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The hydrogen isotopic composition of lake water (δ2Hlw) contains hydrologic information and can be used as a recorder of lake water hydrology, including the extent of evaporation of the lake system. Initial studies indicate that the hydrogen isotopes of highly branched isoprenoids (δ2HHBI), synthesized by lake diatoms and preserved in lake sediments are a promising proxy for constraining past δ2Hlw values that are free from terrestrial in- fluences. However, there are many aspects of this proxy, including the seasonality of HBI production, that are unknown and need to be addressed more fully before the proxy can by widely applied. To determine when HBIs are produced throughout the year, and whether there are seasonal biases in δ2Hlw reconstructions, we deployed two sediment traps at Brown’s Lake, in northeastern Ohio. We present HBI concentrations, δ2HHBI values, HBI carbon isotopes and bulk sediment carbon isotopes from sediment traps collected monthly for 26 months to investigate seasonality of HBIs. We observed HBIs in each of the monthly sediment traps throughout the study interval with an increase in HBI concentration during September and October, suggesting that HBIs are made throughout the year with greater production during fall. We calculated the difference between δ2HHBI and δ2Hlw values (ε2HHBI/lw) and observe a range in ε2HHBI/lw values of up to 64‰, which we speculate is related to changes in the diatom communities that synthesize HBIs throughout the year and between different years. Different diatom communities may have different biosynthetic pathways or metabolisms that result in isotope effects. This study is the first that examines the seasonality of HBIs in lake sediments and provides framework for interpreting the seasonality of hydroclimate records generated from δ2HHBI values in temperate eutrophic lakes. 

White oak, a keystone species of the broadleaf forests of the North American Midwest, has a significant role in providing ecosystems services in a region experiencing warming and increasingly pluvial conditions. A one- hundred-year-old white oak stand in an arboretum, along with two second growth (~200-year-old) stands from Northeast Ohio have consistently responded positively to summer (June-July) precipitation over the past century, whereas four nearby old growth sites (>300 years old) have lost their moisture sensitivity since about the mid 1970s. This “fading drought signal,” which has been previously reported, appears to be more a result of the legacy of land use at the individual sites rather than tree age. The younger oak stands and their relative sustained drought sensitivity is also related to their history of recently attaining the canopy and similar responses associated with intervals of selective logging. All sites are strongly, negatively correlated with summer (June- July) maximum monthly temperatures and in general the maximum temperatures are negatively correlated with precipitation in those months. Future warming in the Midwest is projected to see increases in spring precipitation and likely decreases in late summer precipitation linked to a northward migration of the North American Westerly Jet. This projected decrease in summer precipitation coupled with an increase in maximum and min- imum summer temperatures in the coming decades would increase the moisture stress on these trees. Our ex- amination of these varying climate responses with respect to site characteristics and forest age can help future assessments of tree health and the forest’s ability to sequester carbon, as well as facilitate efforts to reconstruct climate by using a range of tree sites for intervals when sensitivity in old growth sites is lost. 

Abstract How forests respond to accelerated climate change will affect the terrestrial carbon cycle. To better understand these responses, more examples are needed to assess how tree growth rates react to abrupt changes in growing‐season temperatures. Here we use a natural experiment in which a glacier's fluctuations exposed a temperate rainforest to changes in summer temperatures of similar magnitude to those predicted to occur by 2050. We hypothesized that the onset of glacier‐accentuated temperature trends would act to increase the variance in stand‐level tree growth rates, a proxy for forest net primary productivity. Instead, dendrochronological records reveal that the growth rates of five, co‐occurring conifer species became less synchronous, and this diversification of species responses acted to reduce the variance and to increase the stability of community‐wide growth rates. These results warrant further inquiry into how climate‐induced changes in tree‐growth diversity may help stabilize future ecosystem services like forest carbon storage. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 285 to -67 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 36 to -70 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 38 to -71 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 150 to -70 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

In Southeast Alaska, many stands of yellow-cedar (Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little; hereinafter “YC”) contain numerous standing, dead snags. Snag-age estimates based on tree morphology have been used to support the interpretation that a warming climate after ca. 1880 has triggered unprecedented YC dieback. Here, we present new estimates of YC snag longevity by cross-dating 61 snags with morphologies that suggest they stood dead for extended periods. All but four of these snags have lost their outermost rings to decay, so we estimate when they died using a new method based on wood-ablation rates measured in six living trees that display partial cambial dieback. The results indicate that ∼59% of YC snags that lost their branches to decay (Class 5 snags) have remained standing for >200 years, and some for as long as 450 years (snag longevity mean ± SD: 233 ± 92 years). These findings, along with supporting evidence from historical photos, dendrochronology, and snag-morphology surveys in the published literature suggest that episodes of YC dieback also occurred before 1880 and before significant anthropogenic warming began. The roles played by climate change in these earlier dieback events remain to be further explored.