Northern forest ecosystems are projected to experience warmer growing seasons, as well as winters with reduced snowpack depth and duration. Reduced snowpack will expose soils to cold winter air and lead to increased frequency of freeze‐thaw cycles. The interactions between warmer soils in the growing season and colder soils in winter may have important implications for the phenology, productivity and nutrient content of forest plants. We conducted an experiment at Hubbard Brook Experimental Forest, NH, USA, to examine the effects of growing season warming, reduced depth and duration of winter snowpack, as well as increased frequency of soil freeze‐thaw cycles on sugar maple (Acer saccharum) and red maple (Acer rubrum) saplings. We examined the direct effects of soil temperatures on plant root health, timing of leaf‐out, foliar nitrogen, rates of photosynthesis and growth, as well as the indirect effects of snowpack reduction on herbivory on plant stems. A smaller winter snowpack and increased frequency of soil freeze‐thaw cycles in winter led to increased root damage and delayed leaf‐out for maple saplings. Snowpack reduction decreased rates of stem herbivory in winter, indicating that alleviation of above‐ground stem damage in winters with reduced snowpack may offset the root damage incurred from successive soil freeze‐thaw cycles in winters with low snowpack. Synthesis. By examining the response of two dominant tree species to simulated climate change in both the growing season and winter, we find that plant responses are mediated through a combination of changes in soil temperature and plant–herbivore interactions that differentially affect above‐ and below‐ground plant components. These results highlight the feedbacks between trophic levels that shape forest function and demonstrate the need for considering climate change across seasons in global change experiments to determine how forest function may change in the future.

Terrestrial ecosystems regulate Earth's climate through water, energy, and biogeochemical transformations. Despite a key role in regulating the Earth system, terrestrial ecology has historically been underrepresented in the Earth system models (ESMs) that are used to understand and project global environmental change. Ecology and Earth system modeling must be integrated for scientists to fully comprehend the role of ecological systems in driving and responding to global change.Ecological insights can improve ESM realism and reduce process uncertainty, while ESMs offer ecologists an opportunity to broadly test ecological theory and increase the impact of their work by scaling concepts through time and space. Despite this mutualism, meaningfully integrating the two Accepted ArticleThis article is protected by copyright. All rights reserved remains a persistent challenge, in part because of logistical obstacles in translating processes into mathematical formulas and identifying ways to integrate new theories and code into large, complex model structures. To help overcome this interdisciplinary challenge, we present a framework consisting of a series of interconnected stages for integrating a new ecological process or insight into an ESM. First, we highlight the multiple ways that ecological observations and modeling iteratively strengthen one another, dispelling the illusion that the ecologist's role ends with initial provision of data. Second, we show that many valuable insights, products, and theoretical developments are produced through sustained interdisciplinary collaborations between empiricists and modelers, regardless of eventual inclusion of a process in an ESM. Finally, we provide concrete actions and resources to facilitate learning and collaboration at every stage of data-model integration. This framework will create synergies that will transform our understanding of ecology within the Earth system, ultimately improving our understanding of global environmental change and broadening the impact of ecological research.

Past research has shown that plants possess the capacity to alter their instantaneous response of photosynthesis to temperature in response to a longer-term change in temperature (i.e. acclimate). This acclimation is typically the result of processes that influence net photosynthesis (Anet), including leaf biochemical processes such as the maximum rate of Rubisco carboxylation (Vcmax) and the maximum rate of photosynthetic electron transport (Jmax), stomatal conductance (gs) and dark respiration (Rd). However, these processes are rarely examined in the field or in concert with other environmental factors, such as precipitation amount. Here, we use a fully factorial warming (active heating up to +4 °C; mean = +3.1 °C) by precipitation (−50 % ambient to 150 % ambient) manipulation experiment in an old-field ecosystem in the north-eastern USA to examine the degree to which Ulmus americana saplings acclimate through biochemical and stomatal adjustments. We found that rates of Anet at ambient CO2 levels of 400 µmol mol−1 (A400) did not differ across climate treatments or with leaf temperatures from 20 to 30 °C. Canopy temperatures rarely reached above 30 °C in any treatment, suggesting that seasonal carbon assimilation was relatively homeostatic across all treatments. Assessments of the component processes of A400 revealed that decreases in gs with leaf temperature from 20 to 30 °C were balanced by increases in Vcmax, resulting in stable A400 rates despite concurrent increases in Rd. Photosynthesis was not affected by precipitation treatments, likely because the relatively dry year led to small treatment effects on soil moisture. As temperature acclimation is likely to come at a cost to the plant via resource reallocation, it may not benefit plants to acclimate to warming in cases where warming would not otherwise reduce assimilation. These results suggest that photosynthetic temperature acclimation to future warming will be context-specific and that it is important to consider assimilatory benefit when assessing acclimation responses.