Divergent carbon cycle response of forest and grass‐dominated northern temperate ecosystems to record winter warming

Abstract

Northern temperate ecosystems are experiencing warmer and more variable winters, trends that are expected to continue into the foreseeable future. Despite this, most studies have focused on climate change impacts during the growing season, particularly when comparing responses across different vegetation cover types. Here we examined how a perennial grassland and adjacent mixed forest ecosystem in New Hampshire, United States, responded to a period of highly variable winters from 2014 through 2017 that included the warmest winter on record to date. In the grassland, record‐breaking temperatures in the winter of 2015/2016 led to a February onset of plant growth and the ecosystem became a sustained carbon sink well before winter ended, taking up roughly 90 g/m2 more carbon during the winter to spring transition than in other recorded years. The forest was an unusually large carbon source during the same period. While forest photosynthesis was restricted by leaf‐out phenology, warm winter temperatures caused large pulses of ecosystem respiration that released nearly 230 g C/m2 from February through April, more than double the carbon losses during that period in cooler years. These findings suggest that, as winters continue to warm, increases in ecosystem respiration outside the growing season could outpace increases in carbon uptake during a longer growing season, particularly in forests that depend on leaf‐out timing to initiate carbon uptake. In ecosystems with a perennial leaf habit, warming winter temperatures are more likely to increase ecosystem carbon uptake through extension of the active growing season. Our results highlight the importance of understanding relationships among antecedent winter conditions and carbon exchange across land‐cover types to understand how landscape carbon exchange will change under projected climate warming.

Early spring onset increases carbon uptake more than late fall senescence: modeling future phenological change in a US northern deciduous forest

“…However, increasing temperatures are also associated with higher rates of ecosystem respiration (Duveneck and Thompson 2017) and water use (Beamesderfer et al 2020) that can counteract increases in forest carbon uptake (e.g. Sanders-Demott et al 2020). Therefore, the future effects of longer growing seasons on ecosystem-level carbon and water cycling are not fully understood.…”

Improving a Biogeochemical Model to Simulate Surface Energy, Greenhouse Gas Fluxes, and Radiative Forcing for Different Land Use Types in Northeastern United States

“…The improved DNDC model predicted less CO 2 release rates during the late winter to early spring in 2016 at the forest. The high observed CO 2 release rates in this period were likely due to anomalously warm conditions in the winter of 2015/2016 (NOAA National Centers for Environmental Information, 2017) and relatively high temperature sensitivities of ecosystem respiration ( Q 10 ≈ 3.6 to 4.7) during the winter to spring period at the forest that led to warm soil conditions and high CO 2 release rates (Sanders‐DeMott et al, 2019). However, since DNDC integrated equations with lower temperature sensitivities for ecosystem respiration (Li et al, 1992a), the model predicted lower daily NEE values.…”

“…These field measurements provide an opportunity to evaluate the performance of the improved DNDC model for predicting both energy and CO 2 fluxes and to assess the radiative forcing of different land use types in the study region. The technical details regarding the measurements of energy fluxes and NEE, and the relevant auxiliary variables are described by Burakowski et al (2018) and Sanders‐DeMott et al (2019).…”

Increasing evapotranspiration decouples the positive correlation between vegetation cover and warming in the Tibetan plateau

“…For instance, D' Arrigo et al (2004) reported a decline in the temperature sensitivity of tree growth during the late twentieth century, based on dendrochronological data. Research by Sanders-DeMott et al (2020) revealed that the strength of the correlation between vegetation productivity and temperature declined from the early 1980s to 2011 in the northern hemisphere. Moreover, other studies found unimodal relationship curves between vegetation and temperature (Duffy et al, 2021).…”