Ecological interactions of species and thus their spatial pat- terns may differ between homogeneous and heterogeneous forests. To account for this, techniques of point pattern analysis were implemented on mapped locat...Ecological interactions of species and thus their spatial pat- terns may differ between homogeneous and heterogeneous forests. To account for this, techniques of point pattern analysis were implemented on mapped locations of tree individuals from two 1-ha tropicalforest plots in Vietnam. We analyzed the effect of environmental heterogeneity on tree distributions; spatial distribution patterns of dominant species; inter-specific associations; and conspecific associations between life stages. Our analyses showed that： environmental conditions were homo- geneous at plot 1 but heterogeneous at plot 2; in both plots, all six domi- nant species were aggregated at various scales up to 30 m, and tree spe- cies were aggregated at larger scales in the homogeneous site than in the heterogeneous site; attraction between pairs of species was remarkably higher at the homogeneous site while negative associations were more frequent in the heterogeneous site; some species, H. kurzii, T. ilicifolia （homogeneous plot） and D. sylvatica, S. wightianum （heterogeneous plot） showed a lack of early life-stage individuals near conspecific adults. Moreover, additional clustering of young individuals was independent from conspecific adults, except D. sylvatica in both sites. These findings are consistent with the Janzen-ConneU hypothesis. Overall, habitat het- erogeneity influences spatial patterns and inter-specific associations of the tree species and evidences of self-thinning are shown in most species.展开更多
The efficiency of sample-based indices proposed to quantify the spatial distribution of trees is influenced by the structure of tree stands, environmental heterogeneity and degree of aggregation. We evaluated 10 commo...The efficiency of sample-based indices proposed to quantify the spatial distribution of trees is influenced by the structure of tree stands, environmental heterogeneity and degree of aggregation. We evaluated 10 commonly used distance-based and 10 density-based indices using two structurally different stands of wild pistachio trees in the Zagros woodlands, Iran, to assess the reliability of each in revealing stand structure in woodlands. All trees were completely stem-mapped in a nearly pure（40 ha） and a mixed（45 ha） stand. First, the inhomogeneous pair correlation function [g（r）] and the Clark-Evans index（CEI） were used as references to reveal the true spatial arrangement of all trees in these stands. The sampled data were then evaluated using the 20 indices.Sampling was undertaken in a grid based on a square lattice using square plots（30 m 9 30 m） and nearest neighbor distances at the sample points. The g（r） and CEI statistics showed that the wild pistachio trees were aggregated in both stands, although the degree of aggregation was markedly higher in the pure stand. Three distance- and six density-based indices statistically verified that the wild pistachio trees were aggregated in both stands. The distance-based Hines and Hines statistic（ht） and the densitybased standardised Morisita（Ip）, patchiness（IP） and Cassie（CA） indices revealed aggregation of the trees in the two structurally different stands in the Zagros woodlands and the higher clumping in the pure stand, whereas the other indices were not sensitive enough.展开更多
Aims Topography has long been recognized as an important factor in shaping species distributions.Many studies revealed that species may show species-habitat associations.However,few studies inves-tigate how species as...Aims Topography has long been recognized as an important factor in shaping species distributions.Many studies revealed that species may show species-habitat associations.However,few studies inves-tigate how species assemblages are associated with local habitats,and it still remains unclear how the community-habitat associa-tions vary with species abundance class and life stage.In this study,we analyzed the community-habitat associations in a subtropical montane forest.Methods The fully mapped 25-ha(500×500 m)forest plot is located in Badagongshan Nature Reserve in Hunan Province,Central China.It was divided into 625(20×20 m)quadrats.Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics.Indicator species analysis was used to identify the most important species for structuring species assemblages.We also compared the community-habitat associations for two levels of species abundances(i.e.abundant and rare)and three different life stages(i.e.saplings,juveniles and adults),while accounting for sample size effects.Important Findings The Badagongshan plot was divided into five distinct habitat types,which explained 34.7%of the variance in tree species composi-tion.Even with sample size taken into account,community-habi-tat associations for rare species were much weaker than those for abundant species.Also when accounting for sample size,very small differences were found in the variance explained by topography for the three life stages.Indicator species of habitat types were mainly abundant species,and nearly all adult stage indicator species were also indicators in juvenile and sapling stages.Our study manifested that topographical habitat filtering was important in shaping over-all local species compositions.However,habitat filtering was not important in shaping rare species’distributions in this forest.The community-habitat association patterns in this forest were mainly shaped by abundant species.In addition,during the transitions from saplings to juveniles,and from juveniles to adults,the relative importance of habitat filtering was very weak.展开更多
基金supported with funds from the Ministry of Education and Training of Vietnam
文摘Ecological interactions of species and thus their spatial pat- terns may differ between homogeneous and heterogeneous forests. To account for this, techniques of point pattern analysis were implemented on mapped locations of tree individuals from two 1-ha tropicalforest plots in Vietnam. We analyzed the effect of environmental heterogeneity on tree distributions; spatial distribution patterns of dominant species; inter-specific associations; and conspecific associations between life stages. Our analyses showed that： environmental conditions were homo- geneous at plot 1 but heterogeneous at plot 2; in both plots, all six domi- nant species were aggregated at various scales up to 30 m, and tree spe- cies were aggregated at larger scales in the homogeneous site than in the heterogeneous site; attraction between pairs of species was remarkably higher at the homogeneous site while negative associations were more frequent in the heterogeneous site; some species, H. kurzii, T. ilicifolia （homogeneous plot） and D. sylvatica, S. wightianum （heterogeneous plot） showed a lack of early life-stage individuals near conspecific adults. Moreover, additional clustering of young individuals was independent from conspecific adults, except D. sylvatica in both sites. These findings are consistent with the Janzen-ConneU hypothesis. Overall, habitat het- erogeneity influences spatial patterns and inter-specific associations of the tree species and evidences of self-thinning are shown in most species.
基金supported by Vice Chancellor for Research,Shiraz University,IranErasmus Mundus scholarship for travel to Goettingen,Germany
文摘The efficiency of sample-based indices proposed to quantify the spatial distribution of trees is influenced by the structure of tree stands, environmental heterogeneity and degree of aggregation. We evaluated 10 commonly used distance-based and 10 density-based indices using two structurally different stands of wild pistachio trees in the Zagros woodlands, Iran, to assess the reliability of each in revealing stand structure in woodlands. All trees were completely stem-mapped in a nearly pure（40 ha） and a mixed（45 ha） stand. First, the inhomogeneous pair correlation function [g（r）] and the Clark-Evans index（CEI） were used as references to reveal the true spatial arrangement of all trees in these stands. The sampled data were then evaluated using the 20 indices.Sampling was undertaken in a grid based on a square lattice using square plots（30 m 9 30 m） and nearest neighbor distances at the sample points. The g（r） and CEI statistics showed that the wild pistachio trees were aggregated in both stands, although the degree of aggregation was markedly higher in the pure stand. Three distance- and six density-based indices statistically verified that the wild pistachio trees were aggregated in both stands. The distance-based Hines and Hines statistic（ht） and the densitybased standardised Morisita（Ip）, patchiness（IP） and Cassie（CA） indices revealed aggregation of the trees in the two structurally different stands in the Zagros woodlands and the higher clumping in the pure stand, whereas the other indices were not sensitive enough.
基金National Natural Science Foundation of China(31270562,30900178,31200329 and 31500337)Key Laboratory of Aquatic Botany and Watershed Ecology,CAS(Y455432J02)the Chinese Forest Biodiversity Monitoring Network(29200931131101919).
文摘Aims Topography has long been recognized as an important factor in shaping species distributions.Many studies revealed that species may show species-habitat associations.However,few studies inves-tigate how species assemblages are associated with local habitats,and it still remains unclear how the community-habitat associa-tions vary with species abundance class and life stage.In this study,we analyzed the community-habitat associations in a subtropical montane forest.Methods The fully mapped 25-ha(500×500 m)forest plot is located in Badagongshan Nature Reserve in Hunan Province,Central China.It was divided into 625(20×20 m)quadrats.Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics.Indicator species analysis was used to identify the most important species for structuring species assemblages.We also compared the community-habitat associations for two levels of species abundances(i.e.abundant and rare)and three different life stages(i.e.saplings,juveniles and adults),while accounting for sample size effects.Important Findings The Badagongshan plot was divided into five distinct habitat types,which explained 34.7%of the variance in tree species composi-tion.Even with sample size taken into account,community-habi-tat associations for rare species were much weaker than those for abundant species.Also when accounting for sample size,very small differences were found in the variance explained by topography for the three life stages.Indicator species of habitat types were mainly abundant species,and nearly all adult stage indicator species were also indicators in juvenile and sapling stages.Our study manifested that topographical habitat filtering was important in shaping over-all local species compositions.However,habitat filtering was not important in shaping rare species’distributions in this forest.The community-habitat association patterns in this forest were mainly shaped by abundant species.In addition,during the transitions from saplings to juveniles,and from juveniles to adults,the relative importance of habitat filtering was very weak.
