Eastern hemlock (Tsuga canadensis Carriére) and the Carolina hemlock (Tsuga caroliniana Engelmann) are ecologically important tree species in eastern North America forests that are currently threatened by the hem...Eastern hemlock (Tsuga canadensis Carriére) and the Carolina hemlock (Tsuga caroliniana Engelmann) are ecologically important tree species in eastern North America forests that are currently threatened by the hemlock woolly adelgid (HWA, Adelges tsugae Annand, Hemiptera: Adelgidae). HWA has spread rapidly from its original introduction site into new areas. Once present, HWA kills its hosts over a period of 4 to 10 years leading to a phenomenon that is known scientifically and colloquially as hemlock decline. To date, quarantine, chemical management, and biocontrol efforts have failed to curb the spread of the HWA. As such, forest management efforts are now being redirected towards developing an understanding of the effects of hemlock removal on vegetation dynamics, changes in forest composition, and changes in ecosystem function. In this study, we parameterize a spatially explicit landscape simulation model LANDIS II for a specific forested region of the southern Appalachians. Parameterization involves defining the life-history attributes of 37 tree species occupying 11 ecological zones and is based on knowledge of: current vegetation composition data, recent historic management and fire regimes, and life-history traits of each species. The parameterized model is used to explore a simple scenario of catastrophic hemlock mortality likely to occur as a result of HWA herbivory. Our results emphasize that hemlock is an important foundation species. When hemlock is removed from the system, forest composition changes considerably with a greater presence of shade intolerant pine and oak species. Additionally, hemlock removal leads to a period of transient, relatively unstable vegetation dynamics as the forest communities restructure.展开更多
Hemlock woolly adelgid (Adelges Tsugae Annand, HWA) outbreaks are posing a major threat to eastern hemlock (Tsuga canadensis L. Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.) forest landscapes in the eastern ...Hemlock woolly adelgid (Adelges Tsugae Annand, HWA) outbreaks are posing a major threat to eastern hemlock (Tsuga canadensis L. Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.) forest landscapes in the eastern USA. As foundation species, hemlocks play a variety of functional roles in forest landscapes. These species usually occur as isolated canopies and mixed species in landscapes where variation in topography is extreme. Spatially explicit inventory information on HWA induced hemlock mortality at landscape scale does not exist. High resolution aerial imageries enable landscape scale assessment even at the individual tree level. Accordingly, our goal was to investigate spatial pattern and distribution of HWA induced hemlock mortality using a high resolution aerial image mosaic in the Linville River Gorge, Southern Appalachians, western North Carolina. Our study objectives were: 1) to detect dead trees within the Lower Linville River watershed;2) to estimate the area occupied by dead trees in the forest canopy surface;3) to investigate the relationship of dead hemlocks and topography;and 4) to define the spatial pattern of the dead trees. We found ca. 10,000 dead trees within the study area, occupying over 7 ha of the canopy surface with an average area of 36 m2 per dead tree. The density of the dead trees was higher in proximity to the Linville River, at higher elevations, and on northern and northwestern aspects. Spatial pattern of the dead trees was generally clustered at all spatial scales. We suggest that although the reduction in plant biomass resulting from herbivory within the landscapes is modest, impact of the clustered distribution of hemlock mortality, especially in the riparian zones, is noteworthy. Our analysis of the pattern of hemlock decline provides new means for projecting future impacts of HWA on the range of hemlock distribution in eastern North America.展开更多
In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known...In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known detailedly. This study presented two δ13C series in annual tree rings for Chinese hem-lock (Tsuga chinensis Pritz) and alpine pine (Pinus densata Mast),and investigated the relationships between climatic parameters and stable carbon discrimination (△13C) series,and evaluated the poten-tial of climatic reconstruction using △13C in both species,in a temperate-moist region of Chuanxi Pla-teau,China. The raw δ13C series of the two species was inconsistent,which may be a result of different responses caused by tree's inherent physiological differences. After removing the low-frequency ef-fects of CO2 concentration,the high-frequency (year-to-year) inter-series correlation of △13C was strong,indicating that △13C of the two tree species were controlled by common environmental conditions. The △13C series of the species were most significantly correlated with temperature and moisture stress,but in different periods and intensity between the species. During the physiological year,the impacts of temperature and moisture stress on △13C occur earlier for Chinese hemlock (previous December to February for moisture stress and February to April for temperature,respectively) than for alpine pine (March to May for moisture stress and April to July for temperature,respectively). In addition,in temperate-moist regions,the control on △13C of single climatic parameter was not strongly dominant and the op-timal multiple regressions functions just explained the 38.5% variance of the total. Therefore,there is limited potential for using δ13C alone to identify clear,reliable climatic signals from two species.展开更多
Overstory basal area,ericaceous shrub cover(Kalmia latifolia L.and Rhododendron maximum L.),and fuels(i.e.,woody fuel loads and depths and O Horizon thickness) were assessed within Great Smoky Mountains National Park,...Overstory basal area,ericaceous shrub cover(Kalmia latifolia L.and Rhododendron maximum L.),and fuels(i.e.,woody fuel loads and depths and O Horizon thickness) were assessed within Great Smoky Mountains National Park,USA,in 2003-2004.Due to recent wildfire activity within the southern Appalachian Mountain region(including Great Smoky Mountains National Park),the potential spread and expansion of ericaceous shrubs,and the impacts of the hemlock woolly adelgid(Adelges tsugae Annand) on eastern hemlock(Tsuga canadensis(L.) Carrière),these same ecosystem components were again assessed in 2019.Elevation and moisture regime(xeric,intermediate,and mesic) were included in this assessment as potential influential factors.An evaluation of repeated measurements from 40 plots suggested that O Horizon thickness did not change significantly over the 16-year period,but increased as elevation increased,and moisture regime(xeric O Horizon thickness> mesic O Horizon thickness) was a significant,related factor.The sum of 1-,10-,and 100-h fuel loads(fuels less <7.6 cm diameter)increased,whereas woody fuel depth decreased over the16-year period.No significant changes in 1000-h fuel lo ads(>7.6 cm diameter),total woody fuel loads,ericaceous shrub cover,total basal area,or live T.canadensis basal area were observed.Live T.canadensis basal area decreased with increasing elevation.Dead,standing T.canadensis basal area increased from 2003-2019,and that increase was most pronounced as elevation increased on xeric and intermediate sites.Overall,we found that:1.hypothesized increases in total woody fuel loads and ericaceous shrub cover were not present;and 2.elevation and moisture regime were most related to observed changes in vegetation and fuel condition.展开更多
文摘Eastern hemlock (Tsuga canadensis Carriére) and the Carolina hemlock (Tsuga caroliniana Engelmann) are ecologically important tree species in eastern North America forests that are currently threatened by the hemlock woolly adelgid (HWA, Adelges tsugae Annand, Hemiptera: Adelgidae). HWA has spread rapidly from its original introduction site into new areas. Once present, HWA kills its hosts over a period of 4 to 10 years leading to a phenomenon that is known scientifically and colloquially as hemlock decline. To date, quarantine, chemical management, and biocontrol efforts have failed to curb the spread of the HWA. As such, forest management efforts are now being redirected towards developing an understanding of the effects of hemlock removal on vegetation dynamics, changes in forest composition, and changes in ecosystem function. In this study, we parameterize a spatially explicit landscape simulation model LANDIS II for a specific forested region of the southern Appalachians. Parameterization involves defining the life-history attributes of 37 tree species occupying 11 ecological zones and is based on knowledge of: current vegetation composition data, recent historic management and fire regimes, and life-history traits of each species. The parameterized model is used to explore a simple scenario of catastrophic hemlock mortality likely to occur as a result of HWA herbivory. Our results emphasize that hemlock is an important foundation species. When hemlock is removed from the system, forest composition changes considerably with a greater presence of shade intolerant pine and oak species. Additionally, hemlock removal leads to a period of transient, relatively unstable vegetation dynamics as the forest communities restructure.
基金possible by financial aid from Graduate School in Forest Sciences(GSForest),Finnish Academy project“Centre of Excellence in Laser Scanning Research”(CoE-LaSR,decision number 272195)by the US Forest Service through USDA Forest Service cooperative agreement SRS-12-CA-11330129-077.
文摘Hemlock woolly adelgid (Adelges Tsugae Annand, HWA) outbreaks are posing a major threat to eastern hemlock (Tsuga canadensis L. Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.) forest landscapes in the eastern USA. As foundation species, hemlocks play a variety of functional roles in forest landscapes. These species usually occur as isolated canopies and mixed species in landscapes where variation in topography is extreme. Spatially explicit inventory information on HWA induced hemlock mortality at landscape scale does not exist. High resolution aerial imageries enable landscape scale assessment even at the individual tree level. Accordingly, our goal was to investigate spatial pattern and distribution of HWA induced hemlock mortality using a high resolution aerial image mosaic in the Linville River Gorge, Southern Appalachians, western North Carolina. Our study objectives were: 1) to detect dead trees within the Lower Linville River watershed;2) to estimate the area occupied by dead trees in the forest canopy surface;3) to investigate the relationship of dead hemlocks and topography;and 4) to define the spatial pattern of the dead trees. We found ca. 10,000 dead trees within the study area, occupying over 7 ha of the canopy surface with an average area of 36 m2 per dead tree. The density of the dead trees was higher in proximity to the Linville River, at higher elevations, and on northern and northwestern aspects. Spatial pattern of the dead trees was generally clustered at all spatial scales. We suggest that although the reduction in plant biomass resulting from herbivory within the landscapes is modest, impact of the clustered distribution of hemlock mortality, especially in the riparian zones, is noteworthy. Our analysis of the pattern of hemlock decline provides new means for projecting future impacts of HWA on the range of hemlock distribution in eastern North America.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 90211018, 40501076 and 40371118)the International Partnership Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-2)the Innovation Project of the Key Laboratory of Cryosphere and Environment, Cold and Arid Re-gions Environmental and Engineering Research Institute, Chinese Academy of Sciences
文摘In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known detailedly. This study presented two δ13C series in annual tree rings for Chinese hem-lock (Tsuga chinensis Pritz) and alpine pine (Pinus densata Mast),and investigated the relationships between climatic parameters and stable carbon discrimination (△13C) series,and evaluated the poten-tial of climatic reconstruction using △13C in both species,in a temperate-moist region of Chuanxi Pla-teau,China. The raw δ13C series of the two species was inconsistent,which may be a result of different responses caused by tree's inherent physiological differences. After removing the low-frequency ef-fects of CO2 concentration,the high-frequency (year-to-year) inter-series correlation of △13C was strong,indicating that △13C of the two tree species were controlled by common environmental conditions. The △13C series of the species were most significantly correlated with temperature and moisture stress,but in different periods and intensity between the species. During the physiological year,the impacts of temperature and moisture stress on △13C occur earlier for Chinese hemlock (previous December to February for moisture stress and February to April for temperature,respectively) than for alpine pine (March to May for moisture stress and April to July for temperature,respectively). In addition,in temperate-moist regions,the control on △13C of single climatic parameter was not strongly dominant and the op-timal multiple regressions functions just explained the 38.5% variance of the total. Therefore,there is limited potential for using δ13C alone to identify clear,reliable climatic signals from two species.
基金This research is funded by the National Park Service (Task Agreement P19AC01059)。
文摘Overstory basal area,ericaceous shrub cover(Kalmia latifolia L.and Rhododendron maximum L.),and fuels(i.e.,woody fuel loads and depths and O Horizon thickness) were assessed within Great Smoky Mountains National Park,USA,in 2003-2004.Due to recent wildfire activity within the southern Appalachian Mountain region(including Great Smoky Mountains National Park),the potential spread and expansion of ericaceous shrubs,and the impacts of the hemlock woolly adelgid(Adelges tsugae Annand) on eastern hemlock(Tsuga canadensis(L.) Carrière),these same ecosystem components were again assessed in 2019.Elevation and moisture regime(xeric,intermediate,and mesic) were included in this assessment as potential influential factors.An evaluation of repeated measurements from 40 plots suggested that O Horizon thickness did not change significantly over the 16-year period,but increased as elevation increased,and moisture regime(xeric O Horizon thickness> mesic O Horizon thickness) was a significant,related factor.The sum of 1-,10-,and 100-h fuel loads(fuels less <7.6 cm diameter)increased,whereas woody fuel depth decreased over the16-year period.No significant changes in 1000-h fuel lo ads(>7.6 cm diameter),total woody fuel loads,ericaceous shrub cover,total basal area,or live T.canadensis basal area were observed.Live T.canadensis basal area decreased with increasing elevation.Dead,standing T.canadensis basal area increased from 2003-2019,and that increase was most pronounced as elevation increased on xeric and intermediate sites.Overall,we found that:1.hypothesized increases in total woody fuel loads and ericaceous shrub cover were not present;and 2.elevation and moisture regime were most related to observed changes in vegetation and fuel condition.
