2019
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Mioduszewski, J R; Vavrus, S; Wang, M; Holland, M; Landrum, L: Past and future interannual variability in Arctic sea ice in coupled climate models. In: The Cryosphere, vol. 13, no. 1, pp. 113-124, 2019. @article{tc-13-113-2019,
title = {Past and future interannual variability in Arctic sea ice in coupled climate models},
author = {J R Mioduszewski and S Vavrus and M Wang and M Holland and L Landrum},
url = {https://tc.copernicus.org/articles/13/113/2019/},
doi = {10.5194/tc-13-113-2019},
year = {2019},
date = {2019-01-14},
journal = {The Cryosphere},
volume = {13},
number = {1},
pages = {113-124},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Mioduszewski, J R; Vavrus, S; Wang, M; Holland, M; Landrum, L: Past and future interannual variability in Arctic sea ice in coupled climate models. In: The Cryosphere, vol. 13, no. 1, pp. 113-124, 2019. @article{tc-13-113-2019b,
title = {Past and future interannual variability in Arctic sea ice in coupled climate models},
author = {J R Mioduszewski and S Vavrus and M Wang and M Holland and L Landrum},
url = {https://tc.copernicus.org/articles/13/113/2019/},
doi = {10.5194/tc-13-113-2019},
year = {2019},
date = {2019-01-14},
journal = {The Cryosphere},
volume = {13},
number = {1},
pages = {113-124},
abstract = {The diminishing Arctic sea ice pack has been widely studied, but previous research has mostly focused on time-mean changes in sea ice rather than on short-term variations that also have important physical and societal consequences. In this study we test the hypothesis that future interannual Arctic sea ice area variability will increase by utilizing 40 independent simulations from the Community Earth System Model's Large Ensemble (CESM-LE) for the 1920–2100 period and augment this with simulations from 12 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Both CESM-LE and CMIP5 models project that ice area variability will indeed grow substantially but not monotonically in every month. There is also a strong seasonal dependence in the magnitude and timing of future variability increases that is robust among CESM ensemble members. The variability generally correlates with the average ice retreat rate, before there is an eventual disappearance in both terms as the ice pack becomes seasonal in summer and autumn by late century. The peak in variability correlates best with the total area of ice between 0.2 and 0.6 m monthly thickness, indicating that substantial future thinning of the ice pack is required before variability maximizes. Within this range, the most favorable thickness for high areal variability depends on the season, especially whether ice growth or ice retreat processes dominate. Our findings suggest that thermodynamic melting (top, bottom, lateral) and growth (frazil, congelation) processes are more important than dynamical mechanisms, namely ice export and ridging, in controlling ice area variability.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The diminishing Arctic sea ice pack has been widely studied, but previous research has mostly focused on time-mean changes in sea ice rather than on short-term variations that also have important physical and societal consequences. In this study we test the hypothesis that future interannual Arctic sea ice area variability will increase by utilizing 40 independent simulations from the Community Earth System Model's Large Ensemble (CESM-LE) for the 1920–2100 period and augment this with simulations from 12 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Both CESM-LE and CMIP5 models project that ice area variability will indeed grow substantially but not monotonically in every month. There is also a strong seasonal dependence in the magnitude and timing of future variability increases that is robust among CESM ensemble members. The variability generally correlates with the average ice retreat rate, before there is an eventual disappearance in both terms as the ice pack becomes seasonal in summer and autumn by late century. The peak in variability correlates best with the total area of ice between 0.2 and 0.6 m monthly thickness, indicating that substantial future thinning of the ice pack is required before variability maximizes. Within this range, the most favorable thickness for high areal variability depends on the season, especially whether ice growth or ice retreat processes dominate. Our findings suggest that thermodynamic melting (top, bottom, lateral) and growth (frazil, congelation) processes are more important than dynamical mechanisms, namely ice export and ridging, in controlling ice area variability. |
Xiao, Jingfeng; Li, Xing; He, Binbin; Arain, Altaf M; Beringer, Jason; Desai, Ankur R; Emmel, Carmen; Hollinger, David Y; Krasnova, Alisa; Mammarella, Ivan; Noe, Steffen M; Ortiz, Penélope Serrano; Rey-Sanchez, Camilo; Rocha, Adrian V; Varlagin, Andrej: Solar-induced chlorophyll fluorescence exhibits a universal relationship with gross primary productivity across a wide variety of biomes. In: Global Change Biology, vol. 25, no. 4, pp. e4-e6, 2019. @article{https://doi.org/10.1111/gcb.14565,
title = {Solar-induced chlorophyll fluorescence exhibits a universal relationship with gross primary productivity across a wide variety of biomes},
author = {Jingfeng Xiao and Xing Li and Binbin He and Altaf M Arain and Jason Beringer and Ankur R Desai and Carmen Emmel and David Y Hollinger and Alisa Krasnova and Ivan Mammarella and Steffen M Noe and Penélope Serrano Ortiz and Camilo Rey-Sanchez and Adrian V Rocha and Andrej Varlagin},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14565},
doi = {https://doi.org/10.1111/gcb.14565},
year = {2019},
date = {2019-01-05},
journal = {Global Change Biology},
volume = {25},
number = {4},
pages = {e4-e6},
abstract = {In our recent study in Global Change Biology (Li et al., ), we examined the relationship between solar-induced chlorophyll fluorescence (SIF) measured from the Orbiting Carbon Observatory-2 (OCO-2) and gross primary productivity (GPP) derived from eddy covariance flux towers across the globe, and we discovered that there is a nearly universal relationship between SIF and GPP across a wide variety of biomes. This finding reveals the tremendous potential of SIF for accurately mapping terrestrial photosynthesis globally.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In our recent study in Global Change Biology (Li et al., ), we examined the relationship between solar-induced chlorophyll fluorescence (SIF) measured from the Orbiting Carbon Observatory-2 (OCO-2) and gross primary productivity (GPP) derived from eddy covariance flux towers across the globe, and we discovered that there is a nearly universal relationship between SIF and GPP across a wide variety of biomes. This finding reveals the tremendous potential of SIF for accurately mapping terrestrial photosynthesis globally. |
Xiao, Jingfeng; Li, Xing; He, Binbin; Arain, Altaf M; Beringer, Jason; Desai, Ankur R; Emmel, Carmen; Hollinger, David Y; Krasnova, Alisa; Mammarella, Ivan; Noe, Steffen M; Ortiz, Penélope Serrano; Rey-Sanchez, Camilo; Rocha, Adrian V; Varlagin, Andrej: Solar-induced chlorophyll fluorescence exhibits a universal relationship with gross primary productivity across a wide variety of biomes. In: Global Change Biology, vol. 25, no. 4, pp. e4-e6, 2019. @article{https://doi.org/10.1111/gcb.14565b,
title = {Solar-induced chlorophyll fluorescence exhibits a universal relationship with gross primary productivity across a wide variety of biomes},
author = {Jingfeng Xiao and Xing Li and Binbin He and Altaf M Arain and Jason Beringer and Ankur R Desai and Carmen Emmel and David Y Hollinger and Alisa Krasnova and Ivan Mammarella and Steffen M Noe and Penélope Serrano Ortiz and Camilo Rey-Sanchez and Adrian V Rocha and Andrej Varlagin},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14565},
doi = {https://doi.org/10.1111/gcb.14565},
year = {2019},
date = {2019-01-05},
journal = {Global Change Biology},
volume = {25},
number = {4},
pages = {e4-e6},
abstract = {In our recent study in Global Change Biology (Li et al., ), we examined the relationship between solar-induced chlorophyll fluorescence (SIF) measured from the Orbiting Carbon Observatory-2 (OCO-2) and gross primary productivity (GPP) derived from eddy covariance flux towers across the globe, and we discovered that there is a nearly universal relationship between SIF and GPP across a wide variety of biomes. This finding reveals the tremendous potential of SIF for accurately mapping terrestrial photosynthesis globally.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In our recent study in Global Change Biology (Li et al., ), we examined the relationship between solar-induced chlorophyll fluorescence (SIF) measured from the Orbiting Carbon Observatory-2 (OCO-2) and gross primary productivity (GPP) derived from eddy covariance flux towers across the globe, and we discovered that there is a nearly universal relationship between SIF and GPP across a wide variety of biomes. This finding reveals the tremendous potential of SIF for accurately mapping terrestrial photosynthesis globally. |
Krause, Teresa R; Russell, James M; Zhang, Rui; Williams, John W; Jackson, Stephen T: Late Quaternary vegetation, climate, and fire history of the Southeast Atlantic Coastal Plain based on a 30,000-yr multi-proxy record from White Pond, South Carolina, USA. In: Quaternary Research, vol. 91, no. 2, pp. 861–880, 2019. @article{krause_russell_zhang_williams_jackson_2019,
title = {Late Quaternary vegetation, climate, and fire history of the Southeast Atlantic Coastal Plain based on a 30,000-yr multi-proxy record from White Pond, South Carolina, USA},
author = {Teresa R Krause and James M Russell and Rui Zhang and John W Williams and Stephen T Jackson},
doi = {10.1017/qua.2018.95},
year = {2019},
date = {2019-01-02},
journal = {Quaternary Research},
volume = {91},
number = {2},
pages = {861–880},
publisher = {Cambridge University Press},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
Gee, Carole; Sander, Paul; Peters, Shanan; El-Henawy, Mohmmed; Antar, Mohammed; Zalmout, Iyad; Gingerich, Philip: Fossil burrow assemblage, not mangrove roots: reinterpretation of the main whale-bearing layer in the late Eocene of Wadi Al-Hitan, Egypt. In: Palaeobiodiversity and Palaeoenvironments, vol. 99, 2019. @article{article,
title = {Fossil burrow assemblage, not mangrove roots: reinterpretation of the main whale-bearing layer in the late Eocene of Wadi Al-Hitan, Egypt},
author = {Carole Gee and Paul Sander and Shanan Peters and Mohmmed El-Henawy and Mohammed Antar and Iyad Zalmout and Philip Gingerich},
url = {https://www.researchgate.net/publication/326955395_Fossil_burrow_assemblage_not_mangrove_roots_reinterpretation_of_the_main_whale-bearing_layer_in_the_late_Eocene_of_Wadi_Al-Hitan_Egypt},
doi = {10.1007/s12549-018-0337-0},
year = {2019},
date = {2019-01-01},
journal = {Palaeobiodiversity and Palaeoenvironments},
volume = {99},
abstract = {The UNESCO World Heritage Site of Wadi Al-Hitan near Fayum in the Western Desert of Egypt is well-known for its remarkable abundance and diversity of late Eocene marine fossils, especially well-preserved cetaceans and sirenians. However, the taphonomy of the early Priabonian whales and sea cows is still not fully understood. These marine mammals often occur on specific horizons in the Birket Qarun Formation, for example, on a distinctive firmground called the Camp White Layer (CWL). Vertical, rod-like structures in the CWL were previously interpreted as “mangrove pneumatophores,” which have influenced hypotheses about the habitat of early whales. Here, we reexamine the rod-like structures of the CWL and show that they do not represent mangrove rooting structures based on an analysis of their morphology and an extensive comparison with rooting structures of living mangroves. Instead, the morphology of the rod-like structures indicates that they are trace fossils representing five size classes of marine invertebrate burrows, including burrows of weakly umbonate clams and Ophiomorphidae. The complex overprinting of all burrows toward the top of the CWL indicates stratigraphic condensation caused by low overall rates of sedimentation on a marine flooding surface in the transgressive systems tract. The large number of whale carcasses, abundant invertebrate skeletal remains, logs, marine invertebrate-encrusted celestine crystals, and an extensive, diverse burrow network reflect a combination of environmental and temporal condensation. A peculiar feature of the CWL, celestine crystal aggregates and gastropod celestine pseudomorphs, indicate an evaporative phase that is difficult to reconcile with the current sequence stratigraphic framework.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The UNESCO World Heritage Site of Wadi Al-Hitan near Fayum in the Western Desert of Egypt is well-known for its remarkable abundance and diversity of late Eocene marine fossils, especially well-preserved cetaceans and sirenians. However, the taphonomy of the early Priabonian whales and sea cows is still not fully understood. These marine mammals often occur on specific horizons in the Birket Qarun Formation, for example, on a distinctive firmground called the Camp White Layer (CWL). Vertical, rod-like structures in the CWL were previously interpreted as “mangrove pneumatophores,” which have influenced hypotheses about the habitat of early whales. Here, we reexamine the rod-like structures of the CWL and show that they do not represent mangrove rooting structures based on an analysis of their morphology and an extensive comparison with rooting structures of living mangroves. Instead, the morphology of the rod-like structures indicates that they are trace fossils representing five size classes of marine invertebrate burrows, including burrows of weakly umbonate clams and Ophiomorphidae. The complex overprinting of all burrows toward the top of the CWL indicates stratigraphic condensation caused by low overall rates of sedimentation on a marine flooding surface in the transgressive systems tract. The large number of whale carcasses, abundant invertebrate skeletal remains, logs, marine invertebrate-encrusted celestine crystals, and an extensive, diverse burrow network reflect a combination of environmental and temporal condensation. A peculiar feature of the CWL, celestine crystal aggregates and gastropod celestine pseudomorphs, indicate an evaporative phase that is difficult to reconcile with the current sequence stratigraphic framework. |
Burke, Kevin D; Williams, John W; Brewer, Simon; Finsinger, Walter; Giesecke, Thomas; Lorenz, David J; Ordonez, Alejandro: Differing climatic mechanisms control transient and accumulated vegetation novelty in Europe and eastern North America. In: Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 374, no. 1788, pp. 20190218, 2019. @article{doi:10.1098/rstb.2019.0218,
title = {Differing climatic mechanisms control transient and accumulated vegetation novelty in Europe and eastern North America},
author = {Kevin D Burke and John W Williams and Simon Brewer and Walter Finsinger and Thomas Giesecke and David J Lorenz and Alejandro Ordonez},
url = {https://royalsocietypublishing.org/doi/abs/10.1098/rstb.2019.0218},
doi = {10.1098/rstb.2019.0218},
year = {2019},
date = {2019-01-01},
journal = {Philosophical Transactions of the Royal Society B: Biological Sciences},
volume = {374},
number = {1788},
pages = {20190218},
abstract = {Understanding the mechanisms of climate that produce novel ecosystems is of joint interest to conservation biologists and palaeoecologists. Here, we define and differentiate transient from accumulated novelty and evaluate four climatic mechanisms proposed to cause species to reshuffle into novel assemblages: high climatic novelty, high spatial rates of change (displacement), high variance among displacement rates for individual climate variables, and divergence among displacement vector bearings. We use climate simulations to quantify climate novelty, displacement and divergence across Europe and eastern North America from the last glacial maximum to the present, and fossil pollen records to quantify vegetation novelty. Transient climate novelty is consistently the strongest predictor of transient vegetation novelty, while displacement rates (mean and variance) are equally important in Europe. However, transient vegetation novelty is lower in Europe and its relationship to climatic predictors is the opposite of expectation. For both continents, accumulated novelty is greater than transient novelty, and climate novelty is the strongest predictor of accumulated ecological novelty. These results suggest that controls on novel ecosystems vary with timescale and among continents, and that the twenty-first century emergence of novelty will be driven by both rapid rates of climate change and the emergence of novel climate states. This article is part of a discussion meeting issue ‘The past is a foreign country: how much can the fossil record actually inform conservation?’},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Understanding the mechanisms of climate that produce novel ecosystems is of joint interest to conservation biologists and palaeoecologists. Here, we define and differentiate transient from accumulated novelty and evaluate four climatic mechanisms proposed to cause species to reshuffle into novel assemblages: high climatic novelty, high spatial rates of change (displacement), high variance among displacement rates for individual climate variables, and divergence among displacement vector bearings. We use climate simulations to quantify climate novelty, displacement and divergence across Europe and eastern North America from the last glacial maximum to the present, and fossil pollen records to quantify vegetation novelty. Transient climate novelty is consistently the strongest predictor of transient vegetation novelty, while displacement rates (mean and variance) are equally important in Europe. However, transient vegetation novelty is lower in Europe and its relationship to climatic predictors is the opposite of expectation. For both continents, accumulated novelty is greater than transient novelty, and climate novelty is the strongest predictor of accumulated ecological novelty. These results suggest that controls on novel ecosystems vary with timescale and among continents, and that the twenty-first century emergence of novelty will be driven by both rapid rates of climate change and the emergence of novel climate states. This article is part of a discussion meeting issue ‘The past is a foreign country: how much can the fossil record actually inform conservation?’ |
Stegner, Allison M; Ratajczak, Zak; Carpenter, Stephen R; Williams, John W: Inferring critical transitions in paleoecological time series with irregular sampling and variable time-averaging. In: Quaternary Science Reviews, vol. 207, pp. 49-63, 2019, ISSN: 0277-3791. @article{STEGNER201949,
title = {Inferring critical transitions in paleoecological time series with irregular sampling and variable time-averaging},
author = {Allison M Stegner and Zak Ratajczak and Stephen R Carpenter and John W Williams},
url = {https://www.sciencedirect.com/science/article/pii/S0277379118305420},
doi = {https://doi.org/10.1016/j.quascirev.2019.01.009},
issn = {0277-3791},
year = {2019},
date = {2019-01-01},
journal = {Quaternary Science Reviews},
volume = {207},
pages = {49-63},
abstract = {Many ecosystems have abruptly changed in the past and may again in the future, yet prediction and inference of mechanisms causing abrupt changes remains challenging. Critical transitions are one such mechanism, occurring when systems with alternative states cross a threshold. Such transitions are associated with a loss of resilience, often signaled by increasing variability or autocorrelation over time. However, critical transitions are difficult to distinguish from other causal mechanisms, and detection of resilience loss in sedimentary archives can be confounded by time-averaging and discontinuous sampling. Here, we simulate woodland-grassland regime shifts resulting from critical transitions and other mechanisms. We then test the diagnostic ability of two widely-used resilience indicators, standard deviation and autocorrelation time, after alterations common in sedimentary records: time averaging, discontinuous sampling, and varying sedimentation rates. Standard deviation—but not autocorrelation time—still distinguishes gradually forced critical transitions from other regime shifts when sedimentation rates are constant, and can be robust to abrupt changes in sedimentation rate. Unfortunately, shifts in standard deviation alone are rarely definitive evidence of critical transitions. Under exponential sedimentation regimes, which are common in younger upper-column sediments, neither resilience indicator is effective. Discontinuous sampling weakened the strength of resilience indicators. A demonstrative analysis of abrupt early Holocene deforestation recorded at Steel Lake, Minnesota showed signals consistent with resilience loss during early Holocene aridification. Hence, signals of resilience loss can be recovered from sedimentary archives, but efficacy varies among indicators and sedimentation regime. High-resolution and multi-proxy records remain essential to inferring causes, while process-based time series modeling such as this can be calibrated to systems of interest to explicitly test hypotheses about abrupt change causes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Many ecosystems have abruptly changed in the past and may again in the future, yet prediction and inference of mechanisms causing abrupt changes remains challenging. Critical transitions are one such mechanism, occurring when systems with alternative states cross a threshold. Such transitions are associated with a loss of resilience, often signaled by increasing variability or autocorrelation over time. However, critical transitions are difficult to distinguish from other causal mechanisms, and detection of resilience loss in sedimentary archives can be confounded by time-averaging and discontinuous sampling. Here, we simulate woodland-grassland regime shifts resulting from critical transitions and other mechanisms. We then test the diagnostic ability of two widely-used resilience indicators, standard deviation and autocorrelation time, after alterations common in sedimentary records: time averaging, discontinuous sampling, and varying sedimentation rates. Standard deviation—but not autocorrelation time—still distinguishes gradually forced critical transitions from other regime shifts when sedimentation rates are constant, and can be robust to abrupt changes in sedimentation rate. Unfortunately, shifts in standard deviation alone are rarely definitive evidence of critical transitions. Under exponential sedimentation regimes, which are common in younger upper-column sediments, neither resilience indicator is effective. Discontinuous sampling weakened the strength of resilience indicators. A demonstrative analysis of abrupt early Holocene deforestation recorded at Steel Lake, Minnesota showed signals consistent with resilience loss during early Holocene aridification. Hence, signals of resilience loss can be recovered from sedimentary archives, but efficacy varies among indicators and sedimentation regime. High-resolution and multi-proxy records remain essential to inferring causes, while process-based time series modeling such as this can be calibrated to systems of interest to explicitly test hypotheses about abrupt change causes. |
Ramiadantsoa, Tanjona; Stegner, Allison M; Williams, John W; Ives, Anthony R: The potential role of intrinsic processes in generating abrupt and quasi-synchronous tree declines during the Holocene. In: Ecology, vol. 100, no. 2, pp. e02579, 2019. @article{https://doi.org/10.1002/ecy.2579,
title = {The potential role of intrinsic processes in generating abrupt and quasi-synchronous tree declines during the Holocene},
author = {Tanjona Ramiadantsoa and Allison M Stegner and John W Williams and Anthony R Ives},
url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecy.2579},
doi = {https://doi.org/10.1002/ecy.2579},
year = {2019},
date = {2019-01-01},
journal = {Ecology},
volume = {100},
number = {2},
pages = {e02579},
abstract = {Abstract Multiple abrupt and sometimes near-synchronous declines in tree populations have been detected in the temperate forests of eastern North America and Europe during the Holocene. Traditional approaches to understanding these declines focus on searching for climatic or other broad-scale extrinsic drivers. These approaches include multi-proxy studies that match reconstructed changes in tree abundance to reconstructed changes in precipitation or temperature. Although these correlative approaches are informative, they neglect the potential role of intrinsic processes, such as competition and dispersal, in shaping tree community dynamics. We developed a simple process-based community model that includes competition among tree species, density-dependent survival, and dispersal to investigate how these processes might generate abrupt changes in tree abundances even when extrinsic climatic factors do not themselves change abruptly. Specifically, a self-reinforcing (i.e., positive) feedback between abundance and survival can produce abrupt changes in tree abundance in the absence of long-term climatic changes. Furthermore, spatially correlated, short-term environmental variation and seed dispersal can increase the synchrony of abrupt changes. Using the well-studied, late-Holocene crash of Tsuga canadensis (eastern hemlock) populations as an empirical case study, we find that our model generates abrupt and quasi-synchronized crashes qualitatively similar to the observed hemlock patterns. Other tree taxa vary in the frequency and clustering of abrupt change and the proportion of increases and decreases. This complexity argues for caution in interpreting abrupt changes in species abundances as indicative of abrupt climatic changes. Nonetheless, some taxa show patterns that the model cannot produce: observed abrupt declines in hemlock abundance are more synchronized than abrupt increases, whereas the degree of synchronization is the same for abrupt decreases and increases in the model. Our results show that intrinsic processes can be significant contributing factors in abrupt tree population changes and highlight the diagnostic value of analyzing entire time series rather than single events when testing hypotheses about abrupt changes. Thus, intrinsic processes should be considered along with extrinsic drivers when seeking to explain rapid changes in community composition.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Multiple abrupt and sometimes near-synchronous declines in tree populations have been detected in the temperate forests of eastern North America and Europe during the Holocene. Traditional approaches to understanding these declines focus on searching for climatic or other broad-scale extrinsic drivers. These approaches include multi-proxy studies that match reconstructed changes in tree abundance to reconstructed changes in precipitation or temperature. Although these correlative approaches are informative, they neglect the potential role of intrinsic processes, such as competition and dispersal, in shaping tree community dynamics. We developed a simple process-based community model that includes competition among tree species, density-dependent survival, and dispersal to investigate how these processes might generate abrupt changes in tree abundances even when extrinsic climatic factors do not themselves change abruptly. Specifically, a self-reinforcing (i.e., positive) feedback between abundance and survival can produce abrupt changes in tree abundance in the absence of long-term climatic changes. Furthermore, spatially correlated, short-term environmental variation and seed dispersal can increase the synchrony of abrupt changes. Using the well-studied, late-Holocene crash of Tsuga canadensis (eastern hemlock) populations as an empirical case study, we find that our model generates abrupt and quasi-synchronized crashes qualitatively similar to the observed hemlock patterns. Other tree taxa vary in the frequency and clustering of abrupt change and the proportion of increases and decreases. This complexity argues for caution in interpreting abrupt changes in species abundances as indicative of abrupt climatic changes. Nonetheless, some taxa show patterns that the model cannot produce: observed abrupt declines in hemlock abundance are more synchronized than abrupt increases, whereas the degree of synchronization is the same for abrupt decreases and increases in the model. Our results show that intrinsic processes can be significant contributing factors in abrupt tree population changes and highlight the diagnostic value of analyzing entire time series rather than single events when testing hypotheses about abrupt changes. Thus, intrinsic processes should be considered along with extrinsic drivers when seeking to explain rapid changes in community composition. |
Xu, Xiaowu; Yu, Xinxiao; Bao, Le; Desai, Ankur R: Size distribution of particulate matter in runoff from different leaf surfaces during controlled rainfall processes. In: Environmental Pollution, vol. 255, pp. 113234, 2019, ISSN: 0269-7491. @article{XU2019113234,
title = {Size distribution of particulate matter in runoff from different leaf surfaces during controlled rainfall processes},
author = {Xiaowu Xu and Xinxiao Yu and Le Bao and Ankur R Desai},
url = {https://www.sciencedirect.com/science/article/pii/S0269749119322031},
doi = {https://doi.org/10.1016/j.envpol.2019.113234},
issn = {0269-7491},
year = {2019},
date = {2019-01-01},
journal = {Environmental Pollution},
volume = {255},
pages = {113234},
abstract = {The presence of plant leaves has been shown to lower the risks of health problems by reducing atmospheric particulate matter (PM). Leaf PM accumulation capacity will saturate in the absence of runoff. Rainfall is an effective way for PM to “wash off” into the soil and renew leaf PM accumulation. However, little is known about how PM wash-off varies with PM size and health problems caused by particulate pollution vary with PM size. This study thus used artificial rainfall with six plant species to find out how size-fractioned PM are washed off during rain processes. Total wash-off masses in fine, coarse and large fractions were 0.6–10.3 μg/cm2, 1.0–18.8 μg/cm2 and 4.5–60.1 μg/cm2 respectively. P. orientalis (cypress) and E. japonicus (evergreen broadleaved shrub) had the largest wash-off masses in each fraction during rainfall. P. cerasifera (deciduous broadleaved shrub) had the largest cumulative wash-off rates in each fraction. Rainfall intensity had more influence on wash-off masses and rates of large particles for six species and for small particles in evergreen species, but limited effect on wash-off proportions. Wash-off proportions decreased in large particles and increased in small particles along with rainfall. The results provide information for PM accumulation renewal of plants used for urban greening.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The presence of plant leaves has been shown to lower the risks of health problems by reducing atmospheric particulate matter (PM). Leaf PM accumulation capacity will saturate in the absence of runoff. Rainfall is an effective way for PM to “wash off” into the soil and renew leaf PM accumulation. However, little is known about how PM wash-off varies with PM size and health problems caused by particulate pollution vary with PM size. This study thus used artificial rainfall with six plant species to find out how size-fractioned PM are washed off during rain processes. Total wash-off masses in fine, coarse and large fractions were 0.6–10.3 μg/cm2, 1.0–18.8 μg/cm2 and 4.5–60.1 μg/cm2 respectively. P. orientalis (cypress) and E. japonicus (evergreen broadleaved shrub) had the largest wash-off masses in each fraction during rainfall. P. cerasifera (deciduous broadleaved shrub) had the largest cumulative wash-off rates in each fraction. Rainfall intensity had more influence on wash-off masses and rates of large particles for six species and for small particles in evergreen species, but limited effect on wash-off proportions. Wash-off proportions decreased in large particles and increased in small particles along with rainfall. The results provide information for PM accumulation renewal of plants used for urban greening. |
Delorit, Justin D; Parker, Dominic P; Block, Paul J: An agro-economic approach to framing perennial farm-scale water resources demand management for water rights markets. In: Agricultural Water Management, vol. 218, pp. 68-81, 2019, ISSN: 0378-3774. @article{DELORIT201968,
title = {An agro-economic approach to framing perennial farm-scale water resources demand management for water rights markets},
author = {Justin D Delorit and Dominic P Parker and Paul J Block},
url = {https://www.sciencedirect.com/science/article/pii/S0378377419305517},
doi = {https://doi.org/10.1016/j.agwat.2019.03.029},
issn = {0378-3774},
year = {2019},
date = {2019-01-01},
journal = {Agricultural Water Management},
volume = {218},
pages = {68-81},
abstract = {Water rights and corresponding markets work to address water scarcity by establishing tradable, limited-access permits to water resources. Under certain water rights law, rights holders face uncertainty in terms of right allocation value, which is set annually based on reservoir storage, expected inflow, and expected future conditions. Such is the case in the Elqui Valley, Chile, where the economy is driven by agriculture, which requires water rights to ensure profitable yields due to a mismatch between the season of precipitation (May-August) and growing season (September-April). Perennial crop farmers address allocation uncertainty by securing additional water. A farm-scale agro-economic demand modelling framework is developed which utilizes the temporary transferability of rights to describe how grape famers may engage optimally in water markets to maximize annual profits (2000–2015), and produces an upper bound on grape farmer price negotiation space for desired allocation transactions. The results show grape farmers holding 1.0 and 2.25 water rights per-hectare could increase expected profits by 98% and 27%, respectively by engaging optimally in the temporary water market. Over the period evaluated, a grape farmer holding a single water right may expect to engage in market activity 80% of years; two rights require farmers to engage during 30% of years; with seven rights market engagement is avoided. The broader insights of the research suggest where rights holders accurately assess the value of water, optimal engagement strategies can be developed that add to farm-scale profitability, and act as an assessment of whether existing rights ownership matches risk tolerance.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Water rights and corresponding markets work to address water scarcity by establishing tradable, limited-access permits to water resources. Under certain water rights law, rights holders face uncertainty in terms of right allocation value, which is set annually based on reservoir storage, expected inflow, and expected future conditions. Such is the case in the Elqui Valley, Chile, where the economy is driven by agriculture, which requires water rights to ensure profitable yields due to a mismatch between the season of precipitation (May-August) and growing season (September-April). Perennial crop farmers address allocation uncertainty by securing additional water. A farm-scale agro-economic demand modelling framework is developed which utilizes the temporary transferability of rights to describe how grape famers may engage optimally in water markets to maximize annual profits (2000–2015), and produces an upper bound on grape farmer price negotiation space for desired allocation transactions. The results show grape farmers holding 1.0 and 2.25 water rights per-hectare could increase expected profits by 98% and 27%, respectively by engaging optimally in the temporary water market. Over the period evaluated, a grape farmer holding a single water right may expect to engage in market activity 80% of years; two rights require farmers to engage during 30% of years; with seven rights market engagement is avoided. The broader insights of the research suggest where rights holders accurately assess the value of water, optimal engagement strategies can be developed that add to farm-scale profitability, and act as an assessment of whether existing rights ownership matches risk tolerance. |
2018
|
Nolan, Connor; Overpeck, Jonathan T.; Allen, Judy R. M.; Anderson, Patricia M.; Betancourt, Julio L.; Binney, Heather A.; Brewer, Simon; Bush, Mark B.; Chase, Brian M.; Cheddadi, Rachid; Djamali, Morteza; Dodson, John; Edwards, Mary E.; Gosling, William D.; Haberle, Simon; Hotchkiss, Sara C.; Huntley, Brian; Ivory, Sarah J.; Kershaw, A. Peter; Kim, Soo-Hyun; Latorre, Claudio; Leydet, Michelle; Lézine, Anne-Marie; Liu, Kam-Biu; Liu, Yao; Lozhkin, A. V.; McGlone, Matt S.; Marchant, Robert A.; Momohara, Arata; Moreno, Patricio I.; Müller, Stefanie; Otto-Bliesner, Bette L.; Shen, Caiming; Stevenson, Janelle; Takahara, Hikaru; Tarasov, Pavel E.; Tipton, John; Vincens, Annie; Weng, Chengyu; Xu, Qinghai; Zheng, Zhuo; Jackson, Stephen T.: Past and future global transformation of terrestrial ecosystems under climate change. In: Science, vol. 361, iss. 6405, pp. 920-923, 2018. @article{Nolan2018,
title = {Past and future global transformation of terrestrial ecosystems under climate change},
author = {Connor Nolan and Jonathan T. Overpeck and Judy R. M. Allen and Patricia M. Anderson and Julio L. Betancourt and Heather A. Binney and Simon Brewer and Mark B. Bush and Brian M. Chase and Rachid Cheddadi and Morteza Djamali and John Dodson and Mary E. Edwards and William D. Gosling and Simon Haberle and Sara C. Hotchkiss and Brian Huntley and Sarah J. Ivory and A. Peter Kershaw and Soo-Hyun Kim and Claudio Latorre and Michelle Leydet and Anne-Marie Lézine and Kam-Biu Liu and Yao Liu and A. V. Lozhkin and Matt S. McGlone and Robert A. Marchant and Arata Momohara and Patricio I. Moreno and Stefanie Müller and Bette L. Otto-Bliesner and Caiming Shen and Janelle Stevenson and Hikaru Takahara and Pavel E. Tarasov and John Tipton and Annie Vincens and Chengyu Weng and Qinghai Xu and Zhuo Zheng and Stephen T. Jackson},
doi = {https://doi.org/10.1126/science.aan5360},
year = {2018},
date = {2018-08-31},
journal = {Science},
volume = {361},
issue = {6405},
pages = {920-923},
abstract = {Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity. |
2017
|
Lynch, Elizabeth A.; Hotchkiss, Sara C.; Calcote, Randy: Charcoal signatures defined by multivariate analysis of charcoal records from 10 lakes in northwest Wisconsin (USA). In: Quaternary Research, vol. 75, iss. 1, pp. 125-137, 2017. @article{Lynch2017,
title = {Charcoal signatures defined by multivariate analysis of charcoal records from 10 lakes in northwest Wisconsin (USA)},
author = {Elizabeth A. Lynch and Sara C. Hotchkiss and Randy Calcote},
doi = {doi:10.1016/j.yqres.2010.08.007},
year = {2017},
date = {2017-01-20},
journal = {Quaternary Research},
volume = {75},
issue = {1},
pages = {125-137},
abstract = {We show how sedimentary charcoal records from multiple sites within a single landscape can be used to compare fire histories and reveal small scale patterns in fire regimes. Our objective is to develop strategies for classifying and comparing late-Holocene charcoal records in Midwestern oak- and pine-dominated sand plain ecosystems where fire regimes include a mix of surface and crown fires. Using standard techniques for the analysis of charcoal from lake sediments, we compiled 1000- to 4000-yr-long records of charcoal accumulation and charcoal peak frequencies from 10 small lakes across a sand plain in northwestern Wisconsin. We used cluster analysis to identify six types of charcoal signatures that differ in their charcoal influx rates, amount of grass charcoal, and frequency and magnitude of charcoal peaks. The charcoal records demonstrate that while fire histories vary among sites, there are regional patterns in the occurrence of charcoal signature types that are consistent with expected differences in fire regimes based on regional climate and vegetation reconstructions. The fire histories also show periods of regional change in charcoal signatures occurring during times of regional climate changes at ~700, 1000, and 3500 cal yr BP.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We show how sedimentary charcoal records from multiple sites within a single landscape can be used to compare fire histories and reveal small scale patterns in fire regimes. Our objective is to develop strategies for classifying and comparing late-Holocene charcoal records in Midwestern oak- and pine-dominated sand plain ecosystems where fire regimes include a mix of surface and crown fires. Using standard techniques for the analysis of charcoal from lake sediments, we compiled 1000- to 4000-yr-long records of charcoal accumulation and charcoal peak frequencies from 10 small lakes across a sand plain in northwestern Wisconsin. We used cluster analysis to identify six types of charcoal signatures that differ in their charcoal influx rates, amount of grass charcoal, and frequency and magnitude of charcoal peaks. The charcoal records demonstrate that while fire histories vary among sites, there are regional patterns in the occurrence of charcoal signature types that are consistent with expected differences in fire regimes based on regional climate and vegetation reconstructions. The fire histories also show periods of regional change in charcoal signatures occurring during times of regional climate changes at ~700, 1000, and 3500 cal yr BP. |
2016
|
Wigdahl-Perry, Courtney R.; Saros, Jasmine E.; Schmitz, Jennifer; Calcote, Randy; Rusak, James; Anderson, Dennis; Hotchkiss, Sara: Response of temperate lakes to drought: a paleolimnological perspective on the landscape position concept using diatom-based reconstructions. In: Journal of Paleolimnology, vol. 55, pp. 339–356, 2016. @article{nokey,
title = {Response of temperate lakes to drought: a paleolimnological perspective on the landscape position concept using diatom-based reconstructions},
author = {Courtney R. Wigdahl-Perry and Jasmine E. Saros and Jennifer Schmitz and Randy Calcote and James Rusak and Dennis Anderson and Sara Hotchkiss },
doi = {https://doi.org/10.1007/s10933-016-9883-5},
year = {2016},
date = {2016-03-04},
journal = {Journal of Paleolimnology},
volume = {55},
pages = {339–356},
abstract = {The hydrological position of a lake within the landscape can affect a number of lake chemical, physical, and biological features, as well as how lakes respond to environmental change. We present a paleolimnological test of the model for landscape position and lake response to climate change proposed by Webster et al. (2000). To investigate how diatom communities have responded to drought relative to landscape position, we examined sedimentary diatom profiles extending through the twentieth century from an upland site (Crystal Lake) and a lowland site (Allequash Lake) in the Northern Highlands region of north-central Wisconsin (USA). To explore changes in diatom communities at each site, we developed a calibration set and transfer functions from 48 lakes in Wisconsin’s Northern Highland Lake District. We further determined planktic:benthic ratios in the two target lakes, developed lake level models, and investigated the sensitivity of planktic:benthic diatom ratios to climatic variability over the past century. In the upland lake, diatom communities responded indirectly to climate via drought-induced changes in lake level, which resulted in shifts in planktic versus benthic habitat availability. This response of diatoms to changes in habitat availability provides an alternative approach for tracking climate change in upland lakes, though careful consideration must be given to the effect of the bathymetry and its relationship to lake level change and habitat zonation at individual sites. In the lowland lake, changes in diatom communities were related to temperature (and possibly lakewater chemistry) and physical changes secondarily. These results are consistent with the model by Webster et al. (2000), with chemical changes occurring in the lowland system and little chemical response in the upland system. However, the biological changes in sediment records presented here provide additional insight into how lake response to climatic change is shaped by landscape position, contributing to a clearer understanding of potential changes in ecosystem structure and function during drought conditions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The hydrological position of a lake within the landscape can affect a number of lake chemical, physical, and biological features, as well as how lakes respond to environmental change. We present a paleolimnological test of the model for landscape position and lake response to climate change proposed by Webster et al. (2000). To investigate how diatom communities have responded to drought relative to landscape position, we examined sedimentary diatom profiles extending through the twentieth century from an upland site (Crystal Lake) and a lowland site (Allequash Lake) in the Northern Highlands region of north-central Wisconsin (USA). To explore changes in diatom communities at each site, we developed a calibration set and transfer functions from 48 lakes in Wisconsin’s Northern Highland Lake District. We further determined planktic:benthic ratios in the two target lakes, developed lake level models, and investigated the sensitivity of planktic:benthic diatom ratios to climatic variability over the past century. In the upland lake, diatom communities responded indirectly to climate via drought-induced changes in lake level, which resulted in shifts in planktic versus benthic habitat availability. This response of diatoms to changes in habitat availability provides an alternative approach for tracking climate change in upland lakes, though careful consideration must be given to the effect of the bathymetry and its relationship to lake level change and habitat zonation at individual sites. In the lowland lake, changes in diatom communities were related to temperature (and possibly lakewater chemistry) and physical changes secondarily. These results are consistent with the model by Webster et al. (2000), with chemical changes occurring in the lowland system and little chemical response in the upland system. However, the biological changes in sediment records presented here provide additional insight into how lake response to climatic change is shaped by landscape position, contributing to a clearer understanding of potential changes in ecosystem structure and function during drought conditions. |
2015
|
Barak, Rebecca S.; Hipp, Andrew L.; Cavender-Bares, Jeannine; Pearse, William D.; Hotchkiss, Sara C.; Lynch, Elizabeth A.; Callaway, John C.; Calcote, Randy; Larkin, Daniel J.: Taking the Long View: Integrating Recorded, Archeological, Paleoecological, and Evolutionary Data into Ecological Restoration. In: International Journal of Plant Sciences, vol. 177, iss. 1, pp. 90-102, 2015. @article{Barak2015,
title = {Taking the Long View: Integrating Recorded, Archeological, Paleoecological, and Evolutionary Data into Ecological Restoration},
author = {Rebecca S. Barak and Andrew L. Hipp and Jeannine Cavender-Bares and William D. Pearse and Sara C. Hotchkiss and Elizabeth A. Lynch and John C. Callaway and Randy Calcote and Daniel J. Larkin},
doi = {https://doi.org/10.1086/683394},
year = {2015},
date = {2015-11-16},
journal = {International Journal of Plant Sciences},
volume = {177},
issue = {1},
pages = {90-102},
abstract = {Historical information spanning different temporal scales (from tens to millions of years) can influence restoration practice by providing ecological context for better understanding of contemporary ecosystems. Ecological history provides clues about the assembly, structure, and dynamic nature of ecosystems, and this information can improve forecasting of how restored systems will respond to changes in climate, disturbance regimes, and other factors. History recorded by humans can be used to generate baselines for assessing changes in ecosystems, communities, and populations over time. Paleoecology pushes these baselines back hundreds, thousands, or even millions of years, offering insights into how past species assemblages have responded to changing disturbance regimes and climate. Furthermore, archeology can be used to reconstruct interactions between humans and their environment for which no documentary records exist. Going back further, phylogenies reveal patterns that emerged from coupled evolutionary-ecological processes over very long timescales. Increasingly, this information can be used to predict the stability, resilience, and functioning of assemblages into the future. We review examples in which recorded, archeological, paleoecological, and evolutionary information has been or could be used to inform goal setting, management, and monitoring for restoration. While we argue that long-view historical ecology has much to offer restoration, there are few examples of restoration projects explicitly incorporating such information or of research that has evaluated the utility of such perspectives in applied management contexts. For these ideas to move from theory into practice, tests performed through research-management partnerships are needed to determine to what degree taking the long view can support achievement of restoration objectives.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Historical information spanning different temporal scales (from tens to millions of years) can influence restoration practice by providing ecological context for better understanding of contemporary ecosystems. Ecological history provides clues about the assembly, structure, and dynamic nature of ecosystems, and this information can improve forecasting of how restored systems will respond to changes in climate, disturbance regimes, and other factors. History recorded by humans can be used to generate baselines for assessing changes in ecosystems, communities, and populations over time. Paleoecology pushes these baselines back hundreds, thousands, or even millions of years, offering insights into how past species assemblages have responded to changing disturbance regimes and climate. Furthermore, archeology can be used to reconstruct interactions between humans and their environment for which no documentary records exist. Going back further, phylogenies reveal patterns that emerged from coupled evolutionary-ecological processes over very long timescales. Increasingly, this information can be used to predict the stability, resilience, and functioning of assemblages into the future. We review examples in which recorded, archeological, paleoecological, and evolutionary information has been or could be used to inform goal setting, management, and monitoring for restoration. While we argue that long-view historical ecology has much to offer restoration, there are few examples of restoration projects explicitly incorporating such information or of research that has evaluated the utility of such perspectives in applied management contexts. For these ideas to move from theory into practice, tests performed through research-management partnerships are needed to determine to what degree taking the long view can support achievement of restoration objectives. |
Tweiten, Michael A.; Calcote, Randy R.; Lynch, Elizabeth A.; Hotchkiss, Sara C.; Schuurman, Gregor W.: Geophysical features influence the climate change sensitivity of northern Wisconsin pine and oak forests. In: Ecological Applications, vol. 25, iss. 7, pp. 1984-1996, 2015. @article{Tweiten2015,
title = {Geophysical features influence the climate change sensitivity of northern Wisconsin pine and oak forests},
author = {Michael A. Tweiten and Randy R. Calcote and Elizabeth A. Lynch and Sara C. Hotchkiss and Gregor W. Schuurman},
doi = { https://doi.org/10.1890/14-2015.1},
year = {2015},
date = {2015-10-01},
journal = {Ecological Applications},
volume = {25},
issue = {7},
pages = {1984-1996},
abstract = {Landscape-scale vulnerability assessment from multiple sources, including paleoecological site histories, can inform climate change adaptation. We used an array of lake sediment pollen and charcoal records to determine how soils and landscape factors influenced the variability of forest composition change over the past 2000 years. The forests in this study are located in northwestern Wisconsin on a sandy glacial outwash plain. Soils and local climate vary across the study area. We used the Natural Resource Conservation Service's Soil Survey Geographic soil database and published fire histories to characterize differences in soils and fire history around each lake site. Individual site histories differed in two metrics of past vegetation dynamics: the extent to which white pine (Pinus strobus) increased during the Little Ice Age (LIA) climate period and the volatility in the rate of change between samples at 50–120 yr intervals. Greater increases of white pine during the LIA occurred on sites with less sandy soils (R2 = 0.45, P < 0.0163) and on sites with relatively warmer and drier local climate (R2 = 0.55, P < 0.0056). Volatility in the rate of change between samples was positively associated with LIA fire frequency (R2 = 0.41, P < 0.0256). Over multi-decadal to centennial timescales, forest compositional change and rate-of-change volatility were associated with higher fire frequency. Over longer (multi-centennial) time frames, forest composition change, especially increased white pine, shifted most in sites with more soil moisture. Our results show that responsiveness of forest composition to climate change was influenced by soils, local climate, and fire. The anticipated climatic changes in the next century will not produce the same community dynamics on the same soil types as in the past, but understanding past dynamics and relationships can help us assess how novel factors and combinations of factors in the future may influence various site types. Our results support climate change adaptation efforts to monitor and conserve the landscape's full range of geophysical features.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Landscape-scale vulnerability assessment from multiple sources, including paleoecological site histories, can inform climate change adaptation. We used an array of lake sediment pollen and charcoal records to determine how soils and landscape factors influenced the variability of forest composition change over the past 2000 years. The forests in this study are located in northwestern Wisconsin on a sandy glacial outwash plain. Soils and local climate vary across the study area. We used the Natural Resource Conservation Service's Soil Survey Geographic soil database and published fire histories to characterize differences in soils and fire history around each lake site. Individual site histories differed in two metrics of past vegetation dynamics: the extent to which white pine (Pinus strobus) increased during the Little Ice Age (LIA) climate period and the volatility in the rate of change between samples at 50–120 yr intervals. Greater increases of white pine during the LIA occurred on sites with less sandy soils (R2 = 0.45, P < 0.0163) and on sites with relatively warmer and drier local climate (R2 = 0.55, P < 0.0056). Volatility in the rate of change between samples was positively associated with LIA fire frequency (R2 = 0.41, P < 0.0256). Over multi-decadal to centennial timescales, forest compositional change and rate-of-change volatility were associated with higher fire frequency. Over longer (multi-centennial) time frames, forest composition change, especially increased white pine, shifted most in sites with more soil moisture. Our results show that responsiveness of forest composition to climate change was influenced by soils, local climate, and fire. The anticipated climatic changes in the next century will not produce the same community dynamics on the same soil types as in the past, but understanding past dynamics and relationships can help us assess how novel factors and combinations of factors in the future may influence various site types. Our results support climate change adaptation efforts to monitor and conserve the landscape's full range of geophysical features. |
2012
|
Crausbay, Shelley D.; Hotchkiss, Sara C.: Pollen–vegetation relationships at a tropical cloud forest's upper limit and accuracy of vegetation inference. In: Review of Palaeobotany and Palynology, vol. 184, pp. 1-13, 2012. @article{Crausbay2012,
title = {Pollen–vegetation relationships at a tropical cloud forest's upper limit and accuracy of vegetation inference},
author = {Shelley D. Crausbay and Sara C. Hotchkiss},
doi = {https://doi.org/10.1016/j.revpalbo.2012.07.010},
year = {2012},
date = {2012-09-15},
journal = {Review of Palaeobotany and Palynology},
volume = {184},
pages = {1-13},
abstract = {Palaeoecological records are increasingly needed from tropical montane systems. To infer past tropical vegetation dynamics, understanding modern pollen–vegetation relationships is required, but understanding effects of different sampling media between calibration datasets and palaeorecords is also needed. This is especially true when palaeorecords are derived from bogs or lakes with boggy shores and common wetland plants share the same pollen taxon with important upland plants that distinguish tropical vegetation types (e.g., Poaceae and Plantago). We assessed modern pollen–vegetation relationships around an upper cloud forest line in the Hawaiian Islands and tested the utility of a modern pollen calibration dataset derived from 88 surface soil samples when applied in 10 test wetland sites more typical of palaeorecords. We assessed over- and under-representation of pollen/spore taxa with a direct comparison to plant abundance and derived several metrics from the pollen/spore assemblages — analogs, ordinations, relative abundance of life forms, and ratios of life forms. We used the Receiver Operator Characteristic (ROC) to (1) compare metric performance at distinguishing vegetation around the upper forest line, (2) assess whether excluding wetland taxa significantly affected metric performance, and (3) test the accuracy of vegetation inference. Pollen–vegetation relationships were influenced by great ecological breadth and over- or under-representation of pollen and spores, which could be explained by pollination syndrome (wind vs. animal), grain/spore mass and upslope transport in winds. However, we found no evidence that upslope transport significantly blurred the upper-forest-line signal here, likely because winds are predominantly perpendicular to slope, and vertically constrained by the trade-wind inversion. Pollen from Poaceae and Plantago characterizes vegetation around this Hawaiian upper forest line and dominates wetland assemblages. Removing wetland taxa from the modern pollen calibration dataset levied no cost on a metric's performance, and greatly reduced the incidence of inaccurate vegetation inference in test sites. Minor error rates remained when rare, over-represented, or ecologically broad types were used in isolation. Overall, this study demonstrates that inferring forest line position from fossil pollen/spore assemblages requires careful consideration because (1) differences in sampling media between the modern calibration dataset and palaeorecords create opportunity for inaccurate vegetation inference and (2) some metrics perform better than others.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Palaeoecological records are increasingly needed from tropical montane systems. To infer past tropical vegetation dynamics, understanding modern pollen–vegetation relationships is required, but understanding effects of different sampling media between calibration datasets and palaeorecords is also needed. This is especially true when palaeorecords are derived from bogs or lakes with boggy shores and common wetland plants share the same pollen taxon with important upland plants that distinguish tropical vegetation types (e.g., Poaceae and Plantago). We assessed modern pollen–vegetation relationships around an upper cloud forest line in the Hawaiian Islands and tested the utility of a modern pollen calibration dataset derived from 88 surface soil samples when applied in 10 test wetland sites more typical of palaeorecords. We assessed over- and under-representation of pollen/spore taxa with a direct comparison to plant abundance and derived several metrics from the pollen/spore assemblages — analogs, ordinations, relative abundance of life forms, and ratios of life forms. We used the Receiver Operator Characteristic (ROC) to (1) compare metric performance at distinguishing vegetation around the upper forest line, (2) assess whether excluding wetland taxa significantly affected metric performance, and (3) test the accuracy of vegetation inference. Pollen–vegetation relationships were influenced by great ecological breadth and over- or under-representation of pollen and spores, which could be explained by pollination syndrome (wind vs. animal), grain/spore mass and upslope transport in winds. However, we found no evidence that upslope transport significantly blurred the upper-forest-line signal here, likely because winds are predominantly perpendicular to slope, and vertically constrained by the trade-wind inversion. Pollen from Poaceae and Plantago characterizes vegetation around this Hawaiian upper forest line and dominates wetland assemblages. Removing wetland taxa from the modern pollen calibration dataset levied no cost on a metric's performance, and greatly reduced the incidence of inaccurate vegetation inference in test sites. Minor error rates remained when rare, over-represented, or ecologically broad types were used in isolation. Overall, this study demonstrates that inferring forest line position from fossil pollen/spore assemblages requires careful consideration because (1) differences in sampling media between the modern calibration dataset and palaeorecords create opportunity for inaccurate vegetation inference and (2) some metrics perform better than others. |
Ireland, Alex W.; Booth, Robert K.; Hotchkiss, Sara C.; Schmitz, Jennifer E.: Drought as a Trigger for Rapid State Shifts in Kettle Ecosystems: Implications for Ecosystem Responses to Climate Change. In: Wetlands volume, vol. 32, pp. 989–1000, 2012. @article{Ireland2012,
title = {Drought as a Trigger for Rapid State Shifts in Kettle Ecosystems: Implications for Ecosystem Responses to Climate Change},
author = {Alex W. Ireland and Robert K. Booth and Sara C. Hotchkiss and Jennifer E. Schmitz },
doi = {https://doi.org/10.1007/s13157-012-0324-6},
year = {2012},
date = {2012-07-18},
journal = {Wetlands volume},
volume = {32},
pages = {989–1000},
abstract = {Global climate change has raised important questions about ecosystem resilience and the likelihood of unexpected and potentially irreversible ecosystem state shifts. Conceptual models provide a framework for generating hypotheses about long-term ecosystem processes and their responses to external perturbations. In this article, we review the classic model of autogenic peatland encroachment into closed-basin kettle lakes (terrestrialization) as well as studies that document patterns of terrestrialization that are inconsistent with this hypothesis. We then present a new conceptual model of episodic, drought-triggered terrestrialization, which is consistent with existing data and provides a mechanism by which climatic variability could cause non-linear patterns of peatland development in these ecosystems. Next, we review data from comparative studies of kettle lakes along a peatland-development gradient to explore potential ecological and biogeochemical consequences of non-linear patterns of terrestrialization. Finally, we identify research approaches that could be used to test conceptual models of terrestrialization, investigate the ecological implications of non-linear patterns of peatland development, and improve our ability to predict responses of kettle systems to climate changes of the coming decades and century.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Global climate change has raised important questions about ecosystem resilience and the likelihood of unexpected and potentially irreversible ecosystem state shifts. Conceptual models provide a framework for generating hypotheses about long-term ecosystem processes and their responses to external perturbations. In this article, we review the classic model of autogenic peatland encroachment into closed-basin kettle lakes (terrestrialization) as well as studies that document patterns of terrestrialization that are inconsistent with this hypothesis. We then present a new conceptual model of episodic, drought-triggered terrestrialization, which is consistent with existing data and provides a mechanism by which climatic variability could cause non-linear patterns of peatland development in these ecosystems. Next, we review data from comparative studies of kettle lakes along a peatland-development gradient to explore potential ecological and biogeochemical consequences of non-linear patterns of terrestrialization. Finally, we identify research approaches that could be used to test conceptual models of terrestrialization, investigate the ecological implications of non-linear patterns of peatland development, and improve our ability to predict responses of kettle systems to climate changes of the coming decades and century. |
2011
|
Karlin, Eric F.; Hotchkiss, Sara C.; Boles, Sandra B.; Stenøien, Hans K.; Hassel, Kristian; Flatberg, Kjell I.; Shaw, A. Jonathan: High genetic diversity in a remote island population system: sans sex. In: New Phytologist, vol. 193, iss. 4, pp. 1088-1097, 2011. @article{Karlin2011,
title = {High genetic diversity in a remote island population system: sans sex},
author = {Eric F. Karlin and Sara C. Hotchkiss and Sandra B. Boles and Hans K. Stenøien and Kristian Hassel and Kjell I. Flatberg and A. Jonathan Shaw},
doi = {https://doi.org/10.1111/j.1469-8137.2011.03999.x},
year = {2011},
date = {2011-12-21},
journal = {New Phytologist},
volume = {193},
issue = {4},
pages = {1088-1097},
abstract = {It has been proposed that long-distance dispersal of mosses to the Hawaiian Islands rarely occurs and that the Hawaiian population of the allopolyploid peat moss Sphagnum palustre probably resulted from a single dispersal event.
•
Here, we used microsatellites to investigate whether the Hawaiian population of the dioicous S. palustre had a single founder and to compare its genetic diversity to that found in populations of S. palustre in other regions.
•
The genetic diversity of the Hawaiian population is comparable to that of larger population systems. Several lines of evidence, including a lack of sporophytes and an apparently restricted natural distribution, suggest that sexual reproduction is absent in the Hawaiian plants. In addition, all samples of Hawaiian S. palustre share a genetic trait rare in other populations. Time to most recent ancestor (TMRCA) analysis indicates that the Hawaiian population was probably founded 49–51 kyr ago.
•
It appears that all Hawaiian plants of S. palustre descend from a single founder via vegetative propagation. The long-term viability of this clonal population coupled with the development of significant genetic diversity suggests that vegetative propagation in a moss does not necessarily preclude evolutionary success in the long term.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
It has been proposed that long-distance dispersal of mosses to the Hawaiian Islands rarely occurs and that the Hawaiian population of the allopolyploid peat moss Sphagnum palustre probably resulted from a single dispersal event.
•
Here, we used microsatellites to investigate whether the Hawaiian population of the dioicous S. palustre had a single founder and to compare its genetic diversity to that found in populations of S. palustre in other regions.
•
The genetic diversity of the Hawaiian population is comparable to that of larger population systems. Several lines of evidence, including a lack of sporophytes and an apparently restricted natural distribution, suggest that sexual reproduction is absent in the Hawaiian plants. In addition, all samples of Hawaiian S. palustre share a genetic trait rare in other populations. Time to most recent ancestor (TMRCA) analysis indicates that the Hawaiian population was probably founded 49–51 kyr ago.
•
It appears that all Hawaiian plants of S. palustre descend from a single founder via vegetative propagation. The long-term viability of this clonal population coupled with the development of significant genetic diversity suggests that vegetative propagation in a moss does not necessarily preclude evolutionary success in the long term. |
Kellner, James R.; Asner, Gregory P.; Vitousek, Peter M.; Tweiten, Michael A.; Hotchkiss, Sara; Chadwick, Oliver A.: Dependence of Forest Structure and Dynamics on Substrate Age and Ecosystem Development. 2011. @bachelorthesis{Kellner2011,
title = {Dependence of Forest Structure and Dynamics on Substrate Age and Ecosystem Development},
author = {James R. Kellner and Gregory P. Asner and Peter M. Vitousek and Michael A. Tweiten and Sara Hotchkiss and Oliver A. Chadwick },
doi = {https://doi.org/10.1007/s10021-011-9472-4},
year = {2011},
date = {2011-09-07},
journal = {Ecosystems volume},
volume = {14},
pages = {1156–1167},
abstract = {We quantified rates, sizes, and spatial properties of prevailing disturbance regimes in five tropical rain forest landscapes on a substrate-age gradient in Hawaii. By integrating measurements from airborne LiDAR with field studies and statistical modeling, we show that the structure and dynamics of these forests respond to processes that change during the development of ecosystems. On young substrates of 0.3 ky where forests are in primary succession and are limited by N, mean canopy height was 13 m and height decreases more than 1 m occurred in small, isolated events (power-law exponent = 1.69 ± 0.02, n = 61 gaps ha−1). The proportion of the landscape affected by disturbance increased on high-fertility intermediate-aged substrates of 5–65 ky and canopies were heterogeneous. Frequencies of height decreases more than 1 m were n = 14, 18, and 30 gaps ha−1 corresponding to power-law exponents of 2.188 ± 0.02, 2.220 ± 0.03, and 1.982 ± 0.02 on substrates of 5, 20, and 65 ky. There was a substantial difference between forests on a 150 ky substrate and sites of 5–65 ky; trees on the older substrate formed patchworks of stunted cloud-forest and stands of taller-stature trees. The frequency of recent disturbance events more than 1 m was n = 48 gaps ha−1, corresponding to a power-law exponent of 1.638 ± 0.01. Across the substrate-age gradient, the proportion of each landscape that decreased in height by more than 1 m was 0.16, 0.40, 0.41, 0.36, and 0.17, respectively. These findings demonstrate that substrate age and processes associated with ecosystem development can mediate the rates, sizes, and spatial characteristics of disturbance regimes on forested landscapes, and point toward the necessity of large-area samples to obtain robust estimates of natural dynamics.},
keywords = {},
pubstate = {published},
tppubtype = {bachelorthesis}
}
We quantified rates, sizes, and spatial properties of prevailing disturbance regimes in five tropical rain forest landscapes on a substrate-age gradient in Hawaii. By integrating measurements from airborne LiDAR with field studies and statistical modeling, we show that the structure and dynamics of these forests respond to processes that change during the development of ecosystems. On young substrates of 0.3 ky where forests are in primary succession and are limited by N, mean canopy height was 13 m and height decreases more than 1 m occurred in small, isolated events (power-law exponent = 1.69 ± 0.02, n = 61 gaps ha−1). The proportion of the landscape affected by disturbance increased on high-fertility intermediate-aged substrates of 5–65 ky and canopies were heterogeneous. Frequencies of height decreases more than 1 m were n = 14, 18, and 30 gaps ha−1 corresponding to power-law exponents of 2.188 ± 0.02, 2.220 ± 0.03, and 1.982 ± 0.02 on substrates of 5, 20, and 65 ky. There was a substantial difference between forests on a 150 ky substrate and sites of 5–65 ky; trees on the older substrate formed patchworks of stunted cloud-forest and stands of taller-stature trees. The frequency of recent disturbance events more than 1 m was n = 48 gaps ha−1, corresponding to a power-law exponent of 1.638 ± 0.01. Across the substrate-age gradient, the proportion of each landscape that decreased in height by more than 1 m was 0.16, 0.40, 0.41, 0.36, and 0.17, respectively. These findings demonstrate that substrate age and processes associated with ecosystem development can mediate the rates, sizes, and spatial characteristics of disturbance regimes on forested landscapes, and point toward the necessity of large-area samples to obtain robust estimates of natural dynamics. |