Background:Snags(standing dead trees)are important biological legacies in forest systems,providing numerous resources as well as a record of recent tree mortality.From 1997 to 2017,we monitored snag populations in dro...Background:Snags(standing dead trees)are important biological legacies in forest systems,providing numerous resources as well as a record of recent tree mortality.From 1997 to 2017,we monitored snag populations in drought-influenced mixed-conifer and ponderosa pine(Pinus ponderosa)forests in northern Arizona.Results:Snag density increased significantly in both forest types.This increase was driven largely by a pulse in snag recruitment that occurred between 2002 and 2007,fol owing an extreme drought year in 2002,with snag recruitment returning to pre-pulse levels in subsequent time periods.Some later years during the study also were warmer and/or drier than average,but these years were not as extreme as 2002 and did not trigger the same level of snag recruitment.Snag recruitment was not equal across tree species and size classes,resulting in significant changes in species composition and size-class distributions of snag populations in both forest types.Because trees were far more abundant than snags in these forests,the effect of this mortality pulse on tree populations was far smal er than its effect on snag populations.Snag loss rates increased over time during the study,even though many snags were newly recruited.This may reflect the increasing prevalence of white fir snags and/or snags in the smal er size classes,which general y decay faster than snags of other species or larger snags.Thus,although total numbers of snags increased,many of the newly recruited snags may not persist long enough to be valuable as nesting substrates for native wildlife.Conclusions:Increases in snag abundance appeared to be due to a short-term tree mortality"event"rather than a longerterm pattern of elevated tree mortality.This mortality event fol owed a dry and extremely warm year(2002)embedded within a longer-term megadrought.Climate models suggest that years like 2002 may occur with increasing frequency in the southwestern U.S.Such years may result in additional mortality pulses,which in turn may strongly affect trajectories in abundance,structure,and composition of snag populations.Relative effects on tree populations likely wil be smal er,but,over time,also could be significant.展开更多
In a tropical wet montane evergreen forest in the southern peninsular India, the estimated stocking of dead wood is 90 ± 3 stems·ha-1 and the total dead wood volume is 70.7 m3·ha-1. When the logs (downe...In a tropical wet montane evergreen forest in the southern peninsular India, the estimated stocking of dead wood is 90 ± 3 stems·ha-1 and the total dead wood volume is 70.7 m3·ha-1. When the logs (downed dead trees more than 10.1 cm in diameter) constitute about 80% of the total deadwood stocking and volume, the rest is by snags (sound and rotting standing dead trees). Since the shola forest trees are characterized by their short stature with low to medium girth, about 89% of the total number of deadwood is of the size ranging from 10.1 cm to 40.0 cm in diameter. The estimated standing dead wood/standing live tree ratio is 0.16 indicating that the forest represents an old stand. Variations observed between logs and snags to change from a given decay class to the higher decay classes in two year period could be attributed to the facts that the logs would be in contact with soil for a relatively longer time and in turn would be in more contact with microorganisms and other decomposing agents.展开更多
Norway spruce(Picea abies(L.)Karst.)in the Harz Mountains National Park(Germany)has experienced widespread mortality(>97%of trees in the study stands)due to infestation with the large spruce bark beetle(Ips typogra...Norway spruce(Picea abies(L.)Karst.)in the Harz Mountains National Park(Germany)has experienced widespread mortality(>97%of trees in the study stands)due to infestation with the large spruce bark beetle(Ips typographus L.).The dead trees(snags)remain standing in the forest for 2-5 years before harvesting.It is important to identify trees that can still produce quality timber,which may be achieved by examining their outer appearance using selected characteristics.The aim of this study was to identify possible correlations between the standing storage duration and defined external characteristics of the snags.The mean tree height at compartment level was calculated using a vegetation height model,based on light detection and ranging data from 2018,to derive the stem breakage proportion.The condition of the crown and the bark and presence of fungi,wood rot,stem cracks and bark stripping damage were also assessed.The majority of the snags were broken at least once.Windthrows were less likely compared to living spruce trees because of reduced resistance to the wind as a result of needle loss and breakage.The mean stem breakage proportion increased significantly with the duration of the standing storage;however,prolonged storage durations did not always lead to complete breakage.The occurrence of fungal fruiting bodies was significantly correlated with a higher proportion of stem breakage,and the longer the storage,the more snags had fungal fruiting bodies.The condition of the crown,assessed by the presence of branchlets,was a good indicator of the duration of the standing storage.If trees had few or no branchlets,they had been standing for at least 4 years.Overall,this initial description of the external appearance of spruce trees that have been stored standing for many years suggests that time significantly influences the tree condition and breakage intensity,which is reflected by certain tree characteristics.Future studies should examine these aspects in greater depth,particularly with regard to utilization options and safety during timber harvesting.展开更多
基金provided by the USDA Forest Service Rocky Mountain Research Station。
文摘Background:Snags(standing dead trees)are important biological legacies in forest systems,providing numerous resources as well as a record of recent tree mortality.From 1997 to 2017,we monitored snag populations in drought-influenced mixed-conifer and ponderosa pine(Pinus ponderosa)forests in northern Arizona.Results:Snag density increased significantly in both forest types.This increase was driven largely by a pulse in snag recruitment that occurred between 2002 and 2007,fol owing an extreme drought year in 2002,with snag recruitment returning to pre-pulse levels in subsequent time periods.Some later years during the study also were warmer and/or drier than average,but these years were not as extreme as 2002 and did not trigger the same level of snag recruitment.Snag recruitment was not equal across tree species and size classes,resulting in significant changes in species composition and size-class distributions of snag populations in both forest types.Because trees were far more abundant than snags in these forests,the effect of this mortality pulse on tree populations was far smal er than its effect on snag populations.Snag loss rates increased over time during the study,even though many snags were newly recruited.This may reflect the increasing prevalence of white fir snags and/or snags in the smal er size classes,which general y decay faster than snags of other species or larger snags.Thus,although total numbers of snags increased,many of the newly recruited snags may not persist long enough to be valuable as nesting substrates for native wildlife.Conclusions:Increases in snag abundance appeared to be due to a short-term tree mortality"event"rather than a longerterm pattern of elevated tree mortality.This mortality event fol owed a dry and extremely warm year(2002)embedded within a longer-term megadrought.Climate models suggest that years like 2002 may occur with increasing frequency in the southwestern U.S.Such years may result in additional mortality pulses,which in turn may strongly affect trajectories in abundance,structure,and composition of snag populations.Relative effects on tree populations likely wil be smal er,but,over time,also could be significant.
文摘In a tropical wet montane evergreen forest in the southern peninsular India, the estimated stocking of dead wood is 90 ± 3 stems·ha-1 and the total dead wood volume is 70.7 m3·ha-1. When the logs (downed dead trees more than 10.1 cm in diameter) constitute about 80% of the total deadwood stocking and volume, the rest is by snags (sound and rotting standing dead trees). Since the shola forest trees are characterized by their short stature with low to medium girth, about 89% of the total number of deadwood is of the size ranging from 10.1 cm to 40.0 cm in diameter. The estimated standing dead wood/standing live tree ratio is 0.16 indicating that the forest represents an old stand. Variations observed between logs and snags to change from a given decay class to the higher decay classes in two year period could be attributed to the facts that the logs would be in contact with soil for a relatively longer time and in turn would be in more contact with microorganisms and other decomposing agents.
基金supported by the German Federal Ministry of Food and Agriculture(BMEL)and the German Federal Ministry for the Environment,Nature Conservation,Nuclear Safety and Consumer Protection(BMUV)via the Agency for Renewable Resources(FNR)(GRANT no.2220WK49E3)。
文摘Norway spruce(Picea abies(L.)Karst.)in the Harz Mountains National Park(Germany)has experienced widespread mortality(>97%of trees in the study stands)due to infestation with the large spruce bark beetle(Ips typographus L.).The dead trees(snags)remain standing in the forest for 2-5 years before harvesting.It is important to identify trees that can still produce quality timber,which may be achieved by examining their outer appearance using selected characteristics.The aim of this study was to identify possible correlations between the standing storage duration and defined external characteristics of the snags.The mean tree height at compartment level was calculated using a vegetation height model,based on light detection and ranging data from 2018,to derive the stem breakage proportion.The condition of the crown and the bark and presence of fungi,wood rot,stem cracks and bark stripping damage were also assessed.The majority of the snags were broken at least once.Windthrows were less likely compared to living spruce trees because of reduced resistance to the wind as a result of needle loss and breakage.The mean stem breakage proportion increased significantly with the duration of the standing storage;however,prolonged storage durations did not always lead to complete breakage.The occurrence of fungal fruiting bodies was significantly correlated with a higher proportion of stem breakage,and the longer the storage,the more snags had fungal fruiting bodies.The condition of the crown,assessed by the presence of branchlets,was a good indicator of the duration of the standing storage.If trees had few or no branchlets,they had been standing for at least 4 years.Overall,this initial description of the external appearance of spruce trees that have been stored standing for many years suggests that time significantly influences the tree condition and breakage intensity,which is reflected by certain tree characteristics.Future studies should examine these aspects in greater depth,particularly with regard to utilization options and safety during timber harvesting.
