Disturbance is often touted as a management tool, as moderate disturbance is believed to enhance diversity; thus an understanding of frequent and fluctuating disturbance regimes in forests and their effects on stand s...Disturbance is often touted as a management tool, as moderate disturbance is believed to enhance diversity; thus an understanding of frequent and fluctuating disturbance regimes in forests and their effects on stand structure, dominance and diversity is very crucial. Here, the effects of different disturbance regimes, along a gradient, on diversity and dominance of five Shorea robusta Gaertn. f.-dominated forests were investigated in 25 one-ha plots in Nepal. A total of 67 tree species were recorded; of which 41 species were encountered in least disturbed and 10 species in beavily disturbed forest. Significant variations among forests were observed for all measures of alpha diversity. Alpha diversity measures declined linearly along a disturbance gradient while dominance increased linearly. Relative basal area of S. robusta increased as the level of disturbance increased, which in turn produced more than two-fold higher important value index in heavily disturbed forest than the least disturbed forest. All alpha diversity measures declined in an order of three with increasing relative basal area of S. robusta. The similarity in species composition between each pair of disturbed forests was generally low （Jaccard＇s similarity index 〈 57%）, suggesting a higher Beta diversity, It can be concluded that diversity of Sal forests declines with increasing magnitude of disturbance, which in turn favors a higher domi- nance of S. robusta. Controlling the population of the dominant species, mainly S. robusta, is recommended to enhance diversity and to achieve multiple-use forest management objectives.展开更多
Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecologica...Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecological processes and functions, which may affect its recreational and tourism values, compromising local economies and livelihoods. The long-term impacts (1996-2011) of recreational navigation on seagrass benthic community structure were assessed by addressing the question of whether long-term effects of recreational navigation had a significant impact on seagrass community structure and on its benthic faunal assemblages. Findings evidenced: 1) a consistent spatio-temporal gradient in the ecological conditions of seagrasses across the scoured areas, with increased percent seagrass cover, density and canopy height, and seagrass benthic biodiversity with increasing distance from disturbed areas;2) a decline in percent seagrass cover, and an increased macroalgal and cyanobacterial percent cover through time around the disturbed areas;3) a significant shift in seagrass assemblage biodiversity as a response to boating that followed the intermediate disturbance hypothesis;4) an adverse effect on the spatial distribution and survival of multiple benthic invertebrate taxa;and 5) a significant decline in cnidarians, echinoids, ophiuroids, holothurians, and gastropods, and an increase in polychaetes, platyhelminths, and hermit crabs, particularly in areas exposed to boating. Spatio-temporal variation in seagrass community structure explained the observed variation in benthic faunal assemblages. The long-term consequences on ecosystem functions and management needs are discussed to foster the conservation of seagrasses.展开更多
Aims Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarely been examined in detail.In 1996,Hurricane Fran significantly damaged many long-term tree ...Aims Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarely been examined in detail.In 1996,Hurricane Fran significantly damaged many long-term tree census plots in the Duke Forest on the North Carolina Piedmont,thereby providing an exceptional opportunity to examine pre-and post-hurricane forest compositional trajectories.Our goal was to examine immediate,short-term(0–4 years)and longer term(;5 year)hurricane-induced structural,spatial and compositional changes in the tree population(stem d.b.h>1 cm)in the context of our detailed,long-term knowledge of the dynamics of these forests.Methods We surveyed stem damage and tree mortality in 34 long-term permanent plots(ca.70-year record;404–1012 m^(2))and 7 large mapped tree stands(ca.20-year record;5250–65000 m^(2))representing both transition-phase,even-aged pine stands and uneven-aged upland hardwood forests.We employed three types of damage measures to quantify stand-level damage severity:percentage of stems damaged,percentage of basal area lost and a‘stand-level damage index’.Second-order spatial analysis(Ripley’s K-function)was used to investigate patterns in tree mortality.Important findings Our study found hurricane effects on the structural attributes of Piedmont forests to be variable and patchy.Changes in tree species composition,however,were modest.Uprooting was the major damage type for the overstory trees[diameter at breast height(d.b.h.)>10 cm]apparently due to the exposure of the crowns to high wind combined with heavy rainfall prior to and during the storm.Saplings,juvenile trees and small trees(1–10 cm d.b.h.)of the understory and midstory were mainly damaged by being pinned or bent by their damaged large neighbors.Hurricane-induced tree mortality varied weakly among species,was positively correlated with pre-hurricane tree size and remained up to 2-fold higher than pre-hurricane background mortality 5 years after the hurricane.Spatial point pattern analysis revealed a patchy distribution of tree mortality during the hurricane sampling interval.Hurricane Fran resulted in a dramatic increase in average gap size from ca.400 m^(2) pre-hurricane to ca 1100 m^(2) after the hurricane,whereas maximum gap sizes reached 18–34 times larger than the pre-hurricane levels.展开更多
Aims Human land use such as agriculture and logging can have cascad-ing effects on the environment and severely influence forest eco-systems by altering structure,species composition and community processes.These acti...Aims Human land use such as agriculture and logging can have cascad-ing effects on the environment and severely influence forest eco-systems by altering structure,species composition and community processes.These activities may have long-term consequences,which impact forest recovery.We investigated the legacy of his-torical anthropogenic land use on the current reproductive effort(RE)and success of the understory,myco-heterotrophic orchid,Wullschlaegelia calcarata in Puerto Rico’s tropical rain forest after 80 years of forest recovery.Methods Our study site was the 16-ha Luquillo Forest Dynamics Plot in the Luquillo Experimental Forest.We used six 10 m×500 m transect lines that spanned areas with differing levels of historic canopy coverage which are correlated with land use history.We recorded the abundance of W.calcarata plants and measured shoot height,number of flowers,fruit set for all plants and seed set from the most mature,undehisced fruit on a random subset of plants measured.We sought to determine whether or not there is a legacy of land use history on the RE and success of W.calcarata.Of the varying degrees of historic disturbance,we predicted that RE and success would be highest in minimally disturbed old-growth forest,and that soil type differences would be insufficient to affect RE or success.Important Findings We found 1607 plants of W.calcarata,and only one was detected in the most historically disturbed area of the forest.The orchids were most abundant in the two least historically disturbed sites.However,the prevailing trend in all measures of RE is in the opposite direction with greater RE in the forest plots with intermediate levels of histori-cal disturbance.Furthermore,the best model(as a function of AICc and weights)to predict RE is a combination of soil type and cover class.Nevertheless,our measures of reproductive success(fruit and seed set)were best in the least historically disturbed sites and were not associated with soil type.Thus,the best sites for growth are not always the same as those for abundance and reproduction,and after>80 years of recovery,components of the rainforest community have not fully recovered.展开更多
文摘Disturbance is often touted as a management tool, as moderate disturbance is believed to enhance diversity; thus an understanding of frequent and fluctuating disturbance regimes in forests and their effects on stand structure, dominance and diversity is very crucial. Here, the effects of different disturbance regimes, along a gradient, on diversity and dominance of five Shorea robusta Gaertn. f.-dominated forests were investigated in 25 one-ha plots in Nepal. A total of 67 tree species were recorded; of which 41 species were encountered in least disturbed and 10 species in beavily disturbed forest. Significant variations among forests were observed for all measures of alpha diversity. Alpha diversity measures declined linearly along a disturbance gradient while dominance increased linearly. Relative basal area of S. robusta increased as the level of disturbance increased, which in turn produced more than two-fold higher important value index in heavily disturbed forest than the least disturbed forest. All alpha diversity measures declined in an order of three with increasing relative basal area of S. robusta. The similarity in species composition between each pair of disturbed forests was generally low （Jaccard＇s similarity index 〈 57%）, suggesting a higher Beta diversity, It can be concluded that diversity of Sal forests declines with increasing magnitude of disturbance, which in turn favors a higher domi- nance of S. robusta. Controlling the population of the dominant species, mainly S. robusta, is recommended to enhance diversity and to achieve multiple-use forest management objectives.
文摘Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecological processes and functions, which may affect its recreational and tourism values, compromising local economies and livelihoods. The long-term impacts (1996-2011) of recreational navigation on seagrass benthic community structure were assessed by addressing the question of whether long-term effects of recreational navigation had a significant impact on seagrass community structure and on its benthic faunal assemblages. Findings evidenced: 1) a consistent spatio-temporal gradient in the ecological conditions of seagrasses across the scoured areas, with increased percent seagrass cover, density and canopy height, and seagrass benthic biodiversity with increasing distance from disturbed areas;2) a decline in percent seagrass cover, and an increased macroalgal and cyanobacterial percent cover through time around the disturbed areas;3) a significant shift in seagrass assemblage biodiversity as a response to boating that followed the intermediate disturbance hypothesis;4) an adverse effect on the spatial distribution and survival of multiple benthic invertebrate taxa;and 5) a significant decline in cnidarians, echinoids, ophiuroids, holothurians, and gastropods, and an increase in polychaetes, platyhelminths, and hermit crabs, particularly in areas exposed to boating. Spatio-temporal variation in seagrass community structure explained the observed variation in benthic faunal assemblages. The long-term consequences on ecosystem functions and management needs are discussed to foster the conservation of seagrasses.
基金supported by W.C.Coker and A.H.Beers fellowships and a Dissertation Completion Fellowship from the University of North Carolina at Chapel Hill to W.X.and a grant from the National Science Foundation(DEB-97-07551)to R.K.P.and D.L.U.
文摘Aims Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarely been examined in detail.In 1996,Hurricane Fran significantly damaged many long-term tree census plots in the Duke Forest on the North Carolina Piedmont,thereby providing an exceptional opportunity to examine pre-and post-hurricane forest compositional trajectories.Our goal was to examine immediate,short-term(0–4 years)and longer term(;5 year)hurricane-induced structural,spatial and compositional changes in the tree population(stem d.b.h>1 cm)in the context of our detailed,long-term knowledge of the dynamics of these forests.Methods We surveyed stem damage and tree mortality in 34 long-term permanent plots(ca.70-year record;404–1012 m^(2))and 7 large mapped tree stands(ca.20-year record;5250–65000 m^(2))representing both transition-phase,even-aged pine stands and uneven-aged upland hardwood forests.We employed three types of damage measures to quantify stand-level damage severity:percentage of stems damaged,percentage of basal area lost and a‘stand-level damage index’.Second-order spatial analysis(Ripley’s K-function)was used to investigate patterns in tree mortality.Important findings Our study found hurricane effects on the structural attributes of Piedmont forests to be variable and patchy.Changes in tree species composition,however,were modest.Uprooting was the major damage type for the overstory trees[diameter at breast height(d.b.h.)>10 cm]apparently due to the exposure of the crowns to high wind combined with heavy rainfall prior to and during the storm.Saplings,juvenile trees and small trees(1–10 cm d.b.h.)of the understory and midstory were mainly damaged by being pinned or bent by their damaged large neighbors.Hurricane-induced tree mortality varied weakly among species,was positively correlated with pre-hurricane tree size and remained up to 2-fold higher than pre-hurricane background mortality 5 years after the hurricane.Spatial point pattern analysis revealed a patchy distribution of tree mortality during the hurricane sampling interval.Hurricane Fran resulted in a dramatic increase in average gap size from ca.400 m^(2) pre-hurricane to ca 1100 m^(2) after the hurricane,whereas maximum gap sizes reached 18–34 times larger than the pre-hurricane levels.
基金This project was funded by the Research Experience for Undergraduates programme at El Verde Field Station,University of Puerto Rico(NSF-DBI-1559679,Alonso Ramírez,Principal Investigator).
文摘Aims Human land use such as agriculture and logging can have cascad-ing effects on the environment and severely influence forest eco-systems by altering structure,species composition and community processes.These activities may have long-term consequences,which impact forest recovery.We investigated the legacy of his-torical anthropogenic land use on the current reproductive effort(RE)and success of the understory,myco-heterotrophic orchid,Wullschlaegelia calcarata in Puerto Rico’s tropical rain forest after 80 years of forest recovery.Methods Our study site was the 16-ha Luquillo Forest Dynamics Plot in the Luquillo Experimental Forest.We used six 10 m×500 m transect lines that spanned areas with differing levels of historic canopy coverage which are correlated with land use history.We recorded the abundance of W.calcarata plants and measured shoot height,number of flowers,fruit set for all plants and seed set from the most mature,undehisced fruit on a random subset of plants measured.We sought to determine whether or not there is a legacy of land use history on the RE and success of W.calcarata.Of the varying degrees of historic disturbance,we predicted that RE and success would be highest in minimally disturbed old-growth forest,and that soil type differences would be insufficient to affect RE or success.Important Findings We found 1607 plants of W.calcarata,and only one was detected in the most historically disturbed area of the forest.The orchids were most abundant in the two least historically disturbed sites.However,the prevailing trend in all measures of RE is in the opposite direction with greater RE in the forest plots with intermediate levels of histori-cal disturbance.Furthermore,the best model(as a function of AICc and weights)to predict RE is a combination of soil type and cover class.Nevertheless,our measures of reproductive success(fruit and seed set)were best in the least historically disturbed sites and were not associated with soil type.Thus,the best sites for growth are not always the same as those for abundance and reproduction,and after>80 years of recovery,components of the rainforest community have not fully recovered.
