Non-metric Multi Dimensional Scaling(NMDS) were also performed to explore the tree species compositional similarities along the stand characteristics gradient and locations of the sample plots.Our study revealed that,forest patch size has greater influence on species richness.Areas with medium level of disturbances have shown greater species richness.In constrained ordination the selected explanatory variables regulated the richness of common species.Our findings can be useful for better forest management and restoration of landscapes of conservation needs using ecologically important species.展开更多
Theoretical background and an implementation of the p-group generation algorithm by Newman and O’Brien are used to provide computational evidence of a new type of periodically repeating patterns in pruned descendant ...Theoretical background and an implementation of the p-group generation algorithm by Newman and O’Brien are used to provide computational evidence of a new type of periodically repeating patterns in pruned descendant trees of finite p-groups.展开更多
Human activities have severely impacted on many species and ecosystems.Thus,understanding the local biodiversity situation is crucial for implementing effective biodiversity conservation interventions.Mindanao in the ...Human activities have severely impacted on many species and ecosystems.Thus,understanding the local biodiversity situation is crucial for implementing effective biodiversity conservation interventions.Mindanao in the southern Philippines is home to various unique species,particularly in its pristine ecosystems.However,the available biodiversity data for many terrestrial vertebrates and key areas remain incomplete.To address this issue,we synthesized published literature related to biodiversity from 2000 to 2022 in Mindanao.Moreover,this analysis used four key terrestrial vertebrates(amphibians,reptiles,birds,and mammals)in Mindanao as research objects.According to our findings,there was a significant and positive correlation between the number of biodiversity studies and species recorded.In terms of species richness,birds were the most recorded group(n=334 spp.),followed by reptiles(n=108 spp.),mammals(n=70 spp.),and amphibians(n=52 spp.).We also found that the number of endemic and threatened species varies geographically and across taxonomic groups.Yet,we discovered a significant disparity in the information available on biodiversity in different provinces of Mindanao.For example,the western provinces of Mindanao have had no record of biodiversity for more than two decades.Furthermore,we found that the changes in tree cover loss were consistent with biodiversity records,but this correlation is only significant for birds.Finally,we highlighted some critical threats and challenges to biodiversity,including deforestation,agricultural expansion,mining,and their impact on biodiversity conservation in Mindanao.Our findings suggested that biodiversity conservation should focus not only on areas with high levels of biodiversity but also on areas lacking biodiversity information.To do this,we call for strengthening collaboration among various institutions and digitizing and centralizing of information related to biodiversity.By gaining a deeper understanding of biodiversity in Mindanao,we can better and sustainably protect critical ecosystems in this region from the increasing threats posed by human activities.展开更多
Background: In economically optimal management, trees that are removed in a thinning treatment should be selected on the basis of their value, relative value increment and the effect of removal on the growth of remai...Background: In economically optimal management, trees that are removed in a thinning treatment should be selected on the basis of their value, relative value increment and the effect of removal on the growth of remaining trees. Large valuable trees with decreased value increment should be removed, especially when they overtop smaller trees. Methods: This study optimized the tree selection rule in the thinning treatments of continuous cover managemen when the aim is to maximize the profitability of forest management. The weights of three criteria (stem value, relative value increment and effect of removal on the competition of remaining trees) were optimized together with thinning intervals. Results and conclusions: The results confirmed the hypothesis that optimal thinning involves removing predominantly large trees. Increasing stumpage value, decreasing relative value increment, and increasing competitive influence increased the likelihood that removal is optimal decision. However, if the spatial distribution of trees is irregular, it is optimal to leave large trees in sparse places and remove somewhat smaller trees from dense places. However, the benefit of optimal thinning, as compared to diameter limit cutting is not usually large in pure one-species stands. On the contrary, removing the smallest trees from the stand may lead to significant (30-40 %) reductions in the net present value of harvest incomes.展开更多
In many parts of mainland Southeast Asia rubber plantations are expanding rapidly in areas where the crop was not historically found. Monitoring and mapping the distribution of rubber trees in the region is necessary ...In many parts of mainland Southeast Asia rubber plantations are expanding rapidly in areas where the crop was not historically found. Monitoring and mapping the distribution of rubber trees in the region is necessary for developing a better understanding of the consequences of land-cover and land-use change on carbon and water cycles. In this study, we conducted rubber tree growth mapping in Northeast Thailand using Landsat 5 TM data. A Mahalanobis typicality method was used to identify different age rubber trees. Landsat 5 TM 30 m non-thermal reflective bands, NDVI and tasseled cap transformation components were selected as the model input metrics. The validation was carried out using provincial level agricultural statistical data on the rubber tree growth area. At regional (Northeast Thailand) and provincial scales, the estimates of mature and middle-age rubber stands produced from 30 m Landsat 5 TM data compared well (high statistical significance) with the provincial rubber tree growth statistical data.展开更多
The vertices of an infinite locally finite tree T are labelled by a collection of i.i.d. real random variables {Xσ}σ∈T which defines a tree indexed walk Xr. We introduce and study theoscillations of the walk:where ...The vertices of an infinite locally finite tree T are labelled by a collection of i.i.d. real random variables {Xσ}σ∈T which defines a tree indexed walk Xr. We introduce and study theoscillations of the walk:where Φ(n) is an increasing sequence of positive numbers. We prove that for each $ belonging to a certain class of sequences of different orders, there are ξ 's depending on Φ such that 0 < OSCΦ(ξ) <∞. Exact Hausdorff dimension of the set of such ξ's is calculated. An application is given to study the local variation of Brownian motion. A general limsup deviation problem on trees is also studied.展开更多
基金supported by the National Key Research and Development Program of China(No.2019YFA0606603)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA19080303)+1 种基金the National Natural Science Foundation of China(No.42161144001)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2019056).
文摘Africa is covered with extensive woodlands,savannas and rainforests.The tree cover of these biomes has been undergoing substantial changes in recent decades.However,the dynamics of forests in Africa are currently unclear,particularly in the woodlands and savanna areas covered by sparse trees.Here,we assessed the spatio-temporal trend of African forests from 2000 to 2020,using a 250-m resolution fractional tree cover product that can capture the variation of forest density in the widespread mixed vegetation landscapes of the continent.The tree cover trends,interannual change and hotspots of forest gain and loss were evaluated.Results showed that the African forest area increased at a rate of 3.59 million ha/year over the study period,reaching 589 million ha in 2020.Considerable forest gain and loss both occurred in Africa.The net change rate in woodlands’forest area was the fastest(2.28 million ha/year),followed by rainforests(0.80 million ha/year)and savannas(0.34 million ha/year).Hotspots of forest gain were concentrated in the north belt of woodlands and savannas,while forest loss primarily clustered in East and South Africa.This work would help African countries to monitor forest change and promote forest management to achieve the Sustainable Development Goals.
基金Work was performed in service of the Global Forest Cover Change Project(www.forestcover.org),a partnership of the University of Maryland Global Land Cover Facility(www.landcover.org)NASA Goddard Space Flight Center,with funding from the NASA MEaSUREs program.Work was performed at the Global Land Cover Facility+5 种基金The authors would like to thank especially the providers of datasets used in this project:Global Land Survey data were provided by Rachel Headley at the USGS Eros Data CenterMODIS Collection-5 VCF data were provided by Charlene DiMiceli in the University of Maryland Department of Geographical SciencesLidar data were provided by OpenTopography(www.opentopography.org)by Bruce Cook at the NASA Goddard Space Flight Center and Paul Bolstad in the University of Minnesota Department of Forest Resouces with funding from NASA and the University of Minnesota Initiative for Renewable Energy and the Environment(IREE)by James Kellner at the University of Maryland,and by R.Dubayah at the University of Maryland from work funded by the NASA Terrestrial Ecology Program.Lidar processing was done using the US Forest Service FUSION software,Version 3.21.Statistical analyses were conducted in R(R Core Team 2012)using the‘raster’package(Hijmans and Etten 2012)Jeff Masek and Eric Vermote at the NASA Goddard Space Flight Center and Matthew Hansen and Amanda Whitehurst and Hao Tang at the University of Maryland Department of Geographical Sciences provided feedback and insights on algorithms and datasets.T.B.Murphy provided assistance with algorithm development.
文摘We developed a global,30-m resolution dataset of percent tree cover by rescaling the 250-m MOderate-resolution Imaging Spectroradiometer(MODIS)Vegetation Continuous Fields(VCF)Tree Cover layer using circa-2000 and 2005 Landsat images,incorporating the MODIS Cropland Layer to improve accuracy in agricultural areas.Resulting Landsat-based estimates maintained consistency with the MODIS VCF in both epochs(RMSE=8.6%in 2000 and 11.9%in 2005),but showed improved accuracy in agricultural areas and increased discrimination of small forest patches.Against lidar measurements,the Landsat-based estimates exhibited accuracy slightly less than that of the MODIS VCF(RMSE=16.8%for MODIS-based vs.17.4%for Landsat-based estimates),but RMSE of Landsat estimates was 3.3 percentage points lower than that of the MODIS data in an agricultural region.The Landsat data retained the saturation artifact of the MODIS VCF at greater than or equal to 80%tree cover but showed greater potential for removal of errors through calibration to lidar,with post-calibration RMSE of 9.4%compared to 13.5%in MODIS estimates.Provided for free download at the Global Land Cover Facility(GLCF)website(www.landcover.org),the 30-m resolution GLCF tree cover dataset is the highest-resolution multi=temporal depiction of Earth’s tree cover available to the Earth science community.
文摘In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest access. Urban Heat Island Effects are measurable phenomenon that are being experienced by the world’s most urbanized areas, including increased summer high temperatures and lower evapotranspiration from having impervious surfaces instead of vegetation and trees. Tree canopy cover is our natural mitigation tool that absorbs sunlight for photosynthesis, protects humans from incoming radiation, and releases cooling moisture into the air. Unfortunately, urban areas typically have low levels of vegetation. Vulnerable urban communities are lower-income areas of inner cities with less access to heat protection like air conditioners. This study uses mean evapotranspiration levels to assess the variability of urban heat island effects across the state of Tennessee. Results show that increased developed land surface cover in Tennessee creates measurable changes in atmospheric evapotranspiration. As a result, the mean evapotranspiration levels in areas with less tree vegetation are significantly lower than the surrounding forested areas. Central areas of urban cities in Tennessee had lower mean evapotranspiration recordings than surrounding areas with less development. This work demonstrates the need for increased tree canopy coverage.
基金Under the auspices of National Natural Science Foundation of China (No. 40871188) National Key Technologies R&D Program of China (No. 2006BAD23B03)
文摘The main objective of this research is to determine the capacity of land cover classification combining spec- tral and textural features of Landsat TM imagery with ancillary geographical data in wetlands of the Sanjiang Plain, Heilongjiang Province, China. Semi-variograms and Z-test value were calculated to assess the separability of grey-level co-occurrence texture measures to maximize the difference between land cover types. The degree of spatial autocorrelation showed that window sizes of 3×3 pixels and 11×11 pixels were most appropriate for Landsat TM im- age texture calculations. The texture analysis showed that co-occurrence entropy, dissimilarity, and variance texture measures, derived from the Landsat TM spectrum bands and vegetation indices provided the most significant statistical differentiation between land cover types. Subsequently, a Classification and Regression Tree (CART) algorithm was applied to three different combinations of predictors: 1) TM imagery alone (TM-only); 2) TM imagery plus image texture (TM+TXT model); and 3) all predictors including TM imagery, image texture and additional ancillary GIS in- formation (TM+TXT+GIS model). Compared with traditional Maximum Likelihood Classification (MLC) supervised classification, three classification trees predictive models reduced the overall error rate significantly. Image texture measures and ancillary geographical variables depressed the speckle noise effectively and reduced classification error rate of marsh obviously. For classification trees model making use of all available predictors, omission error rate was 12.90% and commission error rate was 10.99% for marsh. The developed method is portable, relatively easy to im- plement and should be applicable in other settings and over larger extents.
基金Under the auspices of National Natural Science Foundation of China(No.41471291,41801283,41070104)Startup Foundation for Doctors of Jilin Jianzhu University(No.861111)13th Five-Year Plan of Technical and Social Research Project for Jilin Colleges(No.JJKH20170257KJ)
文摘The dynamics of snow cover differs greatly from basin to basin in the Songhua River of Northeast China, which is attributable to the differences in the topographic shift as well as changes in the vegetation and climate since the hydrological year(HY) 2003. Daily and flexible multi-day combinations from the HY 2003 to 2014 were produced using Moderate Resolution Imaging Spectroradiometer(MODIS) from Terra and Aqua remote sensing satellites for the snow cover products in the three basins including the Nenjiang River Basin(NJ), Downstream Songhua River Basin(SD) and Upstream Songhua River Basin(SU). Snow cover duration(SCD) was derived from flexible multiday combination each year. The results showed that SCD was significantly associated with elevation, and higher SCD values were found out in the mountainous areas. Further, the average SCDs of NJ, SU and SD basins were 69.43, 98.14 and 88.84 d with an annual growth of 1.36, 2.04 and 2.71 d, respectively. Binary decision tree was used to analyze the nonlinear relationships between SCD and six impact factors, which were successfully applied to simulate the spatial distribution of depth and water equivalent of snow. The impact factors included three topographic factors(elevation, aspect and slope), two climatic factors(precipitation and air temperature) and one vegetation index(Normalized Difference Vegetation Index, NDVI). By treating yearly SCD values as dependent variables and six climatic factors as independent variables, six binary decision trees were built through the combination classification and regression tree(CART) with and without the consideration of climate effect. The results from the model show that elevation, precipitation and air temperature are the three most influential factors, among which air temperature is the most important and ranks first in two of the three studied basins. It is suggested that SCD in the mountainous areas might be more sensitive to climate warming, since precipitation and air temperature are the major factors controlling the persistence of snow cover in the mountainous areas.
基金Ministry of Science,Research and Technology of Iran for the scholarship to Nishtman Hatami to take a short time study in Sweden
文摘The aim of this study was to develop and test a new basal area growth model in mixed species continuous cover forests in northern Iran.Weanalyzed 421 core samples from 6 main species in the forest area to develop our growth model.In each plot,we measured variables such as total tree height(m),diameter at breast height(DBH)(cm)and basal area of larger trees as cumulative basal areas of trees(GCUM)ofDBH[5 cm.The empirical data were analyzed using regression analysis.There was a statistically significant nonlinear function between the annual basal area increment,as the dependent variable,and the basal area of the individual trees and competition as explanatory variables.Reference area from the largest trees,was circular plot with area of 0.1 ha.GCUM was estimated for trees of DBH>5 cm.Furthermore,we investigated the dependencies of diameter growth of different species on stand density at different levels of competition,and diameter development of individual trees through time.The results indicate that competition caused by larger neighborhood trees has a negative effect on growth.In addition,the maximum diameter increment is affected by competition level.Therefore,the maximum diameter increment of species occurs when the trees are about 35–40 cm in dense-forest(40 to 0 m^2 per ha)and when the trees are about 60 to 70 cm in very dense forest(60 to 0 m^2 per ha)which is more likely to Caspian natural forests with high level density due to uneven-aged composition of stands.
文摘为解决均值漂移聚类算法聚类效果依赖于带宽参数的主观选取,以及处理密度变化大的数据集时聚类结果精确度问题,提出一种基于覆盖树的自适应均值漂移聚类算法MSCT(MeanShift based on Cover-Tree)。构建一个覆盖树数据集,在计算漂移向量过程中结合覆盖树数据集获得新的漂移向量结果KnnShift,在不同数据密度分布的数据集上都能自适应产生带宽参数,所有数据点完成漂移过程后获得聚类结果。实验结果表明,MSCT算法的聚类效果整体上优于MS、DBSCAN等算法。
基金supported by the Department of Forestry and Environment Science,Shahjalal University of Science and Technology,Bangladeshsupported by a grant from University Research Center,Shahjalal University of Science and Technology to accomplish the field work for this study
文摘We investigated the effect of tree cover,forest patch and disturbances on tree species richness in a highly diverse conservation area of northeast Bangladesh.A systematic sampling protocol was adopted and 80 sub-plots from twenty five 1 ha plots were used for the vegetation survey.Linear regression analysis was performed to understand the effect of patch area,disturbances and tree cover on tree species richness.Ordination using Redundancy analysis(RDA) and Non-metric Multi Dimensional Scaling(NMDS) were also performed to explore the tree species compositional similarities along the stand characteristics gradient and locations of the sample plots.Our study revealed that,forest patch size has greater influence on species richness.Areas with medium level of disturbances have shown greater species richness.In constrained ordination the selected explanatory variables regulated the richness of common species.Our findings can be useful for better forest management and restoration of landscapes of conservation needs using ecologically important species.
文摘Theoretical background and an implementation of the p-group generation algorithm by Newman and O’Brien are used to provide computational evidence of a new type of periodically repeating patterns in pruned descendant trees of finite p-groups.
基金the ‘Bangsamoro Autonomous Region in Muslim Mindanao (BARMM) in Changing Environment Project’ funded by the Ministry of Science and Technology of the Bangsamoro Autonomous Region in Muslim Mindanao (MOST-BARMM)
文摘Human activities have severely impacted on many species and ecosystems.Thus,understanding the local biodiversity situation is crucial for implementing effective biodiversity conservation interventions.Mindanao in the southern Philippines is home to various unique species,particularly in its pristine ecosystems.However,the available biodiversity data for many terrestrial vertebrates and key areas remain incomplete.To address this issue,we synthesized published literature related to biodiversity from 2000 to 2022 in Mindanao.Moreover,this analysis used four key terrestrial vertebrates(amphibians,reptiles,birds,and mammals)in Mindanao as research objects.According to our findings,there was a significant and positive correlation between the number of biodiversity studies and species recorded.In terms of species richness,birds were the most recorded group(n=334 spp.),followed by reptiles(n=108 spp.),mammals(n=70 spp.),and amphibians(n=52 spp.).We also found that the number of endemic and threatened species varies geographically and across taxonomic groups.Yet,we discovered a significant disparity in the information available on biodiversity in different provinces of Mindanao.For example,the western provinces of Mindanao have had no record of biodiversity for more than two decades.Furthermore,we found that the changes in tree cover loss were consistent with biodiversity records,but this correlation is only significant for birds.Finally,we highlighted some critical threats and challenges to biodiversity,including deforestation,agricultural expansion,mining,and their impact on biodiversity conservation in Mindanao.Our findings suggested that biodiversity conservation should focus not only on areas with high levels of biodiversity but also on areas lacking biodiversity information.To do this,we call for strengthening collaboration among various institutions and digitizing and centralizing of information related to biodiversity.By gaining a deeper understanding of biodiversity in Mindanao,we can better and sustainably protect critical ecosystems in this region from the increasing threats posed by human activities.
文摘Background: In economically optimal management, trees that are removed in a thinning treatment should be selected on the basis of their value, relative value increment and the effect of removal on the growth of remaining trees. Large valuable trees with decreased value increment should be removed, especially when they overtop smaller trees. Methods: This study optimized the tree selection rule in the thinning treatments of continuous cover managemen when the aim is to maximize the profitability of forest management. The weights of three criteria (stem value, relative value increment and effect of removal on the competition of remaining trees) were optimized together with thinning intervals. Results and conclusions: The results confirmed the hypothesis that optimal thinning involves removing predominantly large trees. Increasing stumpage value, decreasing relative value increment, and increasing competitive influence increased the likelihood that removal is optimal decision. However, if the spatial distribution of trees is irregular, it is optimal to leave large trees in sparse places and remove somewhat smaller trees from dense places. However, the benefit of optimal thinning, as compared to diameter limit cutting is not usually large in pure one-species stands. On the contrary, removing the smallest trees from the stand may lead to significant (30-40 %) reductions in the net present value of harvest incomes.
文摘In many parts of mainland Southeast Asia rubber plantations are expanding rapidly in areas where the crop was not historically found. Monitoring and mapping the distribution of rubber trees in the region is necessary for developing a better understanding of the consequences of land-cover and land-use change on carbon and water cycles. In this study, we conducted rubber tree growth mapping in Northeast Thailand using Landsat 5 TM data. A Mahalanobis typicality method was used to identify different age rubber trees. Landsat 5 TM 30 m non-thermal reflective bands, NDVI and tasseled cap transformation components were selected as the model input metrics. The validation was carried out using provincial level agricultural statistical data on the rubber tree growth area. At regional (Northeast Thailand) and provincial scales, the estimates of mature and middle-age rubber stands produced from 30 m Landsat 5 TM data compared well (high statistical significance) with the provincial rubber tree growth statistical data.
文摘The vertices of an infinite locally finite tree T are labelled by a collection of i.i.d. real random variables {Xσ}σ∈T which defines a tree indexed walk Xr. We introduce and study theoscillations of the walk:where Φ(n) is an increasing sequence of positive numbers. We prove that for each $ belonging to a certain class of sequences of different orders, there are ξ 's depending on Φ such that 0 < OSCΦ(ξ) <∞. Exact Hausdorff dimension of the set of such ξ's is calculated. An application is given to study the local variation of Brownian motion. A general limsup deviation problem on trees is also studied.