Climate change is causing more frequent and severe climatic events,such as extreme heat and co-occurring drought,potentially accelerating tree mortality.Which tree species will cope better with those extreme events is...Climate change is causing more frequent and severe climatic events,such as extreme heat and co-occurring drought,potentially accelerating tree mortality.Which tree species will cope better with those extreme events is still being researched.This study focuses on heat as a physiological stress factor and interspecifi c variation of thermal tolerance and sensitivity traits in 15 temperate coniferous and broad-leaved tree species.We investigate(1)whether thermal tolerance and sensitivity traits correlate with a droughtrelated physiological trait,particularly the leaf turgor loss point(πtlp,wilting point),and(2)how thermal tolerance and sensitivity traits co-vary within diff erent tree-functional types classifi ed by morphological and physiological traits of the leaf,i.e.,leaf mass per area(LMA)and percentage loss of area(PLA).The study was carried out in the Traunstein Forest Dynamics Plot of the ForestGEO network in Germany.The temperature response of the maximum quantum yield of photosystem II(F_(v)/F_(m))on leaf discs was determined,from which various physiological leaf traits were estimated,one of which is the breaking point temperature(T_(5)),the temperature at which F_(v)/F_(m)declines by 5%.Additionally,the temperature of 50%(T_(50))and 95%(T_(95))decline in F_(v)/F_(m)was evaluated.The decline width between T_(50)and T 5(DW T_(50)−T_(5))was taken as an indicator of the species’thermal sensitivity.The breaking point temperature ranged from 35.4±3.0 to 47.9±3.9℃among the investigated tree species and T 50 ranged between 46.1±0.4 and 53.6±0.7℃.A large interspecifi c variation of thermal tolerance and sensitivity was found.European ash(Fraxinus excelsior L.)was the most heat-sensitive species,while Wild cherry(Prunus avium L.)was the least heat-sensitive species.Species with a more negativeπtlp tended to have a higher breaking point temperature than species with a less negativeπtlp.A lower thermal sensitivity characterized species with a higher LMA,and high PLA was found in species with low thermal sensitivity.Accordingly,species with thicker and tougher leaves have lower thermal sensitivity which coincides with a lower wilting point.We conclude that species that develop drought-adapted foliage can cope better with heat stress.Further,they might be able to maintain transpirational cooling during combined heat and drought stress,which could lessen their mortality risk during climatic extremes.展开更多
Background Recent increases in tree mortality are often attributed to climate, but climate extremes may just be the last of many stressors that have unfolded over many years resulting in tree death. Potentially it is ...Background Recent increases in tree mortality are often attributed to climate, but climate extremes may just be the last of many stressors that have unfolded over many years resulting in tree death. Potentially it is only those trees weakened by mechanical damage or attacks by insects or fungi that are susceptible to climate-mediated mortality, whereas vigorous trees resist periods of unfavorable climate. Although previous studies have explored immediate and catastrophic effects of mechanical damage via blowdowns and stem breakage, few have investigated the delayed effects of mechanical damage on mortality. Taxus is a shade-tolerant genus of subcanopy trees or shrubs distributed throughout the northern hemisphere. Populations of Taxus are in decline worldwide but owing to the tenacity of Taxus in the face of stressors, this decline is poorly understood. Here, we provide spatial evidence that cumulative stress interactions, particularly mechanical damage, contribute to Taxus mortality.Methods We examined 14 years of annual demographic data from the 27.2 ha Wind River Forest Dynamics Plot(WFDP), where woody stems, snags, and deadwood have been tagged, mapped and identified to species. We analyzed the multiple factors associated with tree death, including mechanical damage, pathogens, suppression, beetles, animal damage, and their combinations. We performed spatial pattern analyses with the pair correlation function to investigate the prevalence of density-dependent mortality, effects of neighboring large-diameter trees, and effects of nearby snag fall and deadwood.Results In 2011, there were 29,827 trees within the WFDP of which 2119 were Taxus. Between 2011 and 2024, Taxus declined to 1523 trees(mean annual mortality of 2.79% yr^(-1)). Taxus mortality was not influenced by intraspecific density dependence or the presence of snags but was mainly driven by mechanical damage, pathogens, and suppression. Dead Taxus were strongly associated with deadwood within 2 m of the bole. Structural equation modeling showed that mechanical damage likely increased the vulnerability of Taxus to pathogen infection and exposure to drier gap areas.Conclusions These results suggest that Taxus mortality is rarely due to a single event, but a cumulative process of interacting stressors initiated by falling wood and often culminating in death by other stressors—potentially many years later. The association of newly dead trees with deadwood suggests that falling snags likely contributed to past crown damage, initiating or accelerating a decline spiral. The results emphasize that previous mechanical damage—evidenced by mapped and persistent deadwood—can disproportionately affect tree species, influencing successional dynamics.展开更多
The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest flo...The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest floor.However,reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass,with potential impacts to fuel accumulation,carbon sequestration,subsequent fire severity,and forest management.In this study,we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation,carbon sequestration,and subsequent fire severity potential.Beginning pre-fire,and continuing 6 years post-fire,we tracked all live,dead,and fallen trees≥1 cm in diameter and mapped all pieces of deadwood(downed woody debris)originating from tree boles≥10 cm diameter and≥1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada,California,USA.We also tracked surface fuels along 2240 m of planar transects pre-fire,immediately post-fire,and 6 years post-fire.Six years after moderate-severity fire,deadwood≥10 cm diameter was 73 Mg ha^(−1),comprised of 32 Mg ha^(−1) that persisted through fire and 41 Mg ha^(−1) of newly fallen wood(compared to 72 Mg ha^(−1) pre-fire).Woody surface fuel loading was spatially heterogeneous,with mass varying almost four orders of magnitude at the scale of 20 m×20 m quadrats(minimum,0.1 Mg ha^(−1);mean,73 Mg ha^(−1);maximum,497 Mg ha^(−1)).Wood from large-diameter trees(≥60 cm diameter)comprised 57%of surface fuel in 2019,but was 75%of snag biomass,indicating high contributions to current and future fuel loading.Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels≥10 cm diameter within 6 years.Repeated fires are needed to reduce surface fuel loading.展开更多
Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowgro...Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure;(ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood;and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results: We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, dead-wood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomy-corrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and dis-tance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions: These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.展开更多
文摘Climate change is causing more frequent and severe climatic events,such as extreme heat and co-occurring drought,potentially accelerating tree mortality.Which tree species will cope better with those extreme events is still being researched.This study focuses on heat as a physiological stress factor and interspecifi c variation of thermal tolerance and sensitivity traits in 15 temperate coniferous and broad-leaved tree species.We investigate(1)whether thermal tolerance and sensitivity traits correlate with a droughtrelated physiological trait,particularly the leaf turgor loss point(πtlp,wilting point),and(2)how thermal tolerance and sensitivity traits co-vary within diff erent tree-functional types classifi ed by morphological and physiological traits of the leaf,i.e.,leaf mass per area(LMA)and percentage loss of area(PLA).The study was carried out in the Traunstein Forest Dynamics Plot of the ForestGEO network in Germany.The temperature response of the maximum quantum yield of photosystem II(F_(v)/F_(m))on leaf discs was determined,from which various physiological leaf traits were estimated,one of which is the breaking point temperature(T_(5)),the temperature at which F_(v)/F_(m)declines by 5%.Additionally,the temperature of 50%(T_(50))and 95%(T_(95))decline in F_(v)/F_(m)was evaluated.The decline width between T_(50)and T 5(DW T_(50)−T_(5))was taken as an indicator of the species’thermal sensitivity.The breaking point temperature ranged from 35.4±3.0 to 47.9±3.9℃among the investigated tree species and T 50 ranged between 46.1±0.4 and 53.6±0.7℃.A large interspecifi c variation of thermal tolerance and sensitivity was found.European ash(Fraxinus excelsior L.)was the most heat-sensitive species,while Wild cherry(Prunus avium L.)was the least heat-sensitive species.Species with a more negativeπtlp tended to have a higher breaking point temperature than species with a less negativeπtlp.A lower thermal sensitivity characterized species with a higher LMA,and high PLA was found in species with low thermal sensitivity.Accordingly,species with thicker and tougher leaves have lower thermal sensitivity which coincides with a lower wilting point.We conclude that species that develop drought-adapted foliage can cope better with heat stress.Further,they might be able to maintain transpirational cooling during combined heat and drought stress,which could lessen their mortality risk during climatic extremes.
基金Utah State University and the Utah Agricultural Experiment Station(Project 1711)
文摘Background Recent increases in tree mortality are often attributed to climate, but climate extremes may just be the last of many stressors that have unfolded over many years resulting in tree death. Potentially it is only those trees weakened by mechanical damage or attacks by insects or fungi that are susceptible to climate-mediated mortality, whereas vigorous trees resist periods of unfavorable climate. Although previous studies have explored immediate and catastrophic effects of mechanical damage via blowdowns and stem breakage, few have investigated the delayed effects of mechanical damage on mortality. Taxus is a shade-tolerant genus of subcanopy trees or shrubs distributed throughout the northern hemisphere. Populations of Taxus are in decline worldwide but owing to the tenacity of Taxus in the face of stressors, this decline is poorly understood. Here, we provide spatial evidence that cumulative stress interactions, particularly mechanical damage, contribute to Taxus mortality.Methods We examined 14 years of annual demographic data from the 27.2 ha Wind River Forest Dynamics Plot(WFDP), where woody stems, snags, and deadwood have been tagged, mapped and identified to species. We analyzed the multiple factors associated with tree death, including mechanical damage, pathogens, suppression, beetles, animal damage, and their combinations. We performed spatial pattern analyses with the pair correlation function to investigate the prevalence of density-dependent mortality, effects of neighboring large-diameter trees, and effects of nearby snag fall and deadwood.Results In 2011, there were 29,827 trees within the WFDP of which 2119 were Taxus. Between 2011 and 2024, Taxus declined to 1523 trees(mean annual mortality of 2.79% yr^(-1)). Taxus mortality was not influenced by intraspecific density dependence or the presence of snags but was mainly driven by mechanical damage, pathogens, and suppression. Dead Taxus were strongly associated with deadwood within 2 m of the bole. Structural equation modeling showed that mechanical damage likely increased the vulnerability of Taxus to pathogen infection and exposure to drier gap areas.Conclusions These results suggest that Taxus mortality is rarely due to a single event, but a cumulative process of interacting stressors initiated by falling wood and often culminating in death by other stressors—potentially many years later. The association of newly dead trees with deadwood suggests that falling snags likely contributed to past crown damage, initiating or accelerating a decline spiral. The results emphasize that previous mechanical damage—evidenced by mapped and persistent deadwood—can disproportionately affect tree species, influencing successional dynamics.
基金Funding was received from the Utah Agricultural Experiment Station(projects 1153,1398,and 1423 to JAL)the Joint Fire Science Program(award 16-1-04-02 to JAL and AJL)+1 种基金the National Park Service(Awards P14AC00122 and P14AC00197 to JAL)the Smithsonian Institution ForestGEO.Re-search was performed under National Park Service research permits YOSE-2013-SCI-0012,YOSE-2014-SCI-0005,YOSE-2015-SCI-0014,YOSE-2016-SCI-0006,YOSE-2017-SCI-0008,YOSE-2018-SCI-0006,and YOSE-2019-SCI-0009 for study YOSE-0051.
文摘The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest floor.However,reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass,with potential impacts to fuel accumulation,carbon sequestration,subsequent fire severity,and forest management.In this study,we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation,carbon sequestration,and subsequent fire severity potential.Beginning pre-fire,and continuing 6 years post-fire,we tracked all live,dead,and fallen trees≥1 cm in diameter and mapped all pieces of deadwood(downed woody debris)originating from tree boles≥10 cm diameter and≥1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada,California,USA.We also tracked surface fuels along 2240 m of planar transects pre-fire,immediately post-fire,and 6 years post-fire.Six years after moderate-severity fire,deadwood≥10 cm diameter was 73 Mg ha^(−1),comprised of 32 Mg ha^(−1) that persisted through fire and 41 Mg ha^(−1) of newly fallen wood(compared to 72 Mg ha^(−1) pre-fire).Woody surface fuel loading was spatially heterogeneous,with mass varying almost four orders of magnitude at the scale of 20 m×20 m quadrats(minimum,0.1 Mg ha^(−1);mean,73 Mg ha^(−1);maximum,497 Mg ha^(−1)).Wood from large-diameter trees(≥60 cm diameter)comprised 57%of surface fuel in 2019,but was 75%of snag biomass,indicating high contributions to current and future fuel loading.Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels≥10 cm diameter within 6 years.Repeated fires are needed to reduce surface fuel loading.
基金Funding was received from the Natural Science and Engineering Council of Canada to JK and the Utah Agricultural Experiment Station(Projects 1153,1398 and 1423 to JAL)which has designated this as Journal Paper 9626.
文摘Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure;(ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood;and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results: We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, dead-wood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomy-corrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and dis-tance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions: These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.
