从适用范围和原理、仪器设备、操作步骤和评级等方面分别进行阐述了中国、美国和日本织物勾丝性能的测试标准GB/T 11047—1989、ASTM D 3929—2003和JISL 1058—2005,分析了其异同点。三种标准方法由于规定的勾丝转数不同,测试结果差异...从适用范围和原理、仪器设备、操作步骤和评级等方面分别进行阐述了中国、美国和日本织物勾丝性能的测试标准GB/T 11047—1989、ASTM D 3929—2003和JISL 1058—2005,分析了其异同点。三种标准方法由于规定的勾丝转数不同,测试结果差异很大。若勾丝测试结果较好,则差异仅为0.5级;若勾丝测试结果较差,则差异可高达2.5级。展开更多
Background： After their death, Scots pine trees can remain standing for decades and sometimes up to 200 years,forming long-lasting and ecologically important structures in boreal forest landscapes. Standing dead pine...Background： After their death, Scots pine trees can remain standing for decades and sometimes up to 200 years,forming long-lasting and ecologically important structures in boreal forest landscapes. Standing dead pines decay very slowly and with time develop into ‘kelo＇ trees, which are characterized by hard wood with silvery-colored appearance. These kelo trees represent an ecologically important, long lasting and visually striking element of the structure of natural pine-dominated forests in boreal Fennoscandia that is nowadays virtually absent from managed forest landscapes.Methods： We examined and mapped the amount, structural features, site characteristics and spatial distribution of dead standing pine trees over a ten hectare area in an unmanaged boreal forest landscape in the Kalevala National Park in Russian Viena Karelia.Results： The mean basal area of dead standing pine trees in the forested part of the landscape was 1.7 m^2·ha^-1 and the estimated volume 12.7 m^3·ha^-1. From the total number of standing dead pine trees 65% were kelo trees, with a basal area of 1.1 m^2·ha^-1 and volume of 8.0 m^3·ha^-1, the remainder consisting of standing dead pines along the continuum between a recently dead tree and a kelo tree. Overall, standing dead pines were distributed throughout the study area, but there was a tendency towards spatial clustering up to 〈100 m distances. Standing dead pines were most commonly situated on flat ground or in the mid slope in the local topography.In addition, standing dead pines contributed to substrate diversity also by commonly having charred wood and broken tops. Based on the presence of dead pine snags in different stage of transition from a recently dead pine to a kelo with silvery surface, it seems evident that the process of kelo recruitment was continuously in action in the studied landscape.Conclusions： Kelo trees are an omnipresent feature in natural pine-dominated forest landscapes with important contribution to forest structural and substrate diversity. B展开更多
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 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
文摘从适用范围和原理、仪器设备、操作步骤和评级等方面分别进行阐述了中国、美国和日本织物勾丝性能的测试标准GB/T 11047—1989、ASTM D 3929—2003和JISL 1058—2005,分析了其异同点。三种标准方法由于规定的勾丝转数不同,测试结果差异很大。若勾丝测试结果较好,则差异仅为0.5级;若勾丝测试结果较差,则差异可高达2.5级。
基金the EBOR-project funded by the Academy of Finland (proj.no.276255)
文摘Background： After their death, Scots pine trees can remain standing for decades and sometimes up to 200 years,forming long-lasting and ecologically important structures in boreal forest landscapes. Standing dead pines decay very slowly and with time develop into ‘kelo＇ trees, which are characterized by hard wood with silvery-colored appearance. These kelo trees represent an ecologically important, long lasting and visually striking element of the structure of natural pine-dominated forests in boreal Fennoscandia that is nowadays virtually absent from managed forest landscapes.Methods： We examined and mapped the amount, structural features, site characteristics and spatial distribution of dead standing pine trees over a ten hectare area in an unmanaged boreal forest landscape in the Kalevala National Park in Russian Viena Karelia.Results： The mean basal area of dead standing pine trees in the forested part of the landscape was 1.7 m^2·ha^-1 and the estimated volume 12.7 m^3·ha^-1. From the total number of standing dead pine trees 65% were kelo trees, with a basal area of 1.1 m^2·ha^-1 and volume of 8.0 m^3·ha^-1, the remainder consisting of standing dead pines along the continuum between a recently dead tree and a kelo tree. Overall, standing dead pines were distributed throughout the study area, but there was a tendency towards spatial clustering up to 〈100 m distances. Standing dead pines were most commonly situated on flat ground or in the mid slope in the local topography.In addition, standing dead pines contributed to substrate diversity also by commonly having charred wood and broken tops. Based on the presence of dead pine snags in different stage of transition from a recently dead pine to a kelo with silvery surface, it seems evident that the process of kelo recruitment was continuously in action in the studied landscape.Conclusions： Kelo trees are an omnipresent feature in natural pine-dominated forest landscapes with important contribution to forest structural and substrate diversity. B
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
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.
